We thank Dr Hwang and associates for their interest in and comments on our article. In our study, we determined the characteristics that were significantly associated with the visual field (VF) defects in highly myopic eyes. We found that significant VF defects were newly developed in 13.2% of the highly myopic eyes after excluding the eyes with any type of myopic macular or peripheral lesions that could cause VF defects. Multiple regression analyses showed that an abrupt change of the scleral curvature was the only factor significantly associated with a progression of the VF defects.
Hwang and associates have recently studied healthy myopic eyes and reported that eyes with a greater degree of horizontal optic disc tilt to the temporal side had thicker temporal retinal nerve fiber layer (RNFL) thickness than eyes without an optic disc tilt. Hwang and associates pointed out the possibility that these biomechanical features may lead to the abrupt changes in the scleral curvature temporal to the optic disc.
We appreciate these comments and would like to measure the RNFL thickness in highly myopic eyes in the future. Our study differs from that of Hwang and associates because all of our patients were severely myopic; the mean spherical equivalent refractive error was -13.4 diopters (D) and the mean axial length was 28.6 mm (up to 33.0 mm). Thus, our eyes were much more myopic than those examined by Hwang and associates (mean, -3.17 D). Also, many of the eyes of our patients had advanced and deep staphylomas according to Curtin’s classification, with a large conus. We have reported that a scleral ridge develops gradually within the area of type I or type II staphyloma and the configuration of the staphyloma changes with age. The sclera in highly myopic eyes is very thin, and we consider that the further thinning of scleral collagen tissue with aging primarily causes the change in the shape of staphylomas.
The relationship between peripapillary RNFL thickness and degree of myopia is still controversial, and recent studies reported that subjects with high myopia had different topographic profiles compared with those with low myopia. We believe that further studies are needed to determine whether extremely myopic eyes that we studied had different RNFL thickness than not extremely myopic eyes.