Article 4 Relative Amblyopia Secondary to Anisometropia in a Patient with Ipsilateral Optic Nerve Hypoplasia

Background: Optic nerve hypoplasia (ONH) is a developmental disorder in which the optic nerve is small and/or there are fewer than normal nerve fibers present. Visual acuity (VA) loss from ONH ranges from none to severe, depending on the extent of macular nerve fiber loss. It is common for patients with decreased vision from unilateral ONH to develop ipsilateral amblyopia secondary to constant unilateral strabismus or high refractive error. We report a case of unilateral ONH and relative amblyopia associated with anisometropia that is less than the expected amblyogenic amount. Case Report: A developmentally appropriate 5-year-old Hispanic female, without complaints or previous spectacle wear, presented for a comprehensive eye examination. Best-corrected distance VA through cycloplegic prescription of OD +0.50-1.00x180, OS -2.50-0.50x180 was OD 20/25, OS 20/100 (HOTV with matching). She was orthophoric at distance and near and showed no response to stereopsis testing. Color vision and pupils were normal. Fundus examination revealed ONH OS. Disc-macula to disc diameter ratio was larger OS. Disc area (Heidelberg Retina Tomograph 3) was noticeably smaller OS. VA improved to 20/40 OS after four months of treatment and has remained stable since then. Stereopsis testing after treatment showed a positive response to random dot forms. Conclusion: Our patient had ONH OS with less than the expected amblyogenic amount of anisometropia. However, VA in the ONH eye improved four logMAR lines with treatment. We conclude that reduced VA from ONH and secondary anisometropia likely led to suppression and relative amblyopia development. We suggest that eye care practitioners attempt patching for selected unilateral ONH patients even if an expected amblyogenic factor is not present. Treatment should be attempted only if the patient’s acuity is adequate for patient compliance.