In this article, Dr Cervino discusses how his recent study examining the quality of anterior segment images obtained with posterior segment OCT devices is good enough to obtain repeatable measures of anterior segment parameters manually using external analysis software.
"Our simple study," he continued, "aimed at finding out whether we could manually obtain repeatable measures of anterior segment parameters from OCT images obtained by posterior segment OCTs using external analysis software."
The parameters that were measured were central thickness of the corneal epithelium, Bowman's layer and stroma. Additionally, using the in situ phakic IOL images, the central, nasal and temporal vault measures were obtained. "We used ultrasound determined central corneal thickness as the reference measure so we could plug that into the analysis software, which would then enable calculation of all the other distances/measures," he said.
Five masked experienced observers were asked to subjectively and manually determine these measurements three times each on separate occasions. Then all the images were compared to determine both inter and intraobserver differences.
Low variance in results
Between observers, less than a 10% variance in measurements was found for all corneal layers and vault measures, and this was lower than 6% for intraobserver repeated measurements. Attending to the specific layer measured, in this sample interobserver measurements varied most for Bowman's layer and least for nasal vault. However, intraobserver measurements varied most greatly for nasal vault and least for the stromal thickness.
"So, from these results we can basically conclude that the image quality of anterior segment images obtained with high resolution, posterior segment OCT is great enough to allow a manual determination of anterior segment parameters even in the absence of specific software tools," Dr Cerviño concluded. "However, it must be noted that a component in the variances between observers relies upon subjective interpretations of boundaries between layers."
1. A. Cerviño et al., 'Repeatability of corneal layer thickness and vault measures from high resolution optical coherence tomography (OCT)', presented at ESCRS 2013, Amsterdam, The Netherlands.