Using a lensometer to check glasses (Video)

This video shows the use of a lensometer, a device used to check the prescription in glasses. This device can be tricky for the novice technician to use, as you must align the glasses well and move two dials at the same time to hone in on the prescription.

Here are the steps:

1. Place glasses on platform and secure
2. Turn axis and focus nobs so that the SMALL lines are straight and focused
Write down the number. This is your sphere.
3. Turn the focus nob until the fat lines become focused, and look at the new number on the focus nob. The DIFFERENCE from your prior sphere value is the CYLINDER value. If you changed from +1.00 to +4.00, then your cylinder is +3.00. If you changed from +1.00 to -1.50, then your cylinder is -2.50. In other words, the cylinder can be a positive or negative number, depending upon the direction you have to turn the focus nob.
4. Check the degrees on the axis dial. This is your cylinder axis.

If you want to check the bifocal add:

5. Move the glasses so that the bifocal segment is being read.
6. Turn the focus nob again until the fat lines again become focussed.
The amount of change needed to refocus the fat lines will give you your bifocal power.

Download this video

To download this video, right click on a link below and choose “Save Target/Link As…”

lensometer.wmv (13 meg, Windows video file)
lensometer.mp4 (13 meg, Ipod Video)

Thumbnails (click to enlarge photo)

This photo shows a lensometer, a device used to check the prescription of glasses.
Lensometer Dial
This photo shows the focus dial on a lensometer. To determine the sphere, you need to move both the focus and axis dials so that the three small lines are straight and clear.
Lensometer lines
This photo shows the lines you see when looking through a lensometer. When you get the three smaller lines oriented correctly and focused (like in this photograph) then you have your sphere.
Dr. Timothy Root is a practicing ophthalmologist and cataract surgeon in Daytona Beach, Florida. His books, video lectures, and training resources can be found at:


  1. I’m glad you liked the video and thank you for commenting. Unfortunately, the video file is just too large in size to e-mail. You can download it directly, however, from the links above.

  2. thanks a lot for the information. please kindly send me in my E Mail Address all more about lensomater technique in reading the amount of prism induce in the lens. thanks

  3. thanks alot for all the information, it refreshes my memory. please kindly send me some slit lamp information technique. thanks.

  4. Very nice, thank you.

    However, I did hear somwhere that one has to turn the glasses upwards to get the correct result for certain lense???

  5. Went back into the wonderful field of optical again and thank-you for the refresher class on the use of the lensometer. Was very helpful. 🙂 🙂 Just hoping to remember how to check prisms. THANKS AGAIN

  6. Hey people, stop asking for junk to be sent “4 ur Email”. Learn some professionalism. Optical work isn’t done in a back alley you know.


  8. These videos are the God’s gift and sure Timothy Root’s gift to ophthalmic Residents. Definitely it is the bible for better eye knowledge. Thank you Timothy Root 🙂
    I hope that you can make a video illustrating Keratometry Readings for calculation of intraocular lens (Non automatic keratometer) .
    Thank you from Russia, Kursk state medical uniVersity

  9. Dear,

    Thank you guys so much for showing me how to use the Lensometer! I just started an optician apprenticeship, and really needed to know how to understand how to use this thing:) You guys made it super simple and easy to understand:) Thanks again!

  10. The one basic thing missing was telling the student about focusing for either plus or minus cylinder. It would also be nice to show how to measure for prism. Maybe you could do that at some point in time. You really have nice video presentations and I really enjoy your site.

    Thank you.

  11. Hi Tim Root
    Congratulations on getting the number 1 google spot for lensometer. Hope all is well and BP doesn’t crush your dream of the beach front gulf coast home in Florida.
    Jake Moore

  12. That is a great Video! This type of information can be very useful when organizing staff meetings. What a great tool for the new hire.

  13. Great video. I’m linking to it from a new site I just started for optician apprentices. It may be useful to also show what it would look like without a cyl and axis as well as what a prism would look like. Thanks!

  14. Tu informacion esta barbara me ayudo muchisimo a refrescar mi memoria,podrias enviarme, algun ejemplo mas con prisma y si es un multifocal.Muchisimas gracias.

  15. I appreciate the video that you have about then lensometer. Can you send me some more information about prism and the calculations on a lensometer?

  16. This video is precise, concise and very lucid. It refreshed my memory and answered my questions spot on.
    Thanks a lot.

  17. Thank you for simplifying the use of the lensmeter. Is it possible for you to demostrate how to read the power of a lens in minus form.

    Thank You.

  18. The add power was read incorrectly. The spectacles should’ve been “turned around” so that the add was read in front vertex power. On the compound hyperopic astigmatic lens you used in your example, you would’ve underestimated the add.

  19. nice video but what about the lensometers that require the optician to transpose the two readings? For ex. I have the NIKON OL-7 that the first reading in a miopic astigmatic lens shows -4,75 and the second -5,25 . What sign should i put and what about the ipermetropic astigmatic lenses. they always confuse me with the transposition! PLZ HELP !

  20. Don’t you need to read that high plus lens from the back surface to determain the add power? My experience is that the add power will read to strong if you only use the front surface.

  21. i think when ur reading from the forcemeter always consider your cyl sign 2 b negative e.g for positive sph take the more positive subtract it from the less positive to be able to get a minus cyl

  22. Alexx, the video is too big to email, but the download link is above. Just RIGHT-MOUSE click on the link, and choose “Save Target …” to save the video to your computer. Good luck.

  23. Hello Dr. Tim,

    Pls when do we expect an App from you so that we could have your excellent videos on our palms.

    Thanks so very much for all your high level of professional work.



  24. l am one of the seles men of optical shop
    l worked more then 10 years.
    l know haw to use lenmeters.and haw to making classes..

    and also haw chaking the the person..
    but l have not any diploma .
    becouse there is not and school of my country
    so help me haw to get diploma of opticain
    thank you my doctor


Please enter your comment!
Please enter your name here