Long-Term Changes in Visual Acuity and Refractive Error in Amblyopes

Efficacy of part-time occlusion in amblyopia in Indian children

Purpose:

To study the effectiveness of part-time occlusion (PTO) in different types of amblyopia in Indian population.

Methods:

Prospective case series of consecutive cases of amblyopia from a tertiary care center were subjected to PTO of the better eye and monitored periodically for 6 months. Those who failed to improve by 6 months were shifted to full-time occlusion of the better eye and followed for a further 3 months.

Results:

175 eyes of 175 patients with amblyopia underwent PTO for 6 months. The mean age of the patients was 10.47 ± 4.69 years (range: 3–26 years). Major subgroups included 94 eyes with strabismic amblyopia and 70 with anisometropic amblyopia. Overall, 168 (96%) children benefited from PTO (improvement being defined as a gain of at least one line of Snellen's visual acuity). The improvement rates for strabismic amblyopes (97.9%) was significantly more than anisometropia (94.3%); P = 0.027. Of the seven patients not responding to PTO, six did not benefit even after full-time patching.

Conclusion:

PTO is a viable and effective modality of management of amblyopia in Indian patients. Strabismic amblyopia was the commonest and responded best to the occlusion therapy in our cohort.

Amblyopia treatment: an evidence‐based approach to maximising treatment outcome

The basis of treatment for amblyopia (poor vision due to abnormal visual experience early in life) for 250 years has been patching of the unaffected eye for extended times to ensure a period of use of the affected eye. Over the last decade randomised controlled treatment trials have provided some evidence on how to tailor amblyopia therapy more precisely to achieve the best visual outcome with the least negative impact on the patient and the family. This review highlights the expansion of knowledge regarding treatment for amblyopia and aims to provide optometrists with a summary of research evidence to enable them to better treat amblyopia. Treatment for amblyopia is effective, as it reduces overall prevalence and severity of visual loss in this population. Correction of refractive error alone significantly improves visual acuity, sometimes to the point where further amblyopia treatment is not required. Atropine penalisation and patch occlusion are effective in treating amblyopia. Lesser amounts of occlusion or penalisation have been found to be just as effective as greater amounts. Recent evidence has highlighted that occlusion or penalisation in amblyopia treatment can create negative changes in behaviour in children and impact on family life. These complications should be considered when prescribing treatment because they can negatively affect compliance. Studies investigating the maximum age at which treatment of amblyopia can still be effective and the importance of near activities during occlusion are ongoing.

Amblyopia: prevalence, natural history, functional effects and treatment

Amblyopia, defined as poor vision due to abnormal visual experience early in life, affects approximately three per cent of the population and carries a projected lifetime risk of visual loss of at least 1.2 per cent. The presence of amblyopia or its risk factors, mainly strabismus or refractive error, have been primary conditions targeted in childhood vision screenings. Continued support for such screenings requires evidence-based understanding of the prevalence and natural history of amblyopia and its predisposing conditions, and proof that treatment is effective in the long term with minimal negative impact on the patient and family. This review summarises recent research relevant to the clinical understanding of amblyopia, including prevalence data, risk factors, the functional impact of amblyopia and optimum treatment regimes and their justification from a vision and life skills perspective. Collectively, these studies indicate that treatment for amblyopia is effective in reducing the overall prevalence and severity of visual loss from amblyopia. Correction of refractive error alone has been shown to significantly reduce amblyopia and less frequent occlusion can be just as effective as more extensive occlusion. Occlusion or penalisation in amblyopia treatment can create negative changes in behaviour in children and impact on family life, and these factors should be considered in prescribing treatment, particularly because of their influence on compliance. Ongoing treatment trials are being undertaken to determine both the maximum age at which treatment of amblyopia can still be effective and the importance of near activities during occlusion. This review highlights the expansion of current knowledge regarding amblyopia and its treatment to help clinicians provide the best level of care for their amblyopic patients that current knowledge allows.

Long-term follow-up of an amblyopia treatment study: change in visual acuity 15 years after occlusion therapy

Purpose

To determine change in visual acuity (VA) in the population of a previous amblyopia treatment study (Loudon 2006) and assess risk factors for VA decrease.

Methods

Subjects treated between 2001 and 2003 were contacted between December 2015 and July 2017. Orthoptic examination was conducted under controlled circumstances and included subjective refraction, best corrected VA, reading acuity, binocular vision, retinal fixation, cover‐uncover and alternating cover test. As a measure for degree of amblyopia, InterOcular VA Difference (IOD) at the end of occlusion therapy was compared with IOD at the follow‐up examination using Wilcoxon’s signed‐rank test. Regression analysis was conducted to determine the influence of clinical and socio‐economic factors on changes in IOD.

Results

Out of 303 subjects from the original study, 208 were contacted successfully, 59 refused and 15 were excluded because of non‐amblyopic cause of visual impairment. Mean IOD at end of therapy (mean age 6.4 years) was 0.11 ± 0.16 logMAR, and IOD at follow‐up examination (mean age 18.3 years) was 0.09 ± 0.21 logMAR; this difference was not significant (p = 0.054). Degree of anisometropia (p = 0.008; univariable analysis), increasing anisometropia (p = 0.009; multivariable), eccentric fixation (p < 0.001; univariable and multivariable); large IOD (p < 0.001; univariable and multivariable) and non‐compliance during therapy (p = 0.028; univariable) were associated with IOD increase.

Conclusion

Long‐term results of occlusion therapy were good. High or increasing anisometropia, eccentric fixation and non‐compliance during occlusion therapy were associated with long‐term VA decrease. Subjects with poor initial VA had a larger increase despite little patching, but often showed long‐term VA decrease.

Optical treatment of amblyopia in older children and adults is essential prior to enrolment in a clinical trial

PURPOSE

Optical treatment alone can improve visual acuity (VA) in children with amblyopia, thus clinical trials investigating additional amblyopia therapies (such as patching or videogames) for children require a preceding optical treatment phase. Emerging therapies for adult patients are entering clinical trials. It is unknown whether optical treatment is effective for adults with amblyopia and whether an optical correction phase is required for trials involving adults.

METHODS

We examined participants who underwent optical treatment in the Binocular Treatment for Amblyopia using Videogames (BRAVO) clinical trial (ANZCTR ID: ACTRN12613001004752). Participants were recruited in three age groups (7 to 12, 13 to 17, or ≥18 years), and had unilateral amblyopia due to anisometropia and/or strabismus, with amblyopic eye VA of 0.30-1.00 logMAR (6/12 to 6/60, 20/40 to 20/200). Corrective lenses were prescribed based on cycloplegic refraction to fully correct any anisometropia. VA was assessed using the electronic visual acuity testing algorithm (e-ETDRS) test and near stereoacuity was assessed using the Randot Preschool Test. Participants were assessed every four weeks up to 16 weeks, until either VA was stable or until amblyopic eye VA improved to better than 0.30 logMAR, rendering the participant ineligible for the trial.

RESULTS

Eighty participants (mean age 24.6 years, range 7.6-55.5 years) completed four to 16 weeks of optical treatment. A small but statistically significant mean improvement in amblyopic eye VA of 0.05 logMAR was observed (S.D. 0.08 logMAR; paired t-test p < 0.0001). Twenty-five participants (31%) improved by ≥1 logMAR line and of these, seven (9%) improved by ≥2 logMAR lines. Stereoacuity improved in 15 participants (19%). Visual improvements were not associated with age, presence of strabismus, or prior occlusion treatment. Two adult participants withdrew due to intolerance to anisometropic correction. Sixteen out of 80 participants (20%) achieved better than 0.30 logMAR VA in the amblyopic eye after optical treatment. Nine of these participants attended additional follow-up and four (44%) showed further VA improvements.

CONCLUSIONS

Improvements from optical treatment resulted in one-fifth of participants becoming ineligible for the main clinical trial. Studies investigating additional amblyopia therapies must include an appropriate optical treatment only phase and/or parallel treatment group regardless of patient age. Optical treatment of amblyopia in adult patients warrants further investigation.

The relationship between anisometropia and amblyopia

This review aims to disentangle cause and effect in the relationship between anisometropia and amblyopia. Specifically, we examine the literature for evidence to support different possible developmental sequences that could ultimately lead to the presentation of both conditions. The prevalence of anisometropia is around 20% for an inter-ocular difference of 0.5D or greater in spherical equivalent refraction, falling to 2-3%, for an inter-ocular difference of 3D or above. Anisometropia prevalence is relatively high in the weeks following birth, in the teenage years coinciding with the onset of myopia and, most notably, in older adults starting after the onset of presbyopia. It has about one-third the prevalence of bilateral refractive errors of the same magnitude. Importantly, the prevalence of anisometropia is higher in highly ametropic groups, suggesting that emmetropization failures underlying ametropia and anisometropia may be similar. Amblyopia is present in 1-3% of humans and around one-half to two-thirds of amblyopes have anisometropia either alone or in combination with strabismus. The frequent co-existence of amblyopia and anisometropia at a child's first clinical examination promotes the belief that the anisometropia has caused the amblyopia, as has been demonstrated in animal models of the condition. In reviewing the human and monkey literature however it is clear that there are additional paths beyond this classic hypothesis to the co-occurrence of anisometropia and amblyopia. For example, after the emergence of amblyopia secondary to either deprivation or strabismus, anisometropia often follows. In cases of anisometropia with no apparent deprivation or strabismus, questions remain about the failure of the emmetropization mechanism that routinely eliminates infantile anisometropia. Also, the chronology of amblyopia development is poorly documented in cases of 'pure' anisometropic amblyopia. Although indirect, the therapeutic impact of refractive correction on anisometropic amblyopia provides strong support for the hypothesis that the anisometropia caused the amblyopia. Direct evidence for the aetiology of anisometropic amblyopia will require longitudinal tracking of at-risk infants, which poses numerous methodological and ethical challenges. However, if we are to prevent this condition, we must understand the factors that cause it to develop.

Two-year follow-up of a randomized trial of spectacles alone or combined with Bangerter filters for treating anisometropic amblyopia

PURPOSE

To compare spectacle correction alone to spectacle correction with Bangerter filters as treatments for anisometropic amblyopia in children 1 year after completion of a 1-year randomized trial.

METHODS

In a randomized clinical trial, 80 children (mean age, 4.4 years) with anisometropic amblyopia and a best median visual acuity (VA) in the amblyopic eye of 0.4 logarithm of the minimum angle of resolution (logMAR) were assigned to treatment with either spectacles or spectacles in combination with a Bangerter filter for 1 year. After 1 year, treatment with spectacles continued. If the VA differed by ≥ 2 lines, treatment with Bangerter filters was continued if originally prescribed. The main outcome measure was the median change in VA of the amblyopic eye after 2 years.

RESULTS

The median change in VA of the amblyopic eye did not differ significantly between the groups (0.4 log unit for both groups) at the 2-year visit. At that time, the VA in the amblyopic eyes and the fellow eyes was 0.0 median logMAR in both groups. Between years 1 and 2, the median VA improved in the amblyopic eyes; in the spectacles group (p = 0.0181) and in the Bangerter filter group (p = 0.0342). The median anisometropia decreased in both groups (p < 0.0001 for both comparisons).

CONCLUSION

We found stability in the VA improvement in both groups. The magnitude of the VA change 2 years after treatment with spectacles alone did not differ significantly from that after treatment with spectacles and a Bangerter filter for anisometropic amblyopia.

Termination of amblyopia treatment: when to stop follow-up visits and risk factors for recurrence

BACKGROUND

This study estimated when it is safe to stop follow-up visits after cessation of amblyopia treatment and to identify factors associated with deterioration of visual acuity.

METHODS

Study patients included 282 patients aged 7 to 13 years who were monitored for deterioration after cessation of amblyopia treatment (median follow-up: 3.9 years).

RESULTS

Six (2.1%) patients lost 2 or more logarithm of the minimum angle of resolution levels of visual acuity and 77 (27.3%) patients lost 1 or more Snellen lines of visual acuity. Good compliance with re-treatment stopped further deterioration and lost visual acuity was regained (average follow-up after re-treatment: 3.3 years). Life table analysis indicated that 95% of the cases that deteriorated occurred within 24 months after cessation of treatment. Multivariable analysis corrected for duration of treatment uncovered factors independently associated with deterioration.

CONCLUSION

A clinically important risk of deterioration of visual acuity was found during the first 2 years after cessation of amblyopia treatment. Follow-up time longer than 2 years is recommended in the presence of a developing risk factor such as increasing anisometropia. With prompt re-treatment and good compliance, deterioration can be stopped and visual acuity can be restored.

Longitudinal changes in refractive error of children with infantile esotropia

Aim

The aim of this study was to quantify changes in refractive status over time in children with infantile esotropia and to analyse a number of clinical factors associated with infantile esotropia to determine how they may affect emmetropisation.

Methods

Longitudinal cycloplegic refraction data were collected for 5-12 years from 143 consecutive children enrolled in a prospective study of infantile esotropia by 6 months of age. Changes in refractive error with age were summarized with descriptive statistics and the influence of amblyopia, undercorrection of hypermetropia, accommodation, and binocular factors on emmetropisation were evaluated by ANOVA and t-tests.

Results

Most had low to moderate hypermetropia on the initial visit (55% had <+3.00 D). While the initial refractive error is similar to normative data, the rapid decrease in hypermetropia that characterizes normal development during the first 9 months of life is absent in children with infantile esotropia. After 9 months of age, children with infantile esotropia follow a developmental course that is similar to the normative course; there is little change in hypermetropia during years 1-7, followed by a decline of approximately -0.5 D/yr beginning at age 8 years. None of the clinical factors examined had a statistically significant effect on the course of refractive changes with age.

Conclusions

Children with infantile esotropia exhibit a different pattern of refractive development than that seen in normative cohorts. The long term changes in refraction observed in children with infantile esotropia suggest that there is a need for long-term clinical follow-up of these children.

Atypical fixation preference with anisometropia

PURPOSE

To describe a child with hyperopia and anisometropia who manifests strabismus and amblyopia in the much less hyperopic eye.

CASE REPORT

A 6-year-old child presented with a history of strabismus and refractive error since infancy, which has been treated with glasses and patching. The present examination revealed 3 D of hyperopic anisometropia, intermittent exotropia, and amblyopia. The strabismus and amblyopia occur in the less hyperopic eye. Ocular health assessment including optical coherence tomography was normal. After patching therapy, the vision improved in the amblyopic eye.

CONCLUSION

Amblyopia and strabismus need not always occur in the more ametropic eye when accompanied by anisometropia.

Contemporary issues in amblyopia treatment

PURPOSE

The aim of this report is to review the contemporary research in amblyopia treatment and how it will affect clinical practice patterns.

METHODS

Topics addressed include prescribing the optimal refractive correction, the most effective treatment, duration and intensity of treatment, regression after treatment, the upper age for treatment, and the chance of the amblyope losing his or her sound eye.

RESULTS AND CONCLUSIONS

The optimal refractive correction is best determined with cycloplegic retinoscopy; pharmacologic penalization can be as effective as patching in children with moderate amblyopia; less-intense treatment regimens have been found to be as effective as more-intense treatment regimens; regression can occur in as many as 25% of all treated patients; some older amblyopes can be treated successfully; and the amblyope has a higher chance of becoming blind than the nonamblyope.

Amblyopia characterization, treatment, and prophylaxis

Amblyopia has a 1.6-3.6% prevalence, higher in the medically underserved. It is more complex than simply visual acuity loss and the better eye has sub-clinical deficits. Functional limitations appear more extensive and loss of vision in the better eye of amblyopes more prevalent than previously thought. Amblyopia screening and treatment are efficacious, but cost-effectiveness concerns remain. Refractive correction alone may successfully treat anisometropic amblyopia and it, minimal occlusion, and/or catecholamine treatment can provide initial vision improvement that may improve compliance with subsequent long-duration treatment. Atropine penalization appears as effective as occlusion for moderate amblyopia, with limited-day penalization as effective as full-time. Cytidin-5'-diphosphocholine may hold promise as a medical treatment. Interpretation of much of the amblyopia literature is made difficult by: inaccurate visual acuity measurement at initial visit, lack of adequate refractive correction prior to and during treatment, and lack of long-term follow-up results. Successful treatment can be achieved in at most 63-83% of patients. Treatment outcome is a function of initial visual acuity and type of amblyopia, and a reciprocal product of treatment efficacy, duration, and compliance. Age at treatment onset is not predictive of outcome in many studies but detection under versus over 2-3 years of age may be. Multiple screenings prior to that age, and prompt treatment, reduce prevalence. Would a single early cycloplegic photoscreening be as, or more, successful at detection or prediction than the multiple screenings, and more cost-effective? Penalization and occlusion have minimal incidence of reverse amblyopia and/or side-effects, no significant influence on emmetropization, and no consistent effect on sign or size of post-treatment changes in strabismic deviation. There may be a physiologic basis for better age-indifferent outcome than tapped by current treatment methodologies. Infant refractive correction substantially reduces accommodative esotropia and amblyopia incidence without interference with emmetropization. Compensatory prism, alone or post-operatively, and/or minus lens treatment, and/or wide-field fusional amplitude training, may reduce risk of early onset esotropia. Multivariate screening using continuous-scale measurements may be more effective than traditional single-test dichotomous pass/fail measures. Pigmentation may be one parameter because Caucasians are at higher risk for esotropia than non-whites.