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Andrea Carrillo Aleman, Frank Schaeffel; Are focusing errors produced by insufficient accommodation responses driving emmetropization in chicks?. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2155.
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Emmetropization has been shown to be controlled by the retina. The retina detects image defocus and fine-tunes the growth rates of the sclera. However, accommodation continuously modifies the retinal defocus error signal and it is a classical problem how this input is taken into account. We have measured accommodation errors and eye growth in high detail in chickens wearing negative spectacle lenses to find out whether larger accommodation errors also lead to larger changes in eye growth.
Two groups of 6 and 5 chicks, aged 10 to 12, were used. They wore lenses (-7D) monocularly for 4-5 days. Fellow eyes remained untreated and served as controls. Vitreous chamber depth (VCD) was measured in alert hand-held chickens with high resolution, using the Lenstar LS 900 (Haag-Streit, Koeniz, Switzerland). Refractive states were measured by automated infrared photoretinoscopy with and without lenses in place. Measurements were done 5 times a day in group 1 to obtain detailed VCD growth curves. To reduce the risk of partial recovery during too frequent removal of the lenses, measurements were only taken at 9am and 4pm in group 2.
Group 1: The chicks did not become exactly as hyperopic as lens powers predicted. VCD became significantly deeper in eyes with negative lenses in only 3 chickens (paired t-test). No correlation was found between the magnitude of the accommodation errors in individual animals and subsequent changes in VCD (R= 0.32, n.s., 27 data points). Group 2: VCD became significantly deeper in all eyes with negative lenses. As found earlier (Weiss & Schaeffel 1992), VCD of lens-wearing eyes grew both during day and at night (by 0.056±0.034mm/day and 0.069±0.046mm/night), while VCD growth in untreated fellow eyes displayed a pronounced diurnal rhythm: it increased only during the day (by 0.068±0.022mm) and shrank during the night (by -0.032±0.028mm, p<0.001). Again, no correlation was found between the magnitude of the accommodation errors in the individual animals and the subsequent changes in VCD, as observed at night (R= 0.34, n.s., 20 data points).
The measured accommodation errors did not predict eye growth rates. This raises the question as to whether accommodation errors in chicks might be too transient to affect eye growth rates as suggested by Winawer et al (2005). As found before, changes in eye growth induced by the lenses, showed up only at night.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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