Prescription conversion question

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SerenaK - 26 May 2007 00:33 GMT

My eyeglass Rx is:

OD: -4.50 -050 155
OS: -2.50 -050 020

I was given trial spherical soft contacts (Proclear) of:
OD: -4.50
OS: -2.75

I found that my vision didn't seem clear (blurring even of large signs at
the airport), so my optometrist suggested that even though my degree of
astigmatism is slight, I should try correcting for it in my left eye to see
if it makes a difference.

I'm trying aspheric lenses at the values above,
and (also)
OD: spherical
OS: -2.75 cyl: -075 Ax: 20 Toric.

My question is: should I be trying Toric: -2.50 or -2.75 on the left eye.
I was under the impression that the bumping up to -2.75 when using
spherical was to compensate for the slight astigmatism. Is this still
required when actually using a Toric lens?

Thanks!

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Mike Tyner - 26 May 2007 00:36 GMT

> My question is: should I be trying Toric: -2.50 or -2.75 on the left eye.
> I was under the impression that the bumping up to -2.75 when using
> spherical was to compensate for the slight astigmatism. Is this still
> required when actually using a Toric lens?

Your suspicion is right. The extra quarter would normally be taken back out.

Ask for an "overrefraction." It's spozed to be part of a good toric fitting.
Ideally it should be +0.25 sph, but OR often reveals other adjustments that
should be made.

-MT

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SerenaK - 26 May 2007 21:26 GMT

> > My question is: should I be trying Toric: -2.50 or -2.75 on the left eye.
> > I was under the impression that the bumping up to -2.75 when using
[quoted text clipped - 8 lines]
>
> -MT

Thanks for the advice! I will at the least ask about a -2.50 toric lens.

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Dom - 26 May 2007 05:55 GMT

I'm surprised that you didn't have clear vision with the first pair of
contacts, and I'm also surprised that your optometrist thought the toric
lens would make much of a difference. With only 0.50 astigmatism you
should have fairly clear vision so I wonder if something else is causing
the blur rather than that.

I would have tried -250sph as the first lens - even though theoretically
-275 is the spherical equivalent, often a little 'less minus' in these
cases gives vision that is a little more comfortable and just as clear.

To answer your question, yes you would have expected the toric lens to
be -250 or maybe even -225, depending on the over-refraction. But a
-275, even if a little strong, shouldn't blur your vision all that much
at all.

Dom

> My eyeglass Rx is:
>
[quoted text clipped - 21 lines]
>
> Thanks!

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SerenaK - 26 May 2007 21:37 GMT

> I'm surprised that you didn't have clear vision with the first pair of
> contacts, and I'm also surprised that your optometrist thought the toric
> lens would make much of a difference. With only 0.50 astigmatism you
> should have fairly clear vision so I wonder if something else is causing
> the blur rather than that.

I have to say that already that there is a subjective sense of improvement
in sharpness using the left toric. I might just be oversensitive, but I've
had the sense for several years using spherical lenses that I can't focus
completely clearly. It's a subjective thing, but it's as if my eyes aren't
working together to provide complete sharpness. It's as if I have to strain
just slightly to see, and because I suffer from migraines, I was concerned
that this could make that problem worse. And then, recently, with a new
prescription, even large signs had a slight sideways blur.

I don't know a lot about toric lenses and what their drawbacks are, but I'm
assuming that if I pick up on an improvement in quality of vision, the
additional cost is worthwhile.

Anyway, thank you for your advice!

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