Limitation of collagen cross-linking with hypoosmolar riboflavin solution: failure in an extremely thin cornea

We report a case of failure of corneal collagen cross-linking (CXL) for progressive keratoconus after preoperative stromal swelling with hypoosmolar riboflavin solution in an extremely thin cornea.

CXL was performed using the protocol established for the treatment of thin corneas. Preoperative minimal thickness after abrasion was 268 μm and increased to 406 μm after swelling with hypoosmolar riboflavin solution.

Despite CXL, a distinct progression of up to 1.9 diopters was observed at 3 months after the procedure on the anterior corneal surface. At 6 months after CXL, progression had increased to 2.3 diopters. Although swelling with hypoosmolar riboflavin solution was effective and led to a preoperative thickness of more than 400 μm, the increase in biomechanical resistance was not sufficient to arrest the progression of the disease.

Little is known about the minimal stromal thickness required for effective CXL to occur. Although swelling with hypoosmolar riboflavin solution over 400 μm and safety of the procedure can be achieved in even thinner corneas, the outcome of this case suggests that a minimal preoperative stromal thickness of 330 μm needs to be respected for a successful CXL procedure.