NONVASCULAR CONTRACTILE CELLS IN SCLERA AND CHOROID OF HUMANS AND MONKEYS

PURPOSE. To investigate by histochemistry and immunohistochemistry the distribution and innervation of nonvascular contractile cells in the sclera and choroid of humans and monkeys. METHODS. Globes were obtaine d from 2 macaque monkeys and 19 human cadavers that ranged in age from fetal life to 94 years. Immunohistochemistry was performed using mono clonal antibody against human smooth muscle (SM) alpha-actin and tyros ine hydroxylase (TH). The nicotinamide-adenine dinucleotide phosphate (NADPH)-diaphorase reaction was used as a marker for nitric oxide synt hase. RESULTS. The scleras of all but fetal, newborn, and infant globe s exhibited myofibroblasts, amelanotic, fibroblastlike cells having SM alpha-actin immunoreactivity. In the choroid of all but fetal eyes, S IM cells were present in the suprachoroidal layer, forming a reticulum of flattened laminae, and in the choriocapillaris where ovoid-to-spin dle-shaped SM cells were arrayed in parallel layers immediately adjace nt to Bruch's membrane. Contractile cells in the sclera and choroid we re most concentrated subfoveally and were sparse anteriorly. Nerve ter minals positive for NADPH-diaphorase were colocalized with SM alpha-ac tin-positive cells in the sclera and choroid, whereas TH-positive nerv e terminals colocalized with SM cells in the choroid. Clusters of gang lion cells were present on the posterior surface of globes near SM cel ls. CONCLUSIONS. The posterior choroid and sclera of humans and monkey s contain nonvascular contractile cells. The presence of nerve termina ls and adjacent ganglion cells suggests neural control of these contra ctile 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 part icipate in regulation of refractive state by maintenance of ocular siz e in the face of intraocular pressure or in intermediate-term regulati on of choroidal thickness.