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PubMed1993

A comparison between donor-recipient corneal size and its effect on the ultimate refractive error induced in keratoconus.

A prospective randomized clinical study was performed to see the effect of donor-recipient corneal size on the ultimate refractive error induced in keratoconus at our facility. The patients were randomly divided into two groups, A and B. In Group A, the difference in size between the donor and the recipient cornea was 0.25 mm (18 patients). In Group B, the difference in size between the donor and the recipient cornea was 0.50 mm (20 patients). Both groups underwent the surgical procedure with the same surgeon (M.A.J.) and the same technique. Two months after suture removal, keratometry readings and refractive errors induced were compared. The mean keratometry reading in Group A was 43.3 diopters; in Group B, the reading was 44.8 diopters. There was a mean difference of 1.5 diopters between the two groups (p = 0.01). The mean refractive error in terms of spherical equivalent in Group A was -1.55 diopters and in Group B was -3.33 diopters. There was a difference of -1.8 diopters between the two groups (p < 0.05).

Adolescent↗
PubMed2002

Refractive errors and 10-year incidence of age-related maculopathy.

PURPOSE: To describe the relationship of refractive errors to the 10-year incidence of age-related maculopathy (ARM) in a defined white population. METHODS: Persons aged 43 to 86 years of age in Beaver Dam, Wisconsin, were invited for a baseline examination from 1988 through 1990, and follow-up examinations 5 and 10 years later (n = 3684). Refraction was measured at baseline, with myopia defined as a spherical equivalent of -1.00 D or less, emmetropia as -0.75 to +0.75 D and hyperopia as +1.00 D or more. At each examination, signs of ARM were ascertained from grading stereoscopic color fundus photographs based on a standard protocol. The association between baseline refractive status and the 10-year incidence and progression of ARM was analyzed. RESULTS: The 10-year cumulative incidence for early ARM was 7.1%, 7.7%, and 11.7%, in eyes with myopia, emmetropia, and hyperopia, respectively. The corresponding 10-year cumulative incidence for late ARM was 0.3%, 0.8%, and 2.2%. When age was controlled for, there was no association between myopia and incident early (relative risk [RR] 1.0, 95% confidence interval [CI], 0.7-1.3) and late (RR 0.5, 95% CI, 0.2-1.5) ARM. Similarly, after controlling for age, hyperopia was not associated with incident early (RR 0.9, 95% CI, 0.7-1.1) or late (RR 1.2, 95% CI, 0.6-2.3) ARM. CONCLUSIONS: These prospective population-based data provide no evidence of an association between refractive errors and risk of ARM.

Adult↗
PubMed1990

Refractive errors in Singapore medical students.

The refraction of 128 third-year medical students aged 20-22 was studied using a Topcon autorefractometer. The population was predominantly Chinese and comprised 44% females and 56% males. The mean refractive error was -3.75 D for males and -4.76D for females. In all, 82% of the students were myopic, 72% were found to have astigmatism. This study confirms clinical impressions that Singapore students have one of the highest prevalence rates of myopia and astigmatism in the world.

Adult↗
PubMed2004

[Correction of refractive errors with LASIK].

Laser in situ keratomileusis (LASIK) is the most prevalent method for correction of refraction errors. Within certain limits, all types of refraction errors may be treated with excellent accuracy and stability of the corrections. Serious complications are rare, but they may be sight-threatening and should be promptly dealt with by an ophthalmologist. This paper presents an overview, aimed at the general practitioner, of this procedure, indications for it, clinical course, and the main complications.

Adult↗
PubMed2001

The effect of degree of refractive error on hydrogel contact lens-induced complications and patient self-management behaviors.

INTRODUCTION: Although many aspects of hydrogel lens wear have been explored over the last 20 years, little attention has been paid to the role of refractive error magnitude in determining patients' ocular responses or associated contact lens behaviors. METHODS: A cross-sectional study was conducted in 32 optometric and ophthalmologic practices. We enrolled 2161 spherical soft contact lens-wearing patients. High ametropes were defined as those with at least +/- 5.00 D spherical equivalent refractive error in the right eye. Data on current contact lenses, prescribed care regimens, and slit lamp biomicroscopic signs were provided by the eye care practitioners, and information on actual lens care behaviors and attitudes toward contact lens wear were gathered by survey directly from the patients. All differences between high and low ametropes were compared using the chi-square test. RESULTS: Compared with low ametropes, high ametropes were more satisfied with their vision with contact lenses (p < 0.001). More high ametropes wore their lenses on an extended-wear schedule (p = 0.015). Both groups of patients reported a similar degree of lens awareness and lens-associated pain, but fewer high ametropes reported foreign body sensation (p = 0.002). In managing contact lens discomfort, high ametropes were more likely to use an old spare lens (p = 0.01) and more likely to continue wearing their lenses (p = 0.016)--indicators of a propensity for self-management. In response to a damaged lens, high ametropes were less likely to remove both of their lenses (p = 0.002). High ametropes showed more conjunctival staining (p = 0.001) and more corneal scars (p = 0.033). High ametropes also presented with more corneal fluorescein staining (p = 0.001) and more corneal vascularization (p < 0.001). These relations between the degree of ametropia and slit lamp signs of contact lens wear were not significantly affected by daily- vs. extended-wear status. CONCLUSIONS: In summary, practitioners should consider the implications of the patient's degree of ametropia when prescribing contact lenses. These results indicate the need for closer observation and specific advice concerning management of contact lens-related problems when caring for patients with high refractive errors.

Adult↗
PubMed2006

Ethnicity-specific prevalences of refractive errors vary in Asian children in neighbouring Malaysia and Singapore.

AIM: To compare the prevalences of refractive errors in Malay, Chinese and Indian children in Malaysia and Singapore. METHODS: Children aged 7-9 years from three schools in the Singapore Cohort study of the Risk factors for Myopia (n = 1962) and similarly aged children from a random cluster sample in the metropolitan Kuala Lumpur area in the Malaysia Refractive Error Study in Children (n = 1752) were compared. Cycloplegic autorefraction was conducted in both countries. RESULTS: The prevalence of myopia (spherical equivalent of at least -0.5 diopters (D) in either eye) was higher in Singapore Malays (22.1%) than in Malays in Malaysia (9.2%; 95% confidence interval (CI) 11.2 to 14.7; p<0.001). Similarly, Singapore Chinese (40.1%) had higher prevalences than Malaysian Chinese (30.9%; 95% CI 1.5 to 16.9). Singapore Indians had a higher prevalence (34.1%) than Malaysian Indians (12.5%; 95% CI 17.4 to 25.9). The multivariate odds ratio of astigmatism (cylinder at least 0.75 D in either eye) in Singapore Malays compared with Malaysian Malays was 3.47 (95% CI 2.79 to 4.32). Ethnicity-specific hyperopia rates did not differ in Singapore and Malaysia. CONCLUSION: The ethnicity-specific prevalences of myopia in Singapore Malays, Chinese and Indians are higher than those in Malaysian Malays, Chinese and Indians. As Malays, Chinese and Indians in Malaysia have genetic make-up similar to that of Malays, Chinese and Indians in Singapore, environmental factors may contribute to the higher myopia rates.

Asian People↗
PubMed1997

Effects of refractive error on detection acuity and resolution acuity in peripheral vision.

PURPOSE: To evaluate the effect of refractive error on detection acuity and resolution acuity in peripheral vision. METHODS: Detection acuity, defined as the highest spatial frequency for which luminance gratings can be discriminated from a uniform field, and resolution acuity, defined as the highest spatial frequency for which spatial patterns are perceived veridically, was determined for vertical and horizontal gratings located at 20 degrees, 30 degrees, and 40 degrees of eccentricity. Resolution was also measured for tumbling-E discrimination at these locations. Refractive state of the eye for test targets was manipulated by introducing an ophthalmic trial lens into the line of sight for the stimulus while holding accommodative state fixed. RESULTS: Detection acuity in the periphery varied significantly with the amount of optical defocus, whereas acuity for grating resolution or letter discrimination was unaffected by defocus over a large range (up to 6 D). These results are consistent with the working hypothesis that detection acuity in the periphery is limited by contrast insufficiency under normal viewing conditions, but resolution is limited by ambiguity because of neural undersampling. CONCLUSIONS: The large depth of focus for resolution acuity measured for peripheral vision indicates that spatial resolution is likely to remain sampling-limited even when peripheral refractive errors are not fully corrected, thus relaxing the methodologic requirements for obtaining noninvasive estimates of neural sampling density of the living eye in a clinical setting.

Contrast Sensitivity↗
PubMed1998

Refractive error and age-related maculopathy: the Blue Mountains Eye Study.

PURPOSE: To assess associations between refractive error (hyperopia, myopia, and spherical equivalent [SEq]) and age-related maculopathy (ARM) in an older population. METHODS: A population-based survey examined 3654 people aged 49 years or older, 82% of whom were permanent residents in an area west of Sydney, Australia. Participants had a detailed eye examination, including standardized refraction and stereo macular photographs. ARM was diagnosed from blinded photographic grading. Autorefractor measurements and subjective refraction were used to assess SEq refractive error for each eye in diopters. Mean SEq of the two eyes was used to define emmetropia, myopia, and hyperopia in each person. RESULTS: After known ARM risk factors (age, sex, ARM family history, current smoking) had been adjusted for, no association was found between mean SEq (two eyes) and late ARM (odds ratio [OR], 1.0; 95% confidence interval [CI], 0.9-1.1). However, a statistically significant increased risk of early ARM was found for each diopter of increase in mean SEq (OR, 1.1; CI, 1.0-1.2). In logistic regression models, moderate to high hyperopia was significantly associated with increased early ARM risk (OR, 2.0; CI, 1.2-3.4). When a generalized estimating equation model (GEE), which assessed the relationship at eye level while accounting for the correlation between the two eyes, was used, this association was marginally insignificant (OR, 1.3; CI, 0.9-1.9). No significant associations were found between myopia and any ARM stage with either model. CONCLUSIONS: These population-based data suggest a weak association between hyperopia and early ARM.

Age Distribution↗
PubMed1977

Refractive error distribution in a profoundly retarded population.

The refractive errors distribution of 103 profoundly retarded individuals (10 of zero to 20) was determined. This distribution was skewed in the direction of myopia. Since no such data were available for any other profoundly retarded population, direct comparison with other studies was not possible. However, a significant difference in mean spherical equivalent was found between the profoundly retarded of this study and the combined severely and profoundly retarded of two earlier studies.

Adolescent↗
PubMed1975

Corneal curvature and refractive error changes associated with wearing hydrogel contact lenses.

To determine if there are corneal curvature and refractive error changes associated with hydrogel lens wear, 27 patients wearing F series Bausch & Lomb SOFLENS-TM contact lenses were examined regularly for nine months. During the first month of lens wear, a mean corneal steepening of 0.23 DK plus or minus 0.18 and an increase in with-the-rule toricity were found, which persisted during the following eight months of wear. A mean increase in myopia of 0.35 DS plus or minus .211 DS was found after nine months of lens wear for five randomly selected patients. This amount of change was statistically significant and was highly correlated with the observed corneal steepening. Their lenses were removed after nine months of lens wear. Both corneal changes and the increase in myopia persisted during the 14 days after lens removal. If long term studies with larger samples show similar results, the effect of hydrogel lenses on corneal curvature and refractive error will have to be considered in the decision to fit this type of lens.

Adult↗
PubMed1999

Refractive errors in an older population: the Blue Mountains Eye Study.

OBJECTIVE: To determine prevalence and associations with refractive errors in a defined older population. DESIGN: Cross-sectional study. PARTICIPANTS: A total of 3654 residents, aged 49-97, of the Blue Mountains, west of Sydney, Australia. METHODS: Comprehensive questionnaire and detailed eye examination, including refraction. MAIN OUTCOME MEASURES: Refractive error of phakic eyes, age, gender, and education. RESULTS: Prevalence rates were determined for myopia (15%), hyperopia (57%), and emmetropia (28%). Hyperopia prevalence was age-related, increasing from 36% in persons aged <60 years to 71 % of persons aged > or = 80 (P < 0.0001), whereas myopia prevalence decreased with age, from 21 % in persons aged <60 years to 10% of persons aged > or = 80 years (P < 0.0001). Younger myopic subjects in this population reported first wearing distance correction at a significantly younger age than older subjects, P < 0.0001. After adjustment for age, women were slightly more hyperopic (mean +0.75 diopters [D]) than men (mean +0.59 D, P = 0.0012. The gender-adjusted mean spherical error increased with age from +0.03 D in persons aged <60 years to +1.2 D in persons aged > or = 80 years (P < 0.0001). The gender-adjusted mean cylinder power also increased with age, from -0.6 D in persons aged <60 years to -1.2 D in persons aged > or = 80 years (P < 0.0001). The mean axis of astigmatism was "against the rule" in all age groups. Anisometropia increased with age, from a mean of 0.4 D in persons aged <60 to 0.9 D in persons aged > or = 80 years (P < 0.0001). Higher education was associated with myopia in men (P = 0.009) but not in women (P = 0.21) after adjustment for age. CONCLUSION: This report has documented the detailed refractive status of an older population, confirming previously described trends but also finding an apparent higher prevalence of myopia among younger members of this community.

Aged↗
PubMed2004

Refractive error and visual impairment in urban children in southern china.

PURPOSE: To assess the prevalence of refractive error and visual impairment in school-age children in a metropolitan area of southern China. METHODS: Random selection of geographically defined clusters was used to identify children 5 to 15 years of age in Guangzhou. Children in 22 clusters were enumerated through a door-to-door survey and examined in 71 schools and 19 community facilities from October 2002 to January 2003. The examination included visual acuity measurements, ocular motility evaluation, retinoscopy, and autorefraction under cycloplegia and examination of the external eye, anterior segment, media, and fundus. RESULTS: A total of 5053 children living in 4814 households were enumerated, and 4364 (86.4%) were examined. The prevalence of uncorrected, presenting, and best-corrected visual acuity 20/40 or worse in the better eye was 22.3%, 10.3%, and 0.62%, respectively. Refractive error was the cause in 94.9% of the 2335 eyes with reduced vision, amblyopia in 1.9%, other causes in 0.4%, and unexplained causes in the remaining 2.8%. External and anterior segment abnormalities were seen in 1496 (34.3%) children, mainly minor conjunctival abnormalities. Media and fundus abnormalities were observed in 32 (0.73%) children. Myopia (spherical equivalent of at least -0.50 D in either eye) measured with retinoscopy affected 73.1% of children 15 years of age, 78.4% with autorefraction. The prevalence of myopia was 3.3% in 5-year-olds with retinoscopy and 5.7% with autorefraction. Females had a significantly higher risk of myopia. Hyperopia (+2.00 D or more) measured with retinoscopy was present in 16.7% of 5-year-olds, 17.0% with autorefraction. The prevalence of hyperopia was below 1% in 15-year-olds, with both methods. Astigmatism (cylinder of > or = 0.75 D) was present in 33.6% of children with retinoscopy and in 42.7% with autorefraction. CONCLUSIONS: The prevalence of reduced vision because of myopia is high in school-age children living in metropolitan Guangzhou, representing an important public health problem. One third of these children do not have the necessary corrective spectacles. Effective strategies are needed to eliminate this easily treated cause of significant visual impairment.

Adolescent↗
PubMed2006

Quantification of refractive error: comparison of autorefractor and focometer.

PURPOSE: The advantages of a focometer (FOCOMETER) over other methods of refraction for use in developing countries are that it is lightweight, compact, relatively inexpensive, fairly quick, and easy to use with minimal training. This clinical trial compared the repeatability, validity, and ease of use of the focometer with an autorefractor. METHODS: The refractive status of the right eye of 80 participants was determined with an autorefractor (Canon RK3). Three measurements were also taken with the focometer. RESULTS: The spherical equivalent (M) of the focometer was 0.25 D more positive than the autorefractor (p < 0.001) and 84% of measurements were within 0.75 D of the autorefractor. The autorefractor detected astigmatism in 91% (73) of the eyes, whereas the focometer identified only 32% (26). The design of the clock target restricts cylinder axis accuracy to the nearest 15 degrees . There was evidence of a learning effect for the focometer: the second and third measurements were more repeatable in the untrained group. There were no differences between the mean (1.03 +/- 2.28) and third focometer (-1.05 +/- 2.32) measurements (p = 0.34). However, using the third focometer measurement, 94% of participants had visual acuities of at least 6/12(-2). CONCLUSIONS: This study highlighted the focometer's restricted power range, inaccuracy of astigmatism and axis determination, and dependence on subject understanding and compliance. Therefore, in most clinical settings, the focometer would not be adequate for quantifying refractive error, but the focometer spherical equivalent was within acceptable limits of the autorefractor, and the visual acuity with lenses determined by the focometer indicates its potential usefulness in public health settings, especially where only spherical ready-made spectacles are dispensed. There may be more cost-effective ways to determine refractive error in these circumstances. A potentially important enhancement in focometer methodology that improves its ease of use was identified: use only the third measurement for each eye.

Adult↗
PubMed1997

High refractive errors and the accident/incident rate in Canadian medical category 1 pilots.

BACKGROUND: Since 1982, the Canadian Civil Aviation Medicine Division has medically certified to Category 1 standard commercial and airline transport pilots whose visual correction was in excess of +/- 3.5 diopters (D). METHOD: A review between the years 1982 and 1991 of the 253 pilots who had been medically certified, although they were outside the standard, was conducted. We determined if there was any difference in the accident/incident rate in this group as compared with the Canadian general aviation population standardized to a rate per 100,000 flying hours. The 253 pilots were divided into two groups with Group A having a refractive error outside the range +/- 5.7 D and Group B having a refractive error range of +/- 3.5 to +/- 5.6 D. RESULTS: The Group A rate was within the expected range of accidents and incidents per 100,000 flying hours. The accident/incident rate in Group B was significantly lower than the expected average. CONCLUSION: In conclusion, the Canadian Civil Aviation Medicine Division's policy on granting "flexibility" to applicants with moderate to high refractive errors has not affected adversely the accident or incident rate and therefore has not compromised aviation safety.

Accidents, Aviation↗
PubMed2005

Correction of large amblyopiogenic refractive errors in children using the excimer laser.

PURPOSE: We sought to determine whether laser subepithelial keratomileusis (LASEK) and photorefractive keratectomy (PRK) are effective methods for correcting amblyopiogenic refractive errors in children. METHODS: Thirty-six eyes in 35 amblyopic children, who ranged in age from 4 to 16 years (mean, 8.4 years), received treatment for large magnitude ametropia. Seventy-two percent (25/35) of the children had a neurobehavioral disorder and/or were noncompliant with spectacle or contact lens wear. Myopia ranged from -3.25 to -24.25 D (mean, -11.48 D); one patient had hyperopia of +5.87 D. Correction was tailored to match the refractive error of the nonamblyopic eye. VISX Star S2/S3 excimer lasers were used in manual or auto-tracking modes, and corneal centration was achieved using brief, general anesthesia. Mean follow-up was 29.2 months (range, 4-42 months). RESULTS: Myopia correction averaged -8.95 +/- 2.89 D (range, -3.25 to -15.50). Eighty-nine percent (31 children) were corrected to within +/- 1.00 D of goal refraction and the remaining 11% to within 2.0 D of the goal (most were undercorrected). Acuity improved postoperatively in 97%; by 1 optotype line in 37% and by 2 or more in 60%. No child lost acuity. Binocularity improved in 69% (24/35) and remained the same in 31%. Corneal haze measured grade 0-1 in 78%, grade 2 in 14%, and grade 3-4 in 8%. Myopic regression exceeding congruent with 1.0 D/year (0.08 D/month) occurred in 50% (18/36) of eyes treated. No substantial differences were observed in PRK- (n = 18) versus LASEK- (n = 17) treated children. CONCLUSIONS: Laser refractive surgery is effective for correcting anisometropic myopia in amblyopic children. Recurrence of myopia is common. Further study is indicated to determine long-term stability and safety of the procedure in this population.

Adolescent↗
PubMed2002

Refractive error and monochromatic aberrations in Singaporean children.

Higher order optical aberrations were measured in 273 cyclopleged Singaporean school children using a Bausch and Lomb Zywave aberrometer, with 268 of these subjects also undergoing corneal topography measurements (Tomey TMS 2 system). Subjects with low myopia (> -3.00 to -0.50 D) showed slightly, but significantly, less positive levels of spherical aberration than other refractive error groups. Chinese subjects also showed significantly higher amounts of aberrations than Malay subjects, particularly for vertical coma, but also for horizontal coma and spherical aberration. Anterior corneal spherical aberration (calculated from topography) was significantly correlated with whole eye spherical aberration, but did not vary significantly with refractive error or racial background. Residual spherical aberration (i.e. of posterior cornea and crystalline lens) did vary significantly with refractive error and race. Our results do not provide any evidence for aberration-driven form-deprivation as a major mechanism of myopia development.

Child↗
PubMed1984

[Refractive errors, amblyopia and strabismus in congenital ptosis].

Fifty-four consecutive surgical cases of congenital ptosis were carefully evaluated to determine the incidence of refractive errors, strabismus and amblyopia. Of these patients, 70% had a refractive error, 43% had an astigmatism of more than 1.0, 55% had anisometropia, 27.5% had concomitant squint and 50% amblyopia.

Amblyopia↗
PubMed2006

Refractive error and visual impairment in school children in rural southern China.

PURPOSE: To assess the prevalence of refractive error and visual impairment in school children in a rural area of southern China. DESIGN: Prospective cross-sectional survey. PARTICIPANTS: Two thousand four hundred children from junior high schools in Yangxi County. METHODS: Random selection of classes from the 3 junior high school grade levels was used to identify the study sample. Children from 36 classes in 13 schools were examined in April 2005. The examination included visual acuity (VA) testing; ocular motility evaluation; cycloplegic autorefraction; and examination of the external eye, anterior segment, media, and fundus. MAIN OUTCOME MEASURES: Distance VA and cycloplegic refraction. RESULTS: Among 2515 enumerated children, 2454 (97.6%) were examined. The study population consisted of the 2400 children between 13 and 17 years old. Prevalences of uncorrected, presenting, and best-corrected VA < or = 20/40 in the better eye were 27.0%, 16.6%, and 0.46%, respectively. Sixty percent of those who could achieve acuity > or =20/32 in at least one eye with best correction were without the necessary spectacles. Refractive error was the cause in 97.1% of eyes with reduced vision; amblyopia, 0.81%; other causes, 0.67%; and unexplained causes, 1.4%. Myopia (spherical equivalent, -0.50 diopters [D] or more in either eye) affected 36.8% of 13-year-olds, increasing to 53.9% of 17-year-olds. Myopia was associated with higher grade level, female gender, schooling in the county urban center, and higher parental education. Hyperopia (+2.00 D or more) affected approximately 1.0% in all age groups. Astigmatism (> or =0.75 D) was present in 25.3% of all children. CONCLUSIONS: Reduced vision because of uncorrected myopia is a public health problem among school-age children in rural China. Effective VA screening strategies are needed to eliminate this easily treated cause of visual impairment.

Adolescent↗