Seeing Monsters

Mrs. C has been a patient of mine for some years. She has advanced Age-Related Macular Degeneration (AMD). She came to see me before Christmas and mentioned that she felt uneasy in crowded places. “It’s hard to explain…I was in the supermarket and suddenly felt quite threatened. I panicked and had to leave.” It’s a complaint I’ve heard numerous times in various forms over the years. Patients with AMD frequently complain of what can only be described as visual unease, especially around lots of people or activity.

Before I go on, it’s important to know that AMD affects only the central area of the retina. In this area mostly one photoreceptor cell (the little light receptors known as cone cells because of their shape) is attached to one nerve fibre, which then transmits the information from that one cell to the brain. Because of this one-cell-to-one-nerve-fibre relationship the ability of a healthy central area of retina to resolve detail is phenomenal. In the other 90% of the retina each single nerve fibre transmits information from many photoreceptor cells (the little light receptors known as rods, again because of their shape). Mostly this peripheral area of the retina is about light collection and motion sensitivity so it makes sense for the receptor cells to pool their resources, but it does means that the peripheral retina is much less good at resolving detail, such as that required for facial recognition.

The human  brain is finely evolved to seek out human faces. If there is just a single face in a large painting then this is what we home in on. We can pick out the faces of those we know well even in a large crowd of strangers. There is even a specialist area of the brain called the fusiform face area which is predominantly tasked with seeking out and recognising human faces. AMD destroys the central retina and deprives the patient of this ability so I always reasoned that may be why they feel so uncomfortable.

Recently I came across an elegant demonstration which may shed even more light on why patients with AMD feel this way (and not just AMD but anyone who has lost their central vision).

You’ll need to click on the image as I could find no way to embed the demo into the post. Follow the instructions on the screen. It’s a rather disturbing but extremely compelling bit of visual psychology. I think it illustrates beautifully why someone with central visual loss, presented with rapidly changing faces, as in a supermarket at Christmas, or at a large social gathering may indeed feel disorientated, uneasy and even panicky.

Seeing Monsters