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PubMed2001

Why do we still not know whether refractive error causes headaches? Towards a framework for evidence based practice.

In this paper, we systematically review the available experimental and clinical evidence concerning the causation of headache by refractive error. Despite the apparent belief of both medical and optometric professionals that provision of an appropriate correction may alleviate various types of headache, there is little if any robust evidence in support of this position. We identify four serious methodological and theoretical difficulties with studies to date, which currently render it impossible to assess the relationship between refractive error and headache. The provision by the International Headache Society of the diagnostic category "headache associated with refractive error" is called into question. Five research questions are posited in the form of a framework for the development of evidence-based practice in optometry and the treatment of headache.

Evidence-Based Medicine↗
PubMed2006

The influence of low birth weight on the prevalence of refractive errors among schoolchildren.

PURPOSE: The aim of the study was to determine in a large population whether low birth weight has an influence on the prevalence of refractive errors among schoolchildren. MATERIAL AND METHODS: 3663 schoolchildren were examined (1738 boys and 1925 girls, aged 6-17 years, mean age 11.1, SD = 3.2). The weight at birth was 1500-2500 grams (mean 2184, SD = 271) in 254 and more than 2500 grams (mean 3398, SD = 441) in the remaining 3409 children. Skiascopy with cycloplegia was done and refractive error readings were reported as the spherical equivalent (SE). Myopia was defined as SE < or = -0.5 D, hyperopia as SE > or = +1.5 D. Anisometropia was diagnosed when the difference in the refraction of both eyes was > 1.0 D. The parents completed a questionnaire on the child's weight and term of birth. Data analysis was performed using chi-square test. P values of less than 0.05 were considered statistically significant. RESULTS: Hyperopia was observed more frequently in 6-7 year-old children whose birth weight was > 2500 grams (p < 0.05) - table 1. Additionally, it was found that anisometropia was less frequent in 10-11 year-old children whose birth weight was > 2500 g (p < 0.05) - table 2. CONCLUSION: Low birth weight may have an effect on the prevalence of refractive errors among schoolchidren.

Adolescent↗
PubMed2001

Correction of refractive error in the Victorian population: the feasibility of "off the shelf" spectacles.

AIMS: To assess the feasibility of providing a stock of ready made spectacles for correction of refractive error in the general population. METHODS: Data were collected in the Visual Impairment Project, a population based survey of Victorian residents aged 40 years or older in randomly selected urban and rural sample areas. This included a refractive eye examination and the proportion of subjects with hypermetropia, emmetropia (defined as -1.0 to +1.0D spherical equivalent), and myopia documented in the 40-60 year age group. RESULTS: 2595 (54.8%) participants were aged between 40 and 60 years. Those with a best corrected visual acuity of less than 6/12, astigmatism of more than 1.25D, and anisometropia of more than 0.5D were excluded. 516 participants had refractive error which was deemed suitable for correction by "off the shelf" spectacles. This represents 19.9% of all participants between 40 and 60 years of age. Provision of spectacles in 0.5D increments would provide suitable stock spectacles for 85.5% of a -3.0 to +3.0D range or 89.2% of a -3.50 to +3.50D range. CONCLUSIONS: Ready made "off the shelf" spectacles could significantly alleviate visual morbidity due to refractive error in up to 20% of an urban population in Australia. This approach may also be useful in developing countries with poor access to optometric services.

Adult↗
PubMed1988

Symptoms in video display terminal operators and the presence of small refractive errors.

Although the effects of using video display terminals (VDTs) have been examined from a number of perspectives, there has been relatively little study of the effect of small uncorrected refractive errors in the production of visual discomfort. The purpose of this study was to examine the level of six commonly assessed symptoms in a sample of 32 VDT operators via a questionnaire and to determine whether these were related to their habitual small refractive errors. The subjects reported substantial prevalence (55-81%) of each of the symptoms except double vision (16%). After a complete vision examination, the VDT operators were classified as relative myopes, hyperopes, astigmats or emmetropes. The criterion was a minimum of 0.50 D in the most ameotropic eye. Using this criterion, analysis showed that small refractive errors were significantly related to the reported level of symptoms of VDT operators. These results suggest the utility of proper refractive correction for the comfortable use of a VDT and the value of further research into this putative causal relationship.

Adolescent↗
PubMed2004

Piggyback intraocular lens implantation to correct myopic pseudophakic refractive error after penetrating keratoplasty.

PURPOSE: To determine the safety and efficacy of implanting a second intraocular lens (IOL) to correct myopic pseudophakic refractive error after penetrating keratoplasty (PKP). SETTING: Department of Ophthalmology, Toronto Western Hospital, Toronto, Ontario, Canada. METHODS: In this retrospective case series, 6 eyes of 6 post-PKP pseudophakic patients had a second piggyback IOL implantation to correct a residual myopic refractive error. The uncorrected visual acuity (UCVA) and the best corrected visual acuity (BCVA) were measured at regular intervals during a 7-month follow-up. Efficacy was determined by the achieved refractive correction and Snellen UCVA measurements. Safety was measured by loss of BCVA and complications (intraoperative and postoperative). RESULTS: The UCVA improved in all cases. Five patients achieved a BCVA of 20/40 or better postoperatively. Before surgery, the mean spherical equivalent (SE) was -8.08 diopters (D) (range -6.13 to -12.00 D). After surgery, the mean SE was -0.94 D (range -2.38 to +0.25 D). Four patients were within +/-1.50 D of emmetropia. There were no intraoperative or postoperative complications. CONCLUSION: Implanting a piggyback IOL was a safe and effective means of correcting myopic pseudophakic refractive error post PKP.

Aged↗
PubMed2007

Refractive errors in neurofibromatosis type 1 and type 2.

OBJECTIVE: To document the prevalence of refractive errors in patients with neurofibromatosis type 1 (NF1) and type 2 (NF2) and to compare it with that of age- and sex-matched controls. METHODS: 82 patients with NF1, 21 patients with NF2 and 103 age- and sex-matched controls were evaluated in this prospective observational case-control study. Cycloplegic autorefraction and dilated fundus examination were performed. Myopia was defined as the spherical equivalent refraction of at least -0.50 diopters (D), hyperopia as the spherical equivalent refraction of at least 2.0 D and astigmatism as the cylinder of at least 1.0 D. Main outcome measures were refractive error, IQ, years of education, height, weight and body mass index (BMI). RESULTS: The prevalence of myopia was 23.1% in patients with NF1, 23.8% in patients with NF2 and 16.5% in age- and sex-matched controls. These differences were significant (p<0.03, p<0.03), and adjusting for intelligence, education, height, weight and BMI increased the significance of this finding (p<0.001, p<0.001). The prevalences of astigmatism and hyperopia were similar in both groups. CONCLUSION: A high prevalence of myopia seems to be an additional feature of NF1 and NF2.

Case-Control Studies↗
PubMed1993

Inter-individual variability in the dynamics of natural accommodation in humans: relation to age and refractive errors.

1. To study the relationship between accommodation under natural viewing conditions, age and refractive errors, we have measured time courses of accommodation in thirty-nine human subjects aged 5-49 years using a newly developed technique. The technique is based on infrared photoretinoscopy and involves fully automated on-line image processing of digitized video images of the eyes with a sampling rate of 5.3 Hz. 2. The distance between the subject and the video camera was about 1.3 m. Head movements of the subject required little restriction because the eyes were automatically tracked in the video image by the computer program. All subjects were tested under binocular viewing conditions. 3. Both refraction of the right eye and pupil diameter were measured with a precision of 0.2-0.4 dioptres (D) and 0.1 mm, respectively, and were plotted on-line. The data were subsequently automatically analysed. 4. Automated infrared photoretinoscopy proved to be very convenient and easy to handle in both children and adults. 5. The maximal speed of accommodation for a target at a distance of 5 D declined in the subjects with age (from up to 21.7 D s-1 for accommodation and 32.7 D s-1 for subsequent accommodation to a distant target ('near to far accommodation') in children down to 2-18 D s-1 in adults). There was a striking inter-individual variability in the maximum possible speed of accommodation and near to far accommodation. 6. Speed of accommodation and of near to far accommodation was correlated for each subject. However, in most of the subjects, the process of near to far accommodation was faster than accommodation (P < 0.005, if averaged over all subjects). This correlation was independent of age. 7. The accommodation-induced pupillary constriction (pupillary near response) was absent in children for a 4 D target; even at 10 D, there was no reliable pupillary response. The pupillary near response increased to about 1.6 mm D-1 of accommodation at the age of 47. Since a pupillary near response could still be elicited in presbyopic subjects unable to accommodate, the ratio of pupillary constriction per dioptre of accommodation approached infinity. 8. The magnitude of the pupillary near response was highly variable even among subjects of the same age but was typical for each subject. There was a correlation (P < 0.01) to refractive error: corrected myopes had weaker pupillary near responses than emmetropes or hyperopes.(ABSTRACT TRUNCATED AT 400 WORDS)

Accommodation, Ocular↗
PubMed1980

Axial lengths and refractive errors in kittens reared with an optically induced anisometropia.

An anisometropia was simulated in kittens during the critical period of development by securing a high-powered negative lens in front of one eye. Refractive error measurements obtained with an objective infrared optometer indicated that the deprived eyes of the anisometropic kittens were significantly more myopic than the normal eyes. A-scan ultrasonography showed that these differences in refractive error were correlated with an increase in the axial dimensions of the deprived eyes. The results of this experiment demonstrate that form deprivation associated with a habitually defocused retinal image produces an experimental myopia which is similar in nature to the refractive error changes produced by lid fusion and corneal opacification.

Age Factors↗
PubMed1990

Survey of spectacle wear and refractive error prevalence in USAF pilots and navigators.

A retrospective survey of 5000 active aircrew records was performed at 12 United States Air Force (USAF) bases to obtain information about the prevalence of spectacle wear and refractive error. The data revealed that 27.4% of pilots and 51.5% of navigators/weapons systems operators (Nav/WSO) required spectacles when flying. Of the spectacle-wearing pilots, 12.4% required bifocals. Myopia was the predominant refractive error and a relatively large percentage of aircrew members had astigmatism of 0.75 D or more, e.g., 33.1% of pilots. At the time of entry into the USAF, refractive error data were clustered around emmetropia with a definite skew toward hyperopia.

Adult↗
PubMed1998

Custom photorefractive keratectomy ablations for the correction of spherical and cylindrical refractive error and higher-order aberration.

Photorefractive keratectomy is an evolving refractive procedure for correcting myopia, hyperopia, and astigmatism. Earlier descriptions of the patterns required for this surgery are based on paraxial optics. In this investigation the required pattern is generalized to account for spherical refractive error (defocus), axial astigmatism of arbitrary orientation, and fourth-order aberrations of the eye. The patterns described in this study can be used to customize photorefractive keratectomy and to provide corrections that account for aberration content as well as paraxial values. Furthermore, a description of the pattern along the boundary of the optical zone is given, which may prove useful in designing blending zones. An example of the use of these techniques is given for a schematic eye model.

Astigmatism↗
PubMed1987

Refractive error change at the United States Air Force Academy--class of 1985.

A retrospective study was conducted at the United States Air-Force Academy (USAFA) to determine the incidence and change in refractive error over a 2.5-year period between the entrance and third academic year physical examinations. For all 994 eyes (497 cadets aged 17 to 21 years) at entrance, there were 37.3% hyperopes, 18.5% emmetropes, and 44.2% myopes of -0.25 D or more, by spherical equivalent (SPEQ). A significant (p less than 0.001) mean SPEQ change of -0.18 D, -0.21 D, and -0.57 D occurred for the hyperopic, emmetropic, and myopic eyes, respectively, over this period. A myopic change of -0.25 D or more was seen in 47.7%, 41.3%, and 74.0% of the hyperopic, emmetropic, and myopic eyes, respectively, with a clinically significant myopic shift of -0.50 D or greater seen in 21.3%, 25.0%, and 55.1% of these refractive error types, respectively. Myopia progression was derived separately from those eyes showing any amount of myopic shift (greater than or equal to -0.12 D), and was -0.42 D, -0.52 D, and -0.75 D for the hyperopic, emmetropic, and myopic eyes, respectively. There was a higher incidence and rate of myopia increase in the higher refractive errors, whether hyperopic or myopic. These findings suggest that 17- to 21-year-olds are not as safe from a myopic change as thought previously, particularly during an intensive educational program.

Adolescent↗
PubMed1993

Refractive error distribution and incidence among U.S. Army aviators.

Spectacle incompatibility has been a major problem in the fielding of advanced Army avionic and electro-optical systems. As a result, routine contact lens wear may be instituted as an option to spectacles. Refractive error data were extracted from the Aviation Epidemiological Data Registry, a computer-accessible repository of flight physical medical information on the entire Army aviation population. Refractive error distribution patterns in the class 1 and class 2 flight physical populations were analyzed in order to provide a contact lens supply reference database, estimate the annual incidence of refractive error development, and estimate costs of possible spectacle-wearer flight-duty deselection. Contact lens wear appears to be a more cost-effective alternative than deselection.

Aerospace Medicine↗
PubMed2003

[Refractive error and the intraocular pressure: findings in the Chinese eyes].

PURPOSE: To analysis the correlation between the refractive error and the intraocular pressure. METHODS: The IOP was measured in 142 eyes with noncontact tonometer. The refractive error were determined with an autorefractometer(TOPCON-7100). RESULTS: The analysis of variance showed that IOP of medium myopia is the highest, and a significant IOP difference between medium myopia and severe myopia, and IOP of patients less than 19yrs is significantly higher than patients more than 30 yrs; and there is also no significant influence of gender on patients' IOP, mean IOP(13.04 +/- 2.97) mmHg. CONCLUSION: These results suggest that when medium myopia IOP is relatively higher, or when a young patient less than 19 whose IOP is relatively higher than usual, that may mean the eye is under an unstable situation.

Adolescent↗
PubMed2004

The age- and gender-specific prevalences of refractive errors in Tehran: the Tehran Eye Study.

PURPOSE: To determine the age- and gender-specific prevalences of refractive errors in Tehran through a population-based study. METHODS: A total of 6497 citizens representing a cross-section of the population of Tehran were sampled from 160 clusters using a stratified, random, cluster sampling strategy. Eligible people were enumerated through a door-to-door household survey in the selected clusters and were invited to participate. All participants were transferred to a clinic for an extensive eye examination and interview. Refractive error was determined using manifest and cycloplegic refraction. Myopia was defined as the spherical equivalent of -0.5 diopters (D) or more and hyperopia was defined as the spherical equivalent of more than +0.5 D. RESULTS: Of those sampled, 4565 (70.3%) people participated in the study. Refraction data for 4354 participants aged five years and over are presented. The age- and gender-standardized prevalence of myopia based on manifest refraction was 21.8% (95% confidence interval [CI], 20.1 to 23.5) and that for hyperopia was 26.0% (95% CI, 24.5 to 27.6). The prevalences based on cycloplegic refraction were 17.2% (95% CI, 15.6 to 18.8) and 56.6% (95% CI, 54.7 to 58.6), respectively. Prevalences of myopia and hyperopia differed significantly among the age and gender groups (P < 0.001). Astigmatism of 0.75 cylinder diopter or greater was present in 29.6% (95% CI, 28.0 to 31.3) of right eyes with manifest refraction and in 30.3% (95% CI, 28.5 to 32.1) with cycloplegic refraction. Among the study population, 6.1% (95% CI, 5.3 to 6.8%) had anisometropia of 1 D or more. CONCLUSIONS: This report has provided details of the refractive status in the population. We have documented prevalences of myopia, hyperopia, astigmatism and anisometropia by age and gender, identifying more affected age- and gender-groups for prevention programs in the community.

Adolescent↗
PubMed2004

The relationship between intraocular pressure and refractive error adjusting for age and central corneal thickness.

PURPOSE: To investigate the relationship between intraocular pressure (IOP) and refractive errors after adjusting for age, central corneal thickness (CCT), and other related factors. METHODS: IOP, CCT and refractive errors were measured in the right eyes of 1855 subjects, aged 40-82 years, in a cross-sectional study design. Subjects were divided into groups by refractive status: hyperopia, emmetropia, mild myopia, moderate myopia, or high myopia. With adjustments for age, CCT, blood pressure, obesity, education, hypertension, diabetes, and smoking status, IOP was estimated for each refractive status using a general linear model. RESULTS: IOP increased with advancing degrees of myopia, even after adjustment for age, CCT, and other related factors (p = 0.011). Estimated IOP of moderate myopia was significantly higher than that of emmetropia (p = 0.022). CONCLUSIONS: Our results confirm the positive association between IOP and increasing degrees of myopia. This finding would support the hypothesis that the relationship between glaucoma and myopia might be pressure mediated.

Adult↗
PubMed2026

Variance Polygenic Scores (vPGS) as a Tool for Studying Gene-Environment Interactions Associated With Refractive Error.

PURPOSE: Conventional polygenic scores predict an individual's phenotype based on their genetics. By contrast, variance polygenic scores (vPGS) quantify genetic predisposition to phenotypic variance. We tested the hypothesis that a vPGS for refractive error can identify individuals with increased susceptibility to environmental risk factors for myopia. METHODS: Six vPGS construction strategies were evaluated in UK Biobank participants: three variance heterogeneity genome-wide association study (vGWAS) methods and two reweighting schemes. vPGS performance was assessed using two metrics: (i) "Diff"-difference in phenotypic variance in vPGS decile ten versus one; (ii) Spearman correlation of phenotypic variance versus vPGS decile. The optimal vPGS was used to test for vPGS &#xd7; time spent reading or vPGS &#xd7; time spent outdoors interactions in children aged 15 years (ALSPAC cohort; n = 3471). RESULTS: Of the vGWAS methods, conditional quantile regression outperformed SCAMPI and Levene's Test. Of the re-weighting schemes, LDpred2 outperformed pruning and thresholding. In an independent sample of UK Biobank participants (n = 19,470), the top-performing vPGS successfully stratified individuals into groups with increasing variance in refractive error, even after adjusting for a conventional PGS (Diff: 2.55, 95% confidence interval [CI], 1.64-3.47; Spearman correlation = 0.87; 95% CI, 0.43-0.93). However, in ALSPAC participants, there was minimal support for vPGS interactions with time reading (P = 0.80) or time outdoors (P = 0.89). CONCLUSIONS: A novel vPGS successfully stratified individuals into groups with relatively high or low genetic susceptibility to refractive error variance. However, the vPGS could not identify individuals at enhanced risk from lifestyle risk factors for myopia.

Humans↗
PubMed2002

Designing lenses to correct peripheral refractive errors of the eye.

The purpose of this work was to design ophthalmic lenses that correct peripheral refractive errors of human eyes along a meridian. We designed lenses with the tangential section of one surface based on a figured spheroid but figured in the tangential section only. The curvature of the sagittal section of this surface was adjusted separately. A merit function was used to modify these surfaces until the lenses had power errors that corrected the eye. Examples are presented of lenses that correct a schematic eye. They do excellent jobs of correcting the peripheral power errors of the eye and are relatively insensitive to small changes in fitting distance. We conclude that it is theoretically feasible to design lenses to correct peripheral refractive errors.

Equipment Design↗
PubMed2000

Refractive Error Study in Children: results from Shunyi District, China.

PURPOSE: To assess the prevalence of refractive errors and vision impairment in school-age children in Shunyi District, northeast of Beijing, the Peoples Republic of China. METHODS: Random selection of village-based clusters was used to identify a sample of children 5 to 15 years of age. Resident registration books were used to enumerate eligible children in the selected villages and identify their current school. Ophthalmic examinations were conducted in 132 schools on children from 29 clusters during May 1988 to July 1998, including visual acuity measurements, cycloplegic retinoscopy, cycloplegic autorefraction, ocular motility evaluation, and examination of the external eye, anterior segment, media, and fundus. Independent replicate measurements of all children with reduced vision and a sample of those with normal vision were done for quality assurance monitoring in three schools. RESULTS: A total of 6,134 children from 4,338 households were enumerated, and 5,884 children (95.9%) were examined. The prevalence of uncorrected, presenting, and best visual acuity 0.5 (20/40) or worse in at least one eye was 12.8%, 10.9%, and 1.8%, respectively; 0.4% had best visual acuity 0.5 or worse in both eyes. Refractive error was the cause in 89.5% of the 1,236 eyes with reduced vision, amblyopia in 5%, other causes in 1.5%, with unexplained causes in the remaining 4%. Myopia -0.5 diopter or less in either eye was essentially absent in 5-year-old children, but increased to 36.7% in males and 55.0% in females by age 15. Over this same age range, hyperopia 2 diopters or greater decreased from 8.8% in males and 19.6% in females to less than 2% in both. Females had a significantly higher risk of both myopia and hyperopia. CONCLUSIONS: Reduced vision because of myopia is an important public health problem in school-age children in Shunyi District. More than 9% of children could benefit from prescription glasses. Further studies are needed to determine whether the upward trend in the prevalence of myopia continues far beyond age 15 and whether the development of myopia is changing for more recent birth cohorts.

Adolescent↗