Validity and repeatability of contour-based visotec distance stereoacuity test.

CLINICAL RELEVANCE: The clinical assessment of distance stereoacuity is important in some ocular conditions. Given the different neurophysiological mechanism for crossed and uncrossed stereoacuities, evaluation of both may provide additional insight into binocular vision disorders. BACKGROUND: Clinical devices measuring distance crossed and uncrossed stereopsis are not readily available. Visotec Distance Stereo Test (VDST) is a contour-based device designed to measure both forms of distance stereoacuity. This study assesses the validity and test-retest reliability of the device in comparison to the random dot-based Randot Distance Stereo Test (RDST). METHOD: VDST and RDST were administered to a total of 107 children, that included 51 'normal' and 56 'abnormal' (37 intermittent exotropia and 19 amblyopia) between the ages of 5 and 15 years. Two examiners retested stereoacuities in a sub-set of 62 randomly selected subjects. Stereoacuity was transformed to log scale. 95% limits of agreement were calculated for test-retest reliability. The Bland-Altman plot was used to demonstrate the agreement between the tests and the examiners. RESULTS: The mean ± SD crossed distance stereoacuities using VDST in normal, intermittent exotropia and amblyopic children were 93.1 ± 43.8, 161.9 ± 89.8 and 236.3 ± 122.4 arcseconds, respectively. For uncrossed stereoacuity, these were 104.7 ± 54.0, 187.6 ± 89.6 and 265.5 ± 144.0 arcseconds, respectively. Crossed stereoacuity was significantly better than uncrossed stereoacuity. 95% limits of test-retest agreement for crossed and uncrossed stereoacuities using the VDST were 0.27 and 0.30, respectively. An exact test-retest match using VDST was 84% in normals and 77% in abnormals for crossed and 83% in normal and 74% in abnormal for uncrossed stereoacuities. CONCLUSION: VDST is a reliable, valid and easy-to-administer distance crossed and uncrossed stereoacuity measuring device. Further studies are required to establish the clinical importance of assessing these two forms stereoacuities in relation to various binocular vision disorders.

Comparison of biometric and refractive changes in intermittent exotropia with and without overminus lens therapy.

BACKGROUND: Overminus lens is an effective non-surgical treatment of intermittent exotropia (IXT). Whether this treatment causes development of myopia is recently debated. This study evaluated ocular biometric changes in IXT children treated with and without overminus lens. METHODS: Children with IXT were randomly assigned to control and overminus groups. Cycloplegic refraction, axial length and other parameters (keratometry, anterior chamber depth and lens thickness) were evaluated for up to 30 months and compared between the groups. Axial length to corneal curvature (AL/CR) ratio was examined as an indicator of myopia progression. Changes prior to and after overminus were also assessed in a subgroup. RESULTS: Mean age of the total 84 subjects (58% women) was 7.2 years (range 4-15 years). Baseline refractive and biometric parameters of 39 control and 45 overminus subjects were not significantly different. Mean±SD change in refraction was -0.34±0.45D in controls and -0.41±0.66D in overminus group (p=0.527). AL increased by 0.29±0.20 millimetre (mm) in controls and 0.28±0.23 mm in overminus group (p=0.766). In the subgroup, the changes before and after overminus therapy was not significantly different (p>0.05). AL/CR ratio was maintained from baseline to follow-up visit (p=0.298) in both groups. CONCLUSION: No significant differences in biometry or refraction were found between the two groups and before and after the therapy. We conclude that the overminus therapy in children, not accounting for other myopia risk factors, does not affect normal refractive growths.

Assessment of distance-near control disparity in basic and divergence excess paediatric intermittent exotropia.

CLINICAL RELEVANCE: In intermittent exotropia (IXT), deviation is better controlled at near fixation. Understanding of the mechanism responsible for this common observation may improve clinical management of IXT. BACKGROUND: The physiological basis for the distance-near difference in control of deviation in IXT is vastly undetermined. A new parameter, 'control score disparity (CSD)', defined as the difference between distance and near control scores, is introduced. Association of CSD with positive fusional amplitude (PFA), accommodative convergence to accommodation (AC/A) ratio and distance angle of deviation was investigated to further understand the mechanisms. METHOD: Patients aged between four and fifteen years with basic and divergence excess IXT were included. Subjects with previous strabismus surgery, amblyopia and inability to perform clinical tests were excluded. A standardized office-based scoring system was used to assess IXT controls. Subjects were sub-divided into group 1 (CSD <2) and group 2 (CSD ≥2). Pearson's univariate and regression analysis were used to determine relationships between CSD and other independent variables. RESULTS: Mean age of the total 141 subjects (57.6% female) was 6.8 ± 2.5 years. Basic IXT was more common (60%) and 60% had CSD ≥2. The mean±SD distance angle of deviation, AC/A ratio, PFA and CSD were 22.1 ± 6.6 prism dioptres, 5.0 ± 1.0, 28.6 ± 6.3 prism dioptre and 2.0 ± 0.5, respectively. CSD was significantly correlated to PFA (r = 0.64, p < 0.001) and AC/A ratio (r = 0.27, p < 0.001) in overall samples and Group 2 subjects (r = 0.41, p = 0.001). CONCLUSIONS: PFA is a major factor associated with the distance/near difference of IXT control. Individuals with a higher PFA demonstrated greater CSD. While AC/A ratio was associated in better control at near in divergence excess IXT, magnitude of angle appears irrelevant.

Accommodative Lag Persistence in Treated Anisometropic, Strabismic, and Mixed Amblyopia.

Background: Amblyopic eyes typically exhibit greater lag of accommodation. Whether this improves after amblyopia treatment is inconclusive. The aim of this study is to report post-treatment accommodative response in amblyopia and to investigate if the lag is associated with visual acuity, treatment duration, and amblyopia type. Methods: Monocular and binocular accommodative responses were measured using Nott's method of dynamic retinoscopy in amblyopia of anisometropic, strabismic, and combined anisometropic-strabismic types and age-matched controls with normal vision. The results were compared using the nonparametric Wilcoxon signed ranks test. Linear regression analysis was used to examine association of the lag to refractive error, duration of therapy, and visual acuity. Results: Mean ± SD age of 46 amblyopic and 20 control subjects were 6.9 ± 1.8 and 6.9 ± 2.2 years, respectively. At the time of the study, 30 amblyopic subjects were receiving patching therapy and ceased in the remainder. In amblyopic eyes, mean ± SD monocular and binocular lags were 1.2 ± 0.6D and 1.0 ± 0.5D (p < 0.001), respectively, compared to 0.6 ± 0.3D and 0.5 ± 0.2D (p < 0.005), respectively, in nonamblyopic eyes and 0.4 ± 0.2D and 0.3 ± 0.2D (p=0.093), respectively, in the controls. By types, the monocular lag was significantly higher than the binocular lag (p=0.001) in mixed amblyopia (p=0.004); they were similar in anisometropic (p=0.283) and strabismic (p=0.743) amblyopia. Monocular lag was significantly correlated to BCVA (r = 0.46; p=0.001) and refraction (r = 0.42; p=0.001) but not to patching duration (r = 0.1; p=0.280). Conclusion: Inadequate accommodative response, a higher lag, persists in amblyopic eyes even after the treatment. Impaired accommodative response is partly determined by posttherapy visual acuity. Further studies investigating the effect of accommodative lag on visual recovery and whether optical correction of the deficiency may improve visual outcome of the treatment are recommended.

Optimised minus lens overcorrection for paediatric intermittent exotropia: A randomised clinical trial.

BACKGROUND: Aim of this study was to evaluate the efficacy of a novel algorithm to customise overminus lens therapy in intermittent exotropia (IXT) based on clinical factors associated with control of the deviation. METHODS: Clinical parameters in IXT vary among individuals. Based on individual's physiological factors, an algorithm was developed. Children aged between 4 and 15 years with IXT were randomised into OML and observation groups. Participants in the observation group were corrected for any significant refractive error. IXT control score, angle of deviation, refraction, axial length and stereopsis were examined at baseline and follow up ranging between 6 and 15 months and compared. Compliance and tolerance to OML was determined by a symptom survey. RESULTS: The OML power ranged between -1.00D and - 6.25D. Of the total 141 participants (mean age 6.8 ± 2.5 year), 77 were in the OML and 66 were in observation group. IXT control score improved (mean difference - 2.5 ± 1.1; p < 0.001) and angle of deviation reduced (6.9 ± 7.2pd; p < 0.001) significantly in the OML group only. Compliance rate to OML wear was 80%; 90% never or rarely experienced asthenopia symptoms. Slightly greater myopic shift (-0.36 ± 0.53D vs. -0.18 ± 0.55D) and change in axial length (0.17 vs. 0.14 mm) were observed in the OML group, but these differences were not statistically significant. CONCLUSIONS: A customised OML, calculated using this novel algorithm was effective in improving distance control, angle of deviation and stereopsis. Glasses wear was highly tolerable.

Comparison of automated and partial coherence keratometry and resulting choice of toric IOL.

PURPOSE: Consistent astigmatism correction with implantation of a toric intraocular lens (IOL) requires accurate preoperative keratometry. This article compares corneal astigmatism determined by an autokeratometer (Topcon KR-7100) and a partial coherence interferometry keratometer (IOLMaster 500) and considers if any discrepancy ultimately alters in final cylindrical power of the toric IOL for implantation. METHODS: Keratometry of 235 eyes was performed using both instruments. Corneal astigmatism was transformed into vector components J0 and J45 and cylindrical power at the IOL plane calculated. Comparisons were made using paired t test and correlation and Bland-Altman analyses. RESULTS: Although interinstrument differences for J0 (p = 0.013), J45 (p = 0.012), and toric IOL cylindrical power (p < 0.001) were statistically significant, a high correlation for these (R = 0.96, 0.90, and 0.90, respectively) was observed. IOLMaster tended to overestimate corneal astigmatism by 0.13 (±0.31) diopters and toric IOL cylinder by 0.11 (±0.18) diopters. Difference in calculated toric IOL cylindrical power correlated poorly with corneal curvature (R = 0.007) and astigmatism (R = -0.004). CONCLUSIONS: The two keratometers were generally concordant in measuring corneal astigmatism. However, the resultant choice of toric IOL cylinder power differed appreciably in 40% of eyes examined. Therefore, postoperative visual outcome with toric IOL implantation may be optimized by a thorough analysis of biometry data before IOL selection, paying special attention to any difference in corneal astigmatism as measured by more than one instrument.