Corneal densitometry measurements comparison between anterior segment OCT and scheimpflug imaging

Abstract

Purpose: To evaluate and compare the repeatability of corneal densitometry (CD) measurements obtained using both an anterior-segment optical coherence tomography (AS-OCT) device and a Scheimpflug camera system, while also assessing the level of agreement. The study also sought to investigate the correlation of CD with age, gender, and central corneal thickness (CCT) in normal eyes.

Methods: CD measurements were obtained using the Casia 2 and the Pentacam AXL Wave. Data were collected on Total Corneal Densitometry and 4 concentric corneal annular areas, these are referred to as zone 1, denoting the central area, through to zone 4, designating the outermost peripheral region. Repeatability was assessed using intra-session test-retest variability, coefficient of variation (CoV), and intraclass correlation coefficient (ICC). The agreement was evaluated using Bland-Altman plots. Correlation analysis was performed between CD, age, gender, and CCT.

Results: The study included 96 healthy volunteers. The Casia 2 demonstrated high repeatability with ICC values exceeding 0.9 in all the corneal zones and lower CoV values compared to the Pentacam AXL Wave (ranging from 1.07% to 2.25% for Casia 2 and from 1.91% to 6.89% for Pentacam).95% LoA were within ± 2 standard deviation from the average mean except from zone 1 (± 2.42).However, the measurements showed a consistent bias among all the corneal zones. CD values were positively correlated with age, except for zone 1 with the Pentacam (p = 0.083).

Conclusions: The findings suggest that the Casia 2 can be a reliable tool for assessing corneal transparency in healthy individuals, however its measurements are not interchangeable with those provided by the Pentacam. The AS-OCT device may be more sensitive in detecting subtle age-related changes in CD within the central zone.

Keywords: AS-OCT; Corneal densitometry; Corneal opacity; Corneal transparency; Scheimpflug Imaging.

Fig. 1

Image illustrating the densitometry screen window of the Casia. Left: Infrared image of the anterior segment; GSU values for cornea, anterior chamber and crystalline lens by means of the “Target Line” position (black arrow), the “Pupil Area”, and the “Optional Area” which has manually modifiable range of values. Center: OCT B scan image. Right: A scan graph of CD values throughout the anterior segment referring to the “Target Line” position

Fig. 2

Bland–Altman plots for each corneal zone showing the average (x-axis) against the difference of each pair of measurements (y-axis). Central dotted line: Bias. Upper and lower dotted line: Limits of Agreement

Fig. 3

Linear regression between Age (x-axis) and Standardized GSU values (y-axis) for TCD. Both instruments demonstrate a positive relationship with age: Casia 2 r²: 0.76, p: < 0.0001. Pentacam AXL Wave r²: 0.8, p: < 0.0001. The difference between the two regression lines was examined using the extra sum of squares F-test, which confirmed that the distinction between the slopes is not statistically significant (p = 0.56). GSU: Gray Scale Unit. TCD: Total Corneal Densitometry

Fig. 4

Casia 2 B scan image showing the central artifact line