Lazy eye, which is also known as amblyopia, is a condition that the vision in one eye is reduced, believed to be caused by abnormal visual development during childhood. The physical appearance of the amblyopic eye is normal. Vision loss occurs because the nerve pathway between the brain and the eyes aren’t properly stimulated.
How does amblyopia affect vision?
Normally, the images each eye sends to the brain are identical. When they differ too much, the brain learns to ignore the poor image sent by one eye and “sees” only with the good eye. If it’s left untreated, a child’s vision will never develop correctly in the affected eye. This is because as the child’s brain matures, it will “ ignore” the image coming from the poorly seeing eye.
How common is amblyopia?
Amblyopia is the most common cause of visual impairment among children, affecting approximately 2 to 3 out of every 100 children. It is also the most common cause of monocular (one eye) visual impairment among young and middle-aged adults.
What Causes Amblyopia?
Amblyopia can result from any condition that prevents the eye from focusing clearly. It can be caused by:
1. Constant misalignment of the two eyes (strabismic amblyopia)
This is the most common cause of amblyopia. With strabismus, the eyes can cross in (esotropia) or turn out (exotropia). When the eyes are misaligned, the straight or straighter eye may become dominant. To avoid double vision caused by the poorly aligned eyes, the brain ignores the visual input from the misaligned eye, leading to amblyopia in that eye.
2. Difference in sharpness of vision between the eyes ( refractive amblyopia).
Sometimes, amblyopia is caused by unequal refractive errors in the two eyes, despite perfect eye alignment. For example, one eye may have significant uncorrected short-sightedness (myopia), long-sightedness (hyperopia), or astigmatism, while the other eye does not. The brain will ignore or suppress the vision of the blurry eye. If this goes on for months or years in a young child, the vision in the eye that sees the blurry image will deteriorate with time.
3. Stimulus deprivation amblyopia
This is lazy eye caused by something that obstructs light from entering and being focused in a child’s eye, such as congenital cataract, corneal ulcer or scar, ptosis (droopy eye lid), eye injury. Again, the brain will ignore the blurry eye and stops using it resulting in amblyopia
What are the signs/symptoms of amblyopia?
Amblyopia usually has few symptoms. Most children with amblyopia do not complain of vision problem. Younger children are often unaware about visual impairment of one eye. Older children may complain that they can’t see well through one eye and have problems with reading, writing and drawing.
It’s usually the parents or teacher who notices that a child is struggling with a vision problem, as those children tend to cross their eyes, squinting or tilting their heads in order to see better.
One way to check your child’s eyes is to cover each eye with your hand, one at a time. They may feel unease when the good eye is covered, but may not mind if you cover the lazy eye. If they try to push your hand away from one eye but not the other, it may be a sign that they can see better out of one eye.
Dr. Wong Ching Lin is an ophthalmologist currently working in Penang General Hospital Ophthalmology Department and is registered with the National Specialist Registry of Malaysia. She obtained her medical degree from University Kebangsaan Malaysia (UKM) in 2004. Dr. Wong started her training in ophthalmology in Penang General Hospital, later in Kuala Lumpur General Hospital and UKM Medical Center. After completed her Master of surgery in Ophthalmology from UKM in 2012, she started to work as a specialist in Penang General Hospital until now. She provides treatment to a broad range of eye conditions which include cataract, eye infection and inflammation, eye injuries, paediatric eye assessment, lazy eye, general eye diseases like glaucoma, pterygium, diabetic retinopathy and other medical retinal disorders. She also involved in research projects and wrote for publications. Dr. Wong has actively taken part in the teaching of medical students, trainees and allied health personals.