An Evaluation of Orthokeratology

An Evaluation of Orthokeratology PERRY S. BINDER, MD, FACS,* CHARLES H. MAY, OD,t STUART C. GRANT, ODt

Abstract: Twenty-three orthokeratology (OK) patients and 16 cosmetic hard contact lens (CL) patients were evaluated. Initially, each patient underwent a complete examination including central and peripheral keratometry, specular microscopy, axial length determination, uncorrected visual acuity, and cycloplegic refraction. The patients were then re-evaluated every three months. When the retainer lens stage was reached, the contacts were removed, and the patients were again re-examined for six additional months. Nine of ten CL patients remained in the study, during which time there was no improvement in unaided visual acuity or spherical equivalent. Both the central horizontal and vertical meridians flattened during this time. Twenty of 21 OK patients were also studied. A different technique of fitting contact lenses was used for this group, which produced significant changes in uncorrected visual acuity (P > 0.01) and spherical equivalent (0.1 > P > 0.05), but not in the central or peripheral corneal curvature. Five of the OK patients failed to respond. Six had variable, unpredictable responses, and nine had good responses. Analysis of the information in this study demonstrates that an OK procedure utilizes techniques of fitting that differ from standard contact lens techniques. The responses to OK are unpredictable and uncontrollable. The quality of uncorrected vision is worse than with contacts or glasses, and the chances of attaining 6/12 (20/40) uncorrected vision are small. Once lenses are removed, the corneal parameters return toward prefit levels. [Key words: contact lens, corneal distortion, corneal warpage, keratometry, orthokeratology.] Ophthalmology 87: 729-744, 1980

The orthokeratology procedure consists of the fitting of a series of contact lenses that are designed to modify the corneal curvature to reduce or eliminate refractive errors. 1 The tempoFrom the Section of Ophthalmology, Veterans Administration Medical Center,* and the Division of Ophthalmology, Alvarado Medical Centert, University of California, San Diego. Presented at the Eighty-Fourth Annual Meeting of the American Academy of Ophthalmology, San Francisco, November 5-9, 1979. Supported in part by the International Orthokeratology Society. Reprint requests to Perry S. Binder, MD, Section of Ophthalmology (112G), Veterans Administration Medical Center, 3350 La Jolla Village Drive, San Diego, CA 92161.

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rary modification of refractive errors that is inadvertently produced as a byproduct of the daily wear of contact lenses-the so-called spectacle blur-has been known for years, but it has only been in the last ten years that people have purposely tried to modify refractive errors with hard contact lenses. 2 Orthokeratology has become popular because of the desire of patients to completely eliminate glasses or contact lenses. Although orthokeratologists claim that the procedure is highly successful and that the majority of patients are able to eliminate hard contact (retainer) lens wear, there have been very few scientific studies to support their claims. 3 On the contrary, previous experience with hard contact lens wear has demonstrated that lens-

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induced refractive errors, for the most part, are temporary and unpredictable, and are not necessarily related to the relationship between the base curve of the contact lens fitted and the curvature of the cornea. 4 - 6 In a very excellent study performed by Kerns/ cosmetic contact lens and orthokeratology patients were fit and followed for 1,000 days. Kerns concluded that responses to orthokeratology were uncontrolled, that there was a significant incidence of induced astigmatism, and that no predictable features could be extracted from the prefit examination to select those candidates who would respond favorably. 7 The major criticism leveled against his study was that the procedure employed was not consistent with standard techniques for orthokeratology fitting. The present study was undertaken to evaluate the orthokeratology procedure as performed not only by experts in the field, but also by those who played a role in its development and its popularity. This study was conceived by two of the authors (C.H.M. and S.C.G.) and was supported in part by the International Orthokeratology Society.

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MATERIALS AND METHODS

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The patients for this study all came from the private practice of two of the authors (C.H.M. and S.C.G.). The patients were those desiring cosmetic contact or orthokeratology lenses. The patients were told they would be entering a study that would last for two to three years and that at some time during the study they would be required to stop wearing their contact lenses completely for a period of six months. Patients were then selected (by C.H.M. and S.C.G.) and referred to the Eye Clinic of the University Hospital. Patients could enter the study if they had never worn contact lenses or if they had not worn contact lenses for at least six months prior to the start of the study. Prior to the study, each patient received an informed consent that outlined the requirements of the study. The initial examination included the following: uncorrected visual acuity, manifest refraction, slit lamp biomicroscopic examination, corneal sensitivity measurement with an anesthesiometer (Cochet-Bonet), corneal and anterior chamber pachometry (Models I and II, Haag Streit Model® 900 slit lamp biomicroscope), central keratometry (Bausch and Lomb), photoelectric keratometry (PEK, Wessley-Jessen, Inc.), cycloplegic refraction, applanation tensions, dilated funduscopic examination, corneal specular microscopic examination (Syber, Inc.), and axial length measurement (Kretz-A-scan®). The pa-

tients were then given three-month appointments and were returned to the care of their orthokeratologist, who would then fit either cosmetic or orthokeratology lenses. All data were recorded on one side of a single sheet of paper, which was filed at a separate hospital and was not part of the patient's chart, so that previous data would not be available to influence a given examination. At each three-month examination a separate examination sheet was filled out and subsequently filed at a separate hospital. On these return examinations, the patient's vision with the contact lenses in situ was first determined, after which the contact lenses were removed and neutralized, and within 10 minutes of lens removal the vision in each eye was recorded. All examinations were performed in one of two 20-foot examination lanes. The patients were then given the following examination: manifest refraction, central keratome try, anesthesiometry, corneal and anterior chamber pachometry, slit lamp biomicroscopic examination, and applanation tension. The patients were individually questioned about their symptoms and quality of vision. All data were recorded on the evaluation sheets. The cosmetic contact lens patients, for the most part, continued to wear their same lenses, whereas the orthokeratology patients had lens changes as determined by the orthokeratologists. The number of lens changes was recorded at each visit. Patients were encouraged to return between scheduled visits if any untoward complications occurred. When the orthokeratologists determined that the orthokeratology patients were in their retainer lens wear stages (or the cosmetic contact lens patients had completed 18 to 24 months of continuous wear), the patients were examined and then were asked to remove their lenses for a period of six months. The patients were then examined three months and six months after lens removal. At the final examination six months after lens removal, all examinations performed at the initial examination were repeated. All clinical photographs, examination sheets, and photoelectric keratometric photographs and negatives were maintained in the same files. The primary evaluator (P.S.B.) did not examine the data until the study was terminated. The study began on June 1, 1976 and was analyzed as of October 10, 1979. The analysis of the photoelectric keratometric (PEK) readings was performed by photographing a steel ball of known radius and projecting the negative of that image using a photographic enlarger. The nega; tive of the PEK was then projected in the same enlarger, and the individual rings were then measured to obtain peripheral corneal curva-

Table 1. Characteristics of Study Groups

Average visual acuity Average refractive error Average keratometric readings KH Kv Number Follow-up (mo) Average age (yr)

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6/18 -2.82 ± 2.39

6/60 -5.15 ± 4.23

6/36 -2.50 ± 1.10

43.77 ± 2.25 44.23 ± 2.09 9 0 24.1

43.29 ± 1.03 44.02 ± 1.06 10 3-24 21.1

43.24 ± 1.02 43.32 ± 4.4 20 3-36 23.37

* KH = horizontal meridian. Kv = Vertical meridian.

Table 2. Characteristics of Lenses

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40.24-41.99 8.8-10.0 1.46-1.53

ture measurements. Analysis of the contact lenses was performed with a radioscope and lensometer (American Optical Company). Statistical analysis was performed using Fisher's t-distribution. Visual acuity analysis was performed by converting Snellen acuities to decimal fractions, eg, 20/200 = 0.1

RESULTS Of thirty-nine patients who entered the study, nine dropped out after their initial visits. The average visual acuity, the average refractive error, and the average keratometric readings are listed in Table 1 for comparison with the two remaining groups. The reasons given for dropping from the study included moving, the distance was too far, or it was too troublesome to continue. Ten contact lens patients who served as controls continued in the study, although two dropped out after several visits. The range of follow-up was from 3 to 24 months (Table 1). Twenty-one orthokeratology patients were referred, but one dropped out after one visit. Of the 20 remaining, the follow-up varied between 6 and 36 months (Table 1). The characteristics of the contact lenses used in the contact lens group are listed in Table 2. All patients wore the lenses for more than 12 hours a day. There was no evidence of corneal abrasion or corneal warpage during the study, but one patient had a subconjunctival hemorrhage associated with insertion of the lens. Spectacle blur was limited to 10 minutes or less, and no patient had problems reading with his contact lenses in place.

The characteristics of the 20 orthokeratology patients are listed in Table 1. These patients were fit with contact lenses whose base curves were flatter (P < 0.01) (Fig 1) and whose sagittal depths were deeper (P < 0.01) (Fig 2) than those lenses fit for the contact lens group. A comparison of the base curve changes between the cosmetic lenses (Fig 1A) and orthokeratology lenses (Fig 1B) demonstrates that the relative flatness of the orthokeratology lenses over time was 0.75 to 1.5 diopters flatter than that of the cosmetic contact lenses. On an individual basis, the orthokeratology lenses were fit between 0.5 and 2. 75 diopters flatter than the flattest (horizontal) corneal meridian during the entire study (Table 3). The OK lenses were changed every four to six weeks until the retainer stage. VISUAL ACUITY

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The average uncorrected vision in the contact lens group did not improve over a 24-month period (Fig 3). Although both the contact lens group and the orthokeratology group started out at about the same average level of vision (Table 1), the average uncorrected visual acuity improved only in the orthokeratology group over the entire range of the study. The average vision changed from an initial starting level of 6/36 (20/120) to an average that was maintained at approximately 6/12 (20/40) through 24 months of the study (P < 0.01) until retainer contact lenses were removed, after which time the average vision began to drop (Fig 3), but remained significantly better than the prefit levels (P < 0.01). Twenty-eight of 40 eyes (70%) were able to reach 6/12 (20/40), and 22 of 40 (55%) were able to attain 6/7.5 (20/25) at some time during the study: for example, 14 eyes (35%) reached 6/6 in the first 15 months, but only six eyes (20%) were recorded at this level after 15 months. Analysis of the final average visual acuity in comparison with the average level of myopia at the start of the study was performed. Eleven OK eyes (Group A, Table 4) had an average initial visual acuity of 6/86 (20/286) with an av-

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There was no significant difference in the final average visions of the group with more than 2.50 diopters of myopia (group A, Table 4, -3.78 diopters average) and the group with less than 2.50 diopters of myopia (Group B, Table 4, -1.87 diopters average), which suggests that the orthokeratology procedure as performed by the authors is partially effective at refractive errors less than -3.78 diopters of myopia. Only five eyes (Group C, Table 4) in the entire OK group had greater refractive errors (average = -4.72 diopters). The average vision in this group started at 6/120 (20/400), reached maximum improvement at 16.8 months (6/45, 20/150), and was 6/30 (20/100) at 25.2 months.

erage of -3.78 diopters of myopia. This group achieved maximum improvement in average uncorrected vision at 18 months (6/13.5, 20/45) and maintained that vision for as long as 23.7 months. This level of improved average vision was significantly different from the pretreatment level (P < 0.01). Twenty-five OK eyes (Group B, Table 4) started the study with less than -2.50 diopters ( -1.87 diopters average) and 6/30 (20/100) vision, achieved maximum improvement in average vision at 11.2 months (6/10, 20/26), and improved slightly to 6/9 (20/30) at 17.4 months. The level of the average improved vision was significant (P < 0.01) compared with prefit levels. It is clear that the major changes in the OK cases took place in the first nine months (Fig 3). If the vision was going to improve, it did so in the majority of cases between 11 and 18 months. If the vision had not improved by 18 months, it did not improve after that time.

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The initial average spherical equivalent of the contact lens group was -5.15 diopters, whereas the orthokeratology group started at -2.50

Table 3. Relationship Between Contact Lens and Flattest Corneal Curvature 1 Yr

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41.00-44.25 (42.85) 41.00-44.25 (42.46)

41.12-44.25 (42.67) 39.00-44.50 (41.99)

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OK 40.37-44.12 (42.54) 39.0-43.25 (41.35)

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diopters (P < 0.01) (Table I, Fig 4). Both groups demonstrated reductions in the average spherical equivalent throughout the duration of the study (Fig 4), but the reduction in the CL group was not significant. The initial difference in the average spherical equivalents between the two groups at the start of the study was maintained throughout the study. The changes in the spherical equivalent for the Group-A (Table 4) OK patients (11 eyes) whose initial average refractive errors were greater than -2.50 diopters (- 3. 78 ± 1.02 SD) were maximal at 15.8 months ( -1.86 ± 1.71) (P < 0.01). At 23.7 months, however, the improvement in the average refraction decreased to -2.26 ± 1.60, but it still represented a significant reduction compared with the prefit levels (P < 0.01). In Group B (Table 4), of 25 OK patients whose initial average refraction was less than -2.50 diopters ( -1.87 ± 0.40

diopters), a significant (P < 0.01) maximum reduction occurred at 11.2 months ( -0.40 ± 0.89 diopters), but by 17.4 months the reduction was only -1.57 ± 1.04 diopters (0.2 > P > 0.1). These results suggest that the orthokeratology procedure has about the same effect on all eyes whose average spherical equivalent is less than -3.78 diopters of myopia: ie, one can achieve a reduction in myopia of 0.3 to 1.50 diopters with refractive errors less than 3.8 diopters of myopia. Only five eyes had refractive errors more than 3. 78 diopters of myopia. Analysis of this subgroup (C, Table 4) revealed an average prefit level of -4.72 diopters (±0.64). At 15.8 months the average refraction was -3.20 diopters (±0.54), and at 23.7 months it remained at -3.27 diopters (±0.49). A comparison of the changes induced by orthokeratology in the various refractive error groups is summarized in Table 4.

Table 4. Effect of Refractive Error on Final Vision and Refraction

Number of eyes Initial refraction Best refraction Final refraction Initial visual acuity Best visual acuity Final visual acuity * Represents a subgroup of Group A.

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Group C* (4.00 diopters)

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25 -1.87 ± 0.40 -0.40 ± 0.89 -1.57 ± 1.04 6/30 (20/1 00) 6/10 (20/26) 6/9 (20/30)

5 -4.72 ± 0.64 -3.20 ± 0.54 -3.27 ± 0.49 6/120 (20/400) 6/45 (20/150) 6/30 (20/1 00)

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Analysis of the results in Table 4 demonstrates that an average improvement in refraction of 1.52 diopters produced an average improvement of five lines of vision, a sixfold improvement (Group A, Table 4). An improvement of 0.30 diopters produced an average 5 line (3-fold) improvement (Group B) (Table 4) and 1.45 diopters produced only an average 3 line (4-fold) improvement in vision (Group C) (Table 4) using the latest data in the study. The average refraction improvement in Group A was 1. 51 diopters ( ± 1. 10) with a range from no improvement to 3.67 diopters. Surprisingly, not only was the average improvement in Group B only 0.39 diopters (±.99), but there was an induced myopia in 7 of 25 eyes of 0.50 to 1.37 diopters. The range of change was ± 1.37 diopters of induced myopia to a reduction of 2.25 diopters. This unexpected induction of myopia in the one group we would expect to have the best results (the low myopia group) demonstrates the unpredictable responses which can occur. KERATOMETRY READINGS

Both groups (OK and CL) started in the horizontal meridian of the central cornea at the same curvature and both groups had an average reduction in the horizontal meridian of approximately 0.75 diopters (Fig 5). There was a slight tendency for the horizontal meridian in the contact lens group to continue a flattening

trend whereas the horizontal meridian for the experimental group remained at approximately 42.50 diopters throughout 30 months of the study. A similar trend in the control and experimental group was found in the vertical meridian (Fig 6). The flattening trend of the vertical meridian stabilized in the OK group at 43.50 diopters whereas the same meridian in the CL group continued a flattening change; there was no significant difference in the vertical meridian between the two groups at any time. The average corneal astigmatism in the contact lens group was 0.71 diopters at the beginning of the study (Table 1). It slowly decreased over the 24 months to an average of 0.41 diopters. At the start of the study there was an average of 0.10 diopters of corneal astigmatism in the OK group, which increased to 0.90 diopters on the average by six months. The corneal astigmatism varied from 0.59 to 0.91 diopters from 9 to 33 months (0.68 diopters average) and was significantly greater than the astigmatism in the CL group at the end of the study (0.1 > P > 0.05). The average central horizontal and vertical meridians of the CL group were significantly different from the prefit readings at 15-24 months (P < 0.005). The average central vertical meridian for the OK group was not significantly flatter than the prefit level at 15-24 months (0.2 > P > 0.1), but the horizontal meridian was significantly flatter than the prefit readings (P < 0.005).

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Analysis of the photoelectric keratometric (PEK) negatives demonstrated no significant change from the central readings in rings 1 to 4, but there was a slight tendency towards peripheral flattening of about 1 diopter from rings 5 to 8 (Fig 7, Table 5). Throughout the study, all eyes maintained their initial, slight, peripheral corneal flattenings compared with

central readings. Not all PEK's were available for analysis at the termination of the study, but enough information was available to analyze the orthokeratology response. Analysis of the peripheral cornea was performed in six eyes of the no response subgroup, in six eyes of the variable responders, and in 12 eyes of the good responders (Fig 7, Table 5).

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Fig 7. Analysis of the corneal shape using photoelectric keratometry (PEK). The upper graphs show the analysis for a patient who was an orthokeratology nonresponder. There was no significant difference in the corneal shape during the 24 months he was studied. The analysis for good orthokeratology responder shown in the lower graphs demonstrates a flattened peripheral cornea after 24 months of treatment. This was the only OK patient examined with PEK who had this response. The horizontal (H) and vertical meridians (V) tended to parallel each other across the cornea.

In all three subgroups there was no significant difference in the PEK readings in rings 1 to 4 from the central readings taken with the Bausch and Lomb keratometer at the start of the study or at the time of evaluation (19-21.6 months) (Table 5). In the subgroup of six eyes that did not improve in any category during this study, there appeared to be a tendency towards peripheral flattening in rings 5 to 8, but there was no significant difference when the readings

were compared with the prefit central readings (Table 5), which suggested these corneas had fairly spherical shapes out to ring 8 (7 -9 mm in diameter). In the good response group of 12 eyes with an average follow-up PEK evaluation of 21.2 months (Table 5), the pre fit readings in the peripheral cornea in rings 1 to 6 did not differ significantly from the central prefit readings, but rings 7 and 8 were significantly flatter (0.02

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Number of eyes Average follow-up (mo) Ring 5 H

No Response

Variable Response

Good Response

6 19

6 21.6

12 21.2

Initial

Final

Initial

Final

Initial

Final

v

43.00 43.37

43.25 43.50

42.37 43.12

42.75 43.12

43.12 43.50

43.00 42.75

v

43.00 43.37

43.12 43.37

42.37 42.87

42.50 42.87

43.00 43.37

43.00 42.87

v

42.75 43.12

42.87 43.37

42.37t 42.75t

41.87t 42.00t

42.67 42.87t

42.75 42.75t

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42.67 42.87

41.87t 42.50

41.12t 42.75t

42.25t 41.75t

42.00t 42.12t

Ring 6 H Ring 7 H Ring 8 H

* Photoelectic keratometry rings 5 to 8: H = horizontal; V = vertical.

t These readings were significantly flatter than prefit central readings (0.02 < P < 0.01), but were not significantly flatter between the

initial and final exam for each ring.

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> P > 0.01) in the horizontal and vertical meridians (Table 5). The latest readings 21 months later had not changed in rings 1 to 6, but were still flatter in rings 7 and 8. However, the prefit readings in rings 7 and 8 were not significantly flatter than the postfit readings in either meridian. The corneas in this group appeared to flatten more in the periphery compared with the corneas in the no response group (Fig 7), but the trend was not significant. The variable response group was very similar to the good response group, with significant flattening in the prefit readings in rings 7 and 8 compared with central readings, but did not have any significant flattening in these rings after an average of 21.5 months of treatment (Table 5).

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The patients in this study chose orthokeratology because they wished to be without glasses or contact lenses even if it were only for a period of hours. The one common fact for the entire experimental group was that there was no universal predictability of when the best unaided visual acuity would occur. Some patients would notice the best improvement in distance vision immediately upon removal of the lenses, whereas others would notice it upon awakening in the morning, and still others found that the best vision would occur on weekends when they would leave their lenses out for 12 to 24 hours. Other patients were unable to predict when their unaided visions would be the best. COMPLICATIONS

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RETAINER LENSES

Fourteen patients reached a follow-up between 18 and 24 months in the orthokeratology group, which is the time when retainer lenses are fit. 3 Of this group, only four were fit with retainer lenses, two at 24 months, one at 26 months, and one at 30 months. The characteristics of the retainer lenses are compared with the patients' corneal and refractive parameters and the previous contact lenses worn (Table 6). In two instances the lenses were flatter than the last lens in the series: in one instance it was exactly the same as the previous lens, and in one instance it was 1 diopter steeper than the latest lens in the series. The average visual acuity in these patients at the time of retainer lens wear removal was 6/9.5 (20/35). Three months after lens removal the average vision deteriorated to 6/24 (20/80) (six eyes), and at six months it averaged 6/27 (20/90) (six eyes). In a similar fashion, the average spherical equivalent increased after removal of the lenses in two of three patients, but remained unchanged in one patient six months after lens removal (Fig 5). Both the horizontal and vertical meridians demonstrated tendencies to return toward prefitting levels after removal of the contact lenses, in contrast to Kerns' study 7 , where the vertical meridian continued to steepen following lens removal, producing with-the-rule astigmatism.

Although minimal distortion in the keratometric mires was found to be more prominent in the orthokeratology group, there was no occurrence of corneal warpage, corneal scars, or endothelial damage, nor was there an undue incidence of corneal abrasions in this group. However, many patients complained of an inability to read with their lenses in place or with their own glasses. Reading glasses were prescribed for 6 ofthe 19 orthokeratology patients. Another feature of the orthokeratology group was the quality of vision. All patients who had improvements in unaided visual acuity stated that the quality was less than it was with their refractions or with their contact lenses: ie, the quality of 20/40 unaided visual acuity without contact lenses was considered to be worse than 20/40 vision with hard contact lenses in place. The patients described their vision as irregular and variable, like "looking through a dirty windshield" or "looking through a fish bowl." There was no significant difference in the slight reductions in corneal sensitivity between the two groups. There was no measurable change in corneal thickness, anterior chamber depth, or axial length in either group throughout the study. OVERALL RESULTS

Three types of responses occurred in the ex-

Table 6. Retainer Lenses in Orthokeratology* Patient Average

Previous Lens

Retainer Lens

42.76 ± 1.48 6/9 (20/33) Power -2.09 ± 1.14 42.17 ± 1.31

Sag 1.51 ± 0.09 mm Diam 9.48 mm Power -0.28 ± 1.29 BC 41.05 ± 0.95

Sag 1.53 ± 0.07 mm Diam 9.6 mm Power -0.06 ± 0.97 BC 43.63 ± 1.83

* K" = central horizontal curvature; KA = uncorrected vision; Kv = central vertical curvature; SpEq = spherical equivalent; BC = base curve contact lens; Sag = saggital depth.

738

perimental (OK) group. The first type of response, representing no change during the study, occurred in ten eyes in five patients (Table 7). Partial or variable responses were found in 12 eyes of six patients. This type of response is characterized by an initial unresponsiveness followed by an improvement in unaided visual acuity, and later, for unexplained reasons, while wearing the same contact lens, there was a deterioration of vision and other parameters. The remaining group, those patients who achieved good responses and in many instances achieved 6/6 unaided visual acuity at some time during the study, included 18 eyes of nine patients with an average follow-up of 24 months (Table 6). No patient in the unresponsive response group ever achieved an uncorrected visual acuity better than three lines from his initial starting unaided visual acuity at any time during the entire study. The patients in the variable response group, as a rule, were able to achieve unaided visions, on the average, four to six lines better than their initial unaided visual acuities at some time during the study, and in a few cases were able to attain better than 6/7.5. However, these responses were highly variable and unpredictable, and as the study progressed, the uncorrected vision tended to decrease for unexplained reasons while the patients were wearing the same contact lenses. The patients who had good responses tended to attain their best unaided visions early in the study and tended to maintain those levels of vision throughout the duration of the study (Table 7). Overall, if a patient was going to attain an improved unaided visual acuity, it would occur within the first nine months of the study in the large majority of the patients, but there were three patients whose best unaided visual acuities did not occur until 18 months into the study. There were no differences in the ages of the patients, the prefitting parameters, or the fitted contact lenses that could be detected among the three subgroups of orthokeratology patients, although the unresponsive cases (ten eyes) had more myopia at the start of the study

compared with the variable and good response groups and, in addition, tended to have spherical corneas.

DISCUSSION Orthokeratology has been practiced for the last ten years, and numerous claims of its success have been made. 3 Most orthokeratologists state that the procedures used are without complications and represent standard techniques of contact lens fitting. 8 In the only scientific orthokeratology study performed to date, the results were mixed and erratic. 7 The major criticism leveled against the study was that the fitter was not using standard orthokeratology techniques. The present study differs from that study 7 in that the orthokeratology fitters were experienced in the technique. The fitters (C.H.M. and S.C.G.) had complete freedom of patient selection and choice of fitting techniques. The purpose of this study was to evaluate the authors' own results in an unbiased fashion. Orthokeratology Procedures are Contact Lens Procedures. In the present study the control patients who were fit with cosmetic contact lenses received lenses whose base curve paralleled the flattest corneal meridian. (Table 3). However, the lenses fit for the orthokeratology group were fit between 0.75 and 2.5 diopters flatter than the flattest corneal meridian (P < 0.01): their diameters were greater, and the sagittal depths were steeper (P < 0.01) (Fig 2, Table 2). Since there was no significant difference in the initial corneal curvatures between the two groups (Table 1), a different technique was utilized in fitting the orthokeratology lenses in this study. Orthokeratology Procedures are Safe and without Risk Compared with Cosmetic Wear of Hard Contact Lenses. In this study no adverse effect was seen in either group, although the orthokeratology group did tend to have mild distortion of the keratometric mires and increased with-the-rule astigmatism compared

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Table 7. Orthokeratology Subgroup Responses* No Response (1 0 Eyes)

VA SpEq KH Kv

Follow-up Kv

*

Variable (12 Eyes)

Good Response (18 Eyes)

0

Last

0

Last

0

Last

6/60 3.95 43.30 43.82

6/30 3.27 42.81 44.09

6/35 1.98 43.35 43.73

6/15 1.74 42.89 43.68

6/30 2.03 43.47 43.62

6/7.5 1.00 42.57 43.40

Last = before retainer removal; 0 central vertical curvature.

24 mo =

18 mo

initial prefit unaided visual acuity; SpEq

=

spherical equivalent; KH

=

24 mo

central horizontal curvature;

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with the contact lens group. The orthokeratology patients did not develop corneal warpage or corneal scars, nor did they have an abnormal incidence of corneal abrasions or central punctate staining. However, the orthokeratology patients did have two significant handicaps. First, approximately a third of them required reading glasses to perform their near activities. Second, the quality of unaided visual acuity was significantly worse than the best corrected visual acuity obtained with glasses or contact lenses. Orthokeratologists Can Select Patients Who Will Be Good Candidates for the Procedure. All patients in this study were selected by two of the authors (S.C.G. and C.H.M.). If there is a way to detect a patient who is going to be a successful candidate, an orthokeratologist would have knowledge not available to the general public. In this study, ten eyes of five patients did not respond to the orthokeratology technique (Table 5). This group of patients had relatively high refractive errors, slight flattenings in the horizontal meridian, steepenings in the vertical meridian, and an average improvement in visual acuity from 6/60 to 6/30. The groups that achieved significant improvements in visual acuity included 12 eyes of six patients with variable responses and 18 eyes of nine patients with good responses (Table 7). In the latter groups the average refractive error was almost 2 diopters less than that in the no response group, but otherwise there was no significant difference in the horizontal or vertical meridian changes in the central cornea for all three groups. The patients who achieved good responses had decreases in their average spherical equivalents of 50%, from an average of2 diopters to 1 diopter (Table 7) associated with an average of 1 diopter flattening of the horizontal meridian. By the end of 23 months, the average horizontal meridian was almost 1 diopter flatter than the vertical meridian, whereas at the start of the study it was only 0.15 diopters flatter. There have been recent claims that analysis of the peripheral cornea can be a useful guide to select who will be a likely orthokeratology success and who will not. 9 Analysis of the peripheral cornea with photoelectric keratometry demonstrated in this study that spherical corneas do not respond to orthokeratology, whereas corneas with peripheral flattening may respond (Table 5). Since the changes in the peripheral cornea did not directly correlate with the changes in vision or refraction, one must assume other factors are involved in the process. If one were to pick who will be successful and who will not, one would choose a low myope

whose horizontal meridian in the central cornea is slightly steeper than the vertical meridian, ie, against-the-rule astigmatism. However, having one of these parameters does not guarantee excellent unaided visual acuity, as shown by the 12 eyes in the variable group that shared the same characteristics as eyes in the good response group. The fact that some patients did not respond to the treatment until nine months into the study makes it very difficult to conceive how one could predetermine who will do well and who will not. When the OK cases were analyzed on the basis of their prefit refractive errors (Table 4), it became apparent that an eye would be able to attain an average of four or five lines of improvement in uncorrected vision if the initial amount of myopia was less than 3.78 diopters of myopia. Although the corneal curvatures and refractive errors could be manipulated to about the same degree regardless of the prefitting status, at refractive errors beyond 4 diopters, little improvement in unaided vision can be expected (Table 4). The Orthokeratology Procedure is Able to Correct 1.75-3 Diopters of Myopia and 1.75-3 Diopters of Astigmatism. 10 • 11 The average improvement in myopia was 1.51 diopters in a group whose pretreatment refraction was -3.78 diopters of myopia. The range of improvement in this group (Group A, Table 4) was from 0 to 3.67 diopters. In the group of OK eyes whose initial average refraction was -1.87 diopters (Group B, Table 4) the average improvement was only 0.39 diopters, with 7 of 25 eyes developing more myopia (0.50 to 1.37 diopters), whereas the decrease in myopia in the remaining 18 eyes was from 0 to 2.25 diopters (Table 4). There were no significant differences in the prefit corneal curvatures or the lenses fit between these two groups. Based on this study, it appears that the procedure used was capable of reducing as much as 1.50 diopters of myopia in eyes with moderate myopia, but was not as successful in reducing myopia in eyes with low refractive errors. One explanation for this confusing result could be that the refractive error in one group was axial and in the other was refractive, but a retrospective analysis of these particular cases failed to demonstrate such a difference. One Diopter of Refractive or Keratometric Change Will Produce an Improvement in Vision of Six to Seven Lines. 3 •8 • 10 • 13 • 14 In the entire orthokeratology group the average prefitting spherical equivalent was -2.50 diopters ( ± 1.10 SD) (Table 1). The spherical equivalents of the orthokeratology group fluctuated throughout the study (Fig 5), but at 18 months and at 33 months the smallest refractive errors

were present (1.26 diopters and 1.29 diopters on the average, respectively) (Fig 5). If a given change in refractive error is able to produce a given change in visual acuity as suggested, 3 the unaided visual acuities at 18 and 33 months should be essentially equal and significantly better than those at the start of the study. The visual acuity results of the orthokeratology group (Fig 4) show that this group started out with an average unaided vision of 6/30 (20/118), and at 18 months achieved 6/12 (20/40) average uncorrected vision with an average spherical equivalent of 1.26 diopters. At 33 months the average best corrected vision was 6/24 (20/80) with essentially the same spherical equivalent (1.29 diopters). At 24 months the average spherical equivalent was increased to 1.53 diopters, but the average unaided visual acuity remained 6/12 (20/40). These results are only one example of the fact that the only consistent feature of the orthokeratology group was the high degree of variability and unpredictability of the results. Results of this study also suggest there is no direct relationship between refractive error and visual acuity in orthokeratology patients during the time lenses are worn (Table 4). It is possible that changes in corneal curvature that cannot be measured account for these results. It is very difficult to equate a change in refractive error with a given change in improvement in visual acuity, although for the most part, when the spherical equivalent is reduced the unaided visual acuity increases. In the variable response (OK) group (Table 7) that started with an average of 6/45 (20/150) visual acuity and finished with 6/15 (20/50) vision before retainer lens removal, an average change in spherical equivalent of 0.25 diopters produced four lines of visual acuity improvement. In the good response group the initial average vision was 6/30 (20/100), and the latest average vision prior to lens removal was 6/7.5 (20/25). In this instance a 1 diopter improvement in spherical equivalent produced six lines of visual acuity improvement, a fourfold change. It appears difficult, therefore, to state that 1 diopter of spherical equivalent improvement will give a stipulated number of lines of visual acuity improvement. 4 ·s· 10 It appears from this study, however, that the patient with a low refractive error will tend to have the greatest improvement in unaided visual acuity per unit of spherical equivalent correction (Table 7). This observation is supported by those of Heikkila 12 and Kirscher. 13 The improvement in the spherical equivalent cannot be directly related to the change in the central or peripheral corneal curvature. For instance, in the variable response group (Table 7)

an average improvement in the spherical equivalent of 0.24 diopters was associated with an average flattening in the central horizontal meridian by 0.47 diopters and in the central vertical meridian by 0.05 diopters. In this example, a flattening of the horizontal meridian of almost 0.5 diopter was associated with a 0.25-diopter change in spherical equivalent and a four-line improvement in vision. Using the same analysis in the good response group, a 0.9-diopter average flattening in the central horizontal meridian was associated with a 1diopter average improvement in spherical equivalent and a five-line improvement in unaided visual acuity (Table 7). One must conclude that it is difficult to equate a change in central corneal curvature with a given change in refraction as has been suggested. L 12- 16 A similar analysis of the peripheral corneal changes provides similar information (Table 5). Since with-the-rule astigmatism tends to make vertical lines stand out sharply, and since most letters in standard Snellen charts have vertical orientations, it is possible that some of the improved unaided vision in orthokeratology may be due to the increase in with-the-rule astigmatism. Retainer Contact Lenses. A review of the orthokeratology literature suggests that retainer lenses can be fit after approximately 18 months 3 • 10 and are worn as frequently as a few hours every day to as infrequently as not at all. 12 •13 •15 •16 In the present study, only four patients reached the retainer lens wear stage, two at 24 months, one at 27 months, and one at 30 months. There is much disagreement among orthokeratologists about which lens should be a retainer lens. In this study, the retainer lenses were flatter than the last lens in the series (Table 6). Since 14 of the 19 patients reached 18 months of study and were not in retainer lenses, and only 4 of 14 were able to wear retainer lenses after 24 to 30 months, it suggests that retainer lens wear does not begin until well after the second year.

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Orthokeratology-induced Changes Can Be "Permanent". Four patients in this study in whom the retainer lenses were removed were followed for three to nine months. In three of the four patients the uncorrected visual acuities immediately deteriorated toward prefit levels. Based on this study and Kerns' evaluation/ it is clear that the corneas will tend to approach their prefitting levels when lens wear is stopped. Further follow-up is needed to document the return to prefit levels. However, patients will fail to keep appointments when the time to remove lenses approaches, since they do not wish

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to lose whatever unaided visual gains they have achieved. The "permanency" of the induced changes cannot be accurately assessed from this study, because of the few patients out of retainer lenses and the relatively short duration of the study. The question will be very difficult to answer because most patients resist the removal of retainer lenses, which leaves them in the gray zone of poor uncorrected vision and poor vision with their old spectacles-chronic , low-grade spectacle blur. Furthermore, the present study provides little information on the possibility that intermittent retainer lens wear can maintain induced changes. Orthokeratology is the Programmed Application of Contact Lenses. Which lens changes should be made to obtain a successful result cannot be determined from the present study. Overall, the lenses were fit with flat base curves and large diameters with appropriate changes in lens power as determined by the fitting orthokeratologists. 1 •3 • 1 I. 15 The lenses were changed every four to six weeks in some cases and not at all in others, and reasons for and against lens changes are unclear from examination of the data. Some patients changed in the "wrong" direction while wearing the same lenses, and some failed to change in spite of numerous lens manipulations, eg, the no response group (Table 7). The same events were documented by Kerns. 7 What are some of the criticisms that can be levelled against this study? First of all, the evaluation technique is subject to error. Since patients were examined between 7 am and 3 pm, they would have had variable amounts of contact lens wear for any given day. The examination techniques that were utilized are subject to error. For instance, the keratometer is accurate to within ±0.25 diopters: the refractions could be off by as much as ±0.50 diopters: the determinations of the base curve and diameters of the contact lenses could be off by as much as ±0.5 diopters and ±0.2 millimeters, respectively: and the various conditions in the individual examination rooms could have varied significantly from visit to visit, affecting the unaided visual acuity determinations. Since some patients claimed their best visions did not occur until the morning after lens removal, the study would tend to analyze visions that might possibly be better if checked 12 hours later, assuming that the patients were correct. Another major criticism is the relatively short evaluation time for many of the orthokeratology patients. Although 14 patients were followed for more than 18 months, eight were followed for between 21 and 27 months, and only four for more than 30 months. It is possible, therefore, that the results in the orthokeratology group

might have improved as time went on. However, most of the orthokeratology responses took place within the first nine months of the study, just as in Kerns' study ,7 so it is difficult to believe that excellent results would occur after 18 months when they had not occurred before then. There was a very high rate of failure to keep appointments in this series. In addition, those OK patients who had poor results did not return for further examinations, thereby slanting this study in favor of the good responders, for whom there was thus more follow-up. Once the time approached to remove lenses, both CL and OK patients tended to refuse to stay in the study, although they had previously signed informed consents that clearly stated they would be without lenses for six months. The patients whoremained were enthusiastic OK patients who were scientifically interested in the study, thereby slanting the study toward more successful cases. Since the orthokeratology patients were examined in a setting other than the orthokeratologist's office, one might claim the patients were nervous and were unable to perform as well visually as they might in a private office setting. However, most patients in the study, control and experimental, were outwardly relaxed and very cooperative. One orthokeratology procedure, as evaluated by this study, appears to utilize the fitting of contact lenses with larger diameters, flatter base curves, and deeper saggital depths, compared with standard contact lenses. The procedure requires at least 24 months to reach the retainer lens stage, and when retainer lenses are stopped, parameters decay towards the prefit levels. The orthokeratology procedure appears to be without short-term risk, but does produce severe spectacle blur, induces with-the-rule astigmatism, induces myopia in some instances, requires reading glasses in a third of the patients, and produces a quality of unaided visual acuity that is less than the same level of best corrected vision. The orthokeratology procedure is able to reduce an average of 1.50 diopters of myopia in about two thirds of selected, moderately myopic patients, but is only able to produce a significant response in less than half of the selected eyes. The results are unpredictable, with most of the improvement in unaided visual acuity occurring during the first nine months of the study and with sudden changes in visual acuity and refractive error occurring while the patient is still wearing the same lens. The mechanism of improvement in visual acuity is directly related to the improvement in the spherical equivalent and indirectly related to the flattening of the

horizontal meridian and possibly to the rounding of the cornea. There appears to be no significant effect on the vertical meridian of the central cornea by the orthokeratology procedure: however, there is a definite but unpredictable effect on the peripheral and central horizontal corneal curvature. Patients considering the orthokeratology procedure can expect to spend more than 24 months before being fit with a retainer lens, which will include visits to the office every six weeks. They can expect to achieve some improvement in unaided visual acuity, and the lower the refractive error, the greater the chance for improvement. If the refractive error is less than 4 diopters at the start of the study, then the patient has about a 50% chance to achieve better than 6/7.5 (20/25) unaided visual acuity at some time during the study, but there is no characteristic that one can pick from the prefitting examination to determine which patient will achieve a stable correction in unaided visual acuity by the time retainer lenses are fit (including analysis of peripheral corneal contours). The retainer lenses must be worn on a regular daily basis to maintain the improvement, and should they be removed, all parameters will tend to return towards the prefit levels. The quality of the unaided vision will be poorer than the best corrected vision for the same line of visual acuity. The time at which this improvement in unaided visual acuity will occur in relationship to the cessation of lens wear will vary from patient to patient, with best results occurring immediateiy upon lens removal, the day after lens removal, or at some other time. In addition, the patient is subject to a very expensive procedure and time away from work. The benefit of orthokeratology is some level of improvement in unaided visual acuity at some time in some patients. For persons whose life's work requires better than 6/12 (20/40) unaided visual acuity, the orthokeratology procedure may be worthwhile if they fall into the responsive group. Orthokeratology would possibly be useful for those whose refractive error is less than 2 diopters of myopia, but there is no guarantee that a level of better than 6/12 (20/40) unaided visual acuity can be attained. In this study, 28 of 40 eyes (70%) were able to attain 6/12 (20/40) at some time during the study, but not necessarily at the end of the study or immediately following lens removal. Since the amount of improvement attained with orthokeratology decreases as the refractive error increases above 4 diopters, and since the time at which the best unaided vision occurs is highly variable, it would probably not be worth the time, effort, and money to undergo this proce-

dure. If the degree of myopia is greater, the chances of improving the unaided vision are small. 3 The improvement in unaided visual acuity is related to a flattening of the central cornea, but why this flattening only occurs in some patients is unclear. When cosmetic contact lenses are fit flat, the cornea responds unpredictably with a flattening, a steepening, or no change. 4 - 6 The corneas respond to orthokeratology lenses by early flattening and later steepening, but when and how this occurs is unpredictable. Once a flattened cornea steepens (and vision drops), no one can predict what to do to reverse the process: eg, a flatter lens may have no effect, or wearing the same lens may have a later positive or negative effect. Such responses occurred in all subgroups of the OK study group. In the present study there was no significant complication, but in Kerns' study, 7 6 of36 eyes in the orthokeratology group began to develop appreciable amounts of astigmatism, which could not be eliminated by lens changes, and Kerns was forced to drop the patients involved from the study. One of us (P.S.B.) has seen two patients with permanent corneal warpage (18 months out oflenses) following orthokeratology performed elsewhere. We all have seen patients who have worn contact lenses for several years who later developed warped corneas 1 H or a keratoconus-like picture/ 9 and in time we expect to see similar cases occurring in orthokeratology patients. The lack of other significant corneal complications in orthokeratology has been documented previously by Tredici. 2 •17 Although the major concern about orthokeratology has been corneal warpage, the present study demonstrates that such a risk is small but does exist even on a short-term basis. The fitting of a flat lens on the corneal apex may not have any short-term adverse effects, but long-term retainer lens pressure may induce trophic changes such as thinning 20 or scarring. However, no such changes have been documented to occur in orthokeratology patients followed since 1962 by the same practitioner. 21 Since the only two orthokeratology studies performed to date, Kerns ' 7 and the present study, had a limited period of observation, studies with much longer follow-ups are needed.

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REFERENCES 1. Grant SC, May CH. Orthokeratology-control of refractive errors through contact lenses. J Am Optom Assoc 1971; 42:1277-83. 2. Tredici TJ, Shacklett PE. Orthokeratology-help or hindrance. TrAm Acad Ophthalmol Otolaryngol 1974;

78425.

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3. Binder PS. Orthokeratology. In Symposium on the Cornea. Transactions of the New Orleans Academy of Ophthalmology. St. Louis: CV Mosby, 1980; 149-66 4. Pratt-Johnson JA, Warner OM. Contact lenses and corneal curvature changes. Am J Ophthalmol 1965;

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