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Introduction

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For many years I used to wear contact lenses but I was never quite comfortable putting a foreign body in my eye.

They can become quite uncomfortable towards the end of the day, have a tendency to fall out and get lost (particularly in dry air) and there is the ever present risk of infection/damage to the cornea.

Despite these risks the traditional view has been that contact lens use is "safer" than LASIK (the commonest type of Laser correction surgery).

A new meta-analysis study suggests that this may not be correct at least when it comes to long term infection risk.

The study from the "Journal of Cataract and Refractive Surgery" by Masters et al [1] suggests that LASIK has a lower long term risk for developing microbial keratitis (MK) than wearing contact lenses.

You can read the study or download it for free here.

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What is Microbial Keratitis

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The Moorfields Eye Hospital has a useful description [2]:

Microbial keratitis is an infection on the cornea – the clear window on the front of the eye. It is often related to contact lens
wear or, less commonly, due to a scratch on the surface of the eye or a pre-existing eye condition. Infection is more likely with incorrect contact lens cleaning or storage, incorrect use of disposable lenses or wearing lenses overnight. Microbial keratitis can be a serious condition if not treated and can sometimes affect your vision and may leave a scar, even with the correct treatment.

Just to be clear MK is is more serious and presents greater risks than the more common and generally milder type of eye infection "conjunctivitis" (AKA "pink eye").

Improper use of contact lens is one of the most common causes [1]:

The burden of microbial keratitis, and specifically microbial keratitis associated with contact lens wear, has more recently come forth. With approximately 38 million contact lens wearers in the United States, there were an estimated 1 million clinical visits secondary to microbial keratitis and contact lens–related ICD-9 codes in the year 2010.

It doesn't just occur with contact lens use though. Any kind of injury to the surface of the eye can be complicated by MK.

This includes accidental injury or eye surgery such as LASIK.

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Methods

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The authors performed a literature search on PubMed (a medical research database) to look for studies that covered contact lens use/MK and LASIK/MK.

Studies with a sample size of at least 1000 cases were then used to create a Meta-Analysis. This is a type of analysis that involves collating the results of multiple studies.

It is not quite as good as doing one massive study but as I have discussed in the past that is really not feasible in most cases due to cost limitations.

A meta-analysis provides a compromise solution.

Nine studies of contact lens use (1998-2008) were used and nine studies for LASIK (1999-2015).

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Results

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The main finding is that LASIK has a lower rate and hence risk of MK than contact lens use in the long term (5-10 years).

The advantage with LASIK is greatest when comparing to extended wear contact lenses - something which one would expect.

The results within the first year are more mixed (see Table 4 in paper) - this also to be expected as this is the post surgical period.

It should also be noted that some of the results did not reach statistical significance as often happens in medical research.

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Problems

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This paper has a nice summary of some of the major problems with their analysis and I would recommend reading this section if you are interested in the subject (p70-72).

One of the biggest problem from my point of view is that the amount of data is limited, particularly when it comes to LASIK.

This is to be expected because many more people use contact lenses than have LASIK eye surgery.

LASIK is also a more recent technology and as a result there is a smaller population of patients to gather statistics and perform research on.

When one is dealing with incidences that are in some cases only double figures this can present a problem for statistical analysis.

In addition we must consider some of the limitations that occur with meta-analyses in general. One of these is that the individual issues, limitations and problems with each study used in the analysis may interact in unforeseen ways.

That is one of the reasons why the ideal situation would be to do a single large scale study to assess the risks - although as I have discussed before this is not usually possible due to cost.

A further issue we must consider is that both contact lens and LASIK/eye surgery technology is constantly advancing.

This might mean that new advancements could shift the balance in terms of risk.

It is also important to mention that although MK is a major and serious complication it is not the only one for LASIK surgery or wearing contact lenses.

The variation in spectrum of complications means that a direct or exact comparison of risk between the two types of treatment may not be possible.

Finally I should also make it clear that I am not an ophthalmologist so there may well be things that I have missed here.

If you happen to be reading this and you are an ophthalmologist I would love to hear your educated opinion on this research.

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Conclusion

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As someone who has had LASIK surgery and previously used to wear contact lenses the findings here are very interesting.

The idea that long term contact lens use is more risky than LASIK certainly makes sense.

LASIK is (in most cases) a one off procedure and exposure to eye injury/infection.

On the other hand wearing contact lenses involves placing a foreign body on the surface of the eye for extended periods of time for as long as you use them.

As someone who is also diabetic (and so at higher infection risk) - MK was a serious concern when I was making my decision.

This research might help to reassure people who are hesitating about undergoing LASIK surgery for this reason.

It does not mean it is 100% safe but then no surgery is.

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Thank you for reading

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References

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1. Masters, Jordan, Mehmet Kocak, and Aaron Waite. 2017. “Risk for Microbial Keratitis: Comparative Metaanalysis of Contact Lens Wearers and Post-Laser in Situ Keratomileusis Patients.” Journal of Cataract and Refractive Surgery 43 (1): 67–73.

2. Hingorani, Melanie, Swan Kang, and Linda Langton. 2014. “Microbial Keratitis - Patient Information Leaflet.” Moorfields Eye Hospital NHS Foundation Trust. http://www.moorfields.nhs.uk/sites/default/files/a-e-microbial-keratitis.pdf.

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