Epithelial Pattern Standard Deviation Can Help Detect Corneal Epithelial Changes

The epithelium pattern standard deviation from optical coherence tomography can be used to detect corneal ectasia.

Epithelial pattern standard deviation (PSD) can be used to detect abnormal epithelial thickness patterns, according to research published in the Journal of Cataract & Refractive Surgery.

Researchers conducted a cross-sectional retrospective study to evaluate whether corneal epithelial PSD from optical coherence tomography (OCT) could distinguish between normal corneas and those with corneal ectasia.

The researchers stratified patients into 4 groups based on clinical data: 1 randomly selected eye of patients with normal corneas (normal, n=105); eyes with bilateral keratoconus (KC; n=86); ectatic eyes with no surgical treatment for keratoconus (VAE-E; n=11); and from patients whose fellow eyes presented with normal topographic patterns (VAE-NT; n=61). 

The patients’ corneas had been evaluated using an OCT system, Scheimpflug corneal tomography, and a tonometer for biomechanical assessment. The researchers analyzed corneal epithelial thickness maps and calculated the PSD value. They used an area under the receiver-operating curve (ROC) analysis to evaluate the diagnostic accuracy of the indices.

[H]igh-resolution Fourier-domain OCT is capable of distinguishing the epithelial thickness profile in normal and KC eyes.

The team found that epithelial PSD was significantly different across the groups (P <.0001). With pairwise comparison, the study shows that the normal group had significantly lower epithelial PSD values than all other groups (KC and VAE-E groups, P<.0001; VAE-NT group, P=.0008). The researchers found no significant differences between the KC group and VAE-E group (P=.4284); however, both ectatic groups had significantly higher values than the VAE-NT group (P <.0001 and P =.0004, respectively).

“[H]igh-resolution Fourier-domain OCT is capable of distinguishing the epithelial thickness profile in normal and KC eyes. Epithelial thickness changes in early forms of corneal ectasia could be integrated with other diagnostic tests to further enhance the accuracy to characterize ectasia susceptibility,” according to the researchers.

Limitations of the study included limitation of the OCT to a 6.00 mm diameter of the thickness map and no investigation of differences in epithelial PSD values according to the stage of keratoconus.


Salomão MQ, Hofling-Lima AL, Gomes Esporcatte LP, et al. Corneal ectasia detection by epithelium pattern standard deviation from optical coherence tomography. J Cataract Refract Surg. Published online October 6, 2022. doi:10.1097/j.jcrs.0000000000001066