In the present study, the keratoconus patients who treated with CXL had statistically significant thinner CCET and LET. Total central epithelial thickness, stromal thickness decreased with CXL. However, there was no statistically significant difference.
Keratoconus is an asymmetrical, non-infective, non-inflammatory progressive corneal ectasia that usually affects both eyes . It starts at an early age and progression usually stops in the middle ages. Compared to previous years, as a result of today's technical and technological studies, the patient is diagnosed early, thanks to measurements during routine examination, before the patient becomes aware of it and the chance of intervention before the disease progresses is achieved . 20% of patients have progressive corneal ectasia. High myopia and irregular astigmatism limit patients' ability to see . Science has sought cures for this disease. Various treatment protocols have been developed. Some of those; corneal cross-linking, keratoconus lens, intrastromal ring segments, keratoplasty[15, 16].
Corneal cross-linking therapy had first applied to humans in 1999-2002 and became a candidate for entry into the medical literature in 2003 [17, 18]. Corneal cross-linking therapy stops the progression of keratoconus. Riboflavin and Ultraviolet-A are used in cross-linking therapy . Purpose in corneal cross linking; It is aimed to increase the number of cross-links in the cornea, biomechanical strength, increase in collagen fiber diameter, increase in shrinkage temperature, increase enzymatic resistance, and increase resistance to edema [20, 21]. At the same time corneal cross-linking and anti-collagenase effect, anterior and middle Apoptosis of keratocytes in the stroma and deep keratocytes in their follow-upit makes it reproduce again .
Various complications have been reported in the literature as a result of corneal cross-linking. These are complications; infection, corneal haze, stromal scar, corneal scar, encountered epithelization delay and uveitis . Infection Presence of epithelial defect as facilitating reasons, contact lens wear and steroid drops may be demonstrated. Escherichia coli, Acanthamoeba, Staphylococcus, Pseudomonas aeruginosa or polymicrobial agents formed after crosslinking blamed for keratitis [24, 25]. In this study, no complications developed in keratoconus eyes that underwent corneal cross-linking.
In our study; keratometric values such as Kmax, Km, K1, and K2 was decreased in keratoconus patients who underwent corneal cross-linking. But there was no significant difference in terms of Schiempflug topography between the treated with untreated. However, by Schiempflug topography, the posterior astigmatism value was decreased in the treated group compared to the untreated group and it was statistically significant. Waszczykowska and Jurowski did not report significant improvement in visual acuity and any significant differences in pre- and postoperative astigmatism .
In the present study, central corneal epithelium and limbal corneal epithelium was found thinner often cross-linking. In the study of Kanellopoulos et al., healthy subjects normal eyes, with keratoconus and corneal crosslink treated patients with keratoconus were investigated and epithelial changes in the corneal center and peripheral zones were analyzed. As a result of the research, it was observed that the thinnest epithelial thickness was found thinner in patients who underwent corneal cross-linking both centrally and peripherally. . In a recent study central and regional thicknesses of the corneal epithelium of healthy subjects and keratoconus patients treated with after corneal cross-linking was compared. They found significant thining in treated patients comparing to healthy subjects .
The Fourier-field Optical Coherence Tomography (OCT) of Yan li et al. detected that there was a statistically significace between keratoconus patients and healthy subjects in CCET and süperior, inferior, epithelial thickness. Central corneal, inferior, temporal limbal epithelium was found thinner after CXL. . In literature multiple studies, investigated the epithelial thickness of the same keratotic eyes before and after corneal crosslinking. While the thickness of the inferior and temporal limbal epithelium of eyes with keratoconus had low before the operation, epithelial thinning occurred in the cornea central and mostly in the quadrant after the operation [30-32].
In our study, we found that stroma and total corneal thickness decreased in keratoconus patients with cross linking with AS OCT, but there had no statistically significant difference. In the study of Kanellopoulos et al. investigated the stroma and total corneal thickness of all three groups. Both stroma and total corneal thickness of the patients who had cross-linking treatment was thinner than healthy eyes and untreated keratoconus .
Our results showed that there was a statistically significant correlation between CCT and CCET in treated patients. CCST correlates with CCET and was statistically significant. There was a sttatistically significant correlation between LCET and LCST. Also, LCET shows a strong correlation with CCET. This result reveals the limbal epithelium acts as a source for the central epithelial cells. The LCET thinning may cause the CCET thinning because of reduced migration of decreased number of stem cells to the center.
There are some limitations of the present study. First it has small sample size, second the OCT measurements had taken manually, third the thickness measurements could not taken with Schiemplug topography. However this study enlightens the limbal thickness and central thickness changes before and after corneal crosslinking.
Corneal cross-linking has gained an important place among the inventions that prevent the progression of keratoconus disease. Thanks to the latest technical and technological developments, the details of the corneal structure are gradually increasing. This leads to the development of new medical and surgical methods.
As a result epithelial thickness and limbal thickness alterations detected with Ant-OCT could be useful for monitorizing the keratoconus patients treated with crosslinking and could show the effectivity of the treatment.