I'll break this into multiple posts. Your comments imply you have cataracts, which may be part of the reason you've noticed reduced contrast sensitivity over time (in addition to the increased adds), in addition to the reality that as we age our eyes need more light and contrast sensitivity declines with age. Just as with presbyopia, the issue may be less noticeable at first but eventually becomes noticeable. One study compared contrast sensitivity with a high add multifocal IOL, +4D, with a monofocal and with the average of people in their sixties:
and shows both IOLS doing better, though with the multifocal fairly comparable to those in their sixties. (so perhaps not as good as someone your age, which I'm guessing from the add is less than that). This article has old data, I don't know if there are more recent summaries, but indicates the decline in contrast sensitivity with age:
Another paper is a reminder that monovision also reduces contrast sensitivity, in this case contact lens monovision didn't do as well as multifocal contacts:
I don't know which brand of multifocal contacts you use, oddly out of curiosity I checked and see one paper that doesn't refer to contrast sensitivity, but it does give an indication of visual acuity for different adds of an air optix multifocal:
The range of vision seems to be better in the data for the Symfony (or low add bifocal IOLs) than those. In terms of how far vision drops off from the best focal point of an IOL, that varies with the IOL and the person's natural depth of focus. Studies only give average (though sometimes a range, rarely a distribution). Often such information is contained in a "defocus curve" rather than a table, which is explained in these articles (I'm assuming since you develop software you can handle some math and data):
In terms of understanding what a particular visual acuity means in terms of what you can read, here is one chart giving visual acuity vs. print size and common examples:
There are charts online to convert logMar (often used on defocus curves) to snellen and other visual acuity metrics:
Often monofocal IOLs are included as control lenses in studies of premium lenses, so the Tecnis monofocal is included in charts of the Symfony's defocus curve, here are a couple of those, one from the EU site and then the US site:
One issue you seem to be concerned about is astigmatism correction postop, however you already have a low level of astigmatism and so it isn't clear how much if any you'll have postop. If you had corneal scans then you could ask the doctor's office for the results to see what they indicate about your level of corneal astigmatism (though scans they do for other purposes may not reflect posterior corneal astigmatism, which is usually minor but they discovered is useful to measure preop when planning).
Although most astigmatism tends to be corneal, there is sometimes lenticular astigmatism and cataracts can add to that. During surgery they either explicitly attempt to reduce your astigmatism by using incisions (often LRIs, limbal relaxing incisions) that cause your eye to reshape, or at least can try to plan the incisions for the surgery itself to be located to try to reduce astigmatism (rather than add surgically induced astigmatism).
Here is one paper on the issue of how much astigmatism should be corrected:
"These results provide a solid argument to leave small values of natural astigmatism, typically below 0.5 D, uncorrected in practical refractive and cataract surgery procedures."
I've seen other papers noting that people's brains do adapt to their habitual astigmatism, which seems to be why sometimes it isn't easy to adapt to prescriptions that alter it.
To explicitly address the questions:
"1) Am I correct in assuming that using multi-focal contacts or glasses with astigmatism correction over monofocal IOLs should be fine? "
Yes, though of course you'd likely use a high add multifocal contact lens with a monofocal set for distance, which may lower contrast sensitivity.
re: "2) How well does using multi-focal contacts work over multi-focal IOLs and extended depth of focus IOLs? I expect the first is a no go, but not sure is that holds true for Symfony IOL. "
I haven't seen any information on that, I'd be curious if anyone discovers any. I had planned out of curiosity to try that with the Symfony but hadn't, I should consider doing so at least with one eye. The reason I hadn't tried is unfortunately my cataract in one eye shifted my correction in that eye greatly preop, from -9D or so to -19D or so, and I needed to switch brands temporarily to get a high enough power and wound up with a GPC bump from the other brand that *still* hasn't gone away so I've avoided putting a contact lens in it.
It seems likely the multifocals wouldn't play well together., but then again perhaps the focal points multiply, e.g a bifocal with a bifocal winding up with 4 focal points and perhaps merging into a more continuous range. Obviously it would reduce contrast sensitivity and the range of light available at each focal point.
re: "3) Can glasses with astigmatism correction be used over multi-focal IOLs and extended depth of focus IOL? As per the last question I expect the first is a no but not sure for the Symfony IOL. "
That shouldn't be a problem with multifocals or the Symfony. I've been in contact with someone with a toric Symfony that wasn't oriented correctly and he was wearing astigmatism correcting glasses temporarily until it was rotated. Again though, it isn't clear whether you'll need or want any residual astigmatism correction, and if you do then they can also consider doing an incision in another procedure.
re: "4) If I have a monofocal IOL targeting -1.5D how fast does focus tail off in either direction? I am thinking of the loss of what little accommodation I have left and using phones/tablet etc. "
I addressed this one in an earlier post.
re: "5) How do the night time issues with Symfony (halos/rings) compare to multi-focal contacts? I appreciate it depends on which contacts but is it generally better/same/worse as I've found all multi-focal contacts have some effects which don't bother me too much."
Unfortunately I haven't seen data on the issue, but I assume it is much lower just as it is compared to multifocal IOLs. In general I don't recall seeing data on halo incidence with multifocal contacts, I'd be curious if you see any. I think the issue is studied more for IOLs because people can't merely stop wearing them if a problem arises. I do see this article mentioning surprising figures:
"The study, titled Needs, Symptoms, Incidence, Global Eye Health Trends (NSIGHT), surveyed 3,800 spectacle and contact lens-corrected subjects, 15 to 65 years of age, from seven countries (China, Korea, Japan, France, Italy, United Kingdom and the U.S.) to better understand the eye-related symptoms that vision-corrected patients experience. The NSIGHT data provided valuable information on how often patients experience halos and glare and the degree to which they found them bothersome.
About half of the spectacle and contact lens wearers surveyed reported suffering from the symptoms of halos (52 per cent and 56 per cent, respectively) and glare (47 per cent and 50 per cent, respectively) more than three times a week. More than four of five patients who experienced these symptoms found them bothersome (84 per cent and 89 per cent for halo and glare, respectively). "
Presumably most of those except some fraction of the older ones aren't even wearing multifocal correction.
I never really noticed any problems with multifocal contacts. My night vision is definitely better overall with the Symfony than I can recall it being even before cataracts, partly due to less glare disability from headlights, their brightness isn't as distracting for some reason, they don't distract from seeing the surrounding areas as much as they used to. So although I am in the minority that see halos with the Symfony, the mild translucent halos that I see through past/through are more then compensated for by less glare disability, and by having better visual acuity than I can remember having (which is sometimes the case for high myopes partly due to getting rid of the minifying effect of the correction they wear).
Thanks SoftwareDeveloper for the detailed replies.
I currently do not have cataracts, just severe floaters which have got to the point I am considering FOV despite the risks as they affect my work. One of the surgeons I have seen normally combines FOV with lens replacement and posterior capsular lasering. This is because he believes that cataracts are inevitable within 2 years at most for patients of my age (52) and wants to minimise risk of further floaters. I will be posting some other questions about that aspect but want to think about IOLs as clear lens replacement was not my expectation with FOV even though I know the cataract risk.
Despite my age I still have good contrast sensitivity and that's why I think I am sensitive to the drop with multifocal contacts versus glasses. I've tried more than 10 types of multifocal contact as many suffer from poor intermediate focus but currently use Alcon Dailies Aqua Comfort Plus. These are good with minimal night time effects, it's just small text on large monitors is harder to read and glasses with just the minor astigmatism correction don't improve matters (it varies between contact lens design but these are the best otherwise).
Biometry showed -1.1 left and -0.65 right eye astigmatism so not quite in line with the glasses prescription allowing for their different distances so perhaps the lens is offsetting this (or rear of cornea). The surgeon said he's not sure the left is enough for a toric IOL but he may be wanting to reduce the risk with positioning and capsular lasering and this is why residual astigmatism is a concern.