Author: Pang, Chi Kong Peter
Title: Fixation stability characteristics in amblyopia and treatment effect from dichoptic video game playing in mild amblyopic eyes
Advisors: Lam, Carly (SO)
Degree: DHSc
Year: 2017
Subject: Hong Kong Polytechnic University -- Dissertations
Amblyopia -- Treatment
Video games -- Health aspects
Department: Faculty of Health and Social Sciences
Pages: xx, 172 pages : illustrations
Language: English
Abstract: Purpose: Contrast balanced dichoptic videogame training has been found to improve sensory functions in adults, with moderate-to-severe amblyopia, such as best corrected visual acuity (BCVA) and stereopsis, but its effect on mild amblyopia and motor function like fixation stability is not established. The aim of this study is to identify if fixation stability is related to the severity of amblyopia and whether fixation stability in mild amblyopes can be improved with perceptual learning via dichoptic video game playing. Method: To investigate the relationship of fixation stability and different levels of BCVA, subjects (aged 7 or above) with amblyopic eye having BCVA from 0.96 to 0.08 log MAR and an interocular acuity difference ≥ 0.2 log units (better BCVA in the fellow eye) were recruited. Fixation stability in terms of Bivariate Contour Ellipse Area (BCEA by Nidek MP-1 micro-perimeter), BCVA (by E-EDTRS log MAR system) and stereo acuity (by Titmus stereo test and Randot preschool stereo test) were assessed. The BCEA measurements were compared amongst three groups of BCVA levels (or amblyopia severity): 1)severe (BCVA ≥ 0.70 and ≤ 1.00 logMAR); 2) moderate (BCVA ≥ 0.30and ≤ 0.68 logMAR) and 3)mild (BCVA ≤ 0.28). In the second part of the study, an anaglyphic, contrast balanced dichoptic video game was provided on an iPod Touch (Apple Inc.) device for 6 weeks of home-based training (60 mins per day) for mild amblyopic subjects. BCEA, BCVA, near visual acuity (NVA) and stereo acuities were measured at weeks 0, 6, 12 and 24 post training. Results: Thirty-three amblyopes (4 severe, 13 moderate and 16 mild) were recruited for the first part of the study. The mean BCEA measurements in the amblyopic eye in the mild, moderate and severe amblyopia groups were -0.13 ± 0.29, 0.08 ± 0.26 and 0.22± 0.36 log deg2 respectively. Results from one-way ANOVA showed a marginally significant difference (F(2,30) = 3.31, p = 0.05) in the means of BCEA amongst the three groups. After combining the severe and moderate groups into 'moderate-to-severe' group, there was a significant difference (t31 = 2.44, p < 0.05**) in BCEA in amblyopic eyes between 'mild' (-0.13 ± 0.29 log deg²) and 'moderate-to-severe' (0.11 ± 0.28 log deg2) amblyopes. In addition, there was a significant positive correlation (rs =0.42, p < 0.05**) between BCVA and BCEA.
In the second part of the study, twelve mild amblyopes (5 children; mean 10 ± 2 years, 7 adults; mean 37 ± 11 years) with an amblyopic eye (8 anisometropic; 1 isometropic; 1 strabismic and 2 mixed) having a BCVA from 0.28 to 0.10 log MAR were treated with dichoptic video game playing. Subjects played for an average of 37 ± 10 hours over six weeks. There was no significant difference between the amblyopic and fellow eye's fixation stability in terms of BCEA (-0.07 ± 0.33 Vs -0.09 ± 0.30 log deg2) before training and the BCEA in the amblyopic eye did not change (t11 = -7.2, p > 0.05) after training (-0.02 ± 0.40 log deg2). The BCVA and NVA of the amblyopic eye significantly improved by 0.09 ± 0.05 log MAR (t11 = 6.4, p < 0.05**) and 0.09 ± 0.06 log MAR (t11 = 5.14, p < 0.05**) respectively. Titmus stereo acuity also improved (Z = -2.50, p < 0.05**) significantly after 6 weeks' training, while there was no significant change in Randot preschool stereo acuity (Z = -1.83, p = 0.07). No significant correlation between the change of BCEA and the changes of BCVA, NVA, Titmus stereo acuity and Randot preschool stereo acuity was found. Repeated measures ANOVA results showed that there was no significant difference amongst the four visits (week 0 - start training; week 6 - stop training; week 12 - six weeks after the cessation of training and week 24 - eighteen weeks after the cessation of training) in BCEA, NVA and Randot preschool stereo acuity, but the BCVA and Titmus stereo acuity differed significantly amongst the four time points (F(3,33) = 16.46, p < 0.05** and X2 (3) = 18.38, p < 0.001** respectively). Discussion: Although it was reported the BCEA in the amblyopic eye in a group of children with moderate amblyopia was 0.56 log deg2 (measured by the same MP-1 system), marked smaller values in with 'moderate-to-severe' (0.11 log deg2) and 'mild' (-0.13 log deg2) amblyopes were found in this study. Since the group of subjects with mild amblyopia had a relatively good fixation stability before the training, it is not surprising to find there was no change in BCEA after the training. The improvement of BCVA (0.09 log MAR) and stereopsis (0.65 log unit) in mild amblyopes in this study were similar to those of a previous study (BCVA improved by 0.11 log MAR, stereopsis improved by 0.61 log unit) using the same treatment method with a group of moderate-to-severe amblyopes. However, the gain in percentage improvement (43%) from the starting BCVA in this study is considerably greater than in the previous study (31%), and this is the first study showing a sustained effect (for 18 weeks) on the improvements in both BCVA and Titmus stereo acuity for mild amblyopes by dichoptic video game playing. Conclusion: The fixation stability of 'mild' amblyopes was better that of 'moderate-to-severe' amblyopic cases, and the fixation stability in the amblyopic eye was comparable to the fellow eye in mild amblyopes. After 6 weeks' home based dichoptic video game playing, there were no changes in fixation stability in the amblyopic eye and in the Randot preschool stereo acuity; but there were significant improvements in the BCVA, NVA in the amblyopic eye, and Titmus stereo acuity. The improvement of BCVA and Titmus stereo acuity could last up to 18 weeks after the cessation of training. Based on the results of this study, it is likely that perceptual learning via dichoptic video game playing is more effective in improving sensory functions like VA and stereopsis than motor function such as fixation stability in mild amblyopes.
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