Introduction:
Many systemic and vascular diseases harm the health of the eye. Infarction of the optic nerve is a rare complication. It may result in partial or complete vision loss in one or both eyes. This disease is characterized by painless acute vision loss. Specific medical conditions are not the causative factors of optic nerve infarction; however, conditions such as diabetes, hypertension, and chronic smoking can worsen the condition. Optic nerve infarction is suspected in individuals of age 55 and older who experience sudden, painless vision loss.
What Is an Infarction?
An infarction is an injury of tissue that causes cell death and necrosis in the affected area. This infarction is caused due to reduced or restricted blood flow to the affected area. Inadequate blood flow resulting in oxygen deprivation of the tissues leads to cell death. An infarction in the optic nerve is also known as Ischemic optic neuritis.
How Does an Infarction Develop in the Optic Nerve?
Infarction in the optic nerve is associated with damage to the optic disk. The optic disk is present at the back of the inside of the eye where the axons (long projection of the nerve cells that transmits electrical impulses through the neurons) of the retinal ganglion cells meet and exit to form the optic nerve. It is also called the optic nerve head.
Optic nerve infarction may be of two types -
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Arteritic anterior ischemic optic neuropathy (A-AION).
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Non-arteritic anterior ischemic optic neuropathy (NA-AION).
What is Arteritic Anterior Ischemic Optic Neuropathy (A-AION)?
This acute, painful neuropathy is seen in individuals aged 55 years and above. Arteritic anterior ischemic optic neuropathy (A-AION) is caused by inflammation of the arteries that supply blood to the optic nerve. As a result, there is an obstruction in blood flow at the optic nerve head. Restricted blood flow to the optic nerve damages the optic nerve as the nerves depend on the blood supply for nutrients and oxygen, which will hamper its function of transmitting signals from the eye to the brain. The inflammation of the arteries supplying the optic nerve is caused due to a condition known as giant-cell arteritis or temporal arteritis. Giant cell arteritis is the inflammation of the medium-sized and large arteries. Giant cell arteritis can permanently damage the optic nerve head leading to massive, permanent vision loss if left untreated. General symptoms of giant cell arteritis are seen before the development of vision loss. 80 % of the affected individuals will experience the following symptoms before any vision loss occurs -
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Pain in the temple region, pain while chewing food.
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General fatigue.
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Loss of appetite, unexplained weight loss.
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Fever.
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Pain in the scalp and neck.
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Muscles pain in the entire body.
The main symptoms related to vision are painlessness, temporary blurring, or vision loss. Before the permanent loss of vision, there will be a few minutes or hours of blurred vision. This temporary blurring of vision is a warning sign. Although initially, one eye is affected, this is a critical period because if an ophthalmologist checks the patient, the vision in the other eye can be saved.
What Is Non-arteritic Anterior Ischemic Optic Neuropathy (NA-AION)?
This is a commonly occurring form of ischemic optic neuropathy. Individuals aged 45 years and above are mostly affected, but it can occur at any age. The cause of this condition is not inflammation of the arteries, but it is caused due to an abnormal drop in blood pressure, especially after the person has woken up from sleep. It is believed that the normal blood pressure of the body drops down when a person is asleep. But this alone cannot cause this condition. The presence of associated risk factors also contributes to this condition. Below are the common causes of this condition.
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Decreased blood pressure leads to a reduced blood supply to the optic nerve.
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Elevated eye pressure happens due to a build-up of fluid inside the eye. This fluid is known as the aqueous humor that flows inside the eye. This condition also leads to NA-AION.
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An increase in the thickness of blood or high viscosity of blood will also cause this condition.
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Decreased blood flow to the optic nerve head (the point where the retinal ganglion cells meet and exit the eyeball to form the optic nerve).
The symptoms of non-arteritic ischemic optic neuropathy comprise sudden, painless loss or blurring of vision that occurs after a person has woken up from sleep or a nap. General symptoms are similar to arteritic anterior ischemic optic neuropathy.
Who Is at High Risk for Developing Optic Nerve Infarction?
Patients with the following conditions are more prone to developing infarction of the optic nerve -
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Patients who are suffering from systemic diseases such as high blood pressure, high cholesterol levels, and diabetes.
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Patients with underlying heart diseases and blocked arteries.
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Chronic smokers.
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Patients who are suffering from anemia due to sudden blood loss.
How Is Optic Nerve Infarction Diagnosed?
Diagnosing optic nerve infarction is mostly done clinically, but laboratory tests are also critical in diagnosing this condition.
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Blood tests are carried out to detect hypertension, diabetes, elevated cholesterol levels, and anemia.
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The ophthalmologist performs a detailed ocular examination and tests for assessing the visual field and clarity of vision. The ophthalmologist also carries out measurements of the fluid pressure within the eye.
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Measurement of blood pressure is done.
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Other blood tests, such as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and platelet count, check for inflammation in the body.
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Angiography may be carried out to determine the blockages in the affected arteries. Angiography involves injecting radioactive dyes into the arteries to visualize the presence of arterial blockages that are interrupting the blood flow.
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A biopsy of the affected nerve may be carried out in the temple region of the head to assess for arterial inflammation.
What Is the Treatment of Optic Nerve Infarction?
The physician aims to treat the underlying health problems that have caused this condition.
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Medications are prescribed to control diabetes and hypertension, medicines to lower cholesterol levels, and medications to treat anemia.
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The inflammation of the arteries is treated with oral corticosteroid medications. An initial high dosage of steroid medications is prescribed to lower the inflammation, and the dosage is tapered over time. However, the patient will have to continue low-dose steroid medications life-long to prevent blindness.
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Surgeries are also recommended in severe cases of arterial blockage, but they have poor outcomes.
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Assistive technology devices like magnifiers are recommended to the patients, which will help with better vision.
What Is the Prognosis of This Condition?
It is difficult to prevent vision loss in optic nerve infarction cases. The timing of diagnosis and initiation of treatment is critical in deciding the outcome of the treatment. If the patient visits the doctor immediately after the appearance of the symptoms, the vision can be preserved. Long-term steroid therapy has been proven to prevent blindness. Patients have been able to live healthy lives with compromised vision.
Conclusion:
The amount of vision loss depends upon the extent of damage to the optic disk. Some patients may have a complete loss of vision, while some may retain vision in one eye. 40 percent of the affected individuals will find improvement in vision after corticosteroid therapy, whereas a small number of patients experience worsening symptoms and do not respond well to treatment. The patients have to learn to live with the disability and make use of vision-assisting devices to carry on their lives with limited visibility.
