In the differential, we are allowed to eliminate cyl correction if it is less than 1 diopter. But why are we not advised to reduce only a quarter diopter? if we reduce by 1D isn’t that too much?
I think that Jake explains that when we eliminate the cyl correction if it is less than 1 diopter, we also adjust by substituting a half diopter in sph for the full diopter of cyl.
So, if my differentials would otherwise be at a -5.50 sph -1.00 cyl, I’d add back .50 to the sph to account for the drop in cyl therefore giving me a -6.00 sph and zero cyl. I think this makes the adjustment easier. It is working well for me.
If someone else can confirm that I’m explaining correctly & clearly, I’d appreciate it!
EDITED TO ADD: Okay, I double-checked and re: differentials and astigmatism, Jake recommends this: “You usually don’t want to have astigmatism correction for your close-up lenses. If your astigmatism is less than -1.00, it’s usually worth eliminating completely. Substitute half a diopter in spherical (just regular myopia diopter) for a full diopter of astigmatism.” Hope this helps you, Stevan!
No DSAs, but can I e.g. do:
N: -8.5/-3.5x180, reduced sph
D: -6.5/-2.5(-3)x180, sph is not increased
I double-checked and added Jake’s recommendation re: reducing cylinder on differentials if you have a -1.0 cyl or less to my note above - Thanks!
Usually / often, certainly not a blanket recommendation.
Thanks for the explanation
Sorry, meant to put that in there! Thanks for taking a look, Jake!