Optic Nerve Diseases

Introduction

The optic nerve carries information from the retina in the eye to the brain where it is processed to produce the visual impression of an image. It may get affected in a number of conditions both involving the optic nerve directly (inflammation or swelling or ischemia or atrophy) or indirectly (in neurological diseases such as Multiple sclerosis, Alzheimer’s disease, Parkinson’s disease, stroke, and brain tumors). In some cases, the optic nerve may appear normal but the visual pathway in the brain may be affected resulting in cortical visual impairment.

The pink disc seen in the image above is the optic nerve

Types of Optic Nerve Diseases

Optic Neuritis: This refers to inflammation of the optic nerve secondary to either a loss of nerve sheath covering (demyelination) as seen in multiple sclerosis or infections in the body or due to unknown causes.

Fundus photograph showing blurred optic nerve margins with pink color suggestive of papillitis(optic neuritis)

Ischemic Optic Neuropathy: This is like a mini stroke of the optic nerve whereby the optic nerve does not receive blood for a short period of time due to blockage of some small blood vessel.

Papilledema: This is optic disc swelling of both the eyes secondary to raised intracranial or brain pressure.

Severe disc edema suggestive of papilledema

Optic Neuropathy: This is a group of optic nerve disorders which result in an abnormal function of the optic nerve and may result in optic atrophy. They may be hereditary or secondary to medications or toxins or after some trauma. They generally do not cause inflammation or swelling of the optic nerve.

Optic Atrophy: This refers to an end stage condition of the optic nerve where the nerve gets permanently damaged and thinned out due to many conditions such as the optic nerve diseases described above or conditions related to neurology and neurosurgery.

Pale yellow appearing optic nerve suggestive of optic atrophy

Symptoms of optic nerve diseases

Optic nerve diseases present with:

·         Blurring of vision

·         Decreased vision

·         Transient vision loss

·         Loss of visual field

·         Pain behind the eyeball on movement of eyes

·         Reduced colour perception

·         Reduced brightness perception

Causes

·         Genetic: Optic nerve diseases are often hereditary which means that they are passed on through the family and result from a defect in some gene.

·         Neurological diseases: Diseases such as Multiple Sclerosis, Alzheimer’s disease, Parkinson’s disease, stroke etc.

·         Brian infections and brain tumors

·          Trauma: Injury to the head can often result in optic neuropathy and atrophy.

Risk Factors

·         Family history

·         Diabetes

·         High blood pressure

·         Low blood pressure

·         High lipids

·         Obesity

·         Multiple sclerosis

·         Neurological disease

·         Neurosurgery

·         Head Trauma

·         Eye diseases such as uveitis, glaucoma

·         Sleep Apnea

Tests and Diagnosis

Optic nerve diseases require careful eye examination and special tests to reach a proper diagnosis

These include:

1.      Visual acuity testing: The vision is tested using a vision chart

2.      Dilated eye examination for viewing the optic nerve and retina.

3.      Colour vision testing: This is done using special charts or books or computer software to determine if there is reduced color perception.

4.      Contrast sensitivity testing is done using special charts or computer softwares to determine the ability to see objects in low contrast.

5.      Stereoacuity: This is a special test used to evaluate the optic nerve and higher brain functions with the use of special glasses and booklets. The test determines the ability of both eyes to see together to give 3-Dimensional sight.

6.      Visual field tests/perimetry: This test is done using a specialised machine to determine the area among our eyes that you are being able to see. In many optic nerve diseases the field of vision seen by the eye reduces or becomes abnormal.

7.      Visual evoked response/electrophysiology: This tests the ability of the optic nerve to conduct signals to the brain. The test involves putting electrodes near the forehead and the back of the skull which detect electric signals when a bright flash of light or patterned stimulus is presented to the eye.

8.      Optic nerve imaging: This is done with the help of equipment such as the optical coherence tomography to get a very detailed vew of the optic nerve.

9.      Brain imaging: A CT scan or MRI of the brain and eyes help establish a clear diagnosis in many cases of optic nerve diseases.

Treatment

·         Lifestyle modifications: Management of diabetes, hypertension, high lipds and obesity are important through lifestyle modifications and medicines.

·         Medical therapy: Intravenous steroids are the treatment of choice for optic nerve diseases such as optic neuritis or traumatic optic neuropathy. Other medicines used include aspirin for ischemic neuropathy and nerve tonics or multivitamin preparations.

·         Surgical therapy: Surgical therapy includes optic nerve decompression for traumatic optic neuropathy or optic nerve sheath fenestration for idiopathic intracranial hypertension.

Prevention

Optic nerve diseases can be prevented by regular eye check-up and control of risk factors such as diabetes high blood pressure or low blood pressure, high cholesterol levels, obesity and sleep apnea.

When to contact the eye doctor

            Contact the doctor if you have

·         Any of the symptoms suggestive of optic nerve disease

·         Neurological disease

·         Brain infections

·         Brain tumors

·         Diabetes, high blood pressure or low blood pressure, high lipids and obesity