OCULAR AXIAL LENGTH AND CHOROIDAL THICKNESS IN NEWLY-HATCHED CHICKS AND ONE-YEAR-OLD CHICKENS FLUCTUATE IN A DIURNAL PATTERN THAT IS INFLUENCED BY VISUAL EXPERIENCE AND INTRAOCULAR-PRESSURE CHANGES

Low coherence laser Doppler interferometry (LDI) allows high precision measurements of the axial length of the eye and of the thickness of t he individual layers of the ocular fundus. Here, we used LDI to monito r diurnal changes in these dimensions in eyes of newly hatched chicks and one-year-old chickens with, normal or altered visual input. In chi cks and chickens with normal visual experience, axial eye length displ ays diurnal fluctuations increasing during the light phase. Choroidal thickness also exhibits a diurnal pattern, shrinking during the day an d expanding during the night. Retinal thickness does not vary. Based o n the pressure compliance of the enucleated chick eye, the diurnal int raocular pressure (IOP) fluctuation could contribute both to the incre ase in axial length and to daytime choroidal shrinkage. Following depr ivation of form vision by unilateral goggle wear, occluded chick eyes demonstrate enhanced axial elongation. Diurnal fluctuations in axial l ength but not in choroidal thickness are temporarily disrupted. The re tina of form deprived eyes thins approximately 10% in five days. In co ntralateral eyes, the diurnal patterns of both axial length and choroi dal thickness fluctuations are also disrupted. Following occluder remo val in chicks, choroidal thickness increases for several days during b oth the light and dark phase, leading to its overall expansion. Retina l thickness returns to baseline. When deprived of form vision for five days, the eyes of year-old chickens do not exhibit measurable axial e longation. Diurnal patterns of fluctuation in axial length and choroid al thickness are however disrupted. After goggle removal, axial length fluctuation is restored to normal, but the diurnal choroidal thicknes s pattern is inverted. In contralateral eyes, choroidal thickness exhi bits normal diurnal fluctuations both during and after form vision dep rivation. In conclusion, axial length and choroidal thickness fluctuat ions are influenced by visual experience in both newborn chicks and on e-year-old chickens. In selected instances a binocular interaction reg arding axial length and choroidal thickness changes is suggested, the effect weakening with age. (C) 1998 Academic Press Limited.