FFSV Compensated RXs and Very High Cyl

[Tallboy]

In cyls of -5.00 and higher are you guys more inclined to use a FFSV with a non-POW compensated aspheric/atoric back surface, such as the Shamir Spectrum SV, or a fully compensated design such as the Individual 2.

I was told by an engineer who works for Shamir that he did NOT recommend using POW compensated designs(PAL/SV) for prescribed prism because although the power range sheets said that all Shamir designs can be done up to 4 prism diopters that they in fact had NOT gotten reliable results, and instead directed everyone to use a fixed design such as the Spectrum SV or PAL. The spectrum SV is now used for ALL of my RX prism jobs, with fantastic results. This has gotten me thinking about where the FFSV designs break down for other extreme powers.

As Barry would say, Discuss...

[Barry Santini]

Mmmm.....

If they have demonstrated extreme sensitivity to axis, do NOT use a compensated design, or at least a compensated design that uses little axis change.

B

[Tallboy]

Okay, should I be concerned that most IOT or Auto II/III designs will probably return a lens with a power of about a quarter less for a cyl of -6.00? Do most ODs take this into account when they write the RX from their manifest refraction? Compensated FFSV scares me sometimes when the fit is somewhat normal, I worry that if a well fit "normal" fit pair of glasses would yield a power shift of losing -.25 of lens cyl power because of the 5degree face form, wouldn't ODs take this into account when writing their RXs by dropping the RX -.25 from their manifest refarction already?

Or is it more the Axis shift that may occur? (I haven't noticed more than 1 degree axis shift on Opticampus' calcuator for the sph -6.00 x 127 job I am about to order btw )
I know I am over-thinking this, but ever since the Auto III CE I went to in Baltimore last year when I talked with that engineer about RX prism in a compensated design I have been thinking about these things.

[Robert Martellaro]

I've had better results using Zeiss for high cylinders. They have narrower power and BC ranges for good reason- the technology breaks down quickly when you push it to the limits.

Barry,

I've also had poor results with high values of prescribed prism and compensated lenses.

[Hayde]

Okay, should I be concerned that most IOT or Auto II/III designs will probably return a lens with a power of about a quarter less for a cyl of -6.00? Do most ODs take this into account when they write the RX from their manifest refraction? Compensated FFSV scares me sometimes when the fit is somewhat normal, I worry that if a well fit "normal" fit pair of glasses would yield a power shift of losing -.25 of lens cyl power because of the 5degree face form, wouldn't ODs take this into account when writing their RXs by dropping the RX -.25 from their manifest refarction already?

Or is it more the Axis shift that may occur? (I haven't noticed more than 1 degree axis shift on Opticampus' calcuator for the sph -6.00 x 127 job I am about to order btw )
I know I am over-thinking this, but ever since the Auto III CE I went to in Baltimore last year when I talked with that engineer about RX prism in a compensated design I have been thinking about these things.

(As always, a doctor chiming in for doctors would carry far more weight than my perspective, but...)

I wouldn't count on the examiner having nearly enough familiarity with lens fabrication outputs to be over-writing cyl powers to outsmart it. If anything, they're usually inclined to pull back on cylinder powers...so if they wrote a 6D odds are good they really mean it.

[Paul Smith LDO]

I have used both the Shamir Spectrum SV and the 5.0 Flex SV thru ABB/DEL. I tried the Auto SV with POW for patients with high cyls. on several occasions with less then satisfactory results. Patient satisfaction was garnered using the above mentioned lenses.

[Barry Santini]

I've had better results using Zeiss for high cylinders. They have narrower power and BC ranges for good reason- the technology breaks down quickly when you push it to the limits.

Barry,

I've also had poor results with high values of prescribed prism and compensated lenses.

Yes. With higher prism. Total fail. Agree Zeiss is best.

B

[HarryChiling]

In cyls of -5.00 and higher are you guys more inclined to use a FFSV with a non-POW compensated aspheric/atoric back surface, such as the Shamir Spectrum SV, or a fully compensated design such as the Individual 2.

I was told by an engineer who works for Shamir that he did NOT recommend using POW compensated designs(PAL/SV) for prescribed prism because although the power range sheets said that all Shamir designs can be done up to 4 prism diopters that they in fact had NOT gotten reliable results, and instead directed everyone to use a fixed design such as the Spectrum SV or PAL. The spectrum SV is now used for ALL of my RX prism jobs, with fantastic results. This has gotten me thinking about where the FFSV designs break down for other extreme powers.

As Barry would say, Discuss...

Aspheric compensation tends to work better with more curvature, high plus tend to work better with front side aspherics and high minus tend to work better with back side aspherics.

Don't specify a base curve let the software optimize. Pick a frame that's optimized for the fit, 2 degrees faceform per 1mm horizontal decentration, roughly 10 - 15 pan to with a set height about 3 - 4mm above datum. If you have fit close to these parameters you can use an IOT design without DRP if you are off you can compensate fully with a DRP design aka Alpha. Try and use the lowest index possible with best abbé for progressives, mitigate thickness with fit first over index for optimal optics. Use a lab with a good quality process for these types of jobs to avoid rounding errors as I like to call them.

Fit wise you should also keep the aperture small to limit the possibility of off axis viewing. High astigmatism will benefit better from shape lenses vs clarity when possible go for a softer design over hard even with a higher adds, you may consider a longer corridor but keep the MFH 16 - 18 preferably.