Macular degeneration or age-related macular degeneration (ARMD) is the most common cause of blindness in the UK. As the name implies, it is degeneration of the macula.
It is more common in females and elderly.
Let’s look at the anatomy of the macula quickly:
The macula is the region of the retina responsible for central vision. It is also the most densely packed region with photoreceptors.
There are 4 layers:
- Photoreceptors - convert light into electrical signals for processing into our visual field.
- Retinal pigment epithelium - aids the retina and photoreceptors in detecting light.
- Bruch’s membrane - an ECM that plays a role in structural and functional support.
- Choroid - supplies outer retina with nutrients and maintains temperature and volume of the eye.
Pathophysiology
AMD is characterised by bilateral degeneration of the macula photoreceptors. What we then get is a collection of lipids and proteins, known as drusen between the RPE and Bruch’s membrane. They may also be referred to as soft exudates.
Small, hard drusen is normal but drusen larger than 63um and of numerous quantity is considered pathological and indicative of ARMD.
🔢 Classification
There are 2 types of ARMD:
Dry macular degeneration (atrophic macular degeneration)
This is the most common kind (90%).
It is characterised by drusen.
Wet macular degeneration (exudative/neovascular macular degeneration)
This is less common (only 10% of cases).
It is characterised by: choroidal neovascularisation from the choroid → retina. It increased the risk of serous fluid and blood into the retina → oedema and rapid vision loss.
It has a worse prognosis.
⚠️ Risk factors
- ⭐️ Increasing age
- ⭐️ Female gender
- ⭐️ Smoking
- Family history
- CVD risk factors
- High fat diet and high BMI
😷 Presentation
- Gradual loss of central visual field
- Reduced visual acuity - especially near-field objects.
- Visual fluctuation - some days vision is better and some days it is worse.
- Straight lines appear wavy
- Poorer vision at night/in dark
Wet AMD is more acute and leads to loss of vision in a few days. Full vision loss bilaterally is seen in 2-3 years.
- Drusen is seen fundoscopy
- Atrophy of RPE
- Photoreceptor degeneration
- Scotoma
- Amsler grid test shows distorted perception of straight lines (metamorphopsia).
🔍 Investigations
- If wet-late ARMD is suspected, an urgent referral is needed, where an OCT would confirm diagnosis.
- Fundus fluorescein angiography (FFA) can also be used for wet ARMD too.
- Amsler grid testing - may be useful in testing patients with suspected ARMD.
🧰 Management
- Avoid smoking
- Blood pressure control
- Vitamin supplementation has also shown evidence in slowing progression. High dose of beta-carotene, vitamins C and E, and zinc can be given to slow deterioration of visual loss
- 🥇 Anti-VEGF medication - once a month. Given the intra-vitreous injection. They slow and even reverse AMD.
- 🏆 Ranbizumab
- Aflibercept
- Laser photocoagulation - slows progression, but there is risk of acute vision loss and that is why anti-VEGF therapies are useful.