Alisa Sivak, MA, DipEd

Alisa assists the Centre for Contact Lens Research by writing and editing publications, reports, grant applications, and educational communications.

The first half of our ARVO synopsis features comfort, wettability and the eye’s physiological response to silicone hydrogel lenses.   

V.E. Evans (Institute for Eye Research, University of New South Wales) and colleagues investigated factors associated with discontinuation of silicone hydrogel daily wear by conducting a retrospective, case-controlled analysis of various combinations of silicone hydrogel lenses and peroxide-, PHMB- and polyquad-based lens care regimens.  Results showed that discontinuations were more likely to be related to subjective comfort than adverse events.  Indicators for drop-out from lens wear included poor comfort, dryness, self-reported redness, self-reported poor vision and reduced wear time.

Deriving data from clinical and self-reported factors from a contact lens and ophthalmic history survey and a socio-demographic survey administered as part of the Contact Lens and Dry Eye Study, P. Ramamoorthy and colleagues (The Ohio State University) found that treatment factors significantly associated with dry eye include:  (1) a recent contact lens refitting and (2) use of artificial tears/rewetting drops.  FDA groups two (ionic) and four (non-ionic) high water content materials were more likely to be associated with dry eye symptoms than group one materials.  Dry eye symptoms were not significantly associated with wear modality, lens material or care solutions.

T.N.Truong and colleagues (School of Optometry Clinical Research Centre, University of California, Berkeley) conducted a series of fitting studies to determine which lens performance and ocular response measures are associated with subjective ratings of comfort and dryness.  The team examined records from 60 studies performed at one research site between 2005 and 2007.  Results suggest that researchers and clinicians should emphasize minimizing surface lens deposits to improve lens comfort and dryness, in addition to minimizing inferior corneal staining.  Lens tightness, primary movement and up-gaze lag were not significantly associated with comfort.

T.P. Kislan (Hazleton Eye Specialists, Pennsylvania) and F.A. Bucci (Bucci Laser Vision Institute, Pennsylvania) compared the performance of galyfilcon A with that of omafilcon A and hixifilcon A in dry eye patients.  Results showed that these specialty lenses were similar, out-performing silicone hydrogel lenses with respect to comfort, wear time, Schirmer’s scores and tear break-up time.

Using videokeratoscopy to investigate changes in tear film surface quality after the commencement of contact lens wear, B.J. Straker (Contact Lens and Visual Optics Laboratory, School of Optometry, Queensland University of Technology) found that the measurement of tear film surface quality differentiates between bare eye and lens-wearing conditions.  Results also showed a systematic improvement in tear surface quality during the first day of silicone hydrogel lens wear compared to baseline measurements.  

J.A. Bonanno (Indiana University) and colleagues set out to determine tear oxygen tensions and corneal oxygen flux under steady-state open and closed eye conditions in subjects wearing silicone hydrogel contact lenses.  The posterior surface of each test lens was coated with an oxygen-quenching phosphorescent dye, after which they measured the dye’s decay rates in open eye and following five minutes of eye closure.  Quenching constants for each lens type was then determined by coating the anterior surface, placing the lens on the eye and measuring decay rates with a goggle in place.  Oxygen flux was also calculated in open and closed eyes.  Results showed that at high Dk/t, in vivo tear oxygen tension under silicone hydrogel lenses is significantly lower and oxygen flux is higher than that predicted from modeling using equivalent oxygen percentage data.

Using two contact lens materials soaked in different MPS, G.A. Zikos and colleagues (Manhattan Vision Associates, New York) evaluated the feasibility of using a Shack-Hartmann wavefront sensor to identify differences in pre-lens tear film stability (and therefore wettability).  They observed a significant improvement in lens wettability with silicone hydrogel lenses combined with polyquad solution.  The researchers noted that the use of their novel wettability index metric is promising with respect to objectively characterizing differences in in vivo surface wettability.

P. Situ and colleagues (Centre for Contact Lens Research, School of Optometry, University of Waterloo) compared pneumatic mechanical and chemical sensitivity at different sites of the ocular surface in hydrogel and silicone hydrogel contact lens wearers.  Results indicated that the cornea and conjunctiva of contact lens wearers have different degrees of sensitivity to mechanical and chemical stimuli.  Silicone hydrogel lens wearers appear to have slightly higher mechanical and chemical sensitivity than hydrogel lens wearers.

R.C. Siwale and colleagues (CIBA Vision, Georgia) used in vitro cell culture models to evaluate the cellular viability of mammalian cells exposed to silicone hydrogel contact lenses cycled in lens care products.  Results indicated that silicone hydrogel lenses are least cytotoxic when cycled with a peroxide solution and most cytotoxic when cycled in a polyquad solution.

“Conjunctival epithelial flap” (CEF) is a condition in which a sheathing of epithelial cell layers occurs on the conjunctiva.  A.D. Graham and colleagues (School of Optometry, University of California, Berkeley) used statistical techniques to address questions such as:  the probability of developing CEF, the wearing time involved and the differences between different types of lenses.  Following gas permeable and silicone hydrogel lens wearers for 30 days of overnight wear, they found 65 occurrences of CEF in 149 subjects:  approximately 43 % in GP wearers and 44% in silicone hydrogel wearers.  Although these results indicate that the probability of developing a CEF is similar in GP and silicone hydrogel wearers, the mean “survival time free of CEF” was 91.3 days for the GP group compared to 70.0 days for the SiHy group when censoring was taken into account.