Intracorneal ring segment depth in keratoconus patients: a long-term follow-up study

To compare the actual depth of the tunnel created with femtosecond laser for intracorneal ring segment (ICRS) implantation with the target depth in keratoconus patients. In this mix design study, eligible keratoconus patients were identified through chart review. The inclusion criterion was a history of ICRS implantation with femtosecond laser more than 6 months prior to enrollment. Participants underwent anterior segment optical coherence tomography using Spectralis (Heidelberg Engineering GmbH, Heidelberg, Germany) for depth measurement defined as the distance from the anterior corneal surface to anterior rim of the ring. The mean age of the 30 participants was 31.4 +/- 7.9 years, and 58.6% were male. Mean follow-up time after ring implantation was 25.8 +/- 10.0 (range 7-41) months. Mean actual depth was 59.9% (42.4-86.8%), and the target depth was 85.0% (74.8-90.0%) (P < 0.001). The ring was at a depth of less than 70% in 25 eyes of the 30 (83.3%) studied eyes. The mean 26 months after implantation, ring segments are placed at a shallower depth than originally intended. Therefore, although femtosecond laser technology is an acceptable method for the surgeon, it is necessary to revisit the depth calculator of the device.