FLATTENING EFFECT OF CORNEAL CROSS LINKING IN ULTRATHIN CORNEAS : SUB 400 PROTOCOL

A retrospective obervational study was conducted to validate the effect of corneal cross-linking ( CXL ) with individualized fluence on eyes with ultrathin cornea and progressing keratoconus ( KC ) 

Thirty-three eyes of twelve patients with progressive KC and corneal stromal thicknesses from 207 to 389 µm were enrolled. Irradiation was performed at 3 mW/cm2 after epithelium removal with irradiation times individually adapted to stromal thickness. 

Examinations were performed at pre, 1, 6 and 12 months after CXL. Pre and postoperative examinations included slit lamp microscopy, corrected distance visual acuity ( CDVA ), refraction, the steepest keratometric value ( Kmax ) and the thinnest corneal thickness ( TCT ). Change in Kmax ( ΔKmax ) was calculated by subtracting the preoperative Kmax from the 12 months postoperative Kmax.

Thirty-one eyes ( 93.9 % ) showed tomographical stability at 12 months after surgery. No eyes showed signs of endothelial decompensation. TCT and CDVA did not change significantly throughout the follow-up period. Kmax was 62.2 ± 7.1 diopter ( D ) preoperatively and 59.7 ± 5.7 D at 12 months after CXL. The average value of ΔKmax was -2.42 ± 4.57 D at 12 months after CXL. The more flattening was obtained after CXL in cases when TCT was 305 ± 19 µm . 

No complications, including corneal endothelial damage, was observed even in advanced cases with TCT under 250 µm. The sub400 protocol clearly extends the indications of CXL in progressing KC. This results suggest that CXL can be performed safely in patients who have an ultrathin cornea.