Optic Neuropathy – Causes (Mnemonic NIGHTTIC), Symptoms, Diagnosis & Treatment

The optic nerve is a vital structure that transmits visual information from the retina to the brain. Damage to this nerve is known as Optic Neuropathy, a condition that can lead to vision loss, visual field defects, and impaired color perception.

Optic neuropathy is not a disease by itself, but rather a clinical manifestation of various underlying causes. Because vision loss from optic nerve damage is often irreversible, early recognition and management are critical.

Medical students and healthcare professionals often use mnemonics to recall causes effectively. One such helpful mnemonic is NIGHTTIC, which summarizes the diverse etiologies of optic neuropathy.

Mnemonic NIGHTTIC for Optic Neuropathy

The mnemonic NIGHTTIC helps remember the main causes:

Letter	Cause	Explanation
N	Neuritis	Inflammation of the optic nerve, commonly seen in optic neuritis (often associated with multiple sclerosis).
I	Ischemia	Reduced blood flow to the optic nerve, leading to Ischemic Optic Neuropathy (ION), often linked with hypertension, diabetes, and arteritis.
G	Granulomatous	Infiltrative conditions like sarcoidosis or tuberculosis can damage the optic nerve.
H	Hereditary	Genetic disorders such as Leber’s Hereditary Optic Neuropathy (LHON) cause progressive vision loss.
T	Traumatic	Direct trauma to the orbit or head injury can lead to optic nerve damage.
T	Toxic	Certain drugs (e.g., ethambutol, isoniazid, methanol poisoning) and chemicals can injure the optic nerve.
I	Irradiation	Radiation therapy for orbital or brain tumors may cause optic neuropathy.
C	Compressive	Tumors, aneurysms, or orbital masses can physically compress the optic nerve.

This mnemonic makes it easier for students and clinicians to systematically recall the wide range of causes during clinical practice.

Anatomy of the Optic Nerve

To understand optic neuropathy, it’s crucial to know the structure of the optic nerve:

The optic nerve is the second cranial nerve (CN II).

It consists of axons of retinal ganglion cells.

Covered by meninges (dura, arachnoid, pia), it is considered part of the central nervous system.

Divided into four segments:

• Intraocular (optic disc)
• Intraorbital
• Intracanalicular
• Intracranial

Lesions at different levels lead to different clinical presentations.

Clinical Features of Optic Neuropathy

The hallmark signs and symptoms include:

Vision Loss – Sudden (ischemic, traumatic) or gradual (hereditary, compressive).

Color Vision Defects – Dyschromatopsia (particularly red-green color loss).

Visual Field Defects – Central scotoma, altitudinal loss, arcuate defects.

Decreased Contrast Sensitivity – Blurred or washed-out images.

Pain on Eye Movement – Typical in optic neuritis.

Pale or Swollen Optic Disc – Seen on fundoscopy depending on etiology.

Causes of Optic Neuropathy – Detailed Explanation

1. Neuritis

• Optic neuritis is often associated with demyelinating diseases like Multiple Sclerosis (MS).
• Presents with sudden painful monocular vision loss.
• May show Uhthoff’s phenomenon (worsening with heat).

2. Ischemia

• Caused by vascular insufficiency in the optic nerve.
• Arteritic Ischemic Optic Neuropathy (AION) occurs due to Giant Cell Arteritis (GCA).
• Non-arteritic ION is linked with diabetes, hypertension, and hyperlipidemia.

3. Granulomatous

• Conditions like sarcoidosis, tuberculosis, and syphilis can infiltrate the optic nerve.

4. Hereditary

• Leber’s Hereditary Optic Neuropathy (LHON): Mitochondrial inheritance, young males affected, bilateral vision loss.
• Dominant Optic Atrophy (DOA): Gradual onset, progressive.

5. Traumatic

• Direct or indirect injury to the optic nerve (e.g., road traffic accidents, orbital fractures).
• Immediate or delayed vision loss possible.

6. Toxic

• Caused by drugs: Ethambutol, isoniazid, amiodarone.
• Toxins: Methanol, lead, tobacco-alcohol amblyopia.

7. Irradiation

• Seen as a complication after radiotherapy for brain, sinus, or orbital tumors.
• Can cause delayed optic neuropathy.

8. Compressive

• Space-occupying lesions like pituitary adenomas, meningiomas, craniopharyngiomas, or orbital tumors.
• Slowly progressive vision loss, often with field defects.

Diagnosis of Optic Neuropathy

Clinical Examination

Visual acuity testing – Determines severity of vision loss.

Color vision tests – Ishihara plates for red-green defects.

Visual field assessment – Automated perimetry.

Fundoscopy – Disc edema (neuritis, ischemia), disc pallor (chronic cases).

Imaging

MRI brain & orbit – Identifies demyelination, compressive lesions, trauma.

CT scan – Useful in trauma and bone involvement.

Laboratory Tests

• ESR, CRP – To rule out Giant Cell Arteritis.
• ANA, ACE levels – For autoimmune or granulomatous causes.
• Toxicology screen – For suspected toxic neuropathy.
• Genetic testing – For hereditary optic neuropathies.

Management of Optic Neuropathy

Management depends on the underlying cause:

1. Medical Treatment

Optic neuritis: High-dose IV corticosteroids (e.g., methylprednisolone).

Ischemic neuropathy: Control of vascular risk factors; steroids for arteritic cases.

Granulomatous: Anti-tubercular drugs, corticosteroids for sarcoidosis.

Toxic: Stopping the offending drug/toxin; vitamin supplementation (B12, folate).

Hereditary: Supportive therapy; idebenone in LHON.

2. Surgical Treatment

Decompression in cases of orbital tumors or fractures.

3. Supportive Management

Low vision aids – Magnifiers, electronic devices.

Rehabilitation programs – To enhance patient independence.

Prognosis

Optic neuritis: Often recovers partially within weeks.

Ischemic optic neuropathy: Poor prognosis; vision loss often permanent.

Hereditary forms: Progressive and irreversible.

Toxic neuropathy: Reversible if recognized early.

Compressive neuropathy: Can improve if decompression is performed timely.

Quick Reference Table – Optic Neuropathy (NIGHTTIC Mnemonic)

Cause	Example/Details
N – Neuritis	Optic neuritis, multiple sclerosis
I – Ischemia	Ischemic optic neuropathy (AION/NAION)
G – Granulomatous	Sarcoidosis, tuberculosis, syphilis
H – Hereditary	Leber’s hereditary optic neuropathy
T – Traumatic	Orbital fractures, head trauma
T – Toxic	Ethambutol, methanol poisoning
I – Irradiation	Post-radiotherapy optic neuropathy
C – Compressive	Pituitary adenoma, orbital tumors

Frequently Asked Questions (FAQ)

Q1. What is optic neuropathy?

Optic neuropathy is a condition caused by damage to the optic nerve, leading to vision loss, color vision defects, and visual field changes.

Q2. What is the mnemonic NIGHTTIC used for?

The mnemonic NIGHTTIC helps remember the main causes of optic neuropathy: Neuritis, Ischemia, Granulomatous, Hereditary, Traumatic, Toxic, Irradiation, and Compressive.

Q3. Can optic neuropathy be reversed?

It depends on the cause. Toxic and inflammatory causes may improve if treated early, but ischemic and hereditary causes often lead to permanent damage.

Q4. How is optic neuropathy diagnosed?

Through visual acuity testing, color vision tests, perimetry, fundoscopy, and imaging (MRI/CT). Blood tests and genetic studies may be required in specific cases.

Q5. Which drugs commonly cause toxic optic neuropathy?

Ethambutol, isoniazid, linezolid, amiodarone, methanol, and chronic alcohol use are major culprits.

Q6. What is the treatment for optic neuritis?

High-dose IV corticosteroids are the standard treatment, often followed by oral tapering.