A patient you prescribed glasses to last week has come back to complain that he can’t see as well as he expected to when driving and the floor seems like it is sloping away from him. His prescription is right -3.25/-1.00×140 and left -3.00/-1.00×55. You are sure you refracted him carefully and provided the optimum prescription. What is going on?

This sounds like a non-tolerance to the prescription that was determined last week.

However, it is important to undertake a health recheck of the anterior and posterior eye. It is unlikely that a new disease will have occurred since the initial eye examination a few days earlier but there may have been a deterioration of a condition that was present at the initial examination but was missed. I think it is in the patient and practitioner’s best interests that a check for a disease is conducted especially if the initial examination was performed by a colleague. I have worked with some brilliant eye specialists but I trust my examination the most.

It is also worth checking for any change in binocular vision status between the old and new glasses or the no glasses and glasses situation.

Most non-tolerances are solved by 0.25 changes in sphere increase or decrease and/or 0.25 changes in cyl and/or less than 5-degree changes in cyl axis, so it is very important to conduct a slow and methodical subjective refraction.

Checking for small cyls; when you have finished the subjective refraction and the patient has some cylindrical correction ask the patient to look at the lowest line of letters and assuming you work in minus cyl hold up +0.25 DC lens from the trial set in front of the eye and ask if the patient can still see the line of letters as clearly, if yes then reduce the minus cyl by 0.25 DC. Some patients will accept 0.25. Remember when they accept minus cyl on the X cyl test they are accepting 0.50 DC and they may only need -0.25 DC for the optimum prescription. Give them the lowest cyl power you can without reducing the distance visual acuity. The patient’s complaint of the ground sloping away from him is likely to be due to too much cyl.

Also, remember to adjust for the 6 m testing distance for those people who have a far distance requirement such as drivers. Some practitioners use the duochrome test (see example below) and leave symbols/letters on the green in better focus than the red by adding more minus sphere or less plus sphere. I prefer not to use the duochrome as patients with active accommodation can sometimes be over over-minused leading to eye and headaches. My preference is to find the optimum prescription for the best possible visual acuity in each eye and then add an extra -0.25 DS or reduce by +0.25 DS. This works well for me. The patient’s complaint about his distance vision not meeting his expectation is most likely because this adjustment for driving vision has not been made.

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