If one eye is weaker than the other, such as in the case of a lazy eye, one method that is used to train the brain to work with both eyes in an optimal manner is patching. This means the stronger eye is closed with a patch, forcing the brain to learn to work with the weaker eye. This method presents advantages and disadvantages. The main challenge with this approach is the fact that we shut down the functionality of the stronger eye for a period of time with the goal of strengthening the weaker eye. This could compromise the stronger eye since it doesn’t get used for some time. Once we stop using the patch, then the brain needs to relearn how to use both eyes together simultaneously which could present a challenge.
There is a wonderful alternative to patching and that is monocular fixation in a binocular field, in short MFBF. This allows both eyes to be open while training and strengthening only one eye at a time, avoiding the need to shut one eye off. In order to achieve the MFBF effect, filters are used. For example, during a vision therapy session, a child is given the task of completing a maze on a paper by tracing the right path to the way out using a red marker. In that case, we would place a green filter in front of the lazy eye or weaker eye that we are working to strengthen. Since there’s a green filter in front of the eye, this specific eye is still able to view the target and perform the task of completing the maze. The other stronger eye which does not require training at the moment, is open however there is a red filter placed on top which prevents this eye from seeing the target. It means that both eyes are open but the weaker eye must meet the challenge to complete the task all on its own. By keeping both eyes open but using filters, we can control which eye is receiving the strength training and which visual signals the brain is able to perceive.
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