Aug 29, 2013

The Pseudofovea: How the Retina Adapts to Central Vision Loss

Science Education

How the Retina Adapts to Central Vision Loss

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Diagram of the parts of the retina

The back of an eye photographed with an ophthalmoscope.

The most devastating vision loss from a retinal disease often occurs when the fovea — a 1.5-millimeter pit in the central retina — is affected. However, despite the loss of photoreceptors in the fovea, the retina has a remarkable, innate ability to adapt somewhat by developing a pseudofovea. A pseudofovea doesn’t arise from the generation of new photoreceptors. Rather, it is a new fixation point that helps stabilize vision and make the best use of a person’s surviving photoreceptors.

To better understand what a pseudofovea is, it helps to understand the role of the naturally occurring fovea. When it comes to good vision, there’s nothing as important as a healthy, full-functioning fovea. It is tightly packed with cones — the photoreceptors that enable us to perceive details, colors and objects in our central field of vision. But we also use it as our visual fixation point. When we gaze at a face, read a book or watch television, we use our fovea to fixate on the words and images of interest, so that they appear to remain stable despite the natural motion of our eyes.

So, it is no surprise that diseases affecting the fovea — such as age-related macular degeneration (AMD) and Stargardt disease — have a profound effect on vision. People with central vision loss from advanced cases of diseases like retinitis pigmentosa may also develop a pseudofovea to compensate for loss of their fovea.

When the fovea is compromised by disease or injury, the brain works, subconsciously, to find a position in the retina that it can use to develop a new fixation point — a pseudofovea — in a region of the retina with surviving photoreceptors. Many people develop multiple pseudofoveae, which may develop in different parts of the retina as degeneration progresses.

According to Gary Rubin, Ph.D., a low-vision researcher at the UCL Institute of Ophthalmology, many people with central vision loss from a macular disease develop a pseudofovea without any training or rehabilitation. In fact, most people aren’t aware that they have them, and he believes that’s a good thing.

Dr. Rubin’s research has shown that people with macular degeneration who unknowingly use their naturally occurring pseudofoveae — without training or rehab — experience the best results in reading tests. Patients in his study who were trained to use specific, alternate  pseudofoveae read less quickly. Dr. Rubin notes that training to use these alternates is “a knotty issue” because some physicians and low-vision experts believe it can be beneficial.

People with new foveal loss from AMD in Dr. Rubin’s studies typically developed  pseudofoveae within six months. However, a recent study from researchers at the University of Southern California (USC) found that normal-sighted young adults whose foveal vision was artificially obstructed to simulate macular disease developed a new point of gaze — like a  pseudofovea — in only three hours. The USC research team says the rapid gaze adjustment was surprising, and leads them to believe that training or practice might speed the adjustment.

People with vision loss — whether fovea-related or not — may benefit from a consultation from a low-vision expert to determine what, if any, accommodations or rehabilitation can be helpful in enhancing their visual experience or improving their quality of life. Everyone’s case is different, and many options, such as special glasses and scanners, are available.

The Foundation offers an online directory of retina doctors under the “resources” section of its website.