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 in basic terms?
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.
Using a plastic ruler, this OC measurement would be approximately 29mm from the centre of his pupil to the bottom of his lens.
On your own
OC height tips
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.
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).
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.
If you’re new to varifocals or need them for your job, you should check out my other article about office 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.
To make life easy, why not download and print this slotted PD ruler?
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.
For horizontal centration, you should check out my other article about how to measure your pupillary distance.