EyeTools Optometry Skills

247: Finding the optimum sphere power

During an eye examination, one of the key points is to find the best spherical lens in the prescription. I am often reaching for the +0.25 and -0.25 spherical lenses in the trial lens set to test the patient to see if they need more minus or more positive on the sphere. This takes time and the lens often has my fingerprints on them so I clean them a lot. Is there another way to get the optimum spherical component for the prescription?

Yes, there is. I use a +0.25 and -0.25 spherical confirmation test. Whether I’m working with a trial frame or a phoropter I find this piece of equipment very useful.

It doesn’t matter if you get your prescription starting point from an auto-refractor, retinoscopy, previous clinical records, or by focimetering the patient’s current spectacles at some point you will need to confirm the optimum spherical lens.

I also used to use the +0.25 and -0.25 lenses from the trial lens set but they discovered the +0.25 and -0.25 confirmation test. I used to have a confirmation test with one +0.25 lens on one side of the holder and one -0.25 lens on the other side but I lost it. I have just replaced it with a confirmation test that has two +0.25 lenses on one side of the holder and two -0.25 lenses on the other side.

When I am working on the monocular subjective refraction, I use one of the +0.25 and one of the -0.25 lenses to work out the optimum spherical lens by asking the patient if the letters on the test chart look better or worse with the +0.25 lens and whether they look better or the same with the -0.25 lens, being careful not to over minus them.

The benefit of having a confirmation test with two +0.25 lenses and two -0.25 lenses is that I can also use the test during the binocular addition element of the refraction. This is towards the end of the refraction when the patient views the letter chart with both eyes at the same time and I hold the two +0.25 lenses of the confirmation test in front of the trial frame to see if they will accept more plus binocularly.

Another benefit of a confirmation test with two +0.25 lenses and two -0.25 lenses is that I can use it to quickly show a presbyopic patient the visual effect of more and lens plus on the near addition element of the prescription.

The confirmation test is so versatile and quick to use that I wouldn’t like to conduct an eye examination without it. It’s certainly in my top three favourite tests when I am working with a trial frame and a trial lens set.



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