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Biomedical subjects

P Percival

Publications and source records attributed to P Percival.

11 recordsLinked to original sources
PubMed1992

An update on multifocal lens implants.

The performance of multifocals is partly determined by the degree to which contrast at the focussed image is reduced by out of focus images. This paper discusses how optical performance may vary with lens design and includes consideration, with available core study results, of multifocal designs marketed by Iolab, 3M, AMO, Ioptex, Storz and Domilens. For most lenses an acuity of 20/40 and J3 can be achieved unaided in over 70% of best case eyes and J2 with the distance correction in over 80%. However the risk of disappointment tends to prevent a more widespread use of multifocals among surgeons, and an explanation is given as to possible reasons.

Cataract Extraction↗
PubMed1990

Indications for the multizone bifocal implant.

A significant improvement in unaided visual standards may be achieved by switching from a monofocal to a 3M diffractive bifocal implant; however, this results in a loss of clarity, particularly for small print, in some patients. In a prospective study of 55 bifocal eyes and 55 monofocal eyes, best-case analysis showed 81% of 52 eyes with bifocal implants could read J5 with their distance correction compared with 21% of the control eyes and 56% could read J2 with the distance correction compared with 2% of the control eyes; 75% of bifocal eyes could read both 20/40 and J3 without any aid compared with 33% of the control eyes. The 3.5 diopter focus difference in the bifocal lens produced commendable results, with 52% requiring no spectacle reading addition. However, the fact that 17% of bifocal eyes could not read J2 highlights certain drawbacks that are relevant to indications for use.

Accommodation, Ocular↗
PubMed1989

Prospective study comparing hydrogel with PMMA lens implants.

A prospective study has been undertaken to assess the relative merits of one-piece polymethylmethacrylate (PMMA) and poly 2 hydroxyethylmethacrylate "hydrogel" (P-HEMA) lenses in uncomplicated eyes after uncomplicated surgery. Two groups of 125 eyes each were matched in terms of patient age and sex. One group received PMMA lenses; the other group received P-HEMA lenses. Six months after surgery the visual acuity of 42% of eyes with P-HEMA lenses was 20/15, whereas that of 29% of eyes with PMMA lenses was 20/15 (p = 0.02). Major decentration occurred in two cases of P-HEMA lens implantation, but asymptomatic subclinical decentration was more common with PMMA lenses (p less than 0.001). The looped PMMA lens was considered adaptable to a wider variety of surgical conditions.

Acrylates↗
PubMed1987

Capsular bag implantation of the hydrogel lens.

Fifty hydrogel lenses were implanted in the capsular bag. Six months after surgery, 96% of eyes had visual acuities of 20/30 and 40% had acuities of 20/15. The age range of patients was 65 to 92 years (mean 76 years). Such visual satisfaction is rarely achieved in this age group and appeared to be related to the low incidence of uveitis and capsular fibrosis associated with these lenses. Excellent lens centration was maintained in 82% of eyes. Despite the small number of cases and short follow-up, these preliminary results merit attention from the medical profession.

Aged↗
PubMed1983

Lens power calculation--is it necessary?

In a group of 70 patients from whom myopes were not excluded, 90 per cent resulted in postoperative refraction between -1.75 and +0.75 when the power of implant was calculated using A Scan biometry. Sixty-nine per cent of these patients would have fallen into this refraction bracket had calculation been made purely on clinical grounds. Comparison was made with 569 previous implantations without biometry. In this group life-long myopes above -3.0D had been excluded and the implants available were in 2.0 dioptre increments, choice of power depending on clinical judgement: 77 per cent of these patients fell into the same postoperative refraction bracket.

Humans↗