what is astigmatism? All the online definitions don’t make any sense. Ty
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It’s a slightly rugby ball shape to the eyeball. The effect is that when looking at sources of light you will see streaks of light. It can be in one eye or both and can be corrected with lenses.
Imagine a plastic bowl. The lens of your eye is shaped kind of like that. Now imagine squeezing the sides of the bowl together so it bends a little. That’s what a lens with astigmatism is shaped like.
Lots of good comments already on the cause. Let me try to explain the effect.
Your eye takes an object and focuses it (by acting as a lens) to an image on the back of your eye. Just as a camera takes an object and focuses it to an image on a sensor (or in the old days, film).
Imagine a screen say 10 m / 30 feet away with a circle on it. For people without astigmatism, their eye would focus the image (onto the back of their eye) into a circle. With astigmatism however, what happens is along one direction (lets say the vertical) the eye’s lens is stronger than in the other. This has two consequences: 1) the image in one direction will be focused at a different location (the “image plane”) than another. Meaning that, say, objects vertically shifted from the center of the object will be blurry while objects along the horizontal will be in focus. 2) That circular object will appear to be slightly elliptical – it will no longer appear as a perfect circle.
There is an optimal image location, where the defocussing effect will be least bad. It will be between the image location of the “weak” and “strong” focus locations. In one of the best namings in science, this point is known as the “circle of least confusion” (technically, this is the size of the spot, not the location).
Interestingly (to me, at least), the directions of the “weak” and “strong” lensing do not generally confirm to vertical. I would have thought gravity would be the driver of the effect, but apparently not, at least as I’ve been told.
The direction and strength of your astigmatism are two of the parameters in the optical prescription your received from your optician.
I have mild astigmatism and I think it’s cute. Basically, my vision is an object, and then a more transparent version of the same object, aligned slightly up of the object. The transparent ‘shadow’ creates a kind of mirage just around the object, so I am basically seeing it floating next to it, but this only happens on the borders of the object.
[Here’s a clip from Home Alone 2 showcasing extreme astigmatism. ](https://youtu.be/smx4Il5i-Tk?si=Myspnoo8xgb4P6fD) The duplicate (transparent) image doesn’t move around, it sticks to the object I’m viewing, and the base object I can see clearly
One cool effect of astigmatism is having street lights shine streched out along their horizontal and vertical axis. I see their shine not round, but vertical, like a [compass star](https://images.app.goo.gl/8hyLpVAuvuVjBgCk7)
I can intensify my astigmatism by squeezing me eyes or making them go out of focus (by tiring them for example)
Eli5 mode:
To see well, both your eyes should point at the same point.
astigmatism people (like me) have one of the eyes not match the other 100%. more like 99%. So you have veeeeeeeeeeery tiny double vision.
Astigmatism is a refractive error, but it doesn’t have anything to do with what some people in this thread are describing. It regards your eye’s two meridians. They bend the light differently to each other, which means you’ll essentially have two different “focuses” (English…) rather than the light being in unison.
You can be astigmatic without myopia/hyperopia or other refractive errors. You can also be myopic/hyperopic etc without astigmatism.
The people saying your eye is shaped like a football/rugby ball are correct. But to picture it don’t look at the ball from the end, rather turn the ball side ways and look at it like that. The up and down curve(vertical ) is different from the side to side curve ( horizontal). That’s astigmatism.
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