Corneal thickness change induced by dozing while wearing hydrogel and silicone hydrogel lenses

The physiologic effects on the cornea of dozing while wearing contact lenses were assessed by using central corneal swelling as an index in relation with lens oxygen transmissibility (Dk/t).

Two hydrogel lens materials (nelfilcon A and etafilcon A) with a power of -0.50 diopters (D) and three silicone hydrogel lens materials (galyfilcon A, senofilcon A, and lotrafilcon A) with a power of -0.50 D were studied on 16 eyes of eight subjects with no previous experience of contact lens wear and no ocular disease. The subjects wore the lenses for seven continuous hours with their eyelids closed for 1 hour after the first 3 hours of lens wear to simulate a dozing condition. Corneal thickness was measured with a specular microscope with a built-in pachometer (Topcon SP-2000P). The same measurement was performed for the non-lens-wearing eyes as the control.

Swelling rates immediately after dozing were 4.8%+/-1.4% for nelfilcon A, 5.2%+/-1.7% for etafilcon A, 2.8%+/-1.2% for galyfilcon A, 1.9%+/-0.8% for senofilcon A, and 1.5%+/-1.6% for lotrafilcon A. The swelling rates for the two hydrogel lenses were significantly higher (P<0.001) than that for the control (1.8%+/-1.5%), and the differences remained significant after 3 hours. Conversely, none of the three silicone hydrogel lenses showed a significant difference (P>0.05) compared to the control at any measurement.

The results indicate that dozing with silicone hydrogel lens wear causes clearly fewer intense physiologic effects in oxygen performance than dozing with hydrogel lens wear.