Testing surround vision
The MeyeSight Test – Surround vision
Surround vision is the third component of the MeyeSight test. It helps you to see how visual field loss may be affecting how you, the person, functions.
Run on a smartphone, the MeyeSight surround vision component shows visual field disturbances in the inner portions of the retina (e.g., for AMD), while on a larger tablet screen the test displays scotomata further out on the retina (e.g., for glaucoma).
Visual field tests map your field of vision and provide quantified evaluation of your vision, showing where and how much vision has been lost.
You might think that surely you would notice where you can’t see! But your eyes and brain are so good at making up for gaps in vision that the effects of field defects often don’t enter conscious awareness.
Visual field testing for eye function
If your doctor suspects disease that can affect your visual fields, you will probably undergo perimetry testing such as the Humphrey field test which maps the sensitivity of the retina.
The Humphrey Field Analyzer, the most commonly used visual field machine, looks much like a large concave bowl. With one eye covered with a patch, you focus your vision on a central spot while small white lights of varying brightness flash at various points around the bowl. When you see a flashing light, you press a button which you hold in your hand. The field test records which lights you see and which you do not, and in this way it creates a map of your visual field.
Because Humphrey field tests take some time to complete and require both expensive equipment and the attention of a trained technician , they are often not given as part of a comprehensive eye exam unless there is a suspicion of disease such as glaucoma. The Humphrey Analyzer is one example of static automated perimetry in which the stimuli you are to observe is stationary, varying in size and intensity.
The Goldmann visual field exam is a form of kinetic perimetry in which the stimulus is moved from beyond the edge of the visual field into the field and the location at which the stimulus is first seen marks the outer perimeter of the visual field. Although Goldmann fields are generally more informative than static fields such as the Humphrey, the exam requires a trained technician to measure and draw the visual field and is, therefore, costly to administer.
A doctor or technician may perform a quick in-office visual field test in which you fixate at a point (for example their nose) while they wiggle and flash fingers at various points on the far edges or periphery of your field of view.
Such quick testing can not function as a diagnostic tool – it will not find subtle defects or early changes in the visual field and. Nevertheless, it can identify gross defects and provide feedback about potential problems in orientation and movement.
Observing field loss
In Going Blind, Joe Lovett sees the defects in his visual field for the first time when Dr. Rosenthal has Joe do a confrontation (face-to-face) field test in his office.
From Going Blind: Coming Out of the Dark about Vision Loss >>>
You can have a friend or family member do this test with you. While you close or cover one eye and gaze at their (the examiner’s) nose. Starting with their hand out toward the far edge of periphery, they move a wiggling finger in towards the center until you can detect its presence. Repeat this in several positions around the field of gaze. Then switch eyes.
While not a substitute for the MeyeSight Visual Fitness test or for the Humphrey or Goldmann field tests, this simple procedure is useful as an assessment and an educational tool for actually experiencing your blind spots.
Amsler grid testing
The Amsler grid has been used for many years as a quick way to evaluate the function of the macula.
Looking with one eye at a time at a central spot on the Amsler grid, you observe irregularities in the lines such as lines that arc, seem to bow or bend, appear gray or fuzzy, or disappear altogether.
As the Amsler grid tests the central 20° of visual field – the entire macula – it is useful test for observing a problem with macular degeneration or a worsening of one’s condition. Because it tests central vision defects, the Amsler grid is often not associated with glaucoma testing, but the Amsler grid does pick up paracentral defects as well, and these are more common in patients with glaucoma than is commonly recognized. While distortion is more common with macular disorders. missing areas may suggest paracentral glaucomatous visual field loss.