At birth, a baby's vision is approximately 20/400, or the level of the big E on the eye chart. Ideally, as children grow, their vision steadily improves, so that sometime between the ages of 3 and 6, both eyes will have 20/20 vision. However, developing good vision is a complex process, and there are several common conditions that can disrupt the normal development of a child's vision.
After birth, the area of a child's brain that processes vision is still developing, and continues to do so until the age of 8 or 9. During this time, the brain develops new nerve connections from the brain to the eye, which causes the vision to gradually improve. However, in order for the brain to establish these new connections, it must receive an image from the eye which it can interpret properly. This means that the image must be in focus, and both eyes must be working together well in order for the brain to create these new connections and improve vision.
A child can be born with nearsightedness, farsightedness or astigmatism, or develop these conditions at any age. It is important that these conditions are detected as early as possible and properly corrected so that a child's vision is able to develop normally.
Amblyopia is the single biggest threat to normal vision development, and the most important reason your child needs to have an eye examination by age 3.
Amblyopia (pronounced 'am-blee-oh-pee-ah', commonly called 'lazy eye') results when the image received from one eye cannot be interpreted properly by the brain, so the brain stops creating new nerve connections to that eye, halting vision development at a sub-normal level. There are several reasons why one eye may have a poor image relative to the other, but the two most common reasons are:
If the eyes have different prescriptions, and this is not corrected with lenses, one eye is more in focus than the other. Therefore, the brain will continue developing normal nerve connections to the better eye, but stop developing new nerve connections to the eye that is out of focus. This will result in the development of normal vision in the better eye, and sub-normal vision in the more out-of-focus eye, which cannot be corrected with lenses.
If one eye is crossed, or turns out or upward, a child would see double, unless the image from one eye is ignored. In fact, this is exactly what the brain does; it supresses the image from the turned eye so that it is only using the image from the straight eye. The brain will therefore continue developing normal nerve connections to the straight eye, but stop developing new nerve connections to the eye that is turned. This will result in the development of normal vision in the straight eye, and sub-normal vision in the turned eye, which cannot be corrected with lenses.
Amblyopia can be successfully treated, but this must be done as young as possible (ideally by age 3) in order for the treatment to be effective. Because the vision loss in amblyopia is only in one eye, it is seldom noticed by either the child or the parents. This unfortunately results in many cases of amblyopia being detected too late or not at all, leaving the child with a lifetime of poor vision.
Be sure to have your child's eyes examined by age 3, even if you do not suspect any problems and even if there is no family history of eye problems.