1. The effect of albinism on emmetropization. A study using chickens as an animal model for human albinism. Presenter: Christine Wildsoet University of California - Berkeley Funded by NIH http://vision.berkeley.edu/VSP/CW/

2. High refractive errors & Congenital vision abnormalities? Alternative explanations  Impaired/disrupted emmetropization, due to poor vision?  Genetic abnormality?  A peculiarity of humans? The albino example

3. Human albinism Ametropia is the rule! Wildsoet et al., 2000 Mean: +1.07 D 1. Wider than normal distribution of refractive errors 2. Refractive errors are axial 3. High WTR astigmatism

4. Does the link between high refractive errors & human albinism generalize to other animals? Is melanin &/or its precursors important?

5. Subjects  Albino White-Leghorn #  oculocutaneous tyrosinase-negative albinism (deletion in exon 1 of tyrosinase gene)  tyrosinase-like molecule produced but inactive  Normal White-Leghorns  Smokey White-Leghorns # Bitgood & Smyth, Poultry Sciences, 1991, 70 (9): 1861-3. # obtained as fertilized eggs from WS Payne, Michigan State Uni.

6.  Eye, including RPE devoid of melanin  Very poor vision  Photophobic  No nystagmus Ocular features of the albino chicks at hatching Also very fragile!!

7. Questions asked about the albino chicks?  Do they have significant congenital refractive errors?  Do they show developmental emmetropization?  Do they show active emmetropization?

8. Answers? ?Do they have significant congenital refractive errors? (probably) Do they show developmental emmetropization? (but abnormal) Do they show active emmetropization? (but abnormal)

9. Albinos & “normal” refractive development?  Higher than normal refractive errors  Overall myopic bias  Some developmental emmetropization

10. Albinos & astigmatism  Higher than normal  Increases with age  Predominantly ATR

11. Albinos & “normal” ocular growth?  Shallower than normal anterior chambers  Longer than normal vitreous chambers

12. Overall growth pattern

13. Active emmetropization: The effects of diffusers & defocusing lenses Two treatment ages:  15 days  35 days Treatments:  +5, +10 D lenses  -7, -10 D lenses  Diffusers Albino Smokey

14. Emmetropization is poorer than normal √Responses to diffusers √Response to negative lenses ?Response to positive lenses Treatment period

15. Younger albinos & active emmetropization

16. Refractive changes have an axial basis Young Older

17. Retinal morphology & visual acuity  RPE devoid of melanin  All photoreceptor subtypes present  INL slightly thinner than normal  VA near normal by 29 days of age (preliminary finding)

18. Summary & Conclusions  Albino chicks show early abnormal refractive errors (at hatching?)  Emmetropization is abnormal  Reduced visual acuity may partly underlie the post-hatch changes  Eye shape abnormalities resemble light-induced avian glaucoma & may represent the precursor to glaucoma as reported in albino quail Acknowledgements to: Kai, Ajay, Michel, Chun-Mei, Vivian, Sigrid, Nina, Kevin, Sabrina & Young