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Marsha Kisilak, Kaitlin Bunghardt, Vivian Choh, Elizabeth Irving, Melanie Campbell; Isoflurane and lid retractors affect the optics of the chick eye. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1918.
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Isoflurane affects blood flow and repeated use in chicks slows growth of the eye. Lid retractors, used with anesthetic, may deform the cornea. We explored effects of isoflurane and lid retractors on the eye’s optics.
23 chicks were obtained on the day of hatching. Hartmann Shack measurements were taken on all eyes. Axial length was measured with A scan ultrasound. Refractive error and higher-order aberrations (HORMS) were analyzed at constant pupils. On day 0, 11 chicks were measured sequentially: 1) awake without lid retractors, 2) awake after recovery (1 min) from brief exposure to isoflurane (2 min), 3) with lid retractors under isoflurane. Differences between conditions were detected using paired t tests or Wilcoxon Signed Rank tests for non-normal data. Of the remaining chicks, 6 awake and 6 chicks with lid retractors under isoflurane were measured. Then, right eyes of all 12 birds were goggled with a -15D lens. Measurements were repeated on days 2, 4, 7. Data were examined for differences in awake vs under isoflurane with lid retractors, lenses worn and time (ANOVA).
On day 0, in awake chicks, brief exposure to isoflurane gave significantly increased pupil size and HORMS. There were significant increases in pupil size, JCC45, HORMS, 3rd and 4th order RMS and cylinder between those under anesthesia with lid retractors and awake birds (either prior to or post anaesthesia). Mean ocular refraction (MOR) decreased significantly in birds with lid retractors under anesthesia vs awake birds pre-anaesthesia. There was no significant difference in axial length in any condition. Prior to goggling, cylinder and 4th order RMS were significantly higher with lid retractors under isoflurane vs awake chicks. Post goggling, with lid retractors under isoflurane, pupil size, JCC0, HORMS, 3rd and 4th order RMS and cylinder increased significantly across all eyes. JCC45 increased only in control eyes. HORMS effects depended on the eye and day. For control eyes, pupil size effects were dependent on day.
Isoflurane alone and with lid retractors change the optical properties of the chick eye. This includes MOR, pupil size, cylinder, its components and HORMS. Effects on HORMS depended on age and effects on HORMS and JCC45 interacted with goggling. Overall, lid retractors with isoflurane decreased MOR and image quality worsened (from HORMS, JCC0 and JCC45).
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