Thin Lens Problems

[Clive Noble]

We've had a problem that's repeated itself several times recently.
It's usually with elderly patients with Rx of over +10.00 who have been wearing thick plastic CR39 lenses for many years.

We give them the 'shpiel' of smart, flat, thinner high index lenses and AR coating and a modern frame and they get quite excited and order the job.

In most cases their Rx has been stable for many years, so we don't even change the Rx.

Well, you can guess the result, even though we explain to the Px beforehand that it will take a day or two to get into the new style lenses, they don't.
The problems they experience are dizziness, peripheral problems, but mostly a smaller retinal image.... yes, we set up the angling and the centration as we should and they do admit that the vision is clearer than the old thick CR39.

We've had to change 2 back recently to large thick 1.49 lenses..........

Anyone else had a problem like this, and any suggestions?

[sarahr]

Are you decentring your aspherics down to allow for pantoscopic tilt? Could the vertex distance have changed from the old pair, heavier thicker lenses may have been causing the frames to be worn further from the eye than the new thinner lighter version causing an induced rx change?
Where you using a high v-value hi-index aspheric(if there is such a thing!) That's the extent of my knowledge.Probably only what you already thought of but at least I tried eh?
P.S Would it be worth trying an aspheric 1.49 alone first without introducing the hi-index to try to place the culprit.

[bwheeler]

It sounds like your patients have adapted to the magnification inherent in their previous lenses so successfully that altering that magnification causes them to lose their perception and spatial reference. I doubt they really want to adapt more than they want
things to remain the same.

[chip anderson]

Woman needs contact lenses. Problem will go away. Lots of problems like ring scotoma (jack in the box) etc. present in these Rx's. We forget these now that most aphakic's have implants so we don't run into them except when we hit the occasional very high hyperope or true aphake (as opposed to pseudophakes). They can learn to live with a good pair of spectacles but it's a poor second as a solution to thier visual needs.

Chip

[care4vision]

sarahr said:
Would it be worth trying an aspheric 1.49 alone first without introducing the hi-index to try to place the culprit.

Hi!
Lets look at the SM(spectacle magnification) formula in which the first term is known as the SHAPE FACTOR and the second term is known as the POWER FACTOR :
SM=[1/(1-t/n*F)]*[1/(1-d*Fv)]
where
F=power of the front surface
Fv=back vertex power of the lens
t=thickness of the lens
n=index of refraction of the lens material
d=distance from the back vertex of the lens to the enrance pupil
What we know is that Fv has not been changed and new lenses were flat,high index ,AR coated and put in a modern frame.
Certain things we dont know and they are of a high importance for us.
1) We know nothing about Fv of old spectacles and Fv of new ones.Inspection of the power factor shows that SM varies directly with back vertex power of the lens. As an example for +10D lenses by changing eyewire distance from 15mm to 11mm magnification will decrease by 4%
2)We know nothing about front base curve of old and new lenses
For example for +10D lens with 7.1mm center thiknes a change in front base curve from +15D to 10.5D magnification will decrease by 4%
3)Nothing is known about change in lens thikness,but for +10D decreasing lens thikness by 1.5mm magnification will decrease by 2%.
4)We dont know about new n , but generally speaking refractive index changes typicably are very small.For example there is decrease in magnification of about 0.05%for a change fromcrown glass to polycarbonate.
All together it can be very strong minification in radical changes of Fv and lenses.However only 2 factors are really important:vertex distance and front base curve.
If you want to fit your client with nice pair of glasses with the same Rx and be careful, I would suggest to select:
-modern small frame
-high index AR coated knife edge lenses with similar to previous front curve.
Best regards
care4vision

[so]

Part of the problem may be the availability of the appropriate base curve.
Most of the mid and high index blanks will accomodate a strong minus rx, but manufacturers don't provide much for plus rx wearers.
The front curve for a +10.00 should be greater than 10. Most manufacturers only go up to a 7 or 8 front curve. The lab will happily try to grind this for you, but you will end up with a convex back. I think this may be difficult to wear.

[Pete Hanlin]

To a much smaller degree, I experienced something similar- but opposite- to the effect that your patients are mentioning when I had LASIK a few years ago. Namely, without my -4.75 lenses in front of me, the changed image size really threw me for a loop for a while (which seemed odd to me at the time, because contact lenses had never had that effect on my vision). Because objects were no longer being minified, things seemed nearer than they were (especially the computer screen and other intermediate objects).

Since you've already changed two patients back, I don't guess the tried and true mantra of "give them a week" worked in these cases. I don't suppose either of these patients had a history of ARMD (or some other condition that might benefit from a larger image)? It could be a costly experiment, but I suppose you could try ordering an aspheric lens with some extra thickness and possibly a longer vertex distance for these patients to see if you can "wean" them towards a better design over time...

Concerning contact lenses for these patients (especially women seniors), in my experience there are often tear film, handling, or lid issues that make contact lens use tricky...

[Clive Noble]

Thanks t'y'all, whilst I really do appreciate and understand fully the text-book explanations, the bottom line with this problem is that the Pt and his brain has gotten used to something, yes, even when it sits crooked on his face and has induced unwanted prism over the years, and the only thing that he's prepared to accept is the same thick lens again, even full of scratches...

Is this a case of Ophthalmic Psycological Security? (like babies and their 'security pieces')

When it's a case of no alternative (after Lasik for instance) and there's no turning back the pt. accepts it and gets used to it, but when you're a 'soft touch' (like we appear to be) and are prepared to listen to every whine and whim of the Pt then you try to help.

Maybe we should take their old glasses away for a week and tell them to go away and get used to it, after all, in most cases they do admit that the vision is better.

Nice to see a fellow Israeli on the board, sorry it's taken me so long to find you.

[Diane]

Clive,

I believe that the experience of the ones who adapt and are tremendously happy offset the couple who don't adapt. We may feel that the older ones don't adapt as well, but they deserve a chance. Depending on the patient, sometimes it may be better to leave the material alone and try for the aspheric design. Depending on how you want to work with these patients, (and I know cost is a factor, whether you pay or they pay), the successes make it all worth while.

Give them the best if they are willing to go for it up front. Question them very well. (This could turn into a reeeeaaallly long post if I gave that course... ). Listen and go with your feelings upfront. Also sometimes it is wise to simply state up front. "Mr./Mrs. Jones, these are premium lenses. They will perform for you in such and such fashion. The benefits to you are so on and so forth. I have to tell you right up front, that we have tremendous success with these lenses. (Sometimes even give a success story, not mentioning a patient's name.) I also need to tell you that because every patient is different and since vision actually is interpreted by the brain, your brain has to want to adjust for this new technology. Sometimes the adjustment is immediate, and sometimes it takes a little longer. It does get better each day, as long as you don't return to the old spectacles. Because, remember, your brain has to do the adjustment, and we don't want to confuse it. However, if after a reasonable attempt at adapting to them, you feel that you simply cannot adapt, I will be happy to replace them at no charge, (or make your own policy), however there certainly cannot be any refund of the difference of the lens price. So it will be in your best interest to at least give it a good try." Then if they simply don't adapt, wean them down to the old plain old thick CR 39 lenses. However, if you think about it, even with same Rx, same material, same vertex distance, but a smaller frame can also have the same effect.

OK, just my few cents worth. The technical side has already been addressed.

Diane

[care4vision]

Clive Noble said:
the Pt and his brain has gotten used to something, yes, even when it sits crooked on his face and has induced unwanted prism over the years, and the only thing that he's prepared to accept is the same thick lens again, even full of scratches...

Hi everybody.I found this topic very interesting,I actually recall a very interesting case that took place at the start of my career.Imagine a patient looking similar to a genius professor from the movie 'A beautiful mind' giving you his old glasses -6.00D
OU and asking you to make exactly the same.So I carefully measured PD ,ordered appropriate lenses and made the glasses.The next day the patient tries on his glasses and says 'excuse me its not my glasses.'So I check again these glasses and finding everything is correct.I ask him to try to adjust to these new glasses.He returns a few days later and complains about the glasses.Now I ask him to come to my checking room and tell him to put his old glasses on .He says with these old glasses his vision is good and he feels comfortable.He puts on his new pair and says that he feels uncomfortable, although he seems to see o.k.So I politelly send him off again asking him to adjust to these new glasses.Two weeks later he returns with a letter from my friend ,senior optometrist, with a request to put down lenses optical centers in his new spectacles exactly like in his old ones- 12 mm below his pupils.And you know what ,it helped a lot.Both of us were happy that this case ended.A quick calculation,I made after that,showed that he had approximately 7 yoke base up prism in two eyes.A known effect of a yoke prism is that brings everything down and closer.And I think that this type of personally that is closed,introverted,learned will very much enjoy this optical arrangement .Unknowingly by eliminating the prismatic effect I would have maybe "opened him up" to a psychological effect that he for sure did not want.Since then I am very careful with this kind of the "personality- glasses" relationship.
I would be happy to hear forum members insights about other personality optical stereotypes.
Best regards.
care4vision

[Bohumila]

This is the first time I have seen this discussed, but it sure hits home. I'm a +18 aphakic who has worn glasses almost exclusively all my life. The few times I have tried contacts I found it absolutely impossible to see with them. In addition to the lack of magnification (which I perceived as minification, of course) which reduced my acuity, things jumped and swirled and danced until I hurled. I spend weeks trying to adapt, thinking that my vision would ultimately improve. Nothing worked. Now I am so contact lens intolerant that they are no longer an option.

When I get my Rx filled, the first priority of the optician is to get the thinnest lens possible, not realising of course that there are not a lot of options for me. Small frames and the smallest bowl may give the best cosmetic effect, but I am almost non-functional with such reduced peripheral vision. (Vanity is not worth much if you feel too visually insecure to venture into the public and have anyone actually see you.)

Finally, after years of trying, I found a specialty optical lab that made me a pair of glasses using a +15 base hyperaspheric full field blank (Signet Armorlite) with a +3 back curve. This person was the first to even offer a biconvex design (and unfortunately did this somewhat illegally, so is unwilling to do so again). The extra visual field makes an enormous difference in my life, though just about everything else is the same--magnification, distortion, etc. It took a day to get used to a slighty different curve to my view on life, as well as the added weight. However, once I did I wondered how I ever got along with the old lentics. (Well, I guess I really didn't; at least, not in a fully functional sense.)

Us high hyperopes are less picky because we are just happy to see anything at all!!

[drillmountmaster]

Let old people keep their CD frames and plastic or glass lenses!!!!! It's not worth the money in remakes to get them to change.