Eye rubbing, floppy eyelids and keratoconus before LASIK: why the cornea is scanned first

Most people think of LASIK as a procedure on the cornea, the clear front window of the eye. Before it, the cornea is scanned for weakness, and two things from my side of the eye, a rubbing habit and a loose upper lid, are among the clues worth asking about. This article explains why.

Does eye rubbing cause keratoconus?

Rubbing is associated with keratoconus, a condition where the cornea slowly thins and bulges into a cone, and it may contribute. Whether it causes it has not been settled. A 2021 meta-analysis found a pooled odds ratio of 6.46, but the studies were few and uneven.

The detail matters. That systematic review found eight case-control studies, six of which could be pooled. The pooled odds ratio was 6.46, with a confidence interval of 4.12 to 10.1, and the studies disagreed with each other considerably. All scored only moderate for methodological quality, and the review states that the cause-and-effect order in time cannot be determined. In other words, people with keratoconus rub more, but we cannot be sure rubbing came first. An Iranian case-control study of 100 people with keratoconus found severe eye rubbing, with an odds ratio of 10.6, among several associated factors, alongside family history and vernal keratoconjunctivitis, a severe allergic eye disease.

A 2007 review argued that it is reasonable to conclude that abnormal rubbing is a cause of some types of keratoconus, not because all rubbing leads to it, but because rubbing may raise the likelihood. It also suggested the same rubbing and ectasia link may extend to ectasia after LASIK, as a hypothesis, not a finding. My reading is cautious: rubbing is a modifiable habit that is worth stopping whether or not it proves causal. Why children rub, and what to do about it, is in Dr Chan Li Yen's article on why kids rub their eyes.

What is floppy eyelid syndrome, and how is it linked to keratoconus?

Floppy eyelid syndrome is an upper lid so lax that it turns inside out easily, with an inflamed, bumpy lining. It is associated with keratoconus and with obstructive sleep apnoea. The association is established, but the reason is not.

A 2020 review defines it as eyelid hyperlaxity with reactive palpebral conjunctivitis, frequently associated with keratoconus and obstructive sleep apnoea, and says all patients with ocular irritation should be evaluated for it. The relation also runs the other way. A 2013 study found people with keratoconus had more lax eyelids and a more rubbery tarsus, the plate that gives the lid its stiffness, than matched controls, and a higher prevalence of sleep apnoea (24%, 14 of 50) and obesity (52%) than the general population. That was a small study, with only 15 people per group for the lid measurements.

The proposed common thread is tissue breakdown. A 2019 review reports that reduced corneal hysteresis, a measure of how well the cornea absorbs and dissipates force, has been found in floppy eyelid, keratoconus, glaucoma and sleep apnoea, and may relate to increased enzyme activity that breaks down elastin. The review itself calls this a potential shared pathway. It also notes that some studies find no link between sleep apnoea and floppy eyelid. A 2023 meta-analysis of nine studies found a positive association (odds ratio 1.89, interval 1.27 to 2.83) that grew with sleep apnoea severity. Evidence on mechanism is thin, and I would not tell anyone that a loose lid proves they have keratoconus, or the reverse. It is a reason to look, nothing more.

If you snore, sleep badly or wake with a red eye, my floppy eyelid page explains the lid itself and what treatment involves.

Why does LASIK need a cornea that is strong enough?

LASIK works by removing tissue to reshape the cornea, so a cornea that is already weak can bulge further afterwards. That complication is called ectasia. A 2023 review calls post-LASIK ectasia one of the most serious complications of refractive surgery.

The FDA lists keratoconus among precautions, thin corneas among its screening risks, and warns that a refractive procedure on a cornea that is too thin may result in blinding complications. Moorfields Private says ectasia occurs infrequently and can often be treated successfully without a transplant, but that surgeons avoid laser in patients who may be at risk. A 2016 review identifies abnormal corneal topography as the most important identifiable risk factor, and a high percentage of tissue altered as the most robust one in people with normal scans. Other recognised factors are a thin remaining stromal bed, a thin cornea and high myopia. Age is also listed, and the review calls it one of the most overlooked. A 2023 review lists eye rubbing among the environmental factors.

What do corneal topography and tomography find?

They map the cornea so that a surgeon can see weakness that a normal eye test misses. Topography images the curvature of the front surface, and tomography, also maps thickness across the whole cornea. Together they screen for keratoconus and for corneas thin enough to be unsafe.

The 2016 review says placido-disc topography patterns act as a surrogate for corneal strength, and that tomography adds pachymetric and epithelial maps, which are thickness maps of the whole cornea and of its outer skin. It also describes the Ectasia Risk Score System, which weighs several risk factors together. No single number decides.

Where the eyelid surgeon comes in is the history that explains the scan. A rubbing habit, allergic eyes, a lid that everts easily, loud snoring or a diagnosis of sleep apnoea, and a family history of keratoconus all raise questions. Laser surgeons run the scans. An eyelid surgeon can look at the lids and tell the laser team what they saw. How the checks fit together is in the pillar article, and the full set is in the refractive section.

What happens if the scan shows keratoconus or a risk of ectasia?

The usual answer is that LASIK is not offered. Moorfields Private says there are plenty of good alternatives if scans suggest LASIK is unsuitable. And for keratoconus itself there is a treatment: corneal collagen cross-linking is widely used to treat progressive keratoconus and other ectasia.

Dr Chan Li Yen sets out what each laser does, and what comes before any of them, in her guide to LASIK, SMILE and PRK. The scan result is the gate, and a surgeon who respects it is doing the job properly.

In one line: cross-linking is used to stop the cone progressing, it is a treatment for the cone and not a way to remove glasses, and a refractive surgeon, not an eyelid surgeon, decides on it. For people with a high prescription whose corneas are not suitable for a laser, an implanted lens is another route, explained in Dr Chan's page on implantable lenses. It is a separate operation with its own risks.

What should I do if my eyes itch and I keep rubbing them?

Find out why they itch, and treat that. Common causes are allergy, dry eye and inflamed lid margins, all of which a doctor can assess. If you are considering laser, tell the surgeon that you rub, even if it seems minor, and say it before the scan.

For allergy and eczema around the lids, see the page on itchy, flaky red eyelids, and for crusting lid margins, the article on blepharitis. For floppy eyelids, the 2020 review lists conservative measures: aggressive lubrication, a night-time eye shield, and avoiding sleeping on the affected eye; where sleep apnoea is present, treatment may improve ocular signs. In refractory cases, corrective lid surgery can bring significant improvement.

The wider map of eyelid problems that make eyes look and feel tired is in the hub article. If anything on this page describes you, my advice is to have the cornea scanned before deciding anything about a laser, and not after.