Purchase this article with an account.
T. C. Tepelus, F. Schaeffel; Responses of Different Retinal Areas to Imposed Defocus in Chicks. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3935.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Recent experiments in monkeys suggest that defocus imposed in the periphery of the visual field can affect the development of central refractive errors. To design spectacle glasses that make use of this observation, it should be known whether certain retinal areas are more responsive or whether changes in eye growth are just proportional to the defocused area. We have studied this question in chickens.
In total, 40 male white leghorn chickenswere used. From day 7 after hatching, they were treated for 5 days either with full field negative (-7D) or positive (+7D) lenses, or with hemi-field lenses of the same powers, or with radial refractive gradient (RRG) lenses which were provided by the industrial partner, Rodenstock, Munich. A macro file was written for "ImageJ" (a publicly available image processing platform) to trace the outlines of excised eyes. Shapes of fellow control eyes and lens-treated eyes were compared in both the horizontal and vertical meridians. Refractions were determined over the horizontal visual field, at the beginning and at the end of experiments, using automated infrared photoretinoscopy.
(1) Eye length, as determined by the tracing technique, was highly correlated to A-scan ultrasound axial length data. (2) Full field -7D lenses increased eye size in axial direction by 0.21mm (from 9.98±0.28 to 10.20±0.35mm), with an increase in eye volume by 3.7%. Full field +7D lenses slowed down the eyes' growth rate, resulting in a decrease in axial direction by 0.08 mm (from 9.84±0.22 to 9.77±0.17mm) with a decrease in eye volume by 2.5%. For both lenses, the changes in eye shape were larger in the temporal than in the nasal segment. (3) RRG lenses had no apparent effect on central refractions but induced small hyperopic shifts in the periphery which were significant only in the temporal retina (+1.83±1.87D, p<0.0001). (4) Morphology of the anterior segment of the eye remained unchanged during the lens treatments, except for the case of hemi-field lenses.
The temporal retina appears more responsive to defocus since it induces larger changes in eye dimension, compared to the nasal retina. (2) Similar to lenses with central holes, RRG lenses used in this study induced changes in refraction in the periphery without influencing central refractive development - an effect that might be different in primates, or with other RRG lens designs.
This PDF is available to Subscribers Only