Ophthalmology and Visual Sciences

  • Special Tests

    There are a number of special tests that are done in the Neuro-ophthalmology Clinic at the University of Iowa.

    1. Kinetic (Goldmann) perimetry ('perimetry' is the quantitative testing of the side vision). These 'visual fields' are done manually by experienced perimetrists. We often use this kind of perimetry at the first visit when we really need to understand the nature of the problem.
    2. Automated (computerized) perimetry is also done by experienced perimetrists -- especially when we are looking to see if anything has changed since the last visit. In this test, spots of light are automatically projected into predetermined areas of the visual field. The test continues until the dimmest light is found that can be seen in each area of the side vision. These visual field tests provide us with important information, so we have 5 full-time perimetrists, and one who works half-time, testing visual fields for patients throughout our whole Department. They have, between them, 80 years of experience doing visual fields all day.
    3. Frequency-Doubling Perimetry is a new visual field test that is performed to screen patients for visual loss. It only takes about 5 minutes per eye. Dr Wall is the expert in this kind of perimetry. We are hoping to find that this quick test will give us the answer in certain kinds of conditions.
    4. Critical Flicker Fusion Frequency. (CFF) Patients view a flickering light to test the ability of the optic nerve to conduct impulses with uniform speed. This test has proven to be very useful in identifying visual loss due to optic nerve damage.
    5. Infra-red video pupillography. This is a way of seeing the pupils clearly in the dark so that a more certain diagnosis can be made. We also use it to transilluminate the iris to identify local iris causes for pupillary abnormalities.
    6. Electroretinography. A regular ERG (eletroretinogram) records the electrical activity of the whole retina in response to light and helps to tell us if the rods and cones of the retina are firing in the way they are supposed to.
    7. The Multi-focal ERG (MERG) does about a hundred ERGs at once by illuminating various little bits of the retina sequentially. It uses a computer to sort out the dizzying torrent of information and then it presents us with a map of the sensitivity of various parts of the retina, based on the electrical activity (in response to light) of all those different regions. If this map matches the map we got from perimetry then the problem is in the retina and not in the optic nerve or brain.
    8. Multi-focal Visual-Evoked Potentials (MVEP). Using a MERG stimulus, information can be picked up from the scalp that tells us if the visual pathways in the brain are damaged.
    9. Computer controlled infra-red sensitive pupillography is used to monitor pupillary movements in response to different types of light in order to quantify how much damage there might be in the visual system.
    10. Computer controlled "Pupil" Perimetry uses the pupil movement in response to small lights presented in the field of vision as an objective indicator of how well the eye sees the light.
    11. Computer recording of eye movements. This instrument can be used for monitoring pupil movements - but it also has the capacity to record the small movements of both eyes at the same time to see if they are tracking together and have normal movements in different directions of gaze.
    12. Optical Coherence Tomography (OCT). This is a new device that looks at the retina at the back of the eye and measures the thickness of the layer of nerves coming from all quadrants of the retina and leading into the optic nerve. This nerve fiber layer may be thickened, thinned or normal, depending on the nature of the disease affecting the optic nerve. Optical Coherence Tomography has become a very important test to help us to understand the extent and the reversibility of optic nerve damage.
    13. Ishihara Color Vision Test Cards. Used for color vision evaluation. A test chart on color dots that appear as identifiable numbers or patterns to individuals who have various types of color vision defects