Current imaging conventions in anterior segment optical coherence tomography (AS-OCT) often misrepresent sectoral anatomical variation in eyes with angle closure, according to findings published in the British Journal of Ophthalmology.

Researchers conducted a retrospective analysis of a subset of participants (n=298, mean age 64.55±8.43 years, 80% women) of the Chinese American Eye Study (CHES). All patients were of Chinese descent and diagnosed with angle closure, defined as ≥3 quadrants where static gonioscopy failed to visualize pigmented trabecular meshwork. Participants underwent a complete ophthalmic exam consisting of applanation tonometry, gonioscopy, and AS-OCT.  The investigators analyzed a random subset of eyes from the cohort (n=10) for each angle opening distance (AOD500) (0°-180°, 45°-225°, 90°-270°, 135°-315° meridians) so that a total of 40 eyes of 40 patients underwent detailed image analysis.

 The mean AOD500 for each of the four quartiles was 0.08, 0.09, 0.13, and 0.18 mm, respectively. Inferior and superior sectors of the angle were narrower compared with the nasal and temporal sectors among participants, and average angle parameter measurements increased within the AOD500 quartile.


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Researchers observed a negative correlation within all quartiles, in which increasing the number of images decreased the deviation in parameters. The deviation in all parameters for 1 image ranged between 0.44% and 19.31%, and between 0.08% and 4.21% for 2 images. When they analyzed 8 images, the deviations became <6.97%, and<3.38% when the number of images increased to 16. Anterior chamber depth and area, which had deviations of 20% and 10%, respectively, were an exception to this pattern. Measurement approximations improved when the first image was analyzed along the 25°-205° meridian.

“We recommend the analysis of 2 AS-OCT images to accurately approximate the mean and eight images to approximate the range of biometric measurements of angle width in angle closure eyes,” the researchers suggest. “Alternatively, four evenly spaced images starting at the 28°−208° meridian is also sufficient with regards to both the mean and range.” 

Study limitations include a retrospective analysis, small sample size, and ethnic homogeneity among participants.

Reference

Shan J, Pardeshi A, Jiang X, et al. Optimal number and orientation of anterior segment OCT images to measure ocular biometric parameters in angle closure eyes: the Chinese American Eye Study. Br J Ophthalmol. Published online January 21, 2022. doi:10.1136/bjophthalmol-2021-319275