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Results for “PRESBYOPIA”

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At least 739 records · Page 41Linked to original sources
PubMed1999

What is the oxygen environment under an encapsulated segment bifocal RGP contact lens?

BACKGROUND: A bifocal rigid gas permeable (RGP) contact lens is now available that totally encapsulates an add segment of a different material within its inferior aspect. The purposes of this study were to determine the effects of the major lens and of its encapsulated segment region on the oxygen uptake rates of underlying cornea. METHODS: Corneal oxygen uptake rates of 10 human corneas were measured--both centrally and inferiorly--for non-wearing conditions and then immediately after 300-second wearing periods of a polymethylmethacrylate (PMMA) lens and of this RGP-encapsulated segment bifocal contact lens. Corneal responses associated with these three environmental conditions were compared statistically (i.e., without the influence of blink-driven tear flow). RESULTS: Under the nonblinking conditions maintained (i.e., with oxygen availability restricted to lens transmissibility alone), central corneal hypoxia was found for the RGP bifocal lens to be only 47% of that induced by the PMMA (Dk/L = 0) condition, while the cornea under the encapsulated segment of the bifocal lens averaged 78% of the hypoxic response induced by that same condition. Central site responses were found to be significantly different for the bifocal and the PMMA lens (p < 0.001), as they were for the two inferior sites with these two lenses (p < 0.001). All lens-related responses were found to be significantly different from the no lens condition (p < 0.001). CONCLUSIONS: Using Smith's model (JAOA, 1997) to estimate lens transmissibility, the major lens of this RGP bifocal design appears to meet approximately 80% of the Holden-Mertz daily-wear oxygen requirement--even without post-lens tear exchange, but only about 25% of that requirement appears to be met beneath the encapsulated segment region. Efficient supplementary infusion of oxygen under this lens by blink-driven tear exchange, then, is necessary to maintain optimal corneal health.

Adult↗
PubMed1999

[Progressive lenses--a new possibility in sight for presbyopes].

Technological advances in the manufacture of the progressive lenses have made an effective and comfortable alternative in presbyopic correction. Nevertheless the small percentage of those patients are knowing and wearing them. The paper shown our clinical experience about prescribe Varilux progressive lenses at the 40 presbyopic patients. At the same time we try demonstrate the visual problems due that lenses, the difficult adaptation to this kind of spectacles and the degree of satisfaction of the subjects.

Adaptation, Physiological↗
PubMed2000

Evaluation of the ZEBRA 2000 (Z-10) Breger Vision bifocal contact lens.

PURPOSE: Evaluate the ZEBRA 2000 (Z-10) bifocal contact lens on presbyopic and aphakic patients. METHODS: Thirty-eight patients, 37 presbyopes and one aphake, were fit in the Z-10 and evaluated for 6 months. RESULTS: Twenty patients (53%) completed 6 months of contact lens wear. Ten (26%) discontinued due to lens related problems, three (8%) discontinued due to other health problems, and five (13%) were lost to follow-up. Average refits per eye were 1.75. Average distance visual acuity was 20/25; average near visual acuity was J1.6; average wear time, 11 hours. Patient satisfaction was rated good in comfort and vision and fair in nighttime glare by patients' subjective evaluation. CONCLUSIONS: The ZEBRA 2000 (Z-10) can be a useful addition in fitting the general presbyopic patient population.

Adult↗
PubMed2000

Clear lens extraction to correct hyperopia in presbyopic eyes with or without arcuate keratotomy for pre-existing astigmatism.

This retrospective study evaluates visual (functional) and refractive outcome of correcting hyperopia (i.e. 2.5 D or more) by means of a cataract procedure and simultaneously the pre-existing clinical significant astigmatism (1.5 D or more with the rule; 1 D or more against the rule), if present, by means of an arcuate keratotomy. Nine eyes undergoing clear lens extractions with intraocular lensimplantation (IOL) in combination with arcuate keratotomy (group one) and 29 eyes without arcuate kertotomy (group two) are included in the study. The mean age at the time of surgery was 62.89 years (range, 50 to 83) in group one and 68.17 years (range, 53 to 86) in group two. For calculation of the lens power a modified SRK II program, aiming at emmetropia was used. In only one highly hyperopic patient the Holladay I formula was used to calculate two piggyback lenses. A modified Istre nomogram was used to determine the surgical parameters of the arcuate keratotomy. The Cravy formula and the Holladay, Cravy, Koch vector analysis were used to determine the change in refractive cylinder results. Patients were followed postoperatively for a mean of 2.8 months in group one and 7.5 months in group two. In group one, 6 out of 9 eyes achieved a postoperative refraction within +/- 0.5 D of intended refraction and 8 out of 9 were within +/- 1 D of intended refraction. In group two, it was 15/29 and 24/29 respectively. Postoperatively, the uncorrected visual acuity was 20/40 or better in all eyes of group one (9/9) and in 27/29 eyes of group two. None of the eyes in both groups lost two or more lines of the best corrected visual acuity. Clear lens extraction with IOL is an effective and safe procedure for the correction of hyperopia in a presbyopic age group. In combination with an arcuate keratotomy, pre-existing astigmatism can be corrected simultaneously.

Aged↗
PubMed2000

Factors influencing success of monovision contact lens fitting: survey of contact lens diplomates.

BACKGROUND: Contact lenses are frequently fitted so that one eye is focused for distance and the other for near (monovision) in order to reduce the dependence of presbyopic patients on bifocal spectacle correction. METHODS: We surveyed Diplomates in the Cornea and Contact Lens section of the American Academy of Optometry (N = 179) regarding their estimates of success with monovision fitting and factors influencing their perception of success. Results were statistically analyzed to determine the fitting philosophies of responders estimating that they achieve high success rates (HSRs) and low success rates (LSRs), respectively. RESULTS: Completed surveys were returned by 98 Diplomates (54.8%), who estimated an overall success rate of approximately 71.7% with monovision; 50.5% "totally successful" (wear monovision correction full-time without problems or need for additional correction) and 21.2% "successful" (wear monovision full-time, but experience some symptoms of blur or other discomfort, may wear over-correction at times for driving or detailed near work). Sighting dominance was the most frequently used method to determine the distant eye, followed by the plus-lens test. The HSR group tended to be more likely to take occupational factors into account when deciding which eye to use for the distance lens, and they used more flexibility in determining the near-add power. The LSR group discontinued monovision sooner than the HSR group, who continued treatment for longer than 4 weeks during the adaptation period much more often for all add ranges. CONCLUSIONS: Practitioners who regard monovision treatment as very successful have somewhat different fitting philosophies than those who regard monovision as unsuccessful. Implementation of highly successful practitioners' fitting techniques may increase success with monovision contact lens fitting.

Adaptation, Ocular↗
PubMed2001

The eyes have it.

Explore the source record for details and available documents.

Corneal Transplantation↗
PubMed2002

A physiological model to measure effects of age on lenticular accommodation and spherical aberration in chickens.

PURPOSE: To assess physiological accommodative function of intact intraocular lenses, as measured by focal length changes, in chickens of various ages. METHODS: Eyes of white leghorn chickens, aged 0 days (hatchlings), 7 days, 14 days, 6 weeks, 1 year, and 2 years, were enucleated and the backs of the globes, except for the ciliary nerve and ganglion, were removed. The ciliary nerve and ganglion were suctioned into the tip of a suction electrode, and lenses were optically scanned before, during, and after accommodation. Accommodation was elicited by delivery of 30-Hz electrical pulses. RESULTS: For all age groups, lenticular focal lengths for stimulated eyes were significantly shorter than for relaxed eyes, indicating that accommodation had been induced. Lenticular accommodative amplitudes decreased significantly with age, with reduced function occurring between 0 and 7 days and again between 14 days and 1 year. Although accommodation was associated with an increased spherical aberration in all age groups, the increase was significant only in some age groups. CONCLUSIONS: Results showing reduction of lenticular accommodation concomitant with increasing age suggest that in spite of major differences in anatomy and physiology of the accommodative mechanism, chickens may become presbyopic. Results showing high amounts of nonmonotonic spherical aberration in hatchling lenses suggest inherently poor optics in these birds.

Accommodation, Ocular↗