Alisa Sivak, MA, DipEd

Alisa is Communications Coordinator at the Centre for Contact Lens Research, University of Waterloo, Canada

Clinical performance

Mark Willcox and colleagues (Institute for Eye Research and School of Optometry and Vision Science UNSW, Molecular and Health Technologies, CSIRO, Australia) reported that lotrafilcon B and galyfilcon A lenses produced corneal staining (but no redness) after soaking in a PHMB-based lens care system. Compared to lenses inserted directly from the blister pack, the lotrafilcon A lenses were less comfortable and produced an increase in burning/stinging after soaking in the PHMB-based solution; the same lenses were associated with an increase in lens awareness and itchiness after soaking in a polyquad-based system. Compared to lenses inserted directly from the blister pack, comfort with galyfilcon A lenses decreased after soaking in the polyquad-based system, along with an increase in burning, staining, lens awareness, redness, and pain and tearing upon insertion. X-ray photoelectron spectroscopy also highlighted significant changes in the composition of the surface of lenses soaked in multipurpose solutions (different for each lens-solution combination).

D. Tilia and colleagues (Institute for Eye Research, University of New South Wales, Australia) reported that comfort and clinical performance of two- and four-week replacement silicone hydrogel lenses (lotrafilcon B+copolymer 845 OR comfilcon A) worn in conjunction with a hydrogen peroxide care system were similar at four vs. two weeks of lens wear.

J. Diec and colleagues (Institute for Eye Research, Australia) compared clinical performance, adverse events, physiological and subjective responses with different combinations of lens care products and silicone hydrogel lenses (galyfilcon A, senofilcon A, lotrafilcon A, lotrafilcon B, balafilcon A or comfilcon A) over three months daily wear. 236 subjects used a polyquad-based lens care system; 237 subjects used a PHMB-based system; 292 subjects used peroxide. The polyquad-based solution was associated with a higher number of “first-event” corneal inflammatory events and poorer handling and comfort compared to the other solutions. 

After determining which items from the Contact Lens Dry Eye Questionnaire (CLDEQ) had the highest correlation to “overall opinion”, R.L. Chalmers and colleagues (Indiana University School of Optometry, USA; Johnson and Johnson, USA) tested a subset of eight items to see how well they reflect change in overall opinion after refitting. Participants wore both senofilcon A and balafilcon A lenses bilaterally (crossing over to the second pair of lenses mid-study).  Frequency and late day intensity of discomfort, dryness and blurry vision that clears with a blink were all significantly and highly correlated with overall opinion.


Oxygen

D. Fonn and colleagues (Centre for Contact Lens Research, University of Waterloo, Canada) compared central and peripheral corneal swelling after eight hours of sleep in eyes wearing silicone hydrogel lenses with varying levels of oxygen transmissibility (lens in one eye, no lens in the other). Although there was no significant difference between lenses, there was a significant difference between subjects, irrespective of lens. There was also a significant correlation between the lens-wearing and control eye.

L.M. Harp and colleagues (The Ohio State University, College of Optometry, USA) reported significant differences between static (no blink for five minutes) and dynamic (blink once every five seconds) lens wear with respect to corneal oxygen uptake. The highest difference was found with lotrafilcon A and lotrafilcon B lenses. In descending order, differences were also found with comfilcon A, Menicon Z, and senofilcon A lenses. The team concluded that differences among contact lens material and designs are related to both corneal oxygen dynamics and tear exchange.

Working with galyfilcon A lenses, B.A. Fink and colleagues (Ohio State University, USA) applied a polarographic electrode at the corneal centre and determined that highly individualized hypoxic stress occurs with blinking. These findings suggest that factors other than lens modulus (e.g. tear viscosity, lid tension, lid movement) may have an influence on post-lens oxygen uptake rate.


Physiology

H.S. Ginis and colleagues (Institute of Vision and Optics, University of Crete, Greece) evaluated forward light scatter induced by hydrogel and silicone hydrogel contact lenses. Subjects wore a hydrogel lens on the left eye and a lotrafilcon B lens on the right eye. Both contact lenses retained their normal transparency over the study period, consistently exhibiting a scatter ratio of 3% with no statistically significant changes. There was no statistically significant difference in visual acuity or contrast sensitivity over time. The silicone hydrogel lenses were associated with higher comfort ratings. 

M.F. Mowrey-McKee and colleagues (Toxicology/Microbiology CIBA Vision; Emory University, USA) reported a decreased level of corneal lactate in the corneas of rabbits wearing lotrafilcon A lenses (compared to no lens wear) over a six-hour period. 

D. Alonso-Caneiro and colleagues (Contact Lens and Visual Optics Lab, Queensland University, Australia) assessed the use of enhanced high speed videokeratoscopy to quantify the tear film surface quality in subjects wearing silicone hydrogel lenses. Values were significantly better on the bare eye compared to eyes wearing contact lenses, including silicone hydrogels.

D.L. Meadows and colleagues (Alcon Research, USA) reported that contact lens-induced conjunctival staining with silicone hydrogel lenses may be the result of changes in lens parameters that occur over a week’s wear of etafilcon A lenses. One study conducted by this group found a decrease in contact lens-induced conjunctival staining (in patients who had staining with habitual lenses) when lens material or base curve was changed. A second study measured base curves of senofilcon A lenses following one or two weeks of wear with a polyquad-based or peroxide solution. With both solutions, the base curves of silicone hydrogel lenses steepened after one week of wear, returning to baseline within a few hours of lens removal.  Base curve changes and recovery are influenced by temperature. The third study confirmed that both base curve and corneal curvature change following one week’s wear of senofilcon A with use of polyquad-based, PHMB-based and peroxide solution. 
Contact lens manufacturers employ surface coating and modifications to mask the hydrophobic nature of the bulk lens. T.Y. Edwards (LSU Eye Center, USA) and colleagues (Alcon Research Laboratories, USA) tried to image hydrophobic domains on lenses exposed to artificial tear fluid or worn for one day. Although exposure to both artificial tears and wear significantly decreased the staining response for all lenses, the trend remained the same. Balafilcon A lenses produced the most staining, followed by galyfilcon A, senofilcon A and lotrafilcon B.

L.E. Khinde and colleagues (Vision Sciences, School of Optometry, University of Alabama, USA) examined the inflammatory response to 30 days of continuous versus daily lens wear.  Tear samples were collected from subjects wearing balafilcon A lenses for 30 days of continuous wear in one eye and daily wear in the other eye.  Cytokine trends indicated that continuous wear presents a more pro-inflammatory ocular surface environment than daily wear.

Investigating the release of surface-active substances from soft contact lenses and their influence on lens-surface wettability in vitro, T. F. Svitova and M.C. Lin (University of California Berkeley Optometry School, USA) measured advancing and receding contact angles along with surface tension, on lotrafilcon A, lotrafilcon B, balafilcon A, Biofinity, senofilcon A and galyfilcon A lenses, straight out of the blister pack and after soaking for seven days in a polyquad-based lens care system.  Surface tension associated with the packaging solution was lower than that associated with the lens care system. 


Lens care and comfort

Nicole Tanti and colleagues (University of Waterloo, Canada) found that the viability of immortalized human corneal epithelial cells decreased to 20% when exposed to lotrafilcon A and balafilcon A lenses soaked in polyquad- and PHMB-based multipurpose solution. After 24 hours of contact with the polyquad-based solution, viability decreased to 50%. 

After soaking balafilcon A lenses in cases pre-conditioned with a PHMB-based solution, J.R. Paugh and colleagues (Southern California College of Optometry; California State University, USA; Alcon Research, USA) used the single drop method and a scanning fluorometer, confirm that higher levels of corneal staining are associated with greater fluorescein dye diffusion and an increase in dye penetration rate.

P. Situ and colleagues (Centre for Contact Lens Research, University of Waterloo, Canada) reported that higher conjunctival staining associated with multipurpose lens care systems is correlated with increased conjunctival chemical sensitivity. Their study examined ocular surface sensitivity to various stimuli a nylon thread (tactile), air at 50°C (pneumatic mechanical) and air mixed with carbon dioxide (chemical) in the eyes of 48 asymptomatic contact lens wearers with balafilcon A lenses. The lenses were disinfected with a polyquad-based solution and a PHMB-based solution, for two weeks at a time. 


Lens care and comfort

Analysing lens care and lens-packaging solutions, H. Sheardown and L. Liu (Chemical Engineering, McMaster University, Canada) found that polyvinyl pyrrolidone (PVP), a wetting agent embedded in narafilcon A lenses, was not released from the lens during a simulated wear period of 15 hours.
M.L. Heynen and colleagues (Centre for Contact Lens Research, University of Waterloo, Canada) determined the degree of lipid deposition associated with senofilcon A lenses when disinfected with a polyquad-based and peroxide system. Approximately 95% of the detectable lipid deposits extracted from lenses after two weeks of wear were cholesterol oleate. The lenses disinfected with the polyquad-based solution had 36% less total lipid than those disinfected with peroxide.

M.L. Read and colleagues (Eurolens Research, University of Manchester, UK) reported very little measurement error associated with semi-automated image analysis software used to measure contact angle assessment of contact lens surfaces. Error was more significant for materials with low contact angles. Contact angles, measured using the sessile drop method, were typically less repeatable than those measured using the captive bubble method, likely due to variability in lens blotting.

C.H. Powell and colleagues (Advanced Medical Optics, USA) reported that one month of a “rub” regimen PHMB-based lens care system left half the levels of lipid and protein recovered from lotrafilcon A lenses cleaned with a polyquad-based, “no-rub” regimen.


Inflammation and infection

J. Ozkan and colleagues (International Clinical Trials Centre, Institute for Eye Research, Australia; School of Optometry and Vision Science, University of New South Wales, Australia) reported that balafilcon A lenses coated with selenium, a biocidal agent, were able to inhibit bacterial colonization after incubation with Staphylococcus aureus 31 or Pseudomonas aeruginosa 6294.  Overall clinical performance was comparable to the commercially available balafilcon A lenses.

Despite better oxygen transmissibility, patients wearing silicone hydrogel lenses continue to experience corneal inflammation and infection. Wondering if this could be due to tear stagnation under the contact lens, M.L. Flint and W. Miller (University of Houston College of Optometry, USA) used in vivo fluorophotometry to determine tear exchange rate (overall, fast, and slow decay) in eight participants wearing seven different silicone hydrogel contact lens materials.  Lens movement and tear exchange rate were not different between silicone hydrogel and other lenses. Lotrafilcon A had the highest rate of slow decay and enfilcon A had the lowest. There was a positive correlation between lens movement and decay rate:  greater decay with increased movement. 

C. Lakkis and colleagues (Clinical Vision Research, Victorian College of Optometry, Australia; Alcon Laboratories, USA) fit 73 subjects with senofilcon A lenses and randomly assigned them to a polyquad- or PHMB-based care system on a contralateral basis. Bacterial culturing showed that cases become contaminated with gram-positive and gram-negative bacteria after just one week of use, but are more likely to show moderate to heavy contamination after two weeks. Lenses become contaminated after one week, but less frequently and to a lesser degree. 

L. Szczotka-Flynn (Case Western Reserve University, USA) fit subjects with lotrafilcon A lenses for continuous wear and then followed them for one year. Results confirmed that lid and conjunctival microbiota are significantly associated with lens contamination. 33.3% of subjects had sterile lenses in both eyes across multiple visits. 31.7% had significant levels of microbial contamination on at least one lens across multiple visits. 53.7% of subjects had contaminated lids; conjunctival contamination was found in 11.2% of subjects.