Abstract
Purpose: :
More myopic eyes are associated with higher prevalence of open angle glaucoma. However, the optic discs in eyes with high myopia are often associated with characteristic myopic changes which make early diagnosis of glaucoma based on the disc appearance difficult. To our knowledge, no study has quantitatively assessed the optic disc topography of highly myopic eyes. We studied structural characteristics of myopic discs using the Heidelberg Retina Tomography (HRT) II in comparison with age–matched emmetropic eyes.
Methods: :
Subjects with spherical equivalent of refraction between –5 and –10 diopters at least in one eye (myopic eyes) and those with spherical equivalent of refraction within < ±1 diopter at least in one eye (emmetropic eyes) were consecutively enrolled. One eye from one subject was used and eyes with any ocular diseases, unreliable results with Humphrey Field Analyzer 30–2 SITA Standard program or HRT II results, or abnormal visual field results according to the Anderson Pattela criteria were excluded. Axial length was measured using an IOL Master (Carl Zeiss Meditec Japan).
Results: :
Intraocular pressure and age showed no significant inter–group difference (P>0.6). The myopic eyes had longer axial length (26.4±0.9 vs. 23.3±0.7 mm, P<0.001), lower mean deviation (–1.88 ± 0.47 vs. +0.14±0.7 dB, P<0.001), smaller disc area (1.88±0.46 vs. 2.14±0.36 mm2, P=0.042), cup area (0.42±0.28 vs. 0.72±0.31 mm2, P=0.002), cup depth (0.22±0.06 vs. 0.28±0.10, P=0.034), greater height variation contour value (HVC, 0.50±0.19 vs. 0.39±0.10, P=0.013) and RNFL thickness (0.33±0.12 vs. 0.26±0.07 mm, P=0.018), while rim area showed no significant inter–group difference (P=0.6). Among the emmetropic eyes, rim area (R=0.60, P<0.001) and cup area (R=0.57, P<0.001) were significantly correlated with disc area, while cup depth, HVC, and RNFL thickness were not (P>0.05). Among the myopic eyes, rim area (R=0.80, P<0.001), HVC (R=–0.55, P<0.033), and RNFL thickness (R=–0.57, P=0.027) were significantly correlated with disc area but cup area was not (P=0.072).
Conclusions: :
Rim area showed no significant difference between eyes with high myopia and emmetropic eyes, but the former had smaller disc and cup area, cup depth, greater RNFL thickness and lower mean deviation value than the latter. Correlations among the HRT II parameters in myopic eyes differed from those in emmetropic eyes.
Keywords: optic disc • visual fields • myopia