Late Unilateral Corneal Ectasia After Combined Photorefractive Keratectomy And Prophylactic Corneal Cross-Linking In Bilaterally Thin Corneas

To report advanced unilateral corneal ectasia occurring four years after combined photorefractive keratectomy and prophylactic corneal collagen cross-linking performed on bilaterally thin and tomographically suspicious corneas.

A 36-year-old man underwent simultaneous bilateral photorefractive keratectomy associated with corneal collagen cross-linking in 2020 for myopic astigmatism. The corneas were thin and considered at biomechanical risk, although no definite ectasia was present preoperatively. The early postoperative course was uneventful.

In December 2024, the patient reported progressive visual deterioration in the left eye. Uncorrected distance visual acuity was 10/10 in the right eye and 8/10 in the left eye with spectacle correction.

Manifest refraction was:

• Right eye: −0.25 (−0.25 × 45°)

• Left eye: +1.50 (−4.75 × 99°), demonstrating a hyperopic shift associated with high irregular astigmatism.

Slit-lamp examination of the left eye revealed an inferior paracentral anterior stromal opacity without epithelial staining or intraocular inflammation. Corneal tomography showed marked asymmetry between the two eyes.

The right eye exhibited a regular axial curvature pattern with a maximum keratometry of 49.9 diopters and a thinnest pachymetry of 404 micrometers. Posterior elevation and epithelial thickness distribution were within normal limits, consistent with a thin but stable cornea.

The left eye demonstrated pronounced inferior steepening with a maximum keratometry of 70.38 diopters and a thinnest pachymetry of 406 micrometers. Significant posterior elevation and asymmetric pachymetric progression were present. Epithelial thickness mapping revealed focal thinning over the cone with surrounding compensatory thickening. Anterior segment optical coherence tomography showed localized anterior stromal scarring consistent with reactive Salzmann nodular degeneration overlying the ectatic area.

Conclusion
Combined photorefractive keratectomy and prophylactic corneal cross-linking does not fully prevent late biomechanical decompensation in bilaterally thin corneas. Advanced unilateral ectasia with reduction of best-corrected visual acuity may occur several years after surgery despite prior cross-linking. These findings underline the need for stricter preoperative screening and long-term multimodal monitoring when considering combined refractive procedures in biomechanically compromised corneas.