Understanding spectacle prescriptions

[wilbobob]

Hello. Can someone point me in the right direction to understand how my spectacle prescription works.
I have some astigmatism, and my prescription has +2 for reading. My prescription reading specs work best at a point slightly further away from a comfortable distance, where text is getting too small for comfort.
I have a £5 pair of specs with a +1.5 magnification (no astigmatism correction) and they are sharp at slightly closer than a comfortable distance.
Now as a fully qualified ignorant person I would have expected those results to be the other way round, the +2 to focus closer than the +1.5. Why am I wrong?
Should I stop trying to work this out and just order up a pair of internet cheapies at prescription +1.75 to see what happens? I could get lots of trial pairs for the cost of one from the optician.
I am aware of the need for regular eye tests, and have them. The prescription has barely changed over the last 10 years
Bob

[Dod101]

I have worn reading glasses all my life but I have no idea what the +2 or +1.5 means because I have never wanted or needed to know, but why not ask your optician about that and discuss the comfortable or otherwise reading distance. The focal length which seems to be what you are really concerned about is surely down to schoolboy physics.

I was/am perfectly happy with my reading glasses as they are but my optician at one point wanted to make a small 'improvement'. When I get them home, I discovered that I could not comfortably read the computer screen as the focal length had changed. I returned them and got them changed back to where they were and have had no problems since.

Dod

[Maroochydore]

my prescription has +2 for reading...I have a £5 pair of specs with a +1.5 magnification
Why am I wrong?

I think you are wrong because you may be confusing the prescription figure and the magnification figure.
Have a read on understanding your prescription. The figures are universal and some of these sites are American but that makes no difference.
The first one shows the calculations but states: Finally, the ADD number of +1.75 represents the power that needs to be "added" to the distance prescription to give the patient clear vision at a close range for reading and near point activities..... Many people mistakenly believe that +1.75 is the power needed when purchasing over-the-counter reading glasses.
https://www.verywellhealth.com/eyeglass ... ns-3421911
https://www.specsavers.co.uk/eye-health ... escription
https://www.webmd.com/eye-health/how-re ... escription

[pochisoldi]

Hello. Can someone point me in the right direction to understand how my spectacle prescription works.
I have some astigmatism, and my prescription has +2 for reading. My prescription reading specs work best at a point slightly further away from a comfortable distance, where text is getting too small for comfort.
I have a £5 pair of specs with a +1.5 magnification (no astigmatism correction) and they are sharp at slightly closer than a comfortable distance.
Now as a fully qualified ignorant person I would have expected those results to be the other way round, the +2 to focus closer than the +1.5. Why am I wrong?
Should I stop trying to work this out and just order up a pair of internet cheapies at prescription +1.75 to see what happens? I could get lots of trial pairs for the cost of one from the optician.
I am aware of the need for regular eye tests, and have them. The prescription has barely changed over the last 10 years
Bob

I suggest finding a "local" optician that is more interested in you as an individual than making a sale, book a midweek appointment when they've got more time, and before they do a full eye test, describe what your problem is, and ask them if they'd mind passing on a bit of their knowledge to you. Then you might be able to either "work it out for yourself" or have be able to describe what you want to the optician in more technical terms so you get what you want.

You should also note that:
The cheapo £5 glasses don't have any astigmatism correction. That lack of correction might make them work better for you. (I'm short sighted with a slight astigmatism in one eye, but I find that unless I get the astigmatism correction removed when the glasses are glazed, the glasses will almost certainly "do my head in" - as in there will be something about them which makes them impossible to wear).
The position of the glasses on your nose will have an effect. Using glasses prescribed for "normal" wear, straight in front of the eyes will give different results when perched on the tip of your nose.
The optical centres of the lenses in the cheapo glasses won't match the optical centres of the prescription glasses. Or put another way the centre of each of each lens in the cheapos won't line up with each of your irises when you look straight ahead. (The same thing applies in the up/downdirection if you wear your prescription glasses on the tip of your nose.)

HTH
PochiSoldi

[Snowbadger]

Hi W,
the reading addition is 2.0D ( a dioptre being 1/focal length in metres). So If you add that onto your distance Rx you are focussed at 50cm. So if you have a closer working distance with a pair of +1.50, this suggests you have a small amount of myopia or myopic astigmatism. If you share your distance Rx I would be able to be more specific.

SB retired Optometrist.

[wilbobob]

Thanks Maroochydore, the first link contained an explanation that the close figure has to be added to the distance figure helps.

Snowbadger You are very kind. My prescription is Distant Right Sph -1.25 , Left Sph -2.5 Cyl +1.5 Axis 95 Close +2.00 Add on both Right and left
There is a comment +1.00 Inter Add
I hadn't realised until looking so closely at my prescription that it appears I am short-sighted in one eye and long sighted in the other, And while I was aware that I had astigmatism I hadn't been aware that that was in one eye only.
It's interesting what you can learn when you start asking yourself questions and can find someone who knows the answer or where you can find it.

[wilbobob]

Ignore the bit about long sight and short sight, I don't know what came over me there.

[Snowbadger]

Hi W,
ok, lets start with the terminology as I don't think lay terms help. Start with your right eye. -1.25 myopic means you are focussed at a distance of 80cm with no correction. A good intermediate range for computer work and on a sunny day probably borderline for driving without glasses. The +2.00 addition corrects your presbyopia ( i.e. the loss of focus due to ageing, not to be confused with "long sightedness" or hyperopia which is an under powered distance error of distance vision which has similar affects as presbyopia ). The +2.00 addition gives you a reading distance of 50cm. This would suggest you are in your mid to late fifties or quite tall as these are factors that come into play when prescribing.
Your left eye has astigmatism. You are -1.00 myopic in the horizontal plane and -2.50 in the vertical plane, think rugby ball flat curve point to point and steep curve around the waist. As a result with ready readers one meridian will always be out of focus, so they can never be perfect.
My advice would be to select the pair that works best for your right eye, however Specsavers will do you a budget range for £25. One final consideration it is quite possible your right eye is your weak eye in which case ready readers are not for you. What working distance were you aiming for?

SB

[wilbobob]

Hello SB
Thanks for the explanations and the favourable estimate of my age, you're out by about 15 years in the right direction. Unfortunately you are spot on about the steep curve around the waist.
You are right that I can see clearly at 800mm without any specs.
My prescription reading specs are focussed at about 700mm and the cheapies at about 350mm. 500mm would be about spot on.
Bob

[Snowbadger]

Hi Bob,
the ability to focus your eyes is lost linearly with age so you probably were given the +2.00 add because you mentioned the 50cm working distance. So if you subtract the -1.25 from the +2.00 Rdg Add you get a +0.75 ready reader. They usually produce them in 0.50 steps, so unless you go the Specslaver £25 pair or one of the even cheaper bucket shops +1.00 is probably the closest compromise. Can I just point out I was referring to the rugby ball waist measurements.

SB

[wilbobob]

Thank you SB. I feel now that I understand what the prescription is telling me, and the difference between the prescription figures and the magnification of the off the shelf readers. Well explained.
Bob