Update from Judith93585

RE sphere: -1.25; cylinder +0.50; axis 015

LE sphere: - 1.25; cylinder +0.25; axis 145

I might go to the affiliated optical shop even though they do not accept my vision insurance because any changes will be covered by their warranty for 60 days. If I go to the optical shop that does accept my insurance it might be more of a problem. Will double check 😃

That is interesting. Converting that to more common optometrist negative cylinder and calculating spherical equivalent gives this for numbers.

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RE sphere: -0.75; cylinder -0.50; axis 105, SE -1.00 D

LE sphere: - 1.00; cylinder -0.25; axis 55, SE -1.125 D

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I am surprised that your reading is good with this low amount of myopia. The difference between the SE is not numerically significant, and it also seems surprising that there would be any detectable difference in vision between the eyes. If anything the right eye with more astigmatism should not be quite as sharp.

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The thickness of those lenses with standard non high index material should be very thin.

Me too! I was able to read the letters but in real life I do feel myopic especially the LE. He took a lot of time with me. I got to wear a trial frame with -1.25 lenses and look down a long hall and within the optical shop. All seemed fine. That said, I'm not sure these glasses will correct me to 20/20. My optometrist mentioned -0.75 but I didn't quite understand whether that was the target or something else. I told my optometrist what I was concerned about and he may have made adjustments to help in that regard. The extras he suggested were anti-reflective coating and transition lenses. I asked about UV protection and blue light filtering but he doesn't think that's medically necessary.

Thanks for making the calculations! I think he may have thought of making the LE sphere -1.0 rather than -1.25 ... do you know how that would have changed my prescription?

I'm confused. Ron, why are you using values for sphere that are different than the ones Judith posted?

There are two different methods of writing refraction numbers for vision. Ophthalmologists who normally are dealing with cataracts and selecting IOLs use a positive cylinder convention. Optometrists who are normally writing prescriptions for eyeglasses or contacts use a negative cylinder convention. The negative cylinder convention makes more sense to me as my eyeglass prescriptions were written that way for as long as I can remember. At the end of the day they are the same, but negative cylinder is more familiar to look at - at least for me.

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And spherical equivalent or SE is a method of combining sphere and cylinder into one number to estimate what the overall vision is like. It assigns a weight of 50% to the cylinder part.

I understand the conventions regarding negative/positive cylinder. It is the values that you are using for sphere that is confusing me. Judith has stated the sphere is -1.25 for both eyes but you are using values of -0.75 (RE) and -1.00 (LE)

To convert one to the other:

1. Algebraically (signed math) add the sphere and cylinder powers to determine the new sphere power.
2. Change the sign of the cylinder.
3. Change the axis by 90 degrees. (axis is always expressed as a number between 1 and 180 )

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If you do the process again, you are back where you started.

Normally distance eyeglasses are set to be the best possible distance vision. If the LE sphere was -1.0 instead of -1.25, it would be a very slight difference. You will have UV filtering in your IOLs and that is not necessary. Anti-reflective coatings are a mixed benefit. The probably do allow more light through the lens, but the coating also makes the lenses very easy to smudge and harder to clean. If you get a lower index lens material you may want to consider a scratch resistant coating, as the material tends to be softer. CR-39 if available is a good lower index material.

Converting from positive to negative cylinder is a bit more complicated than just reversing the sign. You have to add it to the sphere as well as reverse the sign, and the axis has to either be increased or decreased by 90 degrees to get a value between 0 and 180 degrees. Because the sphere changes that is why I like negative cylinder, as that is what I am familiar with.

I was told at the optical shop that rimless glasses like Silhouette require lenses that resist cracking. She suggested hoya trivex. I was surprised since before cataract surgery I had progressive lenses made from high index Zeiss lenses, but then I'm not sporty.

How would you compare hoya trivex and Zeiss high index lenses in terms of thickness, weight, and effectiveness in providing crystal clear vision (within the limits of the prescription)?

I'm seeing an unaffiliated ophthalmologist for dry eye care. I mentioned to my optometrist that Xiidra had made my eyes blurry causing more dizziness so I decided to stop after 2 doses while having eye exams and refractions. He advised me not to restart. Are you aware of why Xiidra might be contraindicated?

Many thanks Ron!

With your very low prescription power, lens thickness or weight is not an issue. They will be thin at that power. You should avoid all of the high index materials now that you only need a very low power lens. They would be a waste of money and would decrease the optical quality of the lens. A measure of optical quality is the Abbe number. The higher the better. A CR-39 lens has a refractive index of 1.5 and an Abbe number of 58 - one of the very highest of all lens materials. The Trivex has a refractive index of 1.53, very slightly higher, but the Abbe number drops to 45. I used to get a high index lens material from Costco called Thin and Light with a refractive index of 1.74. At Costco when you select their best quality lens, it is hard to avoid it. But, it has an Abbe number of 33, quite low. The worst choice for Abbe number is polycarbonate at 30.

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Trivex would be a very good choice. CR-39 might be somewhat better optically, but only if they can make it in your frame. High index is a bad choice. If you google "eyeglass lens material abbe number" and then on images you will get lots of tables showing these numbers. Ignore all the stuff on lens thickness as that is only an issue with lenses of much higher power than what yours will be. They always do comparisons with high lens powers and cover up that there is really no difference in thickness or weight in low power lenses.

Thanks to you and to trilemma for the education.

If you do not want to go through the mental gymnastics of making the conversion there is an on line calculator to do it. Google this:

"ACLens Eyeglass Prescription Positive Cylinder Conversion"

Hi Judith,

May I ask if you have targeted -1.0 for your cataract surgery in both eyes?

We targeted -1 and -1.5 but my optometrist wrote my new glasses prescription for -1.25 in both eyes ...

We targeted -1 and -1.5 but my optometrist wrote my new glasses prescription for -1.25 in both eyes ...

Those were sph. What were the cyl numbers?