Indications for prescribing spectacles

SURVEY OF OPHTHALMOLOGY

VOLUME 26

l

NUMBER 2

l

SEPTEMBER-OCTOBER

1961

REVIEW

Indications

for Prescribing

DAVID D. MICHAELS, Department

Spectacles

M.D.

of Ophthalmology,

School of Medicine,

University of California

Los Angeles.

Los Angeles,

California

Abstract. Indications for spectacle correction are reviewed in the context of symptoms, pathophysiology, and prognostic efficacy. Criteria include improving acuity, restoring comfortable vision, enhancing visual efficiency, preventing progression, and assorted miscellaneous goals. Alternatives to spectacles and side effects are analyzed. Specific guidelines for individualized management are evaluated in terms of current research. (Surv Ophthalmol 26:55-74, 1981)

Key words refractive

ametropia optical symptoms * spectacles l

l

correction

ncorrected refractive errors are by far the most common cause of poor vision. Rehabilitation of such defects has probably added as much to the quality of life and extended its usefulness to society as any advance in biology. Indeed, optical correction safely restores serviceable and comfortable vision to a greater proportion of patients than any other form of ophthalmic therapy. Every refractive examination concludes with three inevitable questions: Are sbectacles indicated? Which lens should be prescribed? What results can be expected? To formalize a task requiring scientific knowledge, technical skill and clinical judgment, and dealing with near inexhaustible varieties of human responses, would require more space than this paper allows, more erudition than the facts warrant, and more audacity than this writer can muster. I have therefore set three more limited aims in constructing this review - first, to place the indications for spectacles in a physiologic as well as an optical context; second, to provide some discriminating guidelines for individualized prescribing; and third, to separate rational prognostic tenets from hopeful guesses. While the conclusions do not guarantee uniform success, they may assist in avoiding unnecessary blunders.

U

l

physiological

optics

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I. Distribution and Definition of Ametropia In the United States, 60% of the population wears eyeglasses at least some of the time; 32% wear them during all waking hours.‘43 Use of spectacles increases with advancing age; 10% in the 1-12 year age group; 34% in the 13-17 age group; 46% in the 18-44 age group; 89% in the 45-64 age group; and over 90% in those over 65. In 1975, approximately 47.9 million diagnostic eye examinations were performed in the United States - one annual examination for every two persons who wear corrective lenses. About 4% to 5% of the population has or has had strabismus or amblyopia or both. Estimates of the number of people with partial visual impairment in the United States range as high as 2.5 million.50 Precise figures are difficult to obtain because such terms as “legally blind,” “partially blind,” or “low vision” have no exact meaning relative to the degree of disability. “The emmetropic eye” wrote Donders,42 “presents both in its structure and function the standard by which anomalies of refraction must be estimated.” No modern practitioner would hold with Donders’ standard for a moment. Emmetropia is an optical ideal,

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26(2) September-October

1981

not a biologic average. The definition of ametropia thus depends on how large a deviation from the standard is considered significant. Although most patients can discriminate 0.25 D differences, diopters are only convenient metric units. There is no assurance that genetic organizers work in 0.25 D steps or that they ever heard of the metric system. And will ametropia be measured with ot without cycloplegia, expressed as spherocylinder or spherical equivalent, at the spectacle, cornea], or pupillary plane? Moreover, clinical refraction, in contrast to ocular biometry, generally measures only the lens giving optimum acuity. Acuity, in turn, varies with type of target, contrast and color, pupil diameter and intensity of illumination, optical properties of the eye and correcting lens, contour interaction and fixational precision, and concurrent systemic or local ocular disease. Besides, optical exactitude may be nullified by perceptual ineptitude in cases of poor resolution, poor discrimination, and poor cooperation. It follows that the more rigid the criteria and the more precise the measurements, the fewer emmetropes one is likely to find by any delinition. Ametropia is neither a single nor a simple entity, but an interaction of optical capacities, visual needs, and adaptational potential; its prevalence depends on age, population sampling, methods of measurement, symptomatic manifestations, and whatever criteria delimit eflicient and safe performance. The eye is made up of approximately fourteen optical components, five of which are generally considered of great importance: axial length, cornea1 and lenticular curvature, anterior chamber depth, and refractive index. There appear in the literature only three studies in which major optical components were measured (not secondarily comactually These show that each component has puted). 16’*1’2~1’0 a statistical distribution even in emmetropic eyes; in fact, most ametropic components fall within this emmetropic range, but are mismatched (correlation ametropia). Only when ametropia exceeds approximately f4.00 D is an abnormal component in the sense that it is outside likely - abnormal emmetropic limits (component ametropia). Refractive errors are therefore largely a result of disproportionate rather than excessive dimensions. High ametropias, on the other hand, suggest that an attempt be made to identify the anomalous compoby ultrasonography, keratometry, nent (e.g., phakometry, and biomicroscopy). Most people, in fact, do not have large refractive errors. To account for process has been this, an “emmetropization” postulated in which optical components are not associated by chance alone, but are correlated.“’ Whether the coordinating mechanism is genetic, environmental, or simply a mathematical artefact

MICHAELS remains

unknown.”

II. Pathogenesis of Ametropia If much has been written about the prevalence of ametropia in general, and the statistical distribution of optical components in particular, much less can be asserted about etiology that is not circumstantial.‘6 In part, this is because longitudinal studies of refractive changes require a long life and loyal patients. Automated objective oculometry and ultrasonography are new techniques that may eventually provide insights unobtainable by other methods. A. HEREDITY That heredity plays a role in ametropia is unquestioned. Whether this is dominant or recessive, simple or multifactorial, involving optical components individually or in combination, is not established.‘6 Studies of families and twins show substantial correlations,‘6* and associations between myopia and mesodermal defects, such as Marfan’s syndrome, are well known. Two possible mechanisms have been suggested. In one, the retina presumably acts as a genetic organizer, regulating axial length and cornea1 curvature.“’ In the other, a stretch factor is postulated to affect axial length through ciliary tone, perhaps controlled by autonomic servomechanisms.“* B. AGE Refractive changes with age strongly suggest a growth process. ‘* Thus, most infants are hyperopic and this decreases progressively. One reported increase in childhood hyperopia** turned out to be a spurious effect of an excessive number of strabismics in the population sample. Children who are emmetropic or less hyperopic than average, are likely to be myopic before they finish school.18 Hyperopia increases again after age 45, and this is attributed to lentitular growth. Against the rule, astigmatism intensifies because of lens changes and lid compression.lW A later increase in myopia may follow cataractous alterations. C. ENVIRONMENT The role of environment is less clear and more controversial than heredity or age. Factors as diverse as diet, disease, drugs, and demanding visual tasks have been implicated. la2 Where there is no physiologic fragmentation prevails. For exunity, speculative ample, myopia increases during adolescence, hence school years. To the effects of normal growth, extraocular muscle compression, postural hyperemia, and ciliary spasm, were added the dire consequences of reading by poor light and writing with pale ink in

INDICATIONS

FOR PRESCRIBING

SPECTACLES

gloomy classrooms. We get rid of such pronouncements by admitting their half-truth. Myopia develops in children not because they attend school, but because they are old enough to attend school. Nevertheless, the notion that near work and ametropia are related (“use-abuse” theory), continues to fascinate and to stimulate both human and animal experiments.‘*” This is because genetic disorders impose a kind of therapeutic impotence, whereas environmental changes imply at least a measure of preventive intervention. Treatment will therefore depend on how critically one distinguishes between possible and probable pathogenic mechanisms. Recent animal experiments demonstrate changes in axial length by surgical lid fusion or artificially induced anisometropia before eye growth is comremains unexplained, pleted.“g*184 The mechanism and though extrapolation to humans is immediately appealing it is not inevitably relevant.

III. Pathophysiology

of Ametropia

The eye is an optical instrument which is often compared to a camera. But the camera picture is an end-result, whereas the retinal image is only the first link in a chain of neurophysiologic processing. Unfortunately, we have little to offer at the neurophysiologic level, so we concentrate on improving the optics. The eye is also a biologic entity, hence refractive changes can be induced by drugs, electrolyte imbalances, trauma, tumors, and ocular disease or surgery. Refraction is therefore part of every ocular examination and methodical ophthalmic evaluation is part of every refraction. Only in this way can interpretation of symptoms and analysis of signs be placed in their appropriate pathophysiologic context. A. HYPEROPIA

A major consideration in the pathophysiology of hyperopia is availability of compensatory accommodation.‘25 The amount of hyperopia that can thus be neutralized is termed “facultative.” The residual is “absolute.” With advancing age, absolute hyperopia increases at the expense of facultative.” The amount of hyperopia clinically measurable without cycloplegia is termed “manifest;” latent hyperopia represents the degree unmasked by relaxing ciliary tone with cycloplegia. Total hyperopia is the sum of latent and manifest hyperopia. Ciliary tone is greater in children than in adults; hence, evaluation of latent hyperopia requires greater concentration of cycloplegia. An essential factor in all methods of refraction is control of accommodation by cycloplegics, fogging, target detail, and eliminating depth of focus if feasible.46 Since accommodation is always binocular, the uncorrected anisometropic hyperope flounders between

57

unequal acuity, aniseikonia, amblyopia, induced heterophorias and potential strabismus. Excessive and prolonged accommodation is also a major cause of eyestrain and spasm. Ciliary spasm in turn can lead to pseudomyopia and convergence excess, or may itself be a response to convergence insufficiency.” Small hyperopic eyes predispose to narrow chamber angles and narrow optic canals which mimic papilledema. Most children and many adults who have visual symptoms are hyperopic. It is easy to attribute one to the other and read into concurrent optical correction evidence for vice or virtue, nature or nurture, dyslexia or dyspepsia, the triumph of statistical credulity over common sense. B. MYOPIA

Fluctuating myopia may be found in premature infants during the neonatal period.52 Marasmic infants have been reported to exhibit myopia.” Congenital myopia occurs in a small number of fullterm neonates, often with associated astigmatism and strabismus.35 Degenerative myopia is characterized by progressive posterior fundus changes, including disc supertraction and crescents, atrophy of the choroid and pigment epithelium, Fuchs’ spot, lacquer cracks, and ectasia.“’ Not every myopic eye need cause anxiety; in fact, most are perfectly healthy and require only restoration of optical focus. The required correction will depend on acceptable visual acuity. In some cases, reduced scleral rigidity may mask increased intraocular pressure unless measured by applanation tonometry. Glaucomatous field changes may also be erroneously attributed to myopic fundus changes. Glaucoma occurs more frequently in myopes, as do vitreous and retinal detachments.“” Field constrictions, enlarged blind spots, reduced light thresholds, color vision defects, and retinochoroidal circulatory disturbances have been reported in degenerative myopia. Tears in Bruch’s membrane and hemorrhage involving the macula remain a leading cause of blindness. C. ASTIGMATISM

It is rare to find an eye completely free of astigmatism; its prevalence depends on the clinician’s enthusiasm for refraction. Only about 2% to 3% of spectacle cylinders exceed 3.00D; hence, an emmetropization mechanism seems to operate here as it does for spherical ametropia. The sources of astigmatism are the cornea, crystalline lens, asymmetric centering of ocular optical elements, intrinsic variations in refractive index, and fovea1 displacement.” Of these, cornea1 curvature is the most important and can be measured by keratometry. Non-cornea1 astig-

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Surv Ophthalmol

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1981

matic errors contribute to the “residual astigmatism” after contact lens correction. Variations in refractive index occur in cataract and diabetes, and may involve both power and axis. Irregular astigmatism results when a given meridian is not uniform and/or when the primary meridians are not at right angles. The most common causes are cornea1 scarring, keratoconus, and warped contact lenses. Unilateral astigmatism occurs in about 30% of patients. Astigmatism is more common with hyperopia than with myopia. Astigmatic vision is compromised because the eye cannot focus both primary meridians simultaneously.” Compensation is possible by variations in pupil size, squinting the lids, accommodating for alternate focal lines, shifting fixation to the opposite eye, and by perceptual adaptations. Although sectional accommodation does not exist, some astigmatic variations are probably induced by crystalline lens irregularities. These should not be confused with differences between distance and near astigmatism from optical effectivity.1s8 Anisometropic astigmatism inevitably induces lateral and vertical prismatic imbalances; oblique cylinders also create meridional aniseikonia. Spatial distortions are more likely to result from correcting spectacle cylinders than from inherent ocular astigmatism.64 D. ANISOMETROPIA Clinical symptoms of anisometropia relate to three major pathophysiologic mechanisms, distinct in theory though intertwined in practice. Without equal acuity, binocular vision may fail to develop; without equal motility, it may be uncomfortable; without equal image size, it may be distorted. In children, unequal visual inputs comprise a potent amblyogenic mechanism which may occur with or without strabismus.” If binocular vision develops only by the skin of the fusional teeth, decompensation and intermittent diplopia may occur whenever the patient is tired, ill, or otherwise stressed.” Unequal prismatic effect of anisometropic spectacles induces anisophoria, to which one can adapt by fusional vergences and recalibration of oculomotor feedback control mechanisms. Spatial distortions accompany differences in size, shape, or inclination of one eye’s image relative to the of such symptoms are other.“’ Specific descriptions rarely offered by patients. Instead they complain of or intolerance to their glasses vague irritability because binocular spatial distortions are masked by monocular cues which can only be eliminated under special laboratory conditions.‘* And this is the chief obstacle to demonstrating spatial anomalies in an office setting. Since the operation of monocular cues take longer, there is less time to use them when the

MICHAELS patient is mobile; hence, difficulties are exaggerated under these circumstances. The management of unilateral aphakia depends on the vision in the phakic eye, the binocular potential, the patient’s age and adaptability. Many of these decisions will have already been made in accepting the patient as a surgical candidate. E. ACCOMMODATION

AND VERGENCE

Accommodation is the remarkable faculty that allows us to focus on objects at various distances. It distinguishes the eye from a camera by giving range to its resolution. Wound-up in infancy, it gradually and inevitably runs down to impotence. The onset of presbyopia is unpredictable; roughly, it is that time at which we cease to practice and begin to preach. Pathophysiologic consequences include decreased facility of aqueous outflow, reduced lens capsule elasticity, moderate ciliary muscle atrophy, and increased exophoria.” Unlike presbyopia, accommodative insufficiency may produce discomfort and can occur at any age. It may be associated with undercorrected hyperopia, overcorrected myopia, cycloplegic drugs, Adie’s syndrome, chronic cyclitis, neuropathies, trauma, or it may be a genetic variant (premature presbyopia). Accommodation responds sluggishly in any eye with poor vision; conversely, when illumination or contrast is greatly reduced, it tends to become positive (night myopia). It is probable that accommodation is a servomechanism, activated (within limits of depth of focus) by retinal blur, chromatic aberration, Stiles-Crawford effect, as well as monocular and binocular depth cues.2s A change in vergence can be demonstrated whenever the eye accommodates, and this association (AC/A ratio) remains constant throughout life.’ Convergence also activates accommodation, but is difficult to evaluate because the resultant blur is selfcorrecting.51”*2 The linkage between accommodation and vergence is analyzed by measuring phorias, fixation disparities, or fluctuations in the angle of strabismic deviation. The relationship between convergence and accommodation is necessarily altered when ametropia is corrected, which may result in symptomatic motility imbalances like convergence insufficiency or excess. 24 The economic problem is then to match fusional reserves to the heterophoric demand by modifying the spherical prescription, prescribing prisms, or improving fusional vergence amplitudes through orthoptic exercises.s2 F. TRANSIENT

REFRACTIVE

CHANGES

Transient refractive changes may accompany endocrine and metabolic disorders, electrolyte imbalances, collagen diseases, malnutrition, cataract, strabismus,

INDICATIONS

FOR PRESCRIBING

59

SPECTACLES

keratoconus, trauma, tumors, serous retinopathy, or ocular surgery, and it may follow use of autonomic and other drugs. Repeated examinations are necessary to demonstrate such fluctuations. Transient obscurations of vision without refractive changes are found in migraine, giant cell arteritis, chronic and carotid artery stenosis. These papilledema, associations emphasize the close relation between refractive disorders and general medicine. G. APHAKIA The aim of cataract surgery is to restore vision; prescribing for aphakia is a necessary means to implement that goal. In this endeavor, the patient is not a spectator but a participant, and the patient judges the issue not by what is taken but by what is left. The pathophysiologic consequences include magnification, anisometropia, diplopia, reduced visual fields, ring scotoma, swim, and distortion, as well as effects secondary to decompression and healing.” H. LOW VISION Patients with diseased eyes respond differently than those with ordinary refractive errors.“’ Low vision may result because light rays are blocked, scattered or not brought into focus; because they do not excite photoreceptors; or because neural messages are imperfectly transmitted or interpreted. Although the common denominator is poor vision, a specific diagnosis requires partitioning the effects of various mechanisms (macular function studies, laser interferometry, pupillary responses, perimetry, electrophysiologic testing, etc). An eye with subnormal vision is a diseased eye, requiring a medical diagnosis and prognosis.” The primary obligation is to preserve what vision is left and prevent further deterioration.

IV. Evaluating Refractive Symptoms Eliciting symptoms is a time-honored technique to solve the diagnostic puzzle, yet it is often ignored in clinical refraction. Lenses are ordered only on the basis of retinoscopy, or astigmatic dial. Refraction may even be delegated to a machine or technician. But no mathematic exactitude defines eyestrain, and no formulas characterize spatial distortions. We must rely on patients to recite what they feel or see or, indeed, whether they can see at all. Moreover, the history is not only a diagnostic but a therapeutic tool. The presence of symptoms determines that, of two patients having identical refractive errors, one receives spectacles and the other does not. On the other hand, the absence of complaints will discourage any inclination to give glasses merely for the sake of doing something positive.

Eyestrain is said to have such pleomorphic manifestations as tearing, itching, burning, and scratching; increased sensitivity to light, glare, motion, and tension; decreased acuity, efficiency, and equanimity; flushing of the eye, quivering of the lids, and tingling of the brow; double vision, distorted vision and dyslexic vision; eyeache, headache, neck ache, and belly ache; and local and general strain, weakness, or tiredness. It has been attributed in part or in whole to weak or excessive accommodation, to low hyperopia and high astigmatism, to an imbalance of extra- and intraocular muscles, and to the small size or great precision of visual tasks, not to mention psychosis, hysteria, and malingering. It is variously considered to be characteristic of, the cause of, and the result of visual “fatigue.” Although eyestrain is neither a sparse nor a specific syndrome, some features are suggestive.% Timing coincides with visual functions; frequency is greater toward evening, severity is moderate, onset is gradual, and relief is obtained by better light, better contrast, better glasses, or avoiding prolonged near work.lz6 The patient is generally aware of and can describe these connections. Some means to obtain relief are recognizable from across the room; the tilted head, turning eye, twisted glasses, and tightly squeezed lids. Refractive symptoms might be classified as those resulting from blurred vision, from uncomfortable vision and from inefficient vision. Such symptomatic analysis allows one to formulate rational principles for prescribing spectacles. Of course, everything depends on how the principles are applied. In evaluating symptoms, allowance must be made for individual differences in tone and temperament. One patient with low ametropia complains bitterly and another wears the wrong prescription with serenity. However such problems are approached whether dogmatically or crustily, with empathy or poetry - they teach us to bear our mistakes with equanimity and respect our colleagues’ delusions.

V. Indications for Prescribing The causes of refractive error remain a historic succession of contradictions, yet the clinician must somehow satisfy the daily needs of patients and translate what no one fully understands into a knowledgeable lens correction. Between the art and science of prescribing, there remains a vast corpus of dogmas, opinions, and assumptions hallowed by textbook repetition and enshrined as traditional wisdoms. As will be evident in the following sections, however, only a paucity of facts prop up many promulgated pearls. For convenience of discussion, I have classified indications for spectacles into those designed to improve acuity, to restore comfort, to enhance efficiency, to

60 prevent goals.

Surv Ophthalmol progression,

A. IMPROVING

26(Z) September-October

and some assorted

1981

miscellaneous

ACUITY

The smooth course of human affairs in all its intellectual, sensual, and emotional variety hinges on sharp vision. We stake our lives by assuming the other driver can see us coming. Blurredness is therefore the most common refractive complaint. Conversely, children may not complain of blurred vision, and even adults tend to ignore unilateral blur. The distinction between blurred vision and loss of vision is not always clear, especially in combined disorders. Blurred vision may result not only from improper optical focus, but also from light scatter by ocular media, unsteady or eccentric fixation, unequal binocular inputs, and anomalous simultaneous or successive contour interaction. The onset of blurred vision may be sudden or gradual, its course stationary or slowly progressive. It may involve distance, near or intermediate targets. It may be better or worse in dim or bright lights, or exaggerated with monocular or binocular viewing. The degree of blur may or may not correlate at far and near. These clinical features are often characteristic in myopia, presbyopia, amblyopia, certain types of cataract and latent nystagmus. In serous maculopathy, blurring is associated with metamorphopsia; in keratitis, it is associated with pain, halos, and photophobia; in strabismics, it may be complicated by intermittent diplopia; in older people, it may cause transient psychotic states; and in hysteria or malingering, measurements tend to be consistently inconsistent. Blurring also increases with age because of senile miosis, diminished light transmission, increased light scatter, and perhaps more subtle perceptual delays and deteriorations.“’ Traditional measures of acuity are optotypes, Landolt rings or hooks, checkerboards, bars, and forms. More recently, results with grating targets suggest that the visual system may contain transmission channels selectively tuned to specific frequencies.” Thus, ametropia reduces high frequency discrimination, media opacities such as cataracts and cornea1 edema affect low frequencies, and an overall decrease has been observed in some types of amblyopia.* In general, low frequency loss suggests non-optical blur mechanisms. The optical principle of restoring the eye’s focal integrity is to make the second focal point of the correcting lens coincide with the far point. In astigmatism, two far point problems must be solved simultaneously. In presbyopia and aphakia, the near point is also rejuvenated to allow clear reading vision.” In patients with low vision, acuity might be enhanced by sharpening the retinal image, improving its illumination and contrast, or making it larger - often in com-

MICHAELS bination.“’ It is not enough, however, to prescribe optical aids; instructions must also be given about how and when to use them. It is amazing how many intelligent people misinterpret the purpose of spectacles; e.g., by using reading glasses for distance vision or other activities they think might breed eyestrain. Individual differences in blur discrimination also qualify the indications; some patients readily tolerate one diopter blur, while others have an exasperating aptitude for one degree of exactitude. Spectacles to improve distance acuity are clearly indicated in myopia, astigmatism, aphakia, and absolute hyperopia. Usually one aims for optimum acuity, but this may be modified by occupational needs, tolerance to spectacle wear, anticipated adaptation problems to large dioptric increments of change, motility imbalances, aniseikonia, and other criteria requiring a trade-off between clear monocular vision and comfortable or efficient binocular vision. To improve near acuity, spectacles provide what an insufficient or inefficient ciliary mechanism can no longer achieve. Indications depend not only on accommodative amplitude, but also on type of near work, lighting, distance, field of vision, fixation shifts, length of arms, and power and style of previous multifocals, among other factors.ss Most people, in fact, require clear vision at more than one distance, necessitating new postural as well as new cosmetic adjustments. Variable focal and occupational multifocals are specialized designs for specialized needs.13s In presbyopia, the required addition is generally symmetrical; in neuropathy and amblyopia, it may be unequal. While indications for lenses to improve acuity are mostly straightforward, results are not always ideal. In infants and young children, acuity is difficult to measure and spectacles are not always accepted.” In amblyopia, form vision may not have developed, requiring patching and perhaps pleoptics as well as optical correction. ss,14’If poor vision in one eye cannot be corrected or if retinal image size is markedly incongruous, binocular acuity is worse than monocular; conversely, in latent nystagmus occluding either eye compromises acuity.” In irregular astigmatism from cornea1 scars and keratoconus, supplementary contact lenses, pinholes, or stenopeic slits may help.161 In near vision is disproporcongenital nystagmus, tionately higher than far vision, and the reverse obtains in subcapsular cataract. When media opacities cause light scatter, acuity can sometimes be improved by antiglare devices, filters, shades, miotics or mydriatics. 12’ Temporary lens changes aid vision in transient refractive disorders.15~6’*‘S8In aphakia, sharp central vision is somewhat offset by magnification, peripheral distortions, and restricted side vision.“’ In advanced glaucoma, constricted peripheral fields

INDICATIONS

FOR PRESCRIBING

61

SPECTACLES

negate orientation despite good central vision, and in night blinding disorders the patient cannot safely function in dim light. On the other hand, even a small visual improvement can often accord the low vision patient a life of relative independence.lBS In summary, indications for spectacles to improve vision depend on how acuity is measured, visual needs, whether a sharp optical focus can be achieved, associated systemic or ocular disease, and what interpretive skills the patient can muster. Spectacles may be indicated for far, near, or intermediate distances; their purpose may be to equalize vision in the two eyes, to reduce glare and light scatter, to restore acuity during transient refractive changes, and to provide optimum (if less than ideal) acuity in diseased eyes (Table 1). B. RESTORING

COMFORTABLE

VISION

Pain is one of the most compelling reasons for which patients consult physicians,“l and discomfort following or accompanying use of the eyes is a recurrent theme in clinical refraction.” Pain associated with refractive disorders is generally dull, rarely throbbing, and worse toward the end of the day. Discomfort associated with motility disorders, such as vergence-induced accommodative changes, tend to produce a drawing or pulling sensation, relieved by prisms or appropriate lens modification.“’ The traditional explanation is muscle fatigue with referred pain along the distribution of the trigeminal nerve, sometimes with reflex nausea, vertigo, lacrimation, or gastrointestinal upset. Intermittent diplopia, spatial distortions, and blurring may cause general irritability which the patient interprets as discomfort. A common, but sometimes unstated factor, is an improperly fitted spectacle frame which hurts the ears or nose. Psychogenic pain may occur in areas not limited by zones of sensory innervation. There may be a history of antecedent injury or disease, with other features of anxiety or depression. Although discomfort is a major indication for prescribing spectacles, symptoms such as pain, headache, fatigue, diplopia, medical tends No

vertigo, practice,

and anxiety span the entire and differential diagnosis

well beyond

refractive

correlations

relate

gamut of often ex-

tests.lz2 degree

of

discomfort

to

degree of ametropia; patients are as likely to complain of low as of high refractive errors. The common complaint of visual fatigue is a semantic chameleon which fails to distinguish between “I am too tired to read” and “reading makes me tired.” In fact, patients may tire, not of seeing, but of their work, their surroundings, or their failure to achieve the goals they have set for themselves. The person complaining of fatigue may or may not demonstrate formance, whereas altered function

impaired perhas been at-

TABLE

1

Indications for Spectacles

To Improve Acuity

Distance Acuity Myopia Astigmatism Regular Irregular Absolute hyperopia Anisometropia Aphakia Accommodative spasm Transient refractive changes Light scatter by media opacities Near

acuity

Presbyopia Other causes of accommodative insufficiency Accommodative inertia Accommodative excess Primary Secondary to motility disorders Transient refractive changes Light scatter by media opacities Far-Near Acuity Dissociation Latent nystagmus Congenital nystagmus Cataract Other media opacities Secondary to motility disorders Low Vision Aids Telescopes Telemicroscopes Microscopic lenses Miscellaneous Filters Pinholes Stenopeic slits Partial occluders

tributed

to

both

fatigue

and

practice.”

Finally,

also occurs in systemic disorders such as anemia, hypothyroidism, mononucleosis, hepatitis, or any chronic illness. If correcting ametropia is a prerequisite for clear vision, treating accommodative anomalies is often affirmed to be indispensable for comfortable vision.81 For example, balancing accommodative demand and supply is the basis of classifying hyperopia into facultative and absolute.“* Spectacles are then prescribed to avoid protracted ciliary effort.” Of course, not all hyperopes have discomfort; indeed, children with high latent hyperopia are less likely to complain than adults. Confirming the notion that it is ciliary effort, not muscular contraction which is responsible, is the absence of discomfort in myopes and presbyopes.7”,‘06 Conversely, direct action of drugs such as eserine do not duplicate the usual generalized

fatigue

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1981

asthenopic symptoms though they cause periorbital discomfort .6g Clinical measures of accommodative amplitude are influenced by so many variables that results are diflicult to interpret.g1*‘81 Some complaints are surely the effect of ill-timed or ill-sustained ciliary effort. This is the basis for tests of ciliary flexibility and relative accommodation.1’5 An acceptable use-reserve ratio probably depends as much on characteristics and timing of the visual task, overall illumination, depth of focus, and blur interpretation, as it does on degree of hyperopia or amplitude.” Nor is it established that hyperopic astigmats exert continuous or variable ciliary effort for one or the other focal line. Symptomatic benefits are therefore unpredictable, making it hard to distinguish between physiologic relevance and happy accident. Ciliary spasm is a diagnosis made not only from the history, but by comparing cycloplegic and manifest refraction.13’ Of course, cycloplegia must be adequate and the subjective fog appropriate, or one will convert just about every emmetrope into a psudomyope. Symptomatic ciliary spasm is an important indication for relaxing lenses, to relieve discomfort and to avoid postulated progression toward true myopia.’ Relaxing lenses may need to be supplemented by temporary cycloplegia, base-in prisms, and orthoptics. Discomfort from horizontal motility imbalances is conventionally evaluated in terms of heterophoric demand and fusional vergence reserve.114J31 Several systems of analysis have been proposed, ranging from Duane’s classification4’ of convergence and divergence excess and insufficiency, to Percival’s”” and Sheard’s’Sg graphic analysis. While generally useful as a basis for prescribing prisms or modifying the spherical correction (to induce phoria changes via the AC/A ratio), some inconsistencies remain.s**11a More recently, fixation disparity and other tests of binocular function have been proposed as criteria for prescribOne of the most coming, with variable success. 2g~1eo mon problems is the relative convergence insufficiency resulting from early presbyopic correction. In such cases, compromising on the bifocal add, ordering some base-in prism, and recommending better illumination are worthwhile. Vertical motility disorders often accompany anisometropic corrections, particularly in presbyopia. Symptoms can usually be alleviated by proper reading or bifocal designs as well as by compensatory prisms. In general, ordering prisms should be tempered with a healthy respect for human adaptability. Some anisometropic problems can be evaded by arbitrarily equalizing lens power or prescribing spherical equivalents.‘62 But vertical imbalances can always be eliminated by allowing the patient to tip the head; unequal acuity from improper

MICHAELS focus cannot be compensated for.‘*l Motility problems induced by an inexpedient spectacle fit or improper lens decentration can be solved by judicious ophthalmic dispensing. Unequal ocular image size, or aniseikonia, is an occasional source of discomfort.lo4 Headaches, intermittent diplopia, dizziness, spatial distortions, and inaccurate distance judgments are suggestive when relieved by closing one eye. These problems are most commonly associated with new spectacles prescribed for anisometropic hyperopia,@ astigmatism,1” and unilateral aphakia corrected by contact or intraocular lenses.155 High cylinders, especially at oblique axes, may induce meridional aniseikonia. Spectacles designed to restore equal acuity then require additional modifications in vertex distance, base curve, or lens thickness. Cylinders can be reduced in power, their axes can be rotated towards meridians to which the patient is adapted, or spectacles can be replaced by contact lenses. Transient anisometropia may require patching one eye to avoid diplopia until the underlying pathology has stabilized. Photophobia is a common complaint to be expected in persons with keratitis, uveitis, glaucoma, albinism, headache, drug-induced mydriasis, photoallergies, and any febrile disease; it is also common in recent aphakes with large iridectomies and beginning contact lens wearersg’ Associated findings might include frowning, increased blink tearing, blepharospasm, rate, and hyperemia. Occasionally there is a true “phobia” to light, commonly in patients with impaired sight. In contrast, dazzling or glare sensitivity is the offensive result of excessive light levels or light scatter. In the absence of disease, tinted lenses may be ordered for functional photophobia, providing they are not too dark for safe night vision. That all symptoms have a functional component conditioned by the patient’s age, personality, cultural background, and past experiences is a postulate that needs little preface.“’ Moreover, some symptoms have no discoverable organic cause, and are thus classified as psychogenic. In addition to mere negativism, however, positive findings such as a history of emotionally charged experiences, altered mannerisms, mood, attitudes, and cognition can often be elicited, suggesting tension, sadness, euphoria, irritability, or apathy. Accidental injuries may result in compensation neurosis or malingering, difficult to diagnose and even more difficult to treat.128 Optical correction in such cases may reinforce the patient’s attachment to a nonexistent illness. In summary, prescribing spectacles to restore comfortable vision depends on history, differential diagnosis of signs and symptoms, and an understanding of relevant pathophysiologic mechanisms. Common sources of discomfort are excessive accommodative de-

INDICATIONS

FOR PRESCRIBING

motility imbalances, ciliary spasm, mand, aniseikonia, glare, and psychogenic factors (Table 2). Although refractive findings often combine into a characteristic picture, individual differences in reacting to symptoms (or expressing them) make prognosis somewhat unpredictable; results are sometimes worse and occasionally better than anticipated. Finally, every prescription has a placebo effect; many a mediocre spectacle has been augmented by a compelling bedside manner. These intangibles must be considered if therapy is to be evaluated with precision and recommended with confidence. C. ENHANCING

63

SPECTACLES

VISUAL EFFICIENCY

If spectacles restore standard acuity, do they also reestablish efficient vision? Obviously not in patients with diplopia, aniseikonia, or intermittent strabismus. The concept of visual efficiency is thus of legitimate concern to the refractionist. It is also a topic that abounds with questionable semantic associations and exhortations more vivid than verified. It is one thing to say that vision involves the “whole organism” and quite another to translate the implications into practical therapeutics. It is therefore appropriate to inquire more closely into some criteria of efficiency. It is evident that Snellen fractions do not express visual efficiency, and indeed the courts take a dim view of claims that 20/60 is 30% and 20/40 is 50% vision. To express visual performance more realistically, particularly in estimating disability following ocular disease or injury, weighted and averaged values of central acuity, visual fields, and motility for each eye are combined.‘65 Thus, unequal loss of near and distance acuity does not signify equal disability, and unilateral blindness represents a 25% (not 50%) decrease in visual efficiency. Unless otherwise qualified, this index is what is meant by visual efficiency in the ophthalmologic literature. While a numerical value is a juridical and economic necessity, it has inevitable practical limitations. Some factors whose value cannot be readily calculated are loss of color vision, night blindness, accommodative insufficiency, metamorphopsia, symptomatic discomfort, cosmetic disfigurements, and potential risks of injuring an only remaining eye. No single number can really express visual disability, which must therefore remain a clinical conclusion based on professional evaluation. The concept of visual efficiency has also been extended, in analogy to engineering practice, to describe least wasteful performance. In fact, the field concerned with design of products and environments that optimally serve their intended use by human beings is called “human factors engineering” or “engineering psychology.“115 It is then a simple, if somewhat simplistic, extrapolation to consider

TABLE 2 Indications

for Spectacles

to Relieve Discomfort

Refractive Disorders Uncorrected hyperopia Uncorrected astigmatism Overcorrected myopia Anisometropia Unequal acuity Unequal motility Unequal ocular images Accommodative Disorders Accommodative insufficiency Accommodative excess Accommodative inertia and fatigue Motility Disorders Horizontal imbalances Convergence excess and insufficiency Divergence excess and insufficiency Vertical imbalances Combined horizontal and vertical imbalances Disorders of Binocular Function Transient diplopia and confusion Sensorimotor incoordination Restricted motor fields and suppression Loss of fine stereopsis; anomalous depth effects Perceptual Disorders Spatial distortions Aniseikonia Magnification After images and after effects Contour interaction and induction Sensory deprivation and agnosia Dyslexia Psychogenic disorders

Optical and Dispensing Problems Magnification and minification Distortions and aberrations Field restrictions; reflections; fogging Reduced range of vision Diminished eccentric acuity Induced size differences Induced prismatic effects Improper frame fitting; frame intolerance Cosmetic problems

humans as machines, subject to stresses and exhibiting strains. If these cannot be precisely defined, they can be plausibly discussed. An obvious starting point is to assemble potentially adverse stress factor? such as poor light, poor focus, glare, small targets, prolonged viewing, unequal visual inputs, flicker, vibration, ambiguous monocular cues, rapid movement, sensory overload, etc., and trace their consequences on visual performance. Of course, environmental modifications are limited at best, and may be viewed as intolerable interference at worst.

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1981

Characterizing physiologic strains is more difficult, and might include changes in vergence, accommodation, phorias, rhythmic ocular movements, etc., which presumably cause or aggravate ametropia, strabismus, reading and learning disabilities. For example, prolonged near work has been cited as stressful because it may induce undesirable ciliary spasm, overconvergence, miosis, and myopia. Treatment would presumably be directed at blunting these by plus lenses, base-in prisms, cycloplegia and orthoptics.“’ Efficient vision has also been described as an aggregate of desirable visual “skills.” Skill means effectiveness in performing an act, presumably learned, which is improved if the same score is reached at a lower threshold or energy cost. A hierarchy of visual skills has been postulated - sensory, motor, and perceptual. If some skills are defective or have failed to develop, remediation would then improve efficiency. In fact it is unlikely that functions such as color vision, phorias, fusion, and stereopsis are learned, and it is certain that skills important in reading differ from those essential in driving. The physiologic basis for remediating such complex activities as spatiotemporal sequencing, visual memory, body-image differentiation, and intersensory integration has yet to be demonstrated.s8 Although the term, “skill,” conjures up a vivid image of action, control, training, and self-improvement, one cannot create a metrology out of a metaphor. Having attested to the difficulties, one must also affirm the laudable aim of implementing optimum performance. It may therefore be useful to consider some specific visual tasks from this point of view. Every refractive condition has motor and sensory effects that shift the binocular balance in a favorable or unfavorable direction.26 Perceptual deficits may therefore result from unequal acuity, restricted motor fields, intermittent diplopia, spatial distortions, and diminished depth discrimination. Each is measurable with appropriate instruments so that merits of optical correction can be demonstrated. Similarly, a basic premise of strabismology is that binocular vision is more efficient than alternating monocular vision. On the other hand, strabismic children do not necessarily suffer learning or reading disabilities.” Visual defects obviously affect learning. The child who cannot see cannot read, and the child who cannot read comfortably cannot learn efficiently. Substandard acuity, amblyopia, diplopia, accommodative and vergence disorders can and do cause disinclination to read. Such deficits can be corrected by optical, or surgical treatments. Beyond this, orthoptic, however, as has been confirmed many times, eye care by itself seldom solves reading problems because vision defects are rarely a dominant cause.“’ Attempts to extend the clinical horizon by looking at more com-

MICHAELS plex psychophysiologic processing have not yet been productive. No visual skill or combination of skills has been specifically implicated, and no training program has been found unequivocally effective. Of course, this may only reflect our limited perspective of human behavior. In the meantime, a multidisciplinary approach remains the most practical method of dealing with learning and reading disabilities.‘e Desirable visual characteristics differ from job to job, some changing with age and others with work experience. ” In older workers, altered color vision, night vision and accommodative flexibility require compensation by better light, better contrast, and periodic spectacle changes. Regular eye examination, maintenance of occupational eyewear, and employee education help sustain industrial safety and efliciency. For example, in substituting an inflexible lens for a flexible ciliary mechanism the presbyope is at a distinct disadvantage. Focusing inertia, restricted range and limited field of vision often necessitate unnatural postures which lead to inefficiency. In the case of moving machinery, or in cases where the operator must drive, climb, or maintain balance, uninitiated bifocal wearers may be a hazard to themselves and to others. Some of these problems can be solved by multifocals, variable focal lenses, or separate reading glasses.148 Among the numerous factors involved in driving, sensory input is obvious.2,*s Whatever other skills may be necessary, adequate acuity and visual fields are definable requirements that can be standardized. Undoubtedly depth perception, stereoacuity, discrimination of moving targets (dynamic acuity), good night vision, and well-grounded spatial orientation are also desirable, although how these should be measured is not established.26 Nor is there a satisfactory criterion of adequate (as contrasted to accident-free) driving performance. Vision takes time, a factor usually ignored in practice not because it is irrelevant but because few clinical techniques are available to measure it.“’ Time becomes crucial, however, with rapidly moving or intermittently exposed targets, flickering light sources, metacontrast effects of successive exposures, and anomalous depth induced by unequal binocular illumination (Pulfrich phenomenon).“’ Time delays in nerve conduction have been measured by electrophysiologic techniques in optic neuropathy analogous to the Marcus Gunn pupil sign. These temporal effects will become increasingly important as more information is transmitted by video screens. Poor focus increases the time required for signals to register and tinted spectacles may obscure it. In summary, visual efficiency is a challenging and largely unexplored area. The ways in which it has been approached, defined, and measured range from

INDICATIONS

FOR PRESCRIBING

factor to system analysis; from input-output to usereserve formulas. Unlike physical systems, however, the human machine is seldom typical, often transitive, and rarely calculable. No visual stress effects comparable to elevated corticosteroid levels of general physiology have ever been demonstrated. Nevertheless, within limits, optical correction can enhance binocular efficiency, reading, driving, and job safety (Table 3). Until considerably more research is done, however, we must be content to achieve the best that can be realized rather than the most that can be imagined.

D. PREVENTING

65

SPECTACLES

PROGRESSION

Preventing visual impairment rests on three cornerstones: understanding the cause of the disorder, reliably diagnosing it, and effectively treating it. Preventive care might include promoting normal visual function by correcting optical and muscular defects, facilitating visual tasks, recognizing disease early, and promoting public awareness of the need for vision screening and periodic eye examinations. Faulty vision is seldom appreciated by children or their parents; hence, screening tests have assumed a deservedly important role in preventive ophUncorrected refractive errors in early thalmology.lgs life may result in amblyopia and strabismus.” Premature infants and children with a family history of strabismus and high myopia deserve particular attention. It is estimated that about 27% of school children need some form of eye care. Between 25% to 40% of adolescents fail to achieve 20/20 acuity. In addition to caring for the physical and optical health of children’s eyes, the clinician may also be called upon to advise parents and teachers about learning and reading disabilities, color defects, and low vision. Common problems include planning a curriculum or career and providing genetic counseling.67 Blurred retinal images are an obstacle to developing normal binocularity which has been documented by both clinical and animal research. Anisometropia, particularly anisohyperopia, means a persistent forced dominance of the less hyperopic eye, which may result in refractive or strabismic amblyopia.** Uncorrected astigmatism may result in meridional amblyopia.” Spectacles can often control strabismic deviation in part or in whole, by inhibiting or stimulating accommodation. Prisms may alleviate diplopia and asthenopic symptoms, and are sometimes useful in restoring normal binocular correspondence. The principles of optical treatment in strabismus, therefore, are to provide clear retinal images, equalize visual inputs, control accommodation, and induce ocular realignment with prisms. Optical treatment may be, and usually is, supplemental to

TABLE 3 Indications for Spectacles to Enhance Efficient Vision

Use-Reserve Ratio Criteria Facultative and absolute hyperopia Positive and negative relative accommodation Positive and negative relative convergence Phorias and fusional vergences Zones of comfort Eliminating Adverse “Stress Factors” Excessive accommodative demand Excessive convergence demand Excessive fusional demand Glare; flicker; poor contrast Improving Visual “Skills” Sensory (e.g., color aptitude; blur interpretation) Motor (e.g., accommodative flexibility) Perceptual (e.g., perceptual span) Perceptuomotor (e.g., hand-eye coordination) Enhancing Binocularity Combating amblyopia Eliminating suppression and eccentric fixation Restoring normal correspondence Promoting stereopsis Inducing realignment with prisms and lenses Engineering Criteria Illumination and contrast Night vision enhancement Job design; time-motion studies Eliminating glare, flicker, vibration Improving threshold detection Reducing errors and accidents Optical Criteria Choosing optimum lens design Selecting best optical quality Ensuring ideal fit Miscellaneous Realistic prognosis Appropriate referral when indicated Advising proper ocular and visual hygiene Periodic examination Genetic and environmental counseling

pharmacologic, orthoptic and surgical management. Of all refractive errors, myopia remains the most challenging.‘58 There is a natural clinical eagerness to retard if not reverse the degenerative vitreous and retinochoroidal changes that cause visual disability. Historically, options have included: undercorrection, cycloplegia, and bifocals to reduce ciliary tone; parasympathomimetics to prevent choroidal stretching; vitamins, hormones, and diets to enhance scleral resistance; avoidance of stooping, bending, and reading to eliminate extraocular muscle compression; flatfitting contact lenses and keratotomy to modify corneal curvature; and eye exercises, palming, staring,

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biofeedback, and hypnosis to improve acuity and blur interpretation.” Not only does myopia beget more myopia, but every treatment seems to generate its opposite with the inevitability of Newton’s law. Many results can be dismissed with a shrug of the shoulders. A century of attempts to limit myopic progression by cycloplegia” or undercorrection has not achieved anything outstanding. There appears to be no difference in progression between myopes fitted with bifocals and those receiving full correction.‘” Orthokeratology and keratotomy do not alter degenerative fundus changes. Many so-called psychodynamic procedures fail to distinguish between enhanced acuity and reduced axial length.ge There is no question that acuity can be improved by training blur interpretation, effort to see, or squeezing the lids together, but this does not alter the currently accepted view that behavioral techniques do not alter myopia per se. In contrast to multiple treatments proposed for myopia, very few have been advanced to prevent hyperopia or astigmatism.88~1sa The most important are correcting hyperopia to prevent pseudomyopia and accommodative squint, and contact lens correction of keratoconus. Interest in learning and reading disabilities has also carried over into measures to prevent such disorders. So called “developmental lenses” are weak plus lenses to be used for reading or other near tasks. Although such spectacles may have a placebo effect, there is no evidence that they improve perceptuomotor peformante.” The association of blepharitis, hordeola, and chalazia with refractive errors is often described. Possibly it is connected with touching or rubbing the eyes, or it may be age-related. Opinion has swung away from ametropia as a cause, but optical treatment is still recommended. Perhaps spectacles simply discourage eye rubbing, thus preventing autoinfecti0n.l” In summary, optical correction is indicated to prevent or limit amblyopia and strabismus. The efficacy of spectacles to prevent myopic progression is confined to their vergence,

inhibitory

and

this

action

is difficult

on accommodation to demonstrate

and because

of the unpredictable course of all refractive errors. Optical therapy does not prevent degenerative vitreous and fundus changes. The benefit of “preventive” spectacles ities has (Table

to avoid

later

learning

yet to be confirmed

and reading disabilby scientific evidence

4).

E. MISCELLANEOUS Among spectacles, categories, cellaneous.

the many a number and are Primarily,

INDICATIONS indications for prescribing do not fall into distinct therefore classified as misthese

involve

considerations

MICHAELS

1981

of

TABLE 4 indications

for Spectacles

to Prevent Progression

General Screening tests Periodic examination Early diagnosis and treatment Public education

Myopia Reducing accommodative demand Reducing convergence demand Balancing accommodation and vergence Correcting night myopia Eliminating ciliary spasm Treating pseudoprogression Keratoconus Electrolyte imbalance Changes in ocular media Drug induced Horner’s syndrome Spasm of near reflex Trauma secondary to ocular surgery Trauma induced by contact lenses Hyperopia Balancing accommodation and vergence Treating pseudohyperopia Changes in ocular media Central serous retinopathy Internal ophthalmoplegia Trauma secondary to ocular surgery Trauma induced by contact lenses Astigmatism Balancing accommodation and vergence Changes induced by optical effectivity Secondary Induced by lid tumors Induced by cornea1 disease Induced by lenticular changes Induced by retinochoroidal disease Trauma secondary to ocular surgery Trauma induced by contact lens wear Amblyopia and Strabismus Correcting anisometropia, aniseikonia, and anisophoria Providing equal visual acuity Early correction of aphakia Balancing accommodation and vergence Inducing realignment with lenses and prism Avoiding induced prismatic effects Providing optimum acuity

Reading and Learning Disabilities Providing optimum acuity Balancing accommodation and vergences Correcting refractive errors Preventing transient refractive changes Treating strabismus and amblyopia Consultation and referral

INDICATIONS

FOR PRESCRIBING SPECTACLES

cosmetic and mechanical safety and protection, reasons, and selected functional disorders. No statistics are needed to emphasize the importance of protecting eyes from injury. In 1972, the Food and Drug Administration issued a policy statement specifying the use of impact-resistant lenses in eyeglasses and sunglasses. The consensus of the ophthalmic community is that the number of eye injuries from shattering of ordinary crown glass has been substantially reduced by using either plastic lenses, heat-treated glass lenses, lenses made impact resistant by chemical treatment, or laminated lenses.40,90 Safety lenses, either with or without prescription, are indicated for occupations subject to mechanical, chemical, and radiation hazards. These may need to be supplemented by special masks, shields, or helmets. Other indications are to protect from perilous sports and hobbies, and to safeguard an only seeing eye.41*184 While there is no documented evidence that ordinary light damages human retinas, some animal studies suggest that it might be prudent to avoid excessive illumination for routine ophthalmoscopy and Filters against ultraviolet fundus photography.“’ radiation are probably desirable after cataract surgery.36 The possibility that filters protect the retinas of patients with night-binding diseases is being studied. In albinism, tinted lenses reduce glare and may improve vision. Cosmetic spectacles can alter the appearance of an unsightly eye or compensate for prosthetic deficiencies. 17’ For example, minus lenses minify the palpebra1 aperture, and spherocylindrics mask lid distortions. Prisms are also advocated to improve cosmesis in strabismus, but they seldom work. A ptosis crutch attached to the upper frame rim may raise the lid enough to provide useful vision when other measures fail. A number of behavior problems have been attributed to refractive errors, and ametropia has itself been ascribed to personality disorders.“’ For example, a disfiguring ocular deviation is a source of psychologic stress during personality development. Parent-child and child-peer interaction may give rise to anxiety, timidity, or boisterous behavior, compromising schoolwork.“’ Patients with unilateral blindness or low vision often avoid activities such as reading, sewing, or watching television, which they imagine are vision-damaging. Optical correction may restore confidence by improving acuity, eliminating discomfort, straightening a deviated eye or hiding an unsightly one. Nevertheless, for some patients spectacles represent almost insuperable cosmetic and psychic obstacles. For others, the need for glasses interdicts particular

67 careers or occupations. Rarely, spectacles are useful as psychologic support. Speculations that hyperropes are “motor-minded” and myopes are introverted and socially awkward give an air of psychodynamic mostly profoundly meaningless. Who profundity, decides on a realistic definition of personality, much less how to measure it within the restricted time of office practice? Undoubtedly, eyestrain and other visual symptoms sometimes represent attempts to gain attention or be excused from conflict-arousing situations. These can usually be managed with clinical common sense and sensibility.1’,‘83 Color discrimination can be enhanced by absorptive spectacles or contact lenses.‘90 Such filters must necessarily be highly specific for certain tasks, but are then useless for others. No single filter can enhance overall color vision, or cure color defects.“‘* Since filters reduce light transmission, they also increase reaction time, impair night vision and may give the wearer a false sense of security. Monocular filters can induce spurious depth effects. Monocular occluders are indicated for diplopia and amblyopia. Occlusion of the better eye in amblyopia does two things; it enforces use of the poor eye and it prevents the inhibitory effect of unequal visual inputs. Partial occlusion offers no advantage over total occlusion, but may be useful in maintenance therapy. This may be combined with a graded neutral density filter over the normal eye. Red filters for the amblyopic eye are occasionally used to enhance cone vision and promote central fixation. Polarized filters eliminate glare from water and snow; yellow filters are advocated to reduce atmospheric haze (shooting glasses); and ultraviolet filters have been said to reduce the incidence of cystoid macular edema following cataract extraction. Any tinted spectacle when combined with tinted windshields can be hazardous to night driving. Minus spheres (or minus overcorrection) may improve acuity in night myopia, especially in patients wearing hard contact lenses.” Night vision may also be reduced in inadequately corrected myopia. Minus lenses sometimes improve vision in emmetropes wearing dark sunglasses. Conversely, patients on antiglaucoma miotic drugs often require a change in prescription and may even abandon bifocals because of enhanced depth of focus. Reading glasses are indicated for patients receiving medications with cycloplegic side effects, such as phenothiazines, belladonna, and psychomimetics. Monocular diplopia from optical causes (including cornea1 irregularities, keratoconus, polycoria, lentitular clefts or vacuoles, subluxation, vitreous condensations, intraocular foreign bodies, and macular edema) sometimes responds to over or undercorrection with spectacles.“’ The most common causes of

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monocular diplopia, however, remain improperly positioned bifocal segment lines and lens reflections. Iseikonic lenses are indicated in refractive anisometropia, and are available on special order. Fresnel lenses and prisms are useful in the temporary or trial correction of ametropia, aphakia, anisometropia, presbyopia, strabismus, eccentric fixation, and other motility imbalances. Bed spectacles are useful for patients

in respirators

spectacles occasionally vision”’ (Table 5).

or in traction. help

expand

Hemianopic the

field

of

VI. Side Effects and Alternatives to Spectacles The chief purpose of spectacles tive errors, but like all therapeutic side effects.

Most

are merely

is to correct refracagents they have

annoying,

but some

may

become intolerable, depending on the prescription and the circumstances. Anticipating and reducing side effects is part of the art of refraction. Ophthalmic lenses not only provide clear vision but also induce distortion, field restrictions, spatial disturbances, and other adverse changes which interfere with their primary therapeutic purpose. For example, the magnification and ring scotomas of aphakic spectacles can seriously compromise patient adjustment .ro2 Lenses also usually alter accommodation, vergence, phorias and image size, which may cause undesirable side effects.ls4 Finally, spectacles have subtle psychologic and cosmetic attributes, difficult to classify, but contributing to their acceptance or rejection. Although many side effects cannot be eliminated, they can often be minimized by choosing an appropriate lens design, by modifying the prescription, and by insisting on quality dispensing.” In some cases, alternative modalities such as contact lenses,“l intraocular lenses,“’ orthoptics,” or surgery’*’ may provide better and longer lasting results with fewer optical complications. Plus lenses magnify, and minus lenses minify the retinal image compared to its size in the uncorrected eye. Even a slight difference in lens design, such as switching from front surface to rear surface tories, may produce aniseikonia. The effect of magnification is to make objects appear closer. Variable magnification over the field of view is called distortion. As the eye encounters progressively more peripheral zones of a lens, a prismatic effect is created. In anisometropic prescriptions, this induces anisophoria. Spectacle apertures act as portholes limiting the field of view. Strong plus lenses add an additional blind wedge or ring scotoma. In all cases, the closer the lens is fitted to the eye, the larger the field of view.“’ Spectacles are primarily ordered to improve acuity, and most lens designs accomplish this at the optical center. Eccentric acuity, however, may suffer from

MICHAELS TABLE 5 Miscellaneous Indications for Spectacles

Protection

and Safety Criteria

Low vision and monocular patients Hazardous occupations Hazardous sports Radiation protection Infrared Ultraviolet High intensity visible light Miscellaneous Shields Helmets Special Occupational Vision Needs Bifocals; trifocals; multifocals; reading Variable focal lenses Sunglasses and filters Loupes and magnifiers Filters to improve color discrimination Bed specs Underwater Night vision enhancers

glasses

Cosmetic Magnification and minification Occluders and partial occluders Filters and tints Prisms Mechanical Ptosis crutches Other Occluders and filters for amblyopia Over and under-correction for strabismus Minus lenses for night acuity Filters to enhance acuity Iseikonic lenses for aniseikonia Fresnel lenses and prisms Hemianopic spectacles Functional and placebo effects

poor lens performance. The primary aberrations involved are marginal astigmatism, distortion, and curvature of !ield.38 Reflections from ophthalmic lens surfaces may cause annoying ghost images which can sometimes be reduced by altering base curve, tilting the spectacle frame, or applying antireflective coatingslo Antifog coatings are designed to make the lens surface more wettable. Few people enjoy wearing glasses, but even fewer prefer the alternative of poor vision or discomfort. Most people also have mistaken notions about the curative or habituating properties of spectacles. Advantages, limitations, and prognosis should therefore be explained and discussed. Yesterday’s fad is today’s fashion and will be tomorrow’s nostalgia. Nowadays, in boutique surroundings, selection of eyewear has

INDICATIONS FOR PRESCRIBING SPECTACLES changed from prosthetic fatalism to a pleasant essay in self-expression. But the dispenser should guide the patient’s cosmetic choices with an optical compass and temper fashion fantasies with anatomic realities of lashes, nose and ears. Ophthalmic lenses fit at the wrong distance or angulation, or lenses of inferior quality or design, will not provide the intended quality of seeing. A working relation with the optician is necessary to resolve such problems.‘3 Contact lenses may provide better seeing than spectacles in high myopia, anisometropia, irregular astigmatism, congenital nystagmus, aphakia, cornea1 and in selected low vision edema and opacities, problems.55 Therapeutic contact lenses may even improve acuity concurrent with relief of pain and maintenance of cornea1 integrity. The optical and cosmetic advantages of intraocular versus spectacle lenses are well known and need not be further detailed.85 Spectacles may be contraindicated if the patient refuses to wear them for cosmetic or psychologic reasons, or because immaturity, a skin lesion or allergy precludes comfortable frame lit. For example, to control the deviation in young accommodative esotropes, pharmacologic therapy is often a useful substitute. Similar considerations apply to amblyopic children who do not tolerate patching. In summary, all optical variables do not automatically mix by writing the prescription. If the elements are unseasonably concocted, it will make a hash of the visual results. The clinician must be aware of some principles of lens design.*” For example, rear surface tories might be a better choice than a plus cylinder series because they reduce meridional magnification, provide faster adaptation when switching to bifocals, and can hide edge thickness variance. Aspheric surfaces are desirable in aphakic spectacles in powers over 7.00 D.120 Plastic lenses are lighter, safer, and have less internal reflection than glass; unhappily, their higher refractive index also makes them thicker, they are not as resistant to scratching, and they cannot be resurfaced. Most manufacturers publish lens performance data (e.g., surfacing charts) from which the laboratory should not deviate for arbitrary reasons.

VII. Discussion Our review of spectacle prescribing has focused on such clinical goals as improving acuity, relieving discomfort, enhancing efficiency, and preventing progression. Since therapeutic horizons expand and contract with advances in laboratory and clinical research, it may be useful to evaluate our list of indications by their reach as well as by their grasp - by their aspirations as well as by the means available to implement them.

69 Spectacles are prescribed not only to correct optical defects but to correct visual defects. The patient with blurred vision sees what there is incorrectly, or fails to see, or sees what there is not. Vision, more than any of the other senses, bridges the outer and subjective worlds. In recent years, remarkable progress has been made in explaining perceptual phenomena by increasingly complex and specialized physiologic mechanisms.e~32~8’ One advantage of piecemeal pathophysiology is that it leads to an integrated clinical perspective. This avoids broad, bland, holistic generalizations, which tend to lack substance &d are It is often more poetic than penetrating. platitudinously true that vision is an affair of the mind as well as the eyes, and we must estimate whether optical corrections alter physical, physiologic, or psychologic variables. But this does not make the refractionist an expert in psychophysics, educational. philosophy, or child development. Nor does a nodding acquaintance with the perceptual literature necessarily provide new insights into the visual process. In most real-life situations, seeing takes place at levels well above threshold. Backgrounds are usually highly structured, involving many targets of variable luminance, contrast, texture, slants, and movement. The time available to see fluctuates as targets flit in and out of the field, or as the observer is moving. Real scenes also have cognitive and emotional aspects depending on previous experience, habituation, and organic or psychopathology. Performance under such conditions may differ vastly from inferences based on resolution thresholds. The conventional 50% psychophysical detection criterion would be useless and dangerous when driving, and contrast sensitivity probably contributes little to gaining meaning from the printed page. Thus, psychophysics, which deals with limiting conditions, may have limited application even when it can be implemented by clinical measurements. Conventional targets to evaluate acuity are optotypes, bars, rings, and simple forms.‘8Q Yet seeing also depends on the capacity to detect slight changes in luminance at regions without distinct contours, i.e., the eye’s contrast sensitivity as measured by gratings.“’ Printed gratings have recently become available for clinical use.“’ Although gratings as such do not occur in nature, there is evidence that the visual system processes signals by tuned frequency channels which can be selectively affected in disease. IQ2 The distinctive physiologic properties of neurons making up these channels allows their individual investigation by perimetric and electrophysiologic techniques.“’ This does not mean that traditional measures of acuity are now outdated and trivial, for no spectacles are available to correct low and middle frequency loss. But it provides an under-

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standing of why a lens deemed adequate for high contrast letters in a dim refracting room may fail miserably when the patient with early cataracts steps out into a brightly lit street. Skill in analyzing symptoms marks the transition from the preclinical to the practical. Any single examination reveals only a stationary tableau; it is the history that frames a three-dimensional picture of the visual problem. The presence of signs and symptoms allows comparison for consistency. Unhappily, the correlation between asthenopic symptoms and refractive measurements is not always clear-cut. One problem, of course, is how to characterize asthenopia and classify its timing, severity, location and progression. Another concerns how to categorize refractive data into more or less specific syndromes. Common criteria involve either accommodative supply and demand,“’ or opposing vergences compensating for oculomotor deficiences.168 It now appears that such concepts may be unduly simplistic. For example, the stimulus to accommodation remains controversial, and few clinical techniques are available to monitor the response objectively. Accommodation also shows asymmetric range-dependent attributes.“’ With respect to oculomotor imbalances, there is no consensus on when to prescribe horizontal prisms or orthoptics, or to modify the sphere to activate the AC/A ratio.‘v5 Despite various methods of visual analysis, the association with asthenopic symptoms is poorly predictable. 21This is in contrast to the effects of lenses and prisms on manifest squint where the criterion is simply the angle of deviation. Therapeutic results are sometimes difficult to judge; a few are achieved more by good luck than by artful design.‘24 Thus, while better acuity is imrelief of discomfort may take mediately evident, weeks, documenting myopic arrest may take years, and verifying gains in learning efficiency still awaits timely criteria. Double-blind trials of optical corrections are rarely feasible and always expensive. There is seldom an opportunity for the patient to distinguish between better and best, between the indifferent and the ideal prescription. Moreover patient evaluation is usually conditioned by motivations and expectations whose dynamics are complex and whose analysis is controversial.‘B Successful treatment of low refractive errors remains a recurring challenge, often easier to rationalize than to demonstrate. Correcting low degrees of myopia and astigmatism is indicated to improve acuity in highly discriminating patients and those with demanding visual tasks. Such refractive errors may also embarrass night vision as the pupil dilates. Small amounts of hyperopia may require correction to balance acuity and accommodation in especially when fusion is already anisometropia,

MICHAELS TABLE 6 Spectacles for Low Refractive Errors

Improving Acuity Distance (e.g., anisometropia, astigmatism) Near (e.g., accommodative inertia) Night vision (e.g., low myopia) Amblyopia Low vision magnifiers Balancing Accommodation and Vergence Binocular motility imbalances Accommodative spasm or insufficiency Over or undercorrecting strabismus Enhancing Equalize Eliminate Promote

Binocularity ocular image size anisophoria sensory and motor fusion

Miscellaneous Safety lenses (e.g., in monocular patients) Filters (glare, eccentric fixation, etc.) Occluders (total or partial) Prisms (nystagmus, strabismus, etc.) Occupational lenses Placebo and functional effects

precarious. Aniseikonia and anisophoria may be symptomatic even in small degrees of anisometropia. The refractive management of strabismus often requires spectacles despite small ametropias to induce realignment of the eyes. Ordering protective lenses, filters, prisms, or occupational eyewear is generally independent of ametropia. Finally, in some patients weak lenses for reading and study do provide symptomatic benefits difficult to predict and even more difficult to explain (Table 6). Some therapeutic indications are more clearly defined because some diagnostic criteria are better understood. Refractive diagnosis depends on ocular biometry, ophthalmic examination, and differentiation of symptoms. Refraction without funduscopy may lead to patching the only good eye of a child with macular toxoplasmosis - a tragic deprivation to improve a phantom amblyopia. Examination without refraction will miss the accommodative component in strabismus, the optical component in optic neuropathy, and the magnification potential in macular degeneration.‘23*‘10 The trend in ocular biometry, as elsewhere, has been to computerize everything in sight. 63*11’While objective optometers expedite measurements, they do not tell what the patient sees, how the patient sees, or even if the patient sees. Nor do inanticipate complaints or analyze struments therapeutic effects. Tests must also be economic in

INDICATIONS

FOR PRESCRIBING

71

SPECTACLES

time and effort as well as modern. If subjective acuity can be checked in a young child it is foolish to duplicate the feat by visual evoked potentials.“’ Implicit in the notion of visual efficiency is the hint, if not the mandate, to prescribe spectacles that will achieve more than discomfort-free vision - optimum rather than just adequate performance. Proponents of this approach like to call themselves functionalists.113 Battalions of environmental stress and organismic strain are drawn up to light imaginary battles with “structuralists” who are presumably interested only in disease. In fact, no practitioner has held such a dualistic view since physiology came of age in the last century. There is no dichotomy between curing illness and caring about wellness; devotion to one does not imply dismissal of the other. Efficient vision cannot be achieved with an impaired eye, and disease cannot be excluded by definition. The concept of visual efficiency is neither simple nor easily defined. Systems criteria, transfer functions, use-reserve ratios, and resistance of the visual mechanism to interference are some variables that have been quantified. Undoubtedly, efficiency also varies with age, experience, environmental factors, and ocular or general health. Therapy has its fads and its factions, and must be judged not only by the goals at which it aims, but by the success with which it achieves them. For example, orthokeratology, radial keratotomy, and orthoptics do not “cure” myopia in the sense of altering the potential damage of posterior ectasia. What they do accomplish, unhappily not always predictably, is to improve acuity by perceptual training and modifying cornea1 curvature.58 In evaluating the effects of other treatments, such as undercorrection, bifocals, prisms, autonomic drugs, or more virtuous hygienic measures, it must be kept in mind that the natural course of myopia is extremely variable; it eventually stops spontaneously whatever the treatment and despite continuing or even increasing near work. Spectacles, like drugs, have been scrutinized from the standpoint of cost-effectiveness. The tyranny of this dogma is that it threatens to turn back medical ethics to the Middle Ages. What is the costeffectiveness of empathy and reassurance? A perpetual competition of underselling soon leads to a permanent deterioration of the product through promotional expedients of unlimited potential mischief. On the other side of this coin are the adoption of voluntary optical standards into law after the fact. While standards are welcome and necessary, they must also be reasonable. Jury awards have been made in injury cases because lenses did not meet certain recommendations. The impact of such enforcement on the optical industry in general, and the price of spectacles in particular, cannot be conjectured. One-hundred years ago, LandolY wrote: “The

choice of glasses is a delicate operation. He alone is successful in it who, to a perfect theoretical acquaintance with the subject adds the intelligent observation of each patient.” No clinician would quarrel with this admonition, yet prescribing remains deceptively complex. The cause of ametropia is still unsettled, its course unpredictable, its symptoms nonspecific, and its prevention uncertain.” Even so, we now have a better understanding and broader perspective of refractive disorders. While Landolt might recognize current concepts of etiology (which have progressed little) or asthenopia (which have progressed not at all), he would surely be impressed by modern contact and intraocular lenses7’ intrigued by innovative lens designs,’ and perhaps intimidated by contemporary refractive keratoplasty.ld2 He would probably admire our diagnostic ultrasonography, laser interferomcomputerized oculometry,“’ and electroetry,” physiologic refractometry.12g Most likely, he would envy our wider choice of therapeutic alternatives and greater options for individualized management.

VIII. Summary Indications for spectacle correction are reviewed in the context of symptoms, pathophysiology, and prognostic efficacy. Criteria are classified according to whether spectacles improve acuity, restore comfortable vision, enhance visual efficiency, or prevent progression of refractive anomalies. Assorted miscellaneous goals, alternatives, and side effects are described. Traditional guidelines for individualized management are evaluated in the light of current research. Results are summarized in table form.

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13. Barry SH, Cochran CL: The perceptual effects of low-power plus lenses. Studies of emmetropic observers. Am 3 @tom 11:667-673, 1979 14. Bartley SH, Chute E: Fatigue and Impairment in Man. New York, McGraw-Hill, 1947 15. Beasley FJ: Transient myopia during trichlormethiazide therapy. Ann Ophthalmol 72:705-706, 1980 16. Behrdndt T: Characteristics of visually impaired persons. Surv Obhthalmol 73:303-305. 1969 17. Belmont 0: Refraction troubles. Znt Ophthalmol Clin 1:261-275, 1961 18. Bennett AG: Emsley and Swaine’s Ophthalmic Lenses. London, Hatton Press, 1968 19. Benton AL, Pearl D (eds): Dyslexia. New York, Oxford U Press, 1979 20. Boeder P: Spectacle correction of aphakia. Arch Ophthalmol 68:870-874, 1962 21. Borish I: Clinical Refraction. Chicago, Professional Press, 1970 22. Brown EVL: Apparent increase of hyperopia up to age 9 years. Am 3 Ophthalmol 79:1106-l 108, 1936 23. Brown EVL: Use-abuse theory of changes in refraction versus biologic theory. Arch Ophthalmol 28:845-850, 1942 24. Burian HM: Anomalies of convergence and divergence function and their treatment, in .New Orleans Acad Ophthalmol Symposium Strabismus. St Louis, CV Mosby, 1971 25. Burian HM, Von Noorden CK: Binocular Vision and Ocular Motility. St. Louis, CV Mosby, 1980 26. Burg A: Vision and driving: a report on research. Hum Factors 13:79-87, 1971 27. Campbell FW, Robson JG: Application of Fourier analysis to the visibility of gratings. 3 Physiol (Land) 15’7:551-566, 1968 28. Campbell FW, Westheimer G: Dynamics of accommodation responses of the human eye. Jfiysiol (Land) 157:285-295,196O 29. Carter DB: Parameters of fixation disparity. Am 3 Optom 57:610-617, 1980 30. Cassin B: Strabismus and learning disabilities. Am OrthopticJ 25:38-45, 1975 31. Chapanis A: Research Techniques in Human Engineering. Baltimore. Iohns Honkins Univ Press. 1959 32. Cornsweet “T: Visual’Perception. New York, Academic Press, 1972 33. Crawford MLJ: The visual deprivation syndrome. Ophthalmology 85:465-477, 1978 34. Curtin BJ: Myopia: A review of its etiology, pathogenesis and treatment. Sum Ophthalmol 15:1-17, 1970 35. Curtin BJ: The pathogenesis of congenital myopia. A study of 66 cases. Arch Ophthalmol 69:166-173, 1963 36. Cyrlin MN, Peduis-Leftick A, Sugar J: Cataract formation in association with ultraviolet photosensitivity. Ann Ophthalmol 72:786-790, 1980 37. Dabezies OH: Defects of vision through aphakic spectacle lenses. Contact Intraocular Lens Med 3 2:8-20, 1976 38. Dalziel CC: Effect of vision training on patients who fail Sheard’s criterion. Am 3 Optom 58:21-23, 1981 HG, Rayner AW: An analysis of 39. Davis JF, Fernald ophthalmic lens design. Am 3 Optom 47:400-421, 1964 40. Davis JK: A polycarbonate ophthalmic prescription lens series. Am 3 Optom 55:543-552, 1978 41. Dobson V, Teller DY: Visual acuity in human infants. Vision Res 78:1469-1483, 1978 42. Donders FC: On the Anomalies of Accommodation and Refraction of the Eye. London, New Sydenhan Sot, 1864 43. Drew R: Professional Ophthalmic Dispensing. Chicago, Professional Press, 1970 of the motor anomalies of the 44. Duane A: A new classification eye based upon physiological principles. Ann Ophthalmol 6~84-122, 1897 45. Duke Elder S: The Practice of Refraction. St Louis, CV Mosby, ed 2, 1969 46. Dyer JA: Medical treatment of myopia: an update. Contact Intraocular Lens Med 3 6:405-406, 1980 M: Eye injuries in racquet sports. Can Med Assoc 47. Easterbrook 3 123:168-270, 1980 48. Emsley HH: Visual Optics. London, Hatton Press Ltd, ed 3, 1944

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INDICATIONS

FOR PRESCRIBING

SPECTACLES

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73 31: 16-27, 1980 122. Michaels DD: Visual Opttcs and Re/raction. A Clinical Approach. St Louis, CV Mosby, 1980 123. Mickatavage RC: Neuro-ophthalmologic disease presenting as orthoptic problems. Am Orthoptic 3 22:44-46, 1972 124. Milder B: Lady Luck. Sum Ophthalmol 20:347-349, 1976 125. Milder B, Rubin ML: The Fine Art of Prescribing Glasses. Gainesville, TRIAD Scientific Pub, 1978 126. Miles PW: Refractive treatment of asthenopia. Am 3 Ophthalmol 32:111-121, 1949 127. Miller D, Brooks SM, Wolf E: The effect of the honeycomb on glare function. .4rch Ophthalmol 94:451-454, 1976 I 28. .Miller WB: A review of practical tests for ocular malingering and hysteria. Suru O~hthulmol 17:241-250, 1973 129. Millodot M. Riggs LA: Refraction determined electroohvsioloeicallv. Arch Obhthalmol a&272-278. 1970 130. b~linassian D’C, Jones’ BR, Zargarizadeh’ A: The Arden grating test of visual function. Br ,7 Ophthalmol 62;2:210-212, 1978 131. hiorgan MW: .4ccommodation and vergence. Am ,3 Optom 15:417-454. 1968 132. .Ilorgan XIW: The nature of ametropia. ‘4m J Optom Monograph 27, 1947 133. Morgan MW: The optical performance of certain bifocal lenses. .4m .7 Optom 40:227-233, 1963 134. Morgan MW: The Optics o/ Ophthalmic Lenses. Chicago, Professional Press, 1978 133. 11~11 HK: XIyopia and introversion. .4m ,3 Pqrhol b’1:575-576, 1948 136. National Advisory Eye Council: C’zszonResearch, a :vational Plan. Washington, CTS Dept Health Education Welfare, 1977 Am 3 Op137. Nerenberg B: A new mirror design for hemianopia. iom 57: 183- 186, 1980 The effect of the ametropic distance correction 138. Seumueller,J: upon the accommodation and reading addition. Am 3 Optom l/:20-28. 1937 VS, Hameroff SB: Spasm of the near reflex. .4nn 139. Nirankari Ophthalmol l-7:1050-1051, 1980 140 Obstfeld H: Opts m I’uzon. Sevenoaks. Kent, Butterworth, 197x 141. Ogle KN, .\ladigan LF: Astigmatism at oblique axes and binocular stereoscopic spatial localization. .4rch Ophthalmol 1?:116-127, 1945 visual acuity and op142. Olson R,J et al: Aphakic keratoplasty: tical errors. Ophthalmology 87:680-684, 1980 143. Ophthalmology manpower study for the United States. Ophthalmolqy 85: 1055-l 130, 1978 I: l’zsron and Acgustt~on. London, Pentech Press, 144. Overinqton 1976 145. Owens DA: The .Mandelbaum effect: Evidence for an accommodative bias toward intermediate viewing distances. 3 Opt .%r .Im n9:646-65 11 1979 146. Percival AS: The Prescnbmg ofSpertacleJ. New York, Wm Wood Co. ed 3, 1928 147 Priestley BS: Pleoptic instruments and methods. Inl Ophthalmol Clrn 1:787-827, 1961 148. Preston WE, Roth N: Pseudoaccommodation and progressive addition lenses. Surza Ophthalmol B3:122-126, 1979 149. Raviola E. Wiesel TN: Effect of dark-rearing in experimental myopia in monkeys. Invest Ophthalmol 17:485-488, 1978 150. Records RE: Monocular diplopia. Sum Ophthalmol Z-2:303-306, 1980 151. Ridley F: Contact lenses in treatment of keratoconus. Br J (Jphthalmol -10:295-304, 1956 152. Roth N: The problem of the undependable cylinder. Sun Llphthalmol 14:112-l 14, 1969 153. Rubin ML, Milder B: Myopia - a treatable disease? Sum Ophthalmol 21:65-69, 1976 154. Rubin M: Relationship of refractive errors to lid disorders. Int Ophthalmol Clzn 2:903-904, 1962 155. Schechter R,J: Elimination of aniseikonia in monocular aphakia with a contact lens - spectacle combination. Sun (Jphthalmol 53:57-61, 1978 156. Sells SB, Fixott RS: Evaluation of research on effects of visual training on visual functions. .4mJ Ophthalmol &t:230-236, 1957

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162 163 164

165

167

168. 169

170 171. 172.

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1961

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sense

of the eye. Invest Ophthalmol

1979

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1949

Outline I. Distribution II. Pathogenesis

and definition of ametropia

of ametropia

A. Heredity B. Age C. Environment III. Pathophysiology of ametropia A. Hyperopia B. Myopia C. Astigmatism D. Anisometropia E. Accommodation and vergence F. Transient refractive changes G. Aphakia H. Low vision IV. Evaluating refractive symptoms V. Indications for prescribing A. Improving acuity B. Restoring comfortable vision C. Enhancing visual efficiency D. Preventing progression E. Miscellaneous indications VI. Side effects and alternatives to spectacles

VII. Discussion VIII. Summary

Reprint requests should be addressed to David D. Michaels, M.D., 1350 West Seventh Street, San Pedro, California 90732.