Reviewed for medical accuracy by Dr Evelyne Jonniaux, Medical Advisor
Last updated 28 September 2026
There is no visual acuity threshold at which a cataract is operated on. The reference American guideline says the opposite explicitly: the decision must not rest on Snellen acuity alone. The threshold is functional, not numerical.
The questions we get asked
At what level of vision should it be done?
The question has no numerical answer, and that is not an evasion. The American Academy of Ophthalmology guideline states that preoperative distance acuity is an unreliable predictor of postoperative functional improvement, and that testing only at distance with high-contrast letters underestimates the problems patients actually experience. Any article quoting a figure as the criterion for surgery departs from the reference.
Does waiting do harm?
Beyond a certain delay, yes, but the boundary is blurred and nobody has tested it directly. A review of 27 studies finds better outcomes below six weeks of waiting, and more visual loss and more falls beyond six months. In between, its authors write that outcomes remain unclear. The American Academy, for its part, speaks of four months. Neither threshold comes from a randomised trial.
Does surgery reduce falls?
For the first eye, yes: a trial in 306 women over 70 gives a 34 percent reduction in the rate of falls, and 4 fractures against 12. For the second eye, the same team with the same protocol finds a 32 percent reduction that does not reach statistical significance. Saying that cataract surgery reduces falls without specifying the first eye is an extrapolation.
What about the second eye then?
Its benefit is real but binocular and self-reported, not a gain on the chart. The 1998 British trial describes clinical differences as “only slight”, with gaps of 11 to 30 percent on reported activities and a clear gain in depth perception. Its cost-effectiveness at one year is poor in patients who are not much bothered, and becomes acceptable over a lifetime.
Which lens should be chosen?
This is where the evidence is most asymmetric, and it deserves saying. For multifocal lenses, the Cochrane review grades the most marketed benefit, spectacle independence, as low certainty with documented publication bias, and the harm, halos, as moderate certainty with risk multiplied by 3.6. The risk is better proven than the benefit.
For toric lenses it is the reverse: benefit established at high certainty, with no cost in photic phenomena. These are not “two premium options”, they are two very different evidence files.
What the figures say
| Finding | Figure | Source |
|---|---|---|
| Acuity threshold for surgery | none, explicitly | AAO, Cataract in the Adult Eye, 2021 |
| Falls after first-eye surgery | reduced by 34 percent | Harwood et al., Br J Ophthalmol, 2005 |
| Falls after second-eye surgery | 32 percent, not significant | Foss et al., Age Ageing, 2006 |
| Multifocal lenses, halos | risk multiplied by 3.6, moderate certainty | Cochrane, 2016 |
| Endophthalmitis, Swedish registry across 464,996 operations | 0.029 percent | Friling et al., 2013 |
| Retinal detachment after cataract surgery, each patient their own control | risk multiplied by 4.23, persisting 10 years | Bjerrum et al., Ophthalmology, 2013 |
Three widespread figures we could not source. “Cataract surgery is the most performed operation in the world”: no global ranking by procedure type is published; “one of the most performed” is defensible, “the most” is not. “The operation succeeds in 98 percent of cases”: no source defines and then quantifies a global success rate. And “halos fade through neuroadaptation” is not a finding of the Cochrane review, which documents no resolution over time.
What Noria Health does, and does not do
We organise an ophthalmology consultation with a specialist team near Brussels, acuity measurement, lens examination and biometry included, and confirm feasibility within 24 to 48 hours. Follow-up is documented at D14, D30 and D90.
We do not set a surgical indication remotely, we do not choose the lens for you, and we never recommend bringing an operation forward on grounds of convenience alone.
Who reviewed this page
Noria Health editorial team.
See also: all our articles on ophthalmology.
Have your case reviewed. Noria Health arranges a specialist consultation near Brussels and confirms feasibility within 24 to 48 hours. Open a case.