Getting accurate results from younger children with vision problems is notoriously difficult, but a new technology may make the process easier.
If kids aren’t yet talking, a particular challenge is diagnosing amblyopia, commonly known as lazy eye. This has several causes. Perhaps the eyes don’t line up as they should (strabismus), or one has much better focus than the other because of astigmatism. The end result is the same. If a child’s brain receives a blurry image from one eye and a clear one from the other, it will start to ignore the blurry one. Over time, the vision in the neglected eye will get worse.
Jason Turuwhenua is a researcher who works at the Auckland Bioengineering Institute and the department of optometry and vision science at the University of Auckland. For the past decade, he has been involved in developing a tool to diagnose lazy eye more easily in very young children.
The condition affects one in 25 kids and typically begins in infancy or early childhood. It is much tougher to treat after the age of seven, as the brain has become locked into relying on the better eye.
Symptoms can be hard to spot, so a traditional way of checking for it has been testing for visual acuity using an eye chart. Rather than the Snellen chart, which requires the ability to recognise alphabetical letters, younger kids have charts with shapes and pictures, but even so, if they are under the age of three, getting an accurate result for lazy eye has been considered almost impossible.
The new test is screen-based. “The idea is that a child will look at a television and be shown patterns moving across it that are specifically designed to induce an eye movement called optokinetic nystagmus,” says Turuwhenua.
Optokinetic nystagmus is a complex nervous-system reflex that involves a sawtooth motion of the eye. It is the way we stabilise a moving image on the retina and it happens quite noticeably if we are on a train and staring out of the window.
“When you look out into a scene from a moving train, your eyes are moving along with the scenery, and your brain is what is making them do that,” he says.
Examples of the involuntary repetitive eye movements of “train nystagmus” can be found on YouTube. The new screening tool recreates the same effect with moving patterns on the screen, which are interspersed with animations in a bid to keep a child’s attention.
In children, optokinetic nystagmus is subtler than in adults, but if it isn’t happening normally it indicates a vision problem.
Treatment options for kids with amblyopia include patching the good eye to force the brain to pay more attention to the visual input from the lazy one. This creates neural change and helps normal vision develop. Atropine eye drops and special contact lenses can also be used to create the same effect. In some cases surgery may be necessary to fix the original cause of the problem.
Even in adults, there are methods now to improve vision loss caused by amblyopia. “But the evidence is get in before the age of three and there’s a better chance of a good outcome,” says Turuwhenua.
The new test is a big step up from older tools such as the optokinetic drum, which has black and white stripes and spins around in front of children. This approach is easy to misuse – distance is an important factor, for instance – and not as sensitive or objective. “We’ve given it a 21st-century update.”
A trial with 200 children has been encouraging and there is international interest in the new technology, with larger trials now running in the US and China. The hope is the test will be more widely available next year.
“As far as we’re aware, it is unique,” says Turuwhenua. “It would be great if it proves to be a solution and becomes a standard, regularly used tool.”
This article was first published in the September 14, 2019 issue of the New Zealand Listener.