Normal Visual Development
by Lisa C. Verderber, MD
Reprinted from VIPS News, 12/6, Nov./Dec. 1996, a publication of Visually Impaired Preschool Services, Louisville, Kentucky.
Editor's Note: Dr. Verderber is with Mahl and Associates Eye Care Center in Louisville. She completed her fellowship in pediatric ophthalmology at the Children's National Medical Center in Washington, DC. Her residency in ophthalmology was done at Northwestern University.
At birth vision is quite poor. A normal baby can see only large objects moving in front of his face. This poor vision is due mainly to immature visual centers in the brain. These visual centers mature as the eye is stimulated with visual input. During the first three months of life there is a very rapid improvement in vision. These first few months are so important that they are known as the critical period of visual development. The development of good vision is dependent on well-focused images during this time. If there is an abnormality in the eye that precludes this focused image, these important visual centers in the brain will not develop. This is why it is so important to recognize correctable conditions that interfere with vision in this early period.
Addressing vision problems early may prevent a lifetime of poor vision. Some of these difficult problems can be corrected. For example, a congenital cataract can be removed. A severe corneal problem can generally be treated early in life. Unfortunately, all conditions that cause decreased vision are not reversible. Structural problems in the optic nerve, for example, can not generally be remedied. The optic nerve consists of over a million axons which extend from the retina to the visual centers in the brain. At the present time we do not have the technology to repair most problems associated with the optic nerve. Though some retinal problems such as retinal detachments may be treated, there are many conditions of the retina that cannot be treated. Severe structural problems such as these will result in permanent visual impairment. The degree of impairment depends on the degree of abnormality.
The visual system in children continues to be flexible throughout the first eight years of life. During these first eight years amblyopia can develop. Amblyopia is a decrease in vision caused by abnormal visual stimulation. Therefore, anything that interferes with a clear retinal image in the first eight years of life may lead to decreased vision. The earlier in life that the stimulation is abnormal, the greater the visual deficit. This helps explain why visual problems in children can be more devastating than a similar problem in an adult. A congenital cataract may lead to a lifetime of decreased vision if it is not removed within the first few weeks. A cataract that develops in an adult does not lead to permanent visual impairment. Since the visual system in an adult is mature, good vision will return when the cataract is removed, even if it has been present for years. As another example, a child who is extremely farsighted but does not receive glasses in the first eight years will have a permanent decrease in vision, even if the glasses are prescribed later in life. An adult who develops far-sightedness will have blurry vision without his glasses, but no permanent visual impairmentgood vision will return when he puts on his glasses. This stresses the importance of screening for and correcting visual problems in children as soon as possible.