Research Activities: Recent Studies

CONTACT LENS RESEARCH

Case contamination during daily wear of silicone hydrogel lenses

Adherence of Pseudomonas aeruginosa to silicone hydrogel contact lenses after continuous wear

Predictive Factors of Contact Lens Case Contamination

Assessment of cytokine levels in the tears of contact lens wearers and non-contact lens wearers

Comparison of cytokine levels in the tears and saliva

VISUAL FUNCTION RESEARCH

The handicap of abnormal colour vision

CONTACT LENS RESEARCH

Case contamination during daily wear of silicone hydrogel lenses

Carol Lakkis, Kate Weidemann, Ka-Yee Lian, Shelly Ames, Shubha Lakkola, Emma Beale

Silicone hydrogel lenses are becoming increasingly popular for daily wear. The aim of this study was to evaluate the incidence and level of microbial contamination of contact lens cases when used with daily wear silicone hydrogel lenses over one month. Forty-two subjects wore Lotrafilcon B (CIBA Vision) lenses and were randomly assigned to use AQuify MPS with the MicroBlock antibacterial case (CIBA Vision) for one lens and Complete Moisture Plus with a standard case (Advanced Medical Optics) for the other lens. Cases were collected for bacterial culture after one month of use, with subjects unaware as to
why the cases were returned.

There was no significant difference in overall rates of contamination between the two care systems, with 90% of MicroBlock and 100% of Complete cases contaminated after one month. However, significantly higher levels of contamination were observed in the Complete cases compared to the antibacterial cases; 43% of Complete cases showed moderate or heavy contamination compared to only 19% of MicroBlock cases (p<0.05, Figure 3). The rate of gram-negative contamination was also significantly higher in the Complete cases (48%) compared to the MicroBlock cases (26%) (p<0.05) and a greater number of bacterial species were isolated from the Complete cases compared to the MicroBlock cases (p<0.05).

Use of antibacterial lens cases may benefit contact lens wearers by decreasing the levels of contamination and numbers of potential pathogens in the lens case; however, contact lens
wearers should be encouraged to replace their cases on a monthly basis.

Figure 3: Levels of case contamination observed after 1 month of use. The MicroBlock cases showed significantly lower levels of contamination compared to the Complete cases (p<0.05).

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Adherence of Pseudomonas aeruginosa to silicone hydrogel contact lenses after continuous wear

Carol Lakkis, Shubha Lakkola

We have previously shown that the incidence of infiltrative events during continuous wear (CW) was significantly higher with balafilcon A (Bausch & Lomb) compared to comfilcon A (CooperVision) and lotrafilcon A (CIBA Vision) contact lenses (CLs).   This study aimed to (1) determine if P. aeruginosa adherence to silicone hydrogel CLs varies between CL materials, and (2) investigate the effect of phenotype (cytotoxic versus invasive) on P. aeruginosa adherence.

Worn CLs were aseptically collected from n=25 subjects participating in a contralateral CW study comparing comfilcon A with lotrafilcon A or balafilcon A.   Primary adherence of invasive (6294) or cytotoxic (6206) P. aeruginosa strains was assessed and compared to unworn control CLs.

There were no significant differences between adherence to worn and unworn comfilcon A CLs (p>0.05).   Greater adherence was observed with unworn lotrafilcon A CLs compared to unworn comfilcon A CLs; however, there were no significant differences between CL types after wear (p>0.05).   For balafilcon A, the cytotoxic strain showed significantly greater adherence after wear (p<0.05, Figure 1).

Figure 1: Mean (± SD) adherence of 6206 (cytotoxic) to unworn (U) and worn (W) lotrafilcon A (LotA), comfilcon A (ComA) and balafilcon A (BalA) CLs.   The cytotoxic strain showed significantly greater adherence to balafilcon A after CW (*p < 0.05).

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Predictive Factors of Contact Lens Case Contamination

Stephen Vincent, Carol Lakkis

Contact lens (CL) cases are potential reservoirs for microorganisms, which may be transferred to the eye during CL wear.   This study examined the relationship between CL case contamination and various potential predictive factors.   74 subjects were fitted with lotrafilcon B (CIBA Vision) daily wear CLs and were randomly assigned to use one of two PHMB preserved disinfecting solutions, with the corresponding regular lens case.   Clinical evaluations were conducted at lens delivery and after 1 month, when cases were collected for microbial culture.

91% of cases were contaminated and 35% contained gram-negative bacteria. Case contamination was significantly associated with type of care system used, reuse of disinfecting solution and subjective dryness symptoms (p<0.05).   Solution reuse significantly increased the likelihood of heavy case contamination (p<0.05, Figure 2).   There was no association between contamination and subject age, ethnicity, gender, average wearing time, volume of solution used, non-compliance score, CL power or subjective redness (p>0.05).  

Case contamination levels vary significantly between care systems, despite use of the same preservative.   It's difficult to predict the development of case contamination from a range of clinical factors; however, reuse of the disinfecting solution significantly increases the likelihood of heavy case contamination.   Case contamination may influence subjective comfort and this relationship is being investigated further.

Figure 2: Subjects who reused their solution were 11.35 (1.05 - 122.91) times more likely to have heavy case contamination compared to subjects who discarded their solution following CL insertion (p = 0.046).

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Assessment of cytokine levels in the tears of contact lens wearers and non-contact lens wearers

Carol Lakkis, Shelly Ames, Paul Connellan,* Linda Banbury,* Carol Morris * (*Southern Cross University, Australia)

Contact lens (CL) wear may be associated with ocular surface inflammation, contributing to dry eye symptoms. This study aimed to determine and compare the concentration of cytokines in the tears of CL wearers and non-contact lens (NCL) wearers.   Reflex tears were collected from n=18 soft CL wearers and n=31 NCL wearers using glass microcapillary tubes and cytokines were measured by flow cytometry.

A number of cytokines can be reliably detected in tears of CL and NCL wearers.   IL-12p70, IL-6 and IL-8 were present in both CL and NCL wearer tear samples but there were no significant differences between CL and NCL wearers (p>0.05).   TNF- a was significantly higher in CL tears compared to NCL tears (p<0.05, Figure 3).

This means that soft CL wear may stimulate TNF- a production, a cytokine involved in acute and chronic inflammatory responses.   Further investigation of the effect of CL type, wearing modality and correlation of cytokine levels with clinical signs and symptoms, will be beneficial for understanding ocular responses to CL wear.

Figure 3: Median concentrations of TNF- a measured in the tears of contact lens (CL) and non-contact (NCL) wearers.   The dotted line shows the detection limit of the assay. TNF- a was significantly higher in the CL tears compared to the NCL tears.

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Comparison of cytokine levels in the tears and saliva.

Carol Lakkis, Shelly Ames, Paul Connellan,* Linda Banbury,* Carol Morris * (*Southern Cross University, Australia)

The tear film is more stable than saliva; however, the potential for the tear film to be used as a source of diagnostic information has received limited attention.   This study aimed to assess the concentration of cytokines in the tear film and saliva and to determine whether a correlation between the cytokine levels in the two physiological fluids exists.   Reflex tears (using glass microcapillary tubes, Figure 4) and saliva (via by drooling into a plastic tube) were collected from n=48 subjects and cytokines were measured by flow cytometry .

IL-12p70, IL-6 and IL-8 were present in both tears and saliva, with IL-12p70 and IL-6 being significantly higher in tears compared to saliva (p<0.05).   IL-8 levels didn't vary significantly between the two fluids (p>0.05).   IL-1? was below the detection limit in tears but was significantly higher in saliva (p<0.05). TNF- a and IL-10 were below the detection limit in both tears and saliva.

When cytokines were detected in tears, the levels did not correlate significantly with concentrations observed in saliva (p>0.05).   The differences in cytokine levels between tears and saliva suggest that tears can be used as a source of diagnostic information; however, are more likely to provide localized rather than systemic information regarding inflammation.

Figure 4: Tear film collection from the inferior meniscus using glass microcapillary tubes.

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VISUAL FUNCTION RESEARCH

The handicap of abnormal colour vision

Barry Cole, Ka-Yee Lian, Ross Harris, Jennifer Maddocks, Carol Lakkis

Over the last two years, CVRA's colour vision group has investigated how clinical tests can be used to predict the extent to which people with abnormal colour vision will have practical problems in everyday life.   Attention has also been given to testing the colour vision of pilots.  

The International Civil Aviation Organization requires its member countries to ensure that all pilots can recognize signal lights and other colour codes used in aviation.   A crash during landing of FedEx flight 1478 at Tallahassee in 2002 was found to be due to the pilot's abnormal colour vision, even though he had passed the Farnsworth lantern and was thought to have had adequate colour vision.   The crash investigation recommended that colour vision testing of pilots be reviewed.

We showed that a pass at the Farnsworth lantern does ensure that pilots with abnormal colour vision will be able to recognise the main colours used in surface colour codes.   We found that the Farnsworth lantern test procedures do not adequately sample testees' ability to recognise signal lights and that the present pass criterion requires amendment (Figure 5).   We have recommended a change to the Farnsworth lantern test procedures and fail criterion in two publications.

Figure 5: Only 8 of 20 subjects who passed the Farnsworth lantern made no errors recognizing red, green and white signal lights and that 7 of the 20 subjects made errors quite often.   Figure from Cole BL, Lian K-L, Lakkis C. Aviat Space Environ Med 2008; 79: 509-513.