Diseases such as age-related macular degeneration, cone-rod dystrophy and Stargardt disease cause scotomas, or blind spots, which often have devastating effects on central vision. They cause gaps in a person’s visual field, making it difficult to see words in a book, images on a computer monitor or TV and the features of someone’s face.
But as clinical researchers are learning, central vision loss also causes people to have problems with fixation, the ability to maintain one’s gaze in a single direction, which is an added challenge in recognizing faces.
A recent research paper from Lighthouse International and the New York University School of Medicine focuses on these fixation problems. Using optical imaging technologies, Dr. William Seiple and his colleagues found that people with normal vision who looked at an image of the Mona Lisa consistently fixated on the eyes, nose and mouth to identify the face. However, people with AMD were unable to fixate on those areas of the image.
The investigators noted that people with normal vision use their fovea — a pit in the center of the retina that is rich in cones — as the focal point for fixation. If the fovea is compromised by retinal disease, a person may develop “pseudofoveas” in the peripheral areas of their retinas. They are the brain’s and retina’s way of trying to compensate for the lost focal point. However, pseudofoveas can’t fixate as well as the natural fovea.
Experts have found that the brain plays an important role in fixation. Using feedback from the retina, it directs eye movements in scanning and fixation. Some people with disorders such as schizophrenia or autism may also have problems perceiving faces because of changes in the area of the brain that controls fixation.
While some retinal conditions such as retinitis pigmentosa affect the peripheral retina first, they, too, can cause fixation problems in advanced stages, when the central retina becomes affected.
There’s no easy answer for overcoming central vision loss, though a low-vision specialist can recommend computer software, reading and scanning devices and other accommodations to help people work, play, travel and maintain their independence.
In addition, the Foundation Fighting Blindness is funding, or helped make possible, several research projects to save and restore cone cells, which provide central vision. These include cone optogenetics, rod-derived cone-viability factor, gene therapies for AMD and Stargardt disease and cell-based treatments.
If you haven’t already, I suggest you register at FFB’s website to get the latest updates on these and other sight-saving research efforts.