The Distant Eye
By: Siddharth Murali
Tags: Infinity, Biology, Eyes, Physics, Vision

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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