Morphologic characteristics of optic disc in normal population with physiologic large cup in Chinese Han people

Background: The early diagnosis of glaucoma is a global problem. Physiologic large cup (PLC) with an abnormally high cup/disc ratio may be confused with changes of the optic disc in early glaucoma. However, fewer reports are available regarding PLC in normal population. Heidelberg Retina Tomograph (HRT) can provide quantitative topographic parameters of the optic discs and be used widely. Consequently, we desire to find the rule of morphologic changes of PLC in Chinese Han people using HRT for differentiating it from glaucoma. Methods: One hundred (100) subjects with PLCs and 74 subjects with normal cups (NCs) were examined by HRT. The topographic parameters were analyzed and the characteristics of the inferior, superior, nasal, and temporal quadrants of PLCs were examined. Parameters obtained from HRT were compared between two groups. The effect of age, refractive error, and disc area on each parameter was analyzed by the multiple linear regression model. This was a prospective study and the mean length of follow-up of the subjects was 28 months. Results: Compared to NC group, PLC group had larger disc (P < 0.0001) but smaller mean retinal nerve fiber layer thickness (mRNFLt) (P<0.0001). The nasal quadrant of disc area was larger than the inferior quadrant. Mean cup depth and maximum cup depth were unaffected by refractive error (P = 0.0539, 0.2228, respectively), age (P = 0.1981, 0.8207, respectively) or disc area (P = 0.1927, 0.3718, respectively). There was no significant change in disc area or cup shape measure (P = 0.847, 0.051, respectively). Conclusions: Optic disc structural parameters in PLC presented a similar pattern to NC, while PLC’s disc area was larger but mRNFL thickness was smaller than the NC’s. There were some changes in the topographic parameters of the optic discs of PLC overtime, but no glaucomatous damage was detected during our follow up.