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Results for “refractive error”

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PubMed1980

[A model to measure the volume of choroidal melanomas (author's transl)].

A formula to calculate the volume of biconvex-shaped malignant melanomata of the choroid is presented. The axial length of the eye, whatever the refractive error, has nearly no influence on the results. A computer printout of the range of results is added for clinical use. The reliability of contact B-Scan ultrasonography to obtain those parameters is examined using various tumor models of defined sizes.

Choroid Neoplasms↗
PubMed2000

Evaluation of the iScreen digital screening system for amblyogenic factors.

BACKGROUND: A digital photoscreener, the iScreen screening system, is now available to detect amblyogenic factors. We carried out a prospective study to evaluate the accuracy of the device in detecting anisometropia, significant refractive error, strabismus and opacities of the ocular media. METHODS: A total of 449 consecutive patients (median age 7 years) from a private pediatric ophthalmology practice underwent screening with the iScreen photoscreener operated by a minimally trained technician. The results were compared to the masked clinical examination of a pediatric ophthalmologist. RESULTS: The iScreen device had a sensitivity of 92.4%, specificity of 89.1%, positive predictive value of 94.1% and false-negative rate of 13.8%. Of the 21 patients with a false-negative result, 12 had myopia of less than -1.50 dioptres. High hyperopia was missed in two patients, high astigmatism in one, unequal cylindrical error in one and strabismus in five. INTERPRETATION: The iScreen digital photoscreener produced accurate and timely screening for potentially amblyogenic defects in the study population.

Adolescent↗
PubMed1994

Changes in refraction and keratometry after surgery for acquired ptosis.

A retrospective study involving 47 lids in 26 patients was conducted to determine changes in refraction and keratometry after surgery for acquired ptosis. Refractive and keratometric data were obtained prior to and 6 months after levator surgery. Data were analyzed for changes in refractive sphere, cylinder, and cylindrical axis, as well as keratometry, toricity, and axis of toricity. Although patients noted subjective change in vision postoperatively and demonstrated changes in their refractive error, the changes were statistically insignificant. Consistency was noted; the cylindrical axis and the axis of toricity remained relatively stable after surgery.

Adult↗
PubMed1990

A longitudinal study of a population based sample of astigmatic children. I. Refraction and amblyopia.

The refraction changes in 310 children with astigmatism greater than or equal to 1.0 D in at least one eye at one year of age were followed during a period of 3 years. At the age 4 years amblyopia was found in 23 children (7%). The refraction data of these children were compared to the rest of the sample. We found that an increasing astigmatism during the test period was associated with an increased risk to develop amblyopia. The majority of children (n = 280) showed a decrease of their astigmatism, whereas all cases with a marked amblyopia (V.A. less than 0.5) or binocular amblyopia, except one, had an increasing or unchanged astigmatism during the age period 1 to 4 years. Strabismus and oblique astigmatism at any time during the test period was also strongly related to amblyopia. The incidence of strabismus (1%) was unexpectedly low. The study also showed that independent of age there was no simple relationship between amblyopia and refraction errors measured at a single test session. The main conclusion of this study is that failure of emmetropization may play an important role in visual development.

Amblyopia↗
PubMed1997

National survey of blindness and low vision in Lebanon.

AIMS: To survey level of blindness and low vision in Lebanon. METHODS: A population survey was undertaken in 10,148 individuals to measure the prevalence and identify the causes of blindness in Lebanon. RESULTS: The prevalence of blindness was 0.6% and that of low vision 3.9%. The major causes of blindness were cataract (41.3%) and uncorrected large refractive error (12.6%). CONCLUSION: Most causes of blindness in Lebanon can be controlled by various educational and medical programmes.

Adolescent↗
PubMed1975

The optical design of intraocular lens implants.

Intraocular lens implants have been around for more than 25 years. On the verge of a major breakthrough to ever widening popularity, there is, however, a general lack of understanding of the pertinent optical principles. A critical comparison is made between this new method and conventional methods of correcting aphakia. From this it appears that the visual needs of the patient are a decisive factor in the selection of the method of correction. Moreover, the full potential of intraocular lens implants can only be realized by appropriate selection of the power of the implant in each situation. To this end, ultrasonic measurement of the ocular axial length is indispensable. The use of standard power lens implants is inadequate. Formulas are presented to make an eye emmetropic or to give it any refractive error. Guidelines are given for the use of these formulas. Two methods for obtaining equal image size in unilateral antiphakia are described.

Aniseikonia↗
PubMed1981

Emmetropization: a vision-dependent phenomenon.

Anomalous visual experience during development has been shown to induce myopia in several species of animals. A retrospective analysis of refractive error among humans subjected to various ocular anomalies that disrupt pattern vision revealed a significant degree of myopia. This result suggests that emmetropization is a vision-dependent phenomenon.

Adult↗
PubMed2003

Effects of blur and repeated testing on sensitivity estimates with frequency doubling perimetry.

PURPOSE: To investigate the effect of blur and repeated testing on sensitivity with frequency doubling technology (FDT) perimetry. METHODS: One eye of 12 patients with glaucoma (mean deviation [MD] mean, -2.5 dB, range +0.5 to -4.3 dB) and 11 normal control subjects underwent six consecutive tests with the FDT N30 threshold program in each of two sessions. In session 1, blur was induced by trial lenses (-6.00, -3.00, 0.00, +3.00, and +6.00 D, in random order). In session 2, only the effects of repeated testing were evaluated. The MD and pattern standard deviation (PSD) indices were evaluated as functions of blur and of test order. By correcting the data of session 1 for the reduction of sensitivity with repeated testing (session 2), the effect of blur on FDT sensitivities was established, and its clinical consequences evaluated on total- and pattern-deviation probability maps. RESULTS: FDT sensitivities decreased with blur (by <0.5 dB/D) and with repeated testing (by approximately 2 dB between the first and sixth tests). Blur and repeated testing independently led to larger numbers of locations with significant total and pattern deviation. Sensitivity reductions were similar in normal control subjects and patients with glaucoma, at central and peripheral test locations and at locations with high and low sensitivities. However, patients with glaucoma showed larger deterioration in the total-deviation-probability maps. CONCLUSIONS: To optimize the performance of the device, refractive errors should be corrected and immediate retesting avoided. Further research is needed to establish the cause of sensitivity loss with repeated FDT testing.

Adult↗
PubMed2004

The effect of optical defocus on the test-retest variability of visual acuity measurements.

PURPOSE: To determine the effect of optical defocus on the test-retest variability (TRV) of visual acuity measurements in normal subjects. METHODS: Normal subjects underwent repeated visual acuity measurement with optical defocus of 0, 0.50, and 1.00 D. All measurements were taken using the Early Treatment Diabetic Retinopathy Study (ETDRS) version of the Bailey-Lovie logMAR chart. TRV was quantified in terms of its 95% range, both empirically and using the approach of Bland and Altman. RESULTS: According to the Bland and Altman approach, the estimated 95% TRV ranges were +/-0.11 logarithm of the minimum angle of resolution (logMAR) for 0-D defocus, +/-0.18 logMAR for 0.50-D defocus, and +/-0.25 logMAR for 1.00-D defocus. CONCLUSIONS: Optical defocus has a considerable effect on the TRV of visual acuity measurements. These findings have important implications for both clinical practice and clinical research. Uncorrected refractive errors as small as 0.50 D may compromise the detection of visual change in individuals, and contribute to unnecessarily large sample sizes in clinical trials in which visual acuity is used as a primary outcome measure.

Adult↗
PubMedDate not supplied

How far can a medial rectus safely be recessed?

Previous studies have suggested that the location of the equator should be important in determining the site of a "safe maximum recession" of a rectus muscle, and that the location of the equator should be a function of axial length. Exactly where in relationship to the equator a muscle can be safely recessed has never been scientifically determined. Over a 4-year period, we measured axial length on all patients we operated on for strabismus. Using a previously derived formula, we were able to calculate the limbus-to-equator distance, given axial length. Based on our analysis of 28 patients in whom we recessed one or both medial recti posterior to the equator, we believe that recessions of the medial recti up to 1.5 mm posterior to the equator should not produce postoperative medial rectus underaction associated with an overcorrection, but recessions that are further than 1.5 mm posterior to the equator may do so. Recessions to a point greater than 11 mm from the limbus do not appear to be associated with late progressive overcorrection provided that the site of recession is not greater than 1.5 mm posterior to the equator. Using our previously determined formula for estimating the location of the equator, given axial length, we have generated easy-to-use reference tables for determining the location of the equator in terms of millimeters posterior to the limbus. Also, based on axial length data from 180 strabismus patients, we have generated an algorithm for predicting axial length, given age, and refractive error, which may be useful to the strabismus surgeon in predicting the location of the equator when A-scan ultrasonography is not available.

Algorithms↗
PubMed1979

Visual evoked potential (VEP): basic concepts and clinical applications.

The Visual Evoked Potential is the objective measurement of visual function monitored at the level of the occipital cortex with scalp electrodes. This article summarizes many of the recent clinical applications of the VEP. Included are basic concepts of the VEP and its clinical utilization for the objective assessment of refractive error, visual acuity, amblyopia, binocularity, demyelinating diseases, psychogenic disorders, pre-surgical prediction of post-surgical visual function, visual fields, color blindness and neurological development.

Amblyopia↗
PubMed1979

Senile macular degeneration and risk factors: a case-control study.

A case-control study of patients ranging in age from 52 to 88 years was done to determine any possible relationship between health factors and senile macular degeneration. Thirty cases and 30 controls were pair-matched according to age, sex, and race. Chart reviews and telephone interviews were the methods of data collection used. The patients were interviewed concerning a history of vascular disease and other health characteristics. The data were analyzed by a paired-sample method. The results of the study showed a definite relationship with age and sex. Moreover, a significant relationship between refractive error and senile macular degeneration was noted. Such an association has not been previously reported. No relationship was found between vascular disease and senile macular degeneration.

Adolescent↗
PubMed2007

Confirmation of linkage to ocular refraction on chromosome 22q and identification of a novel linkage region on 1q.

OBJECTIVE: To localize genes influencing ocular refraction in subjects in the Beaver Dam Eye Study. Previous studies establish that myopia clusters within families and linkage to myopia has been demonstrated on 2q, 4q, 12q, 17q, 18q, 22q, and Xq. Few studies have examined genetic effects across the entire range of refraction, though linkages to 1p, 3q, 4q, 8p, and 11p have been reported, and our previous analysis of the Beaver Dam Eye Study demonstrated substantial heritability for refraction (68%). METHODS: We conducted nonparametric sibling-pair and genome-wide linkage analyses on spherical equivalent adjusting for age, education, and nuclear sclerosis, in 834 sibling pairs in 486 extended pedigrees. RESULTS: We identified a novel region of suggestive linkage on 1q (multipoint, P<.00019) and replicated the 22q region (multipoint, P = .0033) previously linked to myopia. Additionally, there was some evidence of linkage to 7p (multipoint, P = .0023). CONCLUSION: Refraction is a complex trait influenced by both genes and environment. Our work confirms a previously reported linkage region on 22q and identifies 2 novel regions of linkage on 1q and 7p. CLINICAL RELEVANCE: Further, genetic research is needed to finemap this trait to identify the causative gene. Modifying the actions of such a gene might lead to a reduction in the risk of refractive error.

Adult↗
PubMed1993

Visual functions in a Swedish population of dyslexic and normally reading children.

Eighty-six 9-year old dyslexic children were carefully matched to controls with regard to age, sex, class in school, and intelligence and thorough visual functions tests and eye examinations were performed. As a group the dyslexic pupils exhibited a lower distance as well as near visual acuity both with monocular and binocular viewing. Furthermore, the dyslexic pupils had a lower contrast sensitivity at the lower and higher spatial frequencies. These differences were all statistically significant. However, no statistically significant differences between the two groups could be observed regarding refractive errors or contrast sensitivity in the middle spatial frequency range. Although some eyes were amblyopic, any severe eye anomalies or diseases were not found in any of the investigated children.

Child↗
PubMed1976

[Heterotopic fundus (author's transl)].

Fundus heterotopicus is the term used to describe a rare, non-hereditary curvature anomaly of the fundus in the non-myopic eye, which is characterized: 1. functionally, by a slowly increasing myopic-astigmatic refractive error, 2. by correctable bitemporal or binasal refractionscomata and 3. ophthalmoscopically by a posterior out-pouching of the nasal or temporal fundus portions, and including the optic disc and macula in the obliquely descending wall of the extasis.

Adult↗
PubMed1984

Longitudinal study of vision in cerebral palsy.

Sixty-five percent of a predominantly young cerebral palsy population of 34 showed refractive error changes greater than 0.75 D over an average period of 11 years. Tropias were relatively stable. Differences between medical diagnostic categories were found. The current study is related to an earlier study by the same author.

Adolescent↗
PubMed1989

The subjective assessment of cataract.

The medical treatment of cataract now appears to be a distinct possibility. A number of anti-cataract formulations are being clinically tested, and more clinical trials are being planned. To obtain a true assessment of a drug's efficacy, a battery of tests are needed which can accurately assess cataract progress. A clinical trial of the proposed anti-cataract drug Bendalina is being conducted. The six subjective methods used to assess cataract progression in the trial are presented. These are refractive error, LogMAR visual acuity, contrast sensitivity, glare sensitivity, retinal visual acuity and displacement threshold hyperacuity. The reasons for using each technique and their method of measurement is explained.

Aged↗
PubMed1996

Night vision testing in unoperated eyes.

BACKGROUND: We previously described a simple test which evaluates image degradation in post-excimer laser (PRK) patients under scotopic conditions. After refractive surgery, corneal haze, ablation zone decentration, ablation zone/pupillary diameter disparity, and under-correction each result in a characteristic pattern on the Night Vision Recording Chart. METHODS: Using the same method, further studies evaluated night vision image degradation in 118 un-operated emmetropic, myopic, hyperopic, and astigmatic eyes and in 26 contact lens wearers. RESULTS: Scotopic image degradation increases with myopic refractive error, image displacement increases with astigmatism, and contact lens wearers have more image degradation that with spectacle correction. CONCLUSION: Our Night Vision Recording Chart offers a simple, reproducible method to characterize image degradation under scotopic conditions.

Contact Lenses↗