Comparison Of Corneal Thickness Map Measured By Spectral Domain Optical Coherence Tomography And Scheimpflug Tomography In Healthy Myope, Keractoconus And Forme Fruste Subjects

To compare corneal thickness mapping and tomographic parameters measured by spectral domain optical coherence tomography (SD-OCT, MS-39) and Scheimpflug tomography (Pentacam) in normal myopic eyes, keratoconus (KC), and forme fruste keratoconus (FFKC) subjects, and to evaluate their role in detecting early ectatic changes.

A retrospective cross-sectional study was conducted at a tertiary eye center in Saudi Arabia between 2023 and 2025. 

A total of 127 eyes from 77 patients were included and categorized into three groups: normal myopia , FFKC , and KC . Participants underwent corneal imaging using Scheimpflug tomography (Pentacam) and spectral domain OCT (MS-39). Parameters analyzed included keratometry values, corneal thickness, Pentacam indices (ISV, IVA, KI, CKI, IHA, IHD), Belin/Ambrósio Enhanced Display (BAD-D) parameters, and epithelial thickness mapping. Statistical analysis was performed using ANOVA with Bonferroni post-hoc comparisons, and receiver operating characteristic analysis was used to evaluate diagnostic performance.

The KC group demonstrated significantly higher keratometry values, greater astigmatism, and abnormal Pentacam indices compared with the myopia and FFKC groups (p < 0.001). Belin/Ambrósio display parameters, including front and back elevation deviations and BAD-D values, were also significantly elevated in KC eyes. In contrast, most tomographic parameters were similar between FFKC and normal myopic eyes. SD-OCT epithelial mapping revealed regional epithelial thickness variations in KC eyes and subtle differences in FFKC eyes compared with normal myopes. ROC analysis identified minimum radius of curvature (Rmin) and SD-OCT astigmatism as the most effective parameters for distinguishing FFKC from myopia.

Keratoconus eyes demonstrate significant abnormalities in both Scheimpflug tomography and SD-OCT parameters, while FFKC eyes show tomographic profiles largely similar to normal myopes with subtle epithelial changes. SD-OCT epithelial mapping may provide additional sensitivity for detecting early ectatic alterations. The combined use of Scheimpflug tomography and SD-OCT imaging may enhance the early detection of subclinical keratoconus, improving screening strategies for refractive surgery candidates.