Iris colour and astigmatism among Chinese teenagers

BACKGROUND/AIMS

Iris colour might contribute to refractive development, but it is uncertain whether it is related to astigmatism. We aim to examine the association of iris colour with the presence of astigmatism in a school-based sample of Chinese students.

METHODS

2346 grade 7 students from 10 middle schools aged 13 to 14 years in Southwestern China participated in the study. We obtained standardised slit-lamp photographs and developed a grading system assessing iris colour (higher grade denoting darker). Astigmatism was defined as a cylinder power of more than 0.50, 0.75 or 1.00 dioptre (D). Logistic regression models with generalised estimating equation were fitted to assess the relationship between iris colour and astigmatism, accounting for the correlation between both eyes. ORs and 95% CIs were presented.

RESULTS

The overall prevalence of astigmatism for three different definitions was 30.4% (95% CI 28.6% to 32.2%) (<-0.5 D), 12.7 % (95% CI 11.3% to 14.0%) (<-0.75 D) and 5.3% (95% CI 4.4% to 6.2%) (<-1.0 D), respectively. In multivariate analysis adjusting for the effect of gender and height, darker iris colour was associated with an increasing trend of astigmatism (p for trend <0.05). Compared with individuals with iris colour of grade 4 or 5 (the darkest), those with grade 1 or 2 (the lightest) were significantly less likely to be affected by astigmatism (<-0.75 D) in gender-adjusted model (OR 0.67) and multivariate-adjusted model (OR 0.72).

CONCLUSION

Darker iris colour might be a risk factor for astigmatism in Chinese adolescents.

[PREVALENCE OF ASTIGMATISM BEFORE ROUTINE CATARACT SURGERY: COMPARISON BETWEEN BEDOUIN AND JEWISH POPULATION IN SOUTHERN ISRAEL]

OBJECTIVES

To assess the prevalence of corneal astigmatism among patients before routine cataract surgery and overall ocular difference between Jewish and Bedouin population in the south of Israel.

METHODS

Retrospective research collecting biometric information from IOLMaster (Carl Zeiss Meditec AG, Germany) in patients attending cataract surgery at Soroka University Medical Center, Beer-Sheva, Israel between the years 2015 -2016.

RESULTS

Mean corneal astigmatism among all cohorts was 1.20D ± 0.83, with 1.26D ± 0.84 in Bedouins patients vs 1.17D ± 0.82 in Jews patients (p-value=0.08). Corneal astigmatism lower than 0.5D was seen in 20% of the population, 28% of the population had corneal astigmatism above 1.5D and 9% showed corneal astigmatism higher than 2.5D. When comparing axial length and keratometric characteristics between the two populations, Bedouins had shorter axial length (23.41mm± 1.62 vs. 23.67mm ± 1.55, p=0.01), and flatter corneas on both axes (flat - 43.18D ± 1.76 vs. 43.62D ± 1.79, p<0.01); (steep - 44.44D ± 1.84 vs. 44.77D± 1.89, p<0.01). Higher astigmatism was found in men than in women (1.24D vs.1.15D p- value=0.04) of study group.

CONCLUSIONS

In our study we found more than 25% of patients had astigmatism more than 1.5D. Patients attending cataract surgery may therefore benefit the use of advanced IOL types and surgical techniques. In addition, a statistically significant difference between the Bedouin and Jewish populations biometric measurements in patients attending cataract surgery found.

Aspheric Micro-monovision LASIK in Correction of Presbyopia and Myopic Astigmatism: Early Clinical Outcomes in a Chinese Population

PURPOSE

To analyze early clinical outcomes of aspheric micro-monovision LASIK for correction of presbyopia and myopia with or without astigmatism.

METHODS

Prospective, non-comparative case series of 80 eyes of 40 patients with a mean age of 43.4 ± 4.9 years (range: 38 to 63 years) treated bilaterally using an aspheric micro-monovision protocol. The target refraction was plano for the distance eye and between -0.75 and -2.25 diopters (D) for the near eye. Visual acuity, ocular aberrations, contrast sensitivity, corneal topography, amplitude of accommodation, binocular sensorial function, and satisfaction score questionnaires were evaluated at 3 months after surgery.

RESULTS

Three months after surgery, the mean spherical equivalent (SE) refraction in the distance eye was -0.08 ± 0.27 D, whereas the attempted and achieved SE in the near eye were -1.41 ± 0.28 and -1.32 ± 0.35 D, respectively. Ninety-three percent of eyes were within ±0.50 D of target correction of SE. The uncorrected distance visual acuity (UDVA) after surgery was -0.10 ± 0.06 logMAR (20/15.5), 0.22 ± 0.12 logMAR (20/34), and -0.11 ± 0.06 logMAR (20/15), for distance eyes, near eyes, and binocularly, respectively. Ninety-five percent of patients achieved simultaneously uncorrected distance visual acuity 0.0 logMAR (20/20) or better and uncorrected near visual acuity J2 (20/25) or better. Stability was achieved from 1 week of follow-up. The overall satisfaction score for surgery was 92 ± 6.

CONCLUSIONS

The aspheric micro-monovision protocol provided a well-tolerated and effective means for treating myopic astigmatism and alleviating presbyopic symptoms simultaneously. [J Refract Surg. 2016;32(10):680-685.].

Risk factors for astigmatism in the Vision in Preschoolers Study

PURPOSE

To determine demographic and refractive risk factors for astigmatism in the Vision in Preschoolers Study.

METHODS

Three- to 5-year-old Head Start preschoolers (N = 4040) from five clinical centers underwent comprehensive eye examinations by study-certified optometrists and ophthalmologists, including monocular visual acuity testing, cover testing, and cycloplegic retinoscopy. Astigmatism was defined as the presence of greater than or equal to +1.5 diopters (D) cylinder in either eye, measured with cycloplegic refraction. The associations of risk factors with astigmatism were evaluated using the odds ratio (OR) and its 95% confidence interval (CI) from logistic regression models.

RESULTS

Among 4040 Vision in Preschoolers Study participants overrepresenting children with vision disorders, 687 (17%) had astigmatism, and most (83.8%) had with-the-rule astigmatism. In multivariate analyses, African American (OR, 1.65; 95% CI, 1.22 to 2.24), Hispanic (OR, 2.25; 95% CI, 1.62 to 3.12), and Asian (OR, 1.76; 95% CI, 1.06 to 2.93) children were more likely to have astigmatism than non-Hispanic white children, whereas American Indian children were less likely to have astigmatism than Hispanic, African American, and Asian children (p < 0.0001). Refractive error was associated with astigmatism in a nonlinear manner, with an OR of 4.50 (95% CI, 3.00 to 6.76) for myopia (≤-1.0 D in spherical equivalent) and 1.55 (95% CI, 1.29 to 1.86) for hyperopia (≥+2.0 D) when compared with children without refractive error (>-1.0 D, <+2.0 D). There was a trend of an increasing percentage of astigmatism among older children (linear trend p = 0.06). The analysis for risk factors of with-the-rule astigmatism provided similar results.

CONCLUSIONS

Among Head Start preschoolers, Hispanic, African American, and Asian race as well as myopic and hyperopic refractive error were associated with an increased risk of astigmatism, consistent with findings from the population-based Multi-ethnic Pediatric Eye Disease Study and the Baltimore Pediatric Eye Disease Study. American Indian children had lower risk of astigmatism.

Distance refractive error among Aboriginal people attending eye clinics in remote South Australia

PURPOSE

To determine the prevalence of distance refractive error among Aboriginal people attending eye clinics in remote South Australia.

METHODS

A clinic-based cross-sectional study was conducted that involved opportunistic sampling of Aboriginal people attending eye clinics in remote South Australia. There were 189 individuals who were invited to participate in the study all of whom underwent ophthalmic examination. This examination included measurement of pinhole-corrected visual acuity and non-cycloplegic autorefraction.

RESULTS

Automated refractive error examinations were performed on 148 people within this sample. The mean age was 44.8 +/- 14.5 years and women comprised 57.7% of the sample. The overall mean refractive error was -0.01 +/- 1.8 D (SD). The prevalence of myopia (spherical equivalent (SE) < -0.5 D), high myopia (SE less than or equal to -6.0 D), hypermetropia (SE > 0.5 D), astigmatism (cylinder at least -0.5 D) and anisometropia (difference in SE of >0.5 D) was 31.1%, 0.7%, 33.1%, 55.8% and 45.9%, respectively. Further analyses revealed significant age-related trends with both myopia and hypermetropia. There were no gender associations with any form of refractive error. Of those people with clinically significant refractive error, 51/148 (34%), only four people owned distance spectacles.

CONCLUSIONS

There continues to be a level of uncorrected distance refractive error within these patients. This represents a need to screen for refractive error among Aboriginal people in remote locations and to provide them with appropriate spectacle correction.

Higher Order Ocular Aberrations in Eyes With Myopia in a Chinese Population

PURPOSE

To describe the characteristics of higher order ocular aberrations of adult Chinese eyes with myopia.

METHODS

Higher order aberrations in consecutive right eyes of 166 Chinese patients with myopia who enrolled for preoperative assessment for LASIK were retrospectively reviewed. Wavefront aberrations were measured with the Bausch & Lomb Zywave over a 6-mm dilated pupil. The correlations between higher order aberrations and myopia, astigmatism, and age, respectively, were analyzed.

RESULTS

Mean patient age was 32.1 +/- 6.2 years, the mean refractive error was sphere -5.23 +/- 1.79 diopters (D) and cylinder -1.29 +/- 0.98 D. The mean of the total higher order root-mean-square (RMS) (third to fifth order) was 0.49 +/- 0.16 microm. Third-order RMS was largest (mean 0.37 +/- 0.16 microm), followed by fourth-order RMS (mean 0.29 +/- 0.11 microm). For individual higher order Zernike coefficients, spherical aberration (C4(0)) predominated with a mean of 0.23 +/- 0.14 microm. No correlation was found between total higher order RMS and myopia or between total higher order RMS and age. Small but statistically significant relationships were found in the following groups: age and vertical primary coma (C3(-1))(r=-0.206, P=.008); age and spherical aberration (C4(0)) (r=0.196, P=.012); and myopia and horizontal trefoil (C3(3)) (r=-0.158, P=.042).

CONCLUSIONS

Higher order aberrations varied among individuals with myopia. Third-order RMS was the predominant higher order aberration. Spherical aberration and vertical primary coma increased slightly with age. Our study helps establish ocular aberration standards for Chinese refractive surgery candidates.

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.

Prevalence of High Astigmatism, Eyeglass Wear, and Poor Visual Acuity Among Native American Grade School Children

PURPOSE

The purpose of this study was to examine the prevalence of astigmatism and poor visual acuity and rate of eyeglass wear in grade school children who are members of a Native American tribe reported to have a high prevalence of large amounts of astigmatism.

METHODS

Vision screening was conducted on 1,327 first through eighth grade children attending school on the Tohono O'odham Reservation. Noncycloplegic autorefraction was conducted on the right and left eye of each child using the Nikon Retinomax K+ autorefractor, and monocular recognition acuity was tested using ETDRS logarithm of the minimum angle of resolution (logMAR) letter charts.

RESULTS

Tohono O'odham children had a high prevalence of high astigmatism (42% had > or = 1.00 D in the right or left eye) and the axis of astigmatism was uniformly with-the-rule. However, only a small percentage of children arrived at the vision screening wearing glasses, and the prevalence of poor visual acuity (20/40 or worse in either eye) was high (35%). There was a significant relation between amount of astigmatism and uncorrected visual acuity with each additional diopter of astigmatism resulting in an additional 1 logMAR line reduction in visual acuity.

CONCLUSIONS

Uncorrected astigmatism and poor visual acuity are prevalent among Tohono O'odham children. The results highlight the importance of improving glasses-wearing compliance, determining barriers to receiving eye care, and initiating public education programs regarding the importance of early identification and correction of astigmatism in Tohono O'odham children.

Wavefront Analysis in Asian-Brazilians

PURPOSE

To compare the distribution of ocular higher order wavefront aberrations (third to sixth order) in the Brazilian population of Asian and non-Asian refractive surgery patients.

METHODS

Preoperative refractive and wavefront data were reviewed for 648 eyes in 324 patients who underwent custom ablation at the Excimer Laser Santa Cruz refractive surgery center in São Paulo, Brazil, from March 2002 to July 2005. Patients were divided into two groups: Asian patients and non-Asian patients, based on family history. Statistical analysis was performed to assess the differences between the groups with respect to manifest refractive spherical equivalent, astigmatism, pachymetry, OPD-root-square-mean (RMS) for a 6.0-mm pupil, total wavefront aberrations, third- to sixth-order higher order aberrations, and individual aberrations.

RESULTS

The mean spherical equivalent refraction in the Asian group of -4.38 diopters (D) was significantly higher than the spherical equivalent refraction of -3.46 D in the non-Asian group (t= -4.32; P=.00001). Comparison of the differences between groups with respect to higher order aberrations, coma, trefoil, quadrafoil, spherical aberration, higher order astigmatism, and pachymetry was not statistically significant.

CONCLUSIONS

Asian patients have a higher prevalence of myopia than non-Asian patients. No differences were noted in higher order aberrations between Asian and non-Asian patients.

Relationship between astigmatism and aging in middle-aged and elderly japanese

PURPOSE

To study the effect of aging on astigmatism in adult Japanese.

METHODS

Measurements of refractive errors and keratometry were performed on 2161 randomly selected subjects (aged 40-79 years). The relation between age and the net value in diopters (D) of astigmatism was evaluated with a trend test. The relation between age and the polar value was also examined by linear regression analysis.

RESULTS

The mean (+/-SD) value of total and corneal astigmatism was -0.97 +/- 0.72 D and -0.86 +/- 0.63 D, respectively, and the net value of both increased with age (P trend < 0.001). The prevalence of either type of astigmatism also increased with age, according to the Cochran-Mantel-Haenzel test (P < 0.0001 for total and P < 0.01 for corneal astigmatism). The prevalence of against-the-rule astigmatism increased with age for either type of astigmatism (P < 0.0001 for total, P < 0.0001 for corneal). According to the analysis of polar values by age, the regression coefficient (+/-SE) for total and corneal astigmatism was -0.024 +/- 0.002 (P < 0.0001) and -0.028 +/- 0.002 (P < 0.0001), respectively. There was no statistical difference between these two regression coefficients.

CONCLUSIONS

The prevalence of astigmatism increases and the axis turns to against-the-rule with age. The result of the linear regression analysis indicates that the age-related change in astigmatism is mainly associated with changes in the cornea.

Refractive error and ethnicity in children

OBJECTIVE

To report the baseline prevalence of refractive error in the study population.

DESIGN

A multicenter, longitudinal, observational study of refractive error and ocular development in children from 4 ethnic groups.

PATIENTS AND METHODS

The study population included 2523 children (534 African American, 491 Asian, 463 Hispanic, and 1035 white) in grades 1 to 8 (age, 5-17 years). Myopia was defined as -0.75 diopters (D) or more and hyperopia as +1.25 D or more in each principal meridian, and astigmatism was defined as at least a 1.00-D difference between the 2 principal meridians (cycloplegic autorefraction).

RESULTS

Overall, 9.2% of the children were myopic, 12.8% were hyperopic, and 28.4% were astigmatic. There were significant differences in the refractive error prevalences as a function of ethnicity (chi2, P<.001), even after controlling for age and sex (polychotomous logistic regression, P<.001). For myopia, Asians had the highest prevalence (18.5%), followed by Hispanics (13.2%). Whites had the lowest prevalence of myopia (4.4%), which was not significantly different from African Americans (6.6%). For hyperopia, whites had the highest prevalence (19.3%), followed by Hispanics (12.7%). Asians had the lowest prevalence of hyperopia (6.3%) and were not significantly different from African Americans (6.4%). For astigmatism, Asians and Hispanics had the highest prevalences (33.6% and 36.9%, respectively) and did not differ from each other (P =.17). African Americans had the lowest prevalence of astigmatism (20.0%), followed by whites (26.4%).

CONCLUSION

There were significant differences in the prevalence of refractive errors among ethnic groups, even after controlling for age and sex (P<.001).

Corneal and refractive error astigmatism in Singaporean schoolchildren: a vector-based Javal's rule

BACKGROUND

Traditional approaches to Javal's rule do not use data from subjects with oblique astigmatism and have not been used to make predictions about subjects with oblique astigmatism. Vector approaches to analyzing refractive error can circumvent these problems.

METHODS

Subjects were 993 Singaporean schoolchildren. We performed linear regression of refractive error astigmatism on corneal astigmatism, using J0 vectors to describe with-the-rule and against-the-rule astigmatism and J45 vectors to describe oblique astigmatism.

RESULTS

We obtained the following statistically significant regression relationships: RJ0 = 0.931 x CJ0 - 0.276 and RJ45 = 0.638 x CJ45 + 0.010, where R and C denote refractive error astigmatism and corneal astigmatism, respectively.

CONCLUSION

Our vector-based Javal's rule gives closer predictions of refractive astigmatism than the original Javal's rule and the simplified Javal's rule and can be applied in cases of corneal oblique astigmatism.

[Les amétropies statiques du noir camerounais]

PURPOSE

We undertook this study with the aim to determine static ametropias of black Cameroonians as well as their clinical manifestations. It is a prospective study carried out in the Department of Ophthalmology of Douala General Hospital from January 1996 to December 1998.

PATIENTS AND METHOD

During this period, all patients who fulfilled our criteria had a skiascopy done under cycloplegia. We thus examined 2,484 patients (4,968 eyes). 66.2% of them were female and 33.8% were male.

RESULTS

In our series, hyperopia was found in 51% of the cases, hyperopic astigmatism in 27.5% of the cases, myopic astigmatism in 9.3% of cases, mixed astigmatism in 7.7% of cases and myopia in 4.5% of cases. Distribution of ametropias is influenced by age, not by sex or laterality.

DISCUSSION AND CONCLUSION

Functional signs just have an indicative value; only objective refraction under cycloplegia can determine exactly the ametropia.

Comparison of preschool vision screening methods in a population with a high prevalence of astigmatism

PURPOSE

To compare the effectiveness of four methods of screening 3- to 5-year-old children for astigmatism high enough to require spectacle correction.

METHODS

Lea Symbols Visual Acuity Screening (LSVAS), MTI Photoscreening (MTIPS), Nidek KM-500 Keratometry Screening (KERS), and Retinomax K-Plus Noncycloplegic Autorefraction Screening (NCARS) were attempted on 379 preschool children who are members of a Native American tribe having a high prevalence of astigmatism that is primarily corneal in origin. The need for spectacle correction was determined by cycloplegic refraction. Receiver Operating Characteristic (ROC) curves were fit, confidence intervals were determined, and area under the curves was compared.

RESULTS

Astigmatism > or = 1.00 D was present in the right eye of 47.5% and in the left eye of 48.0% of children. Spectacles were prescribed for children < 48 months of age who had cylinder > or = 2.00 D and children > or = 48 months who had cylinder > or = 1.50 D, with the result that 33% of subjects required spectacles. Area under the ROC curve was 0.98 for NCARS, 0.92 for KERS, 0.78 for MTIPS, and 0.70 for LSVAS, and each of these values differed significantly from the other three (all P < 0.007). Testability was significantly higher for NCARS (99.5%) and KERS (99.7%) than for MTIPS (93.5%) and LSVAS (92.0%).

CONCLUSIONS

In a population that included many children with astigmatism, objective, fully automated screening methods (NCARS and KERS) were superior to both visual acuity screening and photoscreening with subjective interpretation in identifying children who had astigmatism requiring spectacle correction.

Astigmatism and Amblyopia among Native American Children (AANAC): design and methods

The overall goal of the AANAC study is to improve detection of astigmatism and prevention of amblyopia in populations with a high prevalence of astigmatism. To meet this goal, the study will evaluate four methods of screening for astigmatism in preschool children and will assess both the short-term and long-term benefits of early correction of astigmatism in improving acuity and preventing amblyopia. This paper presents an overview of the design and methodology of the AANAC study. Subjects are members of the Tohono O'Odham Nation, a Native American tribe with a high prevalence of astigmatism. Preschool-age children who attend Head Start are screened with four tools: the Marco Nidek KM-500 autokeratometer, the MTI photoscreener, the Nikon Retinomax K-Plus autorefractor, and the Lea Symbols acuity chart. Sensitivity and specificity for detection of significant astigmatism, as measured by a technique that uses both cycloplegic retinoscopy and cycloplegic autorefraction, is determined for each of the four screening tools. Presence of amblyopia is evaluated by measurement of best-corrected recognition acuity and acuity for orthogonal gratings. Spectacles are provided to all 3-year-old children with > or =2.00 diopters (D) of astigmatism and all 4- and 5-year-old children with > or =1.50 D of astigmatism. Persistence of amblyopia after glasses wearing is evaluated by follow-up measurement of best-corrected recognition acuity and acuity for orthogonal gratings, conducted 2-5 months after glasses are prescribed. Long-term effectiveness of early screening and glasses prescription is evaluated through measurement of recognition acuity in two groups of first-grade children: one group who participated in the Head Start program before the intensive vision screening program was initiated, and a second group who participated in the study's Head Start vision screening program.

Measurement of refractive error in Native American preschoolers: validity and reproducibility of autorefraction

PURPOSE

To examine (1) reproducibility of cycloplegic retinoscopy (C-RNS), cycloplegic autorefraction (C-Autoref), and noncycloplegic autorefraction (NC-Autoref), and (2) validity of C-Autoref and NC-Autoref compared with C-RNS in preschoolers with astigmatism.

METHODS

Subjects were 36 Native American preschoolers. Three measurements of right eye refractive error were obtained with each of three methods: C-RNS (by three different retinoscopists), C-Autoref, and NC-Autoref (Nikon Retinomax K+). Vector methods (vector dioptric distance, VDD) were used in the analyses.

RESULTS

Mean reproducibility was 0.41 D (SD = 0.18) for C-RNS, 0.25 D (SD = 0.17) for C-Autoref, and 0.37 D (SD = 0.21) for NC-Autoref. Mean agreement between C-Autoref and C-RNS ranged from 0.51 to 0.61 VDD (SD = 0.24 to 0.35), and ranged from 1.66 to 1.74 VDD (SD = 1.11 to 1.25) for agreement between NC-Autoref and C-RNS. Mean bias was -0.07 +0.21 x 149 and -1.33 +0.34 x 178 for C-Autoref and NC-Autoref, respectively.

CONCLUSIONS

C-Autoref provided reliable and valid measurements of refractive error in young children. NC-Autoref measurements were reliable within subjects, but there was large variability in validity among subjects.

Corneal and refractive astigmatism in a sample of 3- to 5-year-old children with a high prevalence of astigmatism

PURPOSE

To examine the relation between corneal and refractive astigmatism in a sample of pre-school-age Native American children with a high prevalence of astigmatism.

METHODS

Subjects were 250 Tohono O'Odham children, 3 to 5 years of age. Each child had corneal astigmatism measured with the Marco Nidek KM-500 portable autokeratometer without pupil dilation, and with the Nikon Retinomax K-Plus portable autorefractor/autokeratometer without and with pupil dilation. Refractive astigmatism was measured using the Retinomax K-Plus, with cycloplegia, confirmed by retinoscopy.

RESULTS

Corneal astigmatism exceeded refractive astigmatism, with a median vector dioptric difference of 0.88 D for the KM-500, 0.76 D for the Retinomax K-Plus without dilation, and 0.75 for the Retinomax K-Plus with dilation. The relation between corneal and refractive astigmatism was adequately described by the modification by Grosvenor et al. of Javal's rule, but not by laval's rule.

CONCLUSIONS

The results are in agreement with data reported previously for older Native American and non-Native American populations. The modified laval's rule adequately describes the relation between corneal and refractive astigmatism in a population; however, this rule does not provide accurate prediction of refractive astigmatism in individual children or adults.

The aging effect on corneal curvature and the validity of Javal's rule in Hong Kong Chinese

PURPOSE

The current study compared the central corneal curvature and the refractive error of Hong Kong Chinese to study the validity of Javal's rule.

METHODS

Subjects without corneal pathology were recruited at different age ranges. Their refractive error and the corneal curvature were measured and compared for the right eye only. Two instruments were used for the measurement of corneal curvature including a conventional Bausch & Lomb (B&L) keratometer and a computer-assisted videokeratoscope (TMS-1).

RESULTS

Subjects age ranged from 21 years to 77 years were recruited and were categorized into five groups according to age. The Bausch & Lomb keratometer was found to provide corneal information similar to that from the TMS-1. The corneal astigmatism was found to change from with-the-rule to against-the-rule with advancing age. The spectacle astigmatism followed a similar trend. There was a hyperopic shift in the spherical component of the refractive error with aging as well. A regression equation: Spectacle astigmatism = 0.93 (Corneal astigmatism) + (-0.58D x 90) was found, which is similar to the simplified Javal's rule. There was a shift of 1.03D in hyperopia (spherical equivalent) for each decade.

CONCLUSIONS

Both the corneal and spectacle astigmatism demonstrated a shift from with-the-rule to against-the-rule with age. The simplified Javal's rule is more suitable for predicting the spectacle astigmatism from corneal astigmatism in Hong Kong Chinese.

Distribution of astigmatism among Sioux Indians in South Dakota

BACKGROUND

Previous studies have reported a greater prevalence of high astigmatism and vision disorders among Native Americans than occurs in the general U.S. population. The majority of these studies, however, have focused on Native American schoolchildren. This study assessed the distribution of astigmatism in a general clinic population at the Rosebud Indian Reservation in South Dakota.

METHODS

From examination of 174 patients, demographic information, visual acuities, refractive error, binocular vision status, and eye health were recorded.

RESULTS

The data showed more high astigmatism than would be expected in a general U.S. population. Three or more diopters of astigmatism were found in 9.2% of the right eyes and 10.8% of the left eyes in the study population. High astigmatism was noted less frequently among those ages 40 years and older (3.3% right eyes, 6.3% left eyes). Most of the astigmatism was with-the-rule, but a shift toward against-the-rule and oblique astigmatism was found in older individuals. No significant gender differences were noted.

CONCLUSIONS

The results suggest an ethnic difference in astigmatism and emphasize thee need for continued and expanded vision services for Native American populations.

Astigmatism in Bangladeshi and white school entrants in East London: a prospective comparative study

A prospective comparative study was undertaken to determine the prevalence of significant astigmatism in school entrants living in the same area of East London. Thirty-one Bangladeshi and thirty-one white school entrants were refracted in two local state schools. In the Bangladeshi group, 7 right and 5 left eyes had more than 1 dioptre of astigmatism. Most of this astigmatism was with the rule. In the white group, 1 left eye had more than 1 dioptre of astigmatism. This study has shown a statistically significant incidence of astigmatism in an ethnic group in East London. This difference between two racial groups living in the same area of East London has not previously been documented. In our study, Bangladeshi school entrants may be at greater risk of amblyopia if their refractive error is not identified and corrected.

Changes in refractive trends and optical components of Hong Kong Chinese aged 19-39 years

The distribution of refractive errors and its relationship to the optical components in 105 Hong Kong Chinese aged 19-39 years was studied. Myopia was most frequent (71%) in this population. The mean spherical equivalent was -3.00 DS. The trend of changes of the direction of refractive and corneal astigmatism from with-the-rule to against-the-rule with increasing age was shown. Significant correlations were found between age and anterior segment distance. Ultrasound examination showed that an increasing axial length was associated with higher myopia. Men had flatter corneal radii, but longer axial length. The prevalence of myopia in the Chinese population seems to be a new trend for the younger Hong Kong Chinese when compared with adults aged over 40 years. Thus the importance of genetics in determination of myopia is called into question by these findings.

Changes in refractive trends and optical components of Hong Kong Chinese aged over 40 years

The age trends of refractive errors, astigmatism and optical components were studied in 220 Chinese subjects aged over 40 years. Myopia did not dominate in this age group. With increasing age, the prevalence of hyperopia increases from 2% at age 40-45 years to 66% at age > 65 years. Against-the-rule astigmatism was more prevalent than the other types. Significant correlations were found between age and spherical equivalent power, age and vitreous depth and axial length. Sex differences were found among the optical components but not in the refractive error. Myopia appears to be more prevalent among the younger age groups than the older age groups of the Hong Kong Chinese population, and the importance of genetics in determination of refractive error is called into question by these findings.

A longitudinal study of corneal astigmatism changes in Asian eyes

This study investigated changes in corneal astigmatism with age of 494 Asian eyes in a retrospective study. The results are compared to previous studies of non-Asian eyes. The current study demonstrates a greater magnitude in the rate of change of corneal astigmatism.

Refraction and its components in Melanesian schoolchildren in Vanuatu

Refraction and its components were measured on 788 Melanesian children and 39 children of other races, aged 6 through 19 years, in the South Pacific island nation of Vanuatu. Of the 788 Melanesian children, 766 (97.2%) were found to have uncorrected visual acuity of 6/6 or better, and 763 (96.8%) were found to have a spherical equivalent refraction between -0.25 and +1.00 D. Only 23 (2.9%) Melanesian children were found to have myopia greater than 0.25 D, only 2 (0.3%) were found to have hyperopia greater than 1.00 D, and only 2 (0.3%) were found to have refractive astigmatism greater than 1.00 D. Mean corneal refracting power was greater for girls than for boys, at all ages, but did not appear to change in any regular manner with age. Mean axial length and mean vitreous length were greater for boys than for girls, at all ages, each increasing approximately 1.0 mm from age 6 and 7 years to age 18 and 19 years. Although the low prevalence of ametropia may be considered to be due mainly to genetic factors, the possibility of environmental factors cannot be excluded.