Question about prescription?!


Question: My eyeglass prescription is
OD (right): -1.75 +0.50 97
OS (left): -2.25 +1.00 85
or...
OD (right):-1.25 -0.50 7 OS -1.25 -1.00 175
So my question is....do I need to buy toric contact lenses for my left eye? I read somewhere that people with astigmatism from -1 to 1 can get away with not wearing toric....but I had trouble seeing with my left eye in the past on regular lenses (but it could have also just been that the prescription was too weak). Also it seems like unless you buy a $100 single lens you can't get a -1.25 -1.00 175 lens....So if I do indeed need the toric should I get a 170 or 180 axis (would 180 be the same as a regular lens with some corr for cylind?)
I have never had trouble with regular contacts on my right eye...but I'm not sure how to adjust the value of the first number to account for the second number...do I just add them together or is there some formula to use for an equilvalent correction by combining the first 2 numbers of script?
thanks in advance.


Answers: My eyeglass prescription is
OD (right): -1.75 +0.50 97
OS (left): -2.25 +1.00 85
or...
OD (right):-1.25 -0.50 7 OS -1.25 -1.00 175
So my question is....do I need to buy toric contact lenses for my left eye? I read somewhere that people with astigmatism from -1 to 1 can get away with not wearing toric....but I had trouble seeing with my left eye in the past on regular lenses (but it could have also just been that the prescription was too weak). Also it seems like unless you buy a $100 single lens you can't get a -1.25 -1.00 175 lens....So if I do indeed need the toric should I get a 170 or 180 axis (would 180 be the same as a regular lens with some corr for cylind?)
I have never had trouble with regular contacts on my right eye...but I'm not sure how to adjust the value of the first number to account for the second number...do I just add them together or is there some formula to use for an equilvalent correction by combining the first 2 numbers of script?
thanks in advance.

Most people would miss the dioptre of astigmatism in the left eye, and not miss the half-dioptre in the right. But there's no exact rule. If you're strongly right eye dominant it may matter less: if you've a perfectionist personality, or a visually demanding job, it may matter more.

Specifying the lens would be down to your prescriber, not for you to guess at.
Apart from the fit mattering (base curve, diameter, material)
the axis of astigmatism is quite frequently different on a contact lens since the nominal horizontal usually stabilises reliably, but often offset 5 or 10 degrees (or more) from the horizontal.
So that 175 left axis might need to be anything from a 160 to a 10 !

The "best sphere" equivalent, if not going for a toric lens, would be found by adding half the cyl power to the sphere.
i.e. -1.75DS...
But again, that's a theoretical rule-of-thumb. The best lens in practice could easily be that, or 0.25 higher or lower. To be proven by testing before the contact lens Rx is finalised.

(edit: "Itsacelebration": you missed the sign of the cylinder!
We've all done it, usually more than once)

The spherical equivalent is the sphere # or -1.25 plus half the cyl -1.00, so it would be -1.75. You can try this but you are right once you get above .75 in cyl most people do need the cyl in the their Rx to see to their best ability. Don't worry about the axis the doctor will work that out.





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