Drusen are extracellular yellowish deposits that accumulate under the retina. They consist of a fatty protein known as lipids. The formation of drusen may take months or years. Drusen do not cause AMD but an individual with drusen has an increased likelihood of developing AMD.
Drusen can also be present in the optic nerve (also known as optic disc drusen). Optic disc drusen consists of calcium salts and protein and affect both eyes. They are not associated with age and can occur in children.
- Hard drusen – They are small and round with sharp borders and are scattered apart from one another. They do not cause problems with vision for a long time. They may also never cause problems at all.
- Small drusen – They are larger with less defined edges and vary in size and shape. Unlike hard drusen, soft drusen cluster closer together. They increase the likelihood of developing age-related macular degeneration (AMD).
Causes and Risk Factors
Drusen occur naturally with age. They are popular with people aged 60 and above. One school of thought holds that drusen are caused by the eye's inability to eliminate some waste products from the cells of the rods and cones.
The exact cause of optic disc drusen is unknown but it is thought to develop from the abnormal flow of material in the optic nerve. Optic disc drusen may be hereditary even though it is usually an autosomal dominant trait (passed on by one parent). Although optic disc drusen is present at birth, the condition grows slowly and may manifest itself by age 12.
How drusen is related to degenerative muscular disease is not yet clear but people with soft drusen may already be having AMD. The following are the risk factors associated with drusen and AMD:
- Caucasians are more likely to develop optic disc drusen and AMD
- A family history of AMD
- Abnormal cholesterol levels
Signs & Symptoms
Drusen do not present any symptoms. A routine eye examination will reveal their presence. While hard drusen are not symptoms of eye disease, soft drusen are. Many soft drusen in the eye are a sign of AMD. AMD may present the following symptoms:
- A blank spot in the field of vision
- A cloudy vision
- Difficulty adjusting from bright to low light
Oftenly, optic disc drusen do not produce symptoms. However, some people with optic disc drusen may complain of:
- Loss of peripheral (side) vision
- Occasional flickering or graying out of vision
- Blank spots in the field of vision
The following may help diagnose drusen:
- A comprehensive dilated eye examination. The eye care professional will use dilating eye drops and an ophthalmoscope. An ophthalmoscope enables the professional to see the retina and the areas at the back of the eye.
- The use of an Amsler grid to look for signs or symptoms of macular degeneration. The symptoms include blurry, wavy or dark places in an individual’s vision.
- Imaging tests if the professional suspects optic disc drusen. These tests may include ocular ultrasound, CT scan and optical coherence tomography (OCT). Imaging enables the machines or instruments to take pictures of the optic nerve.
Treatment of drusen is directed towards reducing the symptoms of AMD and other related complications.
Hard drusen do not require treatment. The eye doctor will need to keep a close watch over a patient with hard drusen to prevent them from developing soft drusen. There is also no treatment for optic disc drusen.
However, if optic disc drusen develops into choroidal neovascular membranes (CNVM), treatment is necessary. CNVM refers to new, destructive blood vessels which form underneath the retina. Treatment for CNVM includes anti-VEGF drugs to slow down the leakage of the blood vessels.
For patients with soft drusen, the doctor will prescribe AMD treatment. An AMD treatment involves a combination of nutritional supplements. These supplements may include copper, zeaxanthin, vitamin C, vitamin E, zinc and lutein.
Optic disc drusen patients who develop CNVM may need surgery. A thermal laser therapy and photodynamic therapy will destroy the unwanted blood vessels.
People with optic nerve drusen need regular monitoring to detect complications like CNVM. A CNVM can bleed suddenly and cause sudden loss of vision. Over 70% of optic disc drusen patients may lose their peripheral vision. Most, however, retain their normal central vision.
Also, individuals with optic disc drusen are at an increased risk of developing branch retinal occlusion (BRVO), non-arteritic anterior ischemic optic neuropathy (NAION) and central retinal vein occlusion (CRVO).
Individuals with soft drusen risk developing AMD, hence need close monitoring.
Generally, people with drusen should take precautions to minimize developing macular degeneration. They can avoid smoking, wear protective sunglasses, take nutritional supplements, watch their diet and exercise regularly.