Download presentation
Presentation is loading. Please wait.
Published byDarrell Owens Modified over 9 years ago
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
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.