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The Clinical Interpretation of Aids to Diagnosis.
249 error. It is commonly met with in children, especially those to whom reading does not yet come easy, and is due to an instinctive effort to see the type as clearly as possible ; the nearer the book is held the larger is the image of the type formed on the retina, and because the accommodative power of the eye decreases as age advances, and is much greater in childhood than in adult life, the young eye can focus objects at a closer range than is possible later on in life. In prescribing glasses the question of normal reading distance is of great importance ; only a correction which will ensure this can be worn with comfort.
The Clinical Interpretation of
Aids A Series
to
Diagnosis.
of Special Articles contributed by Invitation.
XX.—THE SIGNIFICANCE OF OCULAR TESTS.
PART I.-MONOCULAR TESTS.1 VISUAL tests fall into two groups : (1) monocular, Perimetry. The measurement of visual acuity in the peripheral (2) binocular. Monocular tests are carried out on each eye separ- field outside the central fixation point is known as ately, the other being screened off. In considering perimetry, and is carried out by determining the tests for visual acuity it must be remembered that power of perception of movable objects of graduated the central fixation point, an extremely circumscribed sizes in various parts of this field, while the patient area of the retina, is endowed with acute perceptive directs his gaze steadily towards a fixed point. For power, and that immediately outside this area retinal this purpose many different devices and instruments perception falls away steeply towards the periphery. are used, but in all of them there must be a So great is this difference that entirely different tests fixed central object and a rest, or appliance, for are used for central and peripheral acuity of vision. keeping the head in a steady position during the Snellen’s types.-The standardised test for central examination. The test objects consist of white and coloured acuity of distance vision consists of the familiar Snellen’s squares or mscs or types, a series of black letters various sizes. A periDiagranas of Pathological Visual Fields. meter is an instruof diminishing sizes In each case the shaded part represents the blind area. ment consisting of a arranged on a white fixed upright to ground, and placed at FIG. 2. FIG. 1. a uniform distance of which is attached a 6 metres from the movable curved arm, the latter formpatient. Each row of letters from above ing the arc of a circle downwards is of a along which the size which should be tests object may be readable at a certain moved,9 eitherr definite distance, the mechanically or by’ hand, so that the area large letter at the top at 60 metres, the tested may be measecond row at 36 sured and recorded on a chart marked in metres, the fifth row at 12 metres, the degrees radially and seventh at 6 metres, concentrically, with this last being the the fixation point as n o r m a1 standard. centre. Alternatively Right field from a case of chronic field of vision may the Acuity is expressed glaucoma showing a paracentral scotoma joining with a blind Field from a case of detachment be tested on a flat by a fraction, the area in the nasal field. The field of the lower part of the retina numerator indicating screen (Bjerrum’s is contracted peripherally. in the right eye. the distance from the the test screen), objectss being types, and the denominator the distance at which a person of normal mounted on holders, and moved about at will. acuity should be able to read letters of the smallest size which the patient can read. The Interpretation of Blind Areas. Normal vision is expressed as 6/6-that is, the The both of blind areas (scotomata) interpretation patient can read at 6 metres what he ought to read at and of areas of lowered sensibility in the field of that distance. If he can read only the top letter his vision is of very great importance in the diagnosis of vision is 6/60 ; if the second row, 6/36 ; and if the lesions in the nerve path of visual impressions. The fifth, 6/12. 6/6 vision is merely an average standard characteristic changes which occur throw light both of good acuity, and most normal eyes can read even on the position and nature of such lesions, whether smaller letters at 6 metres distance, the acuity being in the nervous elements of the eye itself or in the - 6/5 or even 6/4. path to the visual cortex. Chronic glaucoma is an unless care is taken to correct Obviously, any outstanding example of nerve derangement in the eye existing refractive error which interferes with vision itself, are all important in in which the field by a suitable lens, this test does not show the actual early diagnosis. In this changes condition abnormal pressure .efficiency of the eye. on the optic nerve-fibres at their point of exit from Jaeger’s types.-For testing acuity of near vision, the eye causes them to atrophy, and their destruction Jaeger’s types, which are ordinary printers’ types of is selective in the early stages of the disease as regards different sizes, are commonly used. The distance different parts of nerve. This selective destruction from the eye at which the type is held, as well as the shows itself in the field of vision as blind areas ; these actual size which can be read, must be taken into to the distribution of the atrophied fibres, correspond account. Myopes will hold the type close to the eyes, and appear first in the neighbourhood of the and the higher degree of myopia the nearer will it be blindusually and in the nasal field (Fig. 1), while spot held. Normal-sighted persons and hypermetropes of central vision is possible in association preservation who have reached middle age will, on the contrary, with considerable paracentral and peripheral loss of tend to hold the type far away, the distance increasing field. as age and its attendant presbyopia advance. A In cases of localised detachment of the retina pertendency to hold the book close to the eyes is not, ception is lost, or greatly diminished, over the area however, invariably due to the presence of a myopic of the detachment, which becomes manifest as a blind 1 Part II., on Binocular Tests, will appear in THE LANCET area in the field of vision (Fig. 2) ; this is an extremely valuable adjunct in the detection of small peripheral next week. -
I
I
250
detachments, and in the measurement of increase decrease in the
area
of
a
or
detachment.
Hemianopia. Again, the relative arrangement of the nerve-fibres in the paths conveying visual impressions to the cerebral cortex corresponds with that of the retinal surface, and this arrangement is also reproduced in the
reflected directly from the fundus, and will moveoff the pupil in the opposite direction to that seen inmyopic eyes, in which the rays of the emergent beam cross and form a real image before meeting theobserver’s eye, this real image taking the place of the fundus as the source of light. By determining the strength of lens necessary to’ obtain reversal of the direction of movement in each are
visual cortex itself. Also the nasal half of one retina and the temporal half of the other is represented in FiG. 4. each hemisphere and in each optic tract, for which reason blindness involving half of each visual field (hemianopia) is a common accompaniment of lesions affecting these structures. The hemianopia involving the temporal half of each field (bitemporal hemianopia, Fig. 3), caused by pressure of a pituitary tumour on the inner parts of the optic tracts in the neighbourhood of the chiasma, and the hemianopia involving corresponding temporal and nasal halves of each field (homonymous hemianopia, Fig. 4) which arises from destruction of the occipital cortex of one hemisphere, will serve to illustrate this. Normally the extent of the peripheral field over which colours can be perceived is different for each colour, and pathological disturbin colour perception, whether central or ances from a case of tertiary syphilis, showing homonymous peripheral, are of great significance. For example, Fields hemianopia, the result of pressure from a gumma on the right in cases of tobacco blindness central perception of occipital cortex. red and green is diminished early in the disease and abolished in the later stages ; also in cases of retrobulbar neuritis central perception of red and case, the refraction of the eye and the existence and With the hemianopias of pituitary amount of astigmatism can be estimated within green is lost. enlargement changes in the peripheral colour fields narrow limits of error. Retinoscopy is most easily and quickly performed accompany and may precede diminution of acuity after dilatation of the pupil and inhibition of the for white in the affected areas. When vision is reduced to perception of light and accommodation by use of a mydriatic and cycloplegic shadow, owing to the presence of an opacity in the drug, and with children and young adults especially anterior part of the eye-e.g., a dense cataract or the use of these drugs is advisable ; but in the hands closed pupil-and when operative measures for the of an expert the test often gives an equally accurate restoration of sight are contemplated, it is necessary result with the undilated pupil. Before performing a to form an opinion as to whether the whole of the retinoscopy on the eyes of a child it is usual to employ retina is likely to be active or not. This is done by a solution of atropine, which is instilled twice daily for two or three days beforehand, but in an adult the less potent drug, homatropine, is generally suffiFIG. 3. cient ; not only is it more rapid in action, the full effect being obtained within an hour after instillation. but its time of action is much less prolonged than is. the case with atropine. The indiscriminate use of mydriatics in middleaged and elderly people is extremely dangerous. owing to the possibility of determining the onset of an attack of acute glaucoma in a predisposed person by dilatation of the pupil. For this reason careful examination of the eye must always be made, special attention being paid to the depth of the anterior chamber before any mydriatic drug is instilled. The test is followed by a subjective one, based upon the objective findings, Snellen’s types being used other subjective tests may also be employed-for example, charts showing radiating lines (astigmatic Fields from a case of pituitary tumour, showing bitemporal fans) may be used as aids in the determination of the hemianopia. axis of astigmatism. An ingenious application of thedifference in wave-lengths of colours at opposite of the spectrum has recently been devised. Thisa means of the reflecting ends eye by " directing light upon Duochrome test consists of two strips of letters,. mirror from all directions in turn. If the retina be each on an illuminated transparent ground, one red the normal the patient will be able to project one blue. The short hypermetropic eye sees the light to its source-in other words, will point quickly and and accurately to the mirror in each separate position. blue more clearly, and the long myopic eye the red, and the test is carried out by equalising the clearness. of the colours with lenses of appropriate strength. M eaSU1’ement of Refr’action. The basic test for measurement of refraction is R. AFFLECK GREEVES, F.R.C.S. Eng., retinoscopy (or skiascopy), which is purely an objective Surgeon to Moorfields Eye Hospital; Ophthalmic It is performed by throwing light into the one. Surgeon to the Middlesex Hospital. patient’s eye by means of a mirror so that the light is reflected back from his fundus, making the pupil appear luminous to the observer. The mirror is then HOSPITALS AND STREET ACCIDENTS.——In his first tilted slowly so that its reflected light gradually moves off the patient’s pupil, the direction of this movement annual report Dr. J. N. Deacon, medical superintendent of the Hendon Board of Guardians’ Hospital at Redhill, being meanwhile observed. states that of 313 urgent admissions for treatment In emmetropic and hypermetropic eyes the rays of Edgware, of injuries 270 were the result of street accidents. These light emerging from the pupil of the eyeunder 270 cases cost the ratepayers of the Hendon Union someobservation are parallel and divergent respectively, thing in the region of .S4000." "
"
"
The Clinical Interpretation of
Aids A Series
to
Diagnosis.
of Special Articles contributed by Invitation.
XX.—THE SIGNIFICANCE OF OCULAR TESTS.
PART I.-MONOCULAR TESTS.1 VISUAL tests fall into two groups : (1) monocular, Perimetry. The measurement of visual acuity in the peripheral (2) binocular. Monocular tests are carried out on each eye separ- field outside the central fixation point is known as ately, the other being screened off. In considering perimetry, and is carried out by determining the tests for visual acuity it must be remembered that power of perception of movable objects of graduated the central fixation point, an extremely circumscribed sizes in various parts of this field, while the patient area of the retina, is endowed with acute perceptive directs his gaze steadily towards a fixed point. For power, and that immediately outside this area retinal this purpose many different devices and instruments perception falls away steeply towards the periphery. are used, but in all of them there must be a So great is this difference that entirely different tests fixed central object and a rest, or appliance, for are used for central and peripheral acuity of vision. keeping the head in a steady position during the Snellen’s types.-The standardised test for central examination. The test objects consist of white and coloured acuity of distance vision consists of the familiar Snellen’s squares or mscs or types, a series of black letters various sizes. A periDiagranas of Pathological Visual Fields. meter is an instruof diminishing sizes In each case the shaded part represents the blind area. ment consisting of a arranged on a white fixed upright to ground, and placed at FIG. 2. FIG. 1. a uniform distance of which is attached a 6 metres from the movable curved arm, the latter formpatient. Each row of letters from above ing the arc of a circle downwards is of a along which the size which should be tests object may be readable at a certain moved,9 eitherr definite distance, the mechanically or by’ hand, so that the area large letter at the top at 60 metres, the tested may be measecond row at 36 sured and recorded on a chart marked in metres, the fifth row at 12 metres, the degrees radially and seventh at 6 metres, concentrically, with this last being the the fixation point as n o r m a1 standard. centre. Alternatively Right field from a case of chronic field of vision may the Acuity is expressed glaucoma showing a paracentral scotoma joining with a blind Field from a case of detachment be tested on a flat by a fraction, the area in the nasal field. The field of the lower part of the retina numerator indicating screen (Bjerrum’s is contracted peripherally. in the right eye. the distance from the the test screen), objectss being types, and the denominator the distance at which a person of normal mounted on holders, and moved about at will. acuity should be able to read letters of the smallest size which the patient can read. The Interpretation of Blind Areas. Normal vision is expressed as 6/6-that is, the The both of blind areas (scotomata) interpretation patient can read at 6 metres what he ought to read at and of areas of lowered sensibility in the field of that distance. If he can read only the top letter his vision is of very great importance in the diagnosis of vision is 6/60 ; if the second row, 6/36 ; and if the lesions in the nerve path of visual impressions. The fifth, 6/12. 6/6 vision is merely an average standard characteristic changes which occur throw light both of good acuity, and most normal eyes can read even on the position and nature of such lesions, whether smaller letters at 6 metres distance, the acuity being in the nervous elements of the eye itself or in the - 6/5 or even 6/4. path to the visual cortex. Chronic glaucoma is an unless care is taken to correct Obviously, any outstanding example of nerve derangement in the eye existing refractive error which interferes with vision itself, are all important in in which the field by a suitable lens, this test does not show the actual early diagnosis. In this changes condition abnormal pressure .efficiency of the eye. on the optic nerve-fibres at their point of exit from Jaeger’s types.-For testing acuity of near vision, the eye causes them to atrophy, and their destruction Jaeger’s types, which are ordinary printers’ types of is selective in the early stages of the disease as regards different sizes, are commonly used. The distance different parts of nerve. This selective destruction from the eye at which the type is held, as well as the shows itself in the field of vision as blind areas ; these actual size which can be read, must be taken into to the distribution of the atrophied fibres, correspond account. Myopes will hold the type close to the eyes, and appear first in the neighbourhood of the and the higher degree of myopia the nearer will it be blindusually and in the nasal field (Fig. 1), while spot held. Normal-sighted persons and hypermetropes of central vision is possible in association preservation who have reached middle age will, on the contrary, with considerable paracentral and peripheral loss of tend to hold the type far away, the distance increasing field. as age and its attendant presbyopia advance. A In cases of localised detachment of the retina pertendency to hold the book close to the eyes is not, ception is lost, or greatly diminished, over the area however, invariably due to the presence of a myopic of the detachment, which becomes manifest as a blind 1 Part II., on Binocular Tests, will appear in THE LANCET area in the field of vision (Fig. 2) ; this is an extremely valuable adjunct in the detection of small peripheral next week. -
I
I
250
detachments, and in the measurement of increase decrease in the
area
of
a
or
detachment.
Hemianopia. Again, the relative arrangement of the nerve-fibres in the paths conveying visual impressions to the cerebral cortex corresponds with that of the retinal surface, and this arrangement is also reproduced in the
reflected directly from the fundus, and will moveoff the pupil in the opposite direction to that seen inmyopic eyes, in which the rays of the emergent beam cross and form a real image before meeting theobserver’s eye, this real image taking the place of the fundus as the source of light. By determining the strength of lens necessary to’ obtain reversal of the direction of movement in each are
visual cortex itself. Also the nasal half of one retina and the temporal half of the other is represented in FiG. 4. each hemisphere and in each optic tract, for which reason blindness involving half of each visual field (hemianopia) is a common accompaniment of lesions affecting these structures. The hemianopia involving the temporal half of each field (bitemporal hemianopia, Fig. 3), caused by pressure of a pituitary tumour on the inner parts of the optic tracts in the neighbourhood of the chiasma, and the hemianopia involving corresponding temporal and nasal halves of each field (homonymous hemianopia, Fig. 4) which arises from destruction of the occipital cortex of one hemisphere, will serve to illustrate this. Normally the extent of the peripheral field over which colours can be perceived is different for each colour, and pathological disturbin colour perception, whether central or ances from a case of tertiary syphilis, showing homonymous peripheral, are of great significance. For example, Fields hemianopia, the result of pressure from a gumma on the right in cases of tobacco blindness central perception of occipital cortex. red and green is diminished early in the disease and abolished in the later stages ; also in cases of retrobulbar neuritis central perception of red and case, the refraction of the eye and the existence and With the hemianopias of pituitary amount of astigmatism can be estimated within green is lost. enlargement changes in the peripheral colour fields narrow limits of error. Retinoscopy is most easily and quickly performed accompany and may precede diminution of acuity after dilatation of the pupil and inhibition of the for white in the affected areas. When vision is reduced to perception of light and accommodation by use of a mydriatic and cycloplegic shadow, owing to the presence of an opacity in the drug, and with children and young adults especially anterior part of the eye-e.g., a dense cataract or the use of these drugs is advisable ; but in the hands closed pupil-and when operative measures for the of an expert the test often gives an equally accurate restoration of sight are contemplated, it is necessary result with the undilated pupil. Before performing a to form an opinion as to whether the whole of the retinoscopy on the eyes of a child it is usual to employ retina is likely to be active or not. This is done by a solution of atropine, which is instilled twice daily for two or three days beforehand, but in an adult the less potent drug, homatropine, is generally suffiFIG. 3. cient ; not only is it more rapid in action, the full effect being obtained within an hour after instillation. but its time of action is much less prolonged than is. the case with atropine. The indiscriminate use of mydriatics in middleaged and elderly people is extremely dangerous. owing to the possibility of determining the onset of an attack of acute glaucoma in a predisposed person by dilatation of the pupil. For this reason careful examination of the eye must always be made, special attention being paid to the depth of the anterior chamber before any mydriatic drug is instilled. The test is followed by a subjective one, based upon the objective findings, Snellen’s types being used other subjective tests may also be employed-for example, charts showing radiating lines (astigmatic Fields from a case of pituitary tumour, showing bitemporal fans) may be used as aids in the determination of the hemianopia. axis of astigmatism. An ingenious application of thedifference in wave-lengths of colours at opposite of the spectrum has recently been devised. Thisa means of the reflecting ends eye by " directing light upon Duochrome test consists of two strips of letters,. mirror from all directions in turn. If the retina be each on an illuminated transparent ground, one red the normal the patient will be able to project one blue. The short hypermetropic eye sees the light to its source-in other words, will point quickly and and accurately to the mirror in each separate position. blue more clearly, and the long myopic eye the red, and the test is carried out by equalising the clearness. of the colours with lenses of appropriate strength. M eaSU1’ement of Refr’action. The basic test for measurement of refraction is R. AFFLECK GREEVES, F.R.C.S. Eng., retinoscopy (or skiascopy), which is purely an objective Surgeon to Moorfields Eye Hospital; Ophthalmic It is performed by throwing light into the one. Surgeon to the Middlesex Hospital. patient’s eye by means of a mirror so that the light is reflected back from his fundus, making the pupil appear luminous to the observer. The mirror is then HOSPITALS AND STREET ACCIDENTS.——In his first tilted slowly so that its reflected light gradually moves off the patient’s pupil, the direction of this movement annual report Dr. J. N. Deacon, medical superintendent of the Hendon Board of Guardians’ Hospital at Redhill, being meanwhile observed. states that of 313 urgent admissions for treatment In emmetropic and hypermetropic eyes the rays of Edgware, of injuries 270 were the result of street accidents. These light emerging from the pupil of the eyeunder 270 cases cost the ratepayers of the Hendon Union someobservation are parallel and divergent respectively, thing in the region of .S4000." "
"
"