When is it safe to stop patching?

Prevention of Amblyopia and the Concept of Cure

Amblyopia is used as a comprehensive term for unexplained reduction of visual acuity, usually unilateral. As long as the visual deficit is monocular the visual loss is more of a potential problem than an actual handicap. Amblyopia is one of the most common causes of visual deficit in childhood, and since it is treatable, at least in children, considerable efforts have been made to detect it as early in life as possible. Screening programmes for amblyopia among preschool and school children have been widely organized throughout the world, although questions remain about their utility. This study evaluated amblyopia screening, focussing on some essential points that need thorough consideration before a screening programme is started. We also try to demonstrate some of the pros and cons of a screening system.

Current concepts in the management of amblyopia

Traditional treatment of amblyopia, although still in use and of great value, has recently been challenged by data from studies relative to efficacy of different modalities and regimens of therapy. LogMAR-based acuity charts should be used, whenever possible, for diagnosis and monitoring. Refractive errors of certain magnitude should be prescribed, and correction worn for at least 4 months before occlusion or penalization are used. Occlusion has a linear dose-response effect (1 logMAR line gain per 120 hours of patching), and outcomes of 2 hour/day dosage are similar to more extended therapy, at least in moderate amblyopia, but increasing dosage beyond hastens the response. Pharmacologic, optical, or combined penalization is useful as an alternative or maintaining therapy, and is presumably of particular efficacy in anisometropic amblyopia. At least in moderate amblyopia, atropine penalization is as effective as patching in terms of visual acuity improvement and stereoacuity outcome.

Strabismus might be a risk factor for amblyopia recurrence

BACKGROUND

Previous reports have suggested that one-fourth of amblyopic subjects present with recurrence of amblyopia even after successful primary treatment. Risk factors for amblyopia recurrence are insufficiently studied, but therapy weaning has recently been suggested as a method for reducing the risk of recurrence.

METHODS

In the second phase of a prospective study examining the results of treatment for amblyopia, all 35 children with successful primary amblyopia treatment were put on maintenance therapy. Maintenance therapy consisted of low-intensity patching, atropine, or blurring filter, and all children were regularly examined up to at least 8 years of age. Mean age at start of maintenance therapy was 4.3 years (range, 2-7 years).

RESULTS

Of the 35 cases with successful primary treatment, 6 cases deteriorated >or=0.2 logMAR, which was considered recurrence of amblyopia. Two of these cases had a second recurrence. Notably, all six subjects presenting with recurrence had microstrabismus. This finding was just outside statistical significance at the 95% confidence level (p = 0.06), but the sample size was small. All but one of the recurrences appeared within 6 months after successful primary treatment. Age at successful primary treatment or initial interocular difference of visual acuity did not affect the risk of recurrence.

CONCLUSIONS

Recurrence of amblyopia occurred in 17% of patients despite maintenance therapy and was associated with microstrabismus. The majority of recurrences occurred within the first 6 months after primary treatment.

Stability of visual acuity after the cessation of amblyopia treatment: review of the literature

INTRODUCTION AND PURPOSE

The treatment of amblyopia in children is frequently discussed in the literature. Less attention, however, has been given to the durability of the visual acuity results attained with therapy. The objective of this review is to conduct an in-depth analysis of the existing literature, on the stability of visual acuity following cessation of amblyopia treatment, and to identify any gaps in the literature, which could guide future investigations.

RESULTS

There did not appear to be any one consistent risk factor affecting the stability of vision after cessation of amblyopia treatment. Most of the reviewed studies varied with respect to lengths of follow-up visits, patient population, and method of visual acuity assessment. There was also a generalized lack of standardization of visual acuity measurements in these previous investigations. Only one of the studies analyzed was a prospective design.

CONCLUSION

The area of study in amblyopia is fraught with contradictions. It is obvious from this review that there exists uncertainty regarding the recurrence of amblyopia following treatment. Previous studies have failed to identify any common, predictive, influencing factors necessary for the maintenance of visual acuity after cessation of therapy. Also lacking is discussion on the potential role that therapy tapering plays in the recurrence of amblyopia following the cessation of treatment.

Recurrence of amblyopia after occlusion therapy

PURPOSE

To determine the stability of visual acuity (VA) after a standardized occlusion regimen in children with strabismic and/or anisometropic amblyopia.

DESIGN

Retrospective, population-based, consecutive observational case series.

PARTICIPANTS

Four hundred forty-nine patients younger than 10 years who underwent an occlusion trial for amblyopia and were observed until there was a recurrence of amblyopia or for a maximum of 1 year after decrease or cessation of occlusion therapy.

METHODS

We performed a retrospective chart review of all patients treated by occlusion therapy for strabismic and/or anisometropic amblyopia at our institution over a 34-year period. Of the 1621 patients identified in our database, 449 met the eligibility criteria and were included in this study. Patients having at least a 2 logarithm of the minimum angle of resolution (logMAR)-level improvement in VA by optotypes or a change from unmaintained to maintained fixation preference during the course of occlusion therapy were included. A recurrence of amblyopia was defined as > or =2 logMAR levels of VA reduction or reversal of fixation preference within 1 year after a decrease or cessation of occlusion therapy.

MAIN OUTCOME MEASURE

Recurrence of amblyopia after a decrease or cessation of occlusion therapy and its relationship with patient age and VA of the amblyopic eye at the time of decrease or cessation of occlusion therapy.

RESULTS

Of 653 occlusion trials, 179 (27%) resulted in recurrence of amblyopia. The recurrence was found to be inversely correlated with patient age. There was no statistically significant association between the recurrence of amblyopia and VA of the amblyopic eye at the end of maximal occlusion therapy.

CONCLUSIONS

There is a clinically important risk of amblyopia recurrence when occlusion therapy is decreased before the age of 10 years. The risk of recurrence is inversely correlated with age (P<0.0001).

Factors affecting the stability of visual function following cessation of occlusion therapy for amblyopia

AIM

To identify factors that predict which children with amblyopia are at greatest risk of regression of visual acuity (VA) following the cessation of occlusion therapy.

METHOD

A retrospective analysis was performed of 182 children (mean age at cessation of treatment; 5.9+/-1.6 years) who had undergone occlusion therapy for unilateral amblyopia, and had been followed up at least once within 15 months of cessation. Statistical analysis was used to identify whether change in VA following treatment cessation had any association with various factors, including the child's age, type of amblyopia, degree of anisometropia, initial severity of amblyopia, binocular vision status, length and dose of occlusion therapy, and VA response to treatment.

RESULTS

At 1 year, follow-up from treatment cessation, children with "mixed" amblyopia (both anisometropia and strabismus) demonstrated significantly (p=0.03) greater deterioration in VA (0.11+/-0.11 log units) than children with only anisometropia (0.02+/-0.08 log units) or only strabismus (0.05+/-0.10 log units). However, none of the other factors investigated were found to be significant predictors.

CONCLUSION

This study supports previous research that it is possible to identify those children most at risk of deterioration in VA following cessation of occlusion therapy. The presence of mixed amblyopia was the only risk factor identified in this study. Management of amblyopia should take this into account, with a more intensive follow-up recommended for those with both anisometropia and strabismus (mixed) amblyopia.

Controversy in amblyopia management

BACKGROUND AND PURPOSE

Much has been written about amblyopia treatment. However, there is no consensus on the most efficacious therapeutic modality for amblyopia. The intensity of therapy needed to maximize visual acuity is also widely debated. The diversity of opinions emphasizes that the optimum treatment for amblyopia is unknown. Part of the uncertainty stems from the lack of standardization in the management of amblyopia. The objective of this paper is to conduct an in-depth review of the literature in an attempt to clarify the amblyopia treatment conundrum.

CONCLUSIONS

The treatment of amblyopia in children is frequently discussed in the literature. It is obvious from the literature that there is the need for prospective studies with consistent controls, clear definitions of what constitutes successful therapy endpoints, and standardization of testing procedures.

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.

A cost-utility analysis of therapy for amblyopia

OBJECTIVE

Evaluation of the incremental cost-effectiveness of therapy for amblyopia.

DESIGN

Cost-utility reference-case analysis.

METHODS

A cost-utility analysis was performed from a third-party insurer perspective by using decision analysis, evidence-based data from the literature, and patient preference-based time trade-off utility values.

DATABASE

Patient-derived time trade-off ocular utility values and the American Academy of Ophthalmology Preferred Practice Pattern guidelines for the treatment of amblyopia.

INTERVENTION

Treatment of childhood amblyopia using medical and surgical therapies per the American Academy of Ophthalmology Preferred Practice Pattern.

MAIN OUTCOME MEASURE

Dollars (year 2001 nominal U.S. dollars) expended per quality-adjusted life-year ($/QALY) gained.

RESULTS

Treatment for amblyopia resulted in a $/QALY gained of $2281 with a discount rate of 3% for costs and outcomes. Sensitivity analysis, varying costs and utility values by 10%, resulted in a $/QALY gained range from $2053 to $2509.

CONCLUSIONS

When compared with other interventions in health care, therapy for amblyopia seems to be highly cost-effective. This information is increasingly important for health care policy makers.

Long term visual outcome in amblyopia treatment

AIM

To evaluate long term visual outcome of treatment for amblyopia.

METHODS

In a previous study, 44 children with unilateral amblyopia caused by strabismus or anisometropia were enrolled in a prospective study investigating the results of treatment. All children were regularly examined up to at least 8 years of age and outcome was evaluated. All subjects were invited to a re-examination and in total 26 subjects attended. Two of these were excluded because of insufficient records. The final sample consists of 24 subjects. Mean follow up time was 10.4 (SD 1.9) years.

RESULTS

For the amblyopic eyes, 17% deteriorated in visual acuity, 50% were stable, and 33% gained in visual acuity. For the non-amblyopic eyes, 8% lost one line in visual acuity, 38% were stable, and 54% gained in visual acuity. No eye in any subject shifted more than 0.2 logMAR units. The increase in visual acuity for the non-amblyopic eyes was significant, while the increase for the amblyopic eyes was not. All straight eyed anisometropic amblyopes showed a distinct decrease in magnitude of anisometropia.

CONCLUSIONS

Visual acuity was essentially stable in the amblyopic eyes 10 years after cessation of treatment in the studied population.

The therapy of amblyopia: an analysis comparing the results of amblyopia therapy utilizing two pooled data sets

CONTEXT

We previously presented the results of an original pooled data set of 961 amblyopic patients who underwent patching therapy for amblyopia from 1965 to 1994 (study group 1). Three types of amblyopia were considered: anisometropic, anisometropic-strabismic, and strabismic. Analysis of this group's success was related to the age at which therapy was initiated, the type of amblyopia, and the depth of visual loss before treatment was begun. The purpose of the current study is to test the validity of these findings on a second group of 961 amblyopes employing the data set used by Woodruff and associates in their publications (study group 2). These 2 data sets, after adjustment to conform to the definitions of age, amblyopia, anisometropia, and similar items utilized in common between the 2 study groups, will be compared for the risk factors predictive of successful occlusion therapy.

OUTCOME

As in the previous study, the success of occlusion therapy is defined as a visual acuity of 20/40 or better at the end of treatment.

RESULTS

Success by the 20/40 criteria was achieved in 73.7% in study group 1 and in 59.9% in study group 2. By category, the rate of success in study group 1 was 77.2% in strabismic amblyopia, 67.2% in anisometropic-strabismic amblyopia, and 66.0% in anisometropic amblyopia. In study group 2, success was 61.2% in strabismic amblyopia, 51.2% in anisometropic-strabismic amblyopia, and 63.0% in anisometropic amblyopia. Study group 1 univariate analysis related success in each group to the age at which therapy was initiated, the type of amblyopia, and the depth of visual loss before treatment in each group. In study group 2, univariate analysis related success of occlusion therapy to age and the depth of visual loss before treatment. Type of amblyopia was not related to outcome success in this group. When the 2 data sets were pooled, the risk factors for success were age and depth of visual loss at onset of treatment.

CONCLUSIONS

Factors that appeared closely related to a successful outcome of patching therapy were patient age and depth of visual loss before treatment. These conclusions further support the value of early detection and screening for amblyopia, its prevention, where possible, and its adequate and vigorous treatment when it is detected and diagnosed.

An inner city preschool visual screening programme: long-term visual results

AIMS

The aim of this study was to investigate the long-term outcome of the treatment of amblyopia as a sequel to preschool screening, which has not hither-to been described.

METHODS

All patients originally referred from a preschool screening programme were recalled for examination by letter. 255 patients were reviewed at least 4 years after discharge of which 88 were definitely amblyopic at presentation and 107 were not amblyopic at presentation and were used as controls.

RESULTS

79% of the amblyopes improved or maintained visual acuity after discharge but this was reduced to 42% after an age induced increase (estimated from the controls) was compensated for. The mean drop in visual acuity in the amblyopic eyes which deteriorated was 0.23 (SD 0.15) logMAR units. Stepwise multiple linear regression showed that the best single predictor of post-discharge deterioration in visual acuity was the improvement in visual acuity seen during treatment (R2 = 19%). Eccentric fixation at time of follow up (increasing R2 to 47%) and good presenting acuity (further raising R2 to 57%) contributed additional information, and were both associated with greater post-discharge deterioration in visual acuity.

CONCLUSIONS

The majority of amblyopes who attended for follow up maintained or improved their visual acuities after discharge. Those patients who demonstrated deterioration of their amblyopia had usually improved well during the programme and were often fixating eccentrically at follow up.

The therapy of amblyopia: an analysis of the results of amblyopia therapy utilizing the pooled data of published studies

CONTEXT

Although the treatment of amblyopia with occlusion has changed little over the past 3 centuries, there is little agreement about which regimes are most effective and for what reasons.

OBJECTIVE

To determine the outcome of occlusion therapy in patients with anisometropic, strabismic, and strabismic-anisometropic amblyopia employing the raw data from 961 patients reported in 23 studies published between 1965 and 1994.

DESIGN

Analysis of the published literature on amblyopia therapy results during the above interval, utilizing primary data obtained from the authors of these articles or tables published in the articles detailing individual patient outcomes.

PARTICIPANTS

961 amblyopic patients, participants in 23 studies, undergoing patching therapy for amblyopia from 1965 to 1994 with anisometropia, strabismus, or anisometropia-strabismus.

MAIN OUTCOMES

In the pooled data set, success of occlusion therapy was defined as visual acuity of 20/40 at the end of treatment.

RESULTS

Success by the 20/40 criteria was achieved in 512 of 689 (74.3%) patients. By category, 312 of 402 (77.6%) were successful in strabismic amblyopia, 44 of 75 (58.7%) in strabismic-anisometropic amblyopia, and 72 of 108 (66.7%) in anisometropic amblyopia. Success was not related to the duration of occlusion therapy, type of occlusion used, accompanying refractive error, patient's sex, or eye. Univariate analyses showed that success was related to the age at which therapy was initiated; the type of amblyopia; the depth of visual loss before treatment for the anisometropic patients and the strabismic patients, but not for the anisometropic-strabismic patients; and the difference in spherical equivalents between eyes, for the anisometropic patients. Logistic/linear regression revealed that 3 were independent predictors of a successful outcome of amblyopia therapy.

CONCLUSIONS

Factors that appear most closely related to a successful outcome are age, type of amblyopia, and depth of visual loss before treatment. These may be related to factors, as yet undetermined in the pathogenesis of amblyopia. With present emphasis on the value of screening and prevention and the development of new screening tools, such a look at the results of amblyopia therapy in a large population seems indicated.

Full-time atropine, intermittent atropine, and optical penalization and binocular outcome in treatment of strabismic amblyopia

OBJECTIVE

The purpose of the study is to evaluate the monocular and binocular outcome of three types of "penalization" (blurring of the sound eye) treatment of amblyopia: traditional full-time atropine or optical penalization and a new intermittent atropine regimen involving atropine instillation 1 to 3 days a week.

DESIGN

The study design was a retrospective study.

PARTICIPANTS

A total of 163 patients with strabismic amblyopia treated by full-time atropine (n = 38), intermittent atropine (n = 73), or optical (n = 52) penalization participated.

MAIN OUTCOME MEASURES

Logarithm of the minimum angle of resolution (logMAR) visual acuity, and binocularity index were determined.

RESULTS

All three forms of penalization produced statistically significant mean reduction in amblyopia (1.7-2.7 logMAR lines) and mean improvement in binocularity by the end-of-treatment or long-term follow-up visit or both, with minimal mean loss after discontinuation or slight mean improvement on these measures at long-term mean follow-up of 1.9 to 4 years across groups. Few patients achieved high-grade stereoacuity. Compliance was high. Comparable efficacy was found for all three treatment groups after controlling for age, depth of amblyopia, and binocularity at the initial visit. Initial-visit amblyopia depth was strongly and significantly associated with amblyopia depth at both post-treatment visits. Pretreatment and post-treatment binocularity showed a similar strong relationship. Surprisingly, however, there was no consistent or significant association found between depth of amblyopia and binocularity in any visit combination. Post-treatment measures of these two variables also were not associated with initial-visit age or refractive error at any clinically significant level. Mean treatment duration was 1.1 to 2.9 years and was not found to be associated with visual outcome. Amblyopia reversal was found in one (full-time atropine) case at a clinically important level.

CONCLUSIONS

The authors confirmed previous reports of penalization's efficacy as a primary treatment of moderate amblyopia (20/100 or better acuity) and, in some cases, relatively severe amblyopia (>20/100) and also confirmed its ability to significantly improve mean binocularity. Amblyopia and binocularity appear to respond to treatment independently and, within the postinfancy age range of the sample studied, the responses appear to be independent of initial-visit age. The high acceptability to patients and parents of atropine penalization, and particularly of the intermittent regimen introduced here, suggests the need for prospective-study-based re-evaluation of the relative merits of penalization and occlusion as the standard of care for mild-to-moderate amblyopia.

Preschool vision screening: rationale, methodology and outcome

Although population outcome studies support the utility of preschool screening for reducing the prevalence of amblyopia, fundamental questions remain about how best to do such screening. Infant photoscreening to detect refractive risk factors prior to onset of esotropia and amblyopia seems promising, but our current understanding of the natural history of these conditions is limited, thus limiting the prophylactic potential of early screening. Screening for strabismic, refractive and ocular disease conditions directly associated with amblyopia is more clearly proven, but the diversity of equipment, methods and subject populations studied make it difficult to draw precise summary conclusions at this point about the efficacy of photoscreening. Sensory-based testing of preschool-age children exhibits a similar combination of promise and limitations. The visual acuity tests most widely used for this purpose are prone to problems of testability and false negatives. Moreover, the utility of random-dot stereograms has been confused by misapplication, and new small-target binocularity tests, while attractive, are as yet inadequately field-proven. The evaluation standard for any screening modality is treatment outcome. However, variables in amblyopia classification and quantitative definition differences, timing of presentation, nonequivalent treatment comparisons, and compliance variability have been uncontrolled in virtually all extant studies of amblyopia treatment outcome, making it difficult or impossible to evaluate either the relative efficacy of different treatment regimens for amblyopia or the effects of age on treatment outcome within the preschool age range. The latter issue is a central one, since existence of such an age effect is the primary rationale for screening at younger rather than older preschool ages. The relatively low prevalence of amblyopia makes it difficult to achieve a high screening yield in terms of predictive value, but functionally increasing prevalence by selective screening of high risk populations causes further problems. Unless a "supertest" can be devised, with very high sensitivity and specificity, health policy decisions will be required to determine which of these two characteristics should be emphasized in screening programs. Performance of screening tests can be optimized, however, with adequate training, perhaps via instructional videotapes.

Amblyopia

Over the past thirty years, much has been learned about the physiological basis for amblyopia. For many years amblyopia was considered to be a retinal disorder; it has now been well established through animal studies that amblyopia represents functional and morphological effects of visual deprivation on the visual cortex and the lateral geniculate nucleus. With this knowledge has come the recognition of a "sensitive period" of development of the visual system, during which time visual deprivation causes amblyopia. The best approach to managing amblyopia is to detect amblyogenic factors before the age of two years and prevent it through eliminating the causes of visual deprivation. When amblyopia exists, it can be cured if adequately treated in children less than 6-7 years of age. Even in older patients, visual improvement can be achieved with therapy. Current research is aimed at developing substances and delivery modes that will allow the sensitive period of visual development to be manipulated, increasing the period during which it can develop and enhancing preventative and therapeutic measures. In this review selected literature contributing to current understanding of causes, prevention and treatment of amblyopia is discussed. Although many new treatment modalities have been tried, occlusion still seems to be the most successful therapy.

Factors affecting long term results of successfully treated amblyopia: initial visual acuity and type of amblyopia

AIMS

The study aimed to assess the effect of initial visual acuity and type of amblyopia on the long term results of successfully treated amblyopia.

METHODS

The visual acuity of 94 patients, who had been successfully treated for unilateral amblyopia by occlusion of the good eye and followed up to the age of 9 years, was examined 6.4 years, on average, after cessation of treatment. Patients were divided into two groups according to the depth of amblyopia before occlusion therapy was started: those with visual acuity between 20/60 and 20/100 and those with visual acuity of 20/100 or worse.

RESULTS

Deterioration of visual acuity was observed in 42% of patients in the first group and in 63% of patients in the second group. Their average deterioration, as measured by the Snellen chart, was 0.58 and 1.54 lines, respectively. The results were also assessed by the division of patients into three groups according to the type of amblyopia: strabismic, strabismic anisometropic, and anisometropic. Deterioration of visual acuity occurred in 46%, 79%, and 36% of patients in these three groups, with an average deterioration on the Snellen chart of 0.70, 2.04, and 0.64 lines, respectively.

CONCLUSION

It is concluded that low initial visual acuity and strabismic anisometropic amblyopia are risk factors for deterioration of visual acuity in the long term, following the successful earlier treatment of eyes with amblyopia.