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PubMedDate not supplied

The relationship between soft tissue anomalies around the orbit and globe and astigmatic refractive errors: a preliminary report.

Corneoscleral limbal masses were created in ten rabbit eyes and upper eyelid colobomas were produced in an additional ten eyes. The resultant changes in corneal curvature were recorded over a one-month period using streak retinoscopy and photokeratometry. By these methods, we have determined that forces at or near the corneoscleral limbus can produce changes in the corneal curvature that lead to refractive errors primarily of the astigmatic variety. There is a shift of the axis of astigmatism towards the meridian 90 degrees away from the external force or an increase of astigmatism along the meridian where the force was exerted. In this study, corneal curvature changed significantly in the coloboma and epibulbar mass groups when compared to the control group. This study supported a causal relationship between soft tissue anomalies and astigmatic refractive errors seen clinically in certain syndromes, such as Goldenhar and mandibulo-facial dysostosis. These findings suggest that patients observed with periorbital soft tissue defects may be at risk for the development of unilateral anisometropic refractive errors and secondary amblyopia. Recognition of this entity is essential in order that adequate therapy can be instituted at an early age.

Animals↗
PubMed2002

Population prevalence of tilted optic disks and the relationship of this sign to refractive error.

PURPOSE: To assess the prevalence of tilted disks and its association with refractive error and visual field defects. DESIGN: Population-based cohort study. METHODS: The Blue Mountains Eye Study examined urban Australians aged 49 years or older between 1992-1994. Of 4,433 eligible participants, 3,654 (82.4%) participated. The eye examination included logMAR visual acuity, standardized refraction, cover testing, stereoscopic optic disk photography, and Humphrey automated perimetry. Inferior or nasal optic disk tilting was graded from stereoscopic photographs. RESULTS: Of 3,583 participants with gradable photographs, inferior or nasal optic disk tilting was observed in 77 eyes of 56 participants (1.6%). The prevalence of tilted disks increased from 0.4% in eyes with astigmatism < 1.0 diopters to 17.9% in eyes with astigmatism >or= 5.0 diopters. The mean astigmatic error was 2.2 diopters in eyes with tilted disks compared with 0.7 diopters in eyes with normal disk appearance, P <.001. Myopia was present in 66.2% of eyes with tilted disks compared with 12.4% of eyes with a normal disk appearance, P <.001. The most common associated features were astigmatism (93.5%), pallor, and tessellation of the adjacent chorioretinal tissues (74.0%), situs inversus of the retinal vessels (70.1%), beta-peripapillary atrophy (64.9%), strabismus (30.4%), visual field defects (19.4%), posterior staphyloma (18.2%), inferonasal pigmentary accumulation (9.1%), and chorioretinal atrophy (5.2%). Superotemporal (33.3%) and superior (25.0%) visual field defects were most frequent. CONCLUSIONS: A tilted disk appearance was not a rare finding in our study population and was strongly associated with astigmatism and higher levels of spherical refractive error, particularly myopia. The tilted disk and its associated visual field defect should be distinguished from other sinister causes.

Age Distribution↗
PubMed1984

A review and evaluation of theories of refractive error development.

A review of theories of the development of refractive errors is presented. These are classified into three major groups: the biological-statistical theories, the use-abuse theories and theories of emmetropization. They are commented upon and their merits contrasted. Current research developments which relate to these theories are discussed.

Adolescent↗
PubMed1978

The effect of refractive error on size constancy and shape constancy.

The effect of refractive error was determined for both size constancy and shape constancy. Although an error of 1.5 diopters reduces shape constancy, 3.0 diopters of blur had no effect on size constancy. The results are discussed in terms of the multiple mechanisms subserving the perceptual constancies. The importance of cues from the peripheral visual fields for size constancy and the role of foveally mediated texture and stereopsis cues for shape constancy are emphasized.

Adult↗
PubMed2003

Relationship between refractive error and monochromatic aberrations of the eye.

PURPOSE: To examine the relationship between ametropia and optical aberrations in a population of 200 normal human eyes with refractive errors spanning the range from +5.00 to -10.00 D. METHODS: Using a reduced-eye model of ametropia, we tested the hypothesis that the optical system of the eye is uncorrelated with the degree of ametropia. These predictions were evaluated experimentally with a Shack-Hartmann aberrometer that measured the monochromatic aberrations across the central 6 mm of the dilated pupil in well-corrected, cyclopleged eyes. RESULTS: Optical theory predicted, and control experiments on a model eye verified, that Shack-Hartmann measurements of spherical aberration will vary with axial elongation of the eye even if the dioptric components of the eye are fixed. Contrary to these predictions, spherical aberration was not significantly different from emmetropic eyes. Root mean square of third-order aberrations, fourth-order aberrations, and total higher aberrations (third to 10th) in myopic and hyperopic eyes were also uncorrelated with refractive error. Astigmatic eyes tended to have larger total higher-order aberrations than nonastigmatic eyes. CONCLUSIONS: We conclude that a reduced-eye model of myopia assuming fixed optical parameters and variable axial length is not tenable.

Accommodation, Ocular↗
PubMed1983

Vision screening and photorefraction - the relation of refractive errors to strabismus and amblyopia.

Isotropic photorefraction is a technique well suited for screening infants and young children for refractive errors. The photorefractive measurements have been empirically calibrated against retinoscopic refractions, so errors exceeding selected criteria can be identified in screening and followed up. Such a screening programme is in progress for the population of 6-9 month infants in the City of Cambridge. In 1096 infants screened 5% have been found to have large hypermetropic errors, 1.3% to show a refractive difference between the eyes (anisometropia) and less than 1% to have significant myopia or manifest strabismus. These findings were generally confirmed on retinoscopic examinations. In subsequent follow up of the large hypermetropic errors, most decline with age but a few show little or no change up to age 2 years and some show more change in one eye than the other leading to anisometropia. A trial is underway to examine whether early correction with spectacles can reduce the later incidence of strabismus and amblyopia in hypermetropic infants. Significant astigmatism is found in a large fraction of the infant population; the predominant axis of this astigmatism shows marked and unexplained variations between different locations in England.

Amblyopia↗
PubMed1984

Retinal function in high refractive error assessed electroretinographically.

The retinal function of patients with high refractive error was studied electroretinographically. Thirty-one hypermetropic patients, 7 myopic patients, and 7 patients with either unilateral or bilateral aphakia participated in the study. The ERG responses were measured in the light- and dark-adapted states. It was found that myopic eyes were characterised by subnormal amplitude but normal pattern, expressed by normal relationship between the b-wave amplitude and the a-wave amplitude. In aphakia the ERG responses were of normal amplitude and pattern. However, the hypermetropic patients could be divided into 3 groups. One group included subjects with a subnormal b-wave to a-wave relationship. The second group was characterised by a normal b- to a-wave relationship, while patients belonging to the third group exhibited supernormal b-wave to a-wave relationship. This classification of hypermetropic subjects did not correlate with the axial length of the eye or the refraction of the ocular media.

Adolescent↗
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↗
PubMed1999

Piggybacking intraocular implants to correct pseudophakic refractive error.

OBJECTIVE: To determine the safety and efficacy of implanting a second intraocular lens (IOL) to correct pseudophakic refractive error. DESIGN: Noncomparative, prospective, consecutive case series. PARTICIPANTS: Eight eyes of eight normal pseudophakes and seven eyes of seven postpenetrating keratoplasty (PK) pseudophakes were included in the study. INTERVENTION: A second intraocular lens (IOL) was implanted anterior to the first in each eye in the study. MAIN OUTCOME MEASURES: Efficacy was determined based on the achieved refractive correction and Snellen uncorrected visual acuity measurements. Safety was determined based on loss of best-corrected visual acuity and operative and postoperative complications. RESULTS: Before surgery, spherical equivalents ranged from -5.12 diopters (D) to 7.5 D, with a mean absolute deviation from emmetropia of 3.38 D (1.62). After surgery, spherical equivalents ranged from -2.75 D to 0.5 D, with a mean absolute deviation from emmetropia of 1.21 D (0.90). Before surgery, only 7% of patients had 20/40 or better uncorrected vision, whereas after surgery, 50% had that level of vision. CONCLUSIONS: Implanting a second IOL is a viable option for correcting pseudophakic refractive error.

Humans↗
PubMed1979

Survey of ophthalmic conditions in a Labrador community. I. Refractive errors.

Of the 745 available members of the population of Nain in Labrador 650 (87%) were screened for refractive errors and ocular disease. Refraction by retinoscopy was done in 553 and axial length measured by an optical method in 514. The results showed that the incidence of low degrees of myopia was higher in Inuit (Eskimos) and those of Mixed Inuit-Caucasian blood in the age groups 10 to 40 than in those over 40. 75% of the myopes came from 20 families in which myopia was present in 2 or more generations. Although there was no significant correlation between the refraction of parents and offspring, there were significant correlations between them for axial length. The axial lenths of the myopic eyes of the Inuit and Mixed populations were significantly longer than emmetropic and hypermetropic eyes. The younger memebers of the population were taller than their parents, and except in female Caucasians axial length showed a significant positive correlation with height. More myopes than emmetropes and hypermetropes achieved grade 8 or more in school. It is suggested that the increased incidence of myopia in the younger age groups might be due to environmental factors interfering with the process of emmetropisation in eyes with a genetic predisposition to myopia by virtue of inheriting a slightlt longer eye. Better nutrition resulting in an increase in stature may also have had some influence.

Adolescent↗
PubMed2006

Heritability of refractive error and ocular biometrics: the Genes in Myopia (GEM) twin study.

PURPOSE: A classic twin study was undertaken to assess the contribution of genes and environment to the development of refractive errors and ocular biometrics in a twin population. METHODS: A total of 1224 twins (345 monozygotic [MZ] and 267 dizygotic [DZ] twin pairs) aged between 18 and 88 years were examined. All twins completed a questionnaire consisting of a medical history, education, and zygosity. Objective refraction was measured in all twins, and biometric measurements were obtained using partial coherence interferometry. RESULTS: Intrapair correlations for spherical equivalent and ocular biometrics were significantly higher in the MZ than in the DZ twin pairs (P < 0.05), when refraction was considered as a continuous variable. A significant gender difference in the variation of spherical equivalent and ocular biometrics was found (P < 0.05). A genetic model specifying an additive, dominant, and unique environmental factor that was sex limited was the best fit for all measured variables. Heritability of spherical equivalents of 88% and 75% were found in the men and women, respectively, whereas, that of axial length was 94% and 92%, respectively. Additive genetic effects accounted for a greater proportion of the variance in spherical equivalent, whereas the variance in ocular biometrics, particularly axial length was explained mostly by dominant genetic effects. CONCLUSIONS: Genetic factors, both additive and dominant, play a significant role in refractive error (myopia and hypermetropia) as well as in ocular biometrics, particularly axial length. The sex limitation ADE model (additive genetic, nonadditive genetic, and environmental components) provided the best-fit genetic model for all parameters.

Adolescent↗
PubMed2002

Parental myopia, near work, school achievement, and children's refractive error.

PURPOSE: To quantify the degree of association between juvenile myopia and parental myopia, near work, and school achievement. METHODS: Refractive error, parental refractive status, current level of near activities (assumed working distance-weighted hours per week spent studying, reading for pleasure, watching television, playing video games or working on the computer), hours per week spent playing sports, and level of school achievement (scores on the Iowa Tests of Basic Skills [ITBS]) were assessed in 366 eighth grade children who participated in the Orinda Longitudinal Study of Myopia in 1991 to 1996. RESULTS: Children with myopia were more likely to have parents with myopia; to spend significantly more time studying, more time reading, and less time playing sports; and to score higher on the ITBS Reading and Total Language subtests than emmetropic children (chi(2) and Wilcoxon rank-sum tests; P < 0.024). Multivariate logistic regression models showed no substantial confounding effects between parental myopia, near work, sports activity, and school achievement, suggesting that each factor has an independent association with myopia. The multivariate odds ratio (95% confidence interval) for two compared with no parents with myopia was 6.40 (2.17-18.87) and was 1.020 (1.008-1.032) for each diopter-hour per week of near work. Interactions between parental myopia and near work were not significant (P = 0.67), indicating no increase in the risk associated with near work with an increasing number of parents with myopia. CONCLUSIONS: Heredity was the most important factor associated with juvenile myopia, with smaller independent contributions from more near work, higher school achievement, and less time in sports activity. There was no evidence that children inherit a myopigenic environment or a susceptibility to the effects of near work from their parents.

Adolescent↗
PubMed2005

Software-based compensation of visual refractive errors of computer users.

For human beings, vision is one of the most important senses in interacting with the surrounding environment, as well as with any tools that require visual communication. As such, the ability to interact effectively with computers through typical graphic user interfaces (GUIs) is greatly affected by any refractive errors present in an individual's visual system. If the refractive errors can be mathematically modeled, a system for overcoming these aberrations can be devised which can increase the effective human-computer interaction for these individuals. Several methods, such as Adaptive Optics, have been proposed that attempt to solve this problem using electro-mechanical devices. These methods are costly and impractical, preventing most visually impaired individuals from benefiting from their use. In contrast, an image-processing method, based on deconvolution techniques, has recently been proposed for the pre-compensation of images to be displayed in a computer. This method is much more practical, being completely implemented in software, and has achieved encouraging results. Previous results have yielded an average 50% increase in visual efficiency in the compensation of a known artificial aberration introduced into the field of vision of experimental subjects. This paper describes the difficulties encountered with the present software-only compensation and proposes several methods for overcoming these obstacles. The difficulties, as well as the proposed solutions, are described theoretically and followed by examples using a lens system showing the improvement over previous methods.

Algorithms↗
PubMed2005

[Intraocular lenses for the correction of refraction errors. Part 1: phakic anterior chamber lenses].

In this overview, the current status of intraocular lens surgery to correct refractive error is reviewed. The interventions are divided into additive surgery with intraocular lens implantation without extraction of the crystalline lens (phakic intraocular lens, PIOL) or the removal of the crystalline lens with implantation of an IOL (refractive lens exchange, RLE). Phakic IOLs are constructed as angle-supported or iris-fixated anterior chamber lenses and posterior chamber lenses that are fixated in the ciliary sulcus. The implantation of phakic IOLs has been demonstrated to be an effective, safe, predictable and stable procedure to correct higher refractive errors. Complications are rare and differ for the three types of PIOL; for anterior chamber lenses these are mainly pupil ovalization and endothelial cell loss.

Anterior Chamber↗
PubMed1999

Role of genetic factors in the etiology of juvenile-onset myopia based on a longitudinal study of refractive error.

In an attempt to determine the role of genetic factors in the development of myopia, we examined the relationship of infantile refractive error and parental history to juvenile-onset myopia and analyzed 43 pedigrees affected by juvenile-onset myopia. Refraction data collected at regular intervals from a sample of juvenile subjects participating in a 24-year longitudinal study of refractive error were used. Results showed that children with two myopic parents were 6.42 times as likely to become myopic as children with one or no myopic parents. Furthermore, children who had refractions in the lower half of the distribution at 6 to 12 months of age were 4.33 times as likely to develop myopia as children who had refractions in the upper half of the distribution at 6 to 12 months of age. The pedigree analysis indicated that 63% of individuals considered at risk for developing juvenile-onset myopia actually became myopic, with an equal number of affected males and females. These results suggest that juvenile-onset myopia of moderate amounts may be inherited as a complex trait involving both genetic and environmental factors.

Adolescent↗
PubMed1999

Radial keratotomy to treat myopic refractive error after cataract surgery.

PURPOSE: To assess the predictability and effectiveness of radial keratotomy in patients with myopic refractive error and unacceptable anisometropia after cataract surgery. SETTING: A prospective multicenter study. METHODS: This study comprised 40 eyes of 40 Japanese patients who had had cataract surgery. Radial keratotomy was performed, and the 6 month postoperative data were analyzed. RESULTS: Mean patient age was 71.0 years +/- 7.4 (SD) (range 51 to 84 years) and mean preoperative anisometropia -3.41 +/- 1.69 D (range -1.25 to -7.75 D). The surgery decreased mean anisometropia to -1.01 +/- 0.94 D (P < .000001, Wilcoxon signed-rank test), a mean reduction of 2.22 +/- 1.23 D (range 0.75 to 5.88 D). Postoperative anisometropia ranged from 0.81 to -3.13 D. The surgical effects were overestimated by the nomograms developed for the correction of naturally occurring myopia in the eyes of white patients. Multiple regression analysis revealed that optical zone size and number of incisions were significantly correlated with the amount of myopic correction, and the regression equation (R2 = 0.77) was expressed as follows: Effects = (-1.45 x optical zone size) + (0.24 x incision number) + 7.60. A new nomogram was derived based on this equation. CONCLUSIONS: Radial keratotomy was a safe and efficient procedure to treat myopic refractive error in pseudophakic eyes. Separate nomograms are necessary for white and Asian populations.

Aged↗
PubMed1983

Cylindrical refractive error: a population study in western Newfoundland.

The distribution of cylindrical refractive error (right eye only) is presented for 957 persons, comprising approximately 80% of the population (aged 5 years and over) of three western Newfoundland communities. In 72% of males and 60% of females no cylindrical error was found; 12% of males and 19% of females had errors greater than 0.5 D. Cylindrical errors of 2 D or greater were found in 2.5% of females of but only 0.5% of males, affecting females of all ages but males aged less than 15 years only. Persons aged 45 years and up had fewer cylindrical errors, more against-the-rule and less with-the-rule astigmatism than persons below that age. Cylindrical error and spherical error, and in particular against-the-rule error and myopia, commonly occurred together. Among persons aged 5 to 14 years an association of with-the-rule error with nearwork is suggested.

Adolescent↗