Understanding Vision

Getting to know the aspects of vision

For our purposes, there are four main factors we need to consider when we are determining whether a thing can be seen or not.

Is it in view? Is it obstructed?

This one seems pretty obvious, but it’s important. Some things might be easy to see in every way, but if they are hidden behind something of course we can’t see them. And sometimes things might be in view, but there might be other things partly obstructing the view which makes it uncomfortable, or hard to make sense of what we’re seeing because we can’t see the whole thing in one go.

The basic technique for these problems is to move — either we move ourselves, or we move the object that’s obstructing the view. When it comes to this factor in vision impairment, this is often one of the most problematic, because the obstruction is due to damage within the eye itself.

Is it big enough?

The thing needs to be large enough to see. Clearly, if it’s unreasonably tiny, like a bacterium, nobody can see it — for that, we need special equipment (a microscope). Similarly, for a splinter in our finger we might need a magnifier. Another example would be a sign that is too far away to read — we go closer to it so that it appears larger (or we could use a telescope or binoculars).

Some small things are able to be seen, but they are too small to be seen easily and comfortably. Examples include legal fine print, and some labels on food packaging.

Is it bright enough?

Human eyes have a remarkable ability to see things over a very wide range of illumination levels, from a moonless night to the brightest day — much better than even the most advanced camera. But of course we can’t see with no light at all, so the obvious intervention to let us see in those situations is to turn the light on.

Roughly speaking, the dimmer the light is, the less detail we can see. If it’s too dim for any given detail, we need to make it brighter.

Too much light can also be a problem. For most of us, it’s very rarely so bright that we simply can’t see anything at all, but there are eye conditions where even normal daylight levels are blindingly bright. But all of us are familiar with situations in which the light is uncomfortably bright, which we usually deal with by putting on sunglasses or a hat.

Is it distinct enough?

This relates to how an object stands out from its background. If you drop a black pen, it’s easy to find on a white floor, But if you drop it on a black floor, it can be very difficult to find. Sometimes we might have an old receipt with writing that has become so pale or indistinct they it’s difficult to see.

This is the concept of contrast. When there is too little contrast, it can be very difficult to deal with.

Each of these factors is important. On the next pages we will go through them in depth.