An accurate and fun test for visual acuity in toddlers

Study lead, Professor emerita Susan Leat, of the School of Optometry and Vision Science at the University of Waterloo, told OT that current vision tests for children under the age of three use a preferential looking technique.

“For example, you hold up a card and there are stripy lines on one side and nothing on the other side. And if the child can see the stripy lines, they will make an eye movement to that,” she explained.

Leat shared that this test measures a different type of acuity to the type of acuity which is measured in adults through the letter test – also known as Snellen acuity.

“We call this resolution visual acuity. It’s the ability to detect that the stripes are there, and not particularly to tell you know what shape you’re looking at,” she said.

Leat highlighted that this type of test does not correlate well with the letter test, which is called recognition acuity, and is also less sensitive for detecting conditions such as amblyopia.

She added that the full preferential looking tests can be relatively expensive to buy.

The Waterloo Differential Acuity Test (WatDAT) – which was developed with funding from Fighting Blindness Canada – assesses recognition visual acuity among toddlers from the age of 18-months.

“We wanted to be able to measure visual acuity more accurately in younger children, and in a way that is equivalent to the letter test in adults,” Leat explained.

WatDAT involves showing young children four shapes. Three of the shapes are identical, with the child directed to point at the shape that is different.

The test is performed with progressively smaller shapes until the child can no longer identify the shape that is different.

The research team has developed both a digital and paper-based form of the test, which is currently undergoing beta testing at clinical sites in Canada, the US, and the UK.

“We’ve got some very positive feedback so far, and so that will help us when we hopefully work with a company to commercialise it,” Leat said.

She added that early feedback suggests the paper-based version of WatDAT may be easier to incorporate into a clinical routine, so this is likely to be the form that is commercialised.

Leat shared her hope that the test would make assessments of visual acuity in young children more accurate.

“Visual acuity is a really important component to an eye exam. Visual acuity is one of the key measurements that we use to detect eye disorders or to decide whether to treat, and also to monitor treatment,” she emphasised.

She added that early detection is key when it comes to eye disorders in children, and an early complete eye examination by an optometrist can help to identify these disorders.

Leat shared that these disorders are often not discernable by observing a child’s behaviour.

“Children themselves don’t complain of poor vision because they don’t really have anything to compare it against,” she added.

“If these types of disorders go untreated or uncorrected, they can interfere with a child's learning at school, as well as their future level of vision,” Leat said.

“The earlier you treat some of these types of disorders, the better the final outcome is,” she emphasised.

Researchers have described the performance of WatDAT and compared it with two commercially-available in Ophthalmic and Physiological Optics.