Nancy Keir and colleagues (Centre for Contact Lens Research, University of Waterloo, Canada) examined a variety of hydrogel and silicone hydrogel lenses (including lotrafilcon A and B, balafilcon A, comfilcon A, galyfilcon A and senofilcon A) for differences in visual performance and aberrations. Despite some differences in measurable aberrations, there were no significant differences between lenses with respect to high- and low-contrast visual acuity, contrast sensitivity or subjective ratings of vision.
Reporting the results of a multi-site study of 76 habitual wearers of spherical contact lenses, John Buch and Youssef Toubouti (Johnson & Johnson Vision Care, USA) confirmed that narafilcon B daily disposable silicone hydrogel lenses are associated with excellent clinical performance, physiological response and subjective ratings. Corneal staining remained the same over the course of the three-month study, while both limbal and bulbar redness decreased when the subjects were refit with narafilcon B.
Katherine Osborn (Johnson & Johnson Vision Care, USA) and researchers in the UK (Visioncare Research,UK) confirmed that narafilcon A lenses are associated with higher comfort scores, significantly less bulbar hyperemia, and less inferior corneal staining, when compared to a daily disposable hydrogel lens. Narafilcon A also showed significantly less limbal hyperemia and inferior corneal staining than lotrafilcon B.
Neophyte daily disposable lens wearers and spectacle wearers experience similar levels of
comfort, according to Jeffrey Walline. He and a team from Ohio State University studied 94
subjects aged 15-39, all of whom had never worn contact lenses before. One group was
randomly assigned to wear narafilcon A lenses and the other to wear their own spectacles.
After one month, there were no statistically significant differences between contact lens and spectacle wear with respect to corneal vascularisation, conjunctival hyperemia, limbal hyperemia, corneal staining and papillary conjunctivitis. The contact lens wearers exhibited more conjunctival staining than the spectacle wearers, and contact lens wearers had a slightly higher papillary response at six months. Differences in comfort were also minimal: After one week, contact lens wear was associated with lower comfort ratings toward the end of the day, but after one month ratings were consistent throughout the day.
Despite continuous improvement in soft multifocal contact lens technology, many practitioners
continue to prescribe monovision or modified monovision lenses for presbyopic contact lens
patients. Joe Rappon and Peter Bergenske (CIBA VISION Corporation, USA) reported that the lotrafilcon B multifocal lens design had a positive effect on practitioner attitudes toward fitting multifocals. A total of 295 eye care practitioners were surveyed on their prescribing habits both before and after fitting ten of their presbyopic patients with lotrafilcon B multifocals, in a prelaunch evaluation of 2455 patients. Before the study, practitioners reported that they prescribed multifocal lenses 42.3% of the time; by the end of the study, practitioners reported that they expected to prescribe multifocals 59.6% of the time. Before the study, practitioners reported prescribing monovision 28.6% of the time; after the study, practitioners reported that they expected to prescribe monovision 17.8% of the time.
Dryness, wettability and comfort
Not all dryness symptoms in soft contact lens wearers relate to signs of dryness, according to Graeme Young (Visioncare Research, Ltd, UK) and colleagues at Alcon Research, Ltd., USA. One quarter of 225 subjects reporting a high frequency of dryness symptoms on the Contact Len Dry Eye Questionnaire had no significant signs of dry eye. Results were classified with respect to etiology of contact lens-related dryness: 31% were classified as having tear film instability, 25% aqueous deficiency, 6% lipid anomaly, 6% meibomian gland dysfunction, and 1% incomplete blinking.
The same group also reported a higher prevalence of contact lens-related dryness in North America (39%) compared to the UK (31%). In North America, dryness was significantly more common among female lens wearers (41% vs. 34%). In the UK, toric lens wearers were significantly more likely to report symptoms of dryness (42%) compared to spherical lens wearers (29%). Conventional hydrogel lens wearers were more likely to report dryness (32%) compared to silicone hydrogel wearers (28%). Dry-eyed wearers had significantly shorter habitual wearing times and comfortable wearing times.
Tiana Leung and colleagues (UC Berkeley School of Optometry, USA) reported that the wetting properties of soft contact lenses were affected by the surface-active ingredients in blister pack solutions or the in-built wetting agents in lenses, although this effect was much less pronounced for silicone hydrogel than for conventional lenses. The research team used a modified captive bubble setup, able to measure dynamic contact angles and surface tension, to examine lenses direct from their blister pack and after soaking in a surfactant-free solution. Measurements were also taken after drying each lens and rehydrating in fresh solution.
Thomas Salmon (Northeastern State University, USA) and colleagues (CooperVision, Inc., USA) reported no significant difference between omafilcon A and narafilcon A lenses with respect to in vivo surface drying. Nineteen subjects were included in this study, which examined changes in higher order aberrations in addition to subjective evaluations of comfort, dryness, vision, stability of vision and handling.
Cecile Maissa (Optometric Technology Group, UK) and others (Alcon Research, Ltd., USA) reported that lens edge design is an important factor affecting lens comfort, based on a study in which 27 habitual contact lens wearers wore a variety of contact lenses with different lens edge designs for a period of 10(±2) days. A "knife" edge was associated with the best comfort, whereas a "rounded" edge was associated with lower comfort scores.
Mera Haddad and colleagues (Eurolens Research, UK) reported that faster spreading of liquid across the lens surface (rate of liquid spreading, or "RLS") was associated with improved comfort and lower contact angles. RLS was measured using a novel on-eye wettability analyser, which delivered a drop of liquid (containing hyaluronic acid and fluorescein) onto the ex vivo lens surface, while a camera was used to image the RLS. The study was conducted using etafilcon A, lotrafilcon a, balafilcon A and senofilcon A, worn by ten adapted subjects—both direct from blister pack solution and after soaking in buffered saline.