Optic Nerve Hypoplasia

Optic Nerve Hypoplasia

The optic nerve serves as a connector, carrying visual information from the eye to the brain.  Those that have optic nerve hypoplasia (ONH) have an underdeveloped optic nerve in one or both eyes. Typically each optic nerve has about 1 million connections.  However, those with optic nerve hypoplasia have far fewer connections.  Optic nerve hypoplasia is one of the three most frequently diagnosed visual impairments in children in the United States.  

Often associated with optic nerve hypoplasia are hormonal deficiencies. Therefore, it is critical for a child to be seen by an endocrinologist at the time of diagnosis and then followed up regularly as hormonal deficiencies can develop at any time. The ophthalmologist may also recommend an MRI and/or CT to check for any brain abnormalities, which are also associated with ONH.  In some cases children have a poorly formed or missing septum pellucidum (area in the brain that divides the ventricles).  This is referred to as septo-optic dysplasia (SOD) or DeMorsier's syndrome.  Other areas of the brain may also be affected.

Visual and Behavioral Characteristics of Optic Nerve Hypoplasia

• Vision loss can range from moderate to no light perception
• May have a lack of detailed vision and depth perception
• Nystagmus (involuntary movement of the eyes) may develop around 1 to 3 months
• Strabismus (eyes that do not align in the same direction) may occur
• May be sensitive to light (photophobia)
• ONH is a stable condition.  Vision will not deteriorate; however, you may see an improvement in vision and reduced nystagmus as a result of maturation process of the brain
• If one eye is affected more, patching of the stronger eye is usually recommended to prevent vision loss in the weaker eye
• Color vision is usually normal
• May occur by itself or along with neurological and/or hormonal abnormalities
• Feeding issues as a result of hormonal problems, or a lack of interest in food due to absent or diminished sense of smell and taste.  The child may also exhibit lip smacking while eating.
• Inattentiveness and irritability might be due to low blood sugar (hypoglycemia)
• Poor growth due to hormonal defects may be associated
• Many children with ONH/SOD also have Sensory Integration Disorder, most are tactilely and orally defensive, and some have hypersensitivity to sound.

Diagnosing Optic Nerve Hypoplasia

Using an ophthalmoscope, an ophthalmologist can diagnose optic nerve hypoplasia by looking inside the eye at the front of the optic nerve, called the optic disc.  If the child has ONH, the optic disc will appear smaller than normal.  Ophthalmologists can usually tell your child's ability to see based on the size of the optic disc.  The larger the optic disc is, the better the vision will be. 

Causes of Optic Nerve Hypoplasia

Optic nerve hypoplasia is a congenital defect. It is thought that there may be an exaggeration of the natural dying of nerve fibers as the child develops in utero.  For the majority of cases there is no known cause for why this condition occurs.  A few cases have been associated with young maternal age (under 20 years of age), maternal diabetes, maternal alcohol use, and maternal anti-epileptic drug use. ONH affects all races and socio-economic groups. 

Strategies to Deal with Optic Nerve Hypoplasia

• To help alleviate the effects of light sensitivity adjust lighting levels, have the child sit with his/her back to windows, use a hat or sunglasses, minimize glare on surfaces
• Help develop the aspect of depth perception by using fine and gross motor activities (container play, nesting and stacking, climbing stairs, cardboard box play)
• Present toys and objects in the child's preferred visual field
• Make sure the child is routinely followed by an endocrinologist as hormonal deficiencies can develop at any time 

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