Normal Visual Development

Normal Visual Development

Normal Visual Development

by Lisa C. Verderber, MD

Pediatric Ophthalmologist

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 impairment—good 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.