Lens design, orientation affect toric soft contact lenses performance

Surrey, UK-Results of a non-dispensing, randomized study evaluating four commercially available toric soft contact lenses (TSCLs) highlight product performance differences in response to changes in head position and gaze direction that can be accounted for by differences in lens design, said Graeme Young, MPhil, PhD, FCOptom, FAAO.

The study comprised two parts, included 14 subjects, and compared the Acuvue Oasys for Astigmatism (Vistakon), PureVision Toric (Bausch & Lomb), Air Optix for Astigmatism (CIBA Vision), and Proclear Toric (CooperVision) TSCLs.

The Acuvue Oasys TSCL features the proprietary Accelerated Stabilization Design (ASD) technology, while the PureVision Toric and Proclear Toric have a classic prism ballast design, and the Air Optic TSCL features a modified prism ballast design. The study was performed at Visioncare Research Ltd., Surrey, UK, where Dr. Young is managing director.

One part of the study evaluated the effects of gravity on the rotational characteristics of the lenses by comparing lens orientation and visual acuity (VA) measurements obtained when study subjects were in an upright position and then in a recumbent position with the head positioned horizontally. The second part recorded lens orientation as subjects moved their eyes in the eight cardinal directions of gaze.

The findings, published in the journal of the British Contact Lens Association [Contact Lens & Anterior Eye, 2010;33:23-26], showed that while lens rotation occurred with all four products after a change in posture and head position, both the amount of rotation and corresponding loss of logMAR VA were least for Acuvue Oasys TSCLs.

The differences were statistically significant relative to the other three products for rotation results (p <0.0001) and comparing mean recumbent VA of the Acuvue Oasys TSCL with the PureVision Toric and Proclear Toric (p ≤0.015); the difference between the Acuvue Oasys TSCL and the Air Optix TSCL approached statistical significance (p = 0.076).

In assessing orientation change based on direction of gaze, all lenses tended to rotate inferionasally on both upgaze and downgaze. However, the amount of rotation on inferionasal version was significantly less for the Acuvue Oasys TSCL compared with all three of the other lenses (p = 0.0083).

"The quality of vision with TSCLs has vastly improved over the past few years thanks to both better design and improved manufacturing reproducibility," Dr. Young said. "However, our research shows there are product-related differences in performance with changes in head position and gaze that occur with usual daily activities.

"Given that precise orientation is mandatory for optimal vision and patient satisfaction with TSCL wear," he noted, "practitioners should consider whether the patient's lifestyle involves non-standard gaze activities and how these might affect a lens with a given design in order to make better use of the variety of choices now available.

"Given that the two eyelids move in mutually perpendicular directions, it's surprising that toric lenses work as well as they do," he said.