Validation and Repeatability of Inferior minus Superior Value and its Cut-off Value in Anterior Sagittal Curvature Map Using Pentacam in Early Keratoconus

Abstract

eratoconus, the most common primary corneal ectasia, is a bilateral asymmetric corneal degeneration accompanied with local corneal thinning and occurs mostly in the inferior and central parts of the cornea. Prior to any corneal refractive surgery, early diagnosis of KC is of great importance because it can prevent the possible progression of the ectatic pathology after surgery. This creates a need for proper and accurate diagnostic tests that provide high sensitivity so that no asymptomatic subclinical KC ends up undiagnosed and thus can be precluded from performing corneal refractive surgeries. A diagnosis of KC is most commonly made through slit-lamp examination, corneal topography, and measurement of visual acuity and refraction. Since the slit-lamp examination is unable to show the signs of KC in the early stages and visual acuity may not be affected, corneal topography is more reliable for early KC detection. Pentacam employs the Scheimpflug imaging technique to present the various corneal topographic/tomographic indices with acceptable accuracy and repeatability. Our target in this study was selecting the early KC cases and detecting the IS-value and its cut-off value, besides testing its repeatability in five different scans. The results of our study showed a statistically significant differences between the patients and the control group regarding the IS-value, and its cut-off value was 0.69 with good repeatability in early KC and normal eyes.