The Correlation between Corneal Topographic Indices and Corneal High Order Aberrations in Keratoconus

This study was performed to investigate aberrometric changes of Keratoconus (KC) and its correlation with corneal topographic indices. In a cross sectional study, the researchers included 170 eyes of 138 candidates that were seeking corneal refractive surgery in Sohag refractive center, Sohag, Egypt and had been diagnosed as clinical KC. Patients were divided to mild, moderate, and severe KC. All eyes included in this study were subjected to corneal tomographic evaluation. Corneal aberrometry data was collected from the Sirius topography (Sirius, Costruzione Strumenti Oftalmici, Italy) over a 5-mm diameter. The collected data included Zernike coefficients for corneal aberrations, including total Root Mean Square (RMS), RMS Spherical Aberration (SA), RMS Coma, and RMS astigmatism. The study population was divided to mild, moderate, and severe KC. Mild KC cases included 58 eyes of 46 patients, moderate KC were 64 eyes of 52 patients, and severe KC were 48 eyes of 40 patients. Root mean square total was statistically significant in all groups with a higher p value in moderate KC (P = 0.001) and also was statistically significant when compared in the three groups altogether (P = 0.0001). Coma aberration was statistically significant in mild and moderate KC and when compared between the three groups (P = 0.0001). Root mean square Trefoil aberration was statistically significant only in moderate KC yet was statistically significant when compared in all groups (P = 0.0001). Root mean square astigmatism was statistically significant in mild KC only and when compared in the three groups altogether (P = 0.0001). Spherical aberration was also statistically significant in moderate and severe KC with a P value of < 0.0001 and 0.001, respectively. There was a positive correlation between posterior elevation and RMS values in mild and moderate KC while there was negative or very weak positive correlation in severe KC. There were negative correlations between the thinnest location and RMS values in nearly all variables in the three groups except weak positive correlation with RMS astigmatism in mild KC and with RMS total and coma aberration in severe KC .In conclusion corneal higher order aberrations measured by the Sirius topography system had low to moderate correlation with corneal topographic indices provided by the same device in different grades of KC.