Optic Nerve Hypoplasia
- Optic nerve hypoplasia 377.43
- Optic nerve hypoplasia, right eye H47.031
- Optic nerve hypoplasia, left eye H47.032
- Optic nerve hypoplasia, bilateral H47.033
Optic nerve hypoplasia (ONH) is characterized by decreased number of optic nerve axons. It can present unilaterally or bilaterally. It may present as an isolated anomaly or be associated with midline cerebral structural defect, such as septum pellucidum absence, agenesis of corpus callosum, cerebral hemisphere abnormalities, or pituitary gland abnormalities. A high proportion of patients with ONH have concurrent structural central nervous system abnormalities (90%) and neuro-developmental handicaps (70%).
Septo–optic dysplasia (de Morsier syndrome) is used to describe the association between ONH and the absence of septum pellucidum, deficiency of pituitary hormones and agenesis of corpus callosum. Clinical manifestations of septo-optic dysplasia include may visual impairment, hypopituitarism, and developmental delays. Gillespie syndrome is a genetic disease that presents as a triad of aniridia, cerebellar ataxia, and intellectual disability; it is also sometimes accompanied by other ocular findings such as ONH.
ONH that only involves the superior segment is termed Superior Segmental Optic Nerve Hypoplasia (SSONH). ONH that only involves the nasal quadrant is termed nasal optic disc hypoplasia.
The first case of ONH was described by Briere in 1877, and the first schematic drawing of the appearance of the optic disc was done by Schwarz in 1915. In 1941, Dr. David Reeves at Children’s Hospital Los Angeles first described the association of ONH with agenesis of the septum pellucidum. And subsequently the term of “la dysplasia septo- optique” was described by Georges de Morsier in 1956. In 1970 Dr. William Hoyt’s landmark paper recognized the association between ONH and growth hormone deficiency. Dr. Hoyt attributed the discovery of the association of optic nerve hypoplasia with septum pellucidum agenesis to de Morsier, and resurrected the term septo-optic dysplasia syndrome.
In 2007, ONH was considered the 3rd most prevalent cause of vision impairment in children less than 3 years of age following cortical vision impairment and retinopathy of prematurity. Optic nerve hypoplasia was identified in 12% of blind infants in Harris County in Texas in early 1980s. In more recent studies, the incidence of ONH in all living children under the age of 18 was reported to be 10.9 per 100,000 in England and 17.3 per 100,000 in Sweden. In 2013, a study based in Mayo Clinic reported an incidence of 1/2287 live births and 2.4/100,000 in patients less than 19 years old. ONH is usually diagnosed at 2 years of age.
A number of gene mutations have been associated with ONH:
|Gene||Function||Clinical feature/Associated disorders|
|HESX1||Transcription regulation gene that is critical
to the development of the forebrain, midline brain structures, and pituitary
|Combined pituitary hormone deficiency or
|PAX6||Transcription regulation gene that guides neural
and ocular development
in the iris, nystagmus and foveal hypoplasia, cataracts, corneal abnormalities, glaucoma and bilateral ptosis
|SOX2||Transcription factor that plays an important
role in embryogenesis
|Bilateral ONH, absent septum pellucidum,
bilateral schizencephaly, right porencephalic cyst
|SOX5||Transcription factor that plays an important
role in neurogenesis
|Lamb-Schaffer syndrome (ONH, optic atrophy, developmental delay, behavioral problems, poor expressive speech, mild dysmorphic features, and skeletal abnormalities).|
|COL4A1/COL4A2||Protein coding genes that encode the alpha-1 and alpha-2 subunits of collagen type IV, essential for basement membranes and cell adhesion, migration, proliferation, and differentiation||Small-vessel brain disease (porencephaly and schizencephaly), renal disease, muscular disease, and cerebrovascular disease. Ophthalmological disorders include retinal arterial tortuosity, congenital cataract, anterior segment dysgenesis, glaucoma, microphthalmia/anophthalmia, optic atrophy, and ONH.|
|KIF7||Protein coding gene that is an important regulator for the sonic hedgehog signaling pathway, which is responsible for patterning and brain development||Joubert syndrome, acrocallosal syndrome.|
|CASK||X-linked gene involved in pre- and postsynaptic neuronal signaling||Intellectual disability, microcephaly, pontocerebellar hypoplasia, ONH, and seizures.|
|MED12||Gene that encodes a significant portion of RNA polymerase II, which is critical for gene transcription||Ohdo syndrome, Lujan-Fryns syndrome, Opitz-Kaveggia syndrome, and ocular features such as ptosis, hypertelorism, strabismus, astigmatism, and ONH.|
|NR2F1||Transcription regulation gene that is critical
to neurodevelopment, optic development, oligodendrocyte differentiation, etc
|Intellectual disability seen with ONH/optic
|OTX2||Transcription factor that affects brain
development. Family screening for a possible mutation is important as mutations tend to be hereditary
brain malformations, pituitary abnormalities; short stature, intellectual disabilities, feeding difficulties
|VAX1||Transcription regulation gene in eye development||Bilateral microphthalmia, cleft
lip/palate, corpus callosum defects, hippocampal defects, absent pineal gland
|ATOH7||Transcription regulation gene that controls
ocular development and formation of retinal ganglion cells
|Smaller optic disc|
|KANSL1||Transcription regulation through histone
|Strabismus, astigmatism, myopia|
It is hypothesized that ONH is a result of vascular disruption, primarily of the proximal trunk of the anterior cerebral artery and this hypothesis is supported by risk factors for ONH such as increased first trimester bleeding and maternal smoking. Other risk factors include young maternal age, maternal diabetes, preterm labor and primiparity  Additionally, low maternal weight gain, and maternal weight loss during the first and second trimesters increase the risk of ONH. Recent studies demonstrate that maternal use of alcohol, recreational drugs, anticonvulsants, antidepressants, and viral infections during pregnancy appear to play a smaller role in the development of ONH than previously thought.
In ONH, the optic disc is often pale or gray and appears to be, at most, half the size of a normal optic disc. Optic discs often present with a double ring sign – yellow to white ring around the disc. A ring of hypopigmentation or hyperpigmentation often surrounds the disc defining the area of the putative scleral canal. The outer ring represents the normal junction between the sclera and the lamina cribrosa; the inner ring represents the abnormal extension of retina and pigment epithelium over the outer portion of the lamina cribrosa. Tortuous retinal arterioles, venules, or both may accompany ONH, but retinal vessels can also present with normal caliber. The ratio of the horizontal disc diameter (DD) to the distance between the macula and the temporal edge of the disc (DM) constitutes the DD/DM ratio; DD/DM ratios less than 0.35 are generally indicative of ONH. However, patients’ age needs to be considered when evaluating the DD/DM ratio. For example, the normal DD/DM ratio in premature infants has been reported as ≥ 0.26. Additionally, Optical Coherence Tomography (OCT) studies may reveal foveal thinning of several retinal layers including the RNFL (retinal nerve fiber layer), GCL (ganglion cell layer), IPL (inner plexiform layer), OPL (outer plexiform layer), ONL (outer nuclear layer), and IS (inner segment) layers. The retinal changes observed are similar to foveal hypoplasia; however, ONH results in more severe changes in the RNFL and GCL retinal layers.
In ONH, visual acuity can range from normal to light perception. Most patients suffer from a visual acuity of 20/200 or worse. Visual acuity in ONh patients is related to the structure of the macula and is often not correlated with overall size of the disc. Visual field often has localized defects combined with visual field constrictions, commonly in nasal or inferior fields. ONH can occur unilaterally, bilaterally symmetric, or bilaterally asymmetric. In unilateral and asymmetric bilateral ONH, relative afferent pupillary defects can be seen as well. Congenital sensory nystagmus often presents in bilateral ONH cases at 1-3 month of age, followed by strabismus development by 1 year of age, commonly esotropia. Strabismus often develops in markedly asymmetric or unilateral cases. Hypothalamic dysfunction is the most common nonvisual problem in ONH cases and is reported to be present in 69% of unilateral cases vs 81% of bilateral cases. Absence of the septum pellucidum was not associated with poor vision, pituitary dysfunction or developmental delays. It has been reported that 13-34% of optic nerve hypoplasia cases have pituitary abnormalities: empty sella, ectopic posterior pituitary, non-visualized infundibulum and posterior pituitary. Endocrine abnormalities are associated with the absence of the infundibulum which results in the lack of communication between the hypothalamus and the anterior pituitary. The hypothalamus is then unable to properly stimulate the anterior pituitary leading to low levels of anterior pituitary hormones and hypopituitarism. The following hormonal dysfunctions have been seen in patients with ONH: growth hormone deficiency (70%), moderately elevated serum prolactin (normally suppressed by hypothalamus), hypothyroidism (43%); adrenocorticotropic hormone deficiency (27%) leading to hypercortisolism, and diabetes insipidus (5%) due to posterior pituitary abnormalities. Normal pituitary function at initial evaluation does not preclude development of endocrinopathy in the future. Additionally, early diagnosis of endocrine dysfunction and proper treatment with hormone replacement therapy is critical to reducing mortality. Developmental delays occur in 75% of ONH cases, with higher incidence in bilateral cases (78%) vs unilateral cases (39%). Patients can present with motor delays (75%), and communication delays (44%). Other abnormalities include hypoglycemia (transient or permanent), microgenitalism, and hyperbilirubinemia.
Diagnostic procedures/Laboratory test
Magnetic resonance imaging (MRI) studies are recommended in patients with suspected ONH to assess thesuggested in patients suspected of having ONH. The diameter of the intracranial optic nerve and thinning of the optic chiasm can be assessed on MRI scans. Additionally, the visualization presence of midline abnormalities can be visualized to clinically confirm the diagnosis of SOD. Optical coherence tomography (OCT) is also an effective tool for measuring foveal parameters and detecting ONH. However, ONH is not able to be diagnosed purely off radiographic measurements.
Optic nerve atrophy, optic nerve coloboma, peripapillary staphyloma, morning glory disc anomaly, tilted disc syndrome, glaucoma.
An ophthalmic evaluation is recommended for all neonates with jaundice and recurrent hypoglycemia, as these may be early signs of hypothalamic dysfunction. Additionally, an ophthalmic evaluation is recommended for infants with poor visual behavior, strabismus, or nystagmus by 3 months of age. MRI brain is recommended for confirmed ONH cases to evaluate for hydrocephalus, corpus callosum hypoplasia, schizencephaly or polymicrogyria. Positive MRI brain should prompt a neurologic exam. Endocrinologic and pituitary function evaluations are recommended regardless of the status of the septum pellucidum. Endocrine workups include: fasting morning cortisol and glucose, TSH, free4, growth hormone surrogates (IGF-1, IGFBP-3), LH, SFH, and testosterone (if < 6mo age).
All ONH patients with central nervous system abnormalities or endocrinopathies would benefit from a multi-disciplinary team of physicians including a neurologist, neurosurgeon, endocrinologist and/or other specialists from respective fields such as occupational, physical and speech therapists. The recommended follow-up is semi-annually for growth patterns and annually for visual function. Surgical correction for strabismus is reserved for patients with symmetrical functional vision in both eyes, and potential for binocularity. Otherwise, surgical strabismus can be deferred.
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- Image source: AAO
- 2 Image source: AAO
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