Journal of The British Contact Lens Association最新文献

Experiments are described in which monocular, high-contrast, letter acuity was measured as a function of target vergence (effective distance) for six simulated presbyopic subjects, who were placed under cycloplegia with a 4mm diameter artificial pupil. Measurements were made with the naked eye or single-vision spectacle lens corrected eye, and with three types of simultaneous-vision (simultaneous image) ‡ presbyopic contact lens correction: a centre-near biofocal; a centre-distance varifocal or progressive power lens; and a centre-mear varifocal. Results show that all designs usefully improve the range of distances over which an adequate standard of vision is achieved, the depth of focus typically being increased by about 1–2 dioptres, depending upon the criterion used to define depth of focus. Peak visual acuity at optimal focus is, however, slightly worse with the presbyopic contact lens corrections than with the naked or spectacle-lens corrected eye. Intersubject differences suggest that individual lens characteristics, the aberrations of the individual eye and lens centration may all play a role in determining the optical effectiveness of any particular design.

A survey consisting of a questionnaire, an interview and an anterior eye examination was conducted on 88 university students wearing contact lenses to identify and estimate the extent of clinical problems encountered with the use of contact lenses in Tianjin. In general, hygiene was poor and trachoma is a frequently seen condition, but these were not considered to be contraindications to contact lens wear. Six complications were assessed during the slit-lamp examination: conjunctival hyperaemia, limbal injection, giant papillary conjunctivitis (GPC, follicular changes in the lower tarsal conjunctiva, corneal vascularisation and corneal staining. The most commonly seen complication was GPC but this may have been due to pre-existing trachoma rather than to contact lens wear. The other complications assessed may also, in part, have been due to pre-existing trachoma but, in general, the prevalence of complications appeared to be higher in extended wear contact lenses than in daily wear contact lenses.

Orthokeratology has been shown to be safe over the years but with limited success. The advent of new lens materials,new lens designs, and a better understanding of corneal shape is likely to lead to an upsurge of interest in orthokeratology. This will be greatly assisted by the research for non-invasive and, ideally, reversible methods to match photorefractive keratoplasty. This paper discusses a new mathematical approach to the orthokeratology procedure and discusses those patients suitable for the procedure and those who are not.

A planned-replacement disposable lens (Precision W) has been evaluated in terms of its application as a therapeutic device in a hospital ophthalmology department. Sixty-six eyes were fitted over an 8-month period in order to manage a range of ocular disorders. The lens was found to fit satisfactorily in 80% of cases, producing the desired therapeutic effect. Of the remaining cases, variation in lens fit or physical size was necessary. The lens was considered to be suitable for use as a therapeutic device, providing a convenient and cost-effective approach to this specialist area of contact lens practice.

This study compared the in vivo wettability of four high Dk rigid gas permeable (RGP) materials (Aquila, Menicon, Super EX, Quantum 1 and Quantum 2). The study design was a double-masked right/left eye comparison of 6 months' duration where the lenses were worn on a daily-wear basis. It involved three experimental groups, each using Aquila in one eye and one of the other materials in the fellow eye. The main conclusions obtained are as follows: The in vivo intrinsic wettability, and its alteration during a 6-month period of wear, was similar for all four high Dk materials tested. The in vivo characteristics of these materials were not different from those of lower Dk materials, hence increasing Dk does not result in reduced wettability as suspected by some practitioners. In vivo wettability is highly patient dependent, and so its ongoing monitoring during routine practice is necessary for optimal patient management. In vivo wettability is affected by lens wear; after 6 months' wear the stability of the tear film at the front of the contact lens was significantly reduced and the level of surface contamination increased compared with dispensing. The notion of planned replacement should be extended to RGP contact lenses. Replacement frequencies of 6, or even 3 months would be of benefit for a significant number of patients.

A 6-month prospective study was designed to investigate the range of contact lens-related problems presenting to a24-hour eye casualty department. The influence of different types of contact lenses, wearing patterns, levels of hygiene practised and aftercare attendances were analysed. The commonest diagnoses were conjunctivitis (23.80 and corneal abrasions (19.70; 11.8% of patients presented with marginal keratitis and 3.1 % with a frank corneal abscess. Incidence of the more sight-threatening conditions was higher in the soft lens wearers and the risk of a corneal abscess, in particular, appeared to be greater when a soft lens was regularly worn overnight.