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G.A. Zikos, K.J. Ciuffreda, S.S. Kang, A. Selenow, S. Ali, R. Robilotto, L.W. Spencer; Rotational Stability of Differently Designed Toric Soft Contact Lenses . Invest. Ophthalmol. Vis. Sci. 2006;47(13):80.
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© ARVO (1962-2015); The Authors (2016-present)
To compare objectively the rotational stability of two differently designed toric soft contact lenses over a range of naturalistic viewing conditions using a novel infra–red based technique.
The two lenses tested employed different methods of stabilization: (1) Accelerated Stabilization Design (Acuvue Advance for Astigmatism) and, (2) Lo–Torque® Design (B&L SofLens 66 Toric).
Four tasks involving saccades were performed:
1. Settling – free viewing 15 minutes post lens insertion,
2. Reading extended text (42oH. x 15oV) in primary position at 40 cm.
3.Visual search involving reading newspaper paragraphs randomly presented 12–30o from the center of the field
4. Version (±40o H, ±32o V) with controlled blinking simulating a peripheral vision task at 60 cm.
Lens position was continuously recorded with a head mounted, infra–red 60Hz video system and a digital photo–slit–lamp. The rotational position was determined by using ImageTool and PixelPort software. Measurement noise level was 1.2o(SD), and resolution was 0.2o(SD). All measurements were taken on the left eye under binocular viewing conditions in 20 subjects (10M,10F), ages 23–55 years (mean 35.5years). Contact lens powers ranged from +4.75 to –7.00D sph combined with –0.75 to –1.75D cyl.
The Acuvue lens was significantly more stable by about 2.5–fold during the settling task (mean SD= 3.11o vs. 7.31o, mean range 8.0o vs. 18.7o) and the version task (mean SD= 2.99o vs. 8.02o, mean range 9.4o vs. 23.6o)(paired t–test, p < 0.05). During the reading and search tasks, however, lens stability was similar. During the settling task, the Acuvue settled significantly faster than the SofLens (ANOVA, p<0.05). Off–axis rotation (absolute means in degrees) for the Acuvue and SofLens were, respectively: settling: 7.9 vs.6.7, reading: 6.3 vs. 6.1, search: 6.3 vs. 6.4, version: 6.4 vs. 12.8. These rotations would result in less than 0.50D and 0.75D of induced astigmatism, respectively.
The Acuvue design was more effective in stabilizing the lens than the SofLens design for two of the four conditions tested. This would result in a more stable lens, after insertion, as well as during common peripheral visual tasks involving large saccadic eye movements. Both lens designs provided acceptable performance in terms of the predicted amounts of undesirable induced astigmatism due to off–axis rotation.
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