The Distant Eye

When you lose focus, what do your eyes focus on?

The Distant Eye

When you lose focus, what do your eyes focus on?

Sometimes,  our thoughts drift during conversations, or we mentally ‘switch-off’  during a particularly boring lecture. I’ve especially noticed this with  my friends. I’ll be on a talking spree, and all of a sudden notice that  they’re lost and aren’t paying attention. So I’ll sort of wave my hands  in front of their eyes and say the customary “Hello?”. They then blink  back to the present and apologise and ask me to repeat myself…

If you’re ever in the position of said friend, you’ll notice that your vision becomes unfocused, making you look “lost”.

Have  you ever wondered why this happens? It’s actually very simple — the eye  just relaxes. Since you aren’t paying attention to what’s in front of  you, there is no need for you to look at it. Your eyes can take a break.

Your  vision becomes unfocused to your immediate surroundings and focuses  instead as far as possible: towards infinity! This seems a bit  counter-intuitive. Focusing at infinity seems like a big deal — but yet your eye is, well, relaxed. So, how does that work out?

The eye has two major components: a “lens”, which does all the focusing, and the “ciliary muscles”, which control the shape of the lens.

Schematic Diagram of the Human Eye

The lens becomes stretched and elongated when the ciliary muscles relax. That seemed a bit strange to me, because won’t the muscles be un-relaxed if they’re stretching the lens?

After a bit of research, I realised it works the same way as part of your hand.

Let’s  suppose that your hand is lying flat and outstretched on a table, palms  facing up.Your hand is relaxed. However, the muscles underneath your  biceps and behind your elbow( the triceps), are stretched! They become  relaxed when you bend your elbow.

Similarly,  the suspensory ligaments (part of the ciliary muscles), which hold the  lenses in place, get stretched when the eye relaxes. Those in turn  stretch the lens, making it flat and thin.

Light  is slower in a material like the eye-lens, and gets bent by it. But  since the lens is flat and thin, there is lesser amount of lens for the  light to go through, so the light isn’t bent as much. This allows your  eye to focus at infinity!

When the ciliary muscles contract, the lens becomes rounded and  focuses nearby objects. In this case, the tension on the stretched  ligaments is reduced and the lens become rounded, much like a rubber  band.

Here,  the lens is thicker and rounder and light gets bent much more, because  there’s more material that the light has to travel through. This allows  the eye to focus on nearby objects.

The  closest distance up to which an average eye can see things comfortably  is around 25cm. This minimum distance is called the Least Distance of  Distinct Vision, or LDDV. The eye can focus on anything from 25cm, all  the way to infinity.

Eyes  get strained when looking at close objects. But microscopes don’t cause  any strain, even though they help us look closely at things. Why?  That’s because microscopes focus at infinity, or at the very least, the  minimum distance.

It’s actually impossible to look clearly at things a few centimetres from our eyes — forget micrometres, which is the average size of  microscopic objects! That is to say, our eye cannot even see such small  objects. Given this, there is no question about studying the details of a  tiny cell. That’s why the microscopes magnify the image of the object,  and this image is made to form at infinity. Now, parts of the cell —  like the cell wall and the nucleus — can be observed clearly.

Even  telescopes focus images of planets and distant stars at infinity. You  might ask why this is required, since they are already very far away —  practically at infinity in themselves. Well, the telescopes also magnify  the image, which is necessary to observe the structure and behaviour of  celestial bodies.

So,  in conclusion, whenever we zone out — during class, conversations, or  otherwise — our eyes become focused at infinity. Nearby things become  blurred. And when the teacher calls our name, we come out of our little  trance-like state and focus normally again.

Maybe that’s why it’s so nice to kick back and look at the horizon at the beach: because it’s the epitome of relaxation.

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