Ultrasound Biomicroscopy For Evaluating Anterior Segment Changes by MikeJenny

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									                                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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