Change in corneal endothelial cell density and morphology in different stages of keratoconus

To assess the changes in corneal endothelial cell density (CD) and morphology in patients with different stages of keratoconus.

A cross-sectional study was conducted.One hundred and nineteen patients (199 eyes) with keratoconus who were treated in the Eye Hospital of Shandong First Medical University were included from March 2018 to October 2021.The 199 eyes were classified into stage Ⅰ (111 eyes of 58 cases), stage Ⅱ (41 eyes of 30 cases), stage Ⅲ (47 eyes of 31 cases) keratoconus groups according to the Amsler-Krumeich classification.In the same period, 25 age- and sex-matched healthy subjects (50 eyes) were enrolled as a normal control group.Corneal topography and anterior segment parameters such as keratometry (K), central corneal thickness (CCT), thinnest corneal thickness (TCT), anterior chamber depth (ACD), corneal diameter and corneal volume were obtained by Pentacam 3-dimensional anterior segment imaging and analysis system.The corneal endothelial CD, percentage of hexagonal cells (6A), average cell area (AVE), maximum cell area (MAX), minimum cell area (MIN), cell area standard deviation (SD) and cell area coefficient of variation (CV) in the central area were evaluated by non-contact specular microscopy.The correlation between corneal endothelial CD, morphological parameters and corneal topographic parameters was analyzed by Spearman rank correlation.This study adhered to the Declaration of Helsinki and was approved by the Ethics Committee of Shandong Eye Hospital (No.SDSYKYY201803). All patients were informed of the purpose and methods of the study and written informed consent was obtained before any medical examination.

The CD of the normal control group and stage Ⅰ, Ⅱ, Ⅲ keratoconus groups was 2 941(2 809, 3 072), 2 825(2 667, 3 030), 2 747(2 475, 2 903) and 2 370(2 142, 2 525) cells/mm², respectively.With the progression of keratoconus, CD decreased gradually, and there was a significant difference in CD among the four groups (H=94.862, P<0.001). There were significant differences in CV and 6A among the four groups (H=45.018, 20.421; both at P<0.001). CV was significantly higher in stage Ⅲ keratoconus group than that of the normal control group and stage Ⅰ and Ⅱ keratoconus groups and 6A was significantly lower in stage Ⅲ keratoconus group than that of the normal control group and stage Ⅰ keratoconus group (all at P<0.05). With the progression of keratoconus, MAX, MIN, AVE and SD increased gradually, and there were significant differences in MAX, MIN, AVE and SD among the four groups (H=37.905, 32.437, 110.182, 72.941; all at P<0.001). MAX and MIN in stage Ⅲ keratoconus group were significantly higher than those in stage Ⅰ keratoconus groups and normal control group (all at P<0.05). AVE and SD in stage Ⅲ keratoconus group were significantly higher than those in normal control group and stage Ⅰ and Ⅱ keratoconus groups (all at P<0.05). In patients with keratoconus, CD was moderately positively correlated with CCT (r_s=0.47, P<0.001) and TCT (r_s=0.53, P<0.001), and was moderately negatively correlated with mean keratometry (Km) (r_s=-0.59, P<0.001).6A was weakly positively correlated with CCT (r_s=0.18, P=0.01) and TCT (r_s=0.22, P=0.002), and was weakly negatively correlated with Km (r_s=-0.32, P<0.001). CV was weakly negatively correlated with CCT (r_s=-0.35, P<0.001) and TCT (r_s=-0.37, P<0.001), and was moderately positively correlated with Km (r_s=0.48, P<0.001). There was no correlation between CD, CV, 6A and ACD, or corneal volume.

As the keratoconus progresses, the cornea protrudes and becomes thinner with CD and 6A decreasing while CV increasing.Corneal topographic parameters are related to the density and morphology of corneal endothelial cells.