Yung-Feng Shih

Epidemiologic Study of Ocular Refraction among Schoolchildren in Taiwan in 1995

PURPOSE In order to understand and update the prevalence of myopia in Taiwan, a nationwide survey was performed in 1995. METHODS We stratified the cluster sampling by developmental grading of the city, using a size proportional to the population. Two cities were randomly selected from each city grading. The total number of students enrolled was 11,178, including 5,676 boys and 5,502 girls. The refractive status and corneal radius of each student were measured with an autorefractometer under cycloplegia and checked with retinoscopy. Axial length was measured with biometric ultrasound. RESULTS The myopic rate was from 12% at the age of 6, it increased to 56% at the age of 12, and then to 76% at the age of 15. A myopic rate of 84% was found for the age range of 16 to 18. The prevalence of high myopia (over -6.0 D) at the age of 18 was 20% in girls and 12% in boys. The mean refractive status became myopic at the age of 9, then increased to -3.92 D in girls and -2.71 D in boys at the age of 18. The increase of axial length is correspondent with the progression of myopia. The anterior chamber depth (ACD) was deeper with age and the severity of myopia, whereas the corneal curvature remained unchanged. The lens thickness became thinner from age 7 to 13, then it became thicker with age and the severity of myopia after age 15. The prevalence and degree of myopia in girls was more severe than in boys. CONCLUSIONS The prevalence of myopia in Taiwan increased year by year. The increase in severity and prevalence of high myopia may be due to earlier onset.

Changes in ocular refraction and its components among medical students : A 5-year longitudinal study

Purpose. Myopic progression has been noted, especially during the period of puberty. It is interesting to investigate whether myopia will progress after the age of puberty and at what rate the changes in ocular components occur during its progression. Methods. A 5-year longitudinal study was made of refraction and its components among 345 National Taiwan University medical students (690 eyes). The examinations included corneal curvature and cycloplegic refraction measured by auto-refractor and retinoscopy, and axial length measurement with A scan ultrasonography. The same procedures and instruments were used again after 5 years. Results. The myopic prevalence increased from 92.8 to 95.8%; 21 new cases of myopia developed in the 5 years. The mean refractive error significantly increased from —4.26 ± 2.66 D of freshmen to -4.94 ± 2.70 D of clerks. The change in refractive error at the 5-year follow-up was 0.70 ± 0.65 D more myopic for males and 0.54 ± 0.64 D for females. The main change in the ocular components was in axial length, which increased from 25.54 to 26.05 mm in males and from 24.60 to 24.95 mm in females. Other optical components—including corneal curvature, anterior chamber depth, lens thickness— all remained relatively unchanged from the initial values. Conclusions. Myopia can progress after the age of puberty, but at a slower rate than during childhood. Axial elongation of the eyeball is the main component that changes in myopic progression.

The cornea in young myopic adults.

AIMS To further understand the effect of refractive error on the corneal dimensions and function. METHODS Corneal curvature, corneal thickness, and axial length measurements were performed, as well as specular microscopy and fluorophotometry, on patients with various refractive statuses. 216 subjects, mean age 22.2 (SD 4.2) years, were examined. Patients with previous contact lens wear history, external eye diseases, as well as previous ocular surgeries, were excluded. RESULTS The corneas were flatter in eyes with longer axial length (r = −0.22, p = 0.003). Eyes with more myopic spherical equivalent had longer axial length (r = −0.90, p <0.001) as well as less corneal endothelial density (r = 0.20, p = 0.037). Corneal endothelial density decreased in eyes with longer axial length (r = 0.24, p = 0.019); however, it correlated neither with corneal thickness (r= −0.06, p = 0.59) nor with corneal curvature (r = −0.07, p = 0.52). The corneas had a mean corneal thickness of 533 (SD 29) μm and were thinner in more myopic eyes (r = 0.16, p = 0.021). The corneas tended to be thinner in eyes with longer axial length. However, the correlation did not reach statistical significance (r = −0.11, p = 0.14). Besides, there was no significant correlation between the corneal thickness and the corneal curvature (r = −0.13, p = 0.093) and the endothelial permeability (r = 0.042, p = 0.69). The corneas with higher endothelial density had larger corneal transfer coefficient (r = 0.26, p = 0.024) and higher permeability to fluorescein molecules (r = 0.28, p = 0.014). Nevertheless, the corneal endothelial permeability did not correlate significantly with either the axial length (r = −0.18, p = 0.11) or the degree of myopia (r = 0.12, p = 0.26). CONCLUSION Changes in the anterior segments as the eyeball elongates in myopia progression included flatter corneal curvature, decreased corneal thickness, as well as decreased endothelial density. These factors should be considered in refractive surgery.

Lens Thickness Changes among Schoolchildren in Taiwan

PURPOSE To explore the possible influence of ocular growth, refractive error and age on the crystalline lens in school-age children. METHODS A Taiwan nationwide survey of myopia performed in 2006 was used to determine the prevalence and severity of myopia and the changes in ocular components. A total of 11,656 students were enrolled, including 5,390 boys and 6,266 girls, with ages ranging from 7 to 18 years. Refractive status was measured with an autorefractometer with the subject under cycloplegia. Lens thickness, anterior chamber depth, and axial length were measured with biometric ultrasound. RESULTS Data revealed that the crystalline lens became thinner between the ages of 7 and 11. Subsequent increases in the lens thickness correlated with age and the stability of myopia. This phenomenon was found not only in myopic eyes, but also in emmetropic and hyperopic eyes. The changes in anterior chamber depth inversely correlated with the changes in the lens. In school-age children, the ratio of lens/axial length was found to be significant: approximately 0.147 in the emmetropic group. However the ratio was seen to increase with age. The ratio of anterior segment/axial length was found to be approximately 0.3 in emmetropic eyes among all age groups and less than 0.3 in the myopic eyes of schoolchildren. CONCLUSIONS Lens thinning appeared to be compensatory in nature with respect to the increased axial length of normal eye growth. Myopic eye growth induces the lens to compensate by becoming much thinner. The change in anterior chamber depth corresponded inversely with lens thickness.

Foveola nonpeeling technique in internal limiting membrane peeling of myopic foveoschisis surgery.

Foveola Nonpeeling Technique in Internal Limiting Membrane Peeling of Myopic Foveoschisis Surgery Myopic foveoschisis is a unique complication of posterior staphyloma in highly myopic eyes. The formation of macular hole and posterior retinal detachment are well-known consequences of this unstable condition. Early stages of such degenerative changes can only be detected using the high-resolution imaging technique optical coherence tomography (OCT). Tangential traction is believed to be one of the main causes of the disease, along with anteroposterior traction. The significant role of vitreous and internal limiting membrane (ILM) traction is confirmed by the good results obtained by vitrectomy with gas tamponade and facedown positioning. However, postoperative development of full-thickness macular hole in some of the cases required surgery, jeopardizing the central fovea tissue, which existed preoperatively. The present report describes an ILM peeling technique that leaves the epifoveolar tissue in situ and thus prevents the development of macular hole.

The prevalence of astigmatism in Taiwan schoolchildren.

Purpose. To understand the prevalence and distribution of astigmatism in schoolchildren in Taiwan, we analyzed and compared the nationwide survey data in 1995 and 2000. Methods. A total of 11,175 students were enrolled in 1995, and 10,878 students were enrolled in 2000. The refractive status of each student was measured with an autorefractor during cycloplegia and rechecked with retinoscopy. Results. About half of schoolchildren (57.5% in 1995 and 49.0% in 2000) had no astigmatism (<0.5 D). About one third of schoolchildren’s astigmatism was <1 D (27.9% vs. 32.6%). Eleven percent of schoolchildren in 1995 and 13% in 2000 had astigmatism between 1.0 and 2.0 D. Less than 2% of students had astigmatism >3.0 D (1.3% in 1995 and 1.8% in 2000). Most astigmatism was with-the-rule: 83.3% in 1995 and 89.9% in 2000. Only 16.6% of children in 1995 and 9.7% in 2000 had against-the-rule astigmatism. Very little astigmatism was oblique (0.1% in 1995 and 0.4% in 2000). The rate of myopic astigmatism increased with age. In contrast, the rate of hyperopic and mixed astigmatism decreased with age. In addition, the rate of with-the-rule astigmatism increased and the rate of against-the-rule decreased with respect to age, but oblique astigmatism was rather stable with age. Conclusions. Most schoolchildren had little or no astigmatism. In Taiwan, most astigmatism is <1 D and is myopic with-the-rule astigmatism. There was more myopic astigmatism and with-the-rule astigmatism in 2000 than in 1995.

Association Between High Myopia and Progression of Visual Field Loss in Primary Open-angle Glaucoma

BACKGROUND/PURPOSE Taiwan has a very high prevalence rate of myopia. We retrospectively studied the influence of myopia on the progression of visual field (VF) loss in primary open-angle glaucoma (POAG) patients. METHODS We studied 515 POAG patients for a minimum follow-up period of 5 years. VF examination was performed with Humphrey perimeter, 30-2 SITA standard program, every 6 months. A point-wise numerical comparison was applied to judge the VF changes. Test points showing more than 1.0 dB of sensitivity loss in mean defect were identified. A location was considered to have progression if it was detected on two consecutive visits. Progression of VF loss was confirmed if three or more test points deteriorated. Multivariate logistic regression was used to evaluate the association between progression of VF loss and various risk factors. RESULTS There were 262 cases. Progression of VF loss occurred in 57 eyes (21.8%) during the 5-year follow-up period. Logistic regression revealed that the deterioration was associated with older age, higher mean intraocular pressure, larger vertical cup-to-disc ratio, and greater myopic refraction status. The incidence of VF loss progression was 15.1% in the group of eyes with myopia less than -3 D, 10.5% in the group with -3 D to -6 D, 34.4% in the group with -6 D to -9 D, and 38.9% in the group with myopia greater than -9 D. CONCLUSION POAG patients with myopia greater than -6 D had a greater progression of VF loss.

The Association of Haplotype at the Lumican Gene with High Myopia Susceptibility in Taiwanese Patients

OBJECTIVE To investigate the association of genetic polymorphisms in the dermatan sulfate proteoglycan 3 (DSPG3), lumican (LUM), and decorin (DCN) genes (component genes of the sclera) with high myopia susceptibility in Taiwanese people. DESIGN Prospective case-control study. PARTICIPANTS Hospital clinic-based samples of 120 unrelated patients with extremely high myopia were studied. One hundred thirty-seven unrelated emmetropic individuals served as controls. METHODS Four, 8, and 4 single nucleotide polymorphism (SNPs) were genotyped within the DSPG3, lumican, and decorin genes, respectively, using direct DNA sequencing. Pairwise linkage disequilibrium, haplotype analysis, adjusted logistic regression, and multifactor dimensionality reduction (MDR) methods were used to determine significant associations. MAIN OUTCOME MEASURES The association of haplotypes at the lumican gene with high myopia development. RESULTS The lumican gene SNP rs3759223:T-->C demonstrated a significant association with high myopia (P = 2.83 x 10(-4)). Four lumican SNPs showed significant linkage disequilibrium and formed a haplotype block. Sliding window haplotype analyses revealed that the block consisting of rs3759223 and rs3741834 showed significant goodness of fit (global P = 1.0725 x 10(-6)). Haplotype-specific tests showed that the C-C and T-C haplotypes were associated significantly with high myopia, with odds ratios (95% confidence intervals) of 19.32 (2.55-146.54) and 0.69 (0.46-1.04), respectively. rs3759223 and rs3741834 are in a putative regulatory element of the lumican gene, which influences fibrillogenesis of scleral collagen fibers and the development of myopia. The results of an MDR analysis corroborated the single-locus association and suggested a significant 2-locus interaction model composed of SNPs rs2300588 and rs3741834 in the lumican gene. CONCLUSIONS Genetic variation in the regulatory domains of the lumican gene, where both rs3759223 and rs3741834 are located, are associated with high myopia susceptibility among the Han Chinese, making this region worthy of further investigation.

Comparing myopic progression of urban and rural Taiwanese schoolchildren

PurposeTo compare myopic progression rates in Taiwanese schoolchildren between urban and rural areas.MethodsSeveral longitudinal studies of myopic progression were performed in urban and rural areas. Five primary schools, four junior high schools, and two senior high schools were selected from both urban and rural areas. Ages ranged from 7 to 18 years. The refractive state of each student was measured with an autorefractometer under cycloplegia.ResultsMean myopic progression in primary school children (ages 7 to 12) in the urban areas was around 0.20 D/year for boys and 0.27 D/year for girls. The mean myopic progression rate in urban children from primary to junior high school age (ages 10 to 15) was 0.43 D/year for boys and 0.50 D/year for girls, faster than that in rural children (0.24 and 0.31 D/year, respectively). The average progression rate was fastest in children in junior high school (ages 13 to 15), around 0.45 D/year in urban areas and 0.28 D/year in rural areas. In senior high schools (ages 16 to 18), myopic progression slowed to 0.17 D/ year in boys and 0.33 D/year in girls. Myopic progression in all groups was faster in myopic eyes than in emmetropic or hyperopic eyes.ConclusionsThe average myopic progression in urban areas was greater than that in rural areas. Environmental factors such as urban development and academic grade level may be important contributing factors to myopic progression.

Prevalence of Anisometropia in Taiwanese Schoolchildren

BACKGROUND AND PURPOSE This study investigated the prevalence and distribution of anisometropia in Taiwanese schoolchildren using nationwide data from refractive surveys performed in 1995 and 2000. METHODS Complete survey data was obtained for 11,175 students in 1995 and 10,878 students in 2000. The refractive status of each student was measured using an autorefractometer under cycloplegia and rechecked with retinoscopy. The difference in refractive status between each participants eyes was determined. Chi-squared statistic was used to assess the difference between the 2 surveys. Multiple linear regression was used to determine the trend and effects of covariates. RESULTS Most of the schoolchildren (77.6% in 1995, 71.9% in 2000) were not anisometropic. Most of the anisometropic differences were in the range 0.5 to 1.0 D (14.1% in 1995 vs 17.9% in 2000). About 6% of schoolchildren in 1995 and 7.0% in 2000 had anisometropic differences in the range from -1.0 to -2.0 D. Fewer than 4% of students had a level of anisometropia greater than 2.0 D (2.7% vs 3.2%, respectively). The prevalence of anisometropia and the extent of anisometropic difference both increased with age and with maximal myopic refraction (both p < 0.0001). Both the prevalence and extent of anisometropia showed significant differences between the 2 surveys (both p < 0.0001). CONCLUSIONS Most of the Taiwanese schoolchildren surveyed were non-anisometropic. The prevalence and amount of anisometropia were significantly increased from 1995 to 2000. The mechanisms responsible for these increases have not been determined, but may be related to increase of myopic refraction.