Outcomes of Corneal Collagen Crosslinking Treatment
This retrospective study comprised 96 eyes of 96 patients who underwent unilateral CXL treatment for progressive keratoconus. The study was performed in adherence to the tenets of the Declaration of Helsinki and local ethics committee approved the methodology. Inclusion criteria were biomicroscopic examination and corneal topography consistent with keratoconus, inferior–superior ratio on topographic map >1.5, at least 18 years of age, thinnest corneal pachymetry of ≥400 μm. Progression was defined as ≥1 D steepening of maximum keratometry or an increase of ≥1.00 D in manifest cylinder or an increase of ≥0.50 D in manifest refraction spherical equivalent in 2 years. Eyes with prior corneal surgery or scarring were excluded from the study.
All patients underwent detailed ophthalmological examinations that included corrected (including contact lens) distance visual acuity (CDVA) measurement with Snellen charts, slit-lamp biomicroscopic examination, applanation tonometry, and dilated funduscopic examination. Visual acuity in Snellen format was converted to the logMAR (log of the minimum angle of resolution) equivalent for statistical analysis. The mean CDVA was noted at baseline and 1 year after CXL treatment.
New generation anterior segment tomography devices are capable of determining the topography and pachymetry of the entire cornea. In this study, corneal topography (Allegro Oculyzer, WaveLight AG, Erlangen, Germany) was conducted with undilated pupils under scotopic conditions by a single experienced technician. Scans were taken in automatic mode with proper quality. Maximum keratometry and corneal pachymetry at the thinnest location were recorded at baseline and 1 year after CXL treatment. Cone location was determined according to the topographic coordinates of maximum keratometry as follows: central cone (maximum K within the central 3 mm optical zone), paracentral cone (3–5 mm optical zone), and peripheral cone (outside the central 5 mm optical zone).
Subgroups and cutoff values were created in accordance with the current literature as follows: age (<30 and ≥30 years), gender, preoperative CDVA (<0.3 and ≥0.3 logMAR), preoperative maximum K (<54 and ≥54 D), baseline topographic cone location (central, paracentral, and peripheral cone), and preoperative thinnest pachymetry (<450 and ≥450 μm) to analyze the relationship between preoperative patient characteristics and improvements in CDVA and maximum K after CXL treatment.
CXL was performed under sterile conditions using topical anesthesia as described by Wollensak. Central 9.0 mm corneal epithelium was removed by mechanical debridement. Isotonic riboflavin solution (0.1% in 20% dextran T500 solution) was instilled every 2 min for 30 min until riboflavin absorption was observed in the corneal stroma and anterior chamber under biomicroscopic examination. Then, the cornea was exposed to UVA irradiation at the wavelength of 365 nm and surface irradiance of 3 mW/cm. During the UVA exposure, isotonic riboflavin solution instillation was continued every 2 min for 30 min. Postoperatively, a soft contact lens was placed until corneal epithelial healing completed. Topical antibiotic and corticosteroid drops were administered and continued four times daily for 1 week and 2 weeks, respectively.
Statistical analysis was performed with the Statistical Package for Social Sciences software version 16.0 (SPSS Inc, Chicago, IL, USA). Results were expressed as mean±SD. A paired t-test was used to analyze the changes in mean CDVA and maximum K between baseline and 1 year. Comparison of the quantitative data (changes in mean CDVA and maximum K) between two groups was performed by independent samples t-test. However, non-parametric tests (Wilcoxon signed ranks test and Mann–Whitney U-test) were used to analyze the effects of preoperative topographic cone location on mean CDVA and maximum K. A P-value less than 0.05 was considered statistically significant at 95% confidence interval.
Materials and Methods
Study Population
This retrospective study comprised 96 eyes of 96 patients who underwent unilateral CXL treatment for progressive keratoconus. The study was performed in adherence to the tenets of the Declaration of Helsinki and local ethics committee approved the methodology. Inclusion criteria were biomicroscopic examination and corneal topography consistent with keratoconus, inferior–superior ratio on topographic map >1.5, at least 18 years of age, thinnest corneal pachymetry of ≥400 μm. Progression was defined as ≥1 D steepening of maximum keratometry or an increase of ≥1.00 D in manifest cylinder or an increase of ≥0.50 D in manifest refraction spherical equivalent in 2 years. Eyes with prior corneal surgery or scarring were excluded from the study.
Examinations
All patients underwent detailed ophthalmological examinations that included corrected (including contact lens) distance visual acuity (CDVA) measurement with Snellen charts, slit-lamp biomicroscopic examination, applanation tonometry, and dilated funduscopic examination. Visual acuity in Snellen format was converted to the logMAR (log of the minimum angle of resolution) equivalent for statistical analysis. The mean CDVA was noted at baseline and 1 year after CXL treatment.
New generation anterior segment tomography devices are capable of determining the topography and pachymetry of the entire cornea. In this study, corneal topography (Allegro Oculyzer, WaveLight AG, Erlangen, Germany) was conducted with undilated pupils under scotopic conditions by a single experienced technician. Scans were taken in automatic mode with proper quality. Maximum keratometry and corneal pachymetry at the thinnest location were recorded at baseline and 1 year after CXL treatment. Cone location was determined according to the topographic coordinates of maximum keratometry as follows: central cone (maximum K within the central 3 mm optical zone), paracentral cone (3–5 mm optical zone), and peripheral cone (outside the central 5 mm optical zone).
Subgroups and cutoff values were created in accordance with the current literature as follows: age (<30 and ≥30 years), gender, preoperative CDVA (<0.3 and ≥0.3 logMAR), preoperative maximum K (<54 and ≥54 D), baseline topographic cone location (central, paracentral, and peripheral cone), and preoperative thinnest pachymetry (<450 and ≥450 μm) to analyze the relationship between preoperative patient characteristics and improvements in CDVA and maximum K after CXL treatment.
Surgical Procedure
CXL was performed under sterile conditions using topical anesthesia as described by Wollensak. Central 9.0 mm corneal epithelium was removed by mechanical debridement. Isotonic riboflavin solution (0.1% in 20% dextran T500 solution) was instilled every 2 min for 30 min until riboflavin absorption was observed in the corneal stroma and anterior chamber under biomicroscopic examination. Then, the cornea was exposed to UVA irradiation at the wavelength of 365 nm and surface irradiance of 3 mW/cm. During the UVA exposure, isotonic riboflavin solution instillation was continued every 2 min for 30 min. Postoperatively, a soft contact lens was placed until corneal epithelial healing completed. Topical antibiotic and corticosteroid drops were administered and continued four times daily for 1 week and 2 weeks, respectively.
Statistical Analysis
Statistical analysis was performed with the Statistical Package for Social Sciences software version 16.0 (SPSS Inc, Chicago, IL, USA). Results were expressed as mean±SD. A paired t-test was used to analyze the changes in mean CDVA and maximum K between baseline and 1 year. Comparison of the quantitative data (changes in mean CDVA and maximum K) between two groups was performed by independent samples t-test. However, non-parametric tests (Wilcoxon signed ranks test and Mann–Whitney U-test) were used to analyze the effects of preoperative topographic cone location on mean CDVA and maximum K. A P-value less than 0.05 was considered statistically significant at 95% confidence interval.