Nanotopography by chromatic confocal microscopy of the endothelium in Fuchs endothelial corneal dystrophy, pseudophakic bullous keratopathy and healthy corneas.

Abstract

To investigate the interest of chromatic confocal microscopy (CCM) to characterise guttae in Fuchs endothelial corneal dystrophy (FECD). Descemet's membranes (DM) were obtained during endothelial keratoplasty in patients with FECD and pseudophakic bullous keratopathy (PBK). They were compared with healthy samples obtained from body donation to science. Samples were fixed in 0.5% paraformaldehyde and flat mounted. Surface roughness of DMs was quantified using CCM and the AltiMap software that provided the maximum peak (S_p) and valley (S_v) heights, the mean square roughness (R_q) and the asymmetry coefficient (S_sk). The physiological roughness of healthy samples was characterised by an R_q of 0.12±0.05 µm, which was two times rougher than in PBK (R_q=0.06±0.03 µm), but both were still flat with a symmetrical distribution between peaks and valleys (S_sk close to 0, n_peaks=n_valleys), smaller than 1 µm. In FECD, the maximum peak height was 5.10±2.40 µm, up to 5.8 and 8.3 times higher than the control and PBK, respectively. The maximum valley depth was half than the peak (2.28±0.89 µm). The surface with guttae was very rough (R_q=0.45±0.14 µm) and the S_sk=1.84± 0.43 µm, greater than 0, confirms an asymmetric surface with high peaks and low valleys (n_peaks>n_valleys). Moreover, the CCM provided quantitative parameters allowing to distinguish different types of guttae from different patients. CCM is an innovative approach to describe and quantify different morphologies of guttae. It could be useful to analyse the different stages of FECD and define subgroups of patients.