Confocal laser endomicroscopy: exploring endometrial image quality in relation to the oestrous cycle of mares

Assessment of the endometrium is an essential component of a breeding soundness examination in mares. The current reference standard for evaluating equine endometrial health is histopathological assessment of an endometrial biopsy, however, inconsistencies may arise when a single blinded biopsy is used. Confocal laser endomicroscopy (CLE) is non-invasive and enables real-time in-vivo imaging of the endometrium across multiple locations within the uterine lumen. An initial study revealed variation in CLE image quality between mares.

This study aimed to compare the quality of endometrial CLE images during the oestrous cycle in mares.

Twenty-four mares were examined twice with CLE, once during dioestrus and once in oestrus. A 4-point image grading scale was developed. Four blinded examiners graded the images. Agreement between scores was assessed using an intraclass correlation (ICC).

Moderate agreement (ICC(C,4) = 0.702, p = 9.3 × 10⁻⁷⁷) was observed using the two-way random effect models and average rater. The effect of image depth and stage of the cycle on image quality was assessed. Image quality was lower in images collected at the depth of the luminal epithelium compared with subluminal (2.46 vs 2.68 respectively, p<0.001), and in images from oestrus compared with dioestrus (2.47 vs 2.67 respectively, p<0.001). Image quality score was negatively associated with oedema scores (p=0002).

Quality of CLE images of the uterus is influenced by phase of the oestrous cycle, and a recommendation would be to perform CLE examination when maximal endometrial oedema is not present.