Nonvascular smooth muscle alpha-actin positive cells in the choroid of higher primates

As an elaborated network of non-vascular smooth muscle alpha-actin positive cells (NVSMC) is present in the human eye, the purpose of this investigation was to describe the presence of NVSMC in the sclera and choroid of different mammals and primates.

Whole mounts and tangential serial sections through the sclera and choroid of human donor eyes, of cynomolgus and rhesus monkey, mangabey, owl monkey, tree shrew, pig, cow, rabbit, cat, dog, and rat eyes were stained with a mouse-anti-smooth muscle alpha-actin antibody. The mean number/mm( 2) of NVSMC was calculated in the central region of each quadrant.

In cynomolgus and rhesus monkey eyes, numerous NVSMC were located in the suprachoroidal and inner scleral region. In the temporal quadrant, the density of NVSMC was highest. NVSMC were semicircular arranged around the entering long ciliary artery and nerve. In the mangabey and owl monkey choroid, the number of NVSMC was about ten-fold less than in macaque monkeys. Most of the NVSMC were located parallel to large vessels and only some cells were seen in the suprachoroid and inner sclera. In the tree shrew monkey and in all other mammal eyes, no NVSMC could be detected. In the human eyes, in addition to the suprachoroidal and inner scleral NVSMC numerous cells were located in the choroid proper. The regional distribution and the orientation of the NVSMC was comparable in human and macaque monkey eyes.

Comparing these findings with the literature, the presence of NVSMC correlates with the development of a central fovea and an elaborated accommodative system. Its functional significance remains to be determined.