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First Author: C.Utine TURKEY
Co Author(s): R. Kucumen M. Altunsoy F. Ciftci
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To evaluate short term corneal biomechanical characteristics after collagen cross linking (CXL) for progressive keratoconus.
Yeditepe University, Department of Ophthalmology, Istanbul, Turkey
The surgery was performed under topical anaesthesia. Following de-epithelialization of a central corneal area of 9 mm diameter, photosensitizer solution containing riboflavin-5-phosphate 0.1% (G. Streuli & Co. AG) with dextran T500 20% (Roth AG) was applied for 30 minutes. Corneal pachymetry guidance was performed in all patients prior to operation by a Galilei dual Scheimpflug analyzer to define the area with minimal thickness. Intraoperatively, ultrasonic pachymetry readings (PacScan 300AP, Sonomed Inc., NY) were used to ensure that minimum thickness exceeds 400 ?m. The wavelength was 365 nm at a power of 3 mW/cm2 or 5.4 joule/cm2; distance was approximately 5 cm from corneal apex. During UVA irradiation for 30 minutes, isoosmolar riboflavin 0.1% solution was administered every 3 minutes. Postoperative treatment included topical antibiotic drops (Vigamox®, 4x1), non-steroid and steroid anti-inflammatory drops (Nevanac® 4x1, Predforte® 4x1) and artificial tear drops (Tears Naturale Free®, 8x1). Ocular Response Analyser and non-contact specular microscopy (Konan Medical, Inc., Hyogo, Japan) were used to examine corneal biomechanics and central corneal thickness (CCT) values, respectively. Postoperative measurements were obtained when epithelial healing has been completed. Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann related and corneal compensated intraocular pressure (IOPg and IOPcc, respectively) values were recorded.
A total of 6 eyes of 6 patients were included into the study. The postoperative ORA and CCT measurements were obtained at 2.17 ±1.94 weeks (range: 1 - 6). The mean central corneal thickness was 488.29 ±46.71 ṁ (range: 423 541 ṁ) preoperatively, 492.88 ±49.57 ṁ postoperatively (p=0.87). The mean CH was 8.83 ±1.32 preoperatively, 8.88 ±2.24 postoperatively (p=0.49). The mean CRF was 7.67 ±1.62 preoperatively, 8.64 ±1.71 postoperatively (p=0.03). There was an insignificant increase in the IOPg and IOPcc values postoperatively, as well. The mean IOPg was 10.65 ±2.50 mmHg preoperatively, 13.84 ±2.94 mmHg postoperatively (p=0.15). The mean IOPcc was 13.43 ±1.92 mmHg preoperatively, 16.18 ±4.19 mmHg postoperatively (p=0.30).
In this small case series, we did not note a significant change in CCT and CH measurements in short term after CXL. However, CRF increased significantly after CXL, which indicates improved strength of the keratoconic cornea against deformation, and thus progression of the disease. The improevement in the corneal biomechanics seem to begin in the early postoperative period. There was an insignificant increase in IOP measurements, which might be attributed to postoperative use of corticosteroid eye drops rather than biomechanical changes. A larger series of patients with long term follow-up would be warranted to better analyze the corneal biomechanical changes after CXL.