Working in partnership with our eyes, our brain plays a key role in the complex world of human vision. Unnoticed and with apparently minimal effort, it compensates for the weaknesses of our eyes. This is an example of teamwork at its very best!
When the lensed eye of vertebrates – and thus our own human eye – evolved, something odd happened. Unlike cuttlefish, for example, which have highly sophisticated bubble-shaped, lens-bearing eyes which arose through invagination of the outer skin, the human eye was – seemingly at random – formed quite differently as an outgrowth of the brain. At first glance, this may appear to be a minor difference, and it even offers advantages since it enables the same-sized eye to contain more photoreceptor cells. Yet oddly enough our photosensitive cells are positioned the wrong way around on the retina and point back into our body, while our nerve cells point towards the light source. This essentially means we have an 'inverted eye' which requires our brain to put things in the right perspective. It also means that humans and all vertebrates have what is known as a blind spot.
Everyone knows that when things start looking blurred it's time to get spectacles to correct the defects in our vision. But the real art of producing lenses is to create a lens design that not only restores our sharp central vision, but also gives us comfortable and relaxed peripheral vision. That's why the calculations performed in lens manufacturing require so much mathematical expertise and optical know-how. The aim is that the spectacle wearer's peripheral vision when wearing spectacles should be no different to their peripheral vision with uncorrected eyes. This is particularly challenging when it comes to producing progressive or sports spectacles with wrap lenses.
Did you know that it isn't our central, focused vision which determines how long it takes us to get used to progressive lenses in the near and distance vision zones and transitional range, but rather the changes to our peripheral vision? These changes can have a distorting effect which may be unsettling at first. But there's no need to worry – our brain quickly adapts to these changes, too. We soon get used to our new style of vision and eventually perceive the periphery as perfectly 'normal'.
There are two important things to remember, however:
And what does this mean for people who wear sunglasses?
We'll tell you what happens when your eyes have to work too hard
What's important for tailor-made glasses? Knowing how a patient's eyes interact.
How ZEISS lenses can make driving less stressful and safer.
They changed the world with their ideas