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PubMed1988

Algebra of sphero-cylinders and refractive errors, and their means, variance, and standard deviation.

Sphero-cylinders and refractive errors can be represented by matrices. Matrix algebra provides methods whereby sphero-cylinders can be added, subtracted, multiplied, inverted, and raised to powers and can have roots extracted. These operations are defined for sphero-cylinders and examples are given. In terms of these operations a number of means of refractive errors are defined: the arithmetic, harmonic, and quadratic means. Furthermore it is possible to define a variance and standard deviation for refractive errors. These quantities should provide a basis for a formal approach to the statistical analysis of populations of refractive errors.

Humans↗
PubMed1997

Pulsatile ocular blood flow variations with axial length and refractive error.

Ocular pulse amplitude (PA) and pulsatile ocular blood flow (POBF) were studied in 80 eyes from 80 subjects with a refractive error between +3.00 and -28.00 dpt using the Langham Ocular Blood Flow System. PA and POBF were correlated with axial length and refractive error using linear regression analysis. A significant correlation (p < 0.001) was found between PA and axial length (r = -0.787), PA and refractive error (r = 0.775), POBF and axial length (r = -0.655) and POBF and refractive error (r = 0.650). Myopic eyes were further divided into subgroups according to axial length, refractive error and fundus oculi characteristics. Each subgroup exhibited a significant reduction in PA (p < 0.001) compared to the control group. POBF reduction was significant in every subgroup except the subgroup with a refractive error lower than 6 dpt and the subgroup with an axial length shorter than 26 mm.

Adult↗
PubMed1982

Refractive errors in patients with fundus flavimaculatus.

A total of 59 patients (118 eyes) with fundus flavimaculatus who had atrophic macular lesions were examined for refractive error. Myopic refractions of greater than -0.1 dioptre were seen in 12% of a normal population and in 76% of our patient population. The spherical equivalent refractive errors described a single-peaked skewed distribution with a mean of -1.12 dioptres, which is 2.12 dioptres more myopic than that of a normal population. In addition astigmatic refractive errors of greater than +0.5 dioptres were found in 42% of this patient population, which is considerably more than the 18.6% observed in a normal population.

Adolescent↗
PubMed2001

Accommodation and refractive error in children with Down syndrome: cross-sectional and longitudinal studies.

PURPOSE: To examine the relationship between defective accommodation and refractive errors in children with Down syndrome. METHODS: Children with Down syndrome aged 4 to 85 months were seen at their homes as part of an ongoing study of visual development. Seventy-five children contributed cross-sectional data and 69 children longitudinal data. Accommodation was measured using a modification of Nott dynamic retinoscopy technique, and refractive error measurements were obtained using Mohindra retinoscopy. RESULTS: Accommodation was poor, regardless of the refractive error present. The total accommodation produced by the children was related to the refractive error at the time of the test, with the degree of accommodation deficit increasing with the amount of positive refractive error. The longitudinal results showed that although children with Down syndrome did not accommodate accurately, the amount of accommodation elicited did not reflect their maximum amplitude of accommodation. Each child showed a consistent degree of underaccommodation for a given stimulus. Spectacles to correct hypermetropia did not improve the accommodative response. CONCLUSIONS: In children with Down syndrome, underaccommodation is substantial, even when there is no, or a fully corrected, refractive error. The accommodation system of children with Down syndrome may have the physical capacity to respond to a given stimulus, but the neural control of the system has an anomalous set point. Spectacles do not remedy the situation. This has important implications, especially for children in a learning environment, because near vision is consistently out of focus.

Accommodation, Ocular↗
PubMed2004

Undercorrected refractive error in Singaporean Chinese adults: the Tanjong Pagar survey.

OBJECTIVE: To study the prevalence of undercorrected refractive error and associated sociodemographic factors among Singaporean Chinese adults. DESIGN: Cross-sectional, population-based survey. PARTICIPANTS: Singaporean Chinese adults aged 40 to 79 years (n = 1152). METHODS: The Singapore electoral register of Tanjong Pagar was used as a sampling frame, and disproportionate, stratified, clustered, random sampling was performed. There were 1717 eligible adults and 1232 (71.8%) participated. Analysis was performed among 1152 adults with complete habitual and best-corrected visual acuity data. MAIN OUTCOME MEASURE: Undercorrected refractive error was defined as improvement of better eye visual acuity of at least 2 lines or more with best possible refractive correction. RESULTS: The age- and gender-adjusted rate of undercorrected refractive error standardized directly by age and gender was 17.3% (95% confidence interval, 15.0, 19.5). Undercorrected refractive error rates were more common in older adults who had completed fewer years of education and in those who had cataract. People who did not wear spectacles tended to have poorer vision. CONCLUSIONS: The undercorrected refractive error rate among Singaporean Chinese is relatively common compared with data from other populations.

Adult↗
PubMed2006

Refractive errors in twin studies.

It is estimated that 1.6 billion people worldwide have myopia, a refractive error, and this number is expected to increase to approximately 2.5 billion by the year 2020. It is now well established that both the environment and genetics play a role in the development of myopia. However, the exact contribution of each of these components to myopia development has yet to be completely determined. Twin studies (classical twin model) are commonly used to determine the weighting of genetic and environmental components in disease. Over the last century, twin studies have investigated the heritability of refractive errors in different sample populations and have collectively supported a genetic basis to refractive errors. However, different sample populations and methods of data collection have produced a wide range of heritability estimates ranging from .5 to .9. This article will review those twin studies that have investigated refractive error, particularly myopia, as well as biometric measures linked to refractive error, to compare heritability estimates and methodology designs.

Diseases in Twins↗
PubMed2002

Refractive error in children in a rural population in India.

PURPOSE: To assess the prevalence of refractive error and related visual impairment in school-aged children in the rural population of the Mahabubnagar district in the southern Indian state of Andhra Pradesh. METHODS: Random selection of village-based clusters was used to identify a sample of children 7 to 15 years of age. From April 2000 through February 2001, children in the 25 selected clusters were enumerated in a door-to-door survey and examined at a rural eye center in the district. The examination included visual acuity measurements, ocular motility evaluation, retinoscopy and autorefraction under cycloplegia, and examination of the anterior segment, media, and fundus. Myopia was defined as spherical equivalent refractive error of at least -0.50 D and hyperopia as +2.00 D or more. Children with reduced vision and a sample of those with normal vision underwent independent replicate examinations for quality assurance in seven clusters. RESULTS: A total of 4414 children from 4876 households was enumerated, and 4074 (92.3%) were examined. The prevalence of uncorrected, baseline (presenting), and best corrected visual acuity of 20/40 or worse in the better eye was 2.7%, 2.6%, and 0.78%, respectively. Refractive error was the cause in 61% of eyes with vision impairment, amblyopia in 12%, other causes in 15%, and unexplained causes in the remaining 13%. A gradual shift toward less-positive values of refractive error occurred with increasing age in both boys and girls. Myopia in one or both eyes was present in 4.1% of the children. Myopia risk was associated with female gender and having a father with a higher level of schooling. Higher risk of myopia in children of older age was of borderline statistical significance (P = 0.069). Hyperopia in at least one eye was present in 0.8% of children, with no significant predictors. CONCLUSIONS: Refractive error was the main cause of visual impairment in children aged between 7 and 15 years in rural India. There was a benefit of spectacles in 70% of those who had visual acuity of 20/40 or worse in the better eye at baseline examination. Because visual impairment can have a significant impact on a child's life in terms of education and development, it is important that effective strategies be developed to eliminate this easily treated cause of visual impairment.

Adolescent↗
PubMed2004

Refractive errors among students occupying rooms lighted with incandescent or fluorescent lamps.

The purpose of the study was to determine whether the development of refractive errors could be associated with exposure to light emitted by incandescent or fluorescent lamps. 3636 students were examined (1638 boys and 1998 girls, aged 6-18 years, mean age 12.1, SD 3.4). The examination included retinoscopy with cycloplegia. Myopia was defined as refractive error < or = -0.5 D, hyperopia as refractive error > or = +1.5 D, astigmatism as refractive error > 0.5 DC. Anisometropia was diagnosed when the difference in the refraction of both eyes was > 1.0 D. The children and their parents completed a questionnaire on exposure to light at home. Data were analyzed statistically with the chi2 test. P values of less than 0.05 were considered statistically significant. It was found that the use of fluorescent lamps was associated with an increase in the occurrence of hyperopia (P < 0.01). There was no association between sleeping with the light turned on and prevalence of refractive errors.

Adolescent↗
PubMed2005

Refractive results with secondary piggyback implantation to correct pseudophakic refractive errors.

PURPOSE: To assess the efficacy and safety of implanting a second intraocular lens (IOL) to correct pseudophakic refractive errors. SETTING: Goldschleger Eye Institute, Sheba Medical Center, Tel Hashomer, Israel. METHODS: This prospective noncomparative case series included 10 pseudophakic eyes, 5 with a myopic residual refractive error and 5 with a hyperopic residual refractive error. All eyes had secondary piggyback IOL implantation with the IOL placed in the ciliary sulcus. Five types of IOLs were used to correct the residual refractive error. RESULTS: The mean preoperative myopia was -6.6 diopters +/- 3.3 (SD), and the refractive outcome was within 0.5 +/- 0.7 D of the desired refraction (range -1.5 [undercorrected] and +1.0 D [overcorrected]). The mean preoperative hyperopia was +3.8 +/- 0.8 D, and the refractive outcome was within 0.46 +/- 0.4 D of the desired refraction (range 0 and 1.0 D overcorrected). All patients showed visual acuity improvement. Best spectacle-corrected visual acuity improved from 20/44 to 20/30 (P<.05). CONCLUSION: An IOL type that is appropriate for implantation in the ciliary sulcus is a viable option for correcting pseudophakic refractive error using the piggyback technique.

Adult↗
PubMed1999

LASIK for the correction of residual refractive errors from previous surgical procedures.

BACKGROUND AND OBJECTIVE: To evaluate laser assisted in situ keratomileusis (LASIK) efficacy in correcting residual refractive errors after corneal or intraocular surgery (penetrating keratoplasty, radial keratotomy, photorefractive keratectomy, phacoemulsification with intraocular lens (IOL) implantation, penetrating ocular trauma and phakic IOL implantation). MATERIAL AND METHODS: We performed LASIK in 87 eyes of 62 patients previously operated by means of other surgical techniques to completely correct the residual refractive error. We report the mean refractive error (in terms of spherical equivalent refraction), uncorrected visual acuity (UCVA) and spectacle corrected visual acuity (SCVA) before and after the surgical procedure. We also analyze safety and stability, in these results with a minimum of 12 months follow-up. RESULTS: Mean preoperative spherical equivalent was -5.25 +/- 2.1 diopters (D). Postoperatively, mean spherical equivalent was -0.70 +/- 0.65 D, 76% of eyes were between plano and -1.00 D and 99% were between plano and -2.25 D. At 12 months follow-up the change in the refractive result was equal or less than 0.5 D in 94% of eyes. Preoperatively SCVA was 1.0 or better in 24.13% of cases, and 0.5 or better in 89.65%. Postoperative SCVA was 1.0 or better in 26.43% and 0.5 or better in 95%. Preoperative UCVA was 0.1 in 2 eyes, 0.05 in 4 eyes and count fingers in the rest of the cases. Postoperative UCVA was 1.0 or better in 1.1% and 0.5 or better in 70.1%. We had an extremely low complication rate in this particular group of patients. CONCLUSIONS: LASIK can be successfully used to correct residual refractive errors after other surgical procedures.

Adult↗
PubMed1987

An evaluation of the NR-1000F Auto Refractometer in high refractive errors.

The manifest refractions of 37 high myopic and 16 high hypermetropic eyes in a total of 28 patients, aged 5 to 42 years, were determined on the Nikon NR-1000F Auto Refractometer. The data obtained were compared with the final clinical prescriptions for these eyes and analysed for degree of agreement for the spherical equivalents, sphere components, and cylinder powers and axes. The Auto Refractometer recordings for all the different refractive components were observed to skew towards more minus in the high myopic eyes but more plus in the high hypermetropes. The possible significance of these skewing patterns is discussed with reference to our earlier studies.

Adolescent↗
PubMed1985

Disease-associated visual image degradation and spherical refractive errors in children.

Retrospective clinical data from 496 eyes of 256 children attending a low vision clinic were analyzed to determine the relation between disease states which involve visual image degradation and refractive error. Refractive data from 1023 normal vision children were used as a control. The low vision children were grouped according to their disease classification and the acknowledged age-of-onset of their visual disability. It was found that there was an overall inability to emmetropize and a trend towards myopia. It was also observed that the diseases which led to myopia were associated with a peripheral or peripheral plus central impairment of vision and that those conditions in which foveal vision was primarily impaired showed a mild hypermetropic trend. Eyes in which the visual impairment was not congenital but occurred before the age of 3 years tended to develop hypermetropia. The deviation from emmetropia decreased with increasing age-of-onset of the visual impairment, as did the variation about the mean refraction. The plastic period for emmetropization is estimated to end at 8 to 9 years of age.

Adolescent↗
PubMed1999

Refractive errors in an urban population in Southern India: the Andhra Pradesh Eye Disease Study.

PURPOSE: To assess the prevalence, distribution, and demographic associations of refractive error in an urban population in southern India. METHODS: Two thousand five hundred twenty-two subjects of all ages, representative of the Hyderabad population, were examined in the population-based Andhra Pradesh Eye Disease Study. Objective and subjective refraction was attempted on subjects >15 years of age with presenting distance and/or near visual acuity worse than 20/20 in either eye. Refraction under cycloplegia was attempted on all subjects < or =15 years of age. Spherical equivalent >0.50 D in the worse eye was considered as refractive error. Data on objective refraction under cycloplegia were analyzed for subjects < or =15 years and on subjective refraction were analyzed for subjects >15 years of age. RESULTS: Data on refractive error were available for 2,321 (92.0%) subjects. In subjects < or =15 years of age, age-gender-adjusted prevalence of myopia was 4.44% (95% confidence interval [CI], 2.14%-6.75%), which was higher in those 10 to 15 years of age (odds ratio, 2.75; 95% CI, 1.25-6.02), of hyperopia 59.37% (95% CI, 44.65%-74.09%), and of astigmatism 6.93% (95% CI, 4.90%-8.97%). In subjects >15 years of age, age-gender-adjusted prevalence of myopia was 19.39% (95% CI, 16.54%-22.24%), of hyperopia 9.83% (95% CI, 6.21%-13.45%), and of astigmatism 12.94% (95% CI, 10.80%-15.07%). With multivariate analysis, myopia was significantly higher in subjects with Lens Opacity Classification System HI nuclear cataract grade > or =3.5 (odds ratio, 9.10; 95% CI, 5.15-16.09), and in subjects with education of class 11 or higher (odds ratio, 1.80; 95% CI, 1.18-2.74); hyperopia was significantly higher in subjects > or =30 years of age compared with those 16 to 29 years of age (odds ratio, 37.26; 95% CI, 11.84-117.19), in females (odds ratio, 1.86; 95% CI, 1.33-2.61), and in subjects belonging to middle and upper socioeconomic strata (odds ratio, 2.10; 95% CI, 1.09-4.03); and astigmatism was significantly higher in subjects > or =40 years of age (odds ratio, 3.00; 95% CI, 2.23- 4.03) and in those with education of college level or higher (odds ratio, 1.73; 95% CI, 1.07-2.81). CONCLUSIONS: These population-based data on distribution and demographic associations of refractive error could enable planning of eye-care services to reduce visual impairment caused by refractive error. If these data are extrapolated to the 255 million urban population of India, among those >15 years of age an estimated 30 million people would have myopia, 15.2 million hyperopia, and 4.1 million astigmatism not concurrent with myopia or hyperopia; in addition, based on refraction under cycloplegia, 4.4 million children would have myopia and 2.5 million astigmatism not concurrent with myopia or hyperopia.

Adolescent↗
PubMed2002

Refractive error in children in an urban population in New Delhi.

PURPOSE: To assess the prevalence of refractive error and related visual impairment in school-aged children in an urban population in New Delhi, India. METHODS: Random selection of geographically defined clusters was used to identify a sample of children 5 to 15 years of age. From December 2000 through March 2001, children in 22 selected clusters were enumerated through a door-to-door survey and examined at a local facility. The examination included visual acuity measurements, ocular motility evaluation, retinoscopy and autorefraction under cycloplegia, and examination of the anterior segment, media, and fundus. Myopia was defined as spherical equivalent refractive error of at least -0.50 D and hyperopia as +2.00 D or more. Children with reduced vision and a sample of those with normal vision underwent independent replicate examinations for quality assurance in four of the clusters. RESULTS: A total of 7008 children from 3426 households were enumerated, and 6447 (92.0%) examined. The prevalence of uncorrected, baseline (presenting), and best corrected visual acuity of 20/40 or worse in the better eye was 6.4%, 4.9%, and 0.81%, respectively. Refractive error was the cause in 81.7% of eyes with vision impairment, amblyopia in 4.4%, retinal disorders in 4.7%, other causes in 3.3%, and unexplained causes in the remaining 5.9%. There was an age-related shift in refractive error from hyperopia in young children (15.6% in 5-year-olds) toward myopia in older children (10.8% in 15-year-olds). Overall, hyperopia was present in 7.7% of children and myopia in 7.4%. Hyperopia was associated with female gender. Myopia was more common in children of fathers with higher levels of education. CONCLUSIONS: Reduced vision because of uncorrected refractive error is a major public health problem in urban school-aged children in India. Cost-effective strategies are needed to eliminate this easily treated cause of vision impairment.

Adolescent↗
PubMed2006

Laser eye surgery for refractive errors.

Several laser and non-laser refractive surgical procedures have been used to modify the shape of the cornea and correct myopia, hyperopia, astigmatism, and presbyopia. Introduction of the excimer laser to reshape the cornea has resulted in remarkable developments in the correction of these refractive errors. Combined with other advanced ophthalmological instruments, laser refractive eye surgery has resulted in a substantial rise in the safety, efficacy, and predictability of surgical outcomes. Despite these advances, certain limitations and complications persist. In this review, we describe the history, preoperative assessment, surgical techniques, outcomes, and complications of laser refractive surgery.

Astigmatism↗
PubMed2004

Screening for myopia and refractive errors using LogMAR visual acuity by optometrists and a simplified visual acuity chart by nurses.

PURPOSE: To compare the sensitivity and specificity of a widespread method of screening for refractive errors in Singapore schoolchildren using a simplified acuity screening chart with a more rigorous method using the Early Treatment Diabetic Retinopathy Study (ETDRS) chart. A secondary aim is to estimate the best cutoff values for the detection of refractive errors using these two methods. METHODS: This is a population-based study, involving 1779 schoolchildren from three schools in Singapore. Logarithm of the minimum angle of resolution (logMAR) visual acuity was recorded using a modified Bailey-Lovie chart by trained optometrists, and visual acuity measurement was also undertaken using a simplified 7-line visual acuity screening chart by school health nurses. The main outcome measures were the receiver-operating characteristics (ROC's) of logMAR and the simplified screening visual acuity to detect myopia or any refractive errors. The difference between measurements, simplified screening visual acuity--logMAR visual acuity, was calculated. RESULTS: The optimal threshold using the simplified screening visual acuity chart for the detection of myopia or any refractive error was 6/12 or worse. Using logMAR visual acuity, the most efficient threshold for the detection of myopia was 0.26, but this was 0.18 for the detection of any refractive error. The area under the ROC curves was significantly greater in the case of the logMAR visual acuity measurement compared with the simplified screening visual acuity measurement for the detection of myopia or any refractive errors. The 95% limits of agreement for the two methods (simplified screening--logMAR acuity) was -0.219 to +0.339. CONCLUSIONS: Bearing in mind that the visual acuity measurements were performed by two different groups of professionals, visual acuity screening using the ETDRS method appears to be more accurate than the simplified charts for the detection of myopia or any refractive errors in children.

Child↗
PubMed1994

Refractive errors among engineering students in Norway.

This study reveals the prevalence of refractive errors in a group of young adults (mean age 20.6 years) exposed to high educational demands, including much reading. In all, 224 (117 females, 107 males) first-year engineering students were subjectively refracted. A prevalence of myopia of 46.9% (right eye), 49.1% (left eye) and 42.9% (both eyes), and a prevalence of hyperopia of 29.5% (right eye), 28.1% (left eye) and 23.2% (both eyes) was detected. The mean refractive error in the whole group was -0.6 +/- 2.2 D (right eye), -0.7 +/- 2.4 D (left eye) and -0.7 +/- 2.3 D (both eyes). As many as 56.4% (n = 57) of the myopic students had either no corrective lenses (11.9%, n = 12) or had their first corrective lenses prescribed at the age of 16 years or later (44.6%, n = 45). There was no significant difference in the prevalence of myopia between female and male students. No significant difference regarding body height was found among men in the different groups of refractive errors, but a significant difference was detected among women. We found no statistically significant relationship between intraocular pressure and any refractive error among men or women.

Adult↗
PubMed1990

Distribution of refractive errors in patients from Dominica, West Indies.

A total of 779 consecutive private patients requiring spectacles for correction of refractive errors were categorized according to age, sex, occupation and type of refractive error. Virtually all patients (97.1%) were black. The relationship between age, sex, occupation and refractive error was determined and showed that refractive errors were approximately equally distributed between the sexes, but myopia was more common among those with nearpoint occupations. Data also showed that more of the elderly were hyperopic than myopic in contrast to the younger patients who were more often myopic.

Adolescent↗