Custom thinning on high prism trifocal?

[DanLiv]

I have a patient that's approx +3.00 with +3.00 add and 7.5D BO prism OU, wears trifocal. I'm already going to go with 1.67 (believe he's only in mid index now), but unfortunately this guy loves his classic double-bar 55 eyesize frames which is going to give me 4.5mm additional nasal decentration. Long story short, lenses are going to be thick temporally.

I know Digital Eye Lab and Ice-Tech do custom asphericity/lenticularization to articifically thin lenses (Curve and Thin-Ice), but they only do round segs or bifocals. Anyone know of someone doing custom thinning like this for trifocals? I'd like to be the guy to offer this patient something he's never been offered before.

Thanks!

[jefe]

You may be able to get it through FEA Industries. They'll put their IOT freeform SV design on bifocals and trifocals, and they offer lenticularization as an option.

[Robert Martellaro]

I'd like to be the guy to offer this patient something he's never been offered before.

A reduction in on-axis visual acuity? If he objects to the increase in thickness and weight, the best solution is to use a smaller, rounder frame fit as close as possible to the eyes. Use higher Abbe value materials, Trivex for instance, so that the prism and subsequent chromatic aberration has less of a negative effect on his BCVA.

[braheem24]

What's his pd? As backwards as it sounds, a frame with approx 12.5mm decentration will give him a knife edge nasal as well as horizontal; that combined with trivex Will give him thin, light and low chromatic abberation eyeglasses.

[DanLiv]

A reduction in on-axis visual acuity? If he objects to the increase in thickness and weight, the best solution is to use a smaller, rounder frame fit as close as possible to the eyes. Use higher Abbe value materials, Trivex for instance, so that the prism and subsequent chromatic aberration has less of a negative effect on his BCVA.

What's his pd? As backwards as it sounds, a frame with approx 12.5mm decentration will give him a knife edge nasal as well as horizontal; that combined with trivex Will give him thin, light and low chromatic abberation eyeglasses.

Ya tried to push for better frame selection, but he wasn't having it. He understood the impact on thickness but preferrred his larger style. As far as reduction of acuity, is that just in reference to the lower Abbe 1.67? This pt is BCVA 20/30 in the better eye so I'm not worried about Abbe disrupting the on axis vision. I'll deal with peripheral aberration if it appears.

His current eyewear does have a nasal knife edge and is still temporally very thick (I'm talking 10mm), and I think he's probably in 1.55-1.56 now. Trivex wouldn't be able to do anything for thinness in this case, lightness maybe.

That's cool that FEA will do that. Makes perfect sense, wonder why everyone wouldn't have it as an option. I will contact them, thanks. And if the lenticularization is effective enough I may be able to do Trivex after all and get teh best of both worlds.

[Robert Martellaro]

Ya tried to push for better frame selection, but he wasn't having it. He understood the impact on thickness but preferrred his larger style.

All we can do is advise. It sounds like (below) he's been wearing this type of Rx heretofore, so there shouldn't be any surprises.

As far as reduction of acuity, is that just in reference to the lower Abbe 1.67? This pt is BCVA 20/30 in the better eye so I'm not worried about Abbe disrupting the on axis vision. I'll deal with peripheral aberration if it appears.

Chromatic aberration is a function of prism and Abbe. Sans prescribed prism, the chromatic aberration will occur off-axis, if there's enough induced prism. However, when there is prescribed prism, the chromatic aberration occurs both on and off-axis, with additional off-axis CA due to induced prism. With this much prescribed prism, which I assume is 7.5 PD in each eye, a low Abbe lens will probably drop the BCVA down about one line.

His current eyewear does have a nasal knife edge and is still temporally very thick (I'm talking 10mm), and I think he's probably in 1.55-1.56 now. Trivex wouldn't be able to do anything for thinness in this case, lightness maybe.

Yup. Safer also. That might be a factor if the fellow eye is even more compromised visual acuity-wise.

That's cool that FEA will do that. Makes perfect sense, wonder why everyone wouldn't have it as an option. I will contact them, thanks. And if the lenticularization is effective enough I may be able to do Trivex after all and get teh best of both worlds.

FWIW, the scotoma and blurring from the blend zone can be highly disruptive to the wearer. It would be prudent to make this clear to the client, and maybe steer them towards a more visually practical, but less cosmetically pleasing solution. I'm probably preaching to the choir, but older folks are looking for substance over style, function before fashion.

Best Regards,