Lenses Rx confusion

[FredZq]

Dear Sir,

Initial visit to an ophthalmologist/cataract surgeon recently. The cataract has reached the point where it "bugs" me a little too much. The technician did the usual measurements. The Doc took a look and said "you have a cataract"! "Yep; that's why I'm here".

So, I will see them again for some more measurements,and perhaps an operation. Before I left, I said "where's my prescription"? I sat around for a while and they finally produced a prescription for new lenses.

An amazing (to me) observation is the fact that the lens prescription numbers are vastly different from those of just six months ago, including for the non-cataract afflicted right eye, which is still OK.

March 2007: R.E. Sphere +2.25,   Cylinder -2.75,   Axis 105  
            L.E. Sphere +1.25,   Cylinder -2.25,    Axis 073
            Add +2.25

October 2007: O.D. Sphere -1.00,   Cylinder +2.50,   Axis 017
            O.S. Sphere -1.75,   Cylinder +2.25,   Axis 162
            Add +2.50


I queried them and the technician told me that optometrists and opticians use different numbers than ophthalomologists use, but they mean the same thing. I asked how the people who grind the lenses can know the difference, She said just trust me, They'll know.

This seems kind of screwed-up to me; is it true?

[John C Hagan III, MD, FACS, FAAO]

Yes that is very typical. The cataract causes increased "false" or pseudo-myopia. The sphere gets bigger in #   Because the eye becomes myopic in early stages people that were farsighted and neurtral can read without reading glasses and they called it "second sight"  sounds good but isn't

JCH MD

[sally987]

When you have a cataract, does the SPHERE part of the Rx get significantly higher? I do have cataracts and my numbers have gone like this:

My left eye Rx went from -2.75 in 2007
It was -4.00 in 2008
It is -7.25 in 2009

Is something else wrong or are those just typical cataract development type numbers?

Thanks!

[John C Hagan III, MD, FACS, FAAO]

Glasses prescription can be written in plus cylinder form (your Oct 07 RX) or minus cylinder form (your March 07)   Ophthalmologists generally write in plus cylinder and optometrists in minus cylinder.  Think about it like the weight of something in pounds and in kilograms. The weight is the same its just how your express it.

Opticians covert plus cylinders to minus before grinding the lens.

There is very little different in those two RX. no one screwed anything up.

The formula is to add the sphere and the cylinder algebracially and that is the new sphere,    change the sign of the cylinder to the opposite sign  add 180 degrees to the axis. If its greater than 180 degrees subtract 180 from it.

JCH III MD

[FredZq]

Forgot to mention:  first Rx was by an optometrist; latest was at ophthalmology clinic.