Could Making Wrong Choice on Duochrome Test Affect Prescription?

by Patrick Kleaver
(Saint Louis, MO. USA)

Q: Hello!

I've had a new prescription written based on my eye exam. As part of flipping the various lenses, the optometrist asked me to choose if letters appearing on the green and red side of one lens (the duochrome test) looked the same or if one side looked better.

In previous exams, both red/green sides looked the same. This time, I thought the letters on the red side were slightly sharper. She continued with the exam, and near the end did the duochrome test again and asked if there was a difference. This time, the letters in the green side looked definitely blurry compared with the first test.

Anyway, here is my 2016 bifocal prescription:
(SPH) (CYL) Axis NV-ADD
OD Right -5.50 2.25
OS Left -5.75 +0.50 95

Here is my new 2017 bifocal prescription:
(SPH) (CYL) Axis NV-ADD
OD Right -5.50 +0.25 95 2.25
OS Left -5.75 +0.50 95

The optometrist said this represented a slight change. My concern is that I may have been wrong in choosing the red on the duochrome and that may have thrown off the results for the right eye (my prescription had been extremely stable for years).

Before I get new glasses, should I be retested or would the difference really be so slight I wouldn't notice it?

Thanks!


A: Hello Kleaver

As I see on your prescription, the differences between the old and new prescription are quite small.

I think the best test is still the vision acuity, the duochrome test is just a final touch to see if the diopter is too big or too small, so usually, the color sharpness varies even with small diopter difference.

In the end, if you can see clearly far and close, the little 0.25 diopter difference is not that important. But, if you cannot see clearly far or near, then it is important and I think changes need to be made.

I think the most important is your vision (sharp vision) and comfort. I had clients that had 20/20 vision with a prescription but the duochrome test was slightly off and when I corrected the prescription the vision was not satisfactory, so I went back to the original diopters with 20/20 vision.

So it depends on the person and the vision problem, but I think that when you are examined, you should look for good, sharp vision and comfort on wearing.

Hope this helps
Arpi

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