Sight test prescription issue

[Eve]

I've had a few eye tests in the last few months.

1. Where I had a voucher from my work DSE and went to a different optician than normal. Said my prescription had improved a lot, from about -4.50/4.75 to about 3.50/75 so current glasses too strong. I was quite surprised as my vision has, if anything, got worse since I first needed glasses in junior school but I know vision can change with age.

2. Had another one on an internet voucher for a different optician as wanted to doublecheck as the prescription was so different (before paying out for glasses) and check on my eyes which were very dry and opticians 1 & 2 said my tears are evaporating almost immediately. He said my prescription had improved but not by quite as much as optician 1 said but my glasses were too strong.

3. Last week I went to Red Eye walk in clinic at the opticians I've used for years as was having vision problems on some new arthritis meds (Plaquenil). She said I should have a full eye exam to check them properly. They said my prescription was what they said it was a couple of years ago - 4.50/4.75, no change!

So I'm a bit confused as to what to do! I was looking to update my glasses as they are now quite old and a bit battered but now have no idea which prescription to go with as I have three different ones! I wanted to try a cheaper place than high street opticians to buy them but am I now better paying more to go with one of them for glasses if they then would change them (for free?) if their prescription was wrong. I'm not in a financial position to mess about much.

I'm also not sure if my vision problems on the drugs could have skewed the last eye test (or the dry eye issues generally, optician 3 said they were still really dry and some blocked ducts) - she said she couldn't find any obvious physical cause, macular fine etc... and said it was most likely the drugs or some neurological cause. She faxed my GP practice who said it was almost certainly the drugs and to stop them immediately and they have faxed my rhumatologist. Maybe I should wait until my vision has been stable for a while off the drugs and get tested again?

I'm at a bit of a loss what to do so any suggestions welcome!

[sunny-dave]

I'm sure you'll get some more informed medical comments, but (from a non medical perspective) my eyesight varies enormously depending what I've just been doing.

If you tested me immediately after I've spent 15 minutes reading a book or playing with my smartphone you'd get very different results from a test where I had previously been driving or just relaxing. It's also different depending on whether I've had my glasses on recently too. It sort of invites the question as to exactly what a 'true' prescription is?

[Eve]

That's interesting Dave, thanks. It does make you wonder how accurate the prescriptions actually are.