Ultrasound Biomicroscopy For Evaluating Anterior Segment Changes In Experimental Ametropia In Chicks C.R. Fyffe, E.L. Irving, J.G. Sivak and M.G. Callender School of Optometry University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada Introduction Results Results (continued) The chicken has become a common model for studying the Table 2. Differences, between the treated and untreated excised eyes of effects of visual input on ocular development. Abnormal early each experimental group at 1 week, in refractive states and visual experience can alter normal refractive development of the ocular dimension measurements taken from UBM images. eye. In previous studies, ametropia has been induced through the use of translucent goggles, defocusing lenses and altered ambient light levels.1,2,3 The study of experimental ametropia in chicks Average Lens C orneal Internal Anterior has produced consistent results with regard to vitreous chamber Goggle Am etropia thickness thickness Angle C ham ber depth but inconsistent data with respect to anterior segment T ype results (i.e. anterior chamber depth and lens thickness). In Induced (m m ) (m m ) (degrees) D epth (m m ) addition, little attention has been directed to the effect on the +15 D + 6.13 D +0.016 +0.012 -1.74* -0.062* dimensions of the internal angle of the eye. This study was carried out to evaluate the utility of ultrasound biomicroscopy -15 D - 15.65 D +0.034 -0.003 +2.16* +0.033* (UBM) in addressing these issues. T ranslucent - 15.65 D -0.012 +0.009 +2.64* +0.096* Fig.1 UBM images captured of an excised myopic (-19.5 D) eye from a 1 week old chick, from left to right, at low (5.0 mm x 10.0 mm), medium (5.0 mm x 5.0 mm) and high (2.5 mm x 2.5 mm) resolution. *The differences between myopic and hyperopic eyes in anterior chamber depth and Methods internal angle were significant at p< 0.05. A B C D Twenty-nine newly hatched chicks were fitted unilaterally with Conclusions goggles for one week, inducing either hyperopia or myopia. • Ultrasound biomicroscopy can be used to accurately measure Table 1. Number of chickens anterior ocular dimensions in seven day old chickens. in each experimental group • The changes found in this study are consistent with the corneal and the type of goggle fitted. flattening associated with induced hyperopia found previously in our laboratory. N G o ggle Fig.2. Measurements taken from a UBM image of an excised hyperopic (+9.50 D) eye from a 1 week old chick, of (A) anterior 9 + 15 D chamber, (B) corneal thickness, (C) lens thickness and (D) internal angle of the eye. References 10 -15 D 1. Irving, E.L., Sivak, J.G., and Callender, M.G. (1992) Refractive plasticity of 10 T ranslucent the developing chick eye. Opthal and Physiol Optics 12:448-456. 2. Pickett-Seltner, R.L., Sivak, J.G. and Pasternak, J.J. (1988) Experimentally Refractive states and ocular dimensions (corneal thickness, induced myopia in chicks: morphometric and biochemical analysis anterior chamber depth, lens thickness and internal angle) were during the first 14 days after hatching. Vision Res 27:1779-1782. 3. Moore, S.E., Irving, E.L., Sivak, J.G., Callender, M.G. (1998) Decreased measured at Day 7 by retinoscopy and ultrasound biomicroscopy light levels affect the emmetropization process in chickens. Opt Soc Am, respectively. Refractive states and ocular dimensions are given as Technical Digest Series 1:202-205. the differences between the treated and untreated eyes of each chick. The internal angle is defined as the angle between the anterior surface of the iris and the posterior surface of the cornea. Acknowledgements Fig.3 UBM images captured of an untreated excised hyperopic Fig.4 UBM images captured of an untreated excised hyperopic To obtain ocular dimensions from the UBM, 3 measurements (+3.25 D) eye (left) and a treated excised hyperopic (+2.25 D) eye (left) and a treated excised myopic (-15.5 D) were taken and then averaged for each dimension from a (+10.5 D) eye (right) from a 1 week old chick, showing eye (right), from a 1 week old chick, showing differences in This research was supported by Natural Sciences and Engineering minimum of 2 images per eye. differences in anterior chamber depth and internal angle. anterior chamber depth and internal angle. Research Council of Canada.
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