Color vision is the ability of the visual system to distinguish objects based on the wavelengths of the light that reaches the retina. Human's perception of colors is a subjective process whereby the brain responds to the stimuli generated from the cone photoreceptors. The normality of color vision perception can be clinically tested with different methods, including plates (e.g. the Ishihara plates), colored caps (e.g. D-15, Roth 28 hue, FM 100), and other, more elaborate methods (e.g. anomaloscope). Color testing at the USF Eye Institute is based mostly on color cap tests, but can be configured in a different ways, depending on the specifics of the case.
What to expect from the test?
The testing evaluates the ability of the visual system to discriminate between different colors. In addition, some color tests can differentiate between inherited and acquired color deficiencies.
How to prepare for the test?
The testing takes between 30 and 90 minutes, depending on the specific test/s used.
In a broad sense, the contrast sensitivity is the ability of the visual system to distinguish different levels of contrast, the contrast being determined by the difference in the color and brightness of the object and other objects within the same field of view. In practical terms it is much easier to test only one of the two elements determining contrast, keeping the other one constant or its contribution reduced to the minimum. In most cases, the color is practically eliminated and the visual system is tested based on its ability to distinguish between the differences in the brightness of an object vs. the surrounding objects (achromatic contrast sensitivity). The testing can be done either by using charts (e.g. Pelli-Robson) or by projecting the stimuli on electronic displays. Currently, the contrast sensitivity testing at the USF Eye Institute is chart-based.
The test evaluates the overall ability of the visual system to detect different levels of contrast. Deficits in this ability can be due to optical factors (e.g. cataract, post-Lasik, etc.), diseases of the inner retina (e.g. glaucoma, diabetic retinopathy, etc.), diseases of the optic nerve (e.g. optic neuritis), drug toxicity (e.g. chloroquine toxicity, vigabatrine toxicity, etc.), or other factors.
The testing takes between 20 and 45 minutes, depending on the specific test/s used. Distant vision correction (most recent eyeglasses or contact lenses) is required for successful testing. No other preparation is necessary.
Other psychophysical visual function tests can include tests for dark adaptation, macular glare tests, etc. At this time, these tests are not offered by the USF Eye Institute.