Segment Height

In order to make bifocal and progressive lenses, your Segment Height is required as it will determine exactly where the reading portion has to be fitted. Often known as Seg Height or SH, Segment Height is the vertical measurement from the bottom of the lens to the upper edge of the reading portion of your lenses. This value helps to make your lenses as accurately as possible. The measurement is specific for each frame and the person wearing it.

Segment Height is not necessary for Single Vision lenses. Usually, optometrists do not mention Segment Height measurements but you can comfortably measure it at home by yourself or asking a friend to assist.

How to measure your Seg Height?

To measure your Segment Height on your own at home, you just need:

Ruler (mm)

Mirror

Glasses

Once you're ready follow the steps below:

Wearing your new glasses, face the mirror and stand 8 inches away from it (make sure the space is well lit)
Ensure your face is looking straight ahead, and that you are measuring with the ruler held in a perfectly vertical position. If your head is facing slightly up or down, this can have a significant impact on your measurement, and lead to the transition line between reading and distance vision being located incorrectly.
Align the ruler in a vertical position with 0mm measurement on the bottom of the lens. Remember, the 0mm mark should be placed on the bottom of lens, not the frame
For Multifocals - look straight ahead and check the millimetre line located at the centre of the pupil. This is your Multifocal Segment Height measurement.
For Bi-focals - look straight ahead and check the millimetre line located at the top of your lower eyelid (where your lower eyelid meets your eye). This is your Bi-focal Segment Height measurement.
Repeat the above steps several times to ensure your measurement is accurate.

If you find it difficult to measure yourself, ask a friend or family member to to take the measurement, remembering to take the measurement several times to ensure accuracy.

Prefer to measure with your phone?

If you prefer to use your mobile phone to take the measurement, search ‘Measure Seg Height’ in your preferred App Store to download an app that can help you measure your Seg Height, and also your PD.