I recently got my college diploma and am working in my first job. Many of my patients are coming back to complain that they can’t see with their new glasses or that they are get headaches and eye aches when using them. What is going on?

Sounds as if you have some non‐tolerances to your glasses

Non‐tolerance to spectacles can be divided into two categories:

Dispensing non‐tolerance refers to glasses that a patient finds so hard to tolerate that they return to the practice, and an error is found either with the appliance given, the lenses in the appliance or the dispensing measurements taken. The main causes are incorrect frame fitting, optical centration problems, spectacle magnification problems, cosmetic reasons and mis‐communication. These problems can be taken care of by a person who is experienced with the dispensing of glasses.

Prescription non‐tolerance refer to a prescription that the patient finds so hard to tolerate that they return to the prescriber. These problems can be taken care of by a person who is experienced in the prescription of spectacle lens powers.

I’ve just read a very good research paper on the causes of non-tolerances in a standard town centre practice.

Non-tolerances accounted for 62 of the 3091 eye examinations. The average rate of non‐tolerance, averaged across the practitioners, was 1.8%, varying from 1.3–3.3% for individual practitioners. Presbyopes accounted for 88.1%. The most common reasons for non‐tolerance were, in order of decreasing frequency:

Prescription related (61.0%)

Dispensing related (22.0%)

Eye disease (8.5%)

Data entry error (6.8%)

Binocular vision anomalies (1.7%).

With prescription related errors, gauging the spherical element accounted for the majority of inaccuracies, followed by problems with the near/intermediate addition.

In every case, the final prescription was within 1.00 D of the not tolerated prescription; 84.4% were within ±0.50 D.

The data entry element could be reduced to near zero by asking another person to check the data before lenses are ordered.

My learning from this is that a recheck of the refraction results is a key first step, followed by checking the frame fit and lens centres. In my experience, this is usually done the other way round in practice.

It is also worth bearing in my that non-tolerance can be caused by missed or worsening eye disease. I always check eye health whenever dealing with a non-tolerance case. Even if I checked eye health at the first examination and especially if that was conducted by another practitioner.