by Dr. Joe Fontenot – CLVT Medical Director
What is a “blind spot” or scotoma?
A scotoma is a “blind spot” in one’s vision. It is defined in the Miriam-Webster dictionary as: “scotoma or scotomata: a spot in the visual field in which vision is absent or deficient”.
What causes scotoma?
Blind spots in vision may be caused by eye disease, problems with the optic nerve, brain or even psychological problems.
Migraines may also cause temporary blind spots. However, most blind spots are caused by eye disease that is limited to one part or one spot in the eye (like macular degeneration) which causes a localized, non-functioning area that results in a blind spot or scotoma in the center of the visual field.
Scotoma in Age Related Macular Degeneration (ARMD)
The scotoma of ARMD are usually described by those affected as being a cloudy, ill-defined area rather than discrete and well demarcated. They are rarely absolutely black, but rather gray or off-white. They may have different shapes or colors in different lighting conditions. The normal retinal tissue is replaced by the degenerative lipid and fibrous process of macular degeneration. This occurs in an irregular and sometimes incomplete fashion. No image or an incomplete image is transmitted to the brain from the affected areas, resulting in a “blind spot” or scotoma.
Arrow indicates the pale yellow areas of macular degeneration which can cause a scotoma (blind spot).
When are the scotoma first noticed?
Scotoma are often not noticed if they involve only one eye. The other eye fills in the gap. Even if both eyes have scotoma in the same location, the loss of vision in a small area may not be noted. The brain unconsciously fills in the blind spot with images from the surroundings. This is a process called “perceptual completion”.
Charles Bonnet Syndrome
Some people see images in their blind spots. This is called “Charles Bonnet Syndrome” and is generally thought to be the result of the brain’s unconscious effort to put something into the area where nothing is perceived. These images may occur frequently and may be concerning or alarming. People usually are relieved once the nature if the images are explained to them. They usually occur at rest and may be dispelled by becoming active, getting up and moving about. The images usually become less frequent and disturbing over months or years.
Eccentric Viewing and Preferred Retinal Locus
If you have a scotoma in the center of your visual field and look straight ahead, you will not be able to see what you are looking at. You will have to look to one side or another, or up or down to get your blind spot out of the way. This is “eccentric viewing”, and the place on your retina that you habitually direct the image to is the “preferred retinal locus”. Techniques for making the most of eccentric viewing can be taught by Occupational Therapists (OT’s) to achieve the best reading skill possible despite having scotoma.
What to do if you have a scotoma?
See your eye doctor. Some of the scotoma may improve and become smaller with treatment by Anti-VEGF (injection) therapy, or at least kept from enlarging.
Check your vision frequently with an Amsler grid
Understand and use eccentric viewing techniques