Corneal Flattening Syndrome After Crosslinking

Corneal crosslinking (CXL) is an effective method to halt the progression of ectasia, although it is not free of complications. Following the procedure, a mean corneal flattening of approximately 1 to 1.5 diopters (D) is expected, in addition to transient corneal thinning.

A 57-year-old male patient underwent bilateral LASIK 26 years earlier and subsequently developed bilateral ectasia, more pronounced in the left eye (LE). Review of medical records revealed forme fruste keratoconus in the LE prior to LASIK. Due to documented ectasia progression, accelerated CXL (9 mW/cm² for 10 minutes) was performed in both eyes in 2018.

One year postoperatively, refraction in the right eye (RE) was −3.75 −1.50 × 90 (CDVA 20/20) and in the LE −0.50 −2.75 × 105 (CDVA 20/40). The condition remained stable, and in 2020 the patient underwent uncomplicated bilateral phacoemulsification with toric intraocular lens implantation. After cataract surgery, the RE refraction was +0.25 (CDVA 20/20).

Four years after CXL in the RE, the patient reported progressive visual deterioration, with refraction changing from +0.50 (CDVA 20/25 in 2022) to +2.25 −2.00 × 90 (CDVA 20/30) in 2025. Slit-lamp examination revealed corneal haze in the RE.

Corneal tomography of the RE, previously stable in 2020, demonstrated progressive central keratometric flattening through 2025, associated with increased irregular astigmatism. The tangential map (Figure 1) showed marked inferior paracentral flattening (−6.5 D) and thinning of 35 µm at the thinnest point. The LE remained stable throughout follow-up.

We describe excessive corneal flattening associated with thinning and haze as a possible late complication of accelerated CXL. We hypothesize that this phenomenon may be related to biomechanical redistribution of corneal forces and/or an aberrant wound-healing response.