Ophthalmology – Pediatric Optic Nerve Hypoplasia

Basics

Description

Optic nerve hypoplasia (ONH) is a congenital, nonprogressive optic nerve disorder characterized by an abnormally small optic nerve with a reduced number of retinal ganglion cell axons.

It may be:

• Unilateral
• Bilateral
• Symmetric
• Asymmetric

Visual function ranges from:

• Normal or near-normal
• Mild impairment
• Profound visual loss

ONH may occur as an isolated ocular finding or with:

• Midline brain abnormalities
• Pituitary dysfunction
• Developmental abnormalities

Septo-Optic Dysplasia

Septo-optic dysplasia (SOD) traditionally refers to the presence of at least two of the following:

• Optic nerve hypoplasia
• Pituitary hormone dysfunction
• Midline brain abnormality

Midline abnormalities may include:

• Absent septum pellucidum
• Corpus callosum hypoplasia or agenesis

The term de Morsier syndrome is historical.

Importantly:

Absence of the septum pellucidum alone does not predict endocrine dysfunction, and significant endocrinopathy can occur even with otherwise normal MRI findings.

Epidemiology

ONH is among the most common congenital optic nerve abnormalities in children.

Most cases are:

Sporadic

Bilateral involvement is common, but unilateral disease is frequently encountered.

Risk Factors

Most children have no clearly identifiable prenatal cause.

Reported associations include:

• Maternal alcohol exposure
• Young maternal age
• Prematurity
• Abnormal fetal growth
• Maternal diabetes
• Certain prenatal medication or drug exposures

Older literature has reported associations with:

• Some anticonvulsants
• Quinine
• PCP
• LSD

but these associations are not consistently established.

Maternal Diabetes

Maternal diabetes is particularly associated with:

Superior segmental optic nerve hypoplasia

also called:

Topless disc syndrome

This causes:

• Superior disc hypoplasia
• Superior RNFL loss
• Corresponding inferior visual field defect

Genetics

Most ONH is sporadic.

Rare genetic associations include abnormalities involving:

• HESX1
• SOX2
• SOX3
• OTX2
• PAX6
• Other genes involved in forebrain and pituitary development

Genetic evaluation is especially appropriate when there is:

• Bilateral severe ONH
• Syndromic appearance
• Multiple congenital anomalies
• Strong family history
• Pituitary abnormalities

Associated Genetic and Developmental Disorders

ONH may occur with:

• Aniridia
• Albinism
• Midline developmental syndromes
• Pituitary developmental abnormalities
• Cortical migration disorders

Congenital infection and prenatal cerebral injury may also coexist with optic nerve hypoplasia-like appearances.

Pathophysiology

The primary abnormality is:

Reduced number of optic nerve axons

Possible mechanisms include:

• Abnormal retinal ganglion cell differentiation
• Excessive developmental apoptosis
• Abnormal axonal guidance
• Prenatal injury to the developing visual system

The outer retinal layers are generally preserved unless another retinal disorder is present.

Pathology

Histologically there is:

• Reduced retinal ganglion cell population
• Reduced RNFL
• Reduced optic nerve axons
• Small optic nerve caliber

Clinical Presentation

Bilateral ONH

Usually presents early with:

• Poor visual behavior
• Poor fixation
• Nystagmus
• Developmental concerns

Nystagmus often appears during the first few months of life.

Unilateral ONH

May present later with:

• Strabismus
• Amblyopia
• Failed vision screening
• Incidental optic disc abnormality

A child with unilateral ONH may otherwise be systemically normal.

Visual Acuity

Visual function is highly variable.

It may range from:

20/20 to profound visual impairment

A key principle:

Disc appearance correlates poorly with visual function.

A very small optic nerve may retain useful vision, while a mildly hypoplastic nerve may function poorly.

History

Ask about:

• Poor fixation
• Nystagmus
• Strabismus
• Developmental delay
• Seizures
• Abnormal growth
• Hypoglycemia
• Prolonged neonatal jaundice
• Excessive thirst or urination
• Prenatal alcohol or medication exposure
• Maternal diabetes
• Family history of developmental or endocrine disease

Endocrine Warning Signs

Important clues to pituitary dysfunction include:

• Neonatal hypoglycemia
• Prolonged jaundice
• Poor growth
• Failure to thrive
• Micropenis
• Cryptorchidism
• Recurrent seizures
• Polyuria/polydipsia
• Abnormal puberty

These findings warrant urgent endocrine assessment.

Physical Examination

Perform a complete pediatric ophthalmic examination including:

• Age-appropriate visual acuity
• Pupils
• Ocular alignment
• Motility
• Cycloplegic refraction
• Slit-lamp examination
• Dilated fundus examination

Optic Disc Appearance

Classic findings include:

• Small optic disc
• Pale or gray disc
• Reduced neuroretinal tissue
• Double-ring sign

Double-Ring Sign

The double-ring sign consists of:

• Small true optic nerve
• Surrounding larger ring corresponding to the normal-sized scleral canal and adjacent tissue

It is one of the classic signs of ONH.

Disc–Macula Relationship

Because the optic disc is abnormally small, the distance from:

• Disc center
• Fovea

appears disproportionately large compared with disc diameter.

A reduced disc diameter-to-disc–macula distance ratio supports the diagnosis.

Retinal Vessels

Associated features may include:

• Relative vessel crowding
• Tortuosity
• Immature vascular pattern

These findings are supportive but not diagnostic.

Foveal Hypoplasia

Some children with ONH may have associated:

Foveal hypoplasia

particularly when there is an underlying developmental or syndromic disorder.

OCT can help identify this.

Associated Microphthalmia

ONH may occasionally coexist with:

• Microphthalmia
• Other congenital ocular abnormalities

Nystagmus

Nystagmus is common in:

• Bilateral ONH
• Severe visual impairment

It usually reflects impaired early visual input.

Strabismus

Strabismus is common, especially in:

• Unilateral ONH
• Asymmetric bilateral disease

It may contribute additional amblyopic visual loss.

Pupils

A RAPD may be present with:

• Unilateral ONH
• Markedly asymmetric bilateral ONH

Visual Fields

When reliable testing becomes possible, defects may include:

• Generalized constriction
• Sectoral defects
• Altitudinal defects
• Central defects

Superior segmental ONH classically produces:

Inferior visual field loss

OCT

OCT may demonstrate:

• Reduced RNFL
• Reduced ganglion cell layer
• Small optic nerve head

It is useful for:

• Structural documentation
• Demonstrating asymmetry
• Distinguishing ONH from acquired optic atrophy

Interpretation can be limited by pediatric normative databases.

MRI

MRI of the brain and orbits is generally appropriate in children with ONH to assess for:

• Pituitary abnormalities
• Hypothalamic abnormalities
• Midline brain defects
• Corpus callosum abnormalities
• Cortical migration disorders

MRI Pituitary Findings

Potential findings include:

• Pituitary hypoplasia
• Absent or abnormal pituitary stalk
• Ectopic posterior pituitary bright spot

These increase concern for pituitary hormone deficiency.

However:

A normal MRI does not exclude endocrinopathy.

Important Imaging Principle

MRI can demonstrate associated structural abnormalities, but:

Optic nerve size on neuroimaging correlates imperfectly with visual function.

Clinical examination remains essential.

Endocrine Dysfunction

Pituitary abnormalities are among the most important systemic associations.

Potential deficiencies include:

• Growth hormone
• ACTH/cortisol
• TSH
• Gonadotropins
• Antidiuretic hormone

Growth Hormone Deficiency

Growth hormone deficiency may present with:

• Poor linear growth
• Falling height percentiles
• Delayed growth velocity

Growth charts should be reviewed longitudinally.

Central Hypothyroidism

Central hypothyroidism may be present despite:

• Normal or low-normal TSH

Therefore:

Free T4 is essential

and TSH alone is insufficient to screen for central hypothyroidism.

ACTH Deficiency

ACTH deficiency may cause:

• Hypoglycemia
• Hypotension
• Lethargy
• Adrenal crisis

This is potentially:

Life-threatening

and must not be missed.

Diabetes Insipidus

Central diabetes insipidus may produce:

• Polyuria
• Polydipsia
• Hypernatremia

Further testing may include:

• Serum sodium
• Serum osmolality
• Urine osmolality

Endocrine Evaluation

A low threshold for pediatric endocrinology referral is appropriate.

Initial assessment may include:

• Free T4
• TSH
• Morning cortisol
• Glucose
• IGF-1
• IGFBP-3
• Electrolytes

Additional testing depends on:

• Age
• Growth pattern
• Pubertal status
• Clinical symptoms

Long-Term Endocrine Surveillance

A normal endocrine evaluation in infancy does not guarantee normal future pituitary function.

Hormonal abnormalities may emerge later.

Therefore monitor:

• Height
• Weight
• Growth velocity
• Puberty
• Symptoms of adrenal or thyroid dysfunction

Neurologic Associations

Possible abnormalities include:

• Corpus callosum hypoplasia
• Agenesis of the corpus callosum
• Cortical ectopia
• Pachygyria
• Schizencephaly
• Other migration abnormalities
• Seizure disorders

Developmental Delay

Developmental problems are more common with:

• Bilateral disease
• Severe visual impairment
• Cerebral abnormalities
• Pituitary dysfunction

Assessment may include:

• Developmental pediatrics
• Neurology
• Early-intervention services

Differential Diagnosis

Important differentials include:

• Optic atrophy
• High hyperopia with small crowded discs
• Tilted optic disc
• Optic nerve coloboma
• Peripapillary staphyloma
• Peripapillary atrophy
• Morning glory disc anomaly

ONH vs Optic Atrophy

Optic Nerve Hypoplasia

• Congenitally small disc
• Double-ring sign
• Nonprogressive
• Reduced axon number from development

Optic Atrophy

• Acquired axonal loss
• Usually normal-sized disc initially
• Pallor predominates
• History may reveal previous neurologic or ocular injury

Treatment

There is:

No treatment that can regenerate the hypoplastic optic nerve

Management focuses on maximizing existing visual function and treating associated systemic disease.

Refractive Correction

Perform cycloplegic refraction and correct:

• Hyperopia
• Myopia
• Astigmatism
• Anisometropia

Optimal refractive correction is important during visual development.

Amblyopia Treatment

Amblyopia may coexist with structural optic nerve disease.

Treat when appropriate with:

• Optical correction
• Patching
• Atropine penalization in selected cases

Therapy should be individualized according to visual potential.

Strabismus

Management may include:

• Refractive correction
• Amblyopia treatment
• Strabismus surgery

Surgery may improve:

• Alignment
• Cosmesis
• Binocular function when sufficient vision exists

Nystagmus

Nystagmus surgery may be considered selectively for:

• Significant abnormal head posture
• Null point
• Associated strabismus

It does not treat the underlying optic nerve abnormality.

Protective Eyewear

When visual function is markedly asymmetric:

Protective spectacles should be recommended for the better-seeing eye.

Low-Vision Support

Children with significant bilateral visual impairment should be referred early for:

• Low-vision assessment
• Early-intervention programs
• Educational support
• Orientation and mobility training
• Adaptive technology

Endocrine Treatment

Hormone replacement is directed by pediatric endocrinology.

Examples include:

• Hydrocortisone for adrenal insufficiency
• Levothyroxine for central hypothyroidism
• Growth hormone when appropriate
• Desmopressin for diabetes insipidus

Genetic Counseling

Genetic consultation may be useful in:

• Bilateral severe disease
• Syndromic cases
• Multiple congenital anomalies
• Family history
• Suspected HESX1/SOX-related disease

Stem Cell Therapy

There is currently:

No convincing scientific evidence that stem cell treatment restores visual function in ONH.

It is not an established therapy.

Follow-Up

Ongoing ophthalmic follow-up should assess:

• Visual acuity
• Refraction
• Amblyopia
• Strabismus
• Nystagmus
• Functional visual development

Children often require more frequent review during:

• Amblyopia treatment
• Early visual development

Growth and Development Monitoring

Longitudinal monitoring should include:

• Height
• Weight
• Growth velocity
• Puberty
• Developmental milestones
• Neurologic symptoms

Prognosis

Visual prognosis is:

Highly variable

and depends primarily on residual optic nerve function.

Disc appearance and MRI findings correlate only poorly with visual outcome.

Stability

ONH itself is generally:

Nonprogressive

Apparent visual improvement with age may occur because of:

• Visual maturation
• Improved fixation
• Amblyopia treatment
• Better testing cooperation

This does not represent optic nerve regeneration.

Complications

Potential complications include:

• Severe visual impairment
• Amblyopia
• Strabismus
• Nystagmus
• Developmental delay
• Seizures
• Growth hormone deficiency
• Central hypothyroidism
• ACTH deficiency
• Diabetes insipidus
• Pubertal abnormalities

Ophthalmology Pearls

• Pediatric optic nerve hypoplasia is a congenital, nonprogressive reduction in optic nerve axons.
• The classic fundus finding is a small optic disc with a double-ring sign.
• Bilateral ONH often presents with poor visual behavior and nystagmus; unilateral disease often presents with strabismus or failed screening.
• Visual function correlates poorly with optic disc size or MRI appearance.
• The most important systemic association is hypothalamic-pituitary dysfunction.
• Free T4 is essential because central hypothyroidism may occur with a normal or low-normal TSH.
• ACTH/cortisol deficiency can be life-threatening and should not be missed.
• A normal MRI does not exclude pituitary dysfunction.
• Endocrine abnormalities may appear later, so longitudinal growth and hormonal surveillance is important.
• SOD does not require all three classic findings; ONH, pituitary dysfunction, and midline brain abnormalities may occur in different combinations.
• Maternal diabetes is associated with superior segmental ONH (“topless disc”), which typically causes an inferior visual field defect.
• Treatment focuses on refractive correction, amblyopia therapy, strabismus care, endocrine treatment, developmental support, and low-vision rehabilitation.
• There is currently no proven regenerative or stem-cell treatment for ONH.

Septo-Optic Dysplasia Septo-optic dysplasia (SOD) traditionally refers to the presence of at least two of the following:  Optic nerve hypoplasia Pituitary hormone dysfunction Midline brain abnormality  Midline abnormalities may include:  Absent septum pellucidum Corpus callosum hypoplasia or agenesis  The term de Morsier syndrome is historical. Importantly: Absence of the septum pellucidum alone does not predict endocrine dysfunction, and significant endocrinopathy can occur even with otherwise normal MRI findings.

Epidemiology ONH is among the most common congenital optic nerve abnormalities in children. Most cases are: Sporadic Bilateral involvement is common, but unilateral disease is frequently encountered.

Risk Factors Most children have no clearly identifiable prenatal cause. Reported associations include:  Maternal alcohol exposure Young maternal age Prematurity Abnormal fetal growth Maternal diabetes Certain prenatal medication or drug exposures  Older literature has reported associations with:  Some anticonvulsants Quinine PCP LSD  but these associations are not consistently established.

Maternal Diabetes Maternal diabetes is particularly associated with: Superior segmental optic nerve hypoplasia also called: Topless disc syndrome This causes:  Superior disc hypoplasia Superior RNFL loss Corresponding inferior visual field defect

Genetics Most ONH is sporadic. Rare genetic associations include abnormalities involving:  HESX1 SOX2 SOX3 OTX2 PAX6 Other genes involved in forebrain and pituitary development  Genetic evaluation is especially appropriate when there is:  Bilateral severe ONH Syndromic appearance Multiple congenital anomalies Strong family history Pituitary abnormalities

Associated Genetic and Developmental Disorders ONH may occur with:  Aniridia Albinism Midline developmental syndromes Pituitary developmental abnormalities Cortical migration disorders  Congenital infection and prenatal cerebral injury may also coexist with optic nerve hypoplasia-like appearances.

Pathophysiology The primary abnormality is: Reduced number of optic nerve axons Possible mechanisms include:  Abnormal retinal ganglion cell differentiation Excessive developmental apoptosis Abnormal axonal guidance Prenatal injury to the developing visual system  The outer retinal layers are generally preserved unless another retinal disorder is present.

Pathology Histologically there is:  Reduced retinal ganglion cell population Reduced RNFL Reduced optic nerve axons Small optic nerve caliber

Clinical Presentation Bilateral ONH Usually presents early with:  Poor visual behavior Poor fixation Nystagmus Developmental concerns  Nystagmus often appears during the first few months of life.

Unilateral ONH May present later with:  Strabismus Amblyopia Failed vision screening Incidental optic disc abnormality  A child with unilateral ONH may otherwise be systemically normal.

Visual Acuity Visual function is highly variable. It may range from: 20/20 to profound visual impairment A key principle: Disc appearance correlates poorly with visual function. A very small optic nerve may retain useful vision, while a mildly hypoplastic nerve may function poorly.

History Ask about:  Poor fixation Nystagmus Strabismus Developmental delay Seizures Abnormal growth Hypoglycemia Prolonged neonatal jaundice Excessive thirst or urination Prenatal alcohol or medication exposure Maternal diabetes Family history of developmental or endocrine disease

Endocrine Warning Signs Important clues to pituitary dysfunction include:  Neonatal hypoglycemia Prolonged jaundice Poor growth Failure to thrive Micropenis Cryptorchidism Recurrent seizures Polyuria/polydipsia Abnormal puberty  These findings warrant urgent endocrine assessment.

Physical Examination Perform a complete pediatric ophthalmic examination including:  Age-appropriate visual acuity Pupils Ocular alignment Motility Cycloplegic refraction Slit-lamp examination Dilated fundus examination

Optic Disc Appearance Classic findings include:  Small optic disc Pale or gray disc Reduced neuroretinal tissue Double-ring sign

Double-Ring Sign The double-ring sign consists of:  Small true optic nerve Surrounding larger ring corresponding to the normal-sized scleral canal and adjacent tissue  It is one of the classic signs of ONH.

Disc–Macula Relationship Because the optic disc is abnormally small, the distance from:  Disc center Fovea  appears disproportionately large compared with disc diameter. A reduced disc diameter-to-disc–macula distance ratio supports the diagnosis.

Retinal Vessels Associated features may include:  Relative vessel crowding Tortuosity Immature vascular pattern  These findings are supportive but not diagnostic.

Foveal Hypoplasia Some children with ONH may have associated: Foveal hypoplasia particularly when there is an underlying developmental or syndromic disorder. OCT can help identify this.

Associated Microphthalmia ONH may occasionally coexist with:  Microphthalmia Other congenital ocular abnormalities

Nystagmus Nystagmus is common in:  Bilateral ONH Severe visual impairment  It usually reflects impaired early visual input.

Strabismus Strabismus is common, especially in:  Unilateral ONH Asymmetric bilateral disease  It may contribute additional amblyopic visual loss.

Pupils A RAPD may be present with:  Unilateral ONH Markedly asymmetric bilateral ONH

Visual Fields When reliable testing becomes possible, defects may include:  Generalized constriction Sectoral defects Altitudinal defects Central defects  Superior segmental ONH classically produces: Inferior visual field loss

OCT OCT may demonstrate:  Reduced RNFL Reduced ganglion cell layer Small optic nerve head  It is useful for:  Structural documentation Demonstrating asymmetry Distinguishing ONH from acquired optic atrophy  Interpretation can be limited by pediatric normative databases.

MRI MRI of the brain and orbits is generally appropriate in children with ONH to assess for:  Pituitary abnormalities Hypothalamic abnormalities Midline brain defects Corpus callosum abnormalities Cortical migration disorders

MRI Pituitary Findings Potential findings include:  Pituitary hypoplasia Absent or abnormal pituitary stalk Ectopic posterior pituitary bright spot  These increase concern for pituitary hormone deficiency. However: A normal MRI does not exclude endocrinopathy.

Important Imaging Principle MRI can demonstrate associated structural abnormalities, but: Optic nerve size on neuroimaging correlates imperfectly with visual function. Clinical examination remains essential.

Endocrine Dysfunction Pituitary abnormalities are among the most important systemic associations. Potential deficiencies include:  Growth hormone ACTH/cortisol TSH Gonadotropins Antidiuretic hormone

Growth Hormone Deficiency Growth hormone deficiency may present with:  Poor linear growth Falling height percentiles Delayed growth velocity  Growth charts should be reviewed longitudinally.

Central Hypothyroidism Central hypothyroidism may be present despite:  Normal or low-normal TSH  Therefore: Free T4 is essential and TSH alone is insufficient to screen for central hypothyroidism.

ACTH Deficiency ACTH deficiency may cause:  Hypoglycemia Hypotension Lethargy Adrenal crisis  This is potentially: Life-threatening and must not be missed.

Diabetes Insipidus Central diabetes insipidus may produce:  Polyuria Polydipsia Hypernatremia  Further testing may include:  Serum sodium Serum osmolality Urine osmolality

Endocrine Evaluation A low threshold for pediatric endocrinology referral is appropriate. Initial assessment may include:  Free T4 TSH Morning cortisol Glucose IGF-1 IGFBP-3 Electrolytes  Additional testing depends on:  Age Growth pattern Pubertal status Clinical symptoms

Long-Term Endocrine Surveillance A normal endocrine evaluation in infancy does not guarantee normal future pituitary function. Hormonal abnormalities may emerge later. Therefore monitor:  Height Weight Growth velocity Puberty Symptoms of adrenal or thyroid dysfunction

Neurologic Associations Possible abnormalities include:  Corpus callosum hypoplasia Agenesis of the corpus callosum Cortical ectopia Pachygyria Schizencephaly Other migration abnormalities Seizure disorders

Developmental Delay Developmental problems are more common with:  Bilateral disease Severe visual impairment Cerebral abnormalities Pituitary dysfunction  Assessment may include:  Developmental pediatrics Neurology Early-intervention services

Differential Diagnosis Important differentials include:  Optic atrophy High hyperopia with small crowded discs Tilted optic disc Optic nerve coloboma Peripapillary staphyloma Peripapillary atrophy Morning glory disc anomaly

ONH vs Optic Atrophy Optic Nerve Hypoplasia  Congenitally small disc Double-ring sign Nonprogressive Reduced axon number from development  Optic Atrophy  Acquired axonal loss Usually normal-sized disc initially Pallor predominates History may reveal previous neurologic or ocular injury

Treatment There is: No treatment that can regenerate the hypoplastic optic nerve Management focuses on maximizing existing visual function and treating associated systemic disease.

Refractive Correction Perform cycloplegic refraction and correct:  Hyperopia Myopia Astigmatism Anisometropia  Optimal refractive correction is important during visual development.

Amblyopia Treatment Amblyopia may coexist with structural optic nerve disease. Treat when appropriate with:  Optical correction Patching Atropine penalization in selected cases  Therapy should be individualized according to visual potential.

Strabismus Management may include:  Refractive correction Amblyopia treatment Strabismus surgery  Surgery may improve:  Alignment Cosmesis Binocular function when sufficient vision exists

Nystagmus Nystagmus surgery may be considered selectively for:  Significant abnormal head posture Null point Associated strabismus  It does not treat the underlying optic nerve abnormality.

Protective Eyewear When visual function is markedly asymmetric: Protective spectacles should be recommended for the better-seeing eye.

Low-Vision Support Children with significant bilateral visual impairment should be referred early for:  Low-vision assessment Early-intervention programs Educational support Orientation and mobility training Adaptive technology

Endocrine Treatment Hormone replacement is directed by pediatric endocrinology. Examples include:  Hydrocortisone for adrenal insufficiency Levothyroxine for central hypothyroidism Growth hormone when appropriate Desmopressin for diabetes insipidus

Genetic Counseling Genetic consultation may be useful in:  Bilateral severe disease Syndromic cases Multiple congenital anomalies Family history Suspected HESX1/SOX-related disease

Stem Cell Therapy There is currently: No convincing scientific evidence that stem cell treatment restores visual function in ONH. It is not an established therapy.

Follow-Up Ongoing ophthalmic follow-up should assess:  Visual acuity Refraction Amblyopia Strabismus Nystagmus Functional visual development  Children often require more frequent review during:  Amblyopia treatment Early visual development

Growth and Development Monitoring Longitudinal monitoring should include:  Height Weight Growth velocity Puberty Developmental milestones Neurologic symptoms

Prognosis Visual prognosis is: Highly variable and depends primarily on residual optic nerve function. Disc appearance and MRI findings correlate only poorly with visual outcome.

Stability ONH itself is generally: Nonprogressive Apparent visual improvement with age may occur because of:  Visual maturation Improved fixation Amblyopia treatment Better testing cooperation  This does not represent optic nerve regeneration.

Complications Potential complications include:  Severe visual impairment Amblyopia Strabismus Nystagmus Developmental delay Seizures Growth hormone deficiency Central hypothyroidism ACTH deficiency Diabetes insipidus Pubertal abnormalities

Ophthalmology Pearls  Pediatric optic nerve hypoplasia is a congenital, nonprogressive reduction in optic nerve axons. The classic fundus finding is a small optic disc with a double-ring sign. Bilateral ONH often presents with poor visual behavior and nystagmus; unilateral disease often presents with strabismus or failed screening. Visual function correlates poorly with optic disc size or MRI appearance. The most important systemic association is hypothalamic-pituitary dysfunction. Free T4 is essential because central hypothyroidism may occur with a normal or low-normal TSH. ACTH/cortisol deficiency can be life-threatening and should not be missed. A normal MRI does not exclude pituitary dysfunction. Endocrine abnormalities may appear later, so longitudinal growth and hormonal surveillance is important. SOD does not require all three classic findings; ONH, pituitary dysfunction, and midline brain abnormalities may occur in different combinations. Maternal diabetes is associated with superior segmental ONH (“topless disc”), which typically causes an inferior visual field defect. Treatment focuses on refractive correction, amblyopia therapy, strabismus care, endocrine treatment, developmental support, and low-vision rehabilitation. There is currently no proven regenerative or stem-cell treatment for ONH.