TL; DR The short answer is that the SPHERE correction, the 1st column in a prescription is the diopter correction needed for distance vision. If it’s negative, you’re near-sighted. If it’s positive, you’re far-sighted. The ADD column, further to the right in a prescription is the diopter correction needed for close-up vision when your lenses have hardened and can’t be compressed to focus close-up. The ADD diopter is always positive (because you are ~“far-sighted” for near vision if you have presbyopia). Usually the ADD diopter is a correction for about 18 inches of viewing distance. The effective diopter needed for viewing, if I got it right, would be your SPHERE correction added to your ADD correction. So if you were pretty near-sighted, -2.5 SPHERE and +2.5 ADD, you would need a 0 diopter correction to read 18 inches away and be able to read small print on a medicine bottle perfectly without your glasses, if you don’t have significant astigmatism, which complicates things. But the virtual display images for each eye in VR goggles are not set to be 18 inches away from your eyes.
Question for anyone with a filled prescription lens for VR goggles: Did anyone get back from the prescription lens company the actual optical parameters for the lenses made? Would be interesting to see the prescription submitted to the lens company vs. the returned VR lens parameters. Please post if you have that so the rest of us can learn from it, along with your opinion of how well the prescribed VR lenses work in your goggles. I think that I will go with a company eventually that promised to provide the manufactured lens parameters to me.
Long-winded version of how presbyopia factors into everyday vision and VR goggles: For every day glasses, the correction needed for presbyopia is usually placed in the lower part of the lens of the glasses for each eye - the upper part of the lens is for straight ahead distance vision, the lower part is for closer to close-up vision. You’d think a person would get confused but the wearer quickly learns to reflexively move one’s head without thinking about it to have the head at an angle to the desired line of sight to be able to look through the right part of the glasses. For presbyopia, because the eye lens has hardened with age, your eye muscles can’t squeeze the lens to focus it a differing degrees of nearness the way a younger person’s eye can. Therefore, having bifocals for very close-up and distance vision is a black-and-white hack that leaves out intermediate distances. This problem is addressed by having trifocal glasses or even better graduated bifocals where the amount of presbyopia correction increases from the middle section of the glasses towards the bottom (this type of prescription is the most expensive but the best). The wearer again learns to use graduated bifocals with reflexive head movements to get the clearest vision for a desired viewing distance without even thinking about it.
With an HMD, depending on the OEM, the virtual display images are moved far enough from the eyes that a normal seeing person should be able to focus their eye lenses on the images and see them clearly. I think I read on the web that the original Oculus Rift virtual images were effectively at infinity - where presbyopia, the inability to focus close-up, wouldn’t matter. As CptLucky8 points out in his OP, newer headsets have reduced the virtual image distance to 2 or 3 m, effectively, or less. The closer the virtual image is to the eyes, the more presbyopia correction, if needed for real life vision, factors in, and CptLucky8 suggests for the Reverb G2, based on his presbyopia, he figures the focal distance for the G2 is effectively about 1.5 m.
So if you have presbyopia, when you put on VR goggles and the virtual image isn’t all that far away, you’re going to need some presbyopia correction, and real-life glasses are not going to do the trick, especially if they’re graduated because the amount of presbyopia correction will vary according to what part of the lens you’re looking through, designed for different distance viewing, whereas let’s say the virtual display images for the G2 are effectively always 1.5 m away no matter where you look in the FOV. So therefore you might need the same diopter correction for all parts of the display that you want to look at.
In drug stores and Walmart there’s a reading glasses section, often near the pharmacy section, probably to discourage enterprising customers from just donning the merchandise and wearing it out of the store. There are part-frame and full-frame reading glasses of various diopters and a test reading chart whereby you can check out how well with a particular diopter you can read small print close up. If you wanted to try a diopter correction via reading glasses, you wouldn’t want to stand from the chart at the typical reading distance, about 18 inches or so, but stand away at the distance that you think the virtual display might be set to appear.
The problem with using reading glasses is they might not fit in the headset. If the lens abut the built-in lens that the VR headset comes with, the glasses lenses might scratch the VR lenses by rubbing against them, and if you also have astigmatism (non-spherical eyeball), the reading glasses won’t correct for that.
Theoretically, prescription lenses could correct for both presbyopia and astigmatism and obviously avoid the goggle fit and lens abrasion possible problems as they replace or go over the lenses the goggles came with depending on the options for a particular brand and model goggle.
The thing that I don’t understand having looked at several VR prescription lens websites is the blurbs on the website say that the lens made usually use the far distance correction in a prescription, which is not what a presbyopia sufferer wants - you want the appropriate near-distance presbyopia diopter correction to be factored in in addition to the far distance correction just as you would for a regular glasses prescription when looking through the part of the lens designed for intermediate distance viewing.
I asked one of the online sellers about presbyopia correction and got a less than satisfying answer - suggesting that they only planned on going by the distance vision correction and if I felt I needed a presbyopia correction, I’d have to give them my preferred prescription! That’s why I’d love to know, as I requested in a previous post, who got the best satisfaction from what online VR prescription lens seller, particular if the poster needed presbyopia correction. BTW, the response below is from VR Optician - maybe the “front desk” folks are not the same as the guys/gals in the back who actually make the lenses (one would hope!):
We really need oly the far
distance prescription for the adapters. But the best soulution would be
if you test it before. When the headset arrives you can try out if you
like it better with or without reading glasses and the order the values
you feel/can see best with.
Here’s a WikiHow description of how to read your prescription. Any needed presbyopia diopter correction would appear in the ADD column: How to Read an Eyeglass Prescription: 11 Steps (with Pictures) (wikihow.com)
Foster Grant sells “Multi Focus Reading Glasses” with 3 basic diopter corrections for close-up reading, computer screen reading, and across-a-desk viewing. Foster Grant Multi Focus Reading Glasses - Foster Grant. If you have a base diopter for close-up reading of +2.0, jlacroix of Foster Grant explains in a blog post answer June 23, 2015(see down the page) how the required diopter might change for those increasing distances, according to Foster Grant’s calculations:
Simply put, when you are purchasing Multi Focus readers, order them in the closest diopter you can to what you currently use. The middle area is reduced by approximately half of a diopter from your “base” diopter and the top diopter is approximately one half the strength of the “base” diopter that you order by. IE If you order a +2.00 the 3 areas will be approximately the following diopters:
Top: +1.00
Middle: +1.50
Bottom: +2.00
