We read with great interest the article by Ohno-Matsui and associates describing the visual field (VF) defects in highly myopic eyes. They reported that progressive VF defects were newly developed in 13.2% of the highly myopic eyes and the incidence of VF defects was significantly higher in eyes with an oval optic disc than in eyes with a round optic disc. An abrupt change of the sclera curvature was the only factor correlated with progression of the VF defects. Thus, the authors suggested that stretching and distortion of the retinal nerve fiber layer (RNFL) from an abrupt change of scleral curvature may be the factors associated with VF defects.
In this study, as the authors addressed, the degree of optic disc tilt and RNFL thickness profile were not assessed quantitatively. The degree of optic disc tilt and RNFL thickness profile can be evaluated by optical coherence tomography (OCT), as described in our previous studies. Our previous studies demonstrated that when the degree of myopic optic disc tilt was measured from the cross-sectional images of the Cirrus HD spectral-domain OCT (Cirrus HD OCT; Carl Zeiss Meditec, Dublin, California, USA) in healthy myopic eyes, the degree and direction of myopic optic disc tilt affected the RNFL thickness profile. The eyes with greater degree of horizontal optic disc tilt to the temporal side had more temporally located superior/inferior peaks of RNFL thickness and thicker temporal RNFL thickness than the eyes without optic disc tilt. In addition, among the eyes with myopic optic disc tilt, eyes with rotated optic discs (obliquely oval discs) had more temporally located superior peaks of RNFL thickness and thicker temporal RNFL thickness than eyes without optic disc rotation.
Based on our OCT findings of myopic eyes in healthy young subjects, we speculate that as an optic disc tilts temporally, the temporal side of an optic disc depresses and its nasal side elevates. These biomechanical features may lead to abrupt changes in the scleral curvature temporal to the optic disc and protrusion of the nasal edge of the optic disc, as suggested by Ohno-Matsui and associates. During this process, axons passing the tilted portions of optic disc can be vulnerable to damage by mechanical stretching or kinking. Therefore, we suppose that alterations of RNFL thickness profile resulting from the myopic optic disc tilt may, at least in part, contribute to the VF defects in eyes with high myopia. However, in our previous studies, VF results were not analyzed and the range of myopia was between −11.00 and 0 diopters.
In addition to VF results analyses, investigation of the degree/direction of optic disc tilt and RNFL thickness profile using OCT will help us better understand the long-term development of the VF defects in highly myopic eyes.