In message , VanguardLH
writes:
"J. P. Gilliver (John)" wrote:

The original poster Peter Jason didn't say he only had [astigmatism]
in one eye.

Are your palm prints exactly the same for your right hand as for your
left hand? Nope. Same for your right and left fingerprints for the
matching fingers. Same for your eyes. Irregularities in the shape of
the cornea that generate refractive error (astigmatism) do not progress
equally in both eyes because the tissues are separate, not common. Many
folks with astigmatism have it in only one eye. While astigmatism
usually occurs concurrently in both eyes (bilateral), it is not
necessarily equal in both eyes (i.e., it can be asymmetrical).
Astigmatism in only one eye is often caused by injury (which is my case
due to a cat scratching my right eye when I was a kid) or by
degenerative eye conditions or disease; however, eyes do not degenerate
equally. No pair of disconnected tissue will degenerate equally.

Like you (though for different reason - mine's from birth), I have
dissimilar eyes (to the extent that I don't have 3D vision; both eyes
worked fine when I was younger, but my brain never developed the ability
to use both images at once). I will admit I'd got used to thinking
_most_ other people had eyes that were more similar than mine are.

Regardless of astigmatism, how often do eyeglass wearers get exactly the
same prescription for both eyes? Most users don't even know the specs
for their specs; that is, they go to the optometrist, get their exam,
and get their eyeglasses, and the bill they get never mentions the

That's _probably_ still true here (UK), but less so: several of our
optometry chains offer free eye tests as a marketing exercise from time
to time, and also certain classes (children below a certain age,
pensioners above one, and I think those on certain kinds of benefit
[welfare]) are entitled to free ones too. So the more savvy of us - or,
even those entitled to free glasses as well as tests, but who don't like
the options (frames, coatings, ...) offered at a particular branch - go
for a free test, then take the prescription elsewhere.

sphere, cylinder, and axis measurements. If they want to keep their own

One that's often left off the card is intraocular distance, i. e. how
far apart your pupils are.

history of how their eyesight has degenerated, they have to ask for a
copy of the measurements to know what they are. Several times when I've
asked for the specs, they'd look mildly surpised and asked "Why do you
need to know?". I'd respond "Why shouldn't I know?"

Indeed!

In any case, for a monitor to correct vision impairment would mean the
screen would need to place a lens at your face to correct the refractive
error at the distance for where the pixels are painted. Don't know
about you, but having a large bubble of glass protrude from the monitor
against which I would have to press my face seems extreme compared to
putting on a pair of eyeglasses.

With the one exception of the sort of astigmatism that is purely an
aspect ratio distortion, and similar in both eyes. A monitor and
graphics card combination _could_ sort that, by simply using the "wrong"
ratio - _if_ a ratio "error" that countermatched the astigmatism was
achievable (including by rotating the monitor if necessary). _Maybe_
that type of astigmatism is actually very rare; I don't know. I based my
naïve thoughts on the matter on being told (decades ago) that the reason
some famous painters painted pictures of a stretched world (e. g. tall
thin people) was that they had astigmatism. (I was always suspicious of
that explanation, because surely if they had, and looked at a picture
they'd painted in that manner, it'd still look wrong to them.)

Remember the function of the lens is to correct your focus at a specific

One function ...

distance. My eyeglasses for outside and driving would be impossible to

.... and for most practical glasses, for a _range_ of distances - though
ones for specific occupations, including display screen use, may be
optimised for quite a narrow range.
[]
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

As for cooking, what a bore that is. It's such a faff, thinking of what to
have, buying it and cooking it and clearing up, then all you do is eat it -
and have to start all over again next day. Hunter Davies, RT 2017/2/4-10