Karen Mcmain Orthoptist, Dalhousie University, Canada
Recently, orthoptist Karen McMain from Dalhousie University, Canada, visited Tun Hussein Onn National Eye Hospital (THONEH) to train and share her experiences with local eye care specialists. Despite her busy schedule, Ms McMain managed to find some time to share with us some insight on lazy eye.
HT: In the old days, lazy eye was considered by superstitious people to be a “curse” or the result of sinister supernatural forces. What is lazy eye, actually?
KM: Lazy eye, also known as amblyopia, is a common childhood eye condition in which a child's sight in one eye does not develop as it should.
I personally feel that the term “lazy eye” is inaccurate, as the eye is not really lazy. It would be more accurate to say “lazy brain” as amblyopia, the medical term for lazy eye, is actually a developmental problem within the brain.
What happens is that, normally, the brain and the eyes work together to produce vision. When a child has amblyopia, the brain does not acknowledge the vision from the lazy eye and focuses on the vision from the other eye. If the lazy eye is not stimulated properly, the visual brain cells do not mature normally.
HT: What are the causes of this condition?
KM: Most commonly, it is due to the misalignment of the two eyes – a condition called strabismus. As a result of strabismus, the eyes are not aligned in the same direction, the eyes can cross in (esotropia) or turn out (exotropia). This misalignment prevents the eyes from focusing together on an image and may cause double vision. To overcome the double vision, the child's developing brain chooses to ignore the image from the eye that is not straight, causing the vision in that eye to become lazy.
Differences in the way each eye processes vision can also be a factor, such as when one eye suffers from nearsightedness, farsightedness or astigmatism.
Sometimes but very rarely, the condition can also be caused by obstruction or cloudiness that prevents light from getting through one eye. Such obstructions can be due to cataract, eye tumours or droopy eyelids. Such amblyopia is called deprivation amblyopia.
HT: What happens if the condition is left untreated?
KM: Amblyopia is the most common cause of partial or total blindness in one eye, affecting 3% of children. Studies have shown that sufferers also face a significantly higher risk of losing vision in their good eye, either from injury or eye disorders such as macular degeneration.
HT: What are the treatment options for this condition?
KM: The most common treatment for amblyopia is to force the brain to start using the ‘bad’ eye.
This is done by first correcting any underlying problem in that particular eye. Then, we either put a patch over the ‘good’ eye or blur the vision in the ‘good’ eye with eye drops, to force the ‘bad’ eye to be used. The eye drop method is less commonly used in countries like Malaysia, which has a very sunny climate, as these drops dilate the pupil making the eye very sensitive to bright light.
Treatment is often helped by having the ‘bad’ lazy eye do periods of close work such as drawing or reading. The child will wear a patch over the ‘good’ eye during these activities.
Most children with amblyopia will also need glasses to help them focus their vision.
The doctor will discuss with parents what treatment is most appropriate for their child and their type of amblyopia.
HT: Do you have any advice for parents worried about their children’s eye health?
KM: I recommend all children to be screened for amblyopia, preferably at specialist centres, before they are school-aged. Young children have the greatest potential for successful treatment even though recent studies show that treatment in older children can also improve their vision.