Clinical evaluation of factors affecting soft toric lens orientation.
OBJECTIVE
To evaluate the comparative orientation characteristics of currently available silicone hydrogel torics.


METHODS
The re-orientation characteristics of four toric lenses were assessed: three prism-ballasted (PB) designs, Purevision Toric (PVT), Air Optix Toric (AOT), Proclear Toric (PCT), and an "Accelerated Stabilization Design" (ASD) ACUVUE ADVANCE for Astigmatism (AAfA). In the first part of the study, the toric lenses were rotated, approximately 45 degrees in the infero-temporal direction and a video recording of lens reorientation was made from which blink-by-blink measurements of lens orientation were taken. In the second part of the study, subjects were positioned with their head orientated 90 degrees to the vertical and lens orientation photographed once it had settled.


RESULTS
In Part 1, the speed of re-orientation from oblique mis location was similar for the four designs tested and ranged from 22°/min (PVT) to25°/min (AOT). Lenses showed more rotation during rather than between the blink (p<0.0001). Between blinks, AAfA and AOT showed significantly more rotation than PCT and PVT (p0.04). There were no significant differences between lenses for rotation during the blink. The PB lenses showed faster re-orientation further away from the zero position.AAfA showed no significant difference in rotation speed with varying orientation position. In Part 2, all the PB lenses rotated significantly more under the effect of gravity than the ASD lenses.The mean total rotation of the AAfA lenses,from their settled position, was 11.4° compared with 25.9° for PVT (p0.01), 18.4° with AOT (p0.02) and 37.4° with PCT (p0.0002) [corrected]. The mean total rotation of the AAfA lenses, from their settled position, was 11.2 degrees compared with 32.8 degrees for PVT (p < 0.001), 16.1 degrees with AOT and 33.1 degrees with PCT (p < 0.001).


CONCLUSIONS
The four lens designs show similar re-orientation speeds. In the recumbent position, PB lenses rotate more from their normal settled position than ASD lenses.
Visioncare Research Ltd., Farnham, Surrey, United Kingdom. g.young@visioncare.co.uk
Graeme
G
Young
Roberta
R
McIlraith
Chris
C
Hunt
D001767:Blinking; D003263:Contact Lenses, Hydrophilic; D004867:Equipment Design; D006112:Gravitation; D006801:Humans; D009949:Orientation; D017755:Prosthesis Fitting; D012399:Rotation; D013997:Time Factors; D014741:Video Recording