What is Non-Arteritic Anterior Ischemic Optic Neuropathy?
Non-arteritic anterior ischemic optic neuropathy (NAION), an illness that causes swelling and damage to the optic nerve, is the most common cause of these issues in adults over 50 years old. Certain risk factors have been strongly linked with this condition. These include high blood pressure, high cholesterol levels, diabetes, heart and brain blood vessel diseases, and sleep apnea.
Though the exact process that leads to NAION is not entirely clear, it is mostly believed to be caused by inadequate blood supply to the optic nerve. This inadequate blood supply comes from specific small arteries behind the eye, leading to lack of oxygen, which then causes swelling of part of the optic nerve that travels through a small opening in a stiff outer layer of the eyeball. This swelling leads to pressure on the surrounding nerve fibers, which are now cramped in a space made smaller by the small opening in this outer layer, leading to cell death and damage to the optic nerve.
Research on the progression of NAION has been conducted in the Ischemic Optic Neuropathy Decompression Trial. The results show that about 30% of patients would regain some vision after two years, 20% lose more of their vision, and in most patients, vision stays unchanged after the onset of the disease. What actually happens is that the vision doesn’t really change in most patients after the initial phase of the disease has passed, and those who can see a bit more lines are more likely to learn and improve how they focus their sight.
What Causes Non-Arteritic Anterior Ischemic Optic Neuropathy?
The optic nerve head (the part of the optic nerve we can see in the eye) is divided into four areas: inside the eye, and three regions named prelaminar, lamina cribrosa, and retrolaminar. The optic nerve head gets its blood supply mainly from small arteries at the back of the eye, called short posterior ciliary arteries. There are also some secondary sources that vary from person to person.
These small arteries are connected to each other in a circle, called the “circle of Zinn-Haller.” This circle surrounds the optic nerve as it goes through a layer of the eye, called the sclera, via the region named lamina cribrosa. Every vessel providing blood supply to the optic nerve head, comes from a large artery called the ophthalmic artery.
We’re still trying to understand what exactly causes NAION (Nonarteritic Anterior Ischemic Optic Neuropathy), a condition that leads to sudden vision loss due to the damage in the optic nerve. It is believed that it’s related to an insufficient blood supply to the optic nerve head and other factors. Swelling and a blockage in blood flow can damage the optic nerve fibers, most often in the upper-half of the optic nerve head.
Several factors can increase the risk of NAION, such as a small optic nerve head, eye conditions like optic disc drusen (tiny yellow or white deposits in the optic nerve), high blood pressure, diabetes, sleep apnea (breathing interruption during sleep), and the use of certain medications. Doctors are still studying how each of these factors contributes to NAION.
A significant risk factor for NAION is having what doctors call a “disc-at-risk”: an optic nerve head that is small in size and structure. It’s thought that if the optic nerve head is swollen due to an injury that blocks blood flow, the nerve fibers get compressed, leading to damage. The same happens with optic disc drusen. Other conditions like high blood pressure, diabetes, high cholesterol levels, and smoking also can contribute to NAION by damaging the blood vessels around the eye.
Sleep apnea is a more recently recognized risk factor for NAION. It is thought to increase the risk of NAION because it can affect your blood pressure during sleep.
Risk Factors and Frequency for Non-Arteritic Anterior Ischemic Optic Neuropathy
NAION, or non-arteritic anterior ischemic optic neuropathy, is the most common cause of optic nerve damage in adults over the age of 50. In the United States, the rate of NAION can vary from 2.3 to 10.2 cases per 100,000 people. While this condition can affect anyone, it’s found more often in Caucasians than in African Americans. The reason behind this is that African Americans usually have a larger cup-to-disc ratio in their eyes, making them less likely to have small optic nerve cups – the major risk factor for NAION.
Signs and Symptoms of Non-Arteritic Anterior Ischemic Optic Neuropathy
In a complete neuro-ophthalmological exam, your doctor will ask about when your vision loss started. They’ll also want to know if you’ve had any other symptoms. About 10-15% of patients with Nonarteritic Anterior Ischemic Optic Neuropathy (NAION) experience pain in and around the eye, though unrelated to eye movement. Usually, there are no other neurological symptoms reported. Your doctor will also want to know if you’re taking any specific medications, particularly PD-5 inhibitors, anti-hypertensive medications, and amiodarone. This is because these drugs could be associated with anterior optic neuropathy, a condition that can look a lot like NAION.
In the physical exam, your doctor will measure your visual sharpness, which can range from perfect vision (20/15) to not being able to see light at all. Though, it’s rare to have vision loss severe enough to only detect hand motions in NAION. They’ll also check for a relative afferent pupillary defect, which should show up in all patients during their first visit. The doctor will also look for swelling in the optic nerve head, which should be present in all patients initially and can last for a month or two. During this period, vision can continue to get worse because of increased pressure in the compartment of the eye.
The exam will also include a visual field test, where you’ll be asked to look at different spots of light to check for blind spots in your vision. Typically, these blind spots follow the path of nerve fibers. Altitudinal defects, or loss of vision in the upper or lower visual field, are especially common. This might be because of the arrangement of the short posterior ciliary arteries, the blood vessels that supply blood to the optic nerve head. Your doctor will use a device to get images of the back of your eye, specifically the nerve fibers. This invariably shows thickening of the nerve fibers in patients with NAION.
Finally, your doctor will check for the so-called “disc at risk,” a certain characteristic of the optic disc in the other eye. This is seen in over 95% of patients with NAION. If it’s not there, your doctor might need to reconsider the diagnosis.
Testing for Non-Arteritic Anterior Ischemic Optic Neuropathy
Diagnosing Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION), a medical condition that affects the optic nerve, largely relies on examining symptoms a patient is experiencing at the time they see a doctor. To confirm a diagnosis, doctors will look for swelling of the optic nerve within the patient’s eye. Almost all patients with NAION also have what’s referred to as a ‘disc-at-risk’ in the other eye, which means the ratio of the ‘cup’ (the depression in the middle of the optic nerve) to the ‘disc’ (the area where the optic nerve fits into the eyeball) is 0.2 or less.
People with NAION might experience various changes to their field of vision, but a common symptom is an ‘altitudinal defect’, a condition where half of the field of vision (either the top or bottom half) is obscured or lost. This visual defect is due to how the optic nerve’s top and bottom parts are each supplied by different groups of arteries. The sharpness or clarity of vision (visual acuity) can range from perfect 20/20 vision to complete loss of light perception, but severe vision loss is rare in NAION cases. If a patient does have severe loss of vision, it might be a sign of another condition called giant cell arteritis.
Although most NAION patients are over 50 years old, the condition can also occur in younger individuals. In younger patients, doctors might consider and rule out a different condition called demyelinating optic neuritis. A characteristic of demyelinating optic neuritis is slight swelling of the optic nerve along with seldom presence of blood spots around the optic nerve (less than 5% of cases).
In contrast to optic neuritis, pain with eye movements in NAION cases is highly uncommon, although discomfort in and around the eye can happen in up to 10-15% of patients. When it’s hard to distinguish between NAION and other illnesses affecting the optic nerve, a type of scan called an MRI with gadolinium can help. This type of MRI should appear normal in NAION patients and usually shows enhancement (or, highlighting) of the optic nerve in patients with inflammatory optic neuropathies, conditions involving inflammation of the optic nerve.
Treatment Options for Non-Arteritic Anterior Ischemic Optic Neuropathy
Many different medications and treatment methods have been tested for treating neuro-ophthalmology conditions such as Nonarteritic Anterior Ischemic Optic Neuropathy (NAION), which is a condition that affects the optic nerve in our eyes. However, none have shown to be effective yet.
One of the few rigorous scientific studies tested if a surgical procedure called optic nerve head decompression via vitrectomy would help patients with NAION. This procedure is meant to relieve pressure on the optic nerve, potentially improving eyesight. Unfortunately, the study found that this surgery was not only unhelpful but could also be harmful.
Several attempts have been made to treat the condition using injections of medications directly into the affected eye. Injections of bevacizumab and triamcinolone, which are drugs often used to treat eye disorders, have unfortunately shown disappointing results as well. Similarly, a trial evaluating an injection of QRK207, a medication meant to prevent cell death, did not demonstrate its effectiveness and the study was halted early.
Currently, the only ongoing research is studying the effect of RPh201, a natural compound derived from gum mastic, in patients who had the onset of NAION from 1 to 5 years ago. This treatment is given through subcutaneous injections, meaning it is injected under the skin. The effectiveness of this treatment is still being studied, and so the search continues for an effective treatment method for this eye condition.
What else can Non-Arteritic Anterior Ischemic Optic Neuropathy be?
In simpler terms, when doctors diagnose patients under 50 with optic conditions, they mostly consider two types of optic neuritis – one caused by the immune system attacking the myelin sheath of the optic nerve, and the other caused by specific antibodies. People with the first type usually experience pain when they move their eyes and do not have bleeding around the optic disc. While their vision typically gets better, this is not the case for patients diagnosed with Non-arteritic Anterior Ischemic Optic Neuropathy (NAION), whose visual function doesn’t generally improve.
People with the second type of optic neuritis often show signs of swollen optic nerves with visible hemorrhages, but like the first type, their sight usually recovers, contrasting with those suffering from NAION. Doctors also inquire about patients’ use of specific drugs like amiodarone and erectile dysfunction medications, as they might cause conditions similar to NAION that might improve when the patient stops taking the medicine. However, the link between NAION and phosphodiesterase inhibitors (common in erectile dysfunction medications) is still not clear.
For patients over 50, their diagnosis majorly involves a consideration for a condition called giant cell arteritis. If someone over 60 shows up with a swollen optic nerve, a doctor would test for inflammation markers to rule out this treatable condition. Sometimes, patients with a condition called compressive optic neuropathy might have a swollen optic nerve, but they usually lose their vision slowly, unlike in NAION, where vision loss is sudden.
What to expect with Non-Arteritic Anterior Ischemic Optic Neuropathy
The usual progression of Nonarteritic Anterior Ischemic Optic Neuropathy (NAION), a medical condition affecting the optic nerve, was revealed through a specific treatment study. The study showed that one-third of patients regain significant improvement in their vision at a two-year check-up, while 30% experience a notable loss in vision. The remaining patients’ vision pretty much stays the same.
In reality, most people probably keep their vision level after the initial inflammation of the optic nerve subsides. If any improvements are noted, these are likely due to the patient’s ability to adapt to the visual field defects, or scotomas, which are areas of decreased vision within the normal visual field.
Possible Complications When Diagnosed with Non-Arteritic Anterior Ischemic Optic Neuropathy
Ischemic optic neuropathies are conditions that can cause the optic nerve in one or both eyes to waste away. If not treated, it could lead to permanent loss of vision.
Preventing Non-Arteritic Anterior Ischemic Optic Neuropathy
Anterior ischemic optic neuropathy is a condition that can be affected by various risk factors, some of which can be modified or controlled. If you’ve been diagnosed with sleep apnea, a condition that disrupts your breathing during sleep, your doctor may suggest a sleep study and begin treatment to help manage this condition. This is because improving your sleep can also help manage the risk of this type of optic neuropathy.
Your doctor may also recommend changes to help control any risk factors related to your blood vessels. This could include things like managing high blood pressure, or making changes to your diet or exercise routine. It’s been suggested by many medical professionals that avoiding low blood pressure at night could be a helpful strategy to prevent this condition from affecting your other eye.
Finally, your doctor may also discuss the use of certain medications called phosphodiesterase inhibitors. These are drugs that help to improve blood flow, and so could potentially help in managing your condition. However, it’s important to understand the potential benefits and risks of any medication you take.
