All patients between 12-30 years of age, reporting in ophthalmic outpatient department of Hakeem Abdul Hameed Centenary Hospital, New Delhi, between December 2011 to November 2013 that were diagnosed to have anisometropic amblyopia were included in this prospective study. The patients underwent a thorough ocular examination that included recording of uncorrected visual acuity and best-corrected visual acuity (BCVA) for near and distance after cycloplegic refraction. Ocular motility, slit lamp biomicroscopy and fundus examination was done to rule out any other ocular disease. All patients underwent a trial period of one month of spectacle wear, before being diagnosed as amblyopic. Amblyopia was defined as a difference in the best-corrected visual acuity (BCVA) between the two eyes of two or more lines on the Snellen’s Chart or a visual acuity of less than two lines from the normal. Anisometropia was defined as interocular difference of spherical equivalent of ≥ 1D or difference of refractive astigmatism (anisoastigmatism) ≥1.5D cylinder.

After being diagnosed as anisometropic amblyopic, the patients were subjected to a counseling session before starting the treatment especially where poor compliance was suspected (older patients). Period of occlusion therapy was made flexible in older patients. A minimum of two hours (not more than four hours) of occlusion of better eye was mandatory with stress on near work task. Videogames, computers, mobile phone gaming, colouring in especially designed patterns and hand writing were used as vision training aids. A home work was assigned to younger patients who were rewarded on completion of the task. Older patients were motivated by showing them their results on actual Snellen’s scale or if not improving, the stories of other patients were shared to motivate them.

Static as well as dynamic refraction was done on each visit. Any changes in refraction were corrected to BCVA. Near visual acuity was also recorded at each visit. Follow up was done every month till normal BCVA was achieved or no change was seen for three consecutive months of occlusion. The end-point of therapy was considered as stable visual acuity maintained for a period of at least three months of occlusion. Pre and post therapy results were analysed through unpaired t-test.

A total of 61 patients of anisometropic amblyopia were included in the study out of which 32 were males and 29 females. Mean age was 17 years. Mean BCVA at the start of the treatment was 20/125 or 0.8 log MAR (range from 20/63 to 20/400). Out of 61 patients, 20/400 BCVA was seen in 06 patients (9.8%), 20/200 in 19(31%), 20/125 in 15(24%), 20/80 in 11(18%) and 20/63 in 10 (16%) patients before the start of therapy [Table/Fig-1]. Commonest type of anisometropia was found to be anisohyperopia 24 patients (39.3%) followed by anisoastigmatism 20 patients (32.7%) and anisomyopia 17 patients (27.8%) [Table/Fig-1,2,3 and 4].

Mean BCVA at the end of therapy was 20/32 or 0.2 logMAR. From the total 61 patients under study, 33(54%) had 20/20, 14(23%) had 20/25, 11(18%) had 20/40, while 01(1.6%) had 20/50 and 02 (3.27%) had 20/80 BCVA at the end of therapy [Table/Fig-1].

The patients who did not attain normal vision (20/20) included 02 patients of high anisomyopia. These were 30 year male and 28 year female with BCVA of 20/400 (1.3logMAR) and 20/200 (1 logMAR) respectively at the start of therapy and 20/80 (0.6 logMAR) at the end of the therapy. Third patient was of anisoastigmatism, a 19 year male with BCVA 20/200 (1 logMAR) at the start of therapy and 20/50 (0.4 logMAR) at the end of therapy.

Out of 61 patients, 33 (54%) had BCVA of 20/20, while 58 patients (95%) had ≥ 20/40 BCVA at the end of therapy. The results were statistically significant (p-value <0.0001) with a 95% confidence interval.

It has been suggested in the past, that treatment should be given to amblyopic patients even after the critical period [13]. In recent years a number of studies have shown that occlusion therapy is effective in older children as well [14–16]. Evidence has been accumulating regarding neuronal plasticity of adult brain through experimental studies on animal models [17] and clinical trials using video games [18] or by employing perceptual learning technique [19]. Brar et al., [20] in their study on older amblyopic children have successfully reported use of full-time occlusion. The present study also shows that it is possible to improve visual acuity of older anisometropic amblyopes, though we used occlusion time of 2-4 hours along with near work task. In our study, a success rate of 54% was observed if 20/20 BCVA was taken into account. This success rate increased to 77% if cut-off BCVA was taken as 20/25. If compared with earlier study of Patwardhan et al., [21] on patients of >12 years of age where they reported 60.7% success with BCVA of 20/40, our study shows a success rate of 95%. In PEDIG, 27% of patients between 10-18 years reported improvement of two or more lines with part-time occlusion [22]. Our study had a better success rate perhaps because counseling was given importance where poor compliance was suspected at each visit. Also, stress was given to near visual task in the form of video games, mobile phone gaming, hand writing and colouring using bright colours in special intricate and fine designs. Homework tracking and flexi-timings further resulted in better compliance. Since older children show poor compliance to patching, which is an important factor for the outcome of results, reducing the hours of patching can improve the compliance [23,24]. By decreasing the occlusion time from all waking hours to 2-4 hours/day and flexi-hours, compliance increases as seen in the successful results (54% success rate) in present study. This again is helpful in overcoming amblyopia in adults as it is very difficult to convince the older patients for occlusion all through the waking hours without hindering their routine work.

Although our study included patients of older age group (12-30years), the results are consistent with Paediatric Eye Disease Investigator Group study (PEDIG) where it was shown that in patients aged 7-17 years, decreasing the patching time for two to six hours daily, the response to amblyopia treatment increased to 53% [6].

The present study also highlights the importance of patching combined with near visual task, in the reversal of amblyopia [25]. Patients in which the therapy failed to produce the desired results had poor treatment compliance or perhaps there were other factors responsible. The answers to these questions need to be explored further.

Although there are limitations to this study due to small sample size and shorter follow up time, the present study certainly suggests a role of minimal occlusion therapy of 2-4 hours with stress on near visual task in all anisometropic amblyopic patients irrespective of age. It further shows that it is possible to treat amblyopia even after the critical period although it requires more effort on the part of patient and the care giver. Frequent follow-ups should be done to monitor progress. Successful cost-effective amblyopia treatment not only provides visual rehabilitation but also improves the quality of life as well as self-confidence of the patient and decreases the economic load on the government [26].

With mounting evidence of adult brain plasticity, perceptual learning, effect on visual performance by vision training exercises and significant results, (as seen in our study- 54% had BCVA of 20/20), it is important that all anisometropic amblyopic patients should be treated with minimal 2-4 hours of occlusion or patching of better eye. This was a small study group, to fully explore the effects of occlusion therapy in adult anisometropic amblyope a long-term follow up and a large-scale study is required.