Understanding the effects of distorted vision in people with amblyopia

Perceptual visual distortions in human amblyopia and the effects of occlusion therapy

The most common cause of visual impairment in childhood is amblyopia or ‘lazy eye.’ Animal models of amblyopia have been developed, but little is known about the neural basis of the disorder in humans. This lack of neural characterisation severely hinders clinical efforts to provide an effective treatment or cure. Low-level deficits in amblyopia are well documented, but these have been shown to be insufficient to account for the perceptual distortions that occur. Current work has shown global processing deficits of both form and motion that cannot be attributed to poor visibility and raises the intriguing possibility that the perceptual anomalies reported in amblyopia may arise from anomalous higher-level integration processes, beyond striate cortex.

Recent animal studies show that correlated binocular vision is essential for successful recovery from experimentally induced amblyopia. The uncorrected monocular visual distortions in amblyopia de-correlate binocular vision, suggesting that they may play a critical role in both the development of amblyopia and outcomes of treatment that are currently overlooked.

This investigation examines visual distortions throughout the course of standard clinical treatment, without modification of therapy, in order to study their prevalence, their role in the prognosis of amblyopia treatment and the recovery of visual function in a juvenile population. The technology developed in this proposal will be applied in a computer game-based therapy that will be evaluated as a potential binocular approach to treatment.

The team was able to diagnose and measure distorted vision in children with lazy eye (amblyopia) for the first time, using a new 3D computer test. They found distorted vision is quite common in children with lazy eye (over half of the 80+ children we tested), even those who had equal vision in each eye after treatment and would be considered ‘cured’.

Unfortunately they were unable to identify an effective way to correct for these distortions to try and improve how the brain sees particular shapes (what’s known as ‘form vision’). This was because the distortions weren’t always just a case of seeing things in the ‘wrong’ position, but also because the objects moved around. This makes it hard to correct for the amount the position has shifted due to distortion, as it varies.

Most children will not be aware that their vision is distorted because the brain does a good job of ‘covering it up’ based on their knowledge of what something is supposed to look like, and the team didn’t find any bad effects that could impact on the results of treatment for lazy eye even when the children had severe distortions.

But the research shows that the current treatments for lazy eye might let your child read an eye chart easily with both eyes at the other end of it, but do not completely resolve the other problems with seeing that might occur with lazy eye, like distorted vision.

The distortions they found were closely linked to how well the eyes worked together (binocular vision, such as depth perception) and how big a squint (strabismus) or other drift of the eyes there was, if any. Children with better binocular vision and a smaller squint were less likely to have severe distortions of their vision. So lazy eye treatments focused on allowing the eyes to work together, or encouraging them to work together more than they used to, while still improving the vision in the lazy eye, may be a good direction to aim in for the future. Some researchers are already working on ‘binocular’ treatments for lazy eye using computer games.

• Piano MEF, Bex PJ, Simmers AJ. Perceptual Visual Distortions in Adult Amblyopia and Their Relationship to Clinical Features. Invest Ophthalmol Vis Sci. 2015 Aug; 56(9):5533–42.