In a 276-subject study (18 clinical sites) of adapted contact lens wearers over a two-week period, Susanna Jones and colleagues (Visioncare Research Ltd, UK) found that senofilcon A toric lenses provided better comfort and vision than balafilcon A toric lenses. Senofilcon A lenses also provided more predictable orientation on settling and resulted in less corneal staining.
Anne Brobst and colleagues (CIBA Vision) reported the results of a multi-centre clinical trial comparing the visual performance of two silicone hydrogel toric lenses that utilize different stabilization techniques: lotrafilcon B toric, which uses a prism ballast at the 4 and 8 o’clock positions, and senofilcon A toric, which uses a technique featuring four stability zones. Fit was significantly better with the lotrafilcon B lens: a greater percentage of these lenses had symmetrical centration and significantly less oscillation. The lotrafilcon B lenses were also statistically superior with respect to monocular visual acuity and subjective ratings of vision.
Mary Fahmy and colleagues (CIBA Vision) compared a PVA-based daily disposable lens with nelfilcon A in 44 daily disposable lens wearers. Nelfilcon A had better overall comfort, day and night vision, overall consistency of vision, handling at insertion, as well as overall satisfaction preference.
Multifocal and monovision
Joseph Rappon (CIBA Vision) and Michael Rothschild (private practitioner, USA) reported the results of a study comparing the performance of two centre-near silicone hydrogel multifocal contact lenses (lotrafilcon B and balafilcon A) in a population of emerging presbyopes. Visual acuity, ghosting, and biomicroscopy variables were similar for both lenses, but subjective ratings of vision and comfort, preference ratings, and “intent to purchase” were statistically superior for the lotrafilcon B lens.
Jill Woods and colleagues (Centre for Contact Lens Research, University of Waterloo, Canada) assessed the performance of two lotrafilcon B lenses for presbyopic patients, one monovision and one multifocal, using both objective and subjective ratings under “real world” conditions. Emerging presbyopes experienced with lens wear (not including presbyopic correction) were fit with these lenses, wearing each type daily for one week. Objective data were collected at dispensing and after one week of wear; subjective ratings were collected via Blackberry during lens wear, while participants performed specific, real-life tasks. Low-contrast, low illumination near acuity was better with monovision, while the subjective data revealed a statistically and clinically relevant difference in favour of the multifocal lens.
Jennie Diec and colleagues (Institute for Eye Research, Australia) conducted a retrospective analysis comparing rates of corneal inflammatory events (CIE) in participants wearing lotrafilcon B or senofilcon A lenses bilaterally for three months daily wear, with overnight disinfection in peroxide, PHMB, polyquad-Aldox OR polyquad-Aldox-tearglyde. The rate of significant CIE was not significantly different, but senofilcon A had a higher incidence of total (symptomatic and asymptomatic) CIE compared to lotrafilcon B, due to higher numbers of asymptomatic events. There were also significant lens-solution effects.
Wettability and tear film
Lakshman Subbaraman and Lyndon Jones (Centre for Contact Lens Research, University of Waterloo, Canada) determined that comfilcon A had significantly lower advancing sessile drop contact angles than surface-modified lenses (lotrafilcon A and B), whether they were measured straight from packaging solution or soaked in saline.
Michael Read and colleagues (Eurolens Research, University of Manchester, UK) developed a method of measuring dynamic contact angles on a curved surface, involving a series of still images “sliced” from a dynamic captive bubble movie taken with an OCA-20 contact angle analyser. A comparison of this data with manual contact angle measurements obtained using an elliptical curve-fitting tool indicated good agreement. Mean advancing contact angles ranged from 20.4 degrees with lotrafilcon A to 73.9 degrees with asmofilcon A, and receding contact angles ranged from 17.1 degrees (lotrafilcon A) to 22.1 degrees (senofilcon A).
Manal Gabriel and Walter Nash (CIBA Vision) compared contact angle and lipid adsorption of the new “enhanced” lotrafilcon A lenses (with plasma coating and a comfort additive in the packaging solution) and other silicone hydrogel lenses worn on a daily wear basis and disinfected with peroxide. The enhanced lotrafilcon A exhibited lower lipid adsorption than the other lens materials. It also exhibited lower advancing contact angle measurements, along with comfilcon A.
Mera Haddad and colleagues (Eurolens Research, University of Manchester, UK) reported that increasing temperature is correlated with an increase in contact angle (sessile drop technique) for both etafilcon A and balafilcon a materials.
M. Lira (Centre of Physics/Optometry, University of Minho, Portugal) and colleagues (Institute for Biotechnology and Bioengineering, University of Minho; School of Optics and Optometry, University of Santiago de Compostela, Spain) reported that silicone hydrogel lenses (balafilcon A, lotrafilcon A, lotrafilcon B, and galyfilcon A) became significantly more hydrophyllic after wear, while a conventional lens (etafilcon A) became more hydrophobic. These changes over wear, measured via advancing contact angle, were not accompanied by statistically significant changes in tear film stability.
Physical characteristics of lenses and their effects on the eye
Philip Morgan (Eurolens Research, UK) and Noel Brennan (Brennan Consultants, Australia) confirmed that although silicone hydrogel toric lenses offer clear advantages over hydrogel lenses with respect to corneal oxygenation, the difference between various silicone hydrogel toric lenses is minimal. They calculated this by measuring thickness profiles of commercially available toric and daily disposable contact lenses, and then combining these values with manufacturer-stated oxygen permeability to determine oxygen transmissibility profiles. They then estimated corneal consumption during open eye wear of the lenses, using oxygen diffusion calculations incorporating stromal thickness and posterior corneal oxygen tension changes at the corneal periphery.
Jason Nichols and colleagues (The Ohio State University College of Optometry, USA) determined the effectiveness of ultraviolet-absorbing silicone hydrogel contact lenses. Rabbits wearing senofilcon A (which absorbs 99% of UV-B and 90% of UV-A) or lotrafilcon A (no UV absorption) were exposed to UV-B and UV-A for five days. An examination of post-mortem tissues indicated that UV-blocking contact lenses are capable of protecting the cornea, aqueous humor and crystalline lens from UV-induced pathological processes.
In a double-masked study in which adapted soft contact lens wearers wore lotrafilcon B and etafilcon A lenses in contralateral eyes, Nancy Keir and colleagues (Centre for Contact Lens Research, University of Waterloo, Canada) reported that they were able to use a slit lamp modified to incorporate a customized hand refractometer to measure refractive index during wear without lens removal. The etafilcon A lenses had a statistically significant change in in vivo refractive index across the day; the lotrafilcon B lenses did not.
Jose Manuel Gonzalez-Meijome (Optics and Visual Science Research Group, University of Minho) and colleagues (University of Valencia, University of Santiago de Compostela) used atomic force microscopy to evaluate qualitative and quantitative topographic changes on the surface of worn contact lenses. Galyfilcon A, comfilcon A, lotrafilcon A, lotrafilcon B and balafilcon A had increased surface roughness after even short-term wear. Surface roughness of balafilcon A increased more slowly than the other lens materials.