Son C. Huynh

Outdoor Activity Reduces the Prevalence of Myopia in Children

OBJECTIVE To assess the relationship of near, midworking distance, and outdoor activities with prevalence of myopia in school-aged children. DESIGN Cross-sectional study of 2 age samples from 51 Sydney schools, selected using a random cluster design. PARTICIPANTS One thousand seven hundred sixty-five 6-year-olds (year 1) and 2367 12-year-olds (year 7) participated in the Sydney Myopia Study from 2003 to 2005. METHODS Children had a comprehensive eye examination, including cycloplegic refraction. Parents and children completed detailed questionnaires on activity. MAIN OUTCOME MEASURES Myopia prevalence and mean spherical equivalent (SE) in relation to patterns of near, midworking distance, and outdoor activities. Myopia was defined as SE refraction < or = -0.5 diopters (D). RESULTS Higher levels of outdoor activity (sport and leisure activities) were associated with more hyperopic refractions and lower myopia prevalence in the 12-year-old students. Students who combined high levels of near work with low levels of outdoor activity had the least hyperopic mean refraction (+0.27 D; 95% confidence interval [CI], 0.02-0.52), whereas students who combined low levels of near work with high levels of outdoor activity had the most hyperopic mean refraction (+0.56 D; 95% CI, 0.38-0.75). Significant protective associations with increased outdoor activity were seen for the lowest (P = 0.04) and middle (P = 0.02) tertiles of near-work activity. The lowest odds ratios for myopia, after adjusting for confounders, were found in groups reporting the highest levels of outdoor activity. There were no associations between indoor sport and myopia. No consistent associations between refraction and measures of activity were seen in the 6-year-old sample. CONCLUSIONS Higher levels of total time spent outdoors, rather than sport per se, were associated with less myopia and a more hyperopic mean refraction, after adjusting for near work, parental myopia, and ethnicity.

Ethnic differences in refraction and ocular biometry in a population-based sample of 11-15-year-old Australian children

PurposeTo examine the prevalence of refractive error and distribution of ocular biometric parameters among major ethnic groups in a population-based sample of 11–15-year-old Australian children.MethodsThe Sydney Myopia Study examined 2353 students (75.3% response) from a random cluster-sample of 21 secondary schools across Sydney. Examinations included cycloplegic autorefraction, and measures of corneal radius of curvature, anterior chamber depth, and axial length.ResultsParticipants mean age was 12.7 years (range 11.1–14.4); 49.4% were female. Overall, 60.0% of children had European Caucasian ethnicity, 15.0% East Asian, 7.1% Middle Eastern, and 5.5% South Asian. The most frequent refractive error was mild hyperopia (59.4%, 95% confidence interval (CI), 53.2–65.6), defined as spherical equivalent (SE) +0.50 to +1.99 D. Myopia (SE−0.50 D or less) was found in 11.9%, 95% (CI 6.6–17.2), and moderate hyperopia (SE⩾+2.00 D) in 3.5%, 95% (CI 2.8–4.1). Myopia prevalence was lower among European Caucasian children (4.6%, 95% CI 3.1–6.1) and Middle Eastern children (6.1%, 95% CI 1.3–11.0) than among East Asian (39.5%, 95%, CI 25.6–53.5) and South Asian (31.5%, 95%, CI 21.6–41.4) children. European Caucasian children had the most hyperopic mean SE (+0.82 D) and shortest mean axial length (23.23 mm). East Asian children had the most myopic mean SE (−0.69 D) and greatest mean axial length (23.86 mm).ConclusionThe overall myopia prevalence in this sample was lower than in recent similar-aged European Caucasian population samples. East Asian children in our sample had both a higher prevalence of myopia and longer mean axial length.

Macular and nerve fiber layer thickness in amblyopia: the Sydney Childhood Eye Study.

PURPOSE To examine macular and peripapillary retinal nerve fiber layer (RNFL) thickness in amblyopia. DESIGN Population-based cross-sectional study. PARTICIPANTS Of 4118 children examined in the Sydney Childhood Eye Study (incorporating the Sydney Myopia Study) from 34 randomly selected primary schools and 21 secondary schools from 2003 to 2005, 3529 (85.7%) were included in this analysis. The median age of the 2 samples was 6 years (n = 1395) and 12 years (n = 2134), respectively. METHODS A detailed eye examination was conducted on all children, including determination of best-corrected visual acuity (logarithm of the minimum angle of resolution [logMAR]), autorefraction (RK-F1 autorefractor, Canon, Tokyo, Japan) after cyclopentolate (1%), cover testing to identify strabismus, and optical coherence tomography (StratusOCT, Carl Zeiss Meditec, Dublin, CA) through dilated pupils to obtain macula and peripapillary RNFL thickness. Amblyopia was defined as best visual acuity <0.3 logMAR units not explained by any obvious underlying eye or visual pathway abnormalities. Anisometropia was defined as an interocular difference of at least 1.0 diopter of the spherical equivalent refraction. MAIN OUTCOME MEASURES Macular and peripapillary RNFL thickness. RESULTS Amblyopic eyes had slightly greater foveal minimum thickness than the normal fellow eye (by 5.0 microm; 95% confidence interval 0.1-9.9) and right eyes of non-amblyopic children (by approximately 10 microm), both P<0.05. This was more pronounced in 6-year-old children (6.9 microm) than 12-year-old children (4.2 microm). Amblyopic eyes also had slightly thicker central macula (1 mm diameter region) in both comparisons, although these differences were not statistically significant. The inner macular ring (outer radius 1.5 mm) was thinner in amblyopic than normal fellow eyes. Peripapillary RNFL thickness was not significantly different between amblyopic and normal fellow eyes or normal eyes of non-amblyopic children. CONCLUSIONS In children aged predominantly 6 and 12 years, central macular thickness may be increased in eyes with amblyopia, although it is uncertain if this precedes or follows the development of amblyopia. No differences in peripapillary RNFL thickness were found when compared with normal eyes. FINANCIAL DISCLOSURE(S) The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Prevalence and associations of anisometropia and aniso-astigmatism in a population based sample of 6 year old children

Aim: To study the distribution of anisometropia and aniso-astigmatism in young Australian children, together with clinical and ocular biometry relations. Method: The Sydney Myopia Study examined 1765 predominantly 6 year old children from 34 randomly selected Sydney schools during 2003–4. Keratometry, cycloplegic autorefraction, and questionnaire data were collected. Results: Spherical equivalent (SE) anisometropia (⩾1 dioptre) prevalence was 1.6% (95% confidence interval (CI) 1.1% to 2.4%). Aniso-astigmatism (⩾1D) prevalence was 1.0% (CI: 0.6% to 1.6%). Both conditions were significantly more prevalent among moderately hyperopic (SE ⩾2.0D) than mildly hyperopic (SE 0.5–1.9D) children. Myopic children (SE ⩽−0.5D) had higher anisometropia prevalence. Neither condition varied by age, sex, or ethnicity. In multivariate analyses, anisometropia was significantly associated with amblyopia, odds ratio (OR) 29, (CI: 8.7 to 99), exotropia (OR 7.7, CI: 1.2 to 50), and neonatal intensive care unit (NICU) admission (OR 3.6, CI: 1.1 to 12.6). Aniso-astigmatism was significantly associated with amblyopia (OR 8.2, CI: 1.4 to 47), maternal age >35 years (OR 4.0, CI: 1.3 to 11.9), and NICU admission (OR 4.6, CI: 1.2 to 17.2). Anisometropia resulted from relatively large interocular differences in axial length (p<0.0001) and anterior chamber depth (p = 0.0009). Aniso-astigmatism resulted from differences in corneal astigmatism (p<0.0001). Conclusion: In this predominantly 6 year old population, anisometropia and aniso-astigmatism were uncommon, had important birth and biometry associations, and were strongly related to amblyopia and strabismus.

Ethnic differences in optic nerve head and retinal nerve fibre layer thickness parameters in children.

Aim To examine ethnic differences in optic nerve head and retinal nerve fibre layer (RNFL) parameters between European Caucasian and East Asian children aged 6–12 years. Methods Of 4118 children examined in the Sydney Childhood Eye Study (incorporating the Sydney Myopia Study) from 34 randomly selected primary and 21 secondary schools during 2003–5, 3382 (82.1%) had optical coherence tomography (OCT; Zeiss Stratus) data suitable for analysis. ‘Fast’ optic disc and RNFL scans were used. Ethnicity was defined only when both parents were of the same ethnicity. Results East Asian children tended to have a lower birth weight, were shorter with a smaller body mass index and were less hyperopic than European Caucasian children of the same age. After adjusting for age, gender, axial length, birth weight and optic-disc area, East Asian children had similar mean vertical disc diameters to European Caucasians (p=0.38, p=0.64 for 6–12 years, respectively) but 30–43% larger mean vertical cup diameters (p<0.0001 for both), resulting in larger mean cup/disc ratios (p<0.0001 for both). Compared with European Caucasians (101.95 μm and 104.57 μm, respectively), East Asian children had thicker mean average RNFL (105.45 μm and 107.92 μm, respectively; p=0.0006 and 0.0001) and thicker non-nasal RNFL quadrants in both ages. Conclusions Compared with European Caucasian children, East Asian children generally had thicker RNFL and larger mean cup/disc ratios. Given the relatively lower prevalence of open angle glaucoma in Asians, these anatomical variations could contribute to better understanding of apparent racial differences in glaucoma susceptibility.

Influence of OCT Signal Strength on Macular, Optic Nerve Head, and Retinal Nerve Fiber Layer Parameters

PURPOSE To examine the influence of different signal strengths on measurements made with optical coherence tomography (OCT) of macular, optic nerve head, and retinal nerve fiber layer (RNFL) parameters. METHODS From 2003 to 2005, 2092 children, mostly aged 12 years, were examined, and macular, optic nerve head, and RNFL parameters were measured by OCT. Multiple fast scans were acquired, and only right eyes were included in the analyses. Signal strength category was determined after averaging individual signal strengths from each scan and classifying scans as providing moderate (average signal strength, 5-7.49), good (average signal strength, 7.5-9.49), and excellent (average signal strength, >or=9.5) image quality. General linear models were used after adjustment for covariates. RESULTS Significant differences were observed between measurements obtained at excellent signal strengths compared with those obtained at moderate and good signal strengths for both macular and optic nerve parameters. However, although statistically significant, the magnitude of the differences in macular parameters was very small (approximately 5 microm, or a 2% difference). Differences in optic nerve head parameters were much greater (up to a 32% difference), with larger measurements recorded for most parameters with increasing signal strength category. Significant differences in RNFL parameters with increasing signal strength were not demonstrated. CONCLUSIONS Significantly larger macular and optic nerve head OCT measurements were obtained with increasing signal strength measurements, although absolute differences in macular measurements were small and are of questionable clinical importance. The results support the robustness of OCT in providing precise macular imaging.

Retinal and Optic Disc Findings in Adolescence: A Population-Based OCT Study

PURPOSE To examine the distribution of macular and peripapillary nerve fiber layer (NFL) thickness and optic disc parameters in early-adolescence Australian children and to compare these with previously reported findings in younger children. METHODS The Sydney Childhood Eye Study is a population-based cross-sectional survey of childrens eye health. During 2004 and 2005, 2367 (75.3%) of 3144 eligible year 7 students from a random cluster sample of 21 secondary schools in Sydney, Australia, were examined. The comprehensive eye examination included measurement of macular and NFL thickness and optic disc parameters by optical coherence tomography (StratusOCT; Carl Zeiss Meditec, Dublin, CA). RESULTS Macular, NFL thickness, and optic disc parameters were normally distributed in early-adolescence children. Mean (+/-SD) thicknesses of the central 1 mm, and inner and outer macular rings were 197.4 +/- 18.7, 271.9 +/- 15.0, and 239.5 +/- 13.5 microm, respectively. The foveal minimum thickness was 161.6 +/- 19.9 microm. The mean (+/-SD) of average NFL thickness was 103.6 +/- 10.6 microm. Mean (+/-SD) vertical and horizontal disc diameters were 1.88 +/- 0.25 and 1.61 +/- 0.20 mm; corresponding cup-to-disc ratios were 0.39 +/- 0.14 and 0.44 +/- 0.16. There were minimal sex differences in these parameters after adjustment for multiple ocular and demographic variables. Compared with parameters in the childhood group, the macula was generally slightly thicker and the optic disc slightly larger in the early-adolescence group, although differences between these two age groups were small. The foveal minimum and NFL thickness were similar between the two age groups. CONCLUSIONS This study describes the normative distribution of macular, NFL, and optic disc parameters in early-adolescence children and also demonstrates minimal differences between the sexes. These parameters were also largely unchanged between early childhood and early adolescence, although the comparisons were made in two cross-sectional samples, rather than from longitudinal measures.

An evaluation of keratometry in 6-year-old children.

Purpose: To evaluate the repeatability and comparability of keratometry measured by both the IOLMaster and RK-F1 AutoRef-Keratometer in children. Methods: Keratometry results from a sample (n = 447) of 6-year-old children who were examined in the Sydney Myopia Study were analyzed. Corneal power was analyzed along the flattest and steepest meridians to determine if there were any systematic differences between repeat measurements or between the two instruments. The 95% limits of repeatability (LR) and 95% limits of agreement (LA) (mean difference ± 1.96 × standard deviation of differences) were calculated. Results: There were no systematic differences in repeat measurements for each instrument. For the IOLMaster, mean difference of the flattest corneal meridian was −0.01 (D) (P = 0.3, 95% LR, −0.22, 0.21 D) and of the steepest corneal meridian, 0.01 D (P = 0.3, 95% LR, −0.35, 0.38 D). For the RK-F1, mean difference of the flattest corneal meridian was −0.02 D (P = 0.3, 95% LR, −0.25, 0.21 D); and of the steepest corneal meridian, 0.00 D (P = 0.9, 95% LR, −0.39, 0.39 D). Systematic differences, however, were found between the two instruments. The IOLMaster gave significantly (P < 0.0001) steeper readings than the RK-F1 for both the flattest corneal meridian, 0.29 D (95% LA, −0.08, 0.66 D), and the steepest corneal meridian, 0.18 D (95% LA, −0.29, 0.65 D). Conclusions: Keratometry was highly repeatable for both the IOLMaster and RK-F1 instruments when used in young children. These instruments would be suitable for use in monitoring changes of corneal curvature over time. Small significant systematic differences in keratometry between the two instruments were also found.

Measurement of Optic Nerve Head Parameters: Comparison of Optical Coherence Tomography With Digital Planimetry

PurposeTo compare the measurements of optic nerve head parameters from digital photographic images and optical coherence tomography (OCT) in normal children. MethodsThe Sydney Childhood Eye Study assessed 1765 children aged 6 years from 34 randomly selected primary schools during 2003 to 2005. Optic nerve head parameters were measured from digital photographs captured using a Canon fundus camera (CF-60Uvi)/EOS 10D and OCT3 (Zeiss Stratus) using the “fast” optic disc protocol. Retinal images of 333 sequential child participants were graded using both methods and are included in analyses. Optic disc and cup area, vertical and horizontal disc and cup diameters, vertical and horizontal cup/disc diameter ratios, and cup/disc area ratios were calculated using both modalities. Magnification of the planimetric images was corrected using the Bengtsson formula. ResultsMean vertical and horizontal disc and cup diameter and mean disc and cup area, as measured using OCT (1.76, 1.50, 0.71, and 0.68 mm and 2.15 and 0.47 mm2, respectively) were significantly (P<0.0001; cup area P=0.0014) smaller than when measured using digital photography (1.85, 1.66, 0.76, and 0.74 mm and 2.40 and 0.51 mm2, respectively). All 3 cup/disc ratio measures did not vary significantly (P>0.05) between the 2 methods (0.41, 0.45, and 0.22 vs. 0.41, 0.44, and 0.21, respectively). ConclusionsLinear and area measures by Stratus-OCT, compared with digital planimetry measurements, are around 10% smaller; however, all 3 cup/disc ratios were preserved. Where OCT produces unexpectedly small cup/disc ratios, manual viewing is advisable. However, OCT can be considered moderately reliable in measuring and monitoring cup/disc ratio in clinical settings.

Relationships of retinal vessel diameters with optic disc, macular and retinal nerve fiber layer parameters in 6-year-old children

PURPOSE To describe the normal anatomic relationships of retinal vessel diameters with optic disc, macula, and retinal nerve fiber layer parameters in young children. METHODS This was a population-based, cross-sectional study of 1204 healthy children 6 years of age who were participating in the Sydney Childhood Eye Study. Retinal arteriolar and venular diameters were measured from fundus photographs using standardized computer-based methods. Optical coherence tomography was performed to obtain measurements of the optic disc, macula, and retinal nerve fiber layer parameters. RESULTS In multivariate analyses, each standard deviation (SD) decrease in optic disc area was associated with a 0.14-pixel decrease (P = 0.05) in arteriolar diameter and a 0.31-pixel decrease (P < 0.01) in venular diameter. Each SD decrease in optic cup area was associated with a 0.15-pixel decrease (P = 0.05) in arteriolar diameter and a 0.43-pixel decrease (P < 0.01) in venular diameter. Each SD decrease in macular (inner/outer) thickness or volume was associated with a 0.25- to 0.39-pixel decrease (P < 0.01) in arteriolar diameter and a 0.36- to 0.71-pixel decrease (P < 0.01) in venular diameter, and each SD decrease in retinal nerve fiber layer thickness was associated with a 0.62-pixel decrease (P < 0.01) in arteriolar diameter and a 0.99-pixel decrease (P < 0.01) in venular diameter. CONCLUSIONS Childrens eyes with a smaller optic disc, thinner macula, and thinner retinal nerve fiber layer have narrower retinal vessels. These anatomic relationships may provide new insights into the vascular etiology of various ocular diseases.