what is astigmatism? All the online definitions don’t make any sense. Ty
In: Other
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.
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