Journal of The British Contact Lens Association最新文献

Tear volume, measured using a cotton thread test (CTT), was assessed in 91 Hong Kong (HK)-Chinese (46 females,45 males aged from 8 to 70 years) and 35 Singapore (S)-Chinese (21 females, 14 males aged from 7 to 65 years). The mean (±SD) CTT value of HK-Chinese and S-Chinese was 17.5 (±8.1) mm/min and 19.6 (±12.0) mm/min respectively. No significant difference in the CTT values between the two groups of Chinese was found, so their data were pooled. The mean (±SD) CTT value of the pooled data was 18.1 (±9.3) mm/min; 18.4 (±9.0) mm/min for female subjects and 17.8 (±9.7) mm/min for male subjects. Regression statistics of the pooled CTT values on age showed a correlation of −0.59 (p<0.01), suggesting that tear volume decreases with increasing age. No gender effect on tear volume for either group of Chinese was found.

We describe a method for the collection of cornea-derived lactate from the in vivo human cornea using a hydrogelas a collecting medium. The technique turns out to be precise ±4.8% and to show a good correlation, r = 0.78, with anoxia-induced stromal swelling

Patients with contact lens-associated papillary conjunctivitis have normally been managed using soft contact lenses.The aim of this study was, firstly, to see if these patients could be managed using hard gas permeable contact lenses and, secondly, to find out if there were any differences between the performance of two different types of hard gas-permeable materials. The results show a good refit success with hard gas-permeable contact lenses in a sample of 28 patients with asymptomatic contact lens-associated papillary conjunctivitis. The type of contact lens material used, however, did not affect the success rate.

Oxygen permeability of currently marketed hydrogel contact-lens materials is predictable from water content, asituation that has not changed for 30 years. Experimental hydrogels with greater oxygen permeability than expected from their water content have been tested but none are currently marketed. Rigid gas permeable (RGP) materials are very different. In 1993, RGP lenses manufactured from materials of permeability 10E-11 (cm²/sec) (ml O₂/ml × mmHg) up to 200E-11 (cm²/sec) (ml O₂/ml × mmHg) are available to practitioners. The RGP permeability data are more reliable than in previous years because the measurement methods have become standardised and reference materials are available.

Corneal ulcers induced by contact lens wear constitute the most serious and worrying adverse effect associated with thisform of ametropic correction. Risks have been shown to be higher for SCL than RGP and for EW than DW. Also in the UK, regardless of the modality of wear, disposable contact lenses have been reported to be associated with a much greater relative risk of ulcerative keratitis than conventional contact lenses. The UK studies, however, are case-control studies from referral centres that may not be representative of primary care contact lens practice, where the bulk of contact lens fitting is carried out. The current investigation was therefore a historical cohort study carried out in four UK contact lens practices representative of the UK mode of practice and geographic distribution. The study reviewed 647 conventional daily SCL wearers with a mean wearing time of 1.97 years and 780 disposable daily SCL wearers with a mean length of wear of 1.45 years. The results obtained lead to the following conclusions: the annualised corneal ulcer incidence rates were 1.10% for conventional daily wear soft contact lenses and 0.88% for Acuvue disposable contact lenses worn on a daily wear basis. The annualised incidence rates for corneal ulcers that might have been microbial in origin were 0.39% for conventional DW and 0.18% for disposable DW. With conventional DW, none of the ulcers encountered were central; four were paracentral and the remaining 10 were peripheral. The clinical picture observed suggests that the majority of the ulcers were not of a microbial origin, but self-limiting ‘sterile’ peripheral ulcers of yet unknown aetiology. By not differentiating ulcers by type/origin, other researchers may have substantially overestimated the true risk of contact lens related microbial keratitis. The results of this study seem to support the findings of similar studies carried out in other European countries, whereby DW with disposable contact lenses carries a similar or lower risk of keratitis than conventional DW.