Age related macular degeneration (also known as AMD) is a very common disease that occurs with increasing age; 1 in 7 people over the age of 50 will be affected by the condition and 1 in 4 people over the age of 80 have vision loss due to AMD. The macula is a specialised region of the retina (the tissue located at the back of the eye that detects light) responsible for our high detailed vision. This includes tasks such as recognising faces, reading a book and driving.
The macula’s function is progressively impaired in AMD, leading to permanent loss of high detailed vision. For the macula to be able to function, it must remain flat; and for this to occur, toxic waste products must be removed across the layer of tissue under the macula, known as Bruch’s membrane. In AMD, these waste products are unable to move across this tissue as effectively as in our younger years. As a result, lumps of solid waste (called drusen) accumulate under the macula. As the disease progresses, the size and number of drusen increase, distorting the shape of the macula and thus distorting the central vision. Age related macular degeneration can progress in one of two ways; the dry form or the wet form.
All AMD starts off as dry AMD and can remain that way. In which case, the build-up of toxic waste products continues over time, progressively distorting the macula and eventually resulting in the macula thinning and essentially “dying”, leading to complete loss of the central, high detail vision. Dry AMD can convert to the wet form. In these cases, blood vessels grow underneath the macula alongside the drusen. This type of AMD is called “wet” as the blood vessels that form are not normal blood vessels and leak fluid. Accumulation of this fluid further distorts the macula, causing further vision loss. Eventually the blood vessels burst and bleed, severely damaging and “killing” the macula, leading to formation of a scar where the macula should be. This also results in complete loss of the central, high detail vision.
Dry AMD is the more common form of the disease and progresses slowly. In the earliest stages, dry AMD does not have any symptoms and as the disease progresses the only symptom is gradual blurring of the central vision. However, when dry AMD converts to wet AMD, vision loss can occur suddenly and profoundly, meaning vision can become very poor, very quickly (within minutes).
It is important to note that once AMD develops, it is present for life. Furthermore, once vision loss due to AMD occurs, it cannot be recovered. However, you can prevent severe vision loss from first occurring by having regular eye examinations to detect the condition in its earliest stages. This allows treatment to be initiated as soon as AMD develops, thereby limiting vision loss.
The clinical team at Mortimer Hirst are ever-vigilant for AMD in all patients as we understand the impact the condition can have on your vision and your ability to live life to the fullest. Routine eye examinations are important for everyone, as while AMD generally only affects those over age 50, drusen can form earlier in life and lead to vision loss later if left unchecked. With this in mind, every patient who undertakes a consultation with our optometrists at Mortimer Hirst is assessed for drusen by means of advanced imaging techniques, including retinal photography. Sequential retinal photographs taken over many years are effective in detecting any changes to the macula, including the development of new drusen and drusen that grow in size.
For patients in whom drusen is detected, the optometrists at Mortimer Hirst use the most advanced retinal imaging tool for AMD – known as an optical coherence tomographer (OCT) – to assess and monitor the condition. The OCT is used to take images of the macula and the drusen and is the most sensitive tool for detecting new or growing drusen. The OCT is the only tool that can detect the earliest signs of fluid accumulation in wet AMD; this is significant because if the treatment for wet AMD is initiated quickly (at the first sign of fluid accumulation), it is far more effective at preserving vision than if initiated when the blood vessels leak excessively or bleed in the later stages of the disease.
Fortunately, there are treatments for AMD which can prevent vision loss if initiated early enough. These treatments are primarily aimed at preventing disease progression, namely preventing an increase in the size and number of drusen for dry AMD, while also preventing dry AMD from converting to wet AMD. This is achieved by addressing modifiable lifestyle factors in both wet and dry AMD. Wet AMD is also treated by preventing blood vessel growth and bleeding by means of injections into the eye (which are administered after anaesthetic eye drops are used to numb the surface of the eye).
Age related macular degeneration affects over 200,000 people in New Zealand over the age of 50 and is one of our leading causes of blindness. Early signs of the condition can develop earlier in life and have no symptoms. We recommend having regular eye examinations with our optometrists; the specialised tests can detect AMD in its earliest stages and the steps to prevent vision loss can be taken.
Several lifestyle factors are known to increase the risk of developing AMD, including; being overweight, smoking, amount of sunlight exposure and diet. These factors can be modified, particularly smoking as those who smoke are three times more likely to develop AMD and do so 10 years earlier than non-smokers. There is also a genetic component to AMD (which cannot be modified), so if an immediate family member has the condition, you are at greater risk of developing it yourself.
Diet modification is extremely important. Consuming as much fruit and vegetables as possible, including leafy greens such as kale and silver beet is highly beneficial. There have been two large investigations into what nutrients may be effective at preventing the progression of AMD, called the AREDS or age related eye disease study 1 and 2. These studies have revealed that the following should be consumed as they may prevent AMD progression: 500 mg of vitamin C, 400 international units of vitamin E, 80 mg zinc as zinc oxide, 2 mg copper as cupric oxide, 10 mg lutein and 2 mg zeaxanthin. Obtaining this from diet alone is near impossible, therefore a supplement in the form of a tablet is the best way to obtain these nutrients. Your optometrist will be able to recommend the best supplement for you.
Anti-Vascular Endothelial Growth Factor Injections
Compounds known as anti-vascular endothelial growth factors (anti-VEGFs) are routinely used to treat wet AMD. Anti-VEGFs prevent the development of the new blood vessels and regress those that have already grown. As a result, the fluid accumulation under the macula regresses, a future bleed is prevented, and further vision loss is limited. As previously mentioned, anti-VEGFs are administered through an injection into the eye after local anaesthetic eye drops are used to numb the surface of the eye. Several injections are usually required as the effect typically lasts only for the duration of weeks or months, and the disease would continue to progress if the injections were stopped prematurely.
Monitoring with an Amsler Grid
The Amsler grid is a grid pattern specifically designed to monitor AMD at home. The grid should be looked at with each eye individually; one eye covered, then switch to the other eye. If any of the grid lines are wavy, broken or distorted, or if any part of the grid is blurry or areas are missing, this is an indication that AMD has progressed and care should be sought immediately. Complimentary fridge magnet Amsler grid charts are available from Mortimer Hirst.