Checking image size?

**kaypaula** · 09-21-2011, 01:58 PM

Hi all
Might not be an answer to this but thought I'd give it a shot. I used an online calculator to see what the image size "should" be with certain powers. However; is there a way to check the lenses once they are created to see if they (the lab) have reduced the image size as requested (iseikonic). The only thing I could think of (not very precise) was to check it against a same powered trial lens .. just eyeballing the image size against some writing. Any thoughts?

P.

**Aberdeen Angus** · 09-21-2011, 02:36 PM

Someone may shoot me down here, but as far as I know iseikonic lenses are about equaling retinal image sizes by varying thickness and lens form to achieve a balanced image size WITHOUT affecting the power. I'd be interested to hear from folks who have actually found they have had to try one of these.

Retinal image size will of course be affected by the interaction of the refractive eye with the spectacle lens. I imagine that it would be fairly hard to gauge in normal practice.

Contacts anyone?

**kaypaula** · 09-21-2011, 02:51 PM

The pt is aphakic in one eye, and cannot due to some medical issues with his eyes, wear CL any longer. He is an OD +3.25 -2.00 X170, OS +11.00 -0.50 X015. SO, an iesokonic lense was a good idea here to help reduce image size. I know they do this by playing with the thickness and base curve of the lenses, plus they used an aspheric design. As I had nothing to measure this against, I was wanting to make sure they DID do this, or did they just balance the thickness out a bit and put him in aspheric lenses. After testing it against the +11.00 trial lense I am actually please with the result but it did make me wonder if there were a precise way to determine this.

**Aberdeen Angus** · 09-21-2011, 03:24 PM

What are the VA's in the respective eyes? If the aphakic eye has a reduced VA you may be able to get way with a lower Rx whilst still retaining reasonable vision. An Iseikonic lens will be a)ugly and b) (at least over here) very expensive.

Have you actually tried normal lenses? I have a couple of folks with normal vision who have wildy differing rx's. One has a -1.00 in one eye and a +6 in the othe other. Another has -2.00DS and a Plano/+8.00 cyl. Both have very good VA's with their with specs. It is amazing how plastic the brain is if given a chance.

**braheem24** · 09-21-2011, 03:57 PM

Originally Posted by Aberdeen Angus

I have a couple of folks with normal vision who have wildy differing rx's. One has a -1.00 in one eye and a +6 in the othe other. Another has -2.00DS and a Plano/+8.00 cyl. Both have very good VA's with their with specs. It is amazing how plastic the brain is if given a chance.

Anisometropia from birth is easier to handle then the anisometropia caused by surgery. In both cases, they may think they have normal vision, If you could measure depth perception they would probably not pass with flying colors.

Secondly if the patient is anisometropic due to variances in the axial length they may not have a retinal size difference.

**Robert Martellaro** · 09-21-2011, 05:13 PM

Originally Posted by kaypaula

I was wanting to make sure they DID do this, or did they just balance the thickness out a bit and put him in aspheric lenses.

To get an image size within 5%, the OD would have a CT of >15mm on a steep BC. If he's asymptomatic with his present eyewear (no diplopia, fatigue, etc.) suppression is occurring. They probably balanced the thickness for cosmetic reasons. Concentrate on the dominant eye, but don't completely ignore the non-dominant eye, probably peripheral only but make sure before you use a balance lens. Sometimes it's best to use the manifest for both, sometimes balance the right, sometimes the left, sometimes you might fog the bad eye to minimize distracting distortion from corneal/retinal disease.

**chip anderson** · 09-21-2011, 07:33 PM

If all else fails, frost the lens on the eye with poorest acuity. Used to be SOP before implants between catract surgeries or maturities.

Chip

**kaypaula** · 09-21-2011, 09:32 PM

Thanks for the info. Still wondering how I can "measure" image size differences. Pt picked up today and he was pleased as punch. He hasn't worn glasses in a very long time, he was a contact lense wearer and has been without for about a month now. So he's been relying on his OD for vision. He has close to 20/20 OU corrected. He is also in FT28, first time bifocal wearer as well. He did very well, and the glasses did not look that bad, in fact they looked pretty good .. as good as a +11 can look that is. He's much better this way, instead of fogging or such because he can get close to 20/20 with the glasses. He didn't even notice image size differences. Not a high maintance kind of guy. Nice when you get those. Now tommorow I'll get back to my -1.00 pt's that are whining because they aren't seeing 20/10! ;)

**braheem24** · 09-21-2011, 11:10 PM

Originally Posted by kaypaula

Thanks for the info. Still wondering how I can "measure" image size differences.

Sorry forgot to add

http://www.opticaldiagnostics.com/pr.../ai/index.html

**rdcoach5** · 09-22-2011, 07:13 AM

Or Darryl's calculators http://www.opticampus.com/tools/calculators.php

**Robert Martellaro** · 09-22-2011, 09:18 AM

Originally Posted by kaypaula

However; is there a way to check the lenses once they are created to see if they (the lab) have reduced the image size as requested (iseikonic).

You could probably project an image through the lens, measure the irises, etc., but it would be more accurate to measure the BC, CT, and Vtx distance, with some attempt to determine the refractive index (although that's not critical) for a very good estimate of minification or magnification.