Fluctuation in visual acuity during soft toric contact lens wear.

PURPOSE: To quantify changes in visual acuity (VA) with soft toric contact lenses as a result of lens movement and/or rotational instability caused by versional eye movements. METHODS: A novel chart for vision assessment at near (40 cm) for soft toric contact lenses (VANT chart),consisting of a central, color-coded logMAR panel and eight peripheral letter targets set on a white background measuring 60 × 40 cm was constructed. In the developmental phase of the work, 10 subjects (20 eyes) wore 2 toric lenses in random order, and the impact of rapid and delayed eye versions in 8 directions of gaze on VANT acuity was investigated. In phase 2, 35 subjects (68 eyes) wore 4 toric lenses in random order, and a streamlined clinical protocol using the VANT chart was implemented. Standard assessments of toric lens fit and distance VA were also performed. RESULTS: Testing in the first phase showed no difference for change in VA for rapid vs. delayed version movements, (p = 0.17) but acuity reduction was greater for diagonal compared with horizontal/vertical versions (p = 0.06). As such, testing in phase 2 proceeded using rapid, diagonal versions only. In this second phase, there were differences for low-contrast distance VA measures between lens types (p = 0.02) and for both VANT baseline acuity (p = 0.03) and postversion acuity (p = 0.04), but no differences were found between lenses for magnitude of vision loss (p = 0.91), which was about one line. No relationship was established between the magnitude of vision loss and measured rotational stability (p = 0.75). CONCLUSIONS: This work has demonstrated that conventional approaches to measuring VA do not fully replicate the "real world" experience of soft toric lens wearers. The VANT chart has shown that VA is reduced immediately after versional eye movements and suggests that more dynamic methods of assessing visual performance should be considered for soft toric contact lens wearers, especially given the apparent inability of lens stability measurements to predict visual performance.

Short-term corneal endothelial response to wear of silicone-hydrogel contact lenses in East Asian eyes.

OBJECTIVE: To evaluate corneal endothelial bleb response to wear of silicone-hydrogel contact lenses in eyes of East Asian subjects. METHODS: A total of 24 subjects of East Asian origin, attended 3 separate sessions for a prospective, single-centre, trial. The following contact lenses were used: ACUVUE ADVANCE with HYDRACLEAR (ADVANCE, -3 dioptres), ACUVUE OASYS with HYDRACLEAR Plus (OASYS, -3 dioptres), Focus NIGHT & DAY (NIGHT & DAY, -3 dioptres) and SofLens 38 (+3 dioptres). A modified Balaam's crossover design was used to randomize presentation of sessions and contact lenses within sessions. Session 1 was a comparison between OASYS and SofLens 38 under closed eye conditions, session 2 was a comparison between ADVANCE and NIGHT & DAY under open eye conditions, and session 3 was a comparison between OASYS and NIGHT & DAY worn under closed eye conditions. Corneal endothelial images were captured with the Topcon SP-3000P noncontact Specular Microscope before lens wear, after 20 mins of wear with lenses on and 5 and 10 mins later after lens removal. Blebs were manually identified on these digital images by a masked observer. The area of blebs and total area under consideration were derived using ImageNet software and used to calculate percentage area of blebs. A boundary of equivalence of 1% was used as a clinically significant bleb area difference, and two-sided 95% confidence intervals were utilized to evaluate differences between lenses within each session. RESULTS: In session 1, SofLens 38 produced a mean percentage area of blebs of 8.0% under closed eye conditions, which was significantly different to that produced by OASYS (1.6%). In session 2, both Advance and Night & Day produced a mean percentage bleb area of 0.4% under open eye conditions. In session 3, OASYS and NIGHT & DAY produced statistically similar mean percentage bleb areas of 1.7% and 2.0%, respectively. CONCLUSIONS: The similarity of bleb responses induced by the silicone-hydrogel lenses under the tested wearing conditions is consistent with the proposition that increases in Dk/t above a certain level will produce minimal change in corneal physiologic conditions compared with that when no lens is worn.