what is astigmatism? All the online definitions don’t make any sense. Ty
In: Other
It’s when your vision is blurry in one direction. [Like this but not as extreme](https://i.imgur.com/hflasEe.png). Usually goes with general bad vision so it would be blurry in one direction and more blurry in the direction 90 degrees to it.
First, let me say that I am not an expert and have no medical training. My familiarity with astigmatism is that I had it until it was corrected through lasik.
Astigmatism is where the outer portion of the eye is not circular but rather an oval. This causes the light that passes into the eye to be distorted and causes bluryness. It can either be aligned vertically, horizontally, or as in my case, at a diagonal.
This can be corrected with glasses or contacts, however the contacts have to be specially made so that they align correctly with astigmatism.
My optician said the eyeball was not quite the correct shape. It causes the focal point of image to be slightly in the wrong place, and not perfectly on your retina.
He explained it like this:
For English people:
> Instead of your eye being spherical like a football, it’s shaped more like a rugby ball
For American people:
> instead of your eye being spherical like a soccer ball, it’s shaped more like a football.
I have this. So the lens on your eye (the part that protrudes out a little and covers the iris) is dome shaped. When the dome shape is uneven, so not perfectly smooth, round, or even a little oval, it changes the way the light bends into your eye. This causes blurry vision.
Normally the cornea is symmetrical with a constant curvature, giving the lens a definite focal point. Near/far sightness is if the curve doesn’t focus the light on the retina directly but is still symmetrical. Astigmatism is when the lens itself has either a changing curvature or an asymmetry, preventing the lens from focusing the incoming light at a single point. Making everything out of focus regardless of distance.
It is a bit of a catch-all term.
Astigmatism occurs when the profile of the lens isn’t circular. If you look at a topographical map of a hill that’s shaped like a normal lens, the lines will appear as concentric circles. In an astigmatic lens, the lines will be oval shaped. This causes the image that passes through it to be blurred along a specific direction. In order to correct that, the eyeglasses need to have their focus set for both vertical and horizontal astigmatism, and the combined effect of both bring the light back into focus.
Astigmatism is when your cornea has an irregular shape.
For regular short/long-sightedness the focal point is a bit back or forward of where it should be. But a normal round lens fixes the problem just fine.
In astigmatism however the cornea is curved a bit differently in one direction compared to the other, so you end up with a blurry focal point at all distances. In a simplified example (a 0 degree rotation lens), height and width have different focal points so letters for example would either be blurry in height, or in width or in both depending on how you focus your eye.
To fix astigmatism (as well as it can be fixed, you can rarely compensate 100% for astigmatism) you need a lens that corrects the light in a specific way. An astigmatic lens has the refractive value (how myopic/hyperopic is the eye in general), a cylindrical value (how much of a difference is it between refractive value in direction X vs direction Y) and then a specific axis (rotation of 0-180 degrees, because of course a biological eye is rarely perfectly aligned with just an X/Y up/down/left/right axis).
This also made it difficult to make contact lenses, but these days they have self-righting lenses that you just need to blink a few times and the lens corrects its axis so that it’s aligned with your eye.
Your cornea is the clear part on the surface of your eye, in front of the iris and pupil.
Astigmatism is when the cornea is the wrong shape, or warped. This odd shape bends the light entering your eye, so the lens in your eye (in the center of your eyeball) will not appropriately focus the light on the retina (at the back of the eyeball)
Glasses fix this by bending the light before it enters your eye, so the light being bent by the cornea just undoes what the glasses did, and the lens can then effectively focus light on your retina.
Normal bad vision is caused by the eyeball being too long or too short. Glasses fix this by adjusting the slight so your lens will focus the light in the appropriate spot on the retina
At the front of your eyes is the cornea, which is a transparent “dome” that covers your pupils/iris and lets light in. Astigmatism is when the cornea is irregularly shaped, so that the light gets distorted slightly and does not get focused towards the back of the eye as it should.
Conceptually think of it like taking a picture of a mountain with your smartphone. Regular eyes focus on the mountain as the “focal point”, but astigmatism is as if you had tapped on somewhere closer or slightly off-center so the mountain appears blurry.
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