Abstract
Purpose :
Anterior chamber measurements are clinically useful in ophthalmic disease diagnosis and treatment, such as IOL calculations and glaucoma risk assessment. We used swept-source optical coherence tomography (SS-OCT) to measure the anterior chamber depth and corneal thickness and to assess the impact of dewarping on measurement accuracy.
Methods :
We imaged 3 subjects, 8 times (one or both eyes), using PLEX® Elite 9000 (ZEISS, Dublin, CA) SS-OCT 6x12x18 mm (3072 x 400 x 600 pixels in the axial, fast, and slow directions, respectively). The fast direction was superior to inferior. Six B-scans were randomly selected between 6 mm and 12 mm (temporal and superior). The distance between the posterior corneal surface to the anterior surface of the lens capsule and the corneal thickness at the center of each B-scan were measured manually using ImageJ1 before and after dewarping. Dewarping was based on the method of Tate et al.2 The regression and Bland-Altman plots were reported.
Results :
Fig. 1 shows an image comparison example of an uncorrected and dewarped image. Fig. 2 shows quantitative comparisons for the data set. The anterior chamber depth is greater after dewarping (Fig. 2a) as the refractive index of aqueous (~1.33) is smaller than the cornea (~1.38). The central corneal thickness before and after dewarping are the same (Fig. 2b), as the AS OCT image was reconstructed using the corneal refractive index for the entire OCT data. The regression and mean difference plots (Fig. 2) show that while correlation remains high (0.99), a mean difference of 92 μm was observed.
Conclusions :
Anterior segment OCT Images without dewarping correction yield an under-estimate of anterior chamber depth, which is important for IOL calculations and glaucoma risk assessment.
[1] Schneider, C. A., et al. Nature Methods 2012; 9(7)
[2] Tate, Nelson et al. IOVS 2023; 64(3398)
This abstract was presented at the 2024 ARVO Imaging in the Eye Conference, held in Seattle, WA, May 4, 2024.