PARADOXICAL CLINICAL CASES IN KERATOCONUS AND THEIR TOMOGRAPHIC FEATURES

Purpose – to analyze the tomographic features of paradoxical clinical cases of keratoconus. Material and methods In an analytical and retrospective study, paradoxical clinical cases that contradicted the characteristics of keratoconus were analyzed in 2 groups: 19 eyes with a mean keratometry ≤43.5 D in the low keratometry keratoconus group (LK), and 21 eyes with a central pachymetry ≥550 μm in the thick keratoconus group (TK). For the comparision 60 eyes with classic keratoconus were included in the clinical keratoconus group (CK) and 30 normal eyes without keratoconus in the control group (N). All patients underwent a comprehensive ophthalmological evaluation along with Scheimpflug based corneal tomography examination. Results The keratometric indices were significantly lower in the LK group compared to the CK group, while the central pachymetry was higher in the TK group. In the LK group, the maximum keratometry was positioned more inferiorly along the vertical meridian relative to the corneal center compared to the other groups. In the LK and TK groups, the following parameters from Belin-Ambrósio Enhanced Ectasia Display were statistically different from the indices of normal eyes (p < 0.001): the D parameter, the average pachymetric progression index (PPI average), the anterior elevation index (AE), the posterior elevation index (PE), and from topography map: the surface variation index (ISV), the vertical asymmetry index (IVA), the keratoconus index (KI), and the height decentration index (IHD). These parameters in the LK group did not show statistical differences from the parameters of the eyes in the CK group (p> 0.05). However, the TK group also statistically differed from the CK group in lower values of these parameters, which are considered sensitive for confirming the keratoconus diagnosis (p<0.001). Conclusion In relatively low keratometry and thick keratoconic corneas, which contradicts the clinical course of keratoconus, high values of the sensitive parameters of the Scheimpflug tomography statistically distinguish these eyes from normal eyes. The obtained results, showing the tomographic characteristics of keratoconus in these eyes, will allow the selection of treatment methods, and the analysis of prognostic and tactical approaches in future studies. Key words: keratoconus, low keratometry keratoconus, thick cornea, Scheimpflug tomography