astigmatism & myopia

[melissa]

Is the distance vision of someone with astigmatism and myopia the same as someone with more myopia and no astigmatism? Here's what I mean - someone here has -1.50 and 1-.75 with -.75 and -.5 of astigmatism. He says that's worse than -2.25 with no astigmatism. He reckons the astigmatism means he's myopic at all distances so can't see clearly at all. Is it worse then to have his lower prescription and astigmatism? I can go without my glasses but he says he can't at all. Thanks. Mel

[Texas Ranger]

Melissa, so, you have a -2.25 sphere Rx, and can go without your glasses, likely perhaps in a small room, okay, but not for very far away. Well the meaning of astigmatism is "no focus", i.e. the persons cornea/lens focussing system is "out of round" so it focusses light differently in one meridian than it does 90 degrees away, so the -1.50-.75 actually has a -2.25 in one meridian, but .75 less 90 degrees away, and both come to focus seperately, inside the retina. The "minus" powers diverge the light passing through the lens, thereby twisting it to form one focus, on the retina. without the lenses, the wearer has "no focus"....clear, right?

[melissa]

Texas Ranger - yes I have a straight -2.25 and now I reckon I'm lucky. I'm glad I can still do without my glasses even in a small space.

I'm still learning about vision but very curious so thanks for your patience.

[Cowboy]

I think a good way to help understand astigmatism a little better is to ensvision a baseball and a football. If you have a light source shinning on the baseball, all rays of light will surpass the orb equally. Using the football (american), one side is longer than the other. Therefore, the light source will travel unequally at one meridian than the other. The same concept occurs with the cornea. Some eyes are elongated at one meridian, hence astigmatism. Some people react differently when it comes to "focus" issues. Most with moderate (-1.00) astigmatism and above usually describe the focus problem as 'double images'. This is true because of one light source at one meridian is reaching closer to the retina than the other.
As Texas said, the higher the power of the lens, the less focusing ability there is at distances. Distance power is considered to start at 3feet. But, take my mother who is a severe myopic can't see past her nose without her glasses. She is a
-11.00 in both eyes with mild astigmatism in the left eye.
I hope that I and Texas have clarified your question thus far. If not, perhaps others will lend an opinion that I may have left out. 'Til next time....
:cheers:

Cowboy

[Stopper]

This is how I explain it to patients. ( Assuming all Astigmatism is corneal) Think of the cornes like half a tennis ball. If there is no astigmatism, the surface is spherical but if you squeeze it, that is the shape of the cornea with astigmatism. A sherical surface will all focus at the same point (stigma) in the eye. With astigmatism, it does not focus at the same point (astigma).

The other issue is that vision is very subjective Two people with the same Rx may have different opinions on how blurry things appear and how much they need to wear the glasses. I would expect that your freind with the astigmatism would see better than you when reading an eye chart but that has no baring on how you or they feel about how well you can function with or with out the glasses.
Hope that helps:cheers:

[ripper]

One way to show how astigmatism affects vision is to put up the clock dial on the projector and dial in the spherical correction only in the phoroptor on an astigmatic patient, if they are compound myopic one meridian will be clearer than the others, the other focal point the power of the cyl will be buried in the vitreous, when the patient looks at the clock dial, u can explain to them with uncorrected astigmatism they don't get the whole picture!! Then slowly dial in - cyl until the clock dial is uniform.

[drk]

I explain astigmatism these days like this:

"Astigmatism is a type of blur that affects you at all distances. It is a type of double vision that usually occurs due to the shape of the front of your eye not being round, like the back of a teaspoon."

Or, "Don't bother me with stupid questions".

If they ask about the cyl and axis part of their Rx:
"Don't ask, I know you are trying to learn how to self-prescribe torics and buy them online".

Or, "The cyl indicates how far apart the double images are, and the axis indicates whether the double image is horizontal, vertical, or diagonal".