Introduction
corneal ectasia, keratoconus
CORNEAL ECTASIA, CORNEA, KERATOCONUS
Accurate measurements of the cornea are becoming increasingly important. Clinicians are using precise quantitative measurements of epithelium, stroma and endothelium to evaluate patients and improve surgical outcomes. Surgical planning before femtosecond laser-assisted treatments now requires precise stromal thickness to avoid sacrificing the stromal bed (< 250 μm). Pachymetry maps are relied on for any pre- and post-laser surgery evaluation, especially in subclinical and early diagnosis of corneal ectasia or form fruste keratoconus [Due to operator-dependent accuracy of contact tomography with ultrasound, accurate noncontact topography and tomography have evolved quickly. Scheimpflug systems, such as the Pentacam, allow for analysis of distorted and aberrated corneas, with true elevation measurements of both the anterior and posterior surfaces of the cornea. However, this technique is limited by cornea clarity, pupil diameter, and iris reflections [Since very small differences in corneal measurements alter clinical decisions, reproducibility and repeatability are extremely important in obtaining measurements from noncontact tomography. Studies have examined the inter-operator reproducibility and repeatability of a single Scheimpflug machine with a single OCT machine in corneal thickness and anterior chamber measurements in both healthy and postoperative eyes [