Combined Topography-Guided Prk And Corneal Crossling According To Keratoconus Phenotype: 6-Month Refractive And Topographic Results

To compare the clinical and topographic results in patients with keratoconus treated by topography-guided photorefractive keratectomy (TG-PRK) followed by same-day corneal collagen crosslinking (CXL), according to the morphological phenotype regarding the refractive, topographic and comatic axis deemed to be concordant in croissant phenotype (group 1) and nonconcordant in snowmen or duck phenotypes (group 2).

Private Practice Ophthalmology Departement, Guimarães, Portugal

Patients with grade 2 keratoconus measured by Scheimpflug corneal tomography were treated by transepithelial TG-PRK. The refractive treatment consisted of inputting the full topographic cylinder while the spherical component was adjusted based on the patients’ subjective best-corrected visual acuity (BCVA) in order to maintain the spherical equivalent and accounting for the topographic ablation pattern.The CXL step immediately followed using a 0.1% riboflavin solution and 9.0mW/cm2 light intensity during 10 minutes. All patients completed at least 6 months of follow-up. Clinical and topographic variables (cylinder power, Kmax, anterior elevation, corneal high-order aberrations) results were analyzed and compared between the 2 groups.

From the first month onwards both groups obtained a significant improvement in uncorrected visual acuity (0.75±0.17 to 0.25±0.05, p = 0.009) as well as improved BCVA (0.15±0.10 to 0.05±0.05, p = 0.084). Group 1 achieved a superior but not significant gain in BCVA (-0.60 vs -0.40 LogMAR, p=0.19). Both groups obtained significant improvements in Kmax (50.5±4.92 to 44.46±2.85, p=0.036), best-fit-sphere anterior elevation (22.60±4.92 to 9.80±1.78, p=0.038) and corneal high order aberrations (0.80±0.29 to 0.48±0.11, p=0.046). Group 2 had superior improvement in cylinder power (-2.16±1.36 vs. -1.12±0.88, p=0.38) but also had higher mean preoperative cylinder (3.50±1.87 vs. 2.00±0.70, p=0.12). No significant adverse events were reported.

Combined TG-PRK and CXL is safe and effective for improving VA, reducing corneal high-order aberrations as well as improving corneal topographic parameters in the most common phenotypes of keratoconus even in cases with very steep corneas. Patients with duck-type keratoconus achieved better BCVA perhaps due to more reliable preoperative subjective refraction data.