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Jennifer L. Choi, Radouil T. Tzekov, Stacey S. Choi; Age-Related Changes in Ocular Parameters in White Leghorn Chickens. Invest. Ophthalmol. Vis. Sci. 2012;53(14):141.
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© ARVO (1962-2015); The Authors (2016-present)
White Leghorn chickens (Gallus gallus domesticus) have been widely used as animal models in myopia research. However, in most cases, younger birds (only up to the age of 15 days) are used. Although we have a good understanding of developmental changes in ocular parameters including refractive error and IOP in young birds, there is a lack of similar data on birds that are older than 15 days of age. The goal of the study was to track the same parameters over time in older birds.
Eighteen chickens of both genders and varying ages (20-70 days old) were raised under a 12 hours on - 12 hours off light cycle. A-scan ultrasound operating at 35MHz was used to measure the ocular parameters, including anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD) and retinal thickness (RT). Axial length (AL) was calculated by combining all these measures. A spectral-domain OCT was also used to measure the total RT for a comparison between the A-scan results and the OCT measurements. Refractive error (RE) was measured using a Hartinger refractometer. Prior to ultrasound and RE measurements, all the birds were anesthetized using isofluorane. For IOP measurements, local anesthesia with 0.5% proparacaine was used and the measurements were made with a Tonopen.
IOP was found to be stable over time with the mean value of 13.92 ± 0.79 mmHg. Both OCT and A-scan measurements showed that RT does not change with age, whereas ACD, LT and AL showed linear growth rate which was only 50% of that of published data for younger birds (Avilla et al., J Comp Physiol A, 2010). VCD also showed similar linear growth at the mean rate of ~33 micrometers per day, which differs from the exponential type of growth observed by Avilla et al. in young chicken. RE values were relatively stable during this time period, at day 39, the mean RE was +0.8 ± 0.2 D.
Collectively, our data show a linear growth for the measured parameters, except for RT (stable over time). The growth rate is reduced to half of that in younger birds after age 20 days. The measurements collected in this study could be used to generate an equivalent paraxial schematic eye model for the chicken beyond 15 days of age.
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