Bi-Concave Lenses

[Robert_S]

Hey everyone,

I received a set of Nulux EP (Biaspheric) SV lenses from Hoya today. We use this lens a lot for our patients as we think FFSV is fantastic, but for the first time we have one lens that has a negative base curve on the front (-0.50). I've never come across this before, although I know of course that they are available and my understanding was that biconcave lenses are specifically for high minus prescriptions.

This Rx in particular was a R] -2.50/-2.75. The left eye was a higher minus but with less cyl and was surfaced on a positive base.

My questions are, a) would this affect the performance of the lenses
and b) why did they choose to use a -0.5 base only in the right eye.


Thanks for your help

[idispense]

the full rx and details usually helps

[Wes]

I can't see any reason to put a -2.50/-2.75 on a minus base curve. Maybe a 4 base, or 3 base at the least.

[Robert_S]

The frame was just a regular Bulgari, full metal... nothing special. Not particularly wide at all. PD was fairly central. Full Rx is as follows since requested.

R] -2.25/-2.75 x 46
L] -6.00/-2.50 x 168

Bear in mind these are Biaspheric digital lenses, and as such are always extremely flat.

[Wes]

The off-axis optical performance of biconcave lenses is sub par to say the least, and the disparity between the left and right will likely make them unwearable for the patient.
If you want to see what kind of radial astigmatism and power error you're dealing with, go to opticampus and download a copy of Darryl Meister's Spectacle Optics program and run those numbers.

[Robert_S]

Thanks Wes,

So, why did Hoya produce the job as such? Is it a mistake? As I said, we do dispense this lens a lot and have never received a negative front curve before.

Also, will the double-side freeform surfacing not amend the off-axis astigmatic error?

[Wes]

Aspherics do alleviate some of the issues with off axis aberrations, but I still can't see any sense in making that pair the way you describe unless you ordered isekonics and they're trying to equal out the minification due to the much higher minus power of the other lens. Still, it seems odd.

[sharpstick777]

Wes is right, there was an error somewhere. We shouldn't be looking at bi-concave lenses until about -12 to -14. Ideal BC at a -6.00 is about a +3. That means your base curve is 3.5 D off.

Vision will be terrible.

I still can't see any sense in making that pair the way you describe unless you ordered isekonics Still, it seems odd.

[Robert Martellaro]

unless you ordered isekonics and they're trying to equal out the minification due to the much higher minus power of the other lens.

There's a slight increase in minification with the flatter right lens curve, but labs shouldn't be doing this unless the optician asks for it (Iseikonic lenses).

Interesting note concerning the minus front curve- when it's minus, increasing the center thickness increases the minification (or decreases magnification), the opposite of what you would expect with menicus shaped lenses.

The Nulux EP, to the best of my recollection, uses a very flat aspheric front curve, combined with an aspheric/atoric back. I don't believe it is optimized for the Rx, or for POW. Their "claim to fame", IMO, is thickness reduction. For this Rx, I would recommend Shamir's Auto SV, because it does have the above optimizations, and because the design pole and vertical OC can be coincident on the distance gaze, minimizing vertical imbalance. If you can't get Shamir products, I would recommend Hoya's iD SV design.

[Robert_S]

In the UK, Hoya's best lens is the Nulux EP. They tell me it is ID freeform.

[Robert Martellaro]

In the UK, Hoya's best lens is the Nulux EP. They tell me it is ID freeform.

Robert,

The U.S. started with the Nulux EP for their best SV lens, and was followed by the iD SV.

http://www.hoyavision.com/IDSingleVision

Different names for different markets I suppose. BTW, what was the BC for the left lens?

[Robert Martellaro]

Some additional info on the iD SV- it's the same lens as the Nulux ep. No POW optimizations. I withdraw my above recommendation for the iD. Instead, consider the Zeiss Individual SV or Autograph 2 SV.

[MakeOptics]

The frame was just a regular Bulgari, full metal... nothing special. Not particularly wide at all. PD was fairly central. Full Rx is as follows since requested.

R] -2.25/-2.75 x 46
L] -6.00/-2.50 x 168

Bear in mind these are Biaspheric digital lenses, and as such are always extremely flat.

Just based on prescription alone the lenses seem isekonic to me, chances are the minus front base on the right eye is an attempt to minimize the effects of the shape factor to power factor to better mimic the overall magnification in the left.

[MakeOptics]

There's a slight increase in minification with the flatter right lens curve, but labs shouldn't be doing this unless the optician asks for it (Iseikonic lenses).

Interesting note concerning the minus front curve- when it's minus, increasing the center thickness increases the minification (or decreases magnification), the opposite of what you would expect with menicus shaped lenses.

The Nulux EP, to the best of my recollection, uses a very flat aspheric front curve, combined with an aspheric/atoric back. I don't believe it is optimized for the Rx, or for POW. Their "claim to fame", IMO, is thickness reduction. For this Rx, I would recommend Shamir's Auto SV, because it does have the above optimizations, and because the design pole and vertical OC can be coincident on the distance gaze, minimizing vertical imbalance. If you can't get Shamir products, I would recommend Hoya's iD SV design.

Sorry didn't read that kudos for a great answer.

[RT]

ID SV in the US is known as Nulux EP in the UK. They're the same lens.