Journal of The British Contact Lens Association最新文献

A formula is developed to give the true thickness of a lens at various distances, measured radially, from the optical axiswhen the centre thickness, index of refraction and the power of the lens are known.

Using a non-invasive tear break-up time (NITBUT) technique, we measured the tear stability of 22 asymptomatic Hong Kong (HK)-Chinese before and after performance of the phenol red thread (PRT) test. One eye was used as the test eye while the fellow eye acted as control. The effect of performing the PRT test before NITBUT measurements on NITBUT values was analysed by comparing the pre- and post PRT test NITBUT values of the test eye, and by comparing the post-PRT test NITBUT values of the test eye with the NITBUT values of the control eye. The median pre- and post-PRT test NITBUT values for the test eye were 129s and 10.4s, respectively; for the control eye, the NITBUT values were 17 7s and 14.7s, respectively. The mean±SD PRT value was 19.6±6.8mm/15s. PostPRT test NITBUT values may be longer or shorter than prePRT test NITBUT values. Similar findings were observed for the control eye between the first and second measurement. Performance of the PRT test before NITBUT measurement does not affect the NITBUT values of asymptomatic HK-Chinese. The performance of the PRT test in one eye also does not affect the NITBUT value of the fellow eye. The same procedures were repeated on 14 subjects using the fluorescein-instillation tear break-up time (TBUT) test instead of the NITBUT test. Performing the PRT test did not affect the TBUT values. The median pre- and post-PRT test TBUT values for the test eye were 3.8s and 4.2s, respectively,- for the control eye, the TBUT values were 5.4s and 4.1s, respectively. The mean±SD PRT value was 19.0±5.Omm/15s. The performance of the PRT test before NITBUT measurements does not appear to affect the locations of tear defects in the NITBUT test; the location of tear defects is not random but is most frequent in the inferior periphery of the cornea.

The demographics and contact lens wearing history of two groups, each of 100 patients were examined, one grouphaving been assessed as suitable for photorefractive keratectomy (PRK) treatment but electing not to go ahead, the othergroup having proceeded with PRK treatment. Although only minor differences were found between the two groups in terms of demographics, the group that elected to be treated comprised a large number of contact lens-intolerant individuals. A breakdown is given of the contact lens-related reasons for opting to undergo PRK, emphasising the importance of the role of the contact lens practitioners in the preselection of patients for PRK.

A prospective, single-centre, controlled, double-masked randomised study was conducted to determine the benefits, ifany, of regular replacement of daily-wear rigid gas permeable (RGP) contact lenses. Forty-one subjects, divided into two groups, wore Quantum 2 lenses (Bausch & Lomb, Rochester, New York, USA; Dk=120) for 12 months on a daily-wear basis; subjects in group I replaced lenses every 3 months, whereas those in group II were not scheduled to replace lenses. All subjects were existing RGP lens wearers without any contact lens-induced pathology (>grade 1). The integrity of the lenses and the ocular responses to lens wear were monitored in both groups every 3 months. Compared with lenses worn by subjects in group II, lenses worn by subjects in group I displayed significantly less surface drying (at 9 months), less mucus coating (at 12 months), less surface deposition (at 12 months), and less surface scratching (at 9 and 12 months) (p 0.05, ANOVA). Compared with the ocular response of subjects in group II, the ocular response of subjects in group I displayed significantly less corneal staining at 12 months (p<0.05,- ANOVA). No significant differences between the groups were observed with respect to comfort, vision, or any of the other variables assessed. We advocate that, in order to maintain optimal lens integrity and ocular health, RGP lenses used for daily wear should be replaced every 6 months.