The macula is a small area at the back of the eye, at its centre is the highly specialised fovea, which is what gives us our high standard of vision- this vision normally drops rapidly from the straight ahead position. Try reading this page without looking directly at the words- perhaps try to read 4 or 5 lines below the one you are looking at- it’s very difficult- when we look at something we rotate the eyes so that the image lands on the fovea.
The general (peripheral) retina has a dual blood supply, one in front and one behind. Because the blood supply in front of the retina casts shadows, it would significantly impair the high quality of central vision, so the fovea only has a single blood supply from behind. It is also thinner than the general retina- again to improve vision. This specialisation allows high quality vision, but unfortunately in some people this comes at the expense of durability.
Behind the retina is Bruch’s membrane, and all nutrients to the light sensitive photoreceptors, and waste from them has to cross this. Over the years, Bruch’s membrane can become clogged with waste from the photoreceptors, which then may compromise the blood supply. This can lead to the most common form of Age Related Macular Degeneration (ARMD or just AMD)- the dry or non-exudative form, where vision may gradually decline over a number of years.
This decline in central vision will not result in blindness, but does cause increasing difficulty reading, seeing the Television and recognising faces. By looking at the back of the eyes, it is possible to see this debris build up- seen as yellow dots beneath the retina, called drusen. However, fortunately, not all people with drusen will progress to develop ARMD.
Currently there is no satisfactory treatment for dry AMD, but there is evidence that lifestyle changes such as smoking cessation (halves the risk if one stops early enough) and foods rich in, or dietary supplements containing Vitamins A C & E and minerals Zinc & Selenium may be useful in slowing or even arresting its progression. These are all antioxidants, and similarly, reducing saturated fat intake may also prove helpful. Uncontrolled high blood pressure has also been implicated in development of ARMD, so this too should be closely monitored.
Wet, or exudative AMD occurs when a break in Bruch’s membrane allows new blood vessels to grow beneath the retina. These new vessels are leaky, which can cause swelling within the retina- this can show as distortion of vision- straight lines appearing wavy. The new vessels are also likely to burst, which is catastrophic because the blood clots beneath the retina, and causes scarring and irreparable damage.
Caught early enough, Wet AMD may be treatable by laser to seal the leaky vessels, but if these are too near the centre, a newer lower powered laser along with special chemicals (called Photo-Dynamic Therapy or PDT for short) may be useful.
The latest and very successful treatment for wet AMD is injections into the vitreous jelly of the eye- Lucentis, the injected drug is an Anti-VEGF- (anti Vacular Endothelial Growth Factor)- it stops new vessels forming, and CAN CAUSE REGRESSION OF THOSE ALREADY GROWING.
All treatments are most effective if the condition is caught early- any distortion of vision must be investigated promptly!
Below is an Amsler grid. It should be viewed with each eye in turn. Normally a printed Amsler Grid should be viewed at 14 inches, the correct distance will vary depending on your screen size and resolution, but even if viewed at a slightly incorrect distance, the principle remains.
- Looking at the central spot, can you still see it? You should be able to.
- Looking at the central spot, are you aware of all four corners of the grid? You should be.
- Looking at each corner in turn, are you still aware of the central black dot? You should be.
- Looking back at the spot, do all the lines appear straight, all the squares appear square, are there any bits missing or distorted? There shouldn’t be any distortion, missing or blank areas may indicate dry AMD, rather than the more urgent wet form.
If you are in any way unhappy with your results, you should have a full eye test at your Optometrist as soon as possible, or see you GP-soon.
You can download a copy of the Amsler grid here