Anterior ciliary circulation from the horizontal rectus muscles

Purpose: To quantify the anterior ciliary arteries that accompany horizontal rectus muscles and to correlate these findings with analysis of arterial cross-sectional area in distal tendons of these muscles. Patients and Methods: In 31 consecutive patients, previously unoperated horizontal rectus muscles were photographed intraoperatively. Major and minor anterior ciliary arteries (ACAs) were counted from the photographs by a masked independent observer and compared between medial and lateral rectus muscles. Cross sections from medial and lateral rectus muscle resection specimens were stained for elastin to quantify arterial volume in the distal tendons. Results: Twenty lateral and 22 medial rectus muscles from 31 patients were included. There was no significant difference in the mean number of major anterior ciliary arteries between lateral rectus muscles (2.25 0.79, range 1-4) and medial rectus muscles (2.05 0.65, range 1-3) (p = 0.46). The mean number of minor anterior ciliary arteries was 6.7 in both medial and lateral rectus muscles (p = 0.97). Resected rectus muscle tendons showed no significant difference between lateral and medial rectus muscles for arterial vessel number or cross-sectional area. Conclusions: These results show the contribution from the lateral rectus muscle to the anterior segment circulation may be more robust than is commonly taught.