Optic Disc Size and Visual Field Defects in High Myopia

Abstract

Purpose : The prevalence of glaucoma is higher among patients with myopia. Due to the myopia associated deformity of the optic disc and the atypical visual field defects, however, it is difficult to diagnose glaucoma optic nerve damage. We therefore assessed the prevalence of glaucoma in patients with high myopia.

Methods : The hospital-based observational study included 172 patients (336 eyes) with high myopia (myopic refractive error ≥-8.00 diopters or axial length >26.5 mm). Based on optic disc size, the patients were classified into three groups: normal disc size group, megalodisc (>3.79 mm²) group, and small disc (<1.51 mm²) group. Glaucoma was defined by glaucomatous optic disc appearance and glaucomatous Goldmann visual field defects which did not correspond with myopic macular changes.

Results : Out of the whole study population, 172 eyes (51.2%) had normal-sized discs, 99 eyes (29.5%) had megalodiscs, and 65 eyes (19.3%) had small discs. Glaucoma was detected in 94 (28%) out of all 336 eyes (22.5% of the normal-sized discs, in 43.4% of the megalodiscs, and in 18.8% of small discs). Larger disc area was associated with longer axial length (P<0.001). As assessed by receiver operating characteristic (ROC) analysis, eyes with an optic disc >3.75 mm² had a 3.1-fold increased risk for glaucoma compared to eyes with a disc size below this cut-off value of 3.75 mm² (area under the ROC curve = 0.63). Likewise, in multivariate analysis, glaucoma prevalence was 3.2 times higher (P<0.001) in megalodiscs (>3.79 mm²) than in normal-sized discs or small discs (<1.51 mm²). Interestingly, visual field defects were found in 41 eyes (12.2%) without glaucomatous optic disc appearance. Among these 41 eyes, 44% of the eyes had a microdisc. Axial length was not significantly associated with glaucoma prevalence in that model (P=0.38).

Conclusions : Glaucomatous optic disc appearance and visual field defects were most commonly seen in highly myopic eyes with megalodiscs. Highly myopic megalodiscs as compared to normal sized discs or small discs had a 3.2 times higher risk for glaucomatous optic nerve neuropathy. However, visual field defects were found also in the eyes without detected glaucomatous optic disc appearance, especially in the eyes with small optic discs. Caution might be necessary in highly myopic eyes with small discs, because glaucomatous optic neuropathy may be overlooked.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.