Reviewed for medical accuracy by Dr Evelyne Jonniaux, Medical Advisor
Last updated 28 September 2026
The 20-20-20 rule has no scientific source. It was invented in the late 1990s by an optometrist to simplify a message for the media, by analogy with a carpal tunnel study. The only published experimental test of it is negative on all three outcomes measured.
The questions we get asked
LASIK or PRK?
At one year, the Cochrane review comparing the two most performed techniques concludes they are comparable. What differs is recovery, faster with LASIK, and pain, less. The authors also flag a general methodological fault: nine of thirteen trials randomised eyes rather than people, and none performed the corresponding paired analysis.
Does SMILE avoid dry eye?
It reduces it, it does not avoid it. A meta-analysis finds better tear break-up time and better symptom scores than after LASIK at 1, 3 and 6 months, but no difference on the Schirmer test or on tear osmolarity. At six months the Schirmer remains impaired in both groups. And that meta-analysis rests on a single randomised trial.
What is the real satisfaction rate?
Two figures coexist and they do not contradict each other. The most quoted review gives 95.4 percent satisfaction, but from 19 articles retained out of 309, for operations performed between 1995 and 2003. The prospective studies by the US drug agency give 1 to 4 percent dissatisfaction, which agrees.
But the same studies give the figure that satisfaction masks: 43 to 46 percent of operated patients report new visual symptoms at three months, double images, glare, halos, starbursts. Being satisfied and having new symptoms is not contradictory. It is the heart of the subject.
Does surgery dry the eyes?
The aggregate figure says the opposite of the individual reality, and that is instructive. The prevalence of dry eye falls after the operation, simply because many candidates are already symptomatic contact lens wearers: fewer than half had a normal score before surgery. But among those with no dryness at baseline, about 28 percent develop some at three months. The aggregate masks a transfer, not a general improvement.
What are dry eye treatments worth?
This is the most disappointing field in the specialty, and it should be said. The Cochrane review on artificial tears, 43 trials and 3,497 participants, concludes there is uncertainty including against placebo. It flags 18 further registered trials, totalling 2,079 participants, whose results have never been published.
Punctal plugs: little or no symptom improvement, very low certainty, adverse events “reasonably frequent”. Lifitegrast met its objective endpoint and missed its co-primary subjective one: it improves what the clinician sees, not what the patient feels. Omega 3: negative trial, with a placebo group gaining 12.5 points, which probably explains much of the positive uncontrolled literature.
What the figures say
| Finding | Figure | Source |
|---|---|---|
| New visual symptoms at 3 months after LASIK | 43 to 46 percent | PROWL studies, JAMA Ophthalmol, 2017 |
| Dry eye arising in those who had none | about 28 percent | PROWL, 2017 |
| Dissatisfaction with the surgery | 1 to 2 percent | PROWL, 2017 |
| LASIK against PRK at 1 year | comparable, low-quality evidence | Cochrane, 2013 |
| Artificial tears against placebo | uncertainty, 2,079 participants never published | Cochrane, 2016 |
| Omega 3 in dry eye | no effect, placebo at minus 12.5 points | DREAM trial, N Engl J Med, 2018 |
Two figures we could not source. The prevalence of “computer vision syndrome”, often given as 50 to 90 percent, traces back to no meta-analysis. And we found no prospective study large enough to identify reliable predictors of dry eye after refractive surgery.
What Noria Health does, and does not do
We organise an ophthalmology consultation with a specialist team near Brussels, corneal topography and tear film assessment included, and confirm feasibility within 24 to 48 hours.
We do not declare anyone eligible remotely, we do not choose the technique for you, and we promise no refractive outcome.
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.