AMD is divided into two forms:the dry (nonexudative) form that affects 85-90% of people and the wet (exudative) form, which affects the remainder.The wet form is usually quite aggressive and is responsible for nearly 90% of those with severe vision loss.Most of the time AMD begins as the dry form, which is characterized by deposits in the macula called drusen.The dry form has three stages:early (small drusen), intermediate (large drusen) and late/geographic atrophy (pigment epithelial cells of the retina die affecting the macula).Some people have the early stage and never progress to later stages.However, dry AMD can progress and spontaneously become wet AMD characterized by an overgrowth of blood vessels in the macula (neovascularization).These vessels are weak and leak blood and other fluids into the macular region.
There are several factors that help to determine the risk of developing AMD.Two of the most important non-modifiable risk factors are age (8.5% risk for people between 43-54 and 36.8% risk for people over 75) and family history (up to three time greater risk).Others have been mentioned such as gender (females more susceptible), race (light skin more susceptible) and iris colour (light-coloured more susceptible). Modifiable risk factors include smoking (up to six times greater risk), diet (low in antioxidants and minerals more susceptible), ultraviolet sunlight exposure and excessive weight/obesity.
In the past to the present, therapy has only been available for the wet form of AMD.Treatment is aimed at stopping the abnormal neovascularization in the macula in order to prevent further vision loss.One of the treatments in the past used thermal lasers to destroy the leaking blood vessels in the region of the macula the blood vessels (termed laser photocoagulation), however there was rarely visual improvement with this method.Patients had to be willing to lose vision (three or more lines on the visual acuity chart) in order to reduce the rate of severe vision loss in the long term (5).Photodynamic therapy (PDT) was developed as a method of preventing further vision loss without immediately losing vision as seen with laser photocoagulation.Verteporfin, a dye administered intravenously, is excited with a low energy laser.The dye accumulates inthe abnormal, leaking blood vessels in the macula.A non-thermal laser is applied to these blood vessels in turn destroying them. Treatment with PDT is usually done every three months.
Types of Macular Degeneration
There are three types of macular degeneration: the Dry form, Wet form and Pigment Epithelial Detachment (PED). The Dry form is the most common, affecting 85 to 90% of patients. In the Dry form, the macula thins and stops functioning properly. Also, detached retinal cells can clump up and form small clot-like structures in the eye called drusen. Currently, there is no surgical treatment available for the Dry form of macular degeneration, although research is ongoing.
The Wet form involves the growth of abnormal blood vessels under the retina which lift up the retina and reduce vision. These abnormal blood vessels are called subretinal neovascularization, or SRNV. Laser surgery has been found to be helpful in cases of Wet macular degeneration.
Pigment Epithelial Detachment (PED) is just what it sounds like. The top layer of tissue detaches and therefore vision is damaged. Laser surgery may also help in some cases.
Treatment for macular degeneration varies. Although there is no recognized treatment of the most common form of macular degeneration, the Dry form, advances are being made. Consult your eye doctor regarding the latest in medical treatment.
1. Normal Retina
2. Early Stage Dry AMD:
Thickening of Bruch's membrane. Drusen are the first clinically detectable signs of AMD.
3. Early Stage Wet AMD:
New blood vessels penetrate Bruch's membrane
4. Late Stage Wet AMD:
Disciform scars can form in untreated neovascular AMD.
Treatment for Dry Macular Degeneration is Vitalux (AREDS), taken twice a day with a meal. If diagnosised with Wet Macular Degeneration the treament options may include Photodynamic Therapy(PDT,visudyne therapy), ablation of feeder blood vessels using high speed angiography and laser, an anti-VEGF injection into the back of the eye to stop new leaky blood vessel growth (Avastin,Lucentis) and steroid injection (Kenalog) into the back of the eye. Any one or a combination of treatment options are decided upon by a retinal specialist to best suit the stage of the Wet Macular Degeneration.
If you have Macular Degeneration, than one way you can monitor changes is by use of an Amsler Grid. Your eye doctor will instruct you to use the Amsler Grid weekly or monthly.
Currently, the main target for wet AMD treatment is aimed at reducing vascular endothelial growth factor (VEGF), which is a major stimulus for blood vessel growth.Lucentis (ranibizumab), Avastin (bevacizumab) and Macugen (pegaptanib) are all anti-VEGF therapies injected into the eye that are able to prevent new blood vessels growth in the macula.Most retinal specialists are either using Lucentis or Avastin as the primary therapy for wet AMD.Unlike the past treatments with lasers, treatment with Lucentis has shown that slight improvements of vision can actually occur.Anti-VEGF treatment may be used up to once a month over a 24-month period.However, treatment regimens are determined based on various factors such as vision, presence of blood or fluid in the macula and fluorescein angiography results.There is currently no treatment to halt the progression of dry AMD, but antioxidant and mineral supplements have been found to lower the risk of developing advanced dry AMD by 25% if taken during the intermediate or late stage of the disease.Beta-carotene, vitamins C, E and the minerals zinc and copper have shown to be beneficial. This is known as the AREDS formula now available as Vitalux Plus with Omega 3. Oxidative stress occurs when there are too many free radicals (molecules that are destructive to cells) created by normal metabolic processes of the body.The retina (posterior part of the eye) is particularly susceptible to this oxidative damage.Antioxidants protect against cell damage because they neutralize the free radicals.Lutein and zeaxanthin are two free-radicals that make up the majority of pigment in the macula.Both of these antioxidants have been shown to provide a protective effect against AMD. A genetic test (saliva test) is available to determine the risk of losing vision from AMD.AMD is a progressive disease that is already the leading cause of vision loss in adults over 50 years of age.The numbers of affected patients will only increase since the baby boomers are reaching their late fifties and early sixties.Unfortunately, there is no cure for AMD but much research is being put forward in order to treat this sight threatening disease.
How To Use Your Amsler Grid
If you wear reading glasses, be sure to have them on when using the Amsler Grid.
- Attach the Amsler grid to a wall, fridge or mirror at eye level in a frequently used area with adequate light and no glare.
- Stand 12' - 14' or a comfortable reading distance away.
- Cover one eye and focus with the other on the centre black dot.
- Continue to stare at the centre dot, looking to see that all the lines are straight and the squares are the same size. The first time you use your Amsler Grid, mark any existing areas of visual distortion, blurry or blank spots on the grid for future reference.
- REPEAT THE TEST WITH THE OTHER EYE.
- If any areas of the grid seem blurred, distorted, discoloured, abnormal or changed from your original reference marks, contact your doctor.
Below: This is an example of an Amsler Grid. (not suitable for testing)