Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Hyperopia”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,387 records · Page 77Linked to original sources
PubMed1990

Local ocular compensation for imposed local refractive error.

Chicks were raised in a low-ceiling environment to find out if their eye growth could compensate for locally imposed hyperopic refractive errors. These chicks became selectively more myopic in the upper visual field than chicks raised in a high-ceiling environment. The vitreous chamber in the low-ceiling birds showed a selective elongation in the ventral region that was not seen in the eyes of the high-ceiling birds. This morphological difference was small, but probably adequate to account for the additional myopia in the low-ceiling birds. These results are consistent with the idea of a visually mediated growth mechanism regulating the local refractive state across the entire visual field so that it matches the customary viewing conditions. Such a mechanism might account for the finding of Fitzke, Hayes, Hodos, Holden and Low (Journal of Physiology, London, 369, 33-44, 1985) that the refractive errors in the lower field are exactly appropriate for focusing the image of the ground on the retina.

Animals↗
PubMed1994

Discrimination of changes in the second-order statistics of natural and synthetic images.

It has been suggested that the second-order statistics of different natural images are all remarkably similar and that neurones and channels in the visual system may exploit this similarity. We have measured the ability of human observers to discriminate changes in these statistics using different natural and synthetic stimulus images and have found that the dependence of their discrimination thresholds upon the reference second-order statistics is similar in form, for both kinds of stimuli. However, there is some variety in the magnitudes of the thresholds for the natural stimulus images; in fact, the second-order statistics of different natural images are more diverse than previously suggested. The discrimination task can be modelled as the discrimination of changes in local contrast within restricted spatial frequency bands and is similar to the discrimination of blur.

Contrast Sensitivity↗
PubMed1995

Moving the retina: choroidal modulation of refractive state.

The chick eye is able to change its refractive state by as much as 7 D by pushing the retina forward or pulling it back; this is effected by changes in the thickness of the choroid, the vascular tissue behind the retina and pigment epithelium. Chick eyes first made myopic by wearing diffusers and then permitted unrestricted vision developed choroids several times thicker than normal within days, thereby speeding recovery from deprivation myopia. Choroidal expansion does not occur when visual cues are reduced by dim illumination during the period of unrestricted vision. Furthermore, in chick eyes presented with myopic or hyperopic defocus by means of spectacle lenses, the choroid expands or thins, respectively, in compensation for the specific defocus imposed. Consequently, when the lenses are removed, the eye finds its refractive error suddenly of opposite sign, and the choroidal thickness again compensates by changing in the opposite direction. If a local region of the eye is made myopic by a partial diffuser and then given unrestricted vision, the choroid expands only in the myopic region. Although the mechanism of choroidal expansion is unknown, it might involve either a increased routing of aqueous humor into the uveoscleral outflow or osmotically generated water movement into the choroid. The latter is compatible with the increased choroidal proteoglycan synthesis either when eyes wear positive lenses or after diffuser removal.

Accommodation, Ocular↗
PubMed1996

Diffuser contact lenses retard axial elongation in infant rhesus monkeys.

In each of five monkeys, one eye was fitted with a diffuser lens at birth. This lens allowed pattern vision, but also reduced contrast by about 1 log unit. In four out of five monkeys, the treated eyes were shorter and more hyperopic than the untreated fellow eyes. At 25 weeks of age, interocular differences (OD -- OS) of the experimental group were significantly greater than interocular differences of age-matched normal monkeys for both axial length (P < 0.05) and refractive error (P < 0.02). In addition, while the treated eyes were significantly different from normal eyes for both axial length measurements (P < 0.01) and refractive error (P < 0.01), there were no significant differences between the untreated fellow eyes and normal eyes. In primates less severe pattern deprivation appears to produce an effect on eye growth that is opposite to that of severe pattern deprivation (little or no pattern vision), which typically results in axial myopia.

Aging↗
PubMed1989

On the nature of myopia and the mechanism of accommodation.

An experiment in which pressure was applied to the globe of the eye by artificially-induced contraction of the superior oblique muscles produced two effects: 1) Dual vision, consisting of two separate, superimposed, retinal images, one blurred and one clear; and 2) A 5 diopter increase in myopia. It was concluded that the pressure, transmitted through the sclera to the vitreous, forced the vitreous against the back of the lens, flattening the periphery but not the axial (central) region, resulting in a high degree of negative spherical aberration, combined with accommodation. This suggests that accommodation can be actuated by contraction of the extraocular muscles. When the pressure was released, it took several years for the dual image to subside. This suggests that when the lens is released after a long period of accommodation, the return to the unaccommodated state is extremely slow, and that a significant factor in the etiology of myopia is repeated long periods of accommodation in which periods of rest are insufficient to allow the lens to return completely to the unaccommodated state.

Accommodation, Ocular↗
PubMed2004

Uveal effusion following laser in situ keratomileusis (LASIK) for hypermetropia.

PURPOSE: To describe the first reported cases of uveal effusion syndrome following laser in situ keratomileusis (LASIK). DESIGN: Interventional case reports. METHODS: A 50-year-old woman developed bilateral submacular choroidal folds with subtle fluid elevation of the macula on the first day following uneventful LASIK for hypermetropia. A 48-year-old man developed right, prominent, 360-degree, peripheral choroidal effusions and submacular choroidal and retinal folds several months following LASIK for hypermetropia. RESULTS: Case 1 was treated with systemic diclofenac and case 2 with systemic prednisolone. Both cases showed gradual improvement in vision over several weeks, returning to best-corrected visual acuity of 6/6. CONCLUSIONS: Uveal effusion syndrome is a previously unreported complication that may occur following LASIK for hypermetropia.

Choroid Diseases↗
PubMed2005

Preliminary efficacy and safety of zero diopter lens implantation in highly myopic eyes.

PURPOSE: To report the preliminary efficacy and safety of zero diopter (D) intraocular lens implantation in highly myopic eyes. DESIGN: Retrospective surgical case series. METHODS: Three highly myopic eyes with axial lengths greater than 30 mm were implanted with zero D Alcon model MA60MA 3-piece acrylic posterior chamber lenses at the time of cataract surgery. RESULTS: Uncorrected visual acuity improved from counting fingers to 20/20- and 20/40- in two eyes. Best-corrected visual acuity improved from 20/80 and 20/60+ to 20/20- in the same eyes. A third eye was at counting fingers before and after surgery, because of a staphyloma. The range of preoperative, intended postoperative, and achieved postoperative spherical equivalent refractive errors was -15.1 to -25.0 diopters, -0.20 to -1.44 diopters, and +0.13 to +0.50 diopters respectively. CONCLUSIONS: All eyes experienced mild hyperopic refractive errors after surgery. No retinal detachments occurred during the follow-up interval.

Acrylic Resins↗
PubMed2005

The association between hypermetropia and essential hypertension.

PURPOSE: To explore the relationship between the refractive state of the eye and high blood pressure in a representative population. DESIGN: Case-control study. METHODS: Three hundred twenty-one patients with essential hypertension (mean age 53.9 +/- 15.5 years) and 188 age-matched and sex-matched healthy control subjects (mean age 50.9 +/- 7.3 years) from the same regional Health Maintenance Organization were consecutively included for the study (P > .05 for age and sex). The refractive state of the eyes was identified objectively by an autorefractometer and retinoscopic examination, recording the autorefractometer values. Spherical equivalents between -0.50 (included) and +0.50 (included) diopters were regarded as emmetropia. Values below or above this interval were regarded as either myopia or hypermetropia. Mean spherical equivalents of the groups were compared using independent samples t test; distributions of refraction were compared with chi(2) test. RESULTS: The mean spherical equivalent of the patients with essential hypertension was +0.88 +/- 1.34 diopters (range -3.75 to +6.38 diopters), whereas the mean spherical equivalent of the control subjects was -0.26 +/- 1.12 diopters (range -5.00 to +3.38 diopters) (P < .0001). Whereas 61.4% of hypertensive patients were hypermetropic, 18.1% of normotensive patients were hypermetropic (P < .0001). CONCLUSIONS: There is a strong association of essential arterial hypertension with hypermetropia, which has not been previously reported. Given the findings of this study, we recommend that patients who have hypermetropia and have had no recent systemic examination should at least have their blood pressure checked.

Adult↗
PubMed2006

Hypermetropia is not associated with hypertension: the Blue Mountains Eye Study.

PURPOSE: An association between hypermetropia and hypertension was recently reported. We sought to verify this finding in the Blue Mountains Eye Study cohort (n = 3654; ages 49 to 97 years). DESIGN: Cohort study. METHODS: We defined hypermetropia as mean spheric equivalent refraction (SER) > 1.00 diopter, myopia as mean SER < -1.00 diopters, and emmetropia as mean SER < or = 1.00 diopters and > or = -1.00 diopters, inclusive. We used the 2003 World Health Organization/International Society of Hypertension guidelines to define severe hypertension as grade 2 or higher. RESULTS: Of 1290 people who were at risk of the development of hypertension, 378 people developed incident severe hypertension after five years. The multivariate-adjusted relative risk of incident hypertension in persons with hypermetropia compared with those with emmetropia was 1.06 (95% CI, 0.89 to 1.26); the relative risk in persons with myopia was 1.22 (95% CI, 0.96 to 1.56). CONCLUSION: Neither hypermetropia nor myopia was associated with incident hypertension in this older population.

Aged↗
PubMed2006

Hypermetropia, axial length, and hypertension: the Tanjong Pagar survey.

PURPOSE: To examine the relationship among hypermetropia, axial length, and hypertension in a Chinese population. DESIGN: Population-based cross-sectional study. METHODS: This study included 1213 Chinese individuals aged 40 to 81 years. Hypertension was defined as systolic blood pressure > or =140 mm Hg, diastolic blood pressure > or =90 mm Hg, or self-report history of antihypertension treatment. Refraction was determined with an autorefractor and refined subjectively. A-mode ultrasound scanning was used to measure axial length. RESULTS: The crude odds ratio of hypertension was 2.5 (95% CI, 1.4-4.6) for moderate hypermetropia (> or =+2.00 spheric equivalent diopters) vs high myopia (< or =-6.00 diopters), and 1.4 (95% CI, 0.9-2.1) for highest vs lowest axial length quintile. These associations were no longer significant after adjustment for age, gender, education, housing type, and income. CONCLUSIONS: These data provide no evidence that hypermetropia or shorter axial length is associated independently with hypertension in Chinese individuals.

Adult↗