Optic Nerve Hypoplasia - Symptoms, Risks Factors, and Treatment.

What Is Optic Nerve Hypoplasia?

Optic nerve hypoplasia (ONH) is a clinical condition characterized by a lowered number of optic nerve axons. It can affect unilaterally or bilaterally. It may present as a single defect or be associated with midline cerebral structural defects like the absence of septum pellucidum, corpus callosum may be not formed, and weaknesses in the cerebral hemisphere or pituitary gland. Septo–optic dysplasia (SOD), also known as de Morsier syndrome, is the term that describes the association between ONH and the absence of septum pellucidum, decreased levels of pituitary hormones, and lack of formation of the corpus callosum. It is clinically present as visual impairment, hypopituitarism, and delay in development.

Another syndrome named Gillespie syndrome is a genetic disease that constitutes a triad of cerebellar ataxia, aniridia, and intellectual disability. It is sometimes associated with other findings in the eye, like ONH. ONH can involve either the superior segment or the nasal quadrant. ONH involving the superior segment is called superior segmental optic nerve hypoplasia (SSONH). ONH, which only affects the nasal quadrant, is called nasal optic disc hypoplasia. It is the third most prevalent disease, resulting in vision impairment in children less than three years of age.

Other conditions that mimic this condition include:

• Optic nerve atrophy.

• Optic nerve coloboma.

• Morning glory disc anomaly.

• Peripapillary staphyloma.

• Tilted disc syndrome.

• Glaucoma.

Which Visual Issues Are Connected With Optic Nerve Hypoplasia?

ONH can cause vision impairment in one or both eyes, ranging from mild (20/20) to severe (blindness). Nystagmus can occur in unilateral or bilateral cases. If OHN affects only one eye, further amblyopia-related vision loss could occur. In addition, ONH raises the risk of strabismus.

What Are the Risk Factors of Optic Nerve Hypoplasia?

A hypothesis used to describe ONH mentions that the disruption of vascular structures causes it. It is primarily present in the proximal trunk of the anterior cerebral artery.

The following risk factors support this hypothesis:

1. Increased bleeding in the first trimester.

2. Smoking during pregnancy.

3. Young maternal age.

4. Diabetes-affected mother.

5. Preterm labor.

6. Primiparity.

Apart from these, the following factors can also contribute to the risk of developing this condition:

1. Low maternal weight gain.

2. Weight loss in mothers during the first and second trimesters.

3. Alcohol consumption by mothers.

4. Recreational drugs.

5. Usage of anticonvulsants and antidepressants.

6. Viral infections during pregnancy.

What Are the Signs And Symptoms of Optic Nerve Hypoplasia?

Signs:

• The optical disc looks pale or gray and is almost half the size of a standard optic disc.

• Optic discs often have a double ring sign, a yellow to a white ring around the disc.

• Change in diameter of the optic disc.

Symptoms:

• Visual acuity ranges from normal to light perception.

• Defects in the visual field, mostly localized defects associated with visual field constrictions, are more common in nasal or inferior areas.

• This condition can be present unilaterally or bilaterally and symmetric or asymmetric.

• Unilateral and asymmetric bilateral ONH has pupillary defects.

• Bilateral ONH presents with congenital sensory nystagmus (involuntary rapid eye movements) at one to three months of age, followed by strabismus (crossed eyes) at one year old.

• Strabismus often occurs in asymmetric or unilateral cases.

• Hypothalamic Dysfunction: It is the most commonly occurring non-optic condition in ONH cases. The prevalence is 69 percent in unilateral cases and 81 percent in bilateral issues.

• Pituitary Abnormalities: The prevalence of optic nerve hypoplasia is 13 to 34 percent.

• Endocrine Abnormalities: These are related to the absence of the infundibulum, which leads to poor or lack of communication between the hypothalamus and the anterior pituitary.

Various hormonal dysfunctions have also been reported, which are as follows:

• Growth hormone deficiency.

• Moderately increased level of serum prolactin.

• Hypothyroidism.

• Adrenocorticotropic hormone deficiency leads to hypercortisolism.

• Diabetes insipidus.

How Can Optic Nerve Hypoplasia Be Diagnosed?

When individuals visit their physician, they are asked questions to assess their personal and family histories and the signs and symptoms they face. Following this, a physical examination is performed. The physician might also ask for various laboratory tests to diagnose the condition if necessary.

• Magnetic Resonance Imaging (MRI): Magnetic resonance imaging (MRI) tests are advised to assess soft tissues in patients suspected of ONH. The findings on MRI show the diameter of the intracranial optic nerve, and the optic chiasm appears thin. Also, the presence of midline abnormalities can be observed in MRI, which helps in clinically confirming the diagnosis of SOD. MRI brain is also recommended for those who have been established with ONH. This helps evaluate hydrocephalus, corpus callosum hypoplasia, schizencephaly, or polymicrogyria. A neurological examination should be conducted if the findings are positive in the MRI brain.

• Optical Coherence Tomography (OCT): Another practical test in measuring the foveal parameters and diagnosing ONH is Optical coherence tomography (OCT). However, the diagnosis of ONH is not possible purely through radiographic measurements.

• Ophthalmic Examination: The following evaluation is an ophthalmic examination. This is recommended for all neonates suffering from jaundice and recurrent hypoglycemia. These conditions can be early signs of hypothalamic dysfunction. Also, an ophthalmic evaluation is recommended for infants with poor visual behavior, strabismus, or nystagmus by three months.

• Evaluation of Hormones: Endocrine and pituitary functions should be evaluated regardless of the condition of the septum pellucidum. The tests done to assess the endocrine system are fasting morning cortisol and glucose, TSH (thyroid-stimulating hormone), and growth hormone surrogates like IGF-1, IGFBP-3, LH (luteinizing hormone), and testosterone if the baby is less than six months old.

How Can Optic Nerve Hypoplasia Be Managed?

Early diagnosis helps in better treatment and a better prognosis. All ONH patients with central nervous system defects or endocrinopathies can benefit from the help of a multidisciplinary team of physicians, including a neurologist, neurosurgeon, endocrinologist, and various other specialists from departments like occupational, physical, and speech therapists.

Management depends on the diagnosis and signs and symptoms. After treatment, the follow-up regime should be strictly followed. The recommended follow-up is semi-annual for those suffering from growth patterns and annually for those having visual defects. Also, surgical correction can be considered in those with strabismus, who have symmetrical functional vision in both eyes and the potential to develop binocularity.

What Is the Prognosis of Optic Nerve Hypoplasia?

Optic nerve hypoplasia is incurable, but it is not a progressive disorder, and vision does not typically deteriorate. However, each patient's prognosis will be unique based on co-occurring conditions. Some people will only have mild visual issues, while others might require hormone therapy for the rest of their lives. The best strategy to help a kid succeed is to intervene early on. As a result, children may be able to receive services like physical, occupational, and vision therapy.

Conclusion

Optic nerve hypoplasia may compromise a child's vision. It may also target other areas of the brain related to physical development or hormone production, which support regular bodily functions. A medical professional can diagnose the child and provide a customized treatment plan based on their symptoms. The prognosis becomes better with early diagnosis and regular follow-up. One can consult a specialist online through medical platforms to learn more about this condition.