The optic nerve is connected to the back of the eye near the macula, which is responsible for detailed central vision. When light enters the retina, the optic nerve sends electrical impulses to the brain where visual images are interpreted. When the optic nerve is deficient or absent, proper communication with the brain is impossible.
The term hypoplasia means smaller than normal. Optic Nerve Hypoplasia is a congenital condition resulting in the underdevelopment of the optic nerve. It is a lack of adequate development during gestation, not a hereditary condition.
ONH is the most common defect of the optic nerve. It is the third leading cause of blindness and visual impairment in children. It is a generally stable, non-progressive eye condition, and visual impairment ranges from mild to severe.
The cause of ONH is unknown. It has been associated with maternal diabetes, maternal alcohol use, maternal use of anti-epileptic medications, and young mothers (under age 20). It is not isolated to any particular race or socioeconomic group.
Almost half of children with ONH have associated brain abnormalities. Areas frequently affected are the corpus callosum and the septum pellucidum. The corpus callosum is comprised of more than 200 million nerve fibers that connect the left and right hemispheres of the brain and allow them to communicate with each other. The septum pellucidum is a fluid-filled sac in the midline of the brain, separating the right and left ventricles, and is responsible for regulating strong emotions such as pleasure and rage.
When both optic nerve hypoplasia and absence of the septum pellucidum exist, the condition is known as septo-optic dysplasia or de Morsier’s Syndrome.
The development of the pituitary gland, located at the base of the brain, is often affected. The pituitary gland is the master control gland for hormones, including growth hormones and sexual hormones.
Conditions associated with ONH are:
- Encephaloceles—failure of the neural tubes of the brain to completely close during fetal development, such that a portion of the brain protrudes through the skull
- Anencephaly—failure of the cephalic (head) end of the neural tube to close during fetal development, resulting in the absence of a major portion of the brain and overlying bones of the skull
- Cerebral atrophy—loss of neurons and the connection between them
- Thyroid dysfunction
- Adrenal dysfunction
- Insufficient levels of growth hormones, which stimulate growth and cell reproduction in humans
- Insufficient levels of anti-diuretic hormones, which conserve body water by reducing the loss of water in urine
- Tumors (rarely)
In ONH, one or both eyes may be affected, and the degree of severity in each eye may be different. Color vision is usually normal in ONH versus the loss of color vision that can occur in optic nerve injuries later in life.
Common symptoms are:
- Photophobia (light sensitivity)
- Lack of perception of visual detail
- Low peripheral vision
- Lack of depth perception
Infants and children with ONH often have Nystagmus, a rapid, jittery movement of the eyes. They may also demonstrate autistic behavior or sensory integration dysfunction. They may be extraordinarily sensitive to certain sounds, textures, and smells, or exhibit behaviors such as body-rocking, hand-flapping, or head-banging.
ONH cannot be cured. Because it is a nerve and brain development issue, prescription eyeglasses cannot correct vision loss as with other eye conditions. Treatment is highly individualized, depending upon the mix of medical problems in a specific child. Treatment often includes Occupational Therapy to reduce sensory integration problems. If vision loss is severe, children can be taught Braille and other daily living skills for the blind.