Abstract: Secondary posterior corneal ectasia is a rare disease characterized by the progressive thinning of the corneal thickness and increased anterior surface curvature and posterior surface height following corneal surgery. It is usually observed in months to years following laser corneal refractive surgery. Patients often had or did not have atypical early manifestations of keratoconus before the operation. Corneal cross-linking surgery strengthens the cornea by increasing the connection between the corneal collagen fibers. Laser in situ keratomileusis combined with corneal cross-linking surgery can increase the biomechanics of the cornea after LASIK, and prevent postoperative refractive regression and secondary corneal ectasia. We report the case of a 31-year-old female with rare changes in the corneal morphological parameters following LASIK combined with corneal crosslinking surgery. One month after the operation, Pentacam revealed abnormal thinning of the corneal thickness and increased height of the posterior corneal surface, which was easily misdiagnosed as secondary corneal ectasia. Upon measurement by anterior segment optical coherence tomography, a significant difference in the corneal thickness was observed, and the results of the Pentacam returned to normal during long-term follow-up. Although Pentacam can relatively accurately measure the corneal thickness, corneal curvature, and height of the anterior and posterior surfaces, other equipment should be used simultaneously to examine suspected secondary corneal ectasia following LASIK combined with corneal cross-linking surgery in order to avoid the possibility of a false positive.

Key words: Laser in-situ keratom ileusis(LASIK), Corneal cross-linking, Corneal morphology, Corneal ectasia, Thickness