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HomeminewsAK’s Easily Modified Risk Factors Confirmed

AK’s Easily Modified Risk Factors Confirmed

A study has concluded that compared to daily disposable (DD) contact lenses (CL), daily wear (DW) reusable CLs have a 3.9-fold higher risk of Acanthamoeba keratitis (AK) – the rare, vision threatening, parasitic infection, most often seen in CL wearers.

The study also identified five avoidable AK risk factors for DD lens users that can easily be communicated to patients.

Led by Scientia Associate Professor Nicole Carnt, and published in the United States journal, Ophthalmology, the study was designed to establish whether DD CL wear is protective for the development of AK compared to DW CL wear, and to identify risk factors for AK that are unique to DD users.

Interestingly the study found white British ethnicity was associated with a five-fold higher risk of AK

CL use is the principal cause of microbial keratitis (MK) – an infection on the cornea – in otherwise healthy eyes of people living in major economies. AK accounts for approximately 50% of the MK cases that result in sight loss, and as such, substantially impacts on quality of life and costs to the healthcare system.

Whether due to convenience or the reduced risk of MK compared to DW wear, DD lens wear is increasingly popular, and now accounts for over half the lenses fitted in some countries (60% in Australia in 2020). Despite the advent of new lens materials and (DD) lenses, the incidence of MK has remained unchanged at 2–4 per 10,000 over many decades of whom 0.2–0.6 per 10,000 will have sight loss. This is most likely due to contact lens behaviour – unlike bacterial keratitis in CL users, 90% of AK cases are associated with avoidable risks, making awareness key to maintaining eye health within this population.


The case control study was conducted in the southeast of the United Kingdom. Cases were DD and DW users, diagnosed with AK and either referred or self-referred to an Accident and Emergency (A&E) Department identified from an audit of hospital records from January 2011 until February 2013, and prospectively thereafter until August 2014.

Controls, recruited prospectively from February 2014 to June 2015, were also DW reusable or DD CL users. However, they had attended A&E as new patients with a disorder thought to be unrelated to CL wear.

All participants were asked to complete a questionnaire on their contact lens wear history, disinfectant solution history, lens use environment, eye care and demographics. Cases were asked to provide additional information on events leading up to their episode of keratitis.


The study identified DD CLs as protective for AK compared to both reusable soft and rigid lenses, with the population attributable risk percentage suggesting that approximately 30–62% of AK could be prevented by switching from reusable soft to DD lens use.

Additionally, five modifiable factors were identified that increased risk for AK in users of DD lens users:

  • Showering while wearing lenses – contaminated sea, lake, swimming pool, and domestic water has long been associated with AK.
  • Lens reuse – a lack of disinfection and/or the use of non-sterile liquid to maintain lens hydration.
  • Overnight wear – while bacterial keratitis has commonly been recognised as a risk factor among reusable soft and DD lens wearers, prior to this study, it had not been associated with AK.
  • Shorter wearing times – wearing DD lenses for 12–18 hours per day was protective for AK versus shorter periods; perhaps because of the increased risk of corneal infiltrates associated with overnight lens wear as well as factors like dry eye and microtrauma due to difficulty with insertion and removal.
  • Infrequent appointments with an eye care professional (ECP) – poor, or no aftercare instruction (the latter often associated with CLs purchased online), can negatively impact healthy contact lens wear behaviour.

Interestingly the study found white British ethnicity was associated with a five-fold higher risk of AK. The authors attributed this unmodifiable risk factor as possibly being related to cultural differences such as a greater risk-taking propensity.

Assoc Prof Carnt said ongoing research into AK is vital to protect the eye health of all contact lens wearers.

“While AK is rare, it is a devastating disease that we have shown halves the vision related quality of life of contact lens wearers. Just by avoiding water, using contact lenses in DD or DW lenses can halve the number of cases of AK, yet most contact lens wearers do not realise water exposure is a risk factor for AK and all other forms of keratitis also. Optometrists play a key role in educating wearers about healthy contact lens wear and it is vital that that we take a proactive role in this area of practice.

“As a rare eye disease, it is difficult to secure funding to continue research into AK. A strong AK patient network has worked with Fight for Sight charity in the United Kingdom to raise much needed funds, but more is required. If individuals or companies are interested in donating time or funds to assist this research, please contact me at: [email protected].”


Carnt N, Minassian DC, Dart JKG, Acanthamoeba keratitis risk factors for daily wear contact lens users: a case control study, Ophthalmology (2022), doi: https://doi.org/10.1016/j. ophtha.2022.08.002.