Lazy eye is also known as Amblyopia. Lazy eye is an early childhood condition where a child's eyesight in one eye does not develop as it should. The problem is usually in just one eye, but can sometimes affect both of them.
When a patient has amblyopia the brain focuses on one eye more than the other, virtually ignoring the lazy eye. If that eye is not stimulated properly the visual brain cells do not mature normally. In the USA and UK amblyopia affects approximately 2% to 3% of all children. It is the most common cause of partial or total blindness in one eye (monocular blindness) in the USA.
The term lazy eye is inaccurate, because the eye is not lazy. In fact, it would probably be more accurate to say lazy brain, because it is a developmental problem in the brain, not an organic problem in the eye. What are the symptoms of lazy eye? A child with lazy eye will not be able to focus properly with one of their eyes. The other eye will make up for the problem, so much so that the affected eye suffers as a result. The eye with impaired vision (amblyopia) will not receive clear images; the brain won't receive clear data, and will eventually start to ignore it.
In many cases the brain and the good eye make up for the shortfall so well that the child does not notice he/she has a problem. That is why lazy eye is often first detected after a routine eye test.
The signs and symptoms of a lazy eye may include:
- Blurred vision
- Double vision
- Poor depth perception (of vision)
- Eyes do not appear to work together
- A squint (either upwards, downwards, outwards, or inwards).
It is important for a child to have a Eye Exam. In most countries the first eye exam occurs at the age of 3 to 5 years. It is especially important to have an early eye check if there is a family history of crossed eyes, childhood cataracts or other eye conditions. Parents who see their child's eye wandering after they are a few weeks old should tell their doctor.
What causes lazy eye?
Anything that causes a child's eyes to cross or turn outward, or something that blurs their vision can provoke lazy eye. Below are examples of some possible causes:
- An imbalance in the muscles that position the eye - strabismus - causing them to cross or turn out. The muscle imbalance undermines the two eyes' ability to track objects together (move in harmony with each other, in a synchronized way, to be aligned). Strabismus may be inherited; it could be the result of long- or short-sightedness, a viral illness, or an injury.
- Anisometropic amblyopia - a refractive error occurs due to myopia (short-sightedness), hypermetropia (long-sightedness), or astigmatism (the surface of the lens is uneven, causing blurred vision). A refractive error means light changes direction after going through the lens differently in each eye. A child with anisometropic amblyopia will be more long-sighted or short-sighted in one eye than the other, resulting in amblyopia developing in the eye that is affected more.
- Stimulus deprivation amblyopia - this is the most uncommon form of amblyopia. One eye (or sometimes both) is prevented from seeing, and becomes lazy. This could be due to:
A corneal ulcer, a scar, or some other eye disease
A congenital cataract (baby is born with clouding of the lens)
Ptosis (droopy eye lid)
How is lazy eye diagnosed?
Vision problems, any level of blindness in one eye - amblyopia - ideally, needs to be detected before the child is six years old. Diagnosis can sometimes be made a long time after the onset of problems, especially if the child is unaware that there is something wrong with his/her vision.
Routine eye examination
In developed nations children have their first eye examination between the ages of 3 and 5 years, or before they start school. This means that most cases of amblyopia are diagnosed, and subsequently treated in developed nations.
If the optometrist suspects the child has lazy eye further tests will be carried out before a diagnosis is reached. Each eye is tested separately to determine whether there is any short- or long-sightedness, and how serious it is. The child will also be carefully tested to determine whether there is a squint.
The eye test will also determine whether the child has astigmatism or any other abnormality.
Source: Medica News Today, Christian Norqvist