The evaluation of two new computer-based tests for measurement of Aniseikonia.

PURPOSE: To evaluate the accuracy and repeatability of size lens induced aniseikonia measurement with the Aniseikonia Inspector Version 1 and a newer customized version of the Aniseikonia Inspector, Version 2. METHODS: Aniseikonia was measured on 27 subjects with both versions of the Aniseikonia Inspector in normal room illumination. Measurements of induced aniseikonia were made using size lenses in a randomized order. Twenty-five subjects were further tested in the dark using target sizes of equal visual angle for both tests. Repeatability of the intrinsic aniseikonia measurement was assessed on five subjects using randomized testing order for instrument and light and dark measurements. RESULTS: In normal illumination, the mean slopes for plots of induced aniseikonia vs. size lens magnification for Version 1 were 0.883 and 0.838 for the vertical and horizontal meridians, respectively. For Version 2, the corresponding slopes were 1.162 and 1.043. In the dark and using targets of the same size for both tests, the slopes for Version 1 were 1.038 in the vertical meridian and 0.866 in the horizontal meridian whereas for Version 2, the slopes were 1.195 in the vertical meridian and 1.127 in the horizontal meridian. The amount of underestimation or overestimation within any given testing condition showed considerable intersubject variation. Version 1 was more repeatable than 2, particularly in the vertical meridian. CONCLUSIONS: On average, the most accurate and repeatable measurement of aniseikonia was found with Version 1 in the vertical meridian in the dark. Measurement of aniseikonia in the horizontal meridian appears to be less reliable. Version 2 overestimates size lens-induced aniseikonia under all testing conditions. Intersubject variation in slopes of induced aniseikonia vs. size lens magnification should be further addressed.

Comparison of aniseikonia as measured by the aniseikonia inspector and the space eikonometer.

PURPOSE: The purpose of this study was to compare the new, computerized Aniseikonia Inspector with the Space Eikonometer for the measurement of aniseikonia. METHODS: Eighteen subjects, ages 21 to 61 years, with normal binocular vision and normal visual acuity had aniseikonia measured with both the Aniseikonia Inspector Version I and the Space Eikonometer. Aniseikonia was measured first with the subjects' habitual refractive correction and then with afocal size lenses of 1%, 2%, and 3.5% added in random order before the right and left eyes. Measurements were taken initially with the Aniseikonia Inspector and on a subsequent day with the Space Eikonometer. RESULTS: For the Space Eikonometer, the slopes of the lines for the relationship between the measured aniseikonia and the induced magnification differences in the vertical and horizontal meridians are not significantly different from 1.0. For the Aniseikonia Inspector, the slopes of the lines in the vertical and the horizontal meridians are less than and significantly different from 1.0. On average, the Aniseikonia Inspector underestimates the magnitude of induced aniseikonia, predicting only 68% and 61% of the overall size lens magnification in the vertical and horizontal meridians, respectively. The corresponding values of the Space Eikonometer in the vertical and horizontal meridians are 99% and 93%. Variability is greater with the Space Eikonometer than the Aniseikonia Inspector. CONCLUSION: The Space Eikonometer appears to be measuring the induced aniseikonia appropriately, whereas the Aniseikonia Inspector underestimates the amount of aniseikonia. However, the Space Eikonometer shows greater measurement variability. Modification of the Aniseikonia Inspector or the testing conditions should be pursued in future studies.

Aniseikonia testing in an adult population using a new computerized test, "the Aniseikonia Inspector".

PURPOSE: To determine the measurement characteristics of a new computerized test, the Aniseikonia Inspector Version 1, on a sample of clinic patients. METHODS: Aniseikonia was measured in the vertical, horizontal, and oblique meridians on 320 patients (mean 55 years old, range 17-89 years) prior to their optometric exam using the psychometric methods programmed into the Aniseikonia Inspector Version 1. Statistical analyses were performed to determine the distribution of aniseikonia in the sample of patients and the relationships between the amount of aniseikonia and patients' habitual refractive correction, visual acuity, stereopsis and binocular alignment status. The characteristics of the individual measurements were also examined. RESULTS: The means and standard deviations of the measured aniseikonia in the vertical, horizontal, and oblique meridians were -0.5% (2.5%), -0.1% (3.3%) and 0.3% (2.8%) respectively. The means in the vertical and oblique meridians were significantly different from 0.0 (p=0.0001, p=0.0314) while that in the horizontal was not (p=0.61). The distributions of aniseikonia showed that 65.6%, 57.5% and 64.3% had within +/-1.0% aniseikonia in the vertical, horizontal and oblique meridians, respectively. Correspondingly, 16.9%, 25.6% and 25.8% had aniseikonia of +/-3.0% or greater. The discrepancy between these percentages and those expected in a normal distribution indicate that the distributions were significantly more peaked than a normal distribution. This departure from normal is due to a few extreme values in the tails. The magnitude of aniseikonia had no statistically significant relationship with the patients' habitual refractive correction, visual acuity or stereopsis. The effect of phoria on the amount of aniseikonia was significant, more so for measurements in the horizontal meridian. The individual measurements, which are the average of two trials using the method of adjustment, showed no significant bias, no relationship between the means and differences in the two readings, but large differences between the two readings. Measurements in the vertical direction seem to be more stable than those in the other two meridians. CONCLUSION: As measured with the Aniseikonia Inspector 1.0, the majority of the patients sampled in this study exhibited 1.0% or less aniseikonia and were therefore not likely to have symptoms related to aniseikonia. At least 17% of patients had 3.0% or greater aniseikonia measured in the vertical meridian. The Aniseikonia Inspector warrants further evaluation in a clinical setting because of the large limits of agreement between the two settings that are average to determine the magnitude of the aniseikonia. These limits differ considerably from those established by the designers and, therefore, raise questions regarding the actual resolution of the instrument as compared to the nominal resolution.

Long-term changes in visual acuity and refractive error in amblyopes.

PURPOSE: To report long-term changes in visual acuity and refractive error for strabismic, anisometropic, and isoametropic amblyopes. METHODS: Records of patients with strabismic amblyopia, anisometropic amblyopia, and isoametropic amblyopia who were treated from 1983 to 1993 were reviewed. Excluded were patients having ocular or neurological diseases, developmental delay, and follow-up <4 years after treatment cessation. Data included best-correctable visual acuity and spherical equivalent refractive error of the amblyopic and the nonamblyopic eye at pretreatment, posttreatment, and long-term follow-up. RESULTS: Records for 61 patients met the inclusion criteria. For strabismic amblyopia (n = 22), mean visual acuity in amblyopic and nonamblyopic eyes improved 0.36 and 0.05 logarithm of the minimum angle of resolution (logMAR) units after a mean treatment time of 1 year. At long-term follow-up (mean = 9.3 years after treatment), visual acuity in the amblyopic eye regressed 0.09 logMAR and visual acuity in the nonamblyopic eye improved 0.10 logMAR units. For anisometropic amblyopia (n = 26), mean visual acuity in amblyopic and nonamblyopic eyes improved 0.30 and 0.02 logMAR units, respectively, after a mean treatment period of 1.1 year. At the long-term follow-up visit (mean = 7.1 years after treatment), visual acuity in the amblyopic eye regressed 0.09 logMAR unit and in the nonamblyopic eye improved 0.03 logMAR unit. Repeated-measures analysis of variance showed no significant effect of type of amblyopia on visual acuity of the amblyopic eye and a significant effect of visit due to treatment but not regression. The changes in visual acuity in the nonamblyopic eye from the pretreatment to the follow-up visit were significant and interacted with type, the changes being larger in strabismic amblyopia. For strabismic amblyopia, the mean refractive error in amblyopic and nonamblyopic eyes changed from +2.15 D and +1.85 D, respectively, initially to +0.45 D and +0.58 D, respectively, at the follow-up visit. For anisometropic amblyopia, the mean refractive error in amblyopic and nonamblyopic eyes changed from +1.04 D and +0.12 D, respectively, initially to +0.23 D and -0.94 D, respectively, at the follow-up visit. The effect of visit on amblyopic and nonamblyopic refractive errors was significant. For isoametropic amblyopia (n = 13), visual acuity in both right and left eyes initially was 0.39 logMAR unit and improved to 0.14 logMAR unit in each eye after a mean follow-up of 8.9 years. Refractive error in the right and the left eyes changed from -1.22 D and -1.14 D, respectively, to -2.68 D and -2.56 D, respectively, at follow-up. These differences were all significant. CONCLUSIONS: After treatment and with long-term follow up, visual acuity regresses but not significantly in the amblyopic eye in strabismic amblyopia and anisometropic amblyopia. At the same time, visual acuity in the nonamblyopic eye improves slightly. Visual acuity also improves significantly over time in isoametropic amblyopia. The refractive error of both amblyopic and nonamblyopic eyes tends to show a myopic shift regardless of the type of amblyopia.

The clinical course of intermittent exotropia.

PURPOSE: To report the clinical course for patients with intermittent exotropia. METHODS: The clinical records of patients diagnosed with intermittent exotropia from 1983 to 1991 who had at least 4 years of follow-up were reviewed. All patients with neurological or medical abnormalities, developmental delays, ocular disease, or having strabismus surgery during the follow-up period were excluded. RESULTS: Of the 468 records reviewed, 73 met the inclusion criteria. Forty-four patients were female, and 29 were male. Fifty-two patients had basic intermittent exotropia, 11 patients had divergence excess intermittent exotropia, and 10 patients had convergence insufficiency intermittent exotropia. The mean age at initial visit was 20 years (range, 1 to 63 years). The mean follow-up was 10 years (range, 4 to 23 years). Four patients had amblyopia of 20/30 or worse, nine patients had a vertical deviation in the primary position, and 10 patients had undergone extraocular muscle surgery before coming to our clinic. Sixty patients received some form of treatment during follow-up. The mean stereoacuity at the initial and final visits were 59 and 70 s arc, respectively. The initial mean spherical equivalent refraction was -0.48 D and increased to -1.15 D at the end of the study. The mean exodeviation changed from 17.2 Delta at distance and 17.6 Delta at near at the initial visit to 13.7 Delta at distance and 13.5 Delta at near at the final visit. At the initial visit, 63 patients were exotropic and 10 patients were either heterophoric or orthophoric at distance, whereas, 60 patients were exotropic and 13 patients were either heterophoric or orthophoric at near. At the final visit, 37 patients were exotropic and 36 patients were either heterophoric or orthophoric at distance whereas 33 patients were exotropic and 39 were either heterophoric or orthophoric at near. One patient was esotropic at near at the last visit. Changes in the size and quality of the exodeviation, although statistically significant (p < 0.001), were not associated with any specific treatment regimen or with longer periods of follow-up. Measurements exhibited a regression toward the mean. CONCLUSIONS: Intermittent exotropia improved for many patients quantitatively and qualitatively over time. That the improvement was unrelated to any treatment and length of follow-up suggests that the changes at least quantitatively are not associated with any physiologic process and may be due, in part, to regression toward the mean.