Shayne A. Brown

Prevalence of amblyopia and associated refractive errors in an adult population in Victoria, Australia

The study aimed to describe the prevalence of amblyopia and associated refractive errors among an adult Australian population. The Visual Impairment Project (VIP) is a population-based study of age-related eye disease in the state of Victoria, Australia. Data were collected through standardised interviews and orthoptic and ophthalmic dilated examinations. Amblyopia was defined as best-corrected visual acuity of 6/9 or worse in the absence of any pathological cause. The participants were 3,265 urban residents and 1,456 rural residents of the VIP ranging in age from 40-92 years (mean = 59 years; 53% female). The prevalence of unilateral amblyopia was 3.06% (95% C.I. 2.59, 3.53). Amblyopia was not found to be statistically different by age group (p=0.096), gender (p=0.675), or place of birth (p=0.14). Anisometropia was statistically more common (p<0.001) in amblyopic cases (51.1%) compared to the normal population (9.7%), and 54% of amblyopic eyes had visual acuity of worse than 6/12. Amblyopia is a significant cause of unilateral reduced visual acuity in a population aged 40 years and older. Anisometropia was more prevalent and the degree of anisometropia was greater in the amblyopic group compared with the normal population. Oblique astigmatism was more prevalent in the amblyopic group compared with the normal population.

Effect of Birth Parameters on Retinal Vascular Caliber The Twins Eye Study in Tasmania

Recent studies reported an association between smaller birth size and narrower retinal vascular caliber, but it remains unclear whether this association is attributed to confounding by shared environment or genetic factors. At a mean age of 9.3 years, 266 twins (49 monozygotic and 84 dizygotic pairs) in the Twins Eye Study in Tasmania underwent an ophthalmic examination including retinal photography. Retinal vascular caliber was measured using a validated protocol. The majority of these twins were also in the Tasmanian Infant Health Study, which prospectively collected data on birth parameters and antenatal maternal factors. We conducted the main analysis using linear mixed models, accounting for birth set clustering. Both the within-pair (−9.73; 95% CI: −14.68 to −4.77 &mgr;m per 5-cm decrease in birth length) and between-pair associations (−7.15; 95% CI: −11.54 to −3.01) with retinal arteriolar caliber were significant and of similar magnitude (difference in effect, P=0.61), after adjusting for age, sex, maternal smoking, mean arterial blood pressure, and other confounders. These associations remained within dizygotic and monozygotic pairs. Analyses of head circumference and retinal arteriolar caliber were similar to those of birth length (within-pair regression coefficient: −2.41; 95% CI: −5.09 to 0.28; between-pair regression coefficient: −2.60; 95% CI: −5.00 to −0.19). For birth weight, only a between-pair association was evident (−7.28; 95% CI: −13.07 to −1.48). This study demonstrates a consistent association between smaller birth size and narrower retinal arterioles in twins. The independent effect of shorter birth length on retinal arteriolar caliber supports a role for twin-specific supply line factors affecting fetal growth on vascular structure.

Twins Eye Study in Tasmania (TEST): Rationale and Methodology to Recruit and Examine Twins

Visual impairment is a leading cause of morbidity and poor quality of life in our community. Unravelling the mechanisms underpinning important blinding diseases could allow preventative or curative steps to be implemented. Twin siblings provide a unique opportunity in biology to discover genes associated with numerous eye diseases and ocular biometry. Twins are particularly useful for quantitative trait analysis through genome-wide association and linkage studies. Although many studies involving twins rely on twin registries, we present our approach to the Twins Eye Study in Tasmania to provide insight into possible recruitment strategies, expected participation rates and potential examination strategies that can be considered by other researchers for similar studies. Five separate avenues for cohort recruitment were adopted: (1) piggy-backing existing studies where twins had been recruited, (2) utilizing the national twin registry, (3) word-of-mouth and local media publicity, (4) directly approaching schools, and finally (5) collaborating with other research groups studying twins.

The Association Between Maternal Smoking in Pregnancy, Other Early Life Characteristics and Childhood Vision: The Twins Eye Study in Tasmania

Purpose: To investigate the association between maternal smoking in pregnancy, early-life environment and childhood vision. Methods: Twin and triplet children enrolled in the Twins Eye Study in Tasmania underwent a comprehensive ophthalmic examination and their parents/guardians retrospectively answered a questionnaire regarding crawling, walking and other measures. A subset of these twins was also in the Tasmanian Infant Health Survey, which prospectively collected data on antenatal smoking, gestation, birth weight and other factors. Results: The mean age of the 346 individuals (172 multiple birth sets) at the time of examination was 9.25 ± 2.4 years. Mean unaided visual acuity was 0.0 (6/6). The mean spherical equivalent was +0.87D, and decreased with increasing child age (p < 0.01). A prospective analysis, accounting for birth set clustering and relevant confounders, showed increasing levels of maternal smoking in the third trimester was associated with poor stereoacuity on the Titmus test (worse (>) than 100″, p = 0.05) and Lang test (p = 0.001) and also with the presence of esotropia (p = 0.02). These associations persisted after adjustment for infant postnatal smoke exposure at one month of age. Poor stereoacuity on Titmus stereo test circles was associated with late age of first crawling (RR = 1.23 (1.06, 1.42) p = 0.005 per month) and late age of first walking (RR 1.18 (1.05, 1.22) p = 0.001 per month). Conclusions: Antenatal smoking was independently associated with poor stereovision and the presence of esotropia. Poor stereoacuity may be associated with delayed age at first crawling or walking.

Associations of birth weight with ocular biometry, refraction, and glaucomatous endophenotypes: The Australian twins eye study

PURPOSE To examine the relationship of birth weight with ocular measures in a Caucasian twin population. DESIGN Cross-sectional study of 1498 twins (308 monozygotic and 441 dizygotic pairs) aged between 5 to 80 years participating in the Australian Twins Eye Study. METHODS All participants underwent ophthalmic examination including bilateral cycloplegic autorefraction, keratometry, interpupillary distance (IPD), central corneal thickness, intraocular pressure (IOP), and retinal photography. Birth weight and gestation were obtained from a self-administered questionnaire. A subset of the twins also participated in the Tasmanian Infant Health Study (288) and the Childhood Blood Pressure Study (184), which collected data on birth parameters allowing for verification of data. Linear mixed models were used for the main analysis. RESULTS Both the within-pair (β(w) 0.27, 95% confidence interval [CI] 0.15, 0.38 mm per kg increase in birth weight, P < .001) and between-pair associations (β(B) 0.22, 95% CI 0.08, 0.35, P = .002) of birth weight with axial length were significant and of similar magnitude (difference in effect, P = .56), after adjusting for relevant confounders. In contrast, birth weight was negatively associated with corneal curvature (β(w) -0.82, 95% CI -1.09, -0.55 diopters per kg increase; β(B) -0.69, 95% CI -0.98, -0.41, both P < .001). These associations remained significant within dizygotic and monozygotic pairs. Refraction, anterior chamber depth, IPD, IOP, and optic disc parameters are unrelated to birth weight. CONCLUSIONS Consistent with previous studies in singleton children, lower birth weight is associated with shorter axial length and more curved corneas in this twin study. This also adds new insights into the emmetropization process.