Age-related macular degeneration is a condition where there is degeneration in the macula that cause a progressive deterioration in vision. In the UK it is the most common cause of blindness. A key finding associated with macular degeneration is drusen seen during fundoscopy.
There are two types, wet and dry. 90% of cases are dry and 10% are wet. Wet age-related macular degeneration carries a worse prognosis.
The macula is made of four key layers. At the bottom, there is the choroid layer, which contains blood vessels that provide the blood supply to the macula. Above that is Bruch’s membrane. Above Bruch’s membrane there is the retinal pigment epithelium and above that are the photoreceptors.
Drusen are yellow deposits of proteins and lipids that appear between the retinal pigment epithelium and Bruch’s membrane. Some drusen can be normal. Normal drusen are small (< 63 micrometres) and hard. Larger and greater numbers of drusen can be an early sign of macular degeneration. They are common to both wet and dry AMD.
Other features that are common to wet and dry AMD are:
- Atrophy of the retinal pigment epithelium
- Degeneration of the photoreceptors
In wet AMD there is the development of new vessels growing from the choroid layer into the retina. These vessels can leak fluid or blood and cause oedema and more rapid loss of vision. A key chemical that stimulates the development of new vessels is vascular endothelial growth factor (VEGF) and this is the target of medications to treat wet AMD.
- White or Chinese ethnic origin
- Family history
- Cardiovascular disease
There are some key visual changes to remember for spotting AMD in your exams:
- Gradual worsening central visual field loss
- Reduced visual acuity
- Crooked or wavy appearance to straight lines
Wet age-related macular degeneration presents more acutely. It can present with a loss of vision over days and progress to full loss of vision over 2-3 years. It often progresses to bilateral disease.
- Reduced acuity using a Snellen chart
- Scotoma (a central patch of vision loss)
- Amsler grid test can be used to assess the distortion of straight lines
- Fundoscopy. Drusen are the key finding.
Slit-lamp biomicroscopic fundus examination by a specialist can be used to diagnose AMD.
Optical coherence tomography is a technique used to gain a cross-sectional view of the layers of the retina. It can be used to diagnose wet AMD.
Fluorescein angiography involves giving a fluorescein contrast and photographing the retina to look in detail at the blood supply to the retina. It is useful to show up any oedema and neovascularisation. It is used second line to diagnose wet AMD if optical coherence tomography does not exclude wet AMD.
Refer suspected cases to an ophthalmologist for assessment and management.
There is no specific treatment for dry age-related macular degeneration. Management focuses on lifestyle measure that may slow the progression:
- Avoid smoking
- Control blood pressure
- Vitamin supplementation has some evidence in slowing progression
Anti-VEGF medications are used to treat wet age-related macular degeneration. Vascular endothelial growth factor is involved in the development of new blood vessels in the retina. Medications such as ranibizumab, bevacizumab and pegaptanib block VEGF and slow the development of new vessels. They are injected directly into the vitreous chamber of the eye once a month. They slow and even reverse the progression of the disease. They typically need to be started within 3 months to be beneficial.
Last updated April 2019