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

PURPOSE: 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). METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Comparison of corneal endothelial bleb formation and disappearance processes between rigid gas-permeable and soft contact lenses in three classes of dk/l.

PURPOSE: To compare corneal endothelial bleb formation and disappearance processes between rigid gas-permeable (RGP) contact lenses and soft contact lenses (SCL) in the same class of oxygen transmissibility (Dk/L). METHODS: Experiments were conducted on 20 eyes of 10 nonwearers of contact lenses using six kinds of RGP lenses or soft lenses with hyper (A), high (B), and medium (C) classes of Dk/L. Each subject kept their eyes closed for 20 minutes after putting on each test lens. Starting just after eye opening, the subjects' eyes were examined for blebs every 5 minutes by specular microscopy, and percentage area of the blebs were calculated. For control, the same eyes were also examined without contact lens wear. RESULTS: The percentage area of the blebs just after eye opening was 1.2% for RGP-A, 1.7% for SCL-A, 5.1% for RGP-B, 4.7% for SCL-B, 6.9% for RGP-C, 8.6% for SCL-C, and 0.4% for the control. The difference from the control became insignificant in the bleb disappearance process just after eye opening for RGP-A and SCL-A, after 5 minutes for RGP-B and SCL-B, after 10 minutes for RGP-C, and after 30 minutes for SCL-C. CONCLUSIONS: Regarding bleb formation and disappearance, there was no difference in influence on the corneal endothelium between RGP lenses and soft lenses with similar Dk/L in the high and hyper classes. In the medium class, however, it was suggested that RGP lenses may have less of an impact on the corneal endothelium than soft lenses do.

Differences in contact lens-induced responses in the corneas of Asian and non-Asian subjects.

PURPOSE: To investigate ethnic differences in corneal endothelia bleb formation and corneal swelling during contact lens wear under closed-eye conditions, with the use of lenses of varying oxygen transmissibilities (Dk/L) in Asian and non-Asian subjects METHODS: Asian and non-Asian contact-lens naive subjects were fitted with one of four different types of contact lenses at each 20-minute session. During lens wear, the eyelid was closed Endothelial bleb formation was determined by specular microscopy or confocal microscopy immediately on eye opening. Some Asian contact-lens naive subjects were asked to wear one of two types of lenses (Dk/L values of 24 and 175) on each eye for 1 hour Corneal swelling was determined immediately after opening of the eyes. RESULTS: Asian subjects had a significantly higher degree of endothelial bleb formation than the non-Asian population for all closed eye conditions, p=0.0001. There was no significant difference in endothelial bleb formation between closed eves with or without lenses in the non-Asian population. There was a significantly higher degree of bleb formation with low Dk/L lenses, < or = 40, compared to high Dk/L lenses, > or = 110, in Asian subjects, p=0.0001. CONCLUSIONS: There is a significant difference between Asian and non-Asian subjects in the corneal response to stress. Under a closed eyelid only contact lenses with very high levels of Dk/L do not cause cornea stress in Asian patients.