Nonvascular contractile cells in sclera and choroid of humans and monkeys

To investigate by histochemistry and immunohistochemistry the distribution and innervation of nonvascular contractile cells in the sclera and choroid of humans and monkeys.

Globes were obtained from 2 macaque monkeys and 19 human cadavers that ranged in age from fetal life to 94 years. Immunohistochemistry was performed using monoclonal antibody against human smooth muscle (SM) alpha-actin and tyrosine hydroxylase (TH). The nicotinamide-adenine dinucleotide phosphate (NADPH)- diaphorase reaction was used as a marker for nitric oxide synthase.

The scleras of all but fetal, newborn, and infant globes exhibited myofibroblasts, amelanotic, fibroblastlike cells having SM alpha-actin immunoreactivity. In the choroid of all but fetal eyes, SM cells were present in the suprachoroidal layer, forming a reticulum of flattened laminae, and in the choriocapillaris where ovoid-to-spindle-shaped SM cells were arrayed in parallel layers immediately adjacent to Bruch's membrane. Contractile cells in the sclera and choroid were most concentrated subfoveally and were sparse anteriorly. Nerve terminals positive for NADPH- diaphorase were colocalized with SM alpha-actin-positive cells in the sclera and choroid, whereas TH-positive nerve terminals colocalized with SM cells in the choroid. Clusters of ganglion cells were present on the posterior surface of globes near SM cells.

The posterior choroid and sclera of humans and monkeys contain nonvascular contractile cells. The presence of nerve terminals and adjacent ganglion cells suggests neural control of these contractile cells. The absence of such contractile cells in fetal, newborn, and infant eyes is an argument against a major role of these cells in promoting ocular enlargement. These contractile cells may instead participate in regulation of refractive state by maintenance of ocular size in the face of intraocular pressure or in intermediate-term regulation of choroidal thickness.