fix and fit
Clipping on Shades
by Alex Yoho, ABOM
Clip-on shades have become one of the most prolific items in our industry. Suitable for children through grandparents, these add-ons can be an alternative to sunglasses.
There are several ways one can approach the fitting of a clip-on. Plus or minus lenses of any power over two diopters requires a base curve different than a standard six-base curve.
A +2.50 CR39 lens has an 8 base curve, and the lab must curve the eyewire to allow proper lens mounting. Edging the lens with a +6 curve bevel prevents the need for forming the eyewire, but the lens edge protrudes, causing it to push on the inside of the clip-on.
For minus prescriptions, inform the lab that there will be a clip-on used. Otherwise, the clip may not attach due to the apex, bevel, or thickness on the back side.
| That's the Rub |
|---|
| A steeper base curve will rub on the back surface of the clip-on lens regardless of the bevel. It might work if the lenses rubbed together since the lenses in most clip-ons are much softer than the scratch-resistant coatings on today's ophthalmic lenses. The problem is that there are microscopic rocks blowing in the wind, which land on lens surfaces like sandpaper on lenses that rub against each other. If the lenses touch, caution the patient to clean both their eyewear and their clip-ons. |
FITTING FUN
After adjusting the patient's new eyewear, you may find that the clip-on doesn't fit anymore.
Adjust the face form by gently bending the bridge of the clip-on near the welds, pushing the nasal edge forward to add face form or toward the patient to reduce face form.
High and low: Clip-ons with bridges similar to the frame may ride high. Bend the nasal welds of the clip bridge downward on both sides until it covers the bridge of the eyewear. Reverse this process to raise the bridge of a clip-on that is too low.
Hooks: Metal clips that are designed to hook around the back of the frame may need to be bent. If the hooks are too tight, it can prevent the clip from settling on the frame.
Magnets: Never buy a magnetic clip frame that doesn't have any adjustability. The easiest to work with are made with embedded magnets in the eyewire of the clip-on that adhere to the eyewire of the frame.
The types that have the clip-on magnets mounted on arms of one sort or another do require adjustments to make them work. Usually, it's a matter of bending these arms inward toward the head or outward away from the head.
This horizontal bending is done after the clip-on is adjusted to fit the front of the frame. If you have added face form to the clip-on, this will cause the magnets on the clip to narrow in relation to the magnets on the frame and possibly taper in a bit.
To fix, widen the arms slightly by equal amounts to bring the magnets into alignment with each other. It may be necessary to angle the magnet itself at the end of the arm to allow the magnet faces to match. For a minus lens, do the opposite—bend the magnet arms in. EB
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