Amblyopia Treatment 2009

Core Messages

■Wearing optimum refractive correction before initiation of patching or other amblyopia therapy is associated with improvement in amblyopia in about three quarters of children and a cure in about one fourth. This improvement may facilitate subsequent treatment.

■For initial therapy of moderate anisometropic

and strabismic amblyopia among children 3–7 years of age, patching and atropine are equivalent. Atropine is slightly more acceptable than patching on the basis of parental questioning.

■For initial therapy of moderate amblyopia, 2 h of daily patching or twice weekly topical atropine

administered to the sound eye are equally e ective.

■For initial therapy of severe amblyopia for children 3 to less than 7 years of age, 6 h of daily patching and full-time patching appear to be equally e ective.

■Amblyopia therapy can be beneficial for older children up to 17 years of age, especially if they have not been previously treated.

■There have not been any studies to date which demonstrate the best therapy for patients with residual amblyopia following initial therapy. There are also no studies that have identified the best treatments for deprivation amblyopia.

10.1Amblyopia Treatment 2009

10.1.1Introduction

Amblyopia management, long based on consensus or clinical wisdom [1, 2], has been developing an evidencebased foundation over the last decade. We have seen the completion of a series of randomized treatment trials and prospective observational studies over the last 10 years. These studies have dealt solely with the most common forms of amblyopia, those due to anisometropia, strabismus or a combination. Spectacle correction is the base on which all treatment for amblyopia must be built. Both patching and atropine penalization are e ective as initial management of moderate amblyopia. Initial dosages of 2 h daily of patching or twice weekly atropine have been shown to be e ective and can be considered suitable for initial therapy. Severe amblyopia may be initially managed with 6 h of patching. Intensified treatment for patients who are incompletely treated is logical to prescribe, yet not proven in clinical trials.

The strict age cut-o of 7 or 8 years for therapy has been shown to be incorrect. Children through at least 13 years of age should be considered suitable for a trial of amblyopia therapy, as a large proportion will experience improvement [3]. Management of deprivation amblyopia, such as seen with unilateral aphakia or trauma, remains di cult, frustrating to the families, and often unsuccessful. There is little new information on management of these patients.

10.1.2Epidemiology

Amblyopia is considered the most common cause of monocular visual impairment in both children and young and middle-aged adults, in up to 4% of individuals [4].Simons, 1996 #181; [5]. It has been suggested that the prevalence is higher in underserved communities [6]. A study conducted by the National Eye Institute found amblyopia to be the leading cause of monocular vision loss in the 20–70-year-old age group [4]. These

estimates have been based on schoolor clinic-based studies.

Two very recent population-based studies from the United States have reported prevalence estimates for ambly- 10 opia among preschool-aged children in urban areas. One study from Baltimore, Maryland, found the prevalence of amblyopia to be 1.8% in Whites and 0.8% in AfricanAmericans [7]. The authors extrapolated their finding to suggest that there are approximately 271,000 cases of amblyopia among children 30–71 months of age in the United States. The second study, completed in Los Angeles, California, detected amblyopia in 2.6% of Hispanic/Latino children and 1.5% of African-American children, with 78%

of cases of amblyopia attributable to refractive error [8].

A study of a birth cohort at age 7 years in the United Kingdom found 3.6% of children to have amblyopia [9]. There was a suggestion in this latter study that amblyopia prevalence correlated mildly with lower socioeconomic status.

Whatever the actual percentage of amblyopia in a population, this disease remains a common ocular problem among children. The causes of amblyopia depend on the population studied. In one treatment trial, amblyopia was associated with strabismus (37%), Anisometropia (38%) or both combined (24%) [10]. In another retrospective series, amblyopia was associated with strabismus (57%), anisometropia (17%) or both (27%) [11].

10.1.3Clinical Features of Amblyopia

Visual loss in amblyopia as measured with high-contrast opotoypes varies from mild to severe. The literature suggests that about 25% of cases have visual acuity in the amblyopic eye worse than 20/100 and about 75%, 20/100 or better [12, 13]. The more common causes of amblyopia are strabismus and moderate anisometropia, each accounting for about 35%, with 25% having both anisometropia and strabismus [10, 11]. Much less common is amblyopia related to high anisomyopia, bilateral high ametropia and disease of the anterior visual pathways (e.g., optic nerve hypoplasia). Although good results have been occasionally reported with conventional treatment, these cases are typically more di cult to treat successfully.

Other features of amblyopia include a reduction in contrast sensitivity and possibly reading ability. Most studies have found a reduction in contrast sensitivity in eyes with amblyopia using sinusoidal gratings [14–16], whereas minimal loss has been reported with Pelli-Robson charts, which test intermediate spatial frequencies [16, 17]. Detection of a deficit of contrast sensitivity after treatment

of strabismic and anisometropic amblyopia is slight in the intermediate spatial frequencies tested with the low-con- trast letters of the Pelli-Robson charts [16, 17]. We have recently confirmed this finding of only a minimal deficit with Pelli-Robson charts 3–7 years after enrollment in an amblyopia treatment trial [18].

Most studies of reading ability of amblyopic patients have tested the subjects binocularly, rather than monocularly, generally over a wide range of ages. Some of these studies have indicated that binocular reading ability in children with amblyopia is impaired [19, 20], whereas others have reported that reading ability is not a ected [21]. PEDIG recently reported the monocular oral reading speed, accuracy, fluency and comprehension of 79 children with previously treated amblyopia at a mean age of 10.3 years [22]. We found the amblyopic eyes to be slightly slower and less accurate compared with fellow eyes, while comprehension was similar. Because of our study design we could not compare these children to a non-amblyopic population, so the impact of the monocular loss of vision on the patient’s binocular reading ability remains to be thoroughly explored.

10.1.4Diagnosis of Amblyopia

The diagnosis of amblyopia requires detection of a di erence in visual acuity between the two eyes while wearing a necessary spectacle correction. For children who can have optotype acuity accurately measured, this remains the method of choice, in fact arguably, the only method. The test should employ either crowded or line optotypes. The clinician should exercise caution when interpreting the results of optotype testing. The variability of the instrument needs to be considered. Specifically, what is the expected variability of a second measurement when there has been no actual change in the visual acuity? For the Amblyopia Treatment Study Visual acuity testing protocol of single surrounded HOTV, we found high testability after age 3 years, with 93% of retests within 0.1 logMAR. More importantly, the visual acuity needs to di er by more than 0.18 logMAR for the di erence to likely be true [23]. In my experience a one-line change from a prior visit nearly always led to a change in therapy prescribed, usually an escalation. In children the test– retest variability is very high. For children 7–<13 years, a change in visual acuity must be at least 0.2 logMAR (ten letters) from a previous acuity measure to be unlikely resulting from measurement variability [24]. These two studies of rigorously administered visual acuity testing protocols remind clinicians that substantial variability of visual acuity results is present in children and careful