Comparative clinical performance of rigid versus soft hyper Dk contact lenses used for continuous wear

The purpose of this study is to investigate the comparative clinical performance of two hyper Dk contact lenses: a silicone hydrogel lens (Focus Night & Day, Ciba Vision) and a rigid lens (Z-alpha, Menicon Co. Ltd.) when worn for up to 30 days of continuous wear (CW). The rigid lens was worn on an unplanned replacement basis, whereas the soft lens was replaced monthly.

One hundred subjects were recruited. Fifty neophyte subjects were randomly assigned into one of the lens types (25 subjects per lens type). Twenty-five existing daily wear (DW) rigid lens users wore the rigid study lens and 25 existing DW soft lens users wore the soft study lens. Visual acuity, lens fit, keratometry, refraction, lens surface assessment, physiological response, and subjective response were investigated at baseline and after 1 week of DW and 24 hours, 1 week, and 1, 3, 6, 9, and 12 months of CW. Analysis compared lens type (rigid vs. soft) and subject group (experienced vs. neophyte).

Sixty-eight subjects completed the study. Visual acuity was similar for the two lens types and subject groups. Lens fit was judged to be adequate in all subjects. Corneal curvature of subjects in the rigid groups became flatter by 0.13 mm compared with 0.04 mm for subjects in the soft lens groups (F = 14.7, p = 0.0003); the refractive findings mirrored these corneal changes. The increasing rate of deposition on rigid lenses was consistent with the fact that these lenses were not replaced during the study. Conjunctival hyperemia and staining were similar for the two lens types but greater among experienced wearers at baseline (F = 13.8, p = 0.0005; F = 5.3, p = 0.02, respectively). Corneal staining was higher for the rigid lens wearers (F = 5.6, p = 0.02) but this was mainly the result of the initial higher scores in the rigid lens experienced group. The change in papillary conjunctivitis was greater for subjects in the soft lens groups than rigid lens groups (F = 4.6, p = 0.04). Comfort was initially lower for the rigid lens neophyte group (F = 4.2, p = 0.0001), but after the CW phase started, there were no differences between groups.

Notwithstanding subtle differences in physiological responses, continuous wear hyper Dk rigid and soft silicone-containing contact lenses can be successfully worn by both those with previous contact lens experience and those with no history of contact lens wear.