Role of corneal epithelial thickness mapping in the evaluation of keratoconus

https://doi.org/10.1016/j.clae.2019.04.019Get rights and content

Abstract

Purpose

To investigate the corneal epithelial thickness profiles in patients with a confirmed diagnosis of stable and progressive keratoconus.

Setting

Studio Italiano di Oftalmologia, Rome, Italy.

Design

Observational study.

Methods

86 patients with either stable (n = 52) or progressive (n = 34) keratoconus and 182 healthy controls were enrolled in the study. Disease progression was confirmed by repeated corneal topographies over 1 year follow-up before inclusion in the study. All subjects had full corneal and epithelial thickness mapping taken by spectral domain optical coherence tomography (SD-OCT). The full corneal mapping was investigated by evaluating the central corneal thickness, the thinnest point, the superonasal-inferotemporal thickness difference and the minimum-median thickness difference. The epithelial mapping was investigated by assessing the 2 mm central thickness, the inferior paracentral (2–5 mm) thickness, and the minimum-maximum thickness difference.

Results

No significant differences in full corneal mapping were found between stable and progressive keratoconic eyes. Of note, the inferior paracentral region of the corneal epithelium was significantly thinner in progressive (50 ± 3 μm) than stable (53 ± 4 μm) keratoconus (P < 0.001).

Conclusions

The SD-OCT corneal epithelial mapping was valuable for detecting local thickness changes in eyes with keratoconus. Monitoring the corneal epithelial changes across the inferior area in patients with keratoconus could be worthy for assessing disease progression.

Introduction

Keratoconus is the most frequent degenerative disease of the cornea [1,2]. It is widely known that the disease is strongly correlated with stromal and epithelial thickness changes [3]. The changes of corneal epithelium have been hypothesized to develop in the sub-clinical stage of keratoconus [[4], [5], [6], [7]]; in addition, these alterations may occur even in eyes that do not show severe abnormalities with corneal topography [6,8].

Optical Coherence Tomography (OCT) and Very High-Frequency digital UltraSound (VHF-US) have been the most commonly used tools for mapping the corneal epithelial thickness. In general, OCT and VHF-US have been shown to be in close agreement for epithelial thickness measurement, although OCT usually provided a central epithelial thickness 2–5% thinner than VHF-US in two thirds of cases [9,10].

Studies on normal population have shown moderate or high variability of the central, paracentral, and midperipheral corneal epithelial thickness values in subjects of different age and gender [11]. Since significant differences in the corneal epithelial thickness profile have been found even in normal eyes, there is need of studies with large sample size in order to understand whether the investigation of corneal epithelial mapping could be valuable to detect pathologic changes in eyes with keratoconus and, most importantly, to assess disease progression. Although a number of studies [5,[12], [13], [14]] has shown the accuracy of OCT imaging in assessing the variations of epithelial thickness between patients with keratoconus and healthy subjects, there is no evidence on its role on monitoring diseases progression.

The scope of the present study was to investigate the full corneal and epithelial thickness profiles in subjects with a confirmed diagnosis of stable or progressive keratoconus; a large group of healthy subjects was enrolled in the study and data used as controls.

Section snippets

Patients and methods

Patients with confirmed diagnosis of stable or progressive keratoconus and healthy subjects were invited to participate in this study. Diagnosis of keratoconus was made by two expert corneal specialists (M.L. and S.S.) by complete eye examination, which included corneal topography, corneal pachymetry, slit-lamp bio-microscopy and manifest refraction. Keratoconus was deemed to be progressive if there was an increase of at least 1 diopter (D) in maximum simulated keratometry value (Kmax) derived

Results

The study included 268 eyes of 268 subjects. Eighty-six (86) eyes of 86 patients had a diagnosis of keratoconus; 52 of these had stable keratoconus and 34 had progressive keratoconus. One hundred eighty two (182) healthy eyes of 182 subjects were enrolled as controls (Table 1).

All the full corneal thickness values, such as CCT, thinnest point, SN-IT 2–5 mm and min-med values were significantly thinner (P < 0.001) in keratoconus (either stable or progressive) than controls. No significant

Discussion

This study investigated the full corneal and epithelial thickness mapping in patients with a confirmed diagnosis of stable and progressive keratoconus. A large cohort of healthy controls was enrolled in order to have a powerful control dataset of epithelial mapping values, which was lacking in the scientific literature.

Contact lens wearers (24% of the overall population) were recommended to discontinue their use for a period of at least 3 weeks before eye examination in order to minimize

Financial support

POR FESR 2014–2020 grant n. A0114-2017-13715.

Conflict of interest

No conflicting relationship exists for any author.

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