Comparison Between Gaussian, Sagittal And Tangential Corneal Curvature Maps In Very Early Kc And High Astigmatic Eyes Using As-Oct Combined With A Placido Disc

To investigate and compare the efficacy of Gaussian, Tangential and Sagittal corneal curvature maps obtained with an anterior segment optical coherence tomographer (AS-OCT) combined with Placido disc MS-39 device to distinguish between very early keratoconus (VE-KC) and high astigmatic eyes.

To investigate and compare the efficacy of Gaussian, Tangential and Sagittal corneal curvature maps obtained with an anterior segment optical coherence tomographer (AS-OCT) combined with Placido disc MS-39 device to distinguish between very early keratoconus (VE-KC) and high astigmatic eyes.

Prospective, cross-sectional study including 31 VE-KC and 45 high astigmatic normal eyes that attended to Oftalmosalud Institute in Lima, Peru.  Keratometry (K) at different points were obtained from Gaussian, Tangential and Sagittal curvature maps using the MS-39 (CSO, Firenze, Italy). Inferior–superior  dioptric asymmetry value (I-S) at the 3 mm zone was obtained. Statistical analysis was performed using program R.

Results: In VE-KC group, the mean I-S value was 0.55 ± 0.37 Diopters (D), 0.41 ± 0.34 and 0.68 ± 0.42 D from the Gaussian, Sagittal and Tangential maps respectively (p< 0.047). 83.87% (26/31) of the VE-KC eyes showed asymmetric bowtie patterns in the Sagittal and Tangential maps, but no asymmetric bowtie pattern was observed in any Gaussian maps. 96.77 % (30/31) of the high astigmatic eyes showed a round or oval pattern in the Gaussian maps, but a symmetric bow-tie pattern in 90.32% (28/31) with in the Tangential and Sagittal maps respectively (p<0.001).

Conclusions: Gaussian maps were effective in discriminating between VE-KC and high astigmatic eyes, with the absence of the typical asymmetric bowtie astigmatism pattern commonly seen when using Tangential and Sagittal maps