Does anyone understand eye prescriptions?

Mark__H

Recently found myself in possession of 2 vouchers for free eye tests at different opticians and duly booked 2 appointments about a month apart.
I don’t wear glasses at present but am aware my eyesight is getting worse so was fully expecting a prescription to result from the tests.
Sure enough, both opticians issued prescriptions, principally for reading.
Prescriptions are divided into 4 sections – SPH, CYL, AXIS and ADD.
The SPH, CYL and ADD numbers are very similar on both prescriptions – no more than 0.25 difference.
However the AXIS number is 90 on one prescription and 180 on the other.
I’ve done some research on the internet to understand these abbreviations and figures, but can’t get my head around the difference in the AXIS numbers and I don’t want to spend money on glasses with the ‘wrong’ prescription.
Should I been concerned? Is this a material difference between the 2 prescriptions?

Tom99

“The axis is the orientation of the astigmatism. The value is in degrees, and can be anything from 1 to 180. There is no average value and the number does not have any relevance to the size of the astigmatism (that is indicated in the CYL box).
It’s probably best described as being like a compass bearing. The bearing you walk on does not relate to how far you walk, it’s just the direction of travel.”

https://blog.glassesdirect.co.uk/2009/06/04/ask-an-opticianwhat-is-the-axis-on-a-prescription

Undervalued

Mark__H wrote: »

Recently found myself in possession of 2 vouchers for free eye tests at different opticians and duly booked 2 appointments about a month apart.
I don’t wear glasses at present but am aware my eyesight is getting worse so was fully expecting a prescription to result from the tests.
Sure enough, both opticians issued prescriptions, principally for reading.
Prescriptions are divided into 4 sections – SPH, CYL, AXIS and ADD.
The SPH, CYL and ADD numbers are very similar on both prescriptions – no more than 0.25 difference.
However the AXIS number is 90 on one prescription and 180 on the other.
I’ve done some research on the internet to understand these abbreviations and figures, but can’t get my head around the difference in the AXIS numbers and I don’t want to spend money on glasses with the ‘wrong’ prescription.
Should I been concerned? Is this a material difference between the 2 prescriptions?

Many people can vary by that amount from day to day or even depending on how many cups of coffee they have had!

It is very difficult to measure tiny amounts of astigmatism accurately and again it can vary depending on a whole number of factors.

To be honest, getting two sight tests has probably just worried you unnecessarily. What are you going to do now? Get a third? Then a fourth!

If you are going to get glasses from an optician (rather than online or direct from a manufacturing business) then I would go with whichever of the two you feel will give you the best service in the unlikely even of a problem.

Just to add, I am not an optometrist but I do have a detailed understanding of optics from other work.

theoretica

Do the CYL readings have the same sign +/-? The same prescription can be written in two ways, 90 degrees out, but the CYL sign will be different, and the SPH different by the CYL number.

See https://www.aclens.com/positive-cyl-converter

Mark__H

Prescription 1 reads:
Right – SPH +0.25, ADD +1.50
Left – CYL -0.25, AXIS 180, ADD +1.50
Prescription 2 reads:
Right – ADD +1.75
Left – CYL -0.25, AXIS 90, ADD +1.75
All other values are ‘nil’ or blank
Hope that helps

theoretica

Mark__H wrote: »

Prescription 1 reads:
Right – SPH +0.25, ADD +1.50
Left – CYL -0.25, AXIS 180, ADD +1.50
Prescription 2 reads:
Right – ADD +1.75
Left – CYL -0.25, AXIS 90, ADD +1.75
All other values are ‘nil’ or blank
Hope that helps

Do you feel you need glasses for distance/everyday? Because 0.25 is pretty small - the smallest they measure and I know I seldom bothered with glasses when my better eye was at 0.75. So yes the axis looks different to me, but it is only 0.5 difference and practically did the opticians actually advise you to have anything other than simple reading glasses at +1.5 or 1.75?

Spoonie_Turtle

So basically you just need reading glasses, at either +1.5 or +1.75. Unless you're getting headaches or otherwise struggling with things other than reading, the tiniest of shortsightedness and astigmatism are probably not worth the extra expense of getting 'proper' glasses as you could pick up a pair of reading glasses (or two!) much more cheaply.

Mark__H

theoretica wrote: »

Do you feel you need glasses for distance/everyday? Because 0.25 is pretty small - the smallest they measure and I know I seldom bothered with glasses when my better eye was at 0.75. So yes the axis looks different to me, but it is only 0.5 difference and practically did the opticians actually advise you to have anything other than simple reading glasses at +1.5 or 1.75?

Distance/everyday vision is fine.
Newspaper/book/instructions on the back of microwave meals(!) is a different matter, hence, as you allude to, the prescription is essentially for reading glasses. I could read the smallest font on the opticians reading card with the suggested prescription, compared with the 4th smallest without.
I have given thought to buying cheap 'off the shelf' reading glasses but I felt that it was time to 'do things right'. It was purely the difference in the Axis on the 2 prescriptions that was concerning me and whether this would have material effect on my corrected vision, depending on which one of the prescriptions I had made up into glasses.

Mark__H

Spoonie_Turtle wrote: »

So basically you just need reading glasses, at either +1.5 or +1.75. Unless you're getting headaches or otherwise struggling with things other than reading, the tiniest of shortsightedness and astigmatism are probably not worth the extra expense of getting 'proper' glasses as you could pick up a pair of reading glasses (or two!) much more cheaply.

Hopefully the comments in my previous post will explain my thinking though I do understand your logic here.

Undervalued

Mark__H wrote: »

Distance/everyday vision is fine.
Newspaper/book/instructions on the back of microwave meals(!) is a different matter, hence, as you allude to, the prescription is essentially for reading glasses. I could read the smallest font on the opticians reading card with the suggested prescription, compared with the 4th smallest without.
I have given thought to buying cheap 'off the shelf' reading glasses but I felt that it was time to 'do things right'. It was purely the difference in the Axis on the 2 prescriptions that was concerning me and whether this would have material effect on my corrected vision, depending on which one of the prescriptions I had made up into glasses.

I agree the difference with the axis is slightly strange but I come back to what I said earlier. It can vary from day to day for all sorts of reasons so it may well not be that one prescription is "wrong".

The difference is utterly minimal, -0.25 is the smallest unit used. What that is doing is fractionally reducing the strength of the lens in one direction but not in the other.

The important bit was to have your eye health professionally examined, which you have done twice. Quite frankly with that prescription I would be tempted to buy a pair of 1.5 off the shelf reading glasses and see how you get on.

One final point, your prescription doesn't tell you your PD (how far your eyes are apart). That would be measured when you chose your glasses but the optician is not legally obliged to tell you what it is. Off the shelf glasses are made to an average male (or female) size. With a low prescription like yours it is not that critical so, unless you are a giant or tiny or have a very odd head (!!) they should be fine.

Edit....

Another final point!

You say

I could read the smallest font on the opticians reading card with the suggested prescription, compared with the 4th smallest without.

Which is great but it is very very easy to end up with reading glasses that are too strong for every day use in the real world! Fine if you are going to sit and read a small print book, holding it like a choir boy, or you repair watches for a hobby but less good for a desk full of paperwork at varying distances and a computer screen.

You will learn from experience but many people find that next time they go to the optician it is wise to hold the reading test charts a bit further away!

Mark__H

Thank you for taking the time to add further comments. Much appreciated.
I might look around for off the shelf reading glasses.
In hindsight, I'm thinking vanity (in terms of how they look) and the choice of frames might have been steering me down the made to measure route.