Abstract
Purpose: :
Usher syndrome is a combined deafness and blindness disorder and caused by mutations in several genes with functions in both the retina and the ear. We have chosen to study the Ush2a mouse which carries a mutation in the usherin gene and the only Usher syndrome animal model to exhibit retinal degeneration. Here we examined the morphological and functional changes with ages
Methods: :
Ush2a mice (provided by Dr T Li, Harvard Medical School) were divided into several age groups: postnatal day (P) 60, P180, P360 and P700. The optomotor test, a repeatable method of estimating rodent visual acuity, was conducted. At the end of the testing, animals were sacrificed and eyes were processed for histology.
Results: :
The optomotor test showed that while acuity testing showed only late changes, deterioration in visual function as measured by contrast sensitivity was detected by P60 and continued to deteriorate with age. This visual parameter best correlated with receptive field size and suggested reducing photoreceptor density; visual responses progressively deteriorated in photopic conditions with age.Histological examination revealed that there was slow photoreceptor loss and secondary inner retinal changes with age.
Conclusions: :
This study showed that photoreceptor degeneration progresses slowly in Ush2a mice, however, vision impairment was detected before significant photoreceptor loss was seen. The secondary inner retinal changes occurred as photoreceptor degeneration became evident. This study provides fundamental information for using therapeutic therapy in this model.
Keywords: retinal degenerations: cell biology • visual impairment: neuro-ophthalmological disease • visual acuity