What is Optic Ischemia?
Optic ischemia, also known as ischemic optic neuropathy, is a group of blood vessel-related diseases that affect the optic nerve, which sends images from your eyes to your brain. The condition is divided into two types: anterior and posterior. People with anterior ischemic optic neuropathy often experience swelling of the optic disc, while those with the posterior type do not.
The most common version of the illness, called Nonarteritic Acute Anterior Ischemic Optic Neuropathy (NAION), usually affects individuals who have a small, crowded optic nerve. The exact cause of this disorder is not yet known, and we’re still in the process of finding effective treatments to cure or prevent it. Posterior ischemic optic neuropathy, which is less common, is typically associated with heart problems or conditions related to surgery. This type also does not have a specific treatment yet.
It’s critical to urgently evaluate for giant-cell arteritis (GCA), a disease that may cause inflammation of the arteries. Swift treatment with an intravenous drug called methylprednisolone can limit vision loss in the affected eye and stop the disease from spreading to the other eye.
Your optic nerve, a sort of cable composed of many individual nerve fibers, extends from the eyeball to a part of the brain known as the chiasm. This nerve has 4 sections with varying lengths. These nerve fibers begin from cells in the retina (the light-sensitive layer at the back of the eye) and come together at a spot called the optic disc, also known as “the blind spot.” From there, they travel a short distance within the eye before penetrating a sieve-like structure in the eye’s white outer layer, called the “lamina cribrosa.”
Protective layers surround the optic nerve, including the optic nerve sheath that has a thickness of about 1 mm. This protective covering varies in thickness depending on the section of the optic nerve it’s protecting. The space is filled with a brain fluid, and it has a complex structure with changes along the nerve’s course.
The optic nerve can be damaged by ischemia (lack of blood flow) anywhere along its path. Particularly, it’s supplied by a network of 6 to 12 small arteries that creates a circular network named “circle of Zinn-Haller.” The optic nerve head receives blood in a specific pattern.
The anterior (front) part of the optic nerve contains a tightly packed network of tissues, while the middle section has walls and pillars separating the space into linked rooms. Both these structures are also present in the posterior (back) part where the protective sheath travels through a canal in the bone of the eye socket. The right and left optic nerves cross each other inside the skull to form the optic chiasm, linking with the part of the brain that processes visual information.
What Causes Optic Ischemia?
Anterior ischemic optic neuropathy (AION), a condition that affects your eye’s optic nerve, is much more common than a similar condition called posterior ischemic optic neuropathy (PION). AION itself can be further categorized into two types: arteritic and nonarteritic forms.
Arteritic AION, or AAION, usually occurs in people aged 70 or older, and is caused by an inflammatory condition that blocks the arteries in the eye, leading to poor blood supply. It is often related to systemic vasculitis, a type of inflammation in blood vessels, with Giant Cell Arteritis (GCA) being its most common cause.
The reason behind nonarteritic AION, or NAION, is unclear. However, having a certain kind of structural arrangement in your eye’s optic disc (the part that helps to transmit visual information to the brain), which is commonly known as a “disc at risk”, might increase the chance of developing this condition. This is because, due to any stress factor, the tiny blood vessels in the eye may not fill with adequate blood, resulting in damage. Other potential risks include high blood pressure, diabetes, high cholesterol, certain blood clotting disorders, sleep apnea, nighttime low blood pressure, certain medications for erectile dysfunction such as sildenafil, anemia, smoking, migraine, and optic nerve head drusen (a buildup of protein and calcium salts in the eye).
As for PION, it’s relatively rare compared to AION. Three primary situations can lead to PION. Firstly, it may occur during surgeries especially of the spine, heart, and head and neck due to factors like severe blood loss, extended anesthesia, and low blood pressure affecting the eye’s blood supply. Secondly, PION could occur due to arteritic causes, with GCA being the most common. Lastly, nonarteritic PION could develop due to conditions that are similar to those that cause NAION.
Risk Factors and Frequency for Optic Ischemia
NAION, or Nonarteritic Anterior Ischemic Optic Neuropathy, makes up about 85% of all AION, or Anterior Ischemic Optic Neuropathy, cases. It’s estimated that there are around 6000 new NAION cases each year in the United States. It’s more commonly found in men and white individuals. The rate at which it occurs in the general population is about 10.3 cases per 100,000 people each year. Typically, people who are diagnosed with this condition are around the age of 72. AAION, or Arteritic Anterior Ischemic Optic Neuropathy, is much less common, with only 0.36 cases per 100,000 people each year.
Signs and Symptoms of Optic Ischemia
Optic ischemia is a condition that often leads to a sudden, painless loss of vision. Other symptoms can vary depending on the specific type of optic ischemia a person has. It’s important for doctors to find out when a patient’s visual symptoms started, and for how long they’ve been going on. Some people may also have associated symptoms like a headache, jaw pain or sensitivity on the scalp. Understanding a patient’s vascular risk factors, current medications, surgical history and family history of eye or vascular diseases can be helpful too.
When physically examining a patient with optic ischemia, doctors look at aspects like visual acuity using standard charts, visual field, and the back of the eye. The eye’s pupil response, pressure within the eye, and eye movements will also be assessed. A thorough examination of the patient’s general health, including their vital signs, cardiovascular health, and signs of systemic vasculitis, is also part of the evaluation process. This can guide a doctor as they diagnose and plan treatment.
Arteritic Anterior Ischemic Optic Neuropathy (AAION) is more common in older patients, typically around 70 years old. Vision loss in these cases is often severe, with 70% of patients having less than 20/200 vision, and 20% of patients having no light perception. In most cases, it is linked to vasculitis, with Giant Cell Arteritis (GCA) being the most common cause. Identifying GCA symptoms is crucial because without prompt treatment, the patient’s other eye is at high risk of vision loss. GCA can also lead to serious complications like stroke, aortic dissection, and heart attacks, which can be prevented with timely treatment.
- Systemic GCA symptoms include headaches, sensitivity on the scalp, and jaw pain due to a shortage of blood supply to the jaw muscles.
- Other non-specific signs like weight loss, fever, night sweats, feelings of being unwell and depression can be present.
- Polymyalgia rheumatica, a condition characterized by pain and stiffness in muscles like the shoulders and thighs, is often found in patients with GCA.
Nonarteritic Anterior Ischemic Optic Neuropathy (NAION) is not usually associated with pain. The vision loss in NAION can be sudden, gradual or stepwise and is less severe than AAION. Patients with NAION typically first notice vision loss after waking up and it may continue to worsen over weeks to months before finally stabilizing.
Lastly, Posterior Ischemic Optic Neuropathy (PION) is a rare type of optic ischemia that leads to vision loss that can affect one or both eyes. Patients with PION typically do not have optic disc swelling in the early stages of the disease but tend to develop optic atrophy after a few months.
Testing for Optic Ischemia
If your doctor suspects you might have GCA, a condition called Giant Cell Arteritis that causes inflammation in the arteries of your scalp and other parts of your body, they’ll conduct some tests to rule it out. They will check your blood for signs of inflammation using tests called ESR (Erythrocyte Sedimentation Rate) and CRP (C-reactive protein). However, these tests can suggest other conditions too, they aren’t specific to GCA.
Your doctor may also take a small sample of one of your arteries, specifically the one from your temple, to study it under a microscope (this is known as a biopsy). They need at least 2 cm of the artery to make a proper evaluation. If GCA is present, the artery will usually show symptoms of inflammation. However, biopsies can sometimes miss GCA, leading to negative results even though the patient has the condition. In such cases, non-invasive techniques like MRI (where a large magnet and radio waves create detailed images of your body) and Doppler ultrasound (a test that uses sound waves to create images and check blood flow) might be used.
The doctor will also look at your risk of developing blood vessel diseases. They might ask for tests to check your blood pressure, lipid profile (the cholesterol levels in your blood), blood sugar, and hemoglobin A1c levels (a test to diagnose and monitor your diabetes) because you may have these conditions without knowing it. They’ll also ask about your sleep patterns to check for sleep apnea, review your medications, particularly to see if you’re taking a type of drugs known as phosphodiesterase type 5 inhibitors, and finally, they will test you for high levels of an amino acid called homocysteine, especially if you’re younger than 50.
The doctor will also use a test called fluorescein angiography where a special dye is injected into your bloodstream and pictures are taken as the dye circulates in your eyes. Normally, the dye reaches your choroid, the layer of blood vessels and connective tissue between the sclera (the white part of the eye) and retina (the layer of tissue at the back of your eye), 3 to 5 seconds before it reaches the retinal arteries. However, if you have AAION, there might be a delay in the dye reaching your choroid. Visual field tests, where you might be asked to count fingers in your peripheral vision, or automated perimetry, a computer-based test, could reveal abnormalities often tied to AAION, typically presenting as an area of lost or decreased vision within the visual field, commonly lower down.
Treatment Options for Optic Ischemia
Arteritic Anterior Ischemic Optic Neuropathy is a condition where blood flow to your eye’s optic nerve is blocked. It’s crucial to start treatment as soon as you possibly can if there is a high chance you have this condition. Doctors will first take samples of your blood for tests, but it’s more important to begin treatment right away rather than wait for the results. This condition can cause vision loss in your other eye too, so prompt treatment helps to protect your sight.
Doctors usually recommend starting treatment with a strong corticosteroid medication, given through an intravenous line (directly into your blood) for 3-5 days. After this, you’ll usually switch to an oral steroid medication, reducing the dosage slowly over 3 to 12 months. Your doctor will continue to monitor inflammation markers in your blood through the treatment.
Nonarteritic Anterior Ischemic Optic Neuropathy or NAION is a similar condition, and there’s ongoing debate about the best way to treat it. So far, some treatments have partially helped to improve the vision, including corticosteroids, a type of surgery to relieve pressure on the optic nerve, and a medication called levodopa. There are currently studies exploring the use of stem-cell therapy for repairing the damage – these have had promising results so far. The main focus of managing NAION is to prevent vision loss in the unaffected eye. This involves managing any underlying health conditions such as diabetes, high-blood pressure, high cholesterol, quitting smoking, and treating sleep apnea.
What else can Optic Ischemia be?
Optic ischemia, particularly non-arteritic anterior ischemic optic neuropathy (NAION), can appear similar to optic neuritis. They both can cause sudden vision loss, pupil abnormalities, and swelling of the optic disc. However, optic neuritis has its own unique characteristics. These may include:
- Mostly impacts individuals who are 40 years old or younger
- Pain when moving the eyes
- Loss of central vision
- No delayed disc filling detected during an eye procedure called fluorescein angiography
An MRI that uses a contrast dye may be able to distinguish between these two conditions. In the case of NAION, the affected optic nerve would usually appear normal, whereas in optic neuritis, the presence of the contrast dye enhances the optic nerve.
Other conditions which may appear like Anterior Ischemic Optic Neuropathy, or AION, include optic nerve compression. This may happen due to a tumor, inflammation, or an aneurysm in the optic nerve. Contrast imaging can help to identify the differences.
Drusen in the optic disc, a condition where the optic disc appears to be small and elevated, can also resemble optic ischemia. Although, most often, this condition does not impact vision and does not have symptoms. However, a few people may experience brief visual disturbances.
What to expect with Optic Ischemia
The outlook for any form of ischemic optic neuropathy, a condition that affects the optic nerve due to insufficient blood flow, is typically unfavorable. Vision loss often becomes permanent in these cases. Research has shown that on average, people with a type of this condition known as NAION (non-arteritic anterior ischemic optic neuropathy) had a visual sharpness of 20/200. This means they can see at 20 feet what a person with normal vision can see at 200 feet.
A separate study found that out of 184 eyes affected by NAION, 83 achieved a visual acuity of 20/40 or better, where they see at 20 feet what a normal visioned person can see at 40 feet. However, for a different type of the condition known as AAION (arteritic anterior ischemic optic neuropathy), only 8 out of 45 eyes reached that level of visual sharpness.
Possible Complications When Diagnosed with Optic Ischemia
The gravest and unavoidable result of ignored optic ischemia is optic atrophy. This condition generally develops a few months after the low blood flow event to the eye. Simply put, optic nerve atrophy comes from the death of eye nerve tissue. This can lead to total loss of vision in that particular area of sight because the signal from the retina fails to communicate with the brain.
- Ignores optic ischemia can lead to optic atrophy
- Optic atrophy typically comes up a few months after the ischemic event
- This condition is caused by the death of optic nerve tissue
- Optic atrophy may cause complete vision loss in the corresponding visual field area
- The issue arises when the retina-to-brain signal transmission fails
Preventing Optic Ischemia
To prevent optic ischemia, which is poor blood flow to the eyes, it’s important to manage health issues that can be controlled, such as high blood pressure, high cholesterol, obstructive sleep apnea (a sleep disorder where a person’s breathing is interrupted), smoking, and diabetes. This can be done by living a healthy lifestyle and taking prescribed medications. Keeping a regular check on your overall blood vessel health and early detection of conditions that might lead to poor eye blood flow, like giant cell arteritis (an inflammation of the arteries), is crucial.
It’s also key for patients to understand the importance of preventative measures and getting medical help on time to control these health issues. Doing so can significantly lower the risk of developing optic ischemia.
If someone has optic ischemia in one eye, they should seek immediate medical help if they suddenly and severely lose vision in their other eye. The importance of regular health checkups cannot be overstated for preventing optic ischemia in the second eye, especially for controlling diseases like hypertension (high blood pressure), diabetes, and obstructive sleep apnea.
AAION, a particular type of optic ischemia, is closely linked to GCA (giant cell arteritis). At-risk individuals should be informed about the need for urgent checks for symptoms such as fever, unintended weight loss, scalp tenderness (a sensitive scalp), and jaw claudication (pain in the jaw while eating or speaking). In such cases, a doctor should be consulted for comprehensive care and preventing any long-term complications that might occur from systemic steroid therapy (a type of treatment that involves medications called steroids), considering the extended time needed for AAION treatment.
