Transcript PowerPoint Presentation - The effect of albinism on

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/
High refractive errors &
Congenital vision abnormalities?
The albino example
Alternative explanations
 Impaired/disrupted emmetropization, due
to poor vision?
 Genetic abnormality?
 A peculiarity of humans?
Human albinism
Ametropia is the rule!
2. Refractive errors
are axial
1. Wider than normal distribution
of refractive errors
Mean: +1.07 D
3. High WTR astigmatism
Wildsoet et al., 2000
Does the link between high
refractive errors & human albinism
generalize to other animals?
Is melanin &/or
its precursors
important?
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#
# obtained as fertilized eggs
from WS Payne, Michigan State Uni.
Bitgood & Smyth, Poultry Sciences,
1991, 70 (9): 1861-3.
Ocular features of the albino
chicks at hatching
Eye, including RPE
devoid of melanin
Very poor vision
Photophobic
No nystagmus
Also very fragile!!
Questions asked about the
albino chicks?
 Do they have significant congenital
refractive errors?
 Do they show developmental
emmetropization?
 Do they show active emmetropization?
Answers?
? Do they have significant congenital
refractive errors? (probably)
 Do they show developmental
emmetropization? (but abnormal)
 Do they show active emmetropization?
(but abnormal)
Albinos &
“normal” refractive development?
 Higher than normal
refractive errors
 Overall myopic bias
 Some developmental
emmetropization
Albinos & astigmatism
Higher than normal
Increases with
age
Predominantly
ATR
Albinos &
“normal”
ocular growth?
 Shallower than
normal anterior
chambers
 Longer than normal
vitreous chambers
Overall growth pattern
Active emmetropization:
The effects of diffusers &
defocusing lenses
Two treatment ages:
15 days
35 days
Albino
Treatments:
+5, +10 D lenses
-7, -10 D lenses
Diffusers
Smokey
Emmetropization is poorer than
normal
Treatment period
√ Responses to
diffusers
√ Response to
negative lenses
? Response to
positive lenses
Younger albinos & active
emmetropization
Refractive changes
have an axial basis
Older
Young
Albino retina
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)
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