Isekonic calculator

[rdcoach5]

Rx is:
-2.50-1.50x150
-0.25-1.00x020

Pt had prev. problems adapting. Darryl's calculator shows mag diff of 3.53% Which is better to reduce difference- keep equal base curves and increase thickness on right or both increase base curve and thickness?

[Richard Hom]

Clinically and by rule of thumb, for every 1D, there is 0.6% magnification for every 1D of refractive error. Thus you have 2.0% magnification in the right and about 0.5% in the left. Size difference shouldn't bother this patient. There may be other causes for the adaptation problem.

[braheem24]

"A" and "B" measurement should also be kept down to a minimum to avoid vertical and horizontal imbalances. A small frame will force the patient to do more head movement instead of eye movement.

[rdcoach5]

Again, I can reduce the difference in magnification by increasing the center thickness of right lens or using a higher base curve. Which is better and why? Darryl? Robert? Harry? Awtech? fezz?

[braheem24]

Higher BC OD, flatter BC OS.

[optical24/7]

Higher BC OD, flatter BC OS.

Also increase the thickness of the OD.

Example; OD ct=3.2, BC 8.D / OS ct=1.8 BC 2D

Using 1.60 index lenses and assuming a vertex distance of 13mm would drop mag difference to about 1.78%

[braheem24]

All the calcs for BC, CT, material can be done here:

http://www.opticiansfriend.com/tools/iseikonic.html

OD 3.0 8BC
OS 2.0 4BC

=1.38% mag variance.

[rdcoach5]

Thank you, but as I said I have Darryl's Isekonic calculator but which is better for adaptation, keeping the same base curve or increasing thickness AND base curve

[Richard Hom]

Deare rdcoach5,

Do you know what the axial length of the eyes are? Frequently, the refractive power difference won't create size discrepancies if there are differences in axial length of even a small amount.

[drk]

Agree with Dr. Hom...it's unlikely to be anisekonia.

What does "had trouble adapting" mean? Can the patient be more specific? Spatial distortion/depth perception? Diplopia or eyestrain in gaze directions? What?

Better bet would be to use equal BC and CT to minimize shape factor differences, keep the lens size down (as was alluded to), and even cut the oblique cylinder somewhat if needed.

I think you are overthinking this one, Joe.

[HarryChiling]

Again, I can reduce the difference in magnification by increasing the center thickness of right lens or using a higher base curve. Which is better and why? Darryl? Robert? Harry? Awtech? fezz?

In this case the difference isn't too high around the low 4% range if they used optimal bases for both lenses individually, but if you were trying to reduce the magnification reduceing the base curve can only be done by so much until you start introducing off axis errors. Thickness would be the better variable in the game more room for play and you can still maintain optimal base cuvres. Of course the best combination is a base change of 1.00 to 2.00D max, you can move a bevel forward 0.5mm on one lens and 0.5mm back on the other allowing for a 1mm change in vertex if needed and then any more modification can be applied to the thickness. This is often the order I go in. Of course if the frame was a thin metal frame you have less room for play in the bevel positioning without sacrificing cosmetics, but then again the thickness in these frame could cause cosmetic issues. Also a slight gain or advantage can be had by using 2 different index materials and cosmetically this could help to offset any thickness changes. There will really be no right or wrong answer as long as you reduce magnification, my goal is always less than 5%. If you want to play around with another calculator try: http://onlineopticianry.com/isekonic.php

[Richard Hom]

If there is a problem with the anisometropia, I would also see if there is spectacle-induced vertical prism. Although it is unclear from the original post whether there is a multifocal component, that would also aggravate a fragile binocular vision status, if present.

[rdcoach5]

In this case the difference isn't too high around the low 4% range if they used optimal bases for both lenses individually, but if you were trying to reduce the magnification reduceing the base curve can only be done by so much until you start introducing off axis errors. Thickness would be the better variable in the game more room for play and you can still maintain optimal base cuvres. Of course the best combination is a base change of 1.00 to 2.00D max, you can move a bevel forward 0.5mm on one lens and 0.5mm back on the other allowing for a 1mm change in vertex if needed and then any more modification can be applied to the thickness. This is often the order I go in. Of course if the frame was a thin metal frame you have less room for play in the bevel positioning without sacrificing cosmetics, but then again the thickness in these frame could cause cosmetic issues. Also a slight gain or advantage can be had by using 2 different index materials and cosmetically this could help to offset any thickness changes. There will really be no right or wrong answer as long as you reduce magnification, my goal is always less than 5%. If you want to play around with another calculator try: http://onlineopticianry.com/isekonic.php

Thanks, I was always taught to duplicate base curve, especially with myopes. I was shocked to hear that we could not only change base curve from right and left but also change index of refraction. Thoughts?

[Refractingoptician.com]

Wouldn't it be nice if there were only one calculator program . You would type in all the details for the RX both left and right eyes , the measurements of PD, OC , seg heights wrap , vertex, etc. then the calculator program would display the vertical imbalance , magnification , thickness and best options .

But then who would need us ?