Study suggests no harm to limbal stem cells from CXL

Geneva-Preliminary results of a preclinical study investigating the effect of peripheral collagen crosslinking (CXL) on the limbal stem cells provide some reassurance about the safety of the technique.

The research was conducted by Olivier Richoz, MD, and Farhad Hafezi, MD, PhD, department of ophthalmology, Geneva University Hospitals, Geneva, Switzerland.

In the study, male adult New Zealand white rabbits received crosslinking treatment in the right eye only; left eyes served as controls, receiving riboflavin only and no irradiation. The right eyes were divided into two groups based on area of irradiation: Group 1 (central CXL, 9 eyes) received irradiation to the central 7 mm of the cornea and Group 2 (peripheral CXL, 11 eyes) received irradiation out to the limbus over an 11-mm zone. Within each of the two groups, the eyes were further subdivided to receive different UVA protocols that varied in exposure time and light intensity: 3 mW/cm² for 30 min, 10 mW/cm² for 9 minutes, 10 mW/cm² for 18 minutes, and 10 mW/cm² for 30 min (Group 2 only). All eyes were treated twice daily with a topical fluoroquinolone ointment until re-epithelialization.

The results showed peripheral CXL did not significantly modify mean time to re-epithelialization, which ranged from 62 to 83 hours in the treated eyes and from 74 to 83 hours in the control group. In fact, the shortest mean time to re-epithelialization was in the group of two eyes receiving peripheral CXL with UVA 10 mW/cm² for 30 minutes.

In addition, there were no macroscopic or microscopic signs of vessel thrombosis. Additional evaluations, including immunohistochemical staining and Western blotting for stem cell markers and RT-PCR analysis of cytokine profiles, are ongoing.

“For some corneal disorders, such as pellucid marginal degeneration, UVA irradiation close to the limbus is required when performing CXL. Currently, many surgeons cover the limbus and peripheral cornea to protect the limbus. However, this might compromise the therapeutic effect,” said Dr. Richoz, a resident in the department.

“Our study results show that direct irradiation of the corneal limbus using the standard CXL parameters of 3 mW/cm² for 30 min and even with three times higher energy does not affect the efficacy of re-epithelialization," Dr. Richoz added. "We believe that the limbal stem cells probably remain capable of regenerating the epithelium.”

Dr. Richoz has no financial interest in the subject matter he discussed. This article is based on material Dr. Richoz presented at the 2012 Refractive Surgery Subspecialty Day of the American Academy of Ophthalmology annual meeting.

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