Fresnel Prisms and Getting all the "bubbles" smoothed out

[KrystleClear]

I do a fair amount of Fresnel press on prisms for patients newly experiencing diplopia to trial prism correction. I have such a hard time getting them to look completely clear with no bubbles. I follow the 3M instructions and make sure the lens is pristine. I put a little water on the lens and spend ages smoothing it out. It's never quite perfect. You know how screen protectors for phones sometimes come with a little thing that you use to smooth them out? There needs to be a curved thingy like that for fresnels.

How do you guys do it?

[optical24/7]

Get a bowl, full of water. Clean the back side of the Rx lens. Mark Fresnel at prism poles with an indelible pens like a lens marker (towards outside of the intended used area). Important : NEVER put one on one lens up/down and on the other lens one in/out for compound prism needs. Use just one lens, on their non-dominant eye, and turn the Fresnel to compound the prism for both vertical and horizontal needs. If compounding, take your marked Fresnel and put it on a 360 degree chart, turn the lens to the degree of needed compounding and mark the 180.

Mark your Rx lens up at the 180 ( engravings, seg line, lensometer dots). Draw a line on your Rx lens at the 180, (sometimes it’s easier to line up the Fresnel’s 180 marks you made). As you hold the lenses in each hand, dunk both into your bowl of water. Line up your marks (don’t mark the center of the Fresnel..! You’ll never clean them off like the front of the Rx lens!)

Wipe little bubbles off both Rx and Fresnel surface, make an accurate lineup of the 2 lenses 180’s then press and smooth the 2 together, all while both underwater in the bowl. Once you take them out, bubble free, keep applying pressure as you cut around the lens with some sharp scissors,about 2-5 mm from the edges. Then use a razor or exacto to trim the excess at a 45 degree angle to the bevel of the lens, (so the Fresnel doesn’t come in contact with the frame.)

Sometimes, when it’s all said and done, you might have a small bubble. If it’s small, it will disappear as the moisture dehydrates between the 2, usually a day or 2, let the patient know of this along with proper care when cleaning them, particularly the 1st couple days, discourage cleaning during this time to minimize displacement…

Wow! That was longer than I thought it would be, and I probably forgot something, but others will tell of what they do I’m sure. Practice make perfect!

[Prentice Pro 9000]

Those tiny bubbles are annoying. One thing that has helped me is to have a little dropper of distilled water on-hand. Not sure if it helps more than 10%. I also his the back of the lens and the fresnel with a rush of cold water.

I find with fresnels it’s important to not let perfect be the enemy of good.

[Uilleann]

Another trick, works on all lenses, but particularly higher curves as well. Use HOT water. Not boiling, but hot enough you immediately notice if you put your hands in. That will soften the flat foils, and allow them to better adhere to the compound curvature of a lens with minimal effort. Also, suggest trimming your foils beforehand, and I always suggest at least 2mm smaller than the C of the lens, to avoid frame interaction/possible edge lift. The smaller size (as opposed to trying to frustratingly fit the *entire* foil in one go, then futzing around with trimming, and trying not to mar/damage the base lens) makes for a much easier fitting, and also allows the foil to adhere more readily, usually with zero bubbles.

[CME4SPECS]

I like to dip the Fresnel in tepid water before installing.

[Lensman11]

Make sure the fresnel is smaller than the lens you applying it so it doesn’t touch the frame. Add a few drop of dish detergent to the water it will work wonders in eliminating bubbles.

[KrystleClear]

Another trick, works on all lenses, but particularly higher curves as well. Use HOT water. Not boiling, but hot enough you immediately notice if you put your hands in. That will soften the flat foils, and allow them to better adhere to the compound curvature of a lens with minimal effort. Also, suggest trimming your foils beforehand, and I always suggest at least 2mm smaller than the C of the lens, to avoid frame interaction/possible edge lift. The smaller size (as opposed to trying to frustratingly fit the *entire* foil in one go, then futzing around with trimming, and trying not to mar/damage the base lens) makes for a much easier fitting, and also allows the foil to adhere more readily, usually with zero bubbles.

Ah! I am going to try using hot water next time!

[finefocus]

All of this is easier if you first remove the lens from the frame (ala Uilleann) and trim at 45 degrees as 24/7 suggests. You can thumb-squeege the bubbles if the frame isn't in your way,
Snap the lens back in so you can finalize the position while it's still slippery.

[ChrisBowers]

I used to cut this between two plano lenses just short of the bevel diameter and apply it to the flattest surface (albeit FT not applicable) also use alcohol as it evaporates nicely.

Chris