Setting optical center heights for high myopia, index 1.74.

[donjuan]

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[AngeHamm]

What's the RX? What's the material? How are the OCs of previous pairs aligned?

[donjuan]

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[AngeHamm]

There are a few things going on here. (My more technically experienced colleagues will have much more comprehensive opinions on the subject, though you will probably get more eyes on it in the "General" section than this one.)

1) I recommend placing the OC much, much closer to the pupil than you're talking about here. The higher the power, the less decentration it takes to really muck things up.

2) The higher B measurement is also a likely culprit. There is more lens farther off axis, and that portion of the lens will show more chromatic aberration.

3) 1.74 materials all have pretty low abbe values, so CA will always be an issue. This is where one of the most important things we do is to manage our patients' expectations. With their higher RX, hyper high index lenses are definitely called for, but CA is an unavoidable side effect. Make sure the patient knows it's going to be there before finalizing the sale and your patient will almost always be fine with it.

[dima]

My 2 cents... The old glasses of your patient was spheric or aspheric design? Some people don't "digest" aspheric design.


aspheric design you have to set fitting heigh on the center of rotation of the eye, spot the pupil on glasses with the patient's face at 0 patoscopic tilt... so you will have the right drop oc.

Eventually can you ask to your lab a 1.74 lens with spheric design.


I believe 1.74 lenses was all same material: mr-174 abbe 32

[Robert Martellaro]

My 2 cents... The old glasses of your patient was spheric or aspheric design? Some people don't "digest" aspheric design.


aspheric design you have to set fitting heigh on the center of rotation of the eye, spot the pupil on glasses with the patient's face at 0 patoscopic tilt... so you will have the right drop oc.

Eventually can you ask to your lab a 1.74 lens with spheric design.

Hi Dima.

That would work, however the best form base curve of a spherical surface design and a high refractive index material for a high myope (in this case about -8.00 D) is probably close to +6 or more, resulting in poor cosmesis. In general, as the refractive index increases, so does the best form BC. And once over 8 D, best form breaks down and asphericity must be employed to reduce oblique astigmatism and power error.

http://64.50.176.246/cecourse.php?url=lens_design/

With OC height set to the geo center, there are slightly visible chromatic aberrations when looking straight, the patient tends to look slightly downwards with the head bent upwards to better his vision and it causes discomfort. The geocenter is 5-6mm lower than the pupils, but sweat or regular nose pad deregulation can lower it to 8mm.

Yes, try to position the Prism Reference Points as close to the pupil heights as possible, reducing the pantoscopic tilt as needed to compensate, resulting in a compromise between acuity and cosmesis.

A frame that positions the PRP (180/datum line) closer to the the pupil heights would be ideal.

Hope this helps,

Robert Martellaro

[AngeHamm]

I learned the word "cosmesis" today.

[Robert Martellaro]

I learned the word "cosmesis" today.

It's the "look good" part of the ophthalmic optics battle between cosmesis and functionality.

[AngeHamm]

It's the "look good" part of the ophthalmic optics battle between cosmesis and functionality.

So I intuited. Excellent word. I'm going to be using it a bunch.

[Kwill212]

So I intuited. Excellent word. I'm going to be using it a bunch.

TBF cosmesis is the cosmetic portion of surgery or prosthetic limbs. I wouldn't say it applies to eyeglasses. I believe cosmetics would be the appropriate term for eyeglasses.

[Robert Martellaro]

TBF cosmesis is the cosmetic portion of surgery or prosthetic limbs. I wouldn't say it applies to eyeglasses. I believe cosmetics would be the appropriate term for eyeglasses.

I got it from D. Meister. Paste this into you favorite search engine: "cosmesis" spectacle lenses.

It's a bit of a ten dollar word, but it seems to be common in the ophthalmic community.

Best regards,

Robert Martellaro

[dima]

@ Robert Thanks for explanation on aspherics.

[Kwill212]

I got it from D. Meister. Paste this into you favorite search engine: "cosmesis" spectacle lenses.

It's a bit of a ten dollar word, but it seems to be common in the ophthalmic community.

Best regards,

Robert Martellaro

Someone should tell Merriam-Webster then. It seems like cosmesis could be used in reference to the way glasses or lenses make our eyes/faces appear, not in the way the glasses or lenses themselves look.

[optical24/7]

Is that the same Merriam Webster that sits on a bench next to the Ohio River in Rosiclare Illinois and complains about caterpillars on her tomato bushes? I know her! I’ll let her know!