Design and Methods - Mouse Mutations Causing Eye and Vision Defects
Primary Screen
A - We will first visually inspect mice for dysmorphologies of the eyelids, globe, cornea, and iris. Mice will then be examined with a biomicroscope (slit lamp) for corneal clarity, size (i.e. bupthalmos, microcornea), surface texture, and vascularization. The iris will be checked for pupil size, constriction, reflected luminescence (transillumination), iris atrophy, and synechia. Eyes will then be dilated with 1% atropine. The lens will be examined for cataract formation and pseudoexfoliation. The fundus will be examined using an indirect ophthalmoscope for signs of retinal degeneration, such as retinal vessel constriction or retinal pigment epithelial disturbance, or for other abnormalities including drusen or deposits, structural or optic nervehead anomalies, vitreal abnormalities, and abnormal vascularization. Phenodeviants for any one of the above criteria will be tested for heritability.
B - Mutants with retinal degenerative processes can often be identified prior to observable clinical alterations [194, 197], and functional deficits have been reported in mice that do not lead to immediate morphological alterations [201, 202]. Thus, it is important to perform a functional screen. The comprehensive rod and cone ERG tests have been reduced to 5-10 minutes per mouse by decreasing the number of stimuli intensity and filter changes. Briefly, to assess rod function dark-adapted mice are challenged with three different intensities of stimuli - low, intermediate and high. Cone-mediated responses are obtained with white flashes on a rod-saturating background. This protocol will reveal rod and cone abnormalities that can be examined in further detail.
Future development of primary screens - We plan to further develop screening methods for functional deficits or for eye alterations not detected by a conventional exam, including a) gonioscopy to examine anterior chamber angle structures; b) non-invasive measures of retinal ganglion-cell and optic nerve function, such as pattern ERG, visual-evoked potential, and a contralateral pupillary response assay for evaluating the visual system from the retina through the primary visual cortex; and c) non-invasive IOP measurements. Once fully developed, these non-invasive functional measures may be used for primary screening or as a first line of secondary analysis.
Secondary screen longitudinal screens on all heritable eye mutants of interest - This level of study includes electroretinograms (ERG), photodocumentation (PHO), fluorescein angiography (FLA) or intraocular pressure measurements (IOP) where applicable and histology (HIS). Secondary screens will be performed on mutants to provide further characterization in order to obtain a better classification of the eye disease and to perform analyses such as ERGs and IOPs that are not immediately available in many laboratories. This will enhance the value of the mutants to investigators who have particular research interests within the eye.
