Setting optical center heights for high myopia, index 1.74.

[donjuan]

Crossposting from https://www.optiboard.com/forums/sho...pia-index-1-74

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.

I've read the topic on OC heights: https://www.optiboard.com/forums/sho...238-OC-Heights
I think it makes complete sense to not set the OC height to the very place the pupils are in, as the nose pads will deregulate a bit with time leading to the OC higher than the pupils which is an even worse situation that the current one. Also, the aberrations would be stronger in the lower lens part, fe. when reading or checking one's phone.

I'm planning to set them to 4mm above the geocenter, but I'm worried about the amplified lower lens part aberrations, ie. about discomfort when checking one's phone etc.. If there have to be aberrations the patient prefers to have them below the pupils rather than in front of them. Should I go for 3mm as people in the thread I mentioned do or 4mm, what do you think?

RX: Sphere -7.5D, cylinder -0.75D. Lens: It's a Chinese lens brand, index 1.74, aspheric design, plastic material (I could try asking the producer for precise compound name they use, but it will take a while and I'm not even sure if I manage to obtain it as their support isn't the best, it's definitely not trivex or anything like that). Previous pair is 8 years old, has very narrow lenses (~25mm lens height) with OC=geocentre, is 2 dioptres weaker and has no cylinders, the patient barely sees anything in them and hasn't used them for a year when he started wearing solely contact lenses. The new glasses have round lens, 42mm high, they fit him perfectly.

[dima]

1.74 have low abbe value

If you do not center Aspheric lens design through the eyes center of rotation the lens will not "correct" spherical abberation.


the aberration product by an error on aspheric in more strong

[Journey]

I wear -11.00 SV myself, and I set my OC at pupil.

The best description I can provide of living as a high myope is like viewing the world through binoculars. Vision is sharp through the OC, but deviating just a few millimeters away from OC causes distortion. A few millimeters more causes LOTS of distortion. The top, bottom, and sides of my lenses simply do not work at all, the distortion is too great. I have practically no peripheral vision. Watch a high myope carefully and you'll see we do a lot of head movement, always pointing our noses at what we want to be in focus. We don't sit still and scan our eyes right-to-left when on the computer.

When OC is at geometric center (typically a few mm below the pupil) I find myself subconsciously tilting my head back, viewing through that OC that isn't aligned with my line of sight.

(To clarify, I have roughly the same experience through 1.67 and 1.74, through stock and through fully digitally surfaced.)

Pro tip 1: Put your high minus patients in small round frames. It saves lots of lens weight, and we didn't have any peripheral vision before anyway.
Pro tip 2: High minuses see WORLDS better through contacts, much wider field of view and less distortion, which is probably why your Px doesn't like wearing his glasses.

[Barry Santini]

Optimized FF with a PRP 4mm below the fitting point is your best target. Add cosmetic thinning prism up to a point.
Question why you feel you need 1.74

Barry

[Barry Santini]

“I'm planning to set them to 4mm above the geocenter...”

Please see Invisible Man:

https://www.2020mag.com/article/maki...-invisible-man

B

[CCGREEN]

[QUOTE Watch a high myope carefully and you'll see we do a lot of head movement, always pointing our noses at what we want to be in focus. We don't sit still and scan our eyes right-to-left when on the computer. [/QUOTE]

My wife is a -10.00 (is a Optician also) And I know for a fact she has very little peripheral vision. And I will confess that yes I have taken advantage of that fact if I want to get away with something because I know she cant see me

[donjuan]

Question why you feel you need 1.74

1.74 has a higher (33) abbe value than 1.67 (32). Offering 1.67 instead of 1.74 would result in the same vision, but thicker and heavier lens. The price difference is negligible. We don't offer Hoya, so we can't use EYRY that has slightly higher abbe (36), and it would cost much more than the 1.74 we offer anyway, I don't think it would be worth it.

[AngeHamm]

The best description I can provide of living as a high myope is like viewing the world through binoculars. Vision is sharp through the OC, but deviating just a few millimeters away from OC causes distortion. A few millimeters more causes LOTS of distortion. The top, bottom, and sides of my lenses simply do not work at all, the distortion is too great. I have practically no peripheral vision. Watch a high myope carefully and you'll see we do a lot of head movement, always pointing our noses at what we want to be in focus. We don't sit still and scan our eyes right-to-left when on the computer.

When OC is at geometric center (typically a few mm below the pupil) I find myself subconsciously tilting my head back, viewing through that OC that isn't aligned with my line of sight.

(To clarify, I have roughly the same experience through 1.67 and 1.74, through stock and through fully digitally surfaced.)

I am a -9.50, and I do not have this experience through many digital lens designs. Unity Via Elite, Zeiss Individual 2, and Varilux X Design, in particular, are miles better for me than any other lens I've worn. That said, I do keep my lens size small for obvious reasons.