Visual Improvement in an Adult Amblyopic Eye Following Radiation-InducedVisual Loss in the Contralateral Eye FREE

Amblyopia is a visual deficit defined as decreased best-corrected visualacuity of at least a 2-line difference between the two eyes that is not dueto an organic cause.¹ It is typically associatedwith strabismus, uncorrected asymmetric refractive error, or ocular disordersthat interfere with the development of the fixation reflex. Although the pathophysiologicalmechanisms in amblyogenesis are not completely understood, a fundamental principleof treatment is that therapy can be effective only when the visual systemis sufficiently "plastic" for cortical modification to occur. The sensitiveor critical period of visual development and modification is species specificand age defined; in humans it is thought to occur from birth to the arbitraryage of 9 years.¹

We describe an adult with a childhood history of anisometropic amblyopiawho lost central vision in his dominant eye as a result of radiation-inducedmaculopathy following treatment for a macular choroidal melanoma. The patientsubsequently regained excellent vision in the previously amblyopic eye.

In May 1990, a 42-year-old man experienced decreased vision in his righteye. He had a history of anisometropic amblyopia in his left eye since childhood,with a consistently recorded best-corrected Snellen visual acuity of 20/80OS. Part-time occlusion was instituted in the right eye at age 6 years, withcessation 1 month later because of patch intolerance. This eye was never opticallycorrected.

At examination his visual acuity was 20/30 OD and 20/80 OS. The lefteye was anatomically normal (Figure 1).Fundus examination of the right eye showed an amelanotic, juxtafoveal choroidalmass with a base measuring 6.0 × 4.5 mm and a thickness of 3.8 mm. Asecondary serous retinal detachment was noted over the lesion, extending intothe foveola and inferior fundus. The tumor was echolucent at ultrasonographicexamination and displayed intrinsic vessels on fluorescein angiographic studies,consistent with a choroidal malignant melanoma.

The melanoma was treated with iodine 125 (I₁₂₅) plaque radiotherapy.The tumor apex received 11 500 rad (115 Gy), and the foveola received24 453 rad (244 Gy). Eighteen months later, tumor regression and subretinalfluid resolution were documented. However, radiation-induced maculopathy causedby treatment was found with cystoid macular edema, foveal exudation, retinalhemorrhage, and microvascular ischemia, allowing a visual acuity of only 20/60OD (Figure 2). Given the amblyopiain the left eye and decreased vision in the right eye, severe visual handicapwas anticipated. Suprisingly, visual acuity in the amblyopic eye improvedfrom 20/80 in June 1990 to 20/20 in April 2002 (Table 1).

Amblyopia is generally considered to be a treatable condition when recognizedand managed at an early age.^{2 - 3} Treatmentof amblyopia consists of 2 basic strategies. The first is to optimize theretinal visual image in the amblyopic eye. This is accomplished by providinga clear visual axis and correcting any significant refractive errors. Thesecond strategy is to enhance the neural stimulus to the visual cortex. Inmost cases, this is accomplished by limiting stimuli to the nonamblyopic eyeusing occlusion therapy with patching, pharmacologic penalization, or opticaldefocusing.^{2 - 3}

Recovery of visual function in adult amblyopic eyes has also been documentedfollowing visual loss in the fellow eye^{4 - 8} (Table 2). This finding appears to be independentof the age at which the dominant eye loses vision, whether the loss of visionis total or partial, and previous treatment of amblyopia. In a retrospectivemulticenter study, Vereecken and Brabant⁶ foundan improvement of at least 3 lines in the amblyopic eye in 28.5% of patientswith vision loss in the good eye. A favorable prognostic factor for improvementwas the existence of foveal fixation associated with anisometropic amblyopia.

Improvement of visual acuity in the amblyopic eye is usually gradual.El Mallah et al⁷ retrospectively analyzedthe records of 465 adult patients with age-related macular degeneration andidentified 9 individuals who also had amblyopia in the fellow eye. All but2 of these 9 patients showed improvement in vision that averaged 1.5 linesat each consecutive 6-month visit. At the final visit, the accumulated gainsin the amblyopic eye averaged 3 lines and generally occurred between 1 and12 months from baseline. In our patient the visual recovery was slow, duringnearly 1 decade, possibly related to the slow loss of vision in the dominanteye.

Visual improvement in the amblyopic eye can be sustained even afterrecovery of visual acuity in the nonamblyopic eye. Wilson⁸ described2 adult patients aged 57 and 67 years with documented childhood amblyopiaresulting in a visual acuity of 20/200 and 20/100, respectively, in the affectedeye. Cataract formation in the dominant eye of each patient, to a visual acuityof 20/50 and 20/80, respectively, was associated with improvement in visualacuity of the amblyopic eye to 20/30 and 20/25. Most remarkably, the improvementwas sustained after the nonamblyopic eye was rehabilitated by cataract extractionto a visual acuity of 20/20.

In summary, we describe an adult patient whose childhood anisometropicamblyopia reversed completely during a period of 12 years when the cotralateraleye developed radiation maculopathy secondary to plaque radiotherapy of amacular choroidal melanoma. Acknowledgement of such cases is important whentreating and counseling patients with a vision-threatening ocular conditionin whom the contralateral eye is amblyopic.

This study was supported in part by the Eye Tumor Research Foundation,Philadelphia; the Macula Foundation, New York, NY (Dr C. Shields); the RosenthalAward of the Macula Society, Cleveland, Ohio (Dr C. Shields); and the PaulKayser International Award of Merit in Retina Research, Houston, Tex (Dr J.Shields).

The authors have no relevant financial interest in this article.

Corresponding author and reprints: Carol L. Shields, MD, OncologyService, Wills Eye Hospital, 840 Walnut St, Philadelphia, PA 19107.