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G. Rodriguez, E. Garcia de la Cera, S. Marcos, J. Merayo–Lloves, R.M. Torres; Study of the Development of Axial Length and Refractive Error in Chickens Treated With Corneal Refractive Surgery With Excimer Laser . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1970.
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Purpose: It is well known that both retinal image degradation by diffusers and imposed defocus with negative lenses cause excessive elongation in the chick eye and therefore myopia. Corneal refractive surgery with excimer laser corrects refractive errors, but induce high order aberrations (and therefore retinal blur) We study changes in axial length and refractive error in chicks (Gallus domesticus) after applying myopic corneal refractive surgery with excimer laser, to explore its potential to induce myopia and potential interactions between aberrations and myopia development. Methods:Twelve one–day–old White Legorn chicks were monolaterally treated with myopic corneal refractive surgery with excimer laser (PRK). Refractive error (RE) and Axial Length (AL) were measured (with retinoscopy and adapted ultrasound biometry, respectively) in both eyes before and after treatment. The nominal myopia correction programmed into the laser system was –5.5 D in 4 chicks and –9.90 D in 8 chicks. Chicks were raised in 12/12 hr light/dark cycle conditions. Measurements were made every 2.3 days, for 2–3 weeks. Results: Contralateral control eyes decreased hyperopic refractive error linearly (at a rate of –0.11 D/day), starting with 6.46 ±3.38D and showing 3.84± 1.15 D at day 25. Treated eyes did not show a linear trend, dropping refraction during the first week, and then increasing at a rate of 0.05 D/day (for the –5.5 D treatment) and 0.25 D/day (for the –9.9 D treatment), ending up 0.6 D and 3 D more hyperopic on average (for the –5.5 and –9.9 D on average) than the control eyes. Axial length increased with development both in the non–treated (0.052 mm/day) and treated eyes (0.054 mm/day), at similar rates. While there were not significant differences in axial lengths at the end of the study between –5.5 D–treated eyes and the contralateral eyes, –9.9 D–treated eyes were on average 0.6 mm shorter than the contralateral eyes. Conclusions: Surgical refractive treatment with negative correction did not produce the axial elongations previously obtained with negative lens treatment. However, it interferred emmetropization of the treated eye. Resulting hyperopia (rather than emetropia or myopia) could be due to a failure of the emmetropization process (the eye did not elongate to compensate for the imposed defocus), a shorter axial length at the end of the treatment, or refractive regression following surgery.
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