Blinded by the Light

Being a scholarly man, I have naturally abhorrent eyesight. My visual acuity is about 20/500, in both eyes. When compared to the perfect eyesight of 20/20… I’m not doing too hot. But I wondered, as I put in my contacts for astigmatism, what that number actually measured. What does it mean? How is my eye so horribly out-of-whack?

Leonardo DaVinci was one of the first scientists to observe that the eye’s sole purpose was to gather light beams into the lens, at the pupil of the eye. The lens focuses this light on the retina in the back, the signals from which are then sent through the optic nerve for interpretation. Photoreceptor neurons called rods and cones are responsible for this signal shift from the retina to the brain. Rods provide vision in dim light, working purely in black and white, while cones work in bright light and provide color. A third type of cells, called ganglions, make your eye react to sudden changes in light, like when you come out of a dark room on a sunny day.

Your dark, lonely room.

To get the right optic bend in the light that your eye is gathering, your eye muscles actually contract to bend the lens one way or another using things called the ciliary muscles.

Sometimes, though, this doesn't work. As you mature, your eye changes shape slowly, and this can affect your visual acuity. Longer eyeballs usually mean that a person is myopic, or near-sighted; shorter, and that person is hyperopic, or far-sighted. No matter what the ciliary muscles do, they just can’t compensate for that lack of focus, making that person’s eyesight permanently off-kilter.

The scientist Hermann van Helmholtz actually figured this out by studying the anatomy of the eye itself. He ultimately concluded that, well, the eye was pretty bad at doing its job. Apparently, it gives the brain so little information that the brain has to make assumptions to fill in the gaps, i.e. light comes from above, objects aren’t viewed from the bottom, and faces are always right side up. Messing with these assumptions is what creates optical illusions.

Pictured: not what you pictured

Some or even all of these problems may be happening to me, but my real issue is the astigmatism. An astigmatism, in the purely mathematical sense, is a lens that creates two different foci from two different perpendicular planes. In a biological sense, it means that my eye is creating two images of an object, one in the horizontal plane and one in the vertical plane, and neither of them is in focus where they should be. This, in combination with elongation of my eye, makes my eyesight just horrible. Of course, the miracles of optical science have found a way to fix this: just use the correct lens to cancel out the abhorrent things that mine is doing. Instead of having a perfect dome shape, like a normal contact would, contacts for astigmatism instead look like the side of a football, bending the horizontal and vertical light beams in different patterns to achieve focus on my retina.

With my contacts in, I can see 20/15, or about 1.5x normal acuity. Though this kind of sight is excellent, some people can achieve 20/10 vision, or 2x the normal visual acuity, without the use of ocular aids. Such eagle-eyes include John Glenn, Chuck Yeager, and Ted Williams, all of whom certainly used their superior vision to its capabilities. Sadly, my naturally bad eyesight means that I’ll never be a jet pilot, at least not without some serious surgery. However, I have hope that one day, my children will have even worse eyesight than me.

Or they'll just become Sea Gypsies. No lie.