Carol Y. Cheung

Determinants of ganglion cell-inner plexiform layer thickness measured by high-definition optical coherence tomography.

PURPOSEnTo determine the distribution, variation, and determinants of ganglion cell-inner plexiform layer (GC-IPL) thickness in nonglaucomatous eyes measured by high-definition optical coherence tomography (HD-OCT).nnnMETHODSnSix hundred twenty-three Chinese adults aged 40 to 80 years were consecutively recruited from a population-based study. All subjects underwent a standardized interview, ophthalmic examination, and automated perimetry. HD-OCT with macular cube protocol was used to measure the GC-IPL thickness. Univariate and multiple linear regression analyses were performed to examine the relationship between GC-IPL thickness with ocular and systemic factors.nnnRESULTSnThe mean (±SD) age of study subjects was 52.84 ± 6.14 years, 50.1% were male, and all subjects had normal visual fields with no signs of glaucoma or glaucoma suspect. The mean overall, minimum, superior, and inferior GC-IPL thicknesses were 82.78 ± 7.01 μm, 79.67 ± 9.17 μm, 83.30 ± 7.89 μm, and 80.16 ± 8.31 μm, respectively. In multiple linear regression analysis, GC-IPL thickness was significantly associated with age (β = -0.202, P < 0.001), female sex (β = -2.367, P < 0.001), axial length (β = -1.279, P = 0.002), and mean peripapillary retinal nerve fiber layer (RNFL) thickness (β = 0.337, P < 0.001). IOP, central corneal thickness, disc area, serum glucose level, and history of diabetes mellitus had no significant influence on GC-IPL thickness.nnnCONCLUSIONSnThinner GC-IPL was independently associated with older age, female sex, longer axial length, and thinner RNFL thickness. These factors should be taken into account when interpreting GC-IPL thickness measurements with HD-OCT for glaucoma assessment.

Determinants of Quantitative Optic Nerve Measurements Using Spectral Domain Optical Coherence Tomography in a Population-Based Sample of Non-glaucomatous Subjects

PURPOSEnTo evaluate the ocular and systemic factors influencing measurements of optic nerve head (ONH) parameters and retinal nerve fiber layer (RNFL) thickness with spectral-domain optical coherence tomography (SD-OCT) in healthy Chinese adults.nnnMETHODSnAdults ranging in age from 40 to 80 years were consecutively recruited from the population-based Singapore Chinese Eye Study. A SD-OCT instrument was used to measure ONH and RNFL parameters. A total of 542 eyes from 542 non-glaucomatous Chinese subjects were analyzed. Univariable and multiple linear regression analyses were performed to examine the effects of a range of ocular (e.g., intraocular pressure [IOP], axial length [AL], disc area) and systemic (e.g., blood pressure, serum glucose) factors on ONH and RNFL parameters.nnnRESULTSnIn multiple regression analyses, neuroretinal rim area was independently associated with age (β = -0.006, P < 0.001), disc area (β = 0.183, P < 0.001), IOP (β = -0.009, P = 0.008), AL (β = -0.023, P = 0.004), and lens nuclear color (β = 0.042, P = 0.001). Vertical cup-to-disc ratio was independently correlated with age (β = 0.003, P < 0.001), disc area (β = 0.207, P < 0.001), IOP (β = 0.004, P = 0.014), AL (β = 0.010, P = 0.008), and lens nuclear color (β = -0.017, P = 0.006). Average RNFL thickness was independently related to age (β = -0.204, P = 0.001), disc area (β = 4.218, P < 0.001), signal strength (β = 1.348, P < 0.001), and AL (β = -1.332, P < 0.001). Disc area had the strongest effect on measurements of ONH parameters and RNFL thickness.nnnCONCLUSIONSnIn a non-glaucomatous population, optic nerve measurements with SD-OCT vary with disc area, age, IOP, AL, lens nuclear color, and signal strength, but systemic parameters have little influence. This information may be useful for interpretation of SD-OCT measurements.

Differential Associations of Myopia with Major Age-related Eye Diseases:The Singapore Indian Eye Study

PURPOSEnTo determine the associations of myopia and axial length (AL) with major age-related eye diseases, including age-related macular degeneration (AMD), diabetic retinopathy (DR), age-related cataract, and primary open-angle glaucoma (POAG).nnnDESIGNnPopulation-based, cross-sectional study.nnnPARTICIPANTSnA total of 3400 Indians (75.6% response rate) aged 40 to 84 years in Singapore.nnnMETHODSnRefractive error was determined by subjective refraction, and AL was determined by noncontact partial coherence laser interferometry. Age-related macular degeneration and DR were defined from retinal photographs according to the Wisconsin Age-Related Maculopathy Grading System and Airlie House classification system, respectively. Age-related cataract was diagnosed clinically using the Lens Opacity Classification System (LOCS) III system. Glaucoma was defined according to International Society for Geographical and Epidemiological Ophthalmology criteria.nnnMAIN OUTCOME MEASURESnAge-related macular degeneration, DR, age-related cataract, and POAG.nnnRESULTSnMyopic eyes (spherical equivalent [SE] <-0.5 diopter [D]) were less likely to have AMD (early plus late AMD) (odds ratio [OR], 0.45; 95% confidence interval [CI], 0.25-0.79) or DR (OR, 0.68; 95% CI, 0.46-0.98) compared with emmetropic eyes; each millimeter increase in AL was associated with a lower prevalence of AMD (OR, 0.76; 95% CI, 0.65-0.89) and DR (OR, 0.73; 95% CI, 0.63-0.86). Myopic eyes were more likely to have nuclear (OR, 1.57; 95% CI, 1.13-2.20) and posterior subcapsular (OR, 1.73; 95% CI, 1.10-2.72) cataract, but not cortical cataract (P = 0.64); each millimeter increase in AL was associated with a higher prevalence of posterior subcapsular cataract (PSC) (OR, 1.29; 95% CI, 1.07-1.55), but not nuclear (P = 0.77) or cortical (P = 0.39) cataract. Eyes with high myopia (SE <-6.0 D) were more likely to have POAG (OR, 5.90; 95% CI, 2.68-12.97); each millimeter increase in AL was associated with a higher prevalence of POAG (OR, 1.43; 95% CI, 1.13-1.80).nnnCONCLUSIONSnMyopic eyes are less likely to have AMD and DR but more likely to have nuclear cataract, PSC, and POAG. The associations of myopia with AMD, DR, and POAG are mostly explained by longer AL. However, the association between myopia and nuclear cataract is explained by lens refraction rather than AL.

A New Method to Measure Peripheral Retinal Vascular Caliber over an Extended Area

Please cite this paper as: Cheung, Hsu, Lee, Wang, Mitchell, Lau, Hamzah, Ho and Wong (2010). A New Method to Measure Peripheral Retinal Vascular Caliber over an Extended Area. Microcirculation17(7), 495–503.

Automatic optic disc segmentation with peripapillary atrophy elimination

Optic disc segmentation from retinal fundus image is a fundamental but important step for automatic glaucoma diagnosis. In this paper, an optic disc segmentation method is proposed based on peripapillary atrophy elimination. The elimination is done through edge filtering, constraint elliptical Hough transform and peripapillary atrophy detection. With the elimination, edges that are likely from non-disc structures especially peripapillary atrophy are excluded to make the segmentation more accurate. The proposed method has been tested in a database of 650 images with disc boundaries marked by trained professionals manually. The experimental results by the proposed method show average m1, m2 and mVD of 10.0%, 7.4% and 4.9% respectively. It can be used to compute cup to disc ratio as well as other features for application in automatic glaucoma diagnosis systems.

Assessment of trabecular meshwork width using swept source optical coherence tomography

PurposeMeasurements of the angle width by ultrasound biomicroscopy or anterior segment optical coherence tomography are usually performed 500xa0μm from the scleral spur, as the anterior part of trabecular meshwork (TM) is assumed to lie within this distance. The aim of this study was to measure TM width using swept source optical coherence tomography (SS-OCT, CASIA SS-1000, Tomey Corporation, Nagoya, Japan), and to investigate factors influencing this measurement.MethodsParticipants underwent gonioscopy and SS-OCT imaging in the dark. High-definition SS-OCT images were corrected for refractive distortion; and customized software (ImageJ; National Institutes of Health, Bethesda, MD, USA) was utilized to measure TM width (distance between the scleral spur and Schwalbe’s line). Linear regression analysis was performed to assess the relationship between TM width with demographic and angle parameters.ResultsOne hundred and forty eight Chinese subjects were analyzed. The majority was female (62.4xa0%); the mean age was 59.2u2009±u20098.68xa0years. Identification of the scleral spur and Schwalbe’s line with SS-OCT was possible in 590 (99.7xa0%) and 585 angle quadrants (98.8xa0%) respectively. TM width was wider in the inferior and superior quadrants (mean 889xa0[SD 138] and 793 [136] μm), compared to the nasal and temporal quadrants (712 [137] and 724 [115] μm, Pu2009<u20090.001). There was a difference in average TM width between open (789 [100]) and closed angle eyes (753 [86]) (Pu2009=u20090.048). There was no significant association between TM width and angle parameters, laterality, or demographic factors.ConclusionsIn SS-OCT HD images, the mean TM width varied from 710 to 890xa0μm in the different quadrants of the eye, and the inferior quadrant TM was the widest compared to other quadrants.

Does Retinal Vascular Geometry Vary with Cardiac Cycle

PURPOSEnChanges in retinal vascular parameters have been shown to be associated with systemic vascular diseases. In this study, we assessed the physiologic variations in retinal vascular measurements during the cardiac cycle.nnnMETHODSnFundus images were taken using electrocardiogram-synchronized retinal camera at nine distinct cardiac points from 15 healthy volunteers (135 images). Analyses of retinal vessel geometric measures, including retinal vessel caliber (individual and summary), tortuosity, branching angle, length-diameter ratio (LDR), and optimality deviation, were performed using semiautomated computer software. Repeated-measures ANOVAs were used to obtain the means and to estimate the variation of each cardiac point compared with cardiac point 1.nnnRESULTSnThere was a significant variation of the caliber of the individual arteriolar and venular vessels. However, there was no significant variation found for vessel caliber summary, represented by the central retinal arteriolar equivalent (CRAE) and the central retinal venular equivalent (CRVE). There was also no significant variation found for tortuosity and branching angle, and LDR showed none or very little variations at different cardiac points: variations in caliber ranges between 0 and 4.1%, tortuosity 0 and 1.5%, branching angle 0 and 3.5%, and LDR 0 and 2%; all values for variations, P > 0.1; linear trend, P > 0.5; and nonlinear trend, P > 0.8.nnnCONCLUSIONSnThis study showed that there were minimal variations in the CRAE, CRVE, tortuosity, and branching angle that are clinically used for two-dimensional measures of retinal vascular geometry during cardiac cycles. However, there was significant variation in the caliber of the individual vessels over the cardiac cycle.

Determinants of Macular Thickness using Spectral Domain Optical Coherence Tomography in Healthy Eyes: the Singapore Chinese Eye Study

PURPOSEnWe determined ocular and systemic factors influencing macular thickness measured by spectral-domain optical coherence tomography (SD-OCT) in a population-based sample of healthy eyes.nnnMETHODSnWe recruited 490 healthy Chinese adults, aged 40 to 80 years, from the Singapore Chinese Eye Study, a population-based survey. All participants underwent a comprehensive eye examination and a standardized interview. The SD-OCT (Cirrus HD-OCT, software version 6.0) was used to measure a range of macular thickness parameters (central foveal subfield thickness, average inner macular thickness, average outer macular thickness, overall average macular thickness, and overall macular cube volume). Linear regression analyses were performed to examine the effects of various ocular and systemic factors on macular thickness.nnnRESULTSnThe mean (standard deviation) age of the subjects was 53.17 (6.14) years and 50.0% of them were male. The mean central foveal subfield, average inner, and average outer macular thicknesses were 250.38 (20.58), 319.33 (14.40), and 276.67 (11.94) μm, respectively. The overall average macular thickness was 280.25 (11.42) μm and overall macular cube volume was 10.09 (0.41) mm(3). Sex, age, and axial length (AL) are the factors that influenced macular thicknesses. Thinner overall average macular thickness was associated with female sex (4.46 μm thinner compared to males, P < 0.001), older age (0.38 μm decrease per each year increase in age, P < 0.001), and longer AL (2.34-μm decrease per each mm increase in AL, P < 0.001), whereas thinner central foveal subfield thickness was associated with female sex (13.5 μm thinner compared to males, P < 0.001) and shorter AL (3.33-μm decrease per each mm increase in AL, P < 0.001).nnnCONCLUSIONSnFemale sex, older age, and longer AL were associated independently with thinner overall average macular thickness, whereas female sex and shorter AL were associated with thinner central foveal thickness in ethnic Chinese. These factors should be taken into consideration when interpreting macular thickness measurements with SD-OCT.

Early Retinal Arteriolar Changes and Peripheral Neuropathy in Diabetes

OBJECTIVE To examine the association between early retinal arteriolar abnormalities and diabetic peripheral neuropathy (DPN). RESEARCH DESIGN AND METHODS Data from 608 people (aged 40–80 years) with diabetes from the population-based Singapore Malay Eye Study were analyzed. Participants underwent binocular two-field digital retinal photography and quantitative sensory testing. DPN was defined as an abnormal response to a monofilament or neurothesiometer test. Quantitative changes of retinal vascular caliber and arteriolar bifurcation geometry were measured using a computer-based program. Qualitative retinal signs of retinopathy and retinal arteriolar wall signs were graded by standardized methods. RESULTS DPN was present in 155 people (25.5%). After adjusting for age, sex, diabetes duration, HbA1c, cardiovascular risk factors, antihypertensive medication use, and peripheral arterial disease, people with suboptimal arteriolar caliber (odds ratio 1.94 [95% CI 1.22–3.10]), larger arteriolar branching coefficient (1.58 [1.03–2.42]), diabetic retinopathy (1.82 [1.20–2.75]), and focal arteriolar narrowing (2.92 [1.48–5.76]) were more likely to have DPN. Participants with a greater number of retinal microvascular signs were more likely to have DPN than those without retinal changes (6.11 [2.11–17.71] for two or more signs and 3.47 [1.18–10.21] for one sign compared with none). CONCLUSIONS Individuals with diabetes with early retinal arteriolar abnormalities are more likely to have DPN, independent of hyperglycemia and major vascular risk factors. These data support the hypothesis that early microvascular dysfunction, evident in the retina, is an independent risk factor for DPN.

Associations of iris structural measurements in a Chinese population: the Singapore Chinese Eye Study.

PURPOSEnWe determined the ocular biometric and demographic factors associated with iris parameters in Singaporean Chinese persons from a population-based sample.nnnMETHODSnSubjects were participants in the Singapore Chinese Eye Study, a population-based cross-sectional study of eye disease. Anterior segment optical coherence tomography images were analyzed using customized software to measure iris thickness at 750 μm from the scleral spur (IT750), iris area (I-Area), and iris curvature (I-Curv). Regression analyses were performed to assess the association between iris measurements with a range of demographic and ocular variables. The contribution of each independent variable to the iris parameter of interest was determined sequentially using a stepwise selection algorithm.nnnRESULTSnWe included 1473 participants with a mean age of 57.7 + 8.68 years, and 50.6% were men. The mean IT750, I-Area, and I-Curv were 0.46 ± 0.10 mm, 1.49 ± 0.24 mm(2), and 0.25 ± 0.13 mm, respectively. Statistical regression models, including a range of demographic and ocular parameters, explained 59.3%, 41.9%, and 34.3% of the variability in I-Curv, IT750, and I-Area, respectively. Angle opening distance at 750 μm from the scleral spur (AOD750) was the single factor associated most strongly with I-Curv, and explained 46.6% of its variation.nnnCONCLUSIONSnA significant proportion of the variation in iris area, curvature, and thickness was not explained by other ocular and demographic parameters. Iris curvature was associated strongly with angle width, and of all parameters investigated, AOD750 was most highly correlated with iris curvature.