Intereye asymmetry detected by scheimpflug imaging in subjects with normal corneas and keratoconus

Purpose: To report the intereye asymmetry with regard to pachymetry and corneal elevation variables in subjects with normal corneas and in those with keratoconus. Methods: This is a prospective study that included 151 patients who had Pentacam imaging in both eyes: 53 subjects with bilateral normal corneas and 98 with bilateral keratoconus. Central corneal thickness (CCT), pachymetry at the thinnest point (TP), posterior elevation at the thinnest point of the cornea (PETP), distance, volume, and differential pachymetry were measured. Intereye asymmetry was determined by subtracting the lowest value from the highest value for each variable. The degree of asymmetry between each subject's eyes was calculated with intraclass correlation coefficients for all the variables. Receiver operating characteristic curve was used to determine predictive accuracy and to identify optimal cutoffs of these values. Results: In the normal subjects, the mean intereye asymmetries in CCT, TP, and PETP were 10.28, 11.04, and 3.75 μm, respectively. In the keratoconic patients, the mean intereye asymmetries in CCT, TP, and PETP were 25.89, 30.15, and 20.08 μm, respectively. Normal eyes demonstrated the smallest difference between eyes, compared with the keratoconic eyes, in all of the variables analyzed (P < 0.05). A cutoff value of 6.5 μm in the mean intereye asymmetry at the posterior elevation had an area under the receiver operating characteristic curve of 0.91. Conclusions: There is a greater intereye asymmetry in pachymetry and posterior corneal elevation variables in keratoconic patients than in subjects with normal corneas.