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Materials and methods

Thirty-six hatchling meat chicks were raised in a controlled environment: temperature 28 C to 33 C; a 12-hour light, 12-hour dark cycle; and unlimited food and water. Monocular occlusion from Day 1 to Day 15 was produced in the chicks by gluing translucent heat-formed styrene hemispheres to the periocular feathers with cyanoacrylate glue. Occluders were removed at day 15 and the chicks then given various lengths of unrestricted visual experience (T= 0; 30 minutes; 2 hours; 8 hours; 24 hours; 48 hours; and 72 hours). The refractive status of the eyes was determined with retinoscopy and the axial components analysed by ultrasonography under light intramuscular kete1ar: rompun (30 mg/kg: 3 mg/kg) anaesthesia on Day 1, at occluder removal and immediately before sacrifice.

Animals were sacrificed by barbiturate overdose and the eyes were immediately prepared for light and electron …