Help at Work II

[Barney]

From School of Optometry, Indiana University: http://www.opt.indiana.edu/lowther/html/keratoconus_etiology.htm#rgp

Rigid Contact Lenses
It has been suggested that the wearing of rigid contact lenses can cause keratoconus in some patients. One study (Hartstein) reported on four patients who had worn corneal contact lenses who developed keratoconus. Three of these patients only developed it in one eye, which is rather unusual.

In a study of 162 keratoconus patients (Gasset) a high number of the patients (26.5%) had been wearing rigid lenses an average of 7.15 years prior to the time of diagnosis. In the same study, only one case of keratoconus was found in a control group of 1248 soft lens wearers.

Mascai et al did a retrospective study of 398 eyes (199 keratoconic patients) whose disease was not attributable to other causes such as allergies, family history, or other syndromes commonly associated with keratoconus. They found that 53 patients (106 eyes) had developed keratoconus after having been fitted with contact lenses.

The average age of diagnosis of keratoconus in the patients wearing contact lenses was 32 years, which was significantly older than those not wearing contact lenses (average 19 years old) prior to the diagnosis of keratoconus. They had worn contact lenses for an average of 12.2 years for 15.3 hours per day prior to the diagnosis. Eighty-nine percent of the patients developing keratoconus after contact lens wear were wearing PMMA lenses, which are an older lens, made of a hard plastic that does not transmit oxygen. This is rather strong evidence that there might be an association between wearing PMMA lenses and keratoconus development. A possible alternative explanation is that most keratoconic patients are myopic (near-sighted) prior to a diagnosis of keratoconus and thus would naturally seek contact lenses. Often the patients with developing keratoconus, before diagnosis, have unsatisfactory spectacle vision and thus might ask for contact lenses in an attempt to find a correction resulting in better vision.

[Andrew MacLean]

Barney

the problem is that the epidemiology from both the United States and the Uk does not support contact lens wear as a credible cause of KC.

There is no significant increase in KC among those who started wearing contact lenses before they had KC diagnosed. This is not to say that nobody ever had a diagnosis of KC after wearing lenses, but the possiblity has to exist that the condition was pre-existing.

Andrew

[GarethB]

As I said before, there is as much suggesting contact lens wear has no adverse effect on KC as there is research showing lens wear does have an adverse affect KC.

Bottom line is KC is a lot easier to diagnose, we have had many a newbie in ablind panic as they have gone for laser treatment to be told they have KC and will need a graft! This all because technology has moved on improving detection. In the ned most of these people content themselves with the fact they are lucky as glasses still give them full vision without the hassles we go through.

To me lenses causing KC falls in the same catagory as eye rubbing. They are not the direct cause, but in some cases they can agravate the condition.

[Barney]

It seems that others including the School of Optometry at Indiana University and very many others in the US would disagree with whatever unspecified epidemiology you are referring to Andrew. I would love to hear from the person who claims he knows all the causes of KC.

As I said before, there is as much suggesting contact lens wear has no adverse effect on KC as there is research showing lens wear does have an adverse affect KC.

So either might be true presumably?

To me lenses causing KC falls in the same catagory as eye rubbing. They are not the direct cause, but in some cases they can agravate the condition.

I'd suggest that eye-rubbing that in total is unlikely to occur for more than a few minutes a day is rather different to wearing a piece of rigid plastic covering the cornea for 16 hours a day. We know that the PMMA lenses of the 60s were unsatisfactory which was why others were developed.

If we pretend we know all the answers before we do then we're less likely to find them.

This is a site that sells contact lenses among other services http://www.allaboutvision.com/condition ... oconus.htm
so would be unlikely to be prejudiced against them and yet they say: "Eye damage from keratoconus also can be linked to factors such as overexposure to sunlight, improper fittings of contact lenses, excessive eye rubbing, and continual (chronic) eye irritation."

What evidence or expertise do you have to dismiss their statement out of hand?

[Barney]

And from University of Illinois
http://www.uic.edu/com/eye/LearningAbou ... nses.shtml
http://www.uic.edu/com/eye/LearningAbou ... onus.shtml
http://www.uic.edu/com/eye/index.shtml

"What causes keratoconus?
The cause of keratoconus is unknown.

Who gets keratoconus?
Keratoconus has been found in all races and in both sexes but affects women more often. It occurs more frequently in patients with Down’s syndrome, allergies or congenital amaurosis (a rare form of blindness at birth). Keratoconus may also develop in persons who have worn contact lenses for a long time and who often rub their eyes with too much force. "

I think it's pushing it a bit to suggest that all these bodies are demented fools with lesser judgement than layman posters to this board.

[Matthew_]

I'm afraid I cannot add to the debate about the causes of KC. That debate still has some way to run but....
If you already have KC its seriously academic!

[John Smith]

Barney,

I can't really add much to this debate, but I have been told one of these facts before, and I've repeatedly been told that women and men are EQUALLY LIKELY to suffer from KC; at least in the UK.

The problem is that statistics from one geography do not correlate with similar statistics from another geography. There are just too many variables, I'm afraid.

[Sajeev]

Where are the studies that show the opposite, Gareth? I like to see them...

[GarethB]

Firstly if you go looking for negatives you will find them whatever the subject.

Secondly, let me ask this question;

If the wearing of contact lenses is so bad, why are we all wearing them instead of putting up with slightly less vision which supposedly will not add to the progression of KC?

If KC is caused by contact lens wear, why is it predominently first diagnosed in teenagers who preveously had no sight problems so never worn lenses or glasses?

As has been said on this forum in the past, rather than look at what causes KC perhaps we should be looking at what doesn't cause KC?

[Andrew MacLean]

Barney

Thank you for your gentle rebuke. The problem is that IU does not say that contact lens wear is a cause of KC.

They do say that KC can develop after years of contact lens wear; that is a statement of the obvious. It can aslo develop after many years of not wearing contact lenses.

It is journalistic spin to make the leap from x can develop after y to x is caused by y.

Still it is good to know that even in the great state of Illinois (from where my father came) they are leaving no stone unturned in the effort to track down the elusive cause of Keratoconus.

Andrew