This drew my attention when I am trying to adjust my prescription from https://vr-rock.com for the RayNeo XR Air 3s Pro I bought recently, for extending my smartphone & computer screens.
The power attached to the XR (or AR?) glasses is naturally too high for me perhaps due to its distance from my eyes. While the center of the lenses offer clarity still but combined with the somewhat higher power of the peripherals, I could certainly use less power. And if I push the glasses slightly away from my eyes for a few mm, then the power decreases and I could see the clarity with better comfort. Less power is always less stressful to cope than too much power.
This change in distance is called vertex distance. So in my myopia (short-sighted) case (not hyperopia/long-sighted), the negative degree becomes more negative as the lenses draw closer to my eyes. And this is the formula for the vertex compensation:
To calculate the new effective power (Fe) of a lens based on a change in distance, use the vertex distance formula:
De = Do/(1 + d(Do))
Where:
De= Effective power (new power)
Do= Original lens power (in diopters)
d = The change in vertex distance in meters (e.g., a 3mm shift is 0.003)
Note on Sign: When the lens moves closer to the eye, d is treated as a positive value in this formula.
And there're calculators online for vertex compensation: https://www.omnicalculator.com/physics/contact-lens-vertex
So in order to not risk harming my eyes, I would have to order another set of these prescription lenses from VR-Rock, which did not disappoint. I'll just have to measure how much distance is adjusted.
RayNeo Air 3s & 3s Pro Prescription Lenses × 1 $64 total:
Prescription Type: With Prescription
Model Selection: RayNeo Air 3s Pro
RIGHT SPH: -8.75 (+ $5.00)
RIGHT CYL: -1.00
RIGHT AXIS: 85°
LEFT SPH: -8.50 (+ $5.00)
LEFT CYL: -0.75
LEFT AXIS: 95°
Lens Upgrade: Anti-Fog(Cost-Free), Oil-Resistant (Cost-Free), Scratch-Resistant (Cost-Free), Easy to Clean (lotus effect) (Cost-Free), Radiation-Resistant (Cost-Free), Anti-Glare (+ $5.00)