So, hopefully you’ve read all the preceding chapters, but here’s a refresher.

The ‘macula’ is the small spot in the middle of our vision that is the only part that can see fine detail. We have the impression that all our vision is clear and detailed, but that’s actually a clever illusion. As we shift our attention to things around us, we naturally look at them. And when I say “look at them”, what I mean by that is that we turn our eyes to point our macular field at them. In this way we build up a picture of our world that is full of detail.

The macula can see detail because it has a very dense packing of nerve fibres and photoreceptors. Unfortunately, this also makes it prone to degrading, particularly as we get older. The term ‘macular degeneration’ covers a range of related conditions that degrade the macula.

The macula is quite a small area. If you imagine looking at the middle of a DVD held out at arm’s length, that’s about the size of the functional macula. The good news is that even if macular degeneration gets really bad, it can’t affect much more area than that. That means that all the rest of your vision should be perfectly normal, which means people don’t tend to have any trouble walking around, seeing where people are, seeing where the furniture is, and so on.

Where they do have trouble is seeing the detail — seeing the face of the person over there, seeing the TV properly, seeing the text in a book.

The categorisation of macular degeneration keeps changing. It can be kind of hard for clinicians to keep up!

But in broad brushstrokes, there are two main categories:

Most macular degeneration is dry. It tends to come on slowly, getting gradually worse over many years. Photoreceptors die off, one by one.

The effect is that the macular field gets worse at picking up details, and this is especially apparent when trying to see things where the details are not good contrast, or not well lit.

The other really important change is the development of tiny blind spots in your macular field of view. Most people don’t actually see those spots, as your brain just fills in the gap with its ‘best guess’. But it starts to become really apparent when you’re doing high performance tasks like reading, where the appearance of words can become confusing when parts of letters are missing.

There are two basic subtypes of dry macular degeneration, that relate to the way these blind spots form.

From the centre outwards

In this type, the central macula tends to be affected more than the outer areas. The central area includes the fovea (the very most high detail part of the macula, right in the centre), and so visual acuity tends to be affected earlier on.

From the outer area inwards (Geographic Atrophy)

In this type, blind spots appear throughout the macular field, but tend to avoid the middle of the macula until quite late. The fovea may in fact be the very last bit to be affected, so the blind spots can join up into a ring shape, which can cause some very strange effects. We’ll talk about that more down below.

It’s not uncommon for people to reach a point where they have lost almost their entire macular field, but the fovea is still there so they can still read (slowly) down to almost the bottom of the visual acuity chart. If the person looking after your eyes doesn’t ‘click’ that that’s what’s happening, they might try to reassure you that you are still seeing very well, when you know that it’s not good at all.

The ‘wet’ here means that there is fluid involved, which tends to be leakage from blood vessels. Other words might be used, such as ‘exudative’ or ‘neovascular’ (and the dry type can be called ‘non-exudative’ to match).

The basic difference is that the photoreceptors are still dying off, but the body tries to rescue them by growing blood vessels towards the distressed photoreceptors. Unfortunately, that turns out to be a really bad idea, because in the eye those blood vessels are very fragile — they tend to leak or even burst, and that fluid or blood can cause a sudden and very dramatic drop in vision. And as the area heals, it tends to scar, which causes a large permanent blind spot.

The effect on vision tends to be a larger single blind area, instead of lots of tiny blind spots. If that blind area covers the fovea then the visual acuity will drop a lot, but if it’s in the macula but not the fovea the visual acuity will probably still be good.

There’s often also quite a bit of distortion, so that straight lines appear wiggly. That’s because the fluid causes swelling of the retina, so the light being focused on to the back of the eye falls on a surface with ripples or lumps, making it look distorted. Glasses can’t fix that distortion. Imagine if you were projecting a movie on to a wall, but the wall developed ripples in the wallpaper — the image would look wiggly, and no amount of focusing the projector would be able to get rid of that wiggliness.

Injections for wet macular degeneration

When I started doing optometry, there was no good treatment for wet macular degeneration. The only thing that could be done was to blast the blood vessels with a laser, which itself left behind a scar. The idea was that the resultant scar from the laser would be smaller than the scar if you just left the blood vessels to grow, but it wasn’t a great solution. It was kind of like the way you’d choose to amputate a gangrenous foot to avoid having to amputate the entire leg later on. Nobody was happy.

Nowadays we do have a treatment. There are drugs that can be put in the eyeball that stop the growth of those pesky blood vessels. That puts the eye back into the ‘dry’ situation — sure, photoreceptors will still die off, but vision reduction is slow and gradual instead of sudden and dramatic.

This is a great thing, but there’s no denying that the treatment is quite intensive. It’s normal to feel anxious or even repulsed by the idea of the treatment. Nobody goes “I’m bored today — I think I’ll go and get injections in my eyes.” But the people doing it are quite aware of that, and it’s pretty much down to a fine art nowadays. The injections should be painless, and the staff involved should be taking care to reassure you and put you at ease — if they’re not, consider switching to a different doctor.

The treatment tends to need repeating regularly. It’s like a game of whack-a-mole — whenever the blood vessels pop up, you whack them, and you keep whacking them until they get the message.

For some people, the vessels never seem to get the message, and they have to keep going back for injections for years on end. Other people only have a few injections and then they can stop. It’s hard to predict.

There’s a lot of work going on into drugs that last longer, so that you don’t need the injections so often. It’s normal to need frequent injections to begin with, and then the period between them gets extended out.

Remember, a scotoma is the technical word for a blind (or impaired) area in your vision. And, as mentioned above, the geographic atrophy subtype of macular degeneration is notorious for affecting the rest of the macula but leaving the fovea until last. The effect is gradual formation of a scotoma in the shape of a ring or a donut, and the experience of having a ring scotoma can be very confusing.

So, what might you see if you have a ring scotoma?

Basically, you might still be able to see even very fine individual details, but those details will be isolated — you won’t be able to see them in context. So you might be able to see a person’s eye, or their mouth, or that they have a little bit of spinach stuck in their teeth — but not be able to recognise who that person is, or whether they are smiling or frowning or looking angry or sad, because to recognise faces and facial expressions requires seeing all the facial parts together, in relation to each other.

That can cause a lot of confusion for you and the people around you. Some people might start wondering if you’re making it up — after all, how can it be that one moment you said you couldn’t recognise them, and then the next you’re noticing they have spinach stuck in their teeth? I mean, it’s a hard one to make sense of.

Another common effect is that reading accuracy can be good, but fluency is really bad. In extreme ring scotomas, some people notice that they can read the newspaper article slowly — seeing a few letters or just one word at a time, with the island of vision in the middle of the ring — but they can’t read the headlines, because the letters of the headline print are too large to fit in that island. I remember the first time I had a patient who told me that they could read the article but not the headline — I wondered if they were pulling my leg! But it’s a completely explainable problem, if you realise what’s going on.

I find it’s common that people with ring scotomas are very frustrated with their vision. The small island of very good vision almost seems to tease them — the fact that they can see individual fine details seems to imply the promise that larger details should be quite easy, and it’s actually the reverse.

It’s hard to come up with a practical solution. A bit of magnification can help you see fine details that are too difficult to see, but as you make those details larger there is less context that can fit within the island of vision. It’s helpful to use electronic video magnification because you can adjust it — for any given size of print, you can find the best compromise between how big the letters get, and how many letters you can see in one go.

The other thing is to optimise the light (you need strong illumination) and also the contrast (if possible — again, that’s where electronic video magnification has a strong advantage), since they both can have the effect of slightly widening the island of vision.

If none of that works, the only other thing you can do is to switch to using the vision outside of the scotoma instead of inside the ring. That vision tends to be very poor for ability to see detail, so to read print that means using something like a desktop CCTV magnifier that can magnify a lot — a basic magnifying glass just isn’t going to do it.

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