Visual Psychology

Binocular Vision

Binocular vision is at the core of everything an optometrist does.

Although sight accounts for just 20% of the five major senses (the others being hearing, touch, taste, and smell) about 80% of the way most of us experience the world is through vision.

In order to navigate this world we need to be able to identify objects, track them and perceive their depth (3D vision). In order to navigate school we need to be able to learn to read so that we can assimilate information easily and accurately.

Most people assume that all vision problems can be corrected with spectacles or contact lenses. But a surprisingly high number of children (with and without spectacles) have functional eye disorders. A functional eye disorder is where a little piece (or more than one piece) of the visual pathway doesn’t work or works inefficiently. To a child this may appear as blurred vision, difficulty tracking along a line of text, problems remembering what they’ve read, being a slow reader, difficulty catching or hitting a ball, headaches, or double vision. To an adult such as a teacher, the child might appear to be a slow worker; they might mix up words when they read; they might try to avoid close-up work like reading or writing altogether; they might become anxious or angry, stare out of the window, get up and wander round the class or distract other children.

These children are frustrating to many optometrists. In our consulting room they may appear to have great vision, reading the bottom line of the chart with ease, or conversely they may struggle to read more than half way yet when we examine them we can find nothing that requires them to wear spectacles. These children are also frustrating to their teachers, who are only too aware that they are underperforming without a seemingly good reason. And they are frustrating to their parents who are worried that their child has been labelled a ‘problem’. At the centre of this is a frustrated child, rapidly losing confidence and feeling a failure compared to their peers.

This is where a specialist binocular vision examination can be very useful. Binocular vision disorders are extremely common, but often intermittant, causing symptoms some of the time in some situations but not all of the time in all situations (at least in the early stages).  Because of this these issues can be missed if they aren’t looked for specifically.

Binocular vision disorders may be helped with spectacles, contact lenses or vision therapy (kind of physio exercises for the eyes), or any combination of these. Please note that in spite of claims made in certain corners of the internet none of these solutions are a cure for dyslexia or ADHD and they are definitely not a magic bullet (though the results can seem like magic sometimes). The aim of any vision appliance or therapy is purely to enable child using their visual system in such a way that clear, comfortable, accurate vision is possible. Many children with dyslexia or ADHD may also display or develop an underlying binocular vision problem, the symptoms of which exacerbate the problems they are having with the dyslexia or ADHD! When the binocular vision problem is fixed the dyslexia or ADHD appear to improve, but in reality we’ve simply removed one problem, so they now have more energy and resources to devote the other problem.

Longer lashes! “Should I use Latisse?”

This was a question put to me by a patient recently. She confided that she had bought an eyelash-enhancing product while in the United States. The product was called Latisse and she wanted to know if I felt it was safe to use. I admitted had never heard of it and said I would investigate. At this point she told me she had been using it for about two months, and to be fair she did have amazingly long beautiful eyelashes so it was clearly ‘doing what it said on the tin.’

I realise that this topic doesn’t fall precisely under the heading visual psychology but for most women (and a good many men) body image, beauty, and the disparity between reality and media ideals can have a huge effect on their mental well-being.

Also in the interests of full disclosure I have spent most of my adult life looking for the Holy Grail of mascara; the one which will transform my stubby little lashes into those fit for a Disney Princess.


Yes I am *that* shallow…so sue me.

Latisse, which is manufactured by Allergan, promises all this. The website says that:

LATISSE® is an FDA-approved treatment to grow eyelashes for people with inadequate or not enough lashes.

But Google Latisse and you’ll find all manner of celebrities and beauty-bloggers raving about its lash-lengthening effects. It certainly looks tempting.

But Latisse is not licensed for use in the UK. Even in the US it is a prescription-only drug, albeit licensed for cosmetic purposes.

But what is it and how does it work?

Latisse is actually bimatoprost. For those who don’t know, this is actually the glaucoma medication known as Lumigan, and is formulated to lower the pressure inside the eyes (intra-ocular pressure). One of the unusual side effects of using Lumigan eye drops is that patients start producing darker, thicker lashes.

Allergan presumably decided this was a side-effect with marketing potential and repackaged the drug as Latisse.

But the drug is not without other side effects. The skin around the eyes may become slightly red, and the pigmentation of the lids may increase.

If Latisse is transferred accidentally to the ocular surface the eye pressure can be lowered because after all that is what bimatoprost is prescribed for in glaucoma sufferers. In most non-glaucoma sufferers this effect is harmless. Latisse can also increase the pigmentation of the iris over time if it gets into the eye. Eyes can actually darken in colour. This effect may not be desirable if someone is fond of their naturally blue or green eyes.

More importantly patients who have ocular surface disease such as keratoconus, or corneal ulcers, or who are contemplating ocular surgery such as cataract surgery or LASIK may actually increase their risk of complications if Latisse enters the eye. These risks include the pressure in the eye dropping too low, and a condition called macular oedema, where the retina at the back of the eye becomes compromised.

Bimatoprost (even when it’s used in eye drop form) has also been linked with exacerbating Crohn’s disease.

One of the most striking side effects of Bimatoprost though which I see in practice is something called periorbitopathy. Bimatoprost is something called a prostaglandin analogue. Prostaglandin analogues mimic the prostaglandins made by our own bodies. These are inflammatory molecules formed from a type of fatty acid chain. Prostaglandins have an affinity for the fat cells surrounding the eyes and they change them. This alteration of the fat cells around the eyes can lead to the eyelids drooping, or conversely tightening, the blood vessels becoming more prominent and the upper lid sulcus (the groove between the eye and the brow) deepening. Most of these would be cosmetically unappealing and possibly even negate the positive lash-enhancing effects.

I think this one is a case of proceed with caution. It’s not actually available in the UK yet anyway but we all know that where there’s a will there’s a way! As a cosmetic agent Latisse is powerful and definitely produces longer, thicker lashes, but it is not without risk and I don’t think, having researched it, I would be tempted to try it. My search for mascara Nirvana will have to continue!


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


Hallucination, Illusion or Misinterpretation?


Most people viewing this pattern feel visually uncomfortable and disorientated because it’s designed to make you feel that way. Now imagine feeling like that all the time, as though every surface has that pattern on it. To a person with dementia changes in colour, or shadows on a path,  or the pattern on wallpaper can produce the same effect. The world can be a visually terrifying and uncomfortable place for them. Continue Reading →