Repeatability And Agreement Of Corneal Densitometry Between An As-Oct And A Scheimpflug Camera

The latest software release of the Casia 2 AS-OCT incorporates automated Cornea Densitometry (CD) measurement. Using a 1300nm wavelength, this swept-source AS-OCT provides a deeper penetration of tissues compared to the 420nm blue-led light source from the Scheimpflug camera and may result helpful when measuring corneal opacity. Due to its recent introduction, there is a lack of studies on the repeatability of Casia 2 AS-OCT measurements and their agreement with those provided by Pentacam. This study aimed to define the repeatability of CD measurements from the Casia 2, compare it to the Pentacam AXL Wave scheimpflug camera system, assess their agreement, and evaluate their correlation with age, gender, and central corneal thickness (CCT).

Cornea subunit, Ophthalmology department of the Sant'Orsola University hospital in Bologna.

This was a prospective case series enrolling healthy volunteers. One eye of each subject was evaluated. Each patient underwent three Casia 2 and Pentacam AXL Wave consecutive examinations. Four corneal concentric zones were analyzed for agreement and repeatability: from the corneal apex to 2 mm in diameter, from 2 to 6 mm, from 6 to 10 mm, from 10 to 12 mm, and the total corneal densitometry (TCD), referred to as the area within 0 to 12 mm. The "pupil area", meaning the corneal zone from the apex to 4 mm, was evaluated only for the repeatability of the Casia 2. The output was expressed in Gray Scale Unit (GSU) and then standardized according to the z-score standardization. The statistical analyses were performed using SPSS.

Ninety-six eyes from 96 healthy subjects were included. The mean age was 39.9 years (range: 24-84). the Casia 2 revealed high repeatability for all measured parameters, with lower CoV values (range: 1.07%-2.25%) compared to the Pentacam. The CoV increased progressively from the center to the periphery for both instruments. The 95% LoA ranged from ±2.42 for the 0-2 mm zone and ±0.75 for the 6-10 mm zone. There was a progressive increase in correlation with age toward the limbus. The Casia 2 showed a significant correlation with age in all the corneal zones, unlike the Pentacam which failed to show a correlation in the 0-2 mm zone. CCT was correlated only with the 0-2 mm and the 10-12 mm from the Casia 2. Gender was not correlated with CD.

In conclusion, our data show high repeatability of CD measurements obtained by the Casia 2 and moderate agreement with those obtained by the Pentacam AXL Wave. These results account for differences in the measurement techniques and for the intrinsic limits of each instrument technology, such as the exclusion of the central 0.5mm for the Casia 2 and the lower resolution and penetrability of the Scheimpflug Camera system compared to the AS-OCT.