What makes some people blink more than others?

Keziah Latham from ARU took on this question from Roy...

Keziah Latham - Okay. Well if we think of first of all about why we blink? We want to spread the tears across the surface of the eye and there's two main reasons for that.

First of all, we want a nice smooth surface at the front of the eye so that when light comes into the eye we get a nice clear image that's sent to the back of the eye. If we think about, if you look through a normal window with a nice smooth surface you can see through it. But if you look at the bathroom window which is all bumpy, you can't see through it so well. So we want a nice smooth surface from the tears. But the tears also protect the eye to a certain extent. So they move little bits of debris and dust off the eye and actually there's enzymes called lyzosyme in the tears which have got antibacterial properties as well so it sits in keeping the eye safe.

Now there's there's three types of blinking. The spontaneous blinking which is what we do automatically without thinking about it; there's reflex blinking, which is what you do automatically when there's some sort of threat to your eyes, so you want to close your eyes to protect them. And then there's voluntary blinking, where you kind of think about it. So, really, the spontaneous blinking is the one that we're interested in here and that's incredibly variable between people.

So it's completely right in the question to ask why there is this variation, and there's a whole bunch of different factors. So, to some extent it depends on the quality of the tears. So your tears are actually made up of three layers and the top layer is a fatty layer called lipid, and if you've got too much or too little lipid in your tear film, then your tears will evaporate quicker and so you'll need to blink more often to get the tears spread over the surface; and the same happens in different environments: if it's very dry, or very windy, again the tears will evaporate very quickly and so you need to blink more often. We also know that it varies with task, so if you're concentrating harder, your blink rate tends to go down and you also blink less when you're looking at computer screen, compared to looking at paper, which is quite interesting.

Chris Smith - What about lying? Because I heard that people people may just adjust their blink rate when they are telling porky pies?

Kezaih Latham - There is some suggestion that when people are concentrating harder - and lying may take more concentration - that they might that they might blink faster. Also, if you're attracted to somebody, you might blink faster as well. So there's a whole range of factors and in fact normal blink rate can be anything from four to 20 times a minute. So it's really variable depending on the person.