admin No Comments

Optic Nerve Atrophy: A Detailed Pathophysiology!

Optic Nerve Atrophy: A Detailed Pathophysiology!

Optic Nerve Atrophy (ONA) is mild to severe damage to the optic nerve resulting in loss of some or most of the nerve fibers. This progressive degeneration is in turn associated with variable degree of visual dysfunction.

Optic nerve also known as the second cranial nerve, is a bundle of millions of nerve fibers, conveying the visual information, from retina of the eye to the specific optic centers of the brain. When some of these nerve fibers are severely damaged due to diseased condition; the passage of information from eye to the brain and vice versa is blocked, this in turn can reduce person’s visual acuity. If ignored for a long term; it leads to the permanent blindness.

Thus, optic atrophy itself is not a disease, but an end result of the destruction to the optic nerve, due to several diseased conditions; which may also be progressive, depending upon its Pathophysiology. Common symptoms associated with optic atrophy include visual loss, reduced ability to distinguish colors, blurring of vision , double vision , etc. Clinically pallor of the optic disc/nerve, abnormal reaction of the pupil to light along with reduced visual acuity firmly establishes the diagnosis.With conventional treatment approach, medical fraternity is unable to restore the lost function of an atrophic optic nerve; however the primary focus would always be to pinpoint the possible cause of damage and to stabilize further progression.

Although there are diverse causes ranging from trauma to hereditary causes, that can cause injury to the optic nerve; by far some of the most common causes are Ischemic Optic Neuropathy, Optic Neuritis and Glaucoma.

Ischemic Optic Neuropathy

It is the most common cause of acute optic neuropathy, especially in older adults above 50. Also It is often referred to as the stroke of the optic nerve, occurring due to reduced or blocked blood circulation to the vessels supplying the front or the anterior side of the optic nerve (Anterior optic nerve atrophy or AION).There are two different mechanisms responsible for causing the vision loss from AION, the “arteritic”  and the ‘non arteritic forms.

The “arteritic” form caused by a disease called Giant Cell Arteritis (GCA) predominantly affects those over the age of 55 and it is estimated that women are three times more vulnerable to the condition, than men. In about 80 % of the reported cases, patients exhibit symptoms such as general fatigue, weight loss, fever, pain in neck, difficulty in chewing, headache, anemia and achy joints; which can proceed towards the blurry vision or total vision loss.

The “Non-Arteritic” form is the most common form of AION with a better visual outcome than the arteritic form. It generally affects a patient at any age with about 10% of patients being under the age of 45. Both males and females have equal predilection. It is caused by an acute impairment to the circulation of the arteries supplying the optic nerve due to a temporary fall in blood pressure. Some of the common diseases which can put a patient at higher risk for ‘Non arteritic’ form are Diabetes mellitus, Rheumatoid Arthritis, Herpes Zoster, Anemia, Sickle Cell Trait, Syphilis, and Polyarteritis nodosa.

Optic Neuritis

Optic neuritis is an inflammation of the optic nerve, as a result of damage to its myelin sheath; causing it to pain and leading to the temporary visual loss. The condition often precedes the onset of neurodegenerative autoimmune diseases, such as multiple sclerosis, neuromyelitis optica.

A gradual restoration of vision, back to normal is a characteristic of optic neuritis; althoughvision loss is permanent in some cases., with color vision and high sensitivity to contrast and brightness. Some of the common symptoms of optic neuritis include pain, temporary vision loss in one or both the eyes, loss of ability to discriminate colors, etc. Some people with optic neuritis report seeing flashes or flickers of lights.

Glaucoma

Glaucoma is a condition associated with gradually progressive optic nerve damage. It usually occurs due to increased pressure as a result of fluid accumulation on the front walls of the eye. The studies have indicated that eye pressure is the primary factor for glaucoma and eventually optic nerve damage. According to the recent survey, Glaucoma is the second leading cause of visual damage in the developed countries. As there are no significantly reported early symptoms for glaucoma; more than 60% of cases go unnoticed in their initial stages.

Apart from these common causes, other less noted causes are, inherent underdevelopment of the optic nerve affecting children and young adults; diseased conditions such as brain tumor, cranial arteritis, pituitary gland tumors and swelling of the blood vessels known as cerebral aneurysm can as well pressurize optic nerve; leading to its damage.

Other direct reasons that are responsible for optic nerve damage are trauma, shock, long term exposure to radiations, etc.

Conclusively it has been widely accepted that Optic Nerve Atrophy is relatively very easy to diagnose; but the cause for the same is quite difficult to ascertain. It is thus very important to keep a check on some of the related symptoms and physical presentations for patients complaining sudden visual issues.