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At least 37 records · Page 2Linked to original sources
PubMed2004

Influence of laser polarization on ocular refractive parameters after refractive surgery.

We provide an adjustment factor for ablation algorithms used in photorefractive laser surgery that takes into account how laser polarization in reflection losses affects the cornea. We evaluate the influence of this factor on corneal radius and asphericity after surgery, showing that it is significant for visual performance (effective visual acuity is reduced) and for the correction of eye aberrations. Our data indicate that this adjustment factor should be included in the ablation algorithms (depending on the polarization state of each laser device) that are proposed for customized corneal ablation, which need great accuracy for minimization of eye aberrations.

Eye↗
PubMed1986

A longitudinal study of the age-dependence of human ocular refraction--I. Age-dependent changes in the equivalent sphere.

Following on from a cross-sectional analysis of refraction data (Saunders, 1981), the present paper attempts the evaluation of serial recordings of a new sample of refractive corrections using longitudinal methods. This study compares the results of the cross-sectional and longitudinal methods, investigates whether or not the latter supports the conclusions of the former, examines to what accuracy this is achieved and, where the results differ, seeks a reason for this. It is demonstrated that in spite of such differences the two methods coincide in their conclusions.

Adolescent↗
PubMedDate not supplied

[Ocular refraction in Marfan's syndrome and its surgical problems].

The superior-temporal subluxation of the crystalline lens at the patients with Marfan syndrome makes optic problems who need a surgical solution. It describes one aspiration technique with concomitant support of crystalline lens, underlining the specifics features what are meet here: exessive hardness of crystalloid and the content of crystalline's sack. At eight operated eyes, the postoperatorial visual acuity restored at values over 5/10.

Adult↗
PubMed1998

Detection system for ocular refractive error measurement.

An automatic and objective system for measuring ocular refractive errors (myopia, hyperopia and astigmatism) was developed. The system consists of projecting a light target (a ring), using a diode laser (lambda = 850 nm), at the fundus of the patient's eye. The light beams scattered from the retina are submitted to an optical system and are analysed with regard to their vergence by a CCD detector (matrix). This system uses the same basic principle for the projection of beams into the tested eye as some commercial refractors, but it is innovative regarding the ring-shaped measuring target for the projection system and the detection system where a matrix detector provides a wider range of measurement and a less complex system for the optical alignment. Also a dedicated electronic circuit was not necessary for treating the electronic signals from the detector (as the usual refractors do); instead a commercial frame grabber was used and software based on the heuristic search technique was developed. All the guiding equations that describe the system as well as the image processing procedure are presented in detail. Measurements in model eyes and in human eyes are in good agreement with retinoscopic measurements and they are also as precise as these kinds of measurements require (0.125D and 5 degrees).

Astigmatism↗
PubMed2001

The importance of genes and environment for ocular refraction and its determiners: a population based study among 20-45 year old twins.

AIMS: To estimate the heritability for ocular refraction and its determiners in a population based cohort of 20-45 years old twins. METHODS: 114 twin pairs (53 monozygotic and 61 dizygotic) participated. Refraction was determined in cycloplegia and eye dimensions were measured with ultrasound. Educational length was assessed. The heritability was estimated employing aetiological model fitting. Evidence of gene-environment interaction was analysed. Correlations between intrapairwise differences in educational length and in refraction were evaluated. RESULTS: The heritability was between 0.89 and 0.94 (95% CI: 0.82, 0.96) for refraction, total refraction, axial length, and radius of corneal curvature. Phenotypic variation was mostly due to additive genetic effects. Refraction revealed evidence of gene-environment interaction (r = -0.29 to -0.32; p <0.05). The heritability for anterior chamber depth and lens thickness was between 0.88 and 0.94 (95% CI: 0.81, 0.96) and dominant genetic effects were the most likely explanation. There was no correlation between age and intrapairwise differences in refraction. The dizygotic twins had significant larger intrapairwise differences in educational length (p <0.05), but the differences were not correlated with differences in refraction. CONCLUSIONS: The results indicate a high heritability for ocular refraction and its determiners and thus suggest that environmental impact on refraction is not significant. However, the epidemiological association between educational length (near work) and myopia, the evidence of increasing myopia prevalence within a few generations, and the theory of gene-environment interaction imply that some individuals might be genetically liable to develop myopia if exposed to certain environmental factors.

Adult↗
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↗
PubMed2006

Genomewide scan in Ashkenazi Jewish families demonstrates evidence of linkage of ocular refraction to a QTL on chromosome 1p36.

UNLABELLED: The development of refractive error is mediated by both environmental and genetic factors. We performed regression-based quantitative trait locus (QTL) linkage analysis on Ashkenazi Jewish families to identify regions in the genome responsible for ocular refraction. We measured refractive error on individuals in 49 multi-generational American families of Ashkenazi Jewish descent. The average family size was 11.1 individuals and was composed of 2.7 generations. Recruitment criteria specified that each family contain at least two myopic members. The mean spherical equivalent refractive error in the sample was -3.46D (SD=3.29) and 87% of individuals were myopic. Microsatellite genotyping with 387 markers was performed on 411 individuals. We performed multipoint regression-based linkage analysis for ocular refraction and a log transformation of the trait using the statistical package Merlin-Regress. Empirical genomewide significance levels were estimated through gene-dropping simulations by generating random genotypes at each of the 387 markers in 200 replicates of our pedigrees. Maximum LOD scores of 9.5 for ocular refraction and 8.7 for log-transformed refraction (LTR) were observed at 49.1 cM on chromosome 1p36 between markers D1S552 and D1S1622. The empirical genomewide significance levels were P=0.065 for ocular refraction and P<0.005 for LTR, providing strong evidence for linkage of refraction to this locus. The inter-marker region containing the peak spans 11 Mb and contains approximately 189 genes. CONCLUSION: We found genomewide significant evidence for linkage of refractive error to a novel QTL on chromosome 1p36 in an Ashkenazi Jewish population.

Alleles↗
PubMed1982

Ocular refraction after penetrating keratoplasty with infant donor corneas.

Five adult patients underwent penetrating keratoplasty in which corneal tissue from donors 3 months old or younger was used. In each case, a large myopic shift in refraction was found after surgery (mean, 9 diopters). The average postoperative spherical equivalent was -7.35 diopters. This resulted from the extremely steep curvature of the infant donor cornea (mean keratometric value, 57.67 diopters). The induced anisometropia and steep corneal topography of the infant donor cornea prevented visual rehabilitation with spectacles or contact lenses in four of five patients. Our findings suggested that corneal tissue from donors 3 months old or younger may be unsuitable for penetrating keratoplasty in emmetropic adults or anisometropic patients undergoing surgery in the more myopic eye.

Adult↗