Journal of The British Contact Lens Association最新文献

Thirty-one myopic patients, 20 of whom were experienced contact lens wearers, were fitted with 1-Day Acuvue lenses, −253(±0.18) dioptres (D) on average, at initial dispensing. These lenses are inserted in the morning and disposed of every night. After an initial examination, the patients were followed up after 1 week and 12 weeks of lens wear. Visual acuity was 1.25(±0.02) on average, at the 12-week follow-up, significantly (P <0.005) better with the 1-Day Acuvue lenses than with the patients' previous lenses. Subjectively reported symptoms decreased significantly (P <0.02) after the patients' previous lenses were replaced with the 1-Day Acuvue lenses (20 patients); dryness/burning decreased from 35% to 5% (P <0.001). Slit-lamp findings also decreased significantly (P<0.001), injection from 23% to 0% and tarsal abnormalities from 20% to 0% (20 patients). There were no true complications. All 20 experienced lens wearers had deposit problems before the study, but these disappeared with the 1-Day lenses. When the experienced wearers compared their former lenses with their new 1 -Day Acuvue lenses, the latter were judged significantly (P <0.01–0.001) better regarding comfort and vision, equal regarding determination of lens orientation and worse (P <0.01) regarding lens handling. Overall satisfaction — a general assessment — favoured the 1-Day lenses at a highly significant (P <0.001) level, however. Thus, the 1-Day Acuvue concept appears very attractive with regard to complication rate as well as performance.

A technique for measuring the electrical conductivity of hydrogels (range of water contents 38–75%) is described using samples in button form, the aim being to discover the correlations that exist between conductivity and other measurable variables such as water content and oxygen permeability. The technique overcomes the problem of electrode interface impedance by analysing impedance values over a range of frequencies, and the design of the conductivity cell allows effects of compression to be studied. Results so far indicate that reproducible conductivity values are obtained, that the conductivity rises, at an increasing rate, with increase in water content and that there is a correlation between electrical conductivity and permeability.

Lenses with toric peripheries and spherical optic zones have been advocated to improve the fit of rigid lenses on corneas with moderate astigmatism. However there is usually little discussion of the theoretical background to this fitting technique. A review of the manufacturing process permits the development of a model which will allow the computation of those optic zone data that are dependent on other specified lens parameters. These data then enable tear layer profiling to predict improvements in fit for specific lens designs and corneal models. Results from such calculations indicate that many lenses cannot be manufactured precisely as ordered and this could result in variability in specification and performance. The physical fit of tonic periphery lenses can be shown to be optimal when the selected parameters produce a monocurve back surface along the steep meridian. This is confirmed when fitting lenses in a clinical environment.

Every presbyopic patient (n = 257) attending for routine examination at a suburban optometric practice was offeredthe opportunity to wear disposable contact lenses in the form of monovision correction. Sixty subjects entered the 3-month study. Only 5% of the total number of presbyopis who attended initially, were prepared to continue as fee paying contact lens wearers. As has been found in other studies, monovision correction itself did not cause any significant visual problems (90% acceptance). It is concluded that disposable soft lenses for monovision correction of presbyopia is a viable economical alternative for a small number of selected patients.