EFFECT OF CONGENITAL HYPOTHYROIDISM ON CELL-DENSITY IN THE GANGLION-CELL LAYER OF THE RAT RETINA

The effect of congenital hypothyroidism on the visual system of Wistar rats was studied by determining neuron density in the retinal ganglio n cell layer. Retinae of adult rats from mothers treated with propylth iouracil, 50 mg/day, starting on the 15th day of pregnancy (PTU group) , and of adult rats from untreated mothers (control group) were examin ed. Retinae were prepared, and the neurons in the nasotemporal region located above the optic disc were counted. Hypothyroid rats showed a s ignificant reduction in the retinal area (about 6.8%), when compared t o controls. The cell density in the retinal ganglion cell layer was si gnificantly decreased in 6 PTU-treated compared to 5 control retinae i n total (2,793 +/- 330 vs 3,704 +/- 662 neurons/mm(2)), nasal (3,031 /- 580 vs 3,853 +/- 699 neurons/mm(2)), and temporal (2,555 + 156 vs 3 ,555 + 827 neurons/mm(2)) regions. These alterations in a region consi dered to be one of the most specialized in the visual process suggest a structural deficiency induced by congenital hypothyroidism, with a p ossible decrease in the visual acuity of the rat.