الفهرس 
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Abstract
Keratoconus (KC) is a bilateral non-inflammatory progressive disease characterized by corneal thickness and structural changes (Modabber and Schwab, 2023).
The corneal epithelium is the outermost layer of the cornea. Beyond the protective role of the eye, it plays a major role while contributing to the refractive power of the eye (Loureiro et al., 2021).
Corneal epithelial thickness (ET) is not homogenously distributed and tends to alter its profile to compensate curvature and stromal irregularities in order to re-establish a regular and smooth ocular surface (Reinstein et al., 2023).
The alteration and thinning of the corneal stroma and epithelium in keratoconus leads to corneal protrusion and transfiguration to a conical shape. Consequently, astigmatism (regular and/or irregular) is a common characteristic of the refractive error in individuals with keratoconus (Coelho et al., 2019).
There are several ways to measure the thickness of the epithelium in different parts of the cornea. The Optical Coherence Tomography (OCT) is a non-contact and reliable method which can remarkably delaminate the surface of the cornea and accurately demonstrate the thickness pattern of the corneal epithelium, due to its high axial resolution (Ostadian et al., 2019).
Therefore, the aim of this study was to detect changes in corneal epithelial thickness in keratoconic patients in comparison to normal eyes using the spectral domain Optical Coherence Tomography (SD- OCT).
This cross section comparative case control study included 60 eyes of 60 subjects; 30 eyes of 30 patients with early keratoconus and 30 normal eyes as a control group recruited from outpatient clinic at ophthalmology department; Benha University.
In the current study, a single eye from each subject was included. Keratoconus is generally a bilateral disorder, although initially only one eye might be affected. Approximately 50% of the unaffected fellow eyes will progress to KC within 16 years (Olivo-Payne et al., 2019; Dimacali et al., 2020). In a study by Li et al. more than one-third of clinically normal eyes in patients with unilateral KC developed manifest KC during the 8-year follow-up period (Li et al., 2004).
In this study, the mean uncorrected visual acuity (UCVA) in the keratoconic and control groups was 0.65 and 0.74 respectively, so the case group has significantly lower UCVA (P=0.002).
This is in accordance with Deonarain et al. (2019) who reported that there was statistically significant difference in the mean VA (logmar) between the keratoconus cases and non-keratoconus group (Deonarain et al., 2019).
This agreed with Castro-luna and Pérez-rueda who showed that there was statistically significant difference between the normal and keratoconus groups (p < 0.05) for the BCVA (decimal scale) (CASTRO-LUNA and PÉREZ-RUEDA, 2020).
Similar findings were shown by Ostadian et al. who showed that of 63 participants, 24 patients were in the normal group, 17 in the subclinical group and 22 in early stages of keratoconus group. Patients’ BCVA in normal and sub-clinical keratoconus groups were almost similar, but in the early keratoconus BCVA was lower compared to the other groups (Ostadian et al., 2019).
In the current study, the mean of thinnest pachymetry in the central 5 mm of the cornea in the keratoconics group was statistically significantly lower as compared to the control group was 463.37 ± 36.35 and 509.67 ± 30.47 µ respectively (P value <0.001). Also, the mean of thinnest pachymetry in the central 7 mm of the cornea in the keratoconics group was statistically significantly lower as compared to the control group was 471.97 ± 38.64 and 511.90 ± 29.90 µ respectively (P value <0.001).
This came in accordance with Hamed et al. who showed that the mean pachymetry was significantly lower in cases (448) than controls (544); the P-value was<0.001 (Hamed et al., 2021).
In the current study, mean of location Y in the central 5 mm of the cornea in the keratoconic and control group was -1201.0 ± 630.55 µ and -475.0 ± 434.13 µ respectively. The keratoconic group is Significantly more inferior (P value <0.001). Also, the mean of location Y in the central 7mm of the cornea in the keratoconic and control group was -830.90 ± 441.92 µ and -492.33 ± 417.50 µ respectively. The keratoconic group is Significantly more inferior (P value = 0.002).
This agreed with Catalan et al. who showed that the mean in the cases with keratoconus was −947.5 ± 549.53 that was statistically significantly lower compared to the control group (−155.9 ± 398.43) (Catalan et al., 2016).
In the current study, the mean superior epithelium in the central 5mm of the cornea in the keratoconics group was statistically significantly thinner compared to the control group (49.83 ± 3