Anterior segment optical coherence tomography scanning protocols and corneal thickness repeatability.
PURPOSE
To examine the influence of anterior segment optical coherence tomography imaging protocols on the intraobserver and intrasession repeatability of epithelial, stromal, and total corneal thickness measurements.


METHODS
Repeated anterior segment optical coherence tomography (AS-OCT) images (Spectralis, Heidelberg) were obtained from 15 adults using single 8.3 mm wide horizontal line scans with an average of 2, 10, 20, 30, 50 and 100 B-scans. Volumetric scans consisting of nine 8.3 mm horizontal line scans encompassing a 1.3 mm vertical region were also captured (with 20 B-scans per line scan). Single point thickness measures (at the normal to the tangent of the anterior corneal surface) were compared with thickness measures averaged over the central 6 mm. The impact of B-scan averaging and intraobserver variability were examined for single line scans. For volumetric scans, the impact of the number of line scans upon intraobserver and intrasession variability were calculated.


RESULTS
Intraobserver repeatability did not vary significantly as a function of the number of averaged B-scans per line scan, but was lowest for 20-30 averaged B scans. For volumetric scans, increasing the number of line scans did increase scan duration (p < 0.001), with minimal impact upon the average scan quality index (p = 0.06). Averaging more than 3 line scans did not significantly improve intraobserver or intrasession repeatability for either single point or average thickness measurements.


CONCLUSION
AS-OCT volumetric scans with 3 lines each consisting of 20 B-scans with measurements averaged over a central 6 mm of the cornea provide highly repeatable measures of epithelial, stromal and total corneal thickness (95 % LoA ≤ ±3.2 μm for intraobserver repeatability and ≤ ±3.7 μm for intrasession repeatability). This scanning protocol can provide reliable information when monitoring subtle changes in corneal thickness.
['Fisher|Damien|D|', 'Collins|Michael J|MJ|', 'Vincent|Stephen J|SJ|']
D000328:Adult D003315:Cornea D063171:Corneal Pachymetry D006801:Humans D015588:Observer Variation D015203:Reproducibility of Results D041623:Tomography, Optical Coherence
Corneal thickness Repeatability Anterior segment OCT Corneal oedema