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Results for “refractive error”

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At least 1,711 records · Page 95Linked to original sources
PubMed1991

Inducing myopia, hyperopia, and astigmatism in chicks.

Myopia and hyperopia have been produced in chicks by applying specially designed convex and concave soft contact lenses to the eyes of newly hatched birds. After 2 weeks of wear, the eyes develop refractive states equivalent in sign and amount (+8 and -10 D) to the lens used. However, the lenses produce an artificial hyperopic shift during the first week of wear due to corneal flattening. We have developed a new approach involving the use of goggles with hard convex and concave contact lens inserts placed between the frontal and lateral visual fields. Myopia and hyperopia (+10 and -10 D) can be produced within days (4 days for hyperopia and 7 days for myopia) if the defocus is applied from the day of hatching. We can also produce significant amounts of astigmatism (1 to 5 D) axis at 90 degrees and 180 degrees by using cylindrical contact lens inserts. Although these last results are preliminary, they suggest that accommodation is not likely involved at this stage of refractive development because we do not believe that the accommodative mechanism can cope with cylindrical defocus. All spherical refractive errors produced using the goggle system appear to result from alterations in vitreous chamber depth.

Animals↗
PubMed1986

Diurnal change in refraction, corneal curvature, visual acuity, and intraocular pressure after radial keratotomy in the PERK Study.

Selected patients who complained of fluctuating visual acuity in the Prospective Evaluation of Radial Keratotomy (PERK) Study were examined before 8:00 a.m. and after 7:00 p.m. on the same day to determine diurnal change in uncorrected visual acuity, best corrected visual acuity, manifest refractive error, average central keratometric power, and intraocular pressure. Sixty-three operated eyes were examined at three months, while 46 operated and 40 unoperated contralateral eyes were examined at one year after radial keratotomy. One year after surgery, 42% of the operated eyes had an increase in minus power of the manifest refraction of 0.50 to 1.25 diopters, 26% of the eyes changed their uncorrected visual acuity by 2 to 4 Snellen lines, and 35% of the operated eyes showed central steepening of the cornea by 0.50 to 1.25 diopters. These changes in the operated eyes at one year were similar to the changes at three months. Minimal diurnal changes occurred in the unoperated eyes at one year. Only 11% of the unoperated eyes changed their manifest refraction by 0.50 to 1.00 diopters, none changed their uncorrected visual acuity by 2 to 4 Snellen lines, and only one of the unoperated eyes changed its central keratometric power by 0.50 diopters. This study documents that many patients who experience diurnal fluctuation of vision have steepening of the cornea and an increase in the minus power of their refraction during the day.

Biomechanical Phenomena↗
PubMed2004

Effect of hyperbaric oxygen on guinea pig lens optical quality and on the refractive state of the eye.

The main objective of this study was to investigate the effect of in vivo hyperbaric oxygen (HBO) treatment of albino guinea pigs on ocular refractive state and optical properties of the lens in vitro, as well as on the integrity of the mitochondria of the lens. The animals were treated 30-35 times (2.5-3 months) or 70 times (6 months) with HBO. An increased level of lens nuclear light scattering was evident by slit-lamp at 30 treatments, and this increased at 70 treatments. After 30-35 HBO treatments a myopic shift in refractive state of the eye was seen in two separate studies with two different refractionists. Also, the average back vertex distance of the lens was significantly shorter after 35 HBO treatments while spherical aberration (focal variability) increased after 70 treatments. No difference in refractive state was noted after 70 HBO treatments (a reversal of the initial myopic effect). The mitochondrial distribution and morphology of the lens epithelium and the superficial cortical fibre cells were normal after both 35 and 70 HBO treatments, highlighting that HBO treatment does not affect the superficial cortex of the lens. The results of the in vitro lens optical analysis carried out in this study correlate with the myopia observed after 30-35 HBO in vivo treatments. A similar reversible myopia and increase in lens nuclear light scattering is known to occur in humans treated with HBO for extended periods and the results suggest that the myopia was caused by a change in the refractive index of the lens. The significant loss of sharp focus after 70 HBO treatments can be correlated with previous reports of biochemical and morphological changes associated with HBO-induced loss of lens nuclear transparency in mature guinea pigs. The guinea pig HBO model may be a useful approach for the study of lens development and refractive error.

Animals↗
PubMed2004

[Retinopathy of prematurity].

This review summarizes the knowledge and highlights recent advances in clinical research of retinopathy of prematurity (ROP). This disease is still important, because improvements in neonatal intensive care during the last years have increased the survival of the most immature newborns, but did not diminish the ROP frequency. Ophthalmologic screening and, if applicable, laser treatment at the optimal time for advanced ROP prevents blindness in most cases. The history, classification and the modern concepts of ROP pathophysiology are described. The results of various multicenter treatment trials are summarized. The current German screening guidelines are discussed with the guidelines of other nations. The therapeutic treatment strategies and the treatment results are discussed. The ophthalmologic disorders of former preterm infants, as higher rates of amblyopia, strabismus, and refractive error, are mentioned. Possible future therapies, e. g. anti-angiogenic factors are discussed.

Amblyopia↗
PubMedDate not supplied

[Optimal ocular correction for computer operators].

Different methods of correction of refractive errors with glasses were discussed in the paper. The problem of the use of antireflection coating and tinting or color coating of the lenses was also presented.

Computer Terminals↗
PubMedDate not supplied

Evaluation of night vision disturbances.

BACKGROUND: Evaluation of night vision disturbances has relied on subjective responses. We designed a test to more objectively measure night vision disturbances. METHODS: The test consisted of projecting a small circle onto a visual acuity screen. The patient is asked to draw exactly what he sees on an Amsler grid. We evaluated 118 eyes in photopic and scotopic conditions and under different conditions of refractive correction. RESULTS: Image degradation increased in scotopic conditions for myopes (p = .0001), hyperopes (p = .005), and emmetropes (p = .01). Myopic refractive error correlated with size of glare response (p = .001). Astigmatism correlated with decentration of glare response (p = .0001). Decentration increased in scotopic compared to photopic conditions (p = .002). CONCLUSION: Our test offers a simple, convenient way to evaluate night vision disturbances and may offer a means of assessing night vision disturbances in patients considering refractive surgery.

Adolescent↗
PubMed1975

Macular vision following retinal detachment surgery.

We studied 100 retinal detachment patients with macular involvement who had successful scleral buckling procedures using encircling fascia lata. Aphakic patients and patients with pre-existing ocular pathology in addition to the detachment were not excluded from the series. Follow-ups of one year or more (average 26.1 months) were available for 77 of the patients. Forty-four of these patients (56.5%) achieved acuities of 20/60 or better. The duration of the detachment was an important prognostic factor; one month was the critical period for the duration of the detachment. The existence of preoperative ocular pathology in addition to the detachment was also an important prognostic indicator. There was no significant difference in the visual acuities of phakic versus aphakic patients. Half of the patients studied with respect to refractive error became more myopic with an average change of -1.01 diopters.

Adult↗
PubMed1991

A clinical study of patient acceptance and satisfaction of Varilux Plus and Varilux Infinity lenses.

An independent study was conducted at the UAB School of Optometry to determine the clinical success with Varilux Plus (Varilux 2) and Varilux Infinity progressive addition lenses (PAL). Two hundred eighty patients (280) were fit between June 1988 and May 1989. The acceptance rate of 97.5 percent was based on the number of lenses ordered versus the number of lenses returned. Patients were contacted by telephone and asked to rate their level of satisfaction with their PALs. A chi-square (non-parametric) test revealed no statistically significant differences in levels of satisfaction with respect to gender, PAL type, or degree of presbyopia. Also, neither refractive error nor previous lens history had a measurable impact on patient satisfaction.

Eyeglasses↗
PubMed1987

Abnormal ocular head postures: Part IV.

All patients exhibiting the various types of abnormal head postures of ocular origin that were seen during the last two years are presented in order to determine the relative frequency of the different causes of these postures, and the purposes they serve. The treatment modality and results are also discussed. This manuscript is divided into four parts: Parts I, II, and III concern head postures in incomitant strabismus. In Part IV, head postures in Ciancia's syndrome, restrictions, and refractive errors are described.

Adolescent↗
PubMed2004

Refractive changes after posterior segment surgery.

Retinal surgery can induce significant refractive errors. These errors include spherical changes caused by alterations in axial length after scleral buckle placement, astigmatic changes induced by a scleral buckle or pars plana vitrectomy, and focal alterations in corneal curvature that can significantly limit postoperative visual acuity. The adjunctive use of silicone oil can impose alterations directly, by the oil's interaction with the other refractive elements of the eye, and indirectly, through its effects on intraocular lens power calculations for subsequent cataract surgery.

Corneal Topography↗
PubMed1992

Relationship between axial length and chromatic refraction of the eye.

A new mathematical expression is derived to provide an estimate, alpha x, of the axial length of the human schematic eye. Approximations in the expression are made after considering effects in the Gullstrand-Emsley schematic eye. Parameters required to solve the expression are, for two wavelengths, the refractive indices of the humours, the focal power of the cornea and refractive errors in two states of accommodation. Unlike recognized optical methods, additional intraocular parameters are not required. For emmetropic variants of the Gullstrand-Emsley schematic eye with axial lengths between 19 and 27 mm, alpha x is within 0.06 to 0.26 mm of the actual value. Furthermore, alpha x is essentially independent of variations in the refractive indices of the crystalline lens. However, the estimate of alpha x is critically dependent on the accuracy of values assigned to the parameters. For that reason, the model is considered impractical for clinical application.

Accommodation, Ocular↗
PubMed1983

The incidence of refractive anomalies in the USAF rated population.

A field survey was conducted to determine the percentage of U.S. Air Force pilots and navigators required to wear corrective lenses. A random sample survey stratified by major air commands (MAJCOMS) was designed to retrieve the data. Data requested included initial (entry) visual acuity and refractive error, and current visual acuity and prescription if glasses were required. Of 2,383 forms sent, 2,183 were returned completed. Analysis indicated that almost 20% of pilots and 50% of navigators are required to wear corrective lenses while flying. The percentages are rather consistent among MAJCOMS. Aircrew members who enter undergraduate pilot training with minus or plano refractive values are much more susceptible to develop myopia during their flying careers than those with plus refractive values.

Adult↗
PubMed1977

A study of vision in cerebral palsy.

One hundred twenty-eight patients (most less than 13 years old) with various types of cerebral palsy were examined to assess visual acuity, refractive state, oculomotor functions, sensory fusion, and ocular health. Special procedures for examining these patients are described. Vision or ocular defects were found to be present in 86% of these cerebral palsy patients. Significant refractive errors and strabismus were the most common defects, being present in 50% or more of the patients. Ocular disease was relatively uncommon.

Adolescent↗
PubMed1992

Chromatic aberration and optical power of a diffractive bifocal contact lens.

Although diffractive contact lenses have been well documented in theory, no definitive experimental data have been reported which confirm that the near image is in fact created by diffraction rather than by refraction. We have tested the diffraction hypothesis for one type of diffractive contact lens (the Hydron Echelon bifocal) experimentally by measuring its longitudinal chromatic aberration in isolation and when worn on the eye. The basis of this test is that, according to theory, diffractive lenses should have chromatic aberration which is opposite in sign to that measured for the eye. Objective measurements of chromatic aberration were made with a focimeter when the lens was in a wet cell. Subjective measurements were made with a Badal optometer when the lens was worn on the eye. Four control experiments were conducted to provide baseline measurements of the eye's chromatic aberration, against which we compared the results obtained for the diffractive contact lens. The data were also compared with conventional measurements of refractive error obtained by standard subjective techniques and by an automated infrared refractor. Our results showed that the longitudinal chromatic aberration of the diffraction image of the Echelon bifocal lens was about one-half that obtained under the four control conditions: for the naked eye, for the nondiffraction image of the Echelon lens, or for either image of a refractive bifocal contact lens (CIBA Bisoft). These results are consistent with the theoretical prediction that the negative chromatic aberration of a diffractive contact lens should partially cancel the positive chromatic aberration of the human eye.(ABSTRACT TRUNCATED AT 250 WORDS)

Color Perception↗
PubMed1981

An analysis of treatment of congenital glaucoma by goniotomy.

We used goniotomy as the initial surgical procedure in 34 patients (50 eyes) with congenital glaucoma. An overall success rate of 88% was achieved with one or more goniotomies. The age at disease onset, level of intraocular pressure, and corneal diameter did not significantly influence the surgical outcome. The refractive error proved to be a valuable indicator of operative success or disease progression. A satisfactory visual outcome was associated with treatment by goniotomy.

Child, Preschool↗
PubMed2001

Ophthalmic manifestations of tuberous sclerosis: a population based study.

BACKGROUND/AIMS: Tuberous sclerosis complex (TSC) has retinal and non-retinal ophthalmic manifestations. This study was designed to determine the prevalence of the ophthalmic manifestations and of refractive errors in a population of patients with TSC. METHODS: 179 patients identified were in a prevalence study of TSC in the south of England and 107 of these agreed to full ophthalmic examination which was successful in 100. Ophthalmic examination included examination of the eyelids, cover test, examination of the irides, dilation funduscopy using both direct and indirect ophthalmoscopy, and refraction using retinoscopy. Myopia was defined as a spherical equivalent <-0.5D and hyperopia as a spherical equivalent >+0.5D. RESULTS: Retinal hamartomas were seen in 44 of the 100 patients. The commonest morphological type of hamartoma seen was the flat, translucent lesion in 31 of the 44 patients (70%). The multinodular "mulberry" lesion was seen in 24 of the 44 patients (55%) and the transitional type lesion was seen in four of the 44 patients (9%). Punched out areas of retinal depigmentation were seen in 39 of the 100 patients but only six of 100 controls. 27% of eyes were myopic, 22% were hyperopic, and 27% had astigmatism >0.75D. Of the non-retinal findings, 39 patients had angiofibromas of the eyelids, five had non-paralytic strabismus, and three had colobomas. CONCLUSION: Apart from the higher prevalence of flat retinal hamartomas, the findings of this study compare closely with previous large clinic based series of TSC patients. Refractive findings were similar to previous studies of a similarly aged non-TSC population. This is the first series to document the statistically significant association of punched out chorioretinal depigmentation with TSC and the authors believe that it should be looked for as an aid to diagnosis.

Adolescent↗
PubMed1986

Visual characteristics of natives in Fiji, South Pacific.

Data on natives of rural Fiji who have not previously received any vision care are presented. The Fijians were found to have a distribution of refractive errors showing a strong tendency toward emmetropia. The frequency of ocular health problems was found to be low but to increase with age.

Adult↗