A Silent Threat to Sight- Optic Neuropathy

Dr. Sanjeeta Sitaula

She is a consultant neuro-ophthalmologist and cornea specialist working at B.P. Koirala Lions Centre for Ophthalmic Studies, Maharajgunj Medical Campus, Institute of Medicine. She has more than 14 years of clinical experience in managing various neuro-ophthalmological conditions. Her areas of professional interests include optic nerve disease, systemic diseases and their effect on eye and ocular motor nerve diseases. She is dedicated to providing patient-centric, quality and evidence based care for patients with neuro-ophthalmological diseases.

Somewhere in the crowded lanes of Kathmandu a young man wakes up unable to read the signboard he passed every day. An elderly farmer in the Terai notices the colours of his fields have turned dull. A schoolteacher recovering from a fever finds one eye has gone dim overnight. These are not unrelated stories, they are different faces of the same underlying condition: optic neuropathy, damage to the optic nerve, the nerve that carries images from the eye to the brain.
Unlike cataract or refractive error, which are widely understood and screened for across Nepal, optic neuropathy remains poorly recognised by the public. Yet it is an important cause of irreversible blindness, and in many cases, the damage could have been slowed or even prevented had warning signs been caught early. This article walks through the major types of optic neuropathy and offers guidance for protecting vision.

1. Inflammatory Optic Neuropathy
   This form, commonly called optic neuritis, occurs when the optic nerve becomes inflamed, often in young adults. It can follow viral infections, post-vaccination or autoimmune demyelinating brain diseases like Multiple Sclerosis or Neuromyelitis Optica. Occasionally infections like tuberculosis, sinus disease, or other inflammatory disease like sarcoidosis may be the cause of optic neuropathy.
   Warning signs: The symptoms are sudden blurring of vision in one eye, pain on moving the eye, and dulling of colours (reds appear washed out).
   Health message: Any sudden, painless-to-mildly-painful loss of vision in one or rarely both the eyes is an emergency, not something to “wait and watch.” Delaying a visit to an eye hospital by even a few days can reduce the chances of recovery. People with a history of unexplained fever or other systemic illnesses who notice visual changes should mention this specifically to their doctor.
2. Ischemic Optic Neuropathy
   This occurs when blood supply to the optic nerve is cut off, similar to a “stroke of the eye.” It is most common in people over 50 and is strongly linked to high blood pressure, diabetes, high cholesterol, smoking and obstructive sleep apnea, all of which are rising steadily in Nepal due to changing diets and sedentary urban lifestyles.
   Warning signs: Sudden, painless loss of vision, often noticed on waking, sometimes affecting only the upper or lower half of the visual field.
   Health message: Because this condition shares its root causes with heart attack and stroke, protecting your optic nerve means protecting your whole cardiovascular system:

• Get blood pressure and blood sugar checked regularly, especially after age 40.
• Take prescribed medicines for hypertension and diabetes consistently
• Avoid tobacco in all forms (a major contributor across both urban and rural Nepal).
• If one eye is affected, the other eye is at meaningful risk in the following months, this is the time to control risk factors most strictly, not to relax.

1. Nutritional Optic Neuropathy
   It results from deficiency of vitamin B12, folate, and thiamine, often compounded by chronic alcohol use and poor dietary diversity. It is frequently seen in people who rely heavily on refined carbohydrates with limited intake of pulses, dairy, meat, and green vegetables, and it is worsened by heavy alcohol consumption, which impairs nutrient absorption.
   Warning signs: Gradual, painless blurring in both eyes over weeks to months, difficulty distinguishing colours, and sometimes accompanying numbness or tingling in the hands and feet (suggesting associated nerve involvement).

Health message:

• Include B12-rich foods where possible- eggs, dairy, and meat/fish for those who consume them and consider supplementation particularly for strict vegetarians and the elderly.
• Reduce heavy or regular alcohol intake, which is a major and modifiable risk factor.
• Pregnant women, elderly people living alone, and those with poor appetite are at higher risk and may benefit from nutritional screening.

1. Toxic Optic Neuropathy
   Closely related to the nutritional form, toxic optic neuropathy arises from substances that directly damage the optic nerve. In Nepal, the most relevant causes are tobacco and alcohol combined (“tobacco-alcohol amblyopia”), certain TB medicines (ethambutol, linezolid) when not properly monitored, methanol from illicitly brewed or adulterated alcohol, and exposure to certain pesticides or industrial chemicals.
   Warning signs: Gradual blurring of central vision in both eyes, difficulty with fine detail (such as threading a needle or reading small print), often in someone with heavy smoking or drinking habits, or one on long-term TB treatment.

Health message:

• Anyone taking ethambutol for TB should have vision checked before starting and periodically during treatment, this is a simple, preventable cause of blindness.
• Avoid home-brewed or unregulated alcohol, which carries a real risk of methanol poisoning, a medical emergency that can cause sudden, severe, and permanent vision loss.
• Reducing tobacco and alcohol use protects the optic nerve just as it protects the liver and heart.
• Farmers and workers using pesticides should use protective equipment and follow safety instructions on labels.

1. Traumatic Optic Neuropathy
   Given Nepal’s high rates of road traffic accidents, falls, and workplace injuries, trauma to the head or face, even without direct injury to the eye, can shear or compress the optic nerve leading to traumatic optic neuropathy.
   Warning signs: Vision loss noticed immediately or within hours after a head injury, sometimes with no visible external injury to the eye itself.

Health message:

• Any vision change following a head injury, however minor the injury seemed, warrants same-day medical evaluation.
• Helmet use for motorcyclists and seatbelt use in vehicles are among the simplest, most effective protections against this entirely preventable cause of blindness.
• Workplace safety gear (helmets, protective eyewear) should be used consistently in construction and industrial settings.

Common Threads: What Everyone Should Remember

Across all five types, a few simple messages apply broadly:

1. Sudden vision loss is always an emergency: go to an eye hospital immediately, not after a few days of “seeing if it improves.”
2. Gradual vision loss deserves equal attention: it is easy to dismiss as ageing or tiredness, but early evaluation allows the underlying cause (nutrition, toxins, blood sugar, brain or orbital tumors) to be corrected before permanent damage sets in.
   3.Control the controllable: blood pressure, blood sugar, tobacco, alcohol, and diet are risk factors shared across most types of optic neuropathy.
   4.Medication monitoring matters: patients on anti-tubercular therapy (ethambutol) should never skip the recommended eye checks.
   5.Protect the head: helmets and seatbelts prevent not just death, but blindness too.

Since the optic nerve is part of the brain, adult optic nerve fibres lack the capacity to naturally repair or regenerate once they are severely damaged. However, vision loss from optic neuropathy is frequently preventable and, if caught early, sometimes reversible too. Community awareness, regular health check-ups, and prompt action at the first sign of trouble remain the most powerful tools against this quiet but serious threat to sight.

Let us all try and preserve our gift of sight.