Abstract: Objective To study the correlation between corneal morphology and corneal subbasal nerves in patients with keratoconus(KC). Design Prospective comparative case series. Participants Seventy-four eyes of 74 patients with KC (25 of the other 74 eyes as frustrate keratoconus) and 24 eyes of 24 healthy patients were enrolled in this study from March 2018 to March 2019 in Beijing Tongren Hospital. Methods Patients were diagnosed and grouped as KC, frustrate KC or the normal by ophthalmic examination and Pentacam. Kmax (the maximum anterior corneal refractive power)and Minpachy (the minimum corneal thickness) of KC were applied as parameters of corneal shape. Images of subbasal nerves obtained with in vivo confocal microscopy (IVCM) were analyzed and calculated into 6 parameters by ACCmetrics software: corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), corneal total branch density (CTBD), corneal nerve fiber area (CNFA), and corneal nerve fiber width (CNFW). The correlation between subbasal nerves and corneal morphology in KC group was analyzed, and the differences of parameters between each group pair were compared. Main Outcome Measures Kmax, Minpachy, CNFD, CNBD, CNFL, CTBD, CNFA and CNFW. Results Qualitative analysis of IVCM showed that the subbasal nerves in KC showed a reduced density and increased tortuosity as compared to controls. The subbasal nerves in KC were arranged in bundles sometimes. Intergroup comparison showed statistically significant reduction in CNFD, CNBD, CNFL and CNFW in group KC as compared to group normal (all P<0.05). Intergroup comparison showed statistically significant reduction in CNFL and CNFA in keratoconus as compared to frustrate KC (both P<0.05). Intergroup comparison showed statistically significant reduction in CNFD and CNFL in the normal as compared to frustrate KC (both P<0.05). In correlation analysis, CNFD, CNFLand CNFW of KC patients were correlated with Kmax (P=0.001, 0.001 and 0.006, respectively) and the CNFD, CNFL CNBD, and CNFW of KC patients were correlated with Minpachy (P=0.01, 0.01, 0.004, 0.02). Conclusions In keratoconus, the changes in subbasal nerve may be earlier than the corneal shape. Subbasal nerve will change with the progress of keratoconus. Corneal nerve fiber density (CNFD) and corneal nerve fiber length (CNFL) might be applied as indicators for early diagnosis of keratoconus. (Ophthalmol CHN, 2020, 29: 118-122)

Key words: keratoconus, subbasal nerves, in vivo confocal microscope