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Jennifer Choi, Radouil Tzekov, Stacey Choi; Future Insights on an Ocular Hypertension Model in the White Leghorn Chicken. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6054.
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While White Leghorn chicken (Gallus gallus domesticus) have been used to study physiological optical properties of the eye and conditions such as myopia, there is a lack of in vivo studies that look at the potential of chicken as a model of ocular hypertension or glaucoma. When advanced imaging techniques are to be used in such models, chicken have an advantage over rodents, having bigger eyes with less optical aberrations. The induction of elevated IOP in chicken via anterior chamber injections of microbeads has thus been investigated.
Animals of both genders and varying ages (n=15:12-124 days old) were subject to one of 12 combinations of anterior chamber injections of microbeads: magnetic (4.5 µm) or non-magnetic (12 µm) in one or both eyes with saline as a control. Intraocular pressure (IOP) was monitored frequently before and after injections with Tonopen. In 4 out of the 17 animals A-scan ultrasound was used to measure ocular parameters including anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), retinal thickness (RT) and choroidal thickness (ChT) pre and post all injections. All birds had isofluorane anesthesia prior to injections and ultrasound.
Elevation of IOP with maintenance of a clear visual axis was successful in 2 out of 17 animals after two 70µL injections of magnetic microbeads (concentration 20x108beads/mL). Animal #1943 was injected with 140x106 beads at age 51 days and with the same amount two weeks later; 5 days later IOP was elevated 5 mm Hg greater than the fellow eye for a period of 7 days. Animal #1975 received an injection of 140x106 beads at age 99 days and 160x106 beads at age of 110 days and an average elevation of 8mm Hg greater than the fellow eye was noted from day 4 to day 7 post second injection. In other animals injection of 98x106 magnetic beads at day 40 and again at day 51 blocked the visual axis. Non-magnetic microbeads (125x108 to 875x108 beads) did not elevate the IOP. One to 3 saline injections did not influence the growth rate of ocular parameters measured via ultrasound biometry.
The White Leghorn chicken has potential for in vivo studies of ocular hypertension and/or glaucoma via magnetic microbead anterior chamber injections. Studying the effects of elevated IOP on the chicken retina over a longer time period is indicated. SD-OCT and Adaptive Optics imaging may shed further insights.
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