How can we improve the treatment of amblyopia or 'lazy eye'?

Dr Sarah Waugh, FST
Answer: By refining eye test charts so that they are much more effective in detecting it as early as possible

Dr Sarah Waugh is a Reader in Vision Science and Research Coordinator at our Faculty of Science and Engineering. Sarah's principal research interests are in spatial vision and amblyopia using tools of psychophysics, visual electrophysiology and eye movement recording. Her clinical and research interests are in paediatric and binocular vision.

How did this work come about?
A clinician by background, I am always looking at how the research I do can be directly applied to optometry, and particularly to the treatment of amblyopia, or lazy eye.

What is lazy eye and how is it treated?
It’s not a problem with the eye itself, but a problem in how the brain combines information from the two eyes. Where the images coming to the brain from the eyes are different, for example because one eye is slightly turned, or the image from one is more blurred than the other, the brain is not able to combine those two images into one. To compensate, it will ignore, or suppress, one image: so a person with amblyopia is effectively only using information from one eye, making it harder to do tasks requiring two-eyed (binocular) precision, such as threading a needle, pouring a glass of water or appreciating 3D movies. The earlier we can accurately detect lazy eye, the more effective treatment can be. We need to catch it while a child’s brain is still developing (the sooner the better, but well before the age of eight) so that we can retrain the brain to use information from both eyes. We put a patch over the ‘good’ eye and force the brain to pay attention to the images coming from the ‘lazy’ eye, or we use specially-designed viewing tasks.

What difference might your research make to the detection of lazy eye?
We looked at the effectiveness of commercially used eye charts, and found simple ways in which they could potentially be fine-tuned to aid more accurate detection. When we look at an object, our ability to see it is affected by what else is around it. It’s harder to see something that has a lot of clutter or crowding, and this is particularly the case for a person with amblyopia, so it’s a useful test. The best way to create a crowding effect on a chart is to surround the target letter with other letters, but although this is already being done on commercial eye charts, we found that if the gap between the letters was just a little smaller, the tests could be much more sensitive, revealing a bigger difference in functioning between the two eyes.

A person with normal vision is able to define an object from its background not only on the basis of differences in colour or brightness (a black dog in front of a white wall, for example) but also through a complex calculation of levels of contrast. This calculation occurs in a higher place in the brain and relies on information from both eyes, and so it functions less well in a person with amblyopia. We found through our research on visible letters that the crowding effect was also stronger. Therefore an eye chart that uses optimum crowding positions and tests the ability to calculate contrast differences could be able to pick up issues in this part of the brain too. These findings taken together could make testing for amblyopia more robust, helping us to detect and treat it earlier and therefore more effectively. It’s not a problem with the eye itself, but a problem in how the brain combines information from the two eyes.

What are the next steps in your research?
There is still work to do on the best vision chart arrangements for young children. Our predictions are that children with amblyopia who have a turned eye will be better detected with an improved chart. There is also a need to develop a good crowded test for children under three years of age.

Research matters

What inspired you?

The quest to better understand normal vision; why and how it goes wrong. The potential to optimise visual outcomes in children if we detect conditions early.

Any surprises?

The finding that simple changes to letters or symbols and to their spatial arrangements can have such an impact on detecting losses in spatial vision and on monitoring how they improve with treatment. New understanding of how vision is processed in the brain could help make clinical tests more sensitive and lead to earlier detection of lazy eye, explains Dr Sarah Waugh

Why does this research matter?

A better understanding of how normal neural processing works in vision can lead to the development of better clinical tests for detecting visual anomalies, and to a more sensitive monitoring of disease and treatments, especially in children.

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