Femtosecond corneal collagen crosslinking in treatment of patients with progressive keratoconus stages I–II

Abstract

The aim of the investigation was to assess safety and efficacy of corneal collagen crosslinking technique using femtosecond laser for intrastromal pocket creation in patients with progressive keratoconus. Materials and Methods. Thirty-three patients (34 eyes) with progressive keratoconus stages I–II underwent femto-crosslinking of the corneal collagen. FEMTO LDV Z6 femtosecond laser was used to create an intrastromal pocket of 8.0 mm diameter and 140 μm depth. Normotonic riboflavin solution (0.1% riboflavin and 20% dextran) was instilled into the created pocket every 2 min during 30 min (15 instillations). At the same time UV-irradiation was performed using OPTO-XLink system (OPTO, Brasil) with 365 nm wavelength and an irradiance of 3.0 mW/cm2 (5.4 J/cm2). Changes in uncorrected visual acuity, corneal biomechanical properties, keratometric, topographic, pachymetric and morphological data were evaluated. The follow-up period amounted to 6 months. Results. Preoperative visual acuity level recovered on day 3–5. Six months after the procedure the mean value of astigmatism decreased from 4.35±0.19 to 3.75±0.20 dioptres (p<0.05). The corneal thickness in the area of keratoectasia descended from 437.50±2.84 to 405.0±2.99 μm (p<0.05). Maximal corneal refractive power decreased from 52.15±0.23 to 51.05±0.21 dioptres (p<0.05). Significant elevation of corneal resistance (from 7.70±0.12 to 8.25±0.10 mm Hg) and corneal hysteresis indexes (from 6.90±0.10 to 7.30±0.11 mm Hg) was reported. Confocal microscopy showed increase in extracellular matrix density without the signs of edema, and corrugation due to cross-linkage effect. Regeneration of subepithelial and stromal nerve fibers was visualized. The posterior stroma and endothelium remained intact. Exposure to UV-crosslinking with riboflavin was limited to the anterior and middle corneal stroma (to 320–330 μm) and did not involve the posterior stroma and the endothelium. Six months after the operation OCT examination confirmed the existence of the demarcation line which lay at the depth of 320–330 μm. Conclusion. Corneal collagen crosslinking with creation of an intrastromal pocket using a femtosecond laser appears to be an effective technique for keratoconus progression stabilization. The epithelial layer preservation in femtosecond crosslinking makes it possible to lower the risks of infectious complications of the eroded corneal surface, to reduce the patients’ visual discomfort and pain in the early postoperative period providing a faster recovery.