Evaluation of the distance between Schwalbe's line and the anterior lens capsule as a parameter for the correction of ultrasound biomicroscopic values of the canine iridocorneal angle.

Objective: To determine whether the distance between Schwalbe's line (the peripheral termination of Descemet's membrane, i.e., the borderline between the cornea and sclera) and the anterior lens capsule (SLD) is an applicable parameter for correcting raw ultrasound biomicroscopic values of the canine iridocorneal angle (ICA) and to establish a comparative system for the ICA values in different canine breeds with varied body sizes/weights.

Animal Studied: The dogs were divided into four groups based on body weight (BW): <4 kg, 4-8 kg, 8-20 kg, and >20 kg, and 180 normotensive eyes were studied.

Procedures: The ICA microstructure was examined by ultrasound biomicroscopy (UBM) using 40-MHz probes in dogs with or without anesthesia/sedation. Linear regression analysis and correlation coefficients were evaluated between SLD or SLD(2) and UBM measurements; subsequently, noncorrected and SLD-corrected UBM values were statistically assessed.

Results: Significant linear correlations were detected between SLD and the ciliary cleft width, the minimum distance between the angle recess and the scleral venous plexus, and the scleral thickness. Positive linear correlations were also demonstrated between SLD(2) and the ciliary cleft area as well as the scleral venous plexus area. Raw UBM measurements were corrected by using a ratio with SLD on the distance or SLD(2) on the area. Although noncorrected UBM measurements increased with canine BW, SLD-corrected UBM values remained similar with no significant statistical differences in any of the dogs.

Conclusions: Correction with SLD would be clinically useful for comparing UBM measurements of the ICA in dogs with different body sizes/weights.