What you should know about: Amblyopia

Amblyopia, also known as lazy eye, is a condition where one or both eyes have impaired vision because the eyes and brain aren’t working together properly.  

In North America, it is estimated that amblyopia affects up to four per cent of the population and is one of the most common vision disorders in children. 

With amblyopia, the problem largely lies in the brain. Both eyes can see, but the brain has trouble processing the images seen by each eye and merging them into one cohesive image. As a result, the brain begins relying on one eye to see while ignoring the visual input from the other eye.  

Early intervention is important for optimal improvement of vision. Delayed treatment can lead to permanent vision loss and other problems in areas such as fine and gross motor skills and academic learning.

There are three main causes for amblyopia: 

• Strabismus (also known as crossed eyes): Happens when the eyes are not aligned with each other – one or both eyes may turn in, out, up or down. The brain will ignore the vision in the turned eye to prevent double vision.  

• Refractive errors: If there is a significant difference in the visual acuity (sharpness of vision) of the two eyes, the brain will rely on the better eye and ignore the one with lower vision. 

• Obstruction of vision: Occurs when something, such as a cataract or drooping eyelid, is physically blocking the eye from seeing properly. The visual acuity in the affected eye may be adequate but the obstruction prevents a full range of vision. As a result, the vision in the affected eye will decline as the brain depends on the unaffected eye to see.  

It can be hard for someone to know they have amblyopia, because with both eyes open, a person is typically unaware clearer vision is only being seen with one eye.   

While a crossed eye or drooping eyelid are visible signs of an issue, a high refractive error – that is, significant nearsightedness or farsightedness in one eye – may go undetected.  

Other signs to look out for include: 

• Poor depth perception – can appear as clumsiness or bumping into things (especially if it happens more on one side of their body) 

• Shutting one eye or squinting 

• Head tilting 

• Eye strain or headaches 

• Academic struggles  

Amblyopia can be diagnosed by your optometrist. During an eye exam, the vision in each eye will be measured to check for any significant differences. Your optometrist may use a Snellen chart to measure the visual acuity of each eye, or for young children and babies, other non-verbal eye charts are used. The optometrist may also look to see if a child reacts differently when each eye is covered – when the better seeing eye is covered, often children express frustration and try to pull off or look around the instrument used to cover their eye.  

Treatment for amblyopia can include glasses, patching the better-seeing eye and vision therapy (eye exercises to improve the vision of the poorer-seeing eye). Based on the type of amblyopia, the optometrist will determine the best treatment options for the patient. 

If the condition is unable to be resolved with glasses, there a few treatment options that involve physically blocking the stronger eye to re-teach the brain how to use the weaker eye. Some examples of such treatment include: 

• Eye patches: Opthalmic eye patches for amblyopia are similar to bandages in the sense that they are made of a fabric material with an adhesive backing. They can be used with or without glasses and are typically worn directly on the skin – although some are made to attach to glasses frames. Many patches come in fun colours and patterns to appeal to children. Depending on your child, they are worn between two and six hours during the day for months to years.  

• Eye drops: An alternative to eye patches, special eye drops can be used on the stronger eye to temporarily blur vision. The medication in these drops dilate the pupils, so children might also experience light sensitivity and irritation as side effects.  

If the cause of amblyopia is due to a droopy eyelid or a cataract, sometimes surgery is needed to first correct the underlying cause before efforts are taken to strengthen the weaker eye. 

While your child is going through amblyopia treatment, it is important to keep up with their follow-up visits and stick to their treatment plan, because reverse amblyopia may occur. As the weaker eye strengthens while the stronger eye is covered, the brain may begin to start over-relying on the original weak eye while the vision in the original strong eye begins to decline.

At the Waterloo Eye Institute, we have dedicated services for young children and people with special needs. If you are concerned about amblyopia, or if you’d simply like your child to have a routine check-up, comprehensive eye exams are available for children of all ages and abilities.  

We have a variety of tools and techniques we can use to gather information in whichever method is suitable for your child. For example, we have eye charts with picture icons, instead of letters, for children who don’t know the alphabet yet.  

Based on the recommendations of your optometrist, you can purchase ophthalmic eye patches from various retailers. Prices depend on the brand and quantity, but you can expect to pay between $15-$40.  

If your optometrist recommends eye drops for your child, you will receive a prescription to use at a pharmacy. Prices will vary depending on your insurance situation.  

Children under 19 years old are eligible for one Ontario Health Insurance Plan (OHIP)-covered comprehensive eye examination each year. Some follow-up visits are also covered.  

For visitors or children not covered by OHIP, as of August 2024, a comprehensive eye exam costs $120 and a follow-up visit costs $75. Discounts apply for children of University of Waterloo employees and students.  

The University of Waterloo School of Optometry and Vision Science is ranked fifth worldwide in research output for schools of optometry. Within the School, a variety of projects are underway to improve our understanding of and treatment for amblyopia.  

When eye patches are recommended, it can be hard for parents and children to adhere to the treatment protocol. Currently, Drs. Ben Thompson, Lisa Christian, Marlee Spafford and colleagues are working to improve adherence by using a social robot to educate and motivate children and their caregivers.  

Dr. Thompson is also extensively involved in research exploring how promoting neuroplasticity (the ability of the brain to rewire and adapt to change) can improve patient outcomes from brain-based visual disorders like amblyopia.  

Research investigating the use of movies and video games to encourage both eyes to work together is also showing promise for future amblyopia therapies.  

Interested in participating in research? Check out our current studies recruiting participants.