Keratoconus Corneal Posterior Surface Characterization According to the Degree of Visual Limitation

To characterize posterior corneal surface features in patients with keratoconus and healthy controls and correlate them with the severity of the disease according to visual limitation.

Retrospective, comparative, clinical study including 477 cases, 374 keratoconic eyes and 103 healthy corneas. Patients were classified according to the degree of visual limitation. The corneal posterior surface including shape indices and keratoconus screening indices was evaluated using the rotating Scheimpflug camera and Placido disc topographer.

Dioptric power of the posterior corneal surface increases linearly as corrected distance visual acuity deteriorates (r > 0.700; P < 0.001). A significant correlation was also observed between shape indices root mean square per unit of area (RMS/A) (posterior surface irregularity) and corrected distance visual acuity (r = -0.750; P < 0.001). In addition, keratoconus screening indices such as posterior corneal aberrations and posterior ectasia vertex (KVb) also showed significant correlation with the degree of visual limitation (r = -0.687; P < 0.001 and r = -0.789; P < 0.001, respectively). Receiver operating characteristic curves demonstrate that RMS/A and KVb showed highest discriminating capabilities between normal and mild keratoconus cases with an area under the curve of 0.96 and 0.97, respectively, with a sensitivity and specificity of more than 93% for the RMS/A and 89% and 84% for the KVb.

Posterior corneal surface characteristics correlate with the degree of visual impairment and can be used for classifying patients with keratoconus. RMS/A, KVb, and posterior corneal aberrations are the most representative variables of visual function deterioration and are also useful to differentiate normal from mild keratoconus cases.