We have previously reported decreased choroidal blood flow (CBF) associated with goggle-induced ocular enlargement and myopia. It was uncertain, however, if this change in CBF was related to the occurrence of ocular enlargement or the increased ocular temperature produced by the goggle. We therefore used corneal surgery-induced ocular enlargement that eliminated the thermal effects observed with goggles to investigate the effects of ocular enlargement on CBF. Central corneal incisions (2 mm in length) were made in the right eye of 4 day old chicks and the wound sutured. In one group, the incision was oriented along the vertical meridian (with the head in its natural position -beak tip 30-45 degrees below horizontal), while in another group the incision was oriented along the horizontal meridian (with the head in its natural position). Age matched controls received no corneal incision. Two weeks later, CBF was measured using laser Doppler velocimetry. After determining CBF, the eyes were removed and axial length, nasotemporal length and dorsoventral length were measured. Ocular enlargement was induced in 11 out of 12 chicks with vertical cuts. The CBF in the operated eye of these 11 animals was 62% of that in the nonoperated eye. Ocular enlargement was also induced in eight of 14 chicks with horizontal cuts. The CBF in the operated eye in these eight chicks was 60% of that in the nonoperated eye. The extent of eye growth was greater in all dimensions in the vertical cut chicks with ocular enlargement than in the horizontal cut chicks with ocular enlargement.(ABSTRACT TRUNCATED AT 250 WORDS)