Francis Carbonaro

A genome-wide association study for myopia and refractive error identifies a susceptibility locus at 15q25

Myopia and hyperopia are at opposite ends of the continuum of refraction, the measure of the eye′s ability to focus light, which is an important cause of visual impairment (when aberrant) and is a highly heritable trait. We conducted a genome-wide association study for refractive error in 4,270 individuals from the TwinsUK cohort. We identified SNPs on 15q25 associated with refractive error (rs8027411, P = 7.91 × 10−8). We replicated this association in six adult cohorts of European ancestry with a combined 13,414 individuals (combined P = 2.07 × 10−9). This locus overlaps the transcription initiation site of RASGRF1, which is highly expressed in neurons and retina and has previously been implicated in retinal function and memory consolidation. Rasgrf1−/− mice show a heavier average crystalline lens (P = 0.001). The identification of a susceptibility locus for refractive error on 15q25 will be important in characterizing the molecular mechanism responsible for the most common cause of visual impairment.

Common Genetic Determinants of Intraocular Pressure and Primary Open-Angle Glaucoma

Intraocular pressure (IOP) is a highly heritable risk factor for primary open-angle glaucoma and is the only target for current glaucoma therapy. The genetic factors which determine IOP are largely unknown. We performed a genome-wide association study for IOP in 11,972 participants from 4 independent population-based studies in The Netherlands. We replicated our findings in 7,482 participants from 4 additional cohorts from the UK, Australia, Canada, and the Wellcome Trust Case-Control Consortium 2/Blue Mountains Eye Study. IOP was significantly associated with rs11656696, located in GAS7 at 17p13.1 (p = 1.4×10−8), and with rs7555523, located in TMCO1 at 1q24.1 (p = 1.6×10−8). In a meta-analysis of 4 case-control studies (total N = 1,432 glaucoma cases), both variants also showed evidence for association with glaucoma (p = 2.4×10−2 for rs11656696 and p = 9.1×10−4 for rs7555523). GAS7 and TMCO1 are highly expressed in the ciliary body and trabecular meshwork as well as in the lamina cribrosa, optic nerve, and retina. Both genes functionally interact with known glaucoma disease genes. These data suggest that we have identified two clinically relevant genes involved in IOP regulation.

Genome-wide association identifies ATOH7 as a major gene determining human optic disc size

Optic nerve assessment is important for many blinding diseases, with cup-to-disc ratio (CDR) assessments commonly used in both diagnosis and progression monitoring of glaucoma patients. Optic disc, cup, rim area and CDR measurements all show substantial variation between human populations and high heritability estimates within populations. To identify loci underlying these quantitative traits, we performed a genome-wide association study in two Australian twin cohorts and identified rs3858145, P = 6.2 × 10−10, near the ATOH7 gene as associated with the mean disc area. ATOH7 is known from studies in model organisms to play a key role in retinal ganglion cell formation. The association with rs3858145 was replicated in a cohort of UK twins, with a meta-analysis of the combined data yielding P = 3.4 × 10−10. Imputation further increased the evidence for association for several SNPs in and around ATOH7 (P = 1.3 × 10−10 to 4.3 × 10−11, top SNP rs1900004). The meta-analysis also provided suggestive evidence for association for the cup area at rs690037, P = 1.5 × 10−7, in the gene RFTN1. Direct sequencing of ATOH7 in 12 patients with optic nerve hypoplasia, one of the leading causes of blindness in children, revealed two novel non-synonymous mutations (Arg65Gly, Ala47Thr) which were not found in 90 unrelated controls (combined Fishers exact P = 0.0136). Furthermore, the Arg65Gly variant was found to have very low frequency (0.00066) in an additional set of 672 controls.

Estimating heritability and shared environmental effects for refractive error in twin and family studies

PURPOSE Twin studies have demonstrated a high heritability for refractive error of up to 90%, but some family studies have suggested up to one-third of population variance is attributable to the effects of shared family environment. This large twin study aimed to explore the role of shared environment in refractive error. METHODS Refractive error was measured using autorefraction in 4602 subjects (1152 monozygotic and 1149 dizygotic twin pairs), aged between 16 and 82 years, recruited from the TwinsUK Adult Twin Registry. Maximum-likelihood methods were used to estimate the variance of genetic, environmental, and age variance components. RESULTS Maximum likelihood model fitting estimate of the heritability from the best-fit model was 77% (95% confidence interval [CI], 68%-84%). Shared environmental effects explained 7% (95% CI, 0%-15%) and individual environmental effects explained 16% (95% CI, 15%-18%) of the spherical equivalent variance, respectively. Inclusion of age effects into the modeling reduced shared environmental effects to an estimated 2% of variation. CONCLUSIONS Analysis of 2301 twin pairs confirms that the twin study design results in a very low estimate of shared family environmental effects in refractive error. Several factors may explain these differences; we believe the most likely is that twins are perfectly age matched and do not include cross-generation or cohort effects. This means twin study designs have more power to detect heritable effects in variance component models of myopia, whereas family studies have more power to detect shared environment effects.

The Heritability of Corneal Hysteresis and Ocular Pulse Amplitude: A Twin Study

PURPOSE To examine the roles of genetic and environmental factors in corneal hysteresis and ocular pulse amplitude by performing a classic twin study. DESIGN Cross-sectional twin study. PARTICIPANTS AND/OR CONTROLS Two hundred sixty-four twin pairs: 135 monozygotic (MZ) and 129 dizygotic (DZ). METHODS Corneal hysteresis was measured using the Reichert Ocular Response Analyzer (ORA; Reichert, Buffalo, NY), and ocular pulse amplitude was measured using the Pascal Dynamic Contour Tonometer (DCT; Swiss Microtechnology AG, Port, Switzerland). MAIN OUTCOME MEASURES Contribution of genetic and environmental effects on corneal hysteresis and OPA among MZ and DZ twins. RESULTS The mean corneal hysteresis was 10.24+/-1.54 mmHg and the mean ocular pulse amplitude was 2.88+/-0.97 mmHg. The MZ correlations were higher than DZ for both corneal hysteresis and ocular pulse amplitude (correlation coefficients, 0.75:0.42 and 0.59:0.32 for MZ:DZ twins, respectively). Modeling suggested heritability of corneal hysteresis of 0.77 (95% confidence interval [CI], 0.70-0.82), with the remaining proportion of variance because of individual environmental effects of 0.23 (95% CI, 0.18-0.30). For ocular pulse amplitude, the heritability was 0.62 (95% CI, 0.51-0.70), with the remaining proportion of variance the result of individual environmental effects of 0.38 (95% CI, 0.30-0.49). CONCLUSIONS This study demonstrated that additive genetic influences explained most of the individual differences in corneal hysteresis and ocular pulse amplitude among these twins.

Repeated Measures of Intraocular Pressure Result in Higher Heritability and Greater Power in Genetic Linkage Studies

PURPOSE To analyze the effect of using one reading, the mean of two readings (from the same eye), or the mean of four readings (two from each eye) on the heritability estimates of intraocular pressure (IOP). This was a cohort study in which 344 pairs of twins, 163 monozygotic (MZ) and 181 dizygotic (DZ), were enrolled. METHODS IOP was measured using three tonometers: the gold standard Goldmann applanation tonometer (GAT), the Ocular Response Analyzer (ORA; Reichert Buffalo, NY), and the Dynamic Contour Tonometer (DCT, Pascal; Swiss Microtechnology AG, Port, Switzerland). The main outcome measure was the heritability of IOP correlated with the number of measurements. RESULTS The mean IOPs of all four readings with the three tonometers were: 14.1 +/- 2.9 mm Hg for GAT, 15.9 +/- 3.2 mm Hg for ORA, and 16.9 +/- 2.7 mm Hg for DCT. As the number of readings increased, the calculated heritability (h(2)) of IOP measured using the GAT readings increased from 0.56 for one reading (95% confidence interval [CI], 0.44-0.65) to 0.58 for the mean of two readings (95% CI, 0.46-0.67) to 0.64 for the mean of all four readings (two right and two left; 95% CI, 0.55-0.72). Similar results were seen with the other two instruments. CONCLUSIONS The results demonstrated that the use of the mean of several readings from both eyes reduced measurement error, yielding a higher heritability estimate. The higher heritability would increase the power to detect linkage in a genome-wide analysis.

Heritability of intraocular pressure: a classical twin study.

Aims: To estimate the heritability of intraocular pressure (IOP) by performing a classical twin study and to determine whether the use of different instruments influences calculation of eye IOP heritability. Methods: Twin pairs were recruited to participate from the TwinsUK Adult Twin Registry at St. Thomas’ Hospital London. IOP was measured using Goldmann applanation tonometry (GAT). A subset of twins also had their IOP measured using the Ocular Response Analyser (ORA; Reichert, Buffalo, NY) and the Dynamic Contour Tonometer (DCT, Pascal; Swiss Microtechnology AG, Port, Switzerland). We compared the covariance of IOP within monozygotic (MZ) and dizygotic (DZ) pairs using genetic modelling techniques to determine the relative contribution of genes and environment to the variation in IOP seen in this population. Results: Data for 422 twin pairs (211 MZ; 211 DZ) were analysed. The mean IOP for GAT was 15.4 (SD 2.7) mm Hg (range: 8.7–26.2 mm Hg). The MZ correlations were significantly higher than DZ for IOP measured by GAT, DCT and ORA (correlation coefficients: GAT: 0.57:0.39, DCT: 0.62:0.36, Goldmann-correlated ORA (IOPg) 0.73:0.47, for MZ:DZ twins, respectively). Modelling suggested heritability for GAT IOP of 0.62, with individual environmental factors accounting for 0.38 of the variation. Conclusion: This study demonstrated that genetic effects are important in determining IOP in this twin population. IOP readings differed depending upon the instrument used, and this resulted in different heritability values; genetic factors explained 62%, 63% and 74% of the variation in IOP using GAT, DCT and ORA IOPg, respectively. Environmental factors determined the remainder of the variation.

Comparison of three methods of intraocular pressure measurement and their relation to central corneal thickness

PurposeThe purpose of this study was to compare the reliability of the ‘gold standard’ Goldmann applanation tonometer (GAT), with that of the ocular response analyser (ORA), and the dynamic contour tonometer (DCT).Patients and methodsA total of 694 subjects were recruited to participate from the TwinsUK (UK Adult Twin Registry) at St Thomas’ Hospital, London. Intraocular pressure (IOP) was measured using GAT, ORA, and the DCT. The agreement between the three methods was assessed using the Bland–Altman method. Repeatability coefficients and coefficient of variation between first and second readings of the same eye were used to assess reliability.ResultsMean age was 57.5 years (SD, 13.1; range, 16.1–88.5). The mean IOPs, calculated using the mean of two readings from the right eye were as follows: Goldmann (GAT), 14.1±2.8 mm Hg; IOPg (ORA), 15.9±3.2 mm Hg; IOPcc (ORA), 16.6±3.2 mm Hg; and DCT, 16.9±2.7 mm Hg. The 95% limits of agreement were for ORA (IOPcc): GAT, −2.07 to 7.18 mm Hg; for DCT: GAT, −0.49 to 6.21 mm Hg; and for DCT: ORA (IOPcc), −3.01 to 4.85 mm Hg. Coefficients of variation for the three tonometers were GAT, 8.3%; ORA, 8.2%; DCT, 6.3%. The repeatability coefficients were 3.4 mm Hg for GAT, 3.57 mm Hg for ORA and 3.09 mm Hg for DCT. GAT and ORA (IOPg) readings showed a positive correlation with central corneal thickness (P<0.005).ConclusionsThis study found similar reliability in all three tonometers. Bland–Altman plots showed the three instruments to have 95% limits of agreement outside the generally accepted limits, which means they are not interchangeable. GAT measurements were found to be significantly lower than the two newer instruments.

Optic Disc Planimetry, Corneal Hysteresis, Central Corneal Thickness, and Intraocular Pressure as Risk Factors for Glaucoma

PURPOSE To determine whether corneal hysteresis and central corneal thickness are independent risk factors for glaucoma. DESIGN A cross-sectional population-based cohort study. METHODS Associations were tested between corneal hysteresis, measured in 1754 population-based subjects from the TwinsUK cohort, and glaucoma-related endophenotypes, including intraocular pressure (IOP), vertical cup-to-disc ratio, optic disc area, and optic disc cup area. Corneal hysteresis, IOP, and central corneal thickness (CCT) were measured; optic disc photographs were analyzed; and multivariable linear regression analysis was performed. RESULTS Data were available on 1645 individuals. Multiple regression analysis showed corneal hysteresis to be significantly negatively associated with age (beta coefficient = -0.03, P < .00005) and IOP (beta coefficient = -0.06, P < .00005). Corneal hysteresis was also found to be associated with CCT (beta coefficient = 0.02, P < .0005). There was no significant association between corneal hysteresis and optic disc area (P = .6), cup area (P = .77), vertical cup-to-disc ratio (P = .51), or spherical equivalent (P = .08). CCT was also found to be significantly associated with IOP (beta coefficient = 3.3, P < .0005) and corneal hysteresis (beta coefficient = 9.4, P < .0005), but not with age (P = .59) or spherical equivalent (P = .16). CONCLUSION In this large cohort of healthy British twins, we found no relationship between corneal hysteresis or CCT and quantitative measures of optic disc cupping, suggesting that corneal hysteresis and CCT are not independent risk factors for glaucoma.

Three oncocytomas in a short space of time

Oncocytomas of the caruncle are rare tumours, found in 3–8% of caruncle excision biopsies.1 They occur most commonly in elderly women. Clinically, these tumours tend to present as a slow-growing, asymptomatic mass that is often tan red in colour.2 Treatment is by complete surgical excision and recurrence is unusual, although very rare malignant oncocytomas occurring in the ocular adnexae have been reported,3 and there has been a case of persistent rhinorrhea caused by an oncocytoma occurring in the lacrimal sac with extension into the nasolacrimal duct.4 A 38-year-old woman presented with a two-year history of a slowly enlarging cystic lesion of …