First Differentials with high myopia/presbyopia/cataracts


I am trying to work out my first differentials, but there are a couple of complicating factors, namely, presbyopia and cataract, plus the added inconvenience of not being able to get out to try plus lenses in a store due to the current stay-at-home restrictions here.

My last optometrist script was in November 2019:
R: -11.75 (-1.5 cyl)
L: -12.00 (-0.50 cyl)

These are my current glasses. I was also suggested to get +0.75 reading glasses which I didn’t get.

December 2020: The optometrist said I had a cataract in the right eye and because I couldn’t see the Snellen chart clearly with any of the lenses she used, she didn’t give me a script. I was told to go and get cataract surgery in the right eye and then come back. So now I have an ophthalmologist appointment in a week to discuss surgery.

Cm average is L: 11 and R: 8

Snellen Chart (with current glasses at 3m) - I can’t see anything clearly with the right eye. Left eye: 20/15.

Close up habits: A couple of hours a day at an ergonomic distance of 50cm, if that, mainly researching and watching videos for Endmyopia.

Question 1: In the absence of a current prescription, does it sound sensible to calculate my diopters from my cm readings and start with a 0.5 diopter reduction in each eye?

Question 2: Does anyone have any recommendations for a friendly optometrist in London or surrounds. It would really help us out while we can’t get out to try plus lenses (my 13-year-old son is doing this with me).

Thank you so much.

Hi, sounds like a complicated situation , sorry to read that :frowning:

one tip though: check your axis from your last prescription for that cyl - and try measuring cm to blur separately for strong axis and weak axis (by looking at lines at those angles respectively and seeing where you first see a hint of blur on the edge of a line)- the cm to blur on best axis gives your approximation of SPH (contact lens prescription) and on worst axis gives your SPH+CYL contact lens prescription approximation (so then it is easy to calculate cyl needs as SPH+CYL estimation minus SPH estimation.

So once you are confident you have a reliable cm to blur reading then you can use your vertex distance to find your estimated current glasses prescription


for you with that high prescription vertex distance will make a big difference between contact lens and glasses prescription

following the above you will have a reasonably good estimation of needed differentials (cataract effect not considered )

1 Like

Thank you so much for that.