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Marsha Kisilak, Laura Emptage, Ian Andrews, Melanie C W Campbell; Adaptive optics measurements of cone density in chick eyes during lens-induced myopia. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2174.
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© ARVO (1962-2015); The Authors (2016-present)
In vivo measurements of cones in the chick eye, an animal model of myopia, are desirable as a marker of retinal changes during axial length increases. In vivo images allow longitudinal measurements of the angular cone spacing in the growing chick eye and during lens-induced myopia. We can then compare measured densities with models of retinal changes during eye growth and myopia development.
Four Ross Ross chicks were acquired on the day of hatching. Axial length was measured using A scan ultrasound and aberrations and defocus were measured in a custom built Hartmann-Shack aberrometer. Eyes were imaged in an adaptive optics corrected scanning laser ophthalmoscope modified for small animal use (2.5 mm diameter pupil). After this, the right eyes were goggled with -15D lenses. Measurements were repeated on days 7 and 14. All measurements were taken close to the optical axis and the anatomical position of the area centralis. Angular cone densities were measured directly. Linear cone spacings on the retina were calculated from published schematic eye models modified for measured eye lengths and cone packing properties were assessed. Paired t-tests were performed to compare between days and between treated and control eyes.
By day 14 goggled eyes were on average 15D myopic. Cones were successfully imaged on all days. The angular density of cones was not significantly different between control and goggled eyes (p > 0.2) on any day. As seen in previous control birds, angular density was not significantly different between days 0 and 7 (p = 0.1) in control eyes, after which it significantly increased (p < 0.02). Goggled eyes showed no significant change in angular density with growth. The calculated linear distance between cones increased significantly from 6.4 microns on day 0 to 7.0 microns on day 14 in control eyes and did not differ from goggled values of 6.2 microns on day 0 (before goggling) and 8.3 microns on day 14. On average, cones were 38% hexagonally packed across all days and for both control and treated eyes.
Average cone spacings in control eyes on day 14 were within 10% of some literature values. Results for control eyes, showing initial uniform expansion followed by either cone migration or optic pole elongation are consistent with our previous data. Eyes with lens-induced myopia expand uniformly relative to control eyes.
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