What is Optic Disc Drusen?
Optic nerve drusen are small, hardened lumps that can be found in the optic disc, which is the front part of the optic nerve. This optic disc can be seen in retina examinations. These lumps are often found just before the surface of a sieve-like structure in the eye (lamina cribrosa) and are usually noticed in the nasal area of the disc.
More often than not, these hardened lumps, called “calcifications,” are discovered by surprise during an eye examination. They might grow and become more visible as a person ages, however, they usually stay the same over a person’s lifespan and typically don’t cause any symptoms. That said, in some cases, these optic nerve drusen have been linked to vision-related issues, temporary visual blurring, and even rare complications.
The drusen that are close to the surface can be diagnosed in a routine clinical examination, but the ones deeper inside may appear to be a swollen or fluid-filled optic disc. This condition, known as ‘papilledema’ or swelling of the optic disc due to high pressure in the brain, may actually indicate that further evaluation and testing are needed. Regardless of their position, surface or deep, both types of drusen are considered to be the same condition.
It’s important to note that even though optic nerve drusen can give the impression of a swollen optic disc, their presence doesn’t rule out the possibility of actual swelling or fluid buildup. For instance, it’s noted that a considerable number of young patients with a condition known as idiopathic intracranial hypertension – a condition that causes high pressure in the brain without a known reason – have optic nerve drusen. As of now, the exact pattern of inheritance of these drusen is not well understood, but it is believed that they might be passed down in families in an “autosomal dominant” manner, meaning one of the parents would carry and possibly show signs of the condition. However, this inheritance might not always be evident.
What Causes Optic Disc Drusen?
The cause of optic nerve drusen, small deposits that form in the optic nerve, is thought to be due to a slow-down in the movement of important cellular components within the optic nerve. This slow-down could be due to problems with the blood supply to the optic disc, which is the area where the optic nerve connects to the eye. When this cellular movement slows down, it can lead to a pile-up of hardened and degraded parts of cells, called mitochondria, which in turn can become a starting point for the formation of optic nerve drusen.
This disruption of cellular movement within the optic nerve may be linked to a variety of factors. This could include inherited abnormalities in the structure of the optic nerve head, errors in the process through which cells remove and recycle their own components, known as transcellular mitophagy, and narrow openings in the protective outer covering of the eye, called scleral canals.
Risk Factors and Frequency for Optic Disc Drusen
Optic nerve drusen is a condition that affects anywhere from 3.4 to 24 out of 1000 people. It is found in males and females equally and is more common in Caucasians compared to other ethnic groups.
Signs and Symptoms of Optic Disc Drusen
Typically, people with drusen – small yellow deposits under the retina – may not experience symptoms and the drusen might only be discovered during an eye examination. However, some patients may notice temporary visual disruptions, while others may have visual field defects, including enlarged blind spots.
During a physical exam, these drusen can be spotted without the use of imaging tools. They often give the eye’s nerve a distinct “lumpy, bumpy” look. The drusen, which can be yellow or white, usually appear as rounded bodies on or beneath the nerve. They are often found on the nasal side of the disc. If drusen affect one nerve more than the other, patients may experience an uneven pupil response to light. Additionally, unusual vessel sizing and branching, as well as spontaneous venous pulsations, can be observed.
Initially, the uneven border of the nerve due to drusen might look like swelling, which can lead to diagnostic confusion. However, true swelling and pseudo swelling can be differentiated by paying close attention to the nerve’s appearance. In cases of actual swelling, there will often be “flame” hemorrhages around the optic disc and a reddish tint to the disc. Moreover, in genuine swelling, vessels at the disc’s edge and retinal vessels might be hidden, while they remain clearly visible in cases of pseudo swelling. If the situation appears borderline or deeper drusen are suspected, more detailed imaging may be necessary to confirm the presence of drusen.
Testing for Optic Disc Drusen
If the doctor is unsure about the diagnosis after physically examining you, they might use certain imaging techniques to get a clearer picture and confirm whether or not you have disc edema (swelling in the back of your eye). Some of these techniques are B-Scan ultrasonography, CT scan, fluorescein angiography, fundus autofluorescence, and optical coherence tomography (OCT).
Ultrasonography uses sound waves to create images, and it might show a bright spot at the back of your eye, which could indicate calcification (hardening due to calcium build-up). Similarly, CT scans can also show calcified drusen, little yellow deposits under the retina, but they can’t detect drusen that are not calcified.
Fluorescein angiography, a technique using a special dye and camera to look at blood flow in the retina, has traditionally been used to tell apart true disc edema from hidden nerve drusen. But, studies show it might not always be effective, especially in confusing cases.
Fundus autofluorescence can help see optic nerve drusen (small, rock-like formations in the optic nerve head) as bright spots in the disc. OCT is highly sensitive and can spot nerve drusen as areas of uneven or round, less reflective cores with a uniform structure and more reflective edges at the surface.
While both ultrasonography and OCT are great at identifying nerve drusen, OCT with enhanced depth imaging provides better visuals. It was even found to detect 100% of hidden drusen in a study, compared to 82% by standard OCT and 41% by ultrasonography.
Not only can these imaging techniques detect nerve drusen, they can also help the doctor evaluate potential problems and effects of the drusen. For instance, OCT can track thinning of nerve fibers that can predict loss of visual field.
Treatment Options for Optic Disc Drusen
Optic nerve drusen, a medical condition mostly characterized by deposits in the eye, usually don’t need treatment. Most patients with this condition tend to keep good vision. The condition can be checked from time to time without requiring specific treatments. In some cases, though, if there is loss of vision, doctors might suggest treatments like lowering the pressure inside the eye or making a small hole in the protective layer around the optic nerve.
However, there are no standard surgeries to remove optic nerve drusen. While some surgeries like surgical excision and radial optic neurotomy have been tried, there is no scientific proof yet to show that they work. In fact, surgical excision, a process of removing the drusen, can sometimes have negative effects.
If complications occur because of optic nerve drusen, they may need to be treated. For example, a rare complication is the growth of new blood vessels beneath the retina, known as choroidal neovascularization. If this happens, it can lead to serious problems like blockage of the central retinal vein or damage to optic nerve due to insufficient blood supply. Such conditions can be treated with different methods such as drug injections into the eye, laser treatment, or a treatment that involves using a special light to activate a drug in the blood vessels of the eye, known as photodynamic therapy.
What else can Optic Disc Drusen be?
It’s essential to distinguish between actual swelling of the optic disc (also known as disc edema or papilledema which often affects both optic discs) and other conditions. Special imaging techniques can help doctors make this clear distinction. Sometimes, actual disc swelling can occur alongside nerve drusen (tiny, rock-like formations in the optic nerve). In such instances, an imaging technique called OCT can reveal a thickening in the nerve fibers.
Another technique called Fluorescein angiography can show certain signs such as early widespread increased fluorescence with late leakage around and on the disc when there’s swelling. In cases of actual swelling, B-scan (a type of ultrasound) imaging displays a decrease in signal strength as the imaging sensitivity (gain) is reduced. In contrast, for calcified drusen, the signal intensity remains stable even when the gain is reduced.
Swelling of the optic nerve can sometimes look like other causes including birth defects, infiltrative lesions, vitreopapillary traction (pulling on the optic disc due to changes in the gel inside the eye), and certain genetic diseases like Leber’s hereditary optic neuropathy. A patient’s medical history and broader clinical status in combination with imaging can often help doctors distinguish between these conditions.
Other conditions that may mimic the appearance of disc swelling include:
- Peripapillary hyperreflective ovoid mass-like structures (PHOMS)
- Optic discs that are tilted
- Optic nerves with a coating of myelin (a fatty substance)
- Crowded optic discs (caused by a smaller than normal eye).
- A condition called idiopathic intracranial hypertension, which causes high pressure inside the skull.
When doctors suspect idiopathic intracranial hypertension, certain imaging signs on MRI like the back of the eyeball appearing flat, kinks in the optic nerves, empty pituitary gland area (sella), downward displacement of cerebellar tonsils, slit-like ventricles (cavities in the brain), among others can be helpful in making a diagnosis. Lumbar puncture (a spinal tap) can also be an essential tool in diagnosing idiopathic intracranial hypertension.
What to expect with Optic Disc Drusen
In general, vision problems related to ‘nerve drusen’ – small, yellowish deposits that form in the eye – are minimal. These deposits can be monitored periodically, and they usually do not lead to noticeable loss of visual sharpness. However, they may lead to loss of certain parts of the field of vision. Some experts suggest that as many as half of children and almost 90% of adults with nerve drusen may experience this issue. This typically appears as enlarged blind spots and decreased peripheral (side) vision, or less commonly, curved vision defects. Rarely, more serious vision problems may occur due to complications associated with nerve drusen, such as a condition called ischemic optic neuropathy, which is reduced blood flow to the eye’s optic nerve.
As people grow older, nerve drusen may become more visible. There is also a higher chance of developing visual field defects, or areas where vision is lost. However, both the visibility of nerve drusen and the likelihood of developing visual field defects tend to stabilize when people reach adulthood. It’s important to note that the occurrence of visual field defects is significantly more common than the occurrence of practical visual symptoms, meaning that people with nerve drusen are more likely to have areas of missing vision than noticeable vision loss.
Possible Complications When Diagnosed with Optic Disc Drusen
While not common, there can be complications with optic nerve drusen, which are build-ups in the optic nerve that can affect your vision. These complications include:
- Anterior ischemic optic neuropathy: A condition where blood flow is blocked to the optic nerve.
- Retinal vascular occlusions: Occurrences where blood vessels in the retina are blocked.
- Choroidal neovascular membranes: Abnormal blood vessel growth under the retina.
- Flame disc hemorrhages: Small bleeds in the optic nerve area.
Preventing Optic Disc Drusen
Doctors might explain to their patients that they may not notice any changes with their vision, even if they have nerve drusen. Nerve drusen are small, calcium-like deposits in the nerves in the back of the eye. However, they may have some blind spots that can be picked up when doing vision tests. It’s important to understand that although nerve drusen usually don’t cause problems, regular eye scans are recommended to make sure there are no complications, especially in cases that are not completely straightforward.
Patients also need to know that, although rare, complications can occur due to the presence of nerve drusen. The treatment and the outlook for recovery if such complications arise will depend on the specific complications they face. Lastly, doctors want their patients to be aware that options for directly treating nerve drusen are not common and there is not much research on the subject yet.
