Hi-index lenses vs visual comfort

[douglasrac]

Hi,

I'm wondering if there is a relation between how thin the lenses are and the visual comfort. If the lenses are thin it will improve the visual comfort or hi-index lenses are just aesthetic?

[HIEYEGUY]

The best part of any lens is in the middle and in the area immediately surrounding it. If you take a small frame and put a cr39 high power lens in it, you will be mostly using the middle of that lens, since it has a low index of refraction. So in a sense you are edging off the more aberrated and thick areas.
When you put a high index, high power lens into this same small frame you are getting more of the aberrated area into this visual area. So the wearer will notice more of the (formerly peripheral) distortion than he did with the low power lens.
This is why the aspheric lens makes such a big difference when going to high power, high index lenses. You have eliminated most of this peripheral distortion and created a happier wearer.

[DragonLensmanWV]

Visual comfort can be adversely affected in high powers by using thin, low ABBE lenses. Sometimes a couple of tenths of a millimeter thicker by using a higher ABBE, lower index material is worth the extra visual comfort.

[AngeHamm]

Visual comfort can be adversely affected in high powers by using thin, low ABBE lenses. Sometimes a couple of tenths of a millimeter thicker by using a higher ABBE, lower index material is worth the extra visual comfort.

This is, in my experience, highly subjective. I wear 1.67 and 1.74 lenses with no discomfort whatsoever. I can't abide poly, though.

[Pogu]

Really? You can really tell the difference between 30 and 32?

[braheem24]

There's more to poly discomfort then the abbe.

[Pogu]

There's more to poly discomfort then the abbe.

Educate me, if you will sir.

[braheem24]

Here's a nice thread...

http://www.optiboard.com/forums/showthread.php/42963-Polycarbonate.-Is-it-all-the-same?highlight=birefringence

[AngeHamm]

Educate me, if you will sir.

My eyes don't know what's a 30 and what's a 32. They do know that poly gives me a headache and 1.67 and 1.74 don't.

[skt]

I'm with Angie on this. Have never been able to wear poly comfortably.

[AngeHamm]

I'm with Angie on this. Have never been able to wear poly comfortably.

It's just Ange. But thanks for having my back.

[skt]

:)

[chip anderson]

One must also concider that glass and CR-39 for the most part have posterior base curves designed to give maximum visual performance with rotations of the eye. Higher index materials are designed to allow flatter posterior curves fit frames and allow the use of thinner lens designs.
Of course there are those that say if you use a high class multi-layered AR the problems will go away in higher index(s).

Chip

[AngeHamm]

One must also concider that glass and CR-39 for the most part have posterior base curves designed to give maximum visual performance with rotations of the eye. Higher index materials are designed to allow flatter posterior curves fit frames and allow the use of thinner lens designs.
Of course there are those that say if you use a high class multi-layered AR the problems will go away in higher index(s).

Chip

So my, and my office's, A/R snobbery may explain my lack of difficulty with the materials? Interesting...

[Barry Santini]

One must also concider that glass and CR-39 for the most part have posterior base curves designed to give maximum visual performance with rotations of the eye. Higher index materials are designed to allow flatter posterior curves fit frames and allow the use of thinner lens designs.
Of course there are those that say if you use a high class multi-layered AR the problems will go away in higher index(s).

Chip

Chip:

If one maintains optimal Best form, CC fitting, then the Base Curve (therefore rear curve) of the lens MUST go flatter as the index goes up. So it is not just to "fit" frames.

B

[EyeSeeYou]

I think high index lenses are the greatest; all I swear by is 1.67 with crizal avance and grey transitions. You can also use a digital lens, in both single vision and progressive format, which reduces distortion.

[fistkuen]

Does anyone try the TOKAI 1.76 AS lenses ?

[douglasrac]

Ok thanks for the replies. But my real question is:

Visual comfort is inversely proportional to index of refraction?

If I don't care at all about lens thickness, design or whatever is related to appearance, should I choose CR-39 over 1.7, 1.8 or even 1.9 lenses?

[chip anderson]

Concider that if a high minus lens in CR-39 needed an eight or ten posterior curve. Would not the higher index material returning the posterior curve to something approaching a 6 or at least more acceptable posterior curve that the lower myopes would have in CR-39 be beneficial?

Chip

[Wes]

Higher index lenses do not perform visually as well as lower index lenses in similar low power prescriptions. High power lenses rarely perform in a manner most people would consider great, regardless of index. CL will generally provide better correction to the high rx pt.

Any time you multiply by zero you get zero.
good design X crap material = crap lens
crap design X good material = crap lens
good design X good material = good lens
good design X good material X AR = best lens
good design X crap material X AR = crap lens
crap design X good material X AR = crap lens
good design X good HI material X no AR = crap lens
good design X good HI material X AR = good lens

[douglasrac]

Thanks again for the replies.

So, basically what are you saying is that if you have high power prescription you cannot have best lens, only good lens, no matter what choices you do.

[Barry Santini]

Ok thanks for the replies. But my real question is:

Visual comfort is inversely proportional to index of refraction?

If I don't care at all about lens thickness, design or whatever is related to appearance, should I choose CR-39 over 1.7, 1.8 or even 1.9 lenses?

I think the optical benefits of AR have now reached the point of bordering on being oversold.

Give me a well-designed FF SV lens w/o AR anytime.

Only an individualized, FF SV lens can maximize the thinness benefits of higher-index, lower-abbe materials, finished or conventionally-surfaced, which are typically fitted with little or no regard to best form requirements.

And then the processing of such lenses must be carefully controlled as well.

B

[DragonLensmanWV]

This is, in my experience, highly subjective. I wear 1.67 and 1.74 lenses with no discomfort whatsoever. I can't abide poly, though.

Strange, since poly has the same ABBE as the others. Maybe a better lens design?
Anyway, to answer the OP question: yes, you CAN get thinner lenses that will have good optical clarity. Just not for everyone. I was very sensitive to ABBE and for decades I wore lenses that were thicker than I could get, but would rather see well than have thin lenses (1.67 was the WORST for me). That changed when 1.70 index was invented. That was nice and thin AND had acceptable lower levels of chromatic aberration.Be aware also that AR,while very recommended, does nothing to abate the optical crappiness of most high index lenses, though digital processing does help. What you need for your high minus patients is 1.70 index, digitally optimized.
Ange, next time, try 1.70 and critically compare chromatic aberration by looking at a string of LED Christmas lights in the dark and moving your head from side to side. Pay special attention to the color smearing with the blue and red lights. It will be less with 1.70, especially the red end of the spectrum.The blue will still smear some, just not as much as with other indexes.

[sharpstick777]

Really? You can really tell the difference between 30 and 32?

Poly is always very slightly blurry to me, even in my low -1.00's. I don't get chromatic abberation, but I do get a loss of DVA that is unmistakable.

[sharpstick777]

In reality you don't often need an aspheric lens, just a "true" or "best form" base curve (the cornea is itself aspheric so there is some basis there). The problem is that cosmetically the "true form" lens will be much steeper, thicker and more unattractive than most customers want. So aspheric lenses are a cosmetic compromise.

If you use a premium finished Aspheric lens from Seiko or Zeiss (I don't work with Hoya or Essilor finished to enough verify) you will usually get a aspheric curve optimized for the lenses individual base curve and RX farily precisely. The Aspheric curve and the base curve are in sync to simulate "best" form.

If you use a cheaper aspheric, it may not be optimized individually and it may be a single aspheric curve copied onto multiple powers. If you use a grinder, it will usually be off even if its aspheric because the base curve is typically not optimized for that individual RX, its a curve that will cover a range of RX's. You will probably get poorer vision in a grinder over a quality finished Aspheric lens.

The other factor is that ashperic designs themselves will vary, its not standard. There is full field, and the "button" design, or a combination, there is also dual aspheric (front and back). No one as ever analyzed the effectiveness of brand A vs. brand B or C. Some manufactures design to reduce thickness, some for best optics, but most are somewhere in between. The only sure thing is they will never tell you which it is.

The only sure way around all of this is SV Free-form.