Ischemic optic neuropathy (ION) is a disorder where there exists optic nerve damage due to inadequate supply of blood.
The optic nerve is made up of tiny fibers which carry signals from the eyes to the brain. The brain interprets the information and produces visible images. These fibers require nutrients and oxygen which the blood supplies. When the blood flow is interfered with, the optic nerve stops working and may eventually die.
The damage can either occur on the head or the back part of the optic nerve. Sometimes the whole nerve may be affected.
Ischemic optic neuropathy can be broadly categorized into:
- Anterior ischemic optic neuropathy (AION) – This condition only affects the head of the optic nerve. It accounts for most of the cases.
- Posterior ischemic optic neuropathy (PION) – This involves the retrobulbar portion of the optic nerve. It is rare accounting for only 10% of cases.
Causes and Risk Factors
Ischemic optic neuropathy can further be classified as follows depending on the cause:
- Arteric ION - This is a rare form, caused by an inflammatory disorder of the arteries. Giant cell arteritis (GCA) is responsible for most of the cases. The result is usually a massive loss of vision. The damage begins in one eye but eventually moves to the other eye if the individual is not treated early. The disease affects persons over 50 years of age. It is more popular in women than in men.
- Non-arteric ION – It is a more frequent type, usually occurring due to unapparent causes. However, individuals with underlying vascular diseases are believed to be at a high risk of developing the condition. The vascular diseases include diabetes, hypertension, and atherosclerosis. Certain drugs are also known to contribute to non-arteritic ischemic optic neuropathy. The disease affects individuals over 50 years old.
- Perioperative ION - In rare cases, ischemic optic neuropathy may be related to surgery. This includes spinal, cataract, or cardiac operations. Usually, the patient awakens to sudden unilateral or bilateral loss of vision.
Signs & Symptoms
The signs and symptoms can include:
- Sudden loss of vision/blurred vision – Due to poor blood supply, vision may suddenly darken for a few minutes or seconds and then return to normal. When this happens, it is referred to as a transient ischemic attack (TIA). Other times, the vision may become blurry. There is usually no pain.
- Swollen optic disc – This happens in anterior ION where the head of the nerve swells. It may also occur in posterior ION but after 4 to 8 weeks from the onset of the disease.
- Afferent pupillary defect – This is where the pupils of a person respond differently to light shone on the eyes. It is apparent in posterior ION in cases where the eyes are asymmetrically affected.
Where the condition is caused by GCA, patients will usually have other symptoms at the onset. These include:
- Temple pains
- Scalp tingling/pain
- Muscle aches
- Jaw pains
- Loss of appetite and weight
The following tests may be conducted:
- Ophthalmoscopy exam – A device is used to magnify the eyes in order to see the inside clearly. In anterior ischemic optic neuropathy, the eye professional may observe swelling of the optic disc.
- Dilation test – Light may be shone on both eyes to see the difference in how the pupils dilate. Where there’s afferent pupillary defect, the posterior portion of the optic nerve could be affected.
- Visual acuity and field tests – This tests for clarity as well as the degree of visual field.
Treatment focuses on preventing further damage as well as retaining any vision left.
The eye care professional will prescribe medication based on the cause. For arteric ION, the patient may be issued with high-dose corticosteroids. Methylprednisolone is an example of indicated steroid drugs. It is usually administered intravenously. The drug works to prevent further loss of vision by preventing release of substances that cause inflammation.
For non-arteric ION, treatment is geared towards regulating risk factors. Patients are also required to eat a healthy diet, to avoid smoking, and to exercise. Aspirin may in some instances be indicated to control the vascular conditions.
If not detected early and treated, the patient can go blind within 5-10 days. With proper treatment, however, some useful amount of vision can be retained. Arteric ION causes the greatest loss of vision. It starts in one eye then moves to the other.
Ischemic optic neuropathy can be prevented by controlling the risk factors. For those with vascular diseases, taking medication and paying regular visits to an eye care provider reduces the risk of developing the condition.
Those taking drugs to lower blood pressure or erectile dysfunction medications should avoid taking them before going to bed. The drugs interrupt the supply of blood to the optic nerve. Blood pressure is also usually low at night while sleeping which might contribute to the damage.