You’ve got your prescription sorted. ✓
You’ve even measured your pupillary distance. ✓
But because of the way varifocals work, we need to ensure your pupils are correctly positioned behind your new lenses. So, what is OC measurement when it’s at home?
Ocular centre height refers to vertical positioning of your pupils behind each of their respective lenses. This is measured in mm from the centre of each pupil to the lowermost section of the lens within the rim of a glasses frame.
In other words, we use your pupillary distance and your OC height to horizontally and vertically align your pupils with the middle of each of your lenses.
Oh, and because your new glasses are a different shape, this measurement is entirely unique to how your specific glasses frame rests on your head.
Your OC changes from frame to frame.
HOW DO YOU MEASURE OC HEIGHT FOR GLASSES?
Using a plastic ruler, this OC measurement would be approximately 29mm from the centre of his pupil to the bottom of his lens.
With help
Stand/sit in front of your assistant
Wear the glasses you’re ordering lenses for
Your assistant vertically holds a plastic ruler against one lens
They align the 0mm mark with your pupil centre
They assess the distance to the bottom of your lens
Note heights according to your left & right, not theirs.
On your own
Stand/sit in front of a mirror
Wear the glasses you’re ordering lenses for
Vertically hold a plastic ruler against one lens
Align the 0mm mark with your pupil centre
Assess the distance to the bottom of your lens
Note heights according to your left & right
OC height tips
Only measure the lens, not the frame
Use a plastic ruler to prevent scratches
If it helps, close one of your eyes to help your focus
Brace the ruler against your nose & the frame/lens
Left & right are from your perspective, not your assistants
Measuring your vertical optical centre for sunglasses?
With help from a friend, ask them to shine a torch/light on the lens to illuminate your eye behind. This way they can accurately measure your OC height from the front of each lens.
WHY IS OC HEIGHT IMPORTANT FOR VARIFOCALS?
Every lens has an apex. This is the optical centre of a lens which should always be aligned with the centre of each of your pupils.
Optically speaking, this is called centration which is achieved by locating your pupils directly behind the middle of each lens whilst wearing a specific glasses frame. This is achieved using horizontal and vertical alignment in addition to the distance between your lenses (DBL).
Horizontal centration is measured using your dual pupillary distances
Vertical centration is measured using your ocular heights
In the context of varifocals, the importance of pupillary height is so that the neutral gaze of your eyes aligns with the centre of the lens in order to maximise progressive power.
Accurate centration means your pupil is in the optimal position to select the correct area of your lens to look through to see properly.
For varifocals, proper vertical centration prevents you from having to tilt your head to see through the correct portion of your lenses. In the workplace, this can lead to postural issues such as neck or back pain.
HOW DO YOU MEASURE PD FOR PROGRESSIVE LENSES?
For accuracy, progressive lenses require what’s called a dual pupillary distance.
This is a facial measurement from the centre your pupil to the centre of your nose for each of your eyes. The easiest method to do this is with a pupilometer with a slot for your nose which mimics the bridge of a glasses frame.
Key notes
OC height is always measured in mm
Always measure your OC from the bottom of the lens
Your OC's & dual PD are susceptible to change if your glasses move on your face. Therefore, they aren't static and have a degree of movement tolerance.
Your PD never changes, but your OC height does.
For sunglasses, use a torch to see your pupils
Ordering varifocals online can be simplified if you have the proper centration measurements. If you invest the time to measure your vertical optical centre, you’ll save time and money on your progressive lens investment.
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Maria · 2023-11-15 12:53
I am so disappointed with their customer service. I believe my bifocal was made too low and they wouldn’t even consider looking at it again. I had to return my glasses. Be careful if you need to read with your glasses.