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K.A. Napier, J.R. Mertz; All-trans-retinoic Acid Causes a Decrease in Curvature of Chick Cornea . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2802.
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Purpose:In previous studies we have observed that exogenous all-trans-retinoic acid (at-RA) causes elongation of the chicken eye, though they maintain emmetropia. The purpose of this study is to determine if the cornea of chickens flatten in order to maintain emmetropia. Methods: Baseline corneal curvature was determined by IR keratometry on 20 chicks. Group 1 (G1) consisted of N=10 6-day-old chicks, Group 2 (G2) consisted of N=4 6-day-old chicks, and Group 3 (G3) consisted of N=6 34-day-old chicks. G1 was treated with a drop of 1mM at-RA in, Bridge 78 (a non-ionic detergent, 0.5%), in one eye and the other eye was untreated. G2 was treated with Bridge 78 alone in one eye as a vehicle control, and the other eye was untreated. G3 was treated with at-RA in Bridge 78 in one eye and Bridge 78 as a vehicle control in the other eye. After 4 days corneal curvature was measured in G1 and G2. In G3 corneal curvature was measured after 8 days, and corneal diameter was measured in 2 animals. Results: Compared to controls, the corneas became flatter in the eye treated with at-RA in G1 and G3, paired t-test for G1 p<0.019, paired t-test for G3 p<0.059. There was no change in corneal curvature relative to controls in the eyes treated with Bridge 78 in G2. The corneal diameter of eyes treated with at-RA in G3 did not change (change of –0.11mm and 0.03mm over the treatment period); while in the control eye the diameter increases (change of 0.51mm and 0.55mm). Conclusions: The results confirm that at-RA causes corneal flattening and prevents circumferential growth of the cornea. This indicates that exogenous at-RA alters corneal structure. The lack of change in diameter of the cornea is most likely due to the inhibitory action of at-RA on proteoglycan in the scleral ossicles of the chicken eye.
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