Archive for July, 2011

Correcting for an astigmatism puts it all in fine focus!

Most people understand that nearsightedness means things near to you are clear, things far away from you are  blurry. And on the flip side, farsightedness means that things far away from you are clear while things closest to you are blurry. Got that? If not, let’s simplify it.

Nearsight= near objects clearest, far away ones are blurry

Farsight= far away objects clearest, near objects blurry

Now if I really want to confuse you, I’ll talk about Presbyopia which is what happens to all of us around age 40. That is when our eyes lose their ability to “auto-focus” things near to us to make them clear. You see, there is a crystalline lens behind your iris that changes its shape to autofocus things for near or far, much like the autofocus lens of a camera. As we get older, the lens can’t as easily change its shape anymore and things up close start to feel fuzzy, we can’t get them into focus (like the newspaper, small print on a pill bottle, a menu in a dimly lit restaurant.) It is then that we require a reading prescription to be able to get those objects close to us clear once again.

Presbyopia= the need for a reading prescription after age 40 due to the crystalline lens inside the eye losing its ability to autofocus.

Sometimes people who are nearsighted don’t feel the burden of presbyopia so much at first because they see ‘near objects clearest’ naturally. All they have to do is take off their glasses or peek beneath the frame and the natural focal point of their eyes happens to be at the perfect distance for reading. They can see clear and read very comfortably like this for long periods of time without glasses. It’s ok to use your natural nearsight to read, it won’t harm your eyes, but it may become cumbersome to put the glasses on and off all day long and there may come a point where doing this just doesn’t work for you as well as it did in the beginning. But maybe we can get into that in another article.

What I really wanted to talk to you about today is astigmatisms. An astigmatism has to do with the curvature of the front of the eye, the cornea. If the cornea is not shaped like a perfect sphere, if it is, let’s say, a little more pointed than it is round like the tip of a football, then your view through that imperfectly shaped cornea is distorted and vision will be blurry at ALL distances, (near, far, intermediate and everything in between). The cornea is a clear tissue, you can think of it as the ‘windshield of the eye.’ Notice how your windshield has a certain even curve to it? Now imagine the windshield was distorted, maybe even coming to a point in the middle, it would distort your view through it and everything you saw through it would appear a bit warped and a little blurry. That is what an astigmatism is!

Having an astigmatism is sort of like having a warped windshield, your view through it is distorted at all distances.

Astigmatism= blur at all distances due to imperfectly shaped cornea

You can have an astigmatism by itself in your prescription or it can be accompanied by nearsight or farsight and/or presbyopia. Your eye doctor can tell you precisely which type/types of these ‘refractive errors’ you have during your eye exam. Some people don’t have any refractive error, their eyes see perfect 20/20 vision naturally, we call them ’emmetropes.’

Emmetrope= no refractive error (no astigmatism, nearsight, farsight present), no glasses needed

But back to astigmatisms and our example of the car windshield. This type of visual distortion causes blur. We correct for this distortion or blur in your new glasses and that requires us putting a corrective lens in your glasses that counterbalances the distortion caused by your own cornea. This can sometimes take some getting used to because essentially what the new glasses are doing is taking the picture of the world that you usually see and stretching it in a different way. Glasses that correct for an astigmatism can sometimes feel a little strange when you first try them on, the floor may look curved, the walls may look bowed, you may feel like you are walking around in a fish bowl for the first few days until your eyes and your brain get used to the new way the world is being stretched. Most people adapt to most changes in astigmatism in their glasses within about a week and then they benefit from the extra clarity without experiencing that funny feeling anymore.

It is also possible to correct for an astigmatism with contact lenses, these special contact lenses are often referred to as toric contact lenses. They are a little more complicated to fit than regular spherical contact lenses (the kind that correct for nearsight or farsight) because they have to be lined up at a precise angle and maintain that precise alignment even when you blink or move your eyes a lot in order for you to see clear at all times. It’s common for them to move a little, or come out of a focus maybe a couple of times throughout the day but the majority of the time we want the lenses stable with no rotation and that will ensure the best clarity.

So, see? There is no stigma involved with having an astigmatism (sorry, I had to). Many people have an astigmatism, it is very common for the front of the eye not to be shaped like a mathematically perfect circle. See your eye doctor for an eye exam and get an up-to-date prescription. If you are prescribed glasses that correct for an astigmatism or if you have a change in your astigmatism prescription, the new glasses may take a little getting used to but once you do, you just might be amazed to see what you have been missing!


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