310.jpg

Welcome to question of the day #310

Eyetools question of the day #310

One of my patients complained to me that as I didn’t use the duochrome test during subjective refraction that I was taking a shortcut to speed up the examination and that he wouldn’t be able to see with his new prescription. I didn’t know what to say. Do you have any suggestions?

This has happened to me a few times as I don’t use the duochrome (red bar with two Verhoeff rings above a green bar with two Verhoeff rings) test. Happily, most of the patients I see trust me to make the correct decisions when it comes to which tests to use.

I haven’t used the duochrome test for about 25 years. After a few years of using it after optometry school, I realised that a lot of patients struggled to interpret what was required of them. I also realised that I could determine very accurate prescriptions without using the duochrome test.

The theory is that once the sphere and any cylindrical refractive correction have been determined to ask the patient to look (with each eye in turn) at the black circles (rings) on the red and green lights and to tell you which circles look darkest and sharpest. If the circles on the green look darkest and sharpest then the idea is to reduce the minus or increase the plus to get the circles on the red and green backgrounds to be equally dark and sharp. This is the endpoint and often when the subjective refraction procedure ends. Many patients find this judgment difficult and struggle to decide if the black circles are equally dark and sharp on the red and green backgrounds.

If the patient responds that the circles are darkest and sharpest on the red then the idea is to reduce the plus or increase the minus until to get the circles on the red and green backgrounds are equally dark and sharp. Again, many patients struggle with this decision. This can be made more difficult if the patient accommodates and keeps the black circles sharpest and darkest on the red by overaccommodating. This way the patient can be under-plussed or over-minused.

If a patient asks me why I haven’t used the duochrome test I tell them that it is an outdated test, that I haven’t used it for 25 years and I’ve used more modern tests to determine the best glasses for them.