Retinal area and optic disc rim area in amblyopic, fellow, and normal hyperopic eyes: a hypothesis for decreased acuity in amblyopia.

PURPOSE: Defects in visual functions in amblyopic eyes may have a neuroretinal explanation. The retinal area to optic disc rim area ratios of hyperopic normal, amblyopic, and fellow eyes were evaluated.

DESIGN: Case-controlled study.

PARTICIPANTS: A total of 293 patients with amblyopia and bilateral hyperopia and 77 non-amblyopic bilaterally hyperopic patients without strabismus.

METHODS: Disc areas were measured using magnification correction formulas developed by Bengtsson and Krakau. Axial lengths were determined by ultrasound biometry or laser interferometry with a Zeiss AOL Master (Carl Zeiss Co., Oberkochen, Germany). The visual area of the retina was calculated using axial length measurements.

MAIN OUTCOME MEASURES: Optic disc rim areas, corrected for magnification, retinal areas, and a derived ratio, retinal area/disc rim area (RetA/DRimA).

RESULTS: The RetA/DRimA for the amblyopic eyes was significantly greater than that of the fellow and normal eyes, indicating that amblyopic eyes have larger retinal receptor areas than fellow or normal eyes. The RetA/DRimA of the fellow eyes was smaller than for the amblyopic but larger than that of the normal eyes. These differences were due to smaller optic disc rim areas in the amblyopic and fellow eyes.

CONCLUSIONS: Amblyopic and their fellow eyes, when compared with normal eyes, have reduced innervations of comparable retinal areas. These differences can be attributed to a paucity of nerve fibers, as indicated by the smaller neuroretinal rim areas.

FINANCIAL DISCLOSURE(S): The authors have no proprietary or commercial interest in any materials discussed in this article.