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Relationship Between Peripapillary Choroid and Retinal Nerve Fiber Layer Thickness in a Population-Based Sample of Nonglaucomatous Eyes
Relationship Between Peripapillary Choroid and Retinal Nerve Fiber Layer Thickness in a Population-Based Sample of Nonglaucomatous Eyes PREETI GUPTA, CAROL Y. CHEUNG, MANI BASKARAN, JING TIAN, PINA MARZILIANO, ECOSSE L. LAMOUREUX, CHUI MING GEMMY CHEUNG, TIN AUNG, TIEN YIN WONG, AND CHING-YU CHENG
PURPOSE:
To describe the relationship between peripapillary choroidal thickness and retinal nerve fiber layer (RNFL) thickness in a population-based sample of nonglaucomatous eyes. DESIGN: Population-based, cross-sectional study. METHODS: A total of 478 nonglaucomatous subjects aged over 40 years were recruited from the Singapore Malay Eye Study (SiMES-2). All participants underwent a detailed ophthalmic examination, including Cirrus and Spectralis optical coherence tomography (OCT) for the measurements of RNFL thickness and peripapillary choroidal thickness, respectively. Associations between peripapillary choroidal thickness and RNFL thickness were assessed using linear regression models with generalized estimating equations. RESULTS: Of the 424 included subjects (843 nonglaucomatous eyes), 60.9% were women, and the mean (SD) age was 66.74 (10.44) years. The mean peripapillary choroidal thickness was 135.59 ± 56.74 mm and the mean RNFL thickness was 92.92 ± 11.41 mm. In terms of distribution profile, peripapillary choroid was thickest (150.04 ± 59.72 mm) at the superior and thinnest (110.71 ± 51.61 mm) at the inferior quadrant, whereas RNFL was thickest (118.60 ± 19.83 mm) at the inferior and thinnest (67.36 ± 11.36 mm) at the temporal quadrant. We found that thinner peripapillary choroidal thickness (PPCT) was independently associated with thinner RNFL thickness globally (regression coefficient [b] [ L1.334 mm for per-SD decrease in
Accepted for publication Sep 11, 2015. From the Singapore Eye Research Institute, Singapore National Eye Centre (P.G., C.Y.C., M.B., E.L.L., C.M.G.C., T.A., T.Y.W., C.-Y.C.); Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore and National University Health System (P.G., C.Y.C., M.B., E.L.L., C.M.G.C., T.A., T.Y.W., C.-Y.C.); Duke-NUS Graduate Medical School (C.Y.C., M.B., E.L.L., C.M.G.C., T.A., T.Y.W., C.-Y.C.); and School of Electrical and Electronic Engineering, Nanyang Technological University (J.T., P.M.), Singapore. Inquiries to Ching-Yu Cheng, Associate Professor, Academic Medicine Research Institute, Duke-NUS Graduate Medical School, Head, Ocular Epidemiology Research Group & Statistics Unit, Singapore Eye Research Institute, 20 College Road, The Academia, Level 6, Discovery Tower, Singapore 169856; e-mail: [email protected] 0002-9394/$36.00 http://dx.doi.org/10.1016/j.ajo.2015.09.018
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PPCT, P [ .003), and in the inferior (b [ L2.565, P [ .001) and superior (b [ L2.340, P [ .001) quadrants even after adjusting for potential confounders. CONCLUSIONS: Thinner peripapillary choroid was independently associated with thinner RNFL globally and in the inferior and superior regions. This structurestructure relationship may need further exploration in glaucomatous eyes prior to its application in clinical settings. (Am J Ophthalmol 2015;-:-–-. Ó 2015 by Elsevier Inc. All rights reserved.)
R
ETINAL NERVE FIBER LAYER (RNFL) THICKNESS
changes are the earliest signs of glaucoma. These precede even optic nerve head (ONH) and visual field changes,1,2 making the evaluation of RNFL thickness a crucial assessment in the early diagnosis of glaucoma.3–5 Among the various factors associated with the development and progression of glaucoma, vascular and hemodynamic factors have been suggested to play an important role.6,7 Studies8,9 have now demonstrated vascular insufficiency of the ONH to be an important parameter in the pathogenesis of glaucomatous optic neuropathy. Since RNFL is formed by the expansion of the fibers of the optic nerve, any insufficient blood supply to the ONH could lead to thinner RNFL causing glaucomatous optic neuropathy. Because of the common source of blood supply to the ONH and peripapillary choroid via the short posterior ciliary arteries,10–13 it is likely that a relationship exists between peripapillary choroid and RNFL thickness. However, to date, no studies have explored the quantitative relationship between these parameters in normal subjects, particularly in the general population. Evaluation of the association between peripapillary choroidal thickness and RNFL thickness may help better elucidate the relationship between the structural parameters that may be useful clinically for assessment of ONH damage in glaucoma. With the recent advancement in imaging technology using spectral-domain optical coherence tomography (SD OCT), in particular the enhanced depth imaging (EDI)
ELSEVIER INC. ALL
RIGHTS RESERVED.
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technique of SD OCT, objective and quantitative assessment of the peripapillary choroidal thickness is now possible. The purpose of this population-based, crosssectional study was to evaluate the relationship between peripapillary choroidal thickness and RNFL thickness as measured by SD OCT in a large population sample of nonglaucomatous subjects. We further report the distribution profile of peripapillary choroidal thickness obtained using our automated choroidal segmentation software14 and RNFL thickness in our population.
Carl Zeiss Meditec, Inc, Oberkochen, Germany). Slitlamp biomicroscopy (Haag-Streit model BQ-900; HaagStreit) was performed by the study ophthalmologists to examine the anterior chamber and lens after pupil dilation with tropicamide 1% and phenylephrine hydrochloride 2.5%. Glaucoma was defined using the International Society of Geographic and Epidemiological Ophthalmology scheme,16 based on findings from gonioscopy, optic disc characteristics, and visual fields results (as described below). VISUAL FIELD EXAMINATION:
METHODS STUDY POPULATION AND DESIGN:
Subjects of this study were enrolled from the Singapore Malay Eye Study (SiMES), a population-based cohort study of eye diseases in a Malay population aged 40–80 years in Singapore. The baseline examination was conducted between 2004 and 2006 and a follow-up examination of the SiMES participants was conducted between January 2011 and December 2013.15 For this study, we consecutively recruited 478 subjects from SiMES participants who attended the follow-up examination from February 2012 to July 2013. Written informed consent was obtained from all participants after explanation of the nature and possible consequences of the study. The study adhered to the tenets of the Declaration of Helsinki, and ethics approval was obtained from the Singapore Eye Research Institute Institutional Review Board.
OCULAR EXAMINATIONS:
Each study participant underwent a standard ophthalmic examination including measurement of refraction and visual acuity, slit-lamp biomicroscopy, tonometry, pachymetry, perimetry, ocular biometry, fundus examination, and SD OCT imaging. Refraction and corneal curvature were measured using an autokeratorefractometer (Canon RK 5 Auto RefKeratometer; Canon Inc Ltd, Tochigiken, Japan). Spherical equivalent (SE) was calculated as the sum of the spherical power and half of the cylinder power. Best-corrected visual acuity (BCVA) was measured monocularly using a logarithm of the minimal angle of resolution (logMAR) chart (Lighthouse International, New York, New York, USA) at a distance of 4 m. Central corneal thickness was measured using an ultrasound pachymeter (Advent; Mentor O & O Inc, Norwell, Massachusetts, USA). Ocular biometry, including axial length (AL), was measured using noncontact partial coherence interferometry (IOL Master V3.01; Carl Zeiss Meditec AG, Jena, Germany). Intraocular pressure (IOP) was measured using Goldmann applanation tonometry (Haag-Streit, Bern, Switzerland) before pupil dilation. Standardized visual field testing was performed with static automated white-on-white threshold perimetry (SITA Fast 24-2, Humphrey Field Analyzer II;
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Standardized visual field testing was performed with static automated perimetry (Swedish Interactive Threshold Algorithm standard 24-2, Humphery Field Analyzer II; Carl Zeiss Meditec, Dublin, California, USA). A visual field was defined as reliable when fixation losses were less than 20%, and falsepositive and false-negative rates were less than 33%. A glaucomatous visual field defect was defined as the presence of 3 or more significant (P < .05) nonedge continuous points with at least 1 at the P < .01 level on the same side of the horizontal meridian in the pattern deviation plot, and classified as ‘‘outside normal limits’’ on the Glaucoma Hemifield Test, confirmed on 2 consecutive visual field examinations. SiMES is part of the Singapore Epidemiology Eye Diseases (SEED) study.17 For the purpose of conformity between other studies in SEED, we have used Cirrus HDOCT for RNFL thickness measurements and Spectralis SD OCT with EDI for choroidal measurements. In addition, we believe that the use of 2 SD OCT machines has its own advantages, as systematic measurement error in 1 machine, if existing, could lead to a biased association between peripapillary choroidal thickness and RNFL thickness, whereas this could be taken care of by the use of 2 machines.
RETINAL NERVE FIBER LAYER IMAGING AND MEASUREMENT: Cirrus HD-OCT (software version 6.0; Carl Zeiss
Meditec, Inc, Dublin, California, USA) was used to measure peripapillary RNFL. After pupil dilation, RNFL scan acquisitions were performed for each participant using an optic disc cube 200 3 200 scan protocol, which generates a cube of data in a 6 mm 3 6 mm grid with 200 3 200 axial measurements. In brief, the subject’s pupil was first centered and focused in an iris viewing camera on the acquire screen, and the line scanning ophthalmoscope (LSO) with ‘‘auto focus’’ mode was then used to optimize the view of the retina. The ‘‘center’’ and ‘‘enhance’’ modes were used to optimize the Z-offset and scan polarization, respectively, for the OCT scan to maximize the OCT signal. Rescanning was performed if a motion artifact or saccades through the calculation circle (3.46 mm diameter around the ONH) were detected. The OCT scans were excluded if there was the presence of RNFL or ONH
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algorithm segmentation failure. All the OCT scans included in the study had signal strength of at least 6, which is considered as acceptable quality. RNFL thicknesses (average, clock hours, and quadrants) were derived automatically from a single scan using the in-built automated software for segmentation and parameter measurements without manual operator adjustment.
ness and peripapillary choroidal thickness were excluded. Of the 478 total subjects (947 eyes) examined, 104 eyes were excluded (5 eyes with best-corrected logMAR visual acuity >0.30, 14 eyes with SE greater than -6 diopter, 42 eyes with a diagnosis of glaucoma, and 43 eyes with poor OCT image quality), leaving 843 nonglaucomatous eyes for final analysis.
PERIPAPILLARY CHOROIDAL THICKNESS IMAGING AND MEASUREMENT: Peripapillary choroid was imaged using
STATISTICAL ANALYSIS:
the EDI mode of the Spectralis SD OCT. EDI is a method that improves resolution of choroidal details as the zerodelay line with the highest sensitivity is closer to the choroid, and more accurate image acquisition is possible in comparison with those of standard retinal SD OCT methods.18 Following the Spectralis user manual guidelines, subjects’ keratometry readings and the refraction data were entered into the machine to estimate optical magnification and, therefore, to allow for more accurate comparisons across individuals. The peripapillary region was scanned using a 360 degree, 3.4-mm-diameter circle that was centered on the optic disc, each comprising 100 averaged scans (using the proprietary automatic averaging and eye tracking features of the device). Scans were centered using an internal fixation and centering was confirmed by a scanning laser ophthalmoscope integrated into the instrument. In our study, the Bruch membrane and choroidal-scleral interface were delineated with the automatic segmentation algorithm developed by Tian and associates.14 This algorithm demonstrated good consistency with the manual measurements of choroidal thickness (the average of the Dice coefficients over 45 tested images was 90.5% with standard deviation of 3%).14 The peripapillary choroidal thickness in the optic disc region was automatically measured as the perpendicular distance between the outer portion of the hyperreflective line corresponding to the RPE and the hyporeflective line or margin corresponding to the choroidal-scleral interface at the 12 discrete locations (30 degrees apart) and the 4 quadrants. In our recently published paper19 using automated choroidal segmentation software we have demonstrated excellent intrasession repeatability (intraclass correlation coefficient ranging from 0.9998 to 0.999) of peripapillary choroidal thickness measurement at all 4 quadrants. EXCLUSION CRITERIA:
For our analyses, we excluded subjects based on the following criteria: best-corrected logMAR visual acuity >0.30, SE greater than 6 diopter, and clinical features compatible with a diagnosis of glaucoma. The quality of the SD OCT image was assessed prior to the analysis, and images that had motion artifacts or were of insufficient quality (signal strength of <6 for Cirrus OCT and a quality index of <25 decibels for Spectralis OCT, as suggested by the manufacturer, for the image quality assurance) for a reliable determination of RNFL thickVOL. -, NO. -
Mean and standard deviation (SD) of both peripapillary choroidal thickness and RNFL thickness was calculated in all subjects for clock hours and 4 quadrants. Associations of peripapillary choroidal thickness (independent variable of interest) with RNFL thicknesses (dependent variable) were assessed using linear regression. Generalized estimating equations (exchangeable correlation matrix) were used to account for the correlation between pairs of eyes for each individual. Factors such as age, sex, AL, IOP, diabetic retinopathy, and agerelated macular degeneration were included in the multivariate model to adjust for potential confounding. Statistical significance was set at P < .05 unless otherwise indicated. The data were analyzed with MedCalc version 12.3 (Medcalc Software, Ostend, Belgium) and SPSS version 20.0 (SPSS, Inc, Chicago, Illinois, USA).
RESULTS A TOTAL OF 843 EYES FROM 424 SUBJECTS WERE INCLUDED IN
the study. Of the 424 subjects, 363 (85.6%) did not have any eye diseases; the remaining 61 (14.4%) had eye diseases including diabetic retinopathy (8.5%) and early (5.2%) and late (0.6%) age-related macular degeneration. The included participants’ mean age was 66.74 6 10.44 years and 258 (60.9%) participants were female. The clinical characteristics of the included and excluded eyes are shown in Table 1. Compared to the eyes included in the analysis, excluded eyes were more myopic and had poor BCVA. Table 2 presents the distribution of mean peripapillary choroidal thickness and RNFL thickness measured at 12 clock hours and 4 quadrants (superior, nasal, inferior, and temporal). The average peripapillary choroidal thickness was 135.59 6 56.74 mm and the average RFNL thickness was 92.92 611.41 mm. There are variations in the topographic profile of peripapillary choroidal thickness and RNFL thickness among clock hours and different quadrants. Peripapillary choroid was thickest (150.04 6 59.72 mm) at the superior quadrant and thinnest (110.71 6 51.61) at the inferior quadrant, whereas RNFL was thickest (118.60 6 19.83 mm) at the inferior and thinnest (67.36 6 11.36) at the temporal quadrant. Table 3 shows the linear regression analyses of the associations of peripapillary choroidal thickness (exposure variable of interest) by locations evaluated against RNFL thicknesses (dependent variable) from the same location
RELATIONSHIP BETWEEN PERIPAPILLARY CHOROID AND RNFL THICKNESS
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TABLE 1. Comparison of Ocular Characteristics of Included and Excluded Eyes in Evaluating the Relationship Between Peripapillary Choroid and Retinal Nerve Fiber Layer Thickness Included (n ¼ 843 Eyes)
Characteristics
Axial length, mm Anterior chamber depth, mm Corneal curvature, mm Spherical equivalent, D BCVA, logMAR Central corneal thickness, mm Intraocular pressure, mm Hg Average RNFL thickness, mm
Excluded (n ¼ 61 Eyes)
P Valuea
23.56 (0.98) 3.14 (0.38)
24.27 (1.92) 3.00 (0.42)
.198 .185
7.67 (0.25) 0.23 (1.57) 0.28 (0.45) 539.72 (32.64)
7.64 (0.24) 3.19 (5.54) 0.55 (0.78) 536.10 (32.16)
.876 .002 .028 .063
14.30 (3.17)
15.48 (4.92)
.150
92.92 (11.41)
93.11 (11.09)
.923
BCVA ¼ best-corrected visual acuity; D ¼ diopter; logMAR ¼ logarithm of the minimal angle of resolution; RNFL ¼ retinal nerve fiber layer. Data presented are means (standard deviations). a P value was obtained with generalized estimating equation.
(Figure) to calculate regression coefficients (b). In Model 1, including age, sex, and AL, we found that thinner peripapillary choroidal thickness was independently associated with thinner RNFL thickness globally (b ¼ 1.364 mm for per-SD decrease in peripapillary choroidal thickness, P ¼ .002) and in the inferior (b ¼ 2.539, P ¼ .001) and superior (b ¼ 2.492, P ¼ .001) quadrants. In Model 2, including age, sex, AL, IOP, diabetic retinopathy, and age-related macular degeneration, thinner peripapillary choroidal thickness was independently associated with thinner RNFL thickness globally (b ¼ 1.329 mm for per-SD decrease in peripapillary choroidal thickness, P ¼ .003) and in the inferior (b ¼ 2.566, P < .001) and superior (b ¼ 2.348, P ¼ .001) quadrants. In order to control for potential confounding effect from OCT signal strengths, we further included signal strength from both Cirrus and Spectralis OCT in our regression analyses. The results remained similar after further adjustment for signal strength (Model 3 in Table 3). However, in all models, the association was not present in the temporal quadrant.
DISCUSSION OUR STUDY PROVIDES THE POPULATION-BASED DATA ON
the quantitative relationship between peripapillary choroidal thickness and RNFL thickness measured by SD OCT in nonglaucomatous subjects. We found that thinner 4
TABLE 2. Distribution of Peripapillary Choroid and Retinal Nerve Fiber Layer Thickness in Nonglaucomatous Eyes at Clock-Hour Sectors (30 Degrees Apart) and 4 Quadrants, With 360-Degree, 3.4-mm-Diameter Peripapillary Circle Scans (N ¼ 843 Eyes)
Measurement Location
Clock hours 1 2 3 4 5 6 7 8 9 10 11 12 Quadrants Superior Nasal Inferior Temporal Average thickness
Peripapillary Choroidal
Retinal Nerve Fiber Layer
Thickness (mm)
Thickness (mm)
Mean (SD)
Mean (SD)
138.61 (77.01) 147.09 (70.88) 148.38 (65.03) 150.46 (62.21) 151.06 (59.39) 151.68 (61.06) 145.17 (61.97) 133.58 (58.49) 115.32 (53.67) 102.01 (51.07) 113.25 (57.11) 129.24 (68.31)
56.95 (11.08) 81.10 (16.00) 115.72 (23.97) 116.95 (26.79) 115.26 (24.91) 81.07 (16.87) 57.38 (11.06) 67.01 (14.72) 113.61 (30.65) 127.30 (28.03) 115.00 (30.08) 67.53 (14.04)
150.04 (59.72) 143.12 (58.46) 110.71 (51.61) 138.47 (68.65) 135.59 (56.74)
116.05 (18.42) 69.69 (11.28) 118.60 (19.83) 67.36 (11.36) 92.92 (11.41)
SD ¼ standard deviation. One o’clock corresponded to the temporal region, 4 o’clock to the superior, 7 o’clock to the nasal, and 10 o’clock to the inferior.
peripapillary choroidal thickness was independently associated with thinner RNFL thickness globally, in the inferior and superior quadrants, even after adjusting for relevant confounders. The results of this study provide evidence that thinning of the peripapillary choroid is associated with corresponding RNFL thinning. In terms of topographic profile, the peripapillary choroid was thickest at the superior and thinnest at the inferior quadrants, whereas RNFL was thickest at the inferior and thinnest at the temporal quadrants. Thinnest peripapillary choroid in the inferior quadrant may explain the susceptibility of the inferior optic nerve region to glaucoma. To date, none of the studies has thoroughly investigated the quantitative relationship between peripapillary choroidal thickness and RNFL thickness in normal subjects, particularly in the general population. Only a few studies,20,21 when analyzing RNFL as one of the covariates associated with peripapillary choroidal thickness, reported no significant correlation, a finding contrary to our results. Similarly, Maul and associates in a cross-sectional study of 74 suspects and glaucoma patients reported no significant association of peripapillary choroidal thickness with either degree of glaucoma damage
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TABLE 3. The Associations of Peripapillary Choroidal Thickness With Retinal Nerve Fiber Layer Thickness in a Population-Based Sample of Nonglaucomatous Eyes (N ¼ 843) Using Generalized Estimating Equation
Average peripapillary choroidal thickness Inferior peripapillary choroidal thickness Superior peripapillary choroidal thickness
Model 1a
Model 2b
Model 3c
Retinal Nerve Fiber Layer Thickness
Retinal Nerve Fiber Layer Thickness
Retinal Nerve Fiber Layer Thickness
Beta (95% CI)
P Value
Beta (95% CI)
P Value
Beta (95% CI)
P Value
1.364 (0.497, 2.232) 2.539 (1.099, 3.979) 2.492 (1.086, 3.898)
.002 .001 .001
1.329 (0.463, 2.196) 2.566 (1.124, 4.009) 2.348 (0.937, 3.760)
.003 <.001 .001
1.334 (0.464, 2.205) 2.565 (1.119, 4.010) 2.340 (0.923, 3.757)
.003 .001 .001
CI ¼ confidence interval. Average, inferior, and superior peripapillary choroidal thickness was regressed with average, inferior, and superior retinal nerve fiber layer thickness, respectively. Average, inferior, and superior peripapillary choroidal thicknesses were analyzed per standard deviation decrease. a Adjusted for age, sex, and axial length. b Adjusted for age, sex, axial length, intraocular pressure, diabetic retinopathy, and age-related macular degeneration. c Adjusted for age, sex, axial length, intraocular pressure, diabetic retinopathy, age-related macular degeneration, and signal strength from Cirrus and Spectralis optical coherence tomography.
FIGURE. Scatterplot showing positive correlation of (Left) average retinal nerve fiber layer (RNFL) thickness with average peripapillary choroidal thickness, (Middle) inferior RNFL thickness with inferior peripapillary choroidal thickness, and (Right) superior RNFL thickness with superior peripapillary choroidal thickness.
or RNFL thickness.22 There are several reasons for this. First, their peripapillary choroidal thickness measurements were not automated but involved manual delineation of the choroidal boundaries, making it not only time consuming, but also prone to measurement errors. Second, these studies were performed in clinic-based settings with a potential selection bias and involved smaller sample sizes (36 and 76 normal subjects in studies by Ho and associates and Huang and associates, respectively).20,21 To address these issues, we therefore developed and used a novel technique of automated choroidal segmentation14,19 to objectively and efficiently obtain the thickness of the peripapillary choroid and investigate its association with RNFL thickness in a population-based sample. Interestingly, our results demonstrate significant positive association between inferior, superior, and average peripapillary choroidal thickness and RNFL thickness (ie, VOL. -, NO. -
thinner peripapillary choroid in these quadrants was associated with thinner RNFL). A possible reason for the positive association between these structural features could be because both ONH and peripapillary choroid shares the common source of blood supply via the short posterior ciliary arteries.10–13 Our study supports the hypothesis that since glaucomatous neurodegeneration occurs at the ONH,23 it is likely that concurrent choroidal changes would also occur in the peripapillary region underlying areas of RNFL thinning. It is also interesting to note that although the association between peripapillary choroidal thickness and RNFL in the temporal region was significant in the univariate analysis, it was abolished after incorporating age, sex, and AL. We believe that the association in the temporal region is primarily driven by AL, given that the temporal region is most influenced by AL measurements compared to the other regions.
RELATIONSHIP BETWEEN PERIPAPILLARY CHOROID AND RNFL THICKNESS
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In terms of topographic profile of peripapillary choroid and RNFL thicknesses, our results confirmed the asymmetric distribution of both the peripapillary choroid and RNFL thicknesses.19,24–26 The mean peripapillary choroidal thickness and RNFL thickness measurements showed regional differences, peripapillary choroid being thickest superiorly and thinnest inferiorly, whereas RNFL was thickest inferiorly and thinnest temporally. Our observations of the distribution of peripapillary choroidal thickness are similar to the results of previous EDI-OCT studies in normal eyes, which have consistently shown the inferior region to be the thinnest, compared to other regions.19–21,27,28 Although it remains unclear why the inferior choroid demonstrates such prominent thinning, we favor the theory that both the vascular watershed zone and the embryonic location of the optic fissure closure may be responsible.29 As the optic fissure is located in the inferior aspect of the optic cup and is the last part of the globe to close,30 this regional difference in ocular development may contribute to the thinner choroid found in the inferior region. Therefore, development of the ONH and peripapillary choroid needs to be considered to explain the spatial distribution of peripapillary choroidal thickness at different sectors. Despite RNFL being thickest in the inferior quadrant, this region is most vulnerable to glaucomatous damage. Selective and predominant inferior RNFL loss in early glaucoma is multifactorial. One of the known reasons for the vulnerability of the inferior region is that the lamina cribrosa of the inferior pole has larger pores and thinner connective tissue and glial support for passing retinal ganglion cell axons.31–33 Based on our findings, this could also possibly be because of the thinnest peripapillary choroid in the inferior region. We speculate that thinnest peripapillary choroid in the inferior quadrant, which represents an area of lower blood supply, may predispose the inferior region of the optic nerve to glaucomatous ischemic damage, suggesting a possible explanation for the observation that glaucoma typically affects the inferior optic nerve region first. Peripapillary choroidal thickness as a surrogate to vascular supply12,13 found a mild to moderate association, more so with inferior RNFL thickness, in our study of nonglaucomatous eyes. The magnitude of association is weak, thus again suggesting involvement of multiple factors related to inferior RNFL susceptibility in glaucoma pathogenesis. Further examination in glaucoma patients would be needed to confirm this association and to see whether such association is stronger in glaucomatous eyes.
The strengths of this study include its population-based design and a relatively large sample size with a single common ethnicity. Hence, our findings were unlikely to be confounded by ethnic heterogeneity. Unlike other studies, which involved manual delineation of choroidal boundaries, we used an automated choroidal segmentation technique to objectively obtain the thickness of the peripapillary choroid. Therefore, our measurements of peripapillary choroidal thickness are less prone to measurement errors. The relationship between peripapillary choroidal thickness and RNFL was confirmed after adjusting for potential clinical factors. Nevertheless, this study has a few limitations. First, recent studies have reported diurnal fluctuations in choroidal thickness in the macular region.34–36 To the best of our knowledge, there are no data on the association between diurnal variation and choroidal thickness in the peripapillary region. Our subjects were examined only at a single time point, and thus we are not able to take account of any diurnal variation of peripapillary choroidal thickness. However, the peripapillary choroidal thickness measurements in our study were not performed at the same time of the day; each participant underwent the OCT examination in a randomized manner with respect to when the readings were obtained. It seems unlikely that circadian changes may have influenced the results of our investigation. Second, owing to the cross-sectional nature of our study we could identify a structural relationship between peripapillary choroidal thickness and RNFL thickness, but cannot address the temporal relationship between these structures. More longitudinal data are needed to clarify this relationship. Last, our investigation included consecutive participating subjects from a population-based study and thus some of them had eye diseases. Therefore, the distribution of peripapillary choroidal thickness and RNFL thickness determined in this study may represent the thickness not in healthy eyes but in the general adult and elderly populations. However, this would not affect the observed associations, because in the multiple regression analysis models we have adjusted for the potential ocular diseases in elderly people that might influence peripapillary choroidal thickness. In conclusion, the current study demonstrates significant positive associations between peripapillary choroid and RNFL thicknesses and examines this structure-structure relationship. Understanding of the relationship between these structural parameters may be useful clinically for assessment of ONH damage in glaucoma. However, this relationship needs to be explored further in glaucomatous eyes of varying severity before it is applied in clinical settings.
FUNDING/SUPPORT: THIS STUDY WAS SUPPORTED BY A GRANT FROM NATIONAL MEDICAL RESEARCH COUNCIL (SINGAPORE) and National Research Foundation University Fund (Singapore). The sponsor or funding organization had no role in the design or conduct of this research. Financial Disclosures: C.Y. Cheung: received grant support from National Medical Research Council (NMRC) and Biomedical Research Council, Singapore directed to Singapore Eye Research Institute; T.A.: received grant support from National Medical Research Council (NMRC) and Biomedical Research Council, Singapore directed to Singapore Eye Research Institute; T.Y.W.: received grant support from National Medical Research Council
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(NMRC) and Biomedical Research Council, Singapore directed to Singapore Eye Research Institute; Advisory Board member for Abbot, Novartis, Pfizer, Allergan, and Bayer; independent consultant for Abbot, Novartis, Pfizer, Allergan, and Bayer; C.Y. Cheng: received grant support from National Medical Research Council (NMRC) and Biomedical Research Council, Singapore directed to Singapore Eye Research Institute. All authors attest that they meet the current ICMJE requirements to qualify as authors.
REFERENCES 1. Sommer A, Katz J, Quigley HA, et al. Clinically detectable nerve fiber atrophy precedes the onset of glaucomatous field loss. Arch Ophthalmol 1991;109(1):77–83. 2. Tuulonen A, Lehtola J, Airaksinen PJ. Nerve fiber layer defects with normal visual fields. Do normal optic disc and normal visual field indicate absence of glaucomatous abnormality? Ophthalmology 1993;100(5):587–597. 3. Bowd C, Weinreb RN, Williams JM, Zangwill LM. The retinal nerve fiber layer thickness in ocular hypertensive, normal, and glaucomatous eyes with optical coherence tomography. Arch Ophthalmol 2000;118(1):22–26. 4. Schuman JS, Hee MR, Puliafito CA, et al. Quantification of nerve fiber layer thickness in normal and glaucomatous eyes using optical coherence tomography. Arch Ophthalmol 1995; 113(5):586–596. 5. Zangwill LM, Williams J, Berry CC, Knauer S, Weinreb RN. A comparison of optical coherence tomography and retinal nerve fiber layer photography for detection of nerve fiber layer damage in glaucoma. Ophthalmology 2000;107(7): 1309–1315. 6. Chen FK, Yeoh J, Rahman W, Patel PJ, Tufail A, Da Cruz L. Topographic variation and interocular symmetry of macular choroidal thickness using enhanced depth imaging optical coherence tomography. Invest Ophthalmol Vis Sci 2012; 53(2):975–985. 7. Horecky J, Baciak L, Kasparova S, Pacheco G, Aliev G, Vancova O. Minimally invasive surgical approach for threevessel occlusion as a model of vascular dementia in the ratbrain bioenergetics assay. J Neurol Sci 2009;283(1-2): 178–181. 8. Hayreh SS. Blood supply of the optic nerve head and its role in optic atrophy, glaucoma, and oedema of the optic disc. Br J Ophthalmol 1969;53(11):721–748. 9. Nicolela MT, Hnik P, Drance SM. Scanning laser Doppler flowmeter study of retinal and optic disk blood flow in glaucomatous patients. Am J Ophthalmol 1996;122(6): 775–783. 10. Duijm HF, van den Berg TJ, Greve EL. Choroidal haemodynamics in glaucoma. Br J Ophthalmol 1997;81(9):735–742. 11. Flammer J, Orgul S, Costa VP, et al. The impact of ocular blood flow in glaucoma. Prog Retin Eye Res 2002;21(4): 359–393. 12. Hayreh SS. The blood supply of the optic nerve head and the evaluation of it - myth and reality. Prog Retin Eye Res 2001; 20(5):563–593. 13. Hayreh SS. The 1994 Von Sallman Lecture. The optic nerve head circulation in health and disease. Exp Eye Res 1995; 61(3):259–272. 14. Tian J, Marziliano P, Baskaran M, et al. Automatic segmentation of the choroid in enhanced depth imaging optical coherence tomography images. Biomed Opt Express 2013; 4(3):397–411.
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15. Rosman M, Zheng Y, Wong W, et al. Singapore Malay Eye Study: rationale and methodology of 6-year follow-up study (SiMES-2). Clin Experiment Ophthalmol 2012;40(6): 557–568. 16. Foster PJ, Buhrmann R, Quigley HA, Johnson GJ. The definition and classification of glaucoma in prevalence surveys. Br J Ophthalmol 2002;86(2):238–242. 17. Chua J, Tham YC, Liao J, et al. Ethnic differences of intraocular pressure and central corneal thickness: the Singapore Epidemiology of Eye Diseases study. Ophthalmology 2014; 121(10):2013–2022. 18. Spaide RF, Koizumi H, Pozzoni MC. Enhanced depth imaging spectral-domain optical coherence tomography. Am J Ophthalmol 2008;146(4):496–500. 19. Gupta P, Jing T, Marziliano P, et al. Peripapillary choroidal thickness assessed using automated choroidal segmentation software in an Asian population. Br J Ophthalmol 2015;99(7):920–926. 20. Ho J, Branchini L, Regatieri C, Krishnan C, Fujimoto JG, Duker JS. Analysis of normal peripapillary choroidal thickness via spectral domain optical coherence tomography. Ophthalmology 2011;118(10):2001–2007. 21. Huang W, Wang W, Zhou M, et al. Peripapillary choroidal thickness in healthy Chinese subjects. BMC Ophthalmol 2013;13:23. 22. Maul EA, Friedman DS, Chang DS, et al. Choroidal thickness measured by spectral domain optical coherence tomography: factors affecting thickness in glaucoma patients. Ophthalmology 2011;118(8):1571–1579. 23. Jonas JB, Budde WM, Panda-Jonas S. Ophthalmoscopic evaluation of the optic nerve head. Surv Ophthalmol 1999;43(4): 293–320. 24. Wang YX, Pan Z, Zhao L, You QS, Xu L, Jonas JB. Retinal nerve fiber layer thickness. The Beijing Eye Study 2011. PLoS One 2013;8(6):e66763. 25. Zhao L, Wang Y, Chen CX, Xu L, Jonas JB. Retinal nerve fibre layer thickness measured by Spectralis spectral-domain optical coherence tomography: The Beijing Eye Study. Acta Ophthalmol 2014;92(1):e35–e41. 26. Cheung CY, Chen D, Wong TY, et al. Determinants of quantitative optic nerve measurements using spectral domain optical coherence tomography in a population-based sample of non-glaucomatous subjects. Invest Ophthalmol Vis Sci 2011; 52(13):9629–9635. 27. Tanabe H, Ito Y, Terasaki H. Choroid is thinner in inferior region of optic disks of normal eyes. Retina 2012;32(1): 134–139. 28. Ouyang Y, Heussen FM, Mokwa N, et al. Spatial distribution of posterior pole choroidal thickness by spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci 2011; 52(9):7019–7026. 29. Ikuno Y, Kawaguchi K, Nouchi T, Yasuno Y. Choroidal thickness in healthy Japanese subjects. Invest Ophthalmol Vis Sci 2010;51(4):2173–2176.
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30. Schoenwolf G, Bleyl S, Brauer P, Francis-West P. Larsen’s Human Embrology. Philadelphia: Elsevier; 2009:602– 616. 31. Jonas JB, Mardin CY, Schlotzer-Schrehardt U, Naumann GO. Morphometry of the human lamina cribrosa surface. Invest Ophthalmol Vis Sci 1991;32(2):401–405. 32. Quigley HA, Addicks EM. Regional differences in the structure of the lamina cribrosa and their relation to glaucomatous optic nerve damage. Arch Ophthalmol 1981;99(1): 137–143. 33. Radius RL, Gonzales M. Anatomy of the lamina cribrosa in human eyes. Arch Ophthalmol 1981;99(12):2159–2162.
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34. Chakraborty R, Read SA, Collins MJ. Diurnal variations in axial length, choroidal thickness, intraocular pressure, and ocular biometrics. Invest Ophthalmol Vis Sci 2011;52(8): 5121–5129. 35. Tan CS, Ouyang Y, Ruiz H, Sadda SR. Diurnal variation of choroidal thickness in normal, healthy subjects measured by spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci 2012;53(1):261–266. 36. Usui S, Ikuno Y, Akiba M, et al. Circadian changes in subfoveal choroidal thickness and the relationship with circulatory factors in healthy subjects. Invest Ophthalmol Vis Sci 2012; 53(4):2300–2307.
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Biosketch Preeti Gupta graduated with masters in Optometry from Queensland University of Technology, Australia in 2008. She then joined the Ocular Epidemiology Research Group at Singapore Eye Research Institute, Singapore, where she conducts and coordinates epidemiological and population-based projects under the Singapore Epidemiology of Eye Disease programme. Her area of interest includes epidemiology of major eye diseases and ocular imaging using novel image processing techniques.
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Biosketch Ching-Yu Cheng leads Ocular Epidemiology Research group at Singapore Eye Research Institute and co-directs the Singapore Epidemiology of Eye Diseases (SEED) program. His primary research interests are related to epidemiology and genetics of major eye diseases. His current work involves a variety of epidemiological, clinical, and image research on glaucoma; and identification of susceptibility genes for complex ocular diseases, such as glaucoma, macular degeneration and cataract, using both genome-wide association approaches and next-generation sequencing technology.
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PURPOSE:
To describe the relationship between peripapillary choroidal thickness and retinal nerve fiber layer (RNFL) thickness in a population-based sample of nonglaucomatous eyes. DESIGN: Population-based, cross-sectional study. METHODS: A total of 478 nonglaucomatous subjects aged over 40 years were recruited from the Singapore Malay Eye Study (SiMES-2). All participants underwent a detailed ophthalmic examination, including Cirrus and Spectralis optical coherence tomography (OCT) for the measurements of RNFL thickness and peripapillary choroidal thickness, respectively. Associations between peripapillary choroidal thickness and RNFL thickness were assessed using linear regression models with generalized estimating equations. RESULTS: Of the 424 included subjects (843 nonglaucomatous eyes), 60.9% were women, and the mean (SD) age was 66.74 (10.44) years. The mean peripapillary choroidal thickness was 135.59 ± 56.74 mm and the mean RNFL thickness was 92.92 ± 11.41 mm. In terms of distribution profile, peripapillary choroid was thickest (150.04 ± 59.72 mm) at the superior and thinnest (110.71 ± 51.61 mm) at the inferior quadrant, whereas RNFL was thickest (118.60 ± 19.83 mm) at the inferior and thinnest (67.36 ± 11.36 mm) at the temporal quadrant. We found that thinner peripapillary choroidal thickness (PPCT) was independently associated with thinner RNFL thickness globally (regression coefficient [b] [ L1.334 mm for per-SD decrease in
Accepted for publication Sep 11, 2015. From the Singapore Eye Research Institute, Singapore National Eye Centre (P.G., C.Y.C., M.B., E.L.L., C.M.G.C., T.A., T.Y.W., C.-Y.C.); Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore and National University Health System (P.G., C.Y.C., M.B., E.L.L., C.M.G.C., T.A., T.Y.W., C.-Y.C.); Duke-NUS Graduate Medical School (C.Y.C., M.B., E.L.L., C.M.G.C., T.A., T.Y.W., C.-Y.C.); and School of Electrical and Electronic Engineering, Nanyang Technological University (J.T., P.M.), Singapore. Inquiries to Ching-Yu Cheng, Associate Professor, Academic Medicine Research Institute, Duke-NUS Graduate Medical School, Head, Ocular Epidemiology Research Group & Statistics Unit, Singapore Eye Research Institute, 20 College Road, The Academia, Level 6, Discovery Tower, Singapore 169856; e-mail: [email protected] 0002-9394/$36.00 http://dx.doi.org/10.1016/j.ajo.2015.09.018
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PPCT, P [ .003), and in the inferior (b [ L2.565, P [ .001) and superior (b [ L2.340, P [ .001) quadrants even after adjusting for potential confounders. CONCLUSIONS: Thinner peripapillary choroid was independently associated with thinner RNFL globally and in the inferior and superior regions. This structurestructure relationship may need further exploration in glaucomatous eyes prior to its application in clinical settings. (Am J Ophthalmol 2015;-:-–-. Ó 2015 by Elsevier Inc. All rights reserved.)
R
ETINAL NERVE FIBER LAYER (RNFL) THICKNESS
changes are the earliest signs of glaucoma. These precede even optic nerve head (ONH) and visual field changes,1,2 making the evaluation of RNFL thickness a crucial assessment in the early diagnosis of glaucoma.3–5 Among the various factors associated with the development and progression of glaucoma, vascular and hemodynamic factors have been suggested to play an important role.6,7 Studies8,9 have now demonstrated vascular insufficiency of the ONH to be an important parameter in the pathogenesis of glaucomatous optic neuropathy. Since RNFL is formed by the expansion of the fibers of the optic nerve, any insufficient blood supply to the ONH could lead to thinner RNFL causing glaucomatous optic neuropathy. Because of the common source of blood supply to the ONH and peripapillary choroid via the short posterior ciliary arteries,10–13 it is likely that a relationship exists between peripapillary choroid and RNFL thickness. However, to date, no studies have explored the quantitative relationship between these parameters in normal subjects, particularly in the general population. Evaluation of the association between peripapillary choroidal thickness and RNFL thickness may help better elucidate the relationship between the structural parameters that may be useful clinically for assessment of ONH damage in glaucoma. With the recent advancement in imaging technology using spectral-domain optical coherence tomography (SD OCT), in particular the enhanced depth imaging (EDI)
ELSEVIER INC. ALL
RIGHTS RESERVED.
1
technique of SD OCT, objective and quantitative assessment of the peripapillary choroidal thickness is now possible. The purpose of this population-based, crosssectional study was to evaluate the relationship between peripapillary choroidal thickness and RNFL thickness as measured by SD OCT in a large population sample of nonglaucomatous subjects. We further report the distribution profile of peripapillary choroidal thickness obtained using our automated choroidal segmentation software14 and RNFL thickness in our population.
Carl Zeiss Meditec, Inc, Oberkochen, Germany). Slitlamp biomicroscopy (Haag-Streit model BQ-900; HaagStreit) was performed by the study ophthalmologists to examine the anterior chamber and lens after pupil dilation with tropicamide 1% and phenylephrine hydrochloride 2.5%. Glaucoma was defined using the International Society of Geographic and Epidemiological Ophthalmology scheme,16 based on findings from gonioscopy, optic disc characteristics, and visual fields results (as described below). VISUAL FIELD EXAMINATION:
METHODS STUDY POPULATION AND DESIGN:
Subjects of this study were enrolled from the Singapore Malay Eye Study (SiMES), a population-based cohort study of eye diseases in a Malay population aged 40–80 years in Singapore. The baseline examination was conducted between 2004 and 2006 and a follow-up examination of the SiMES participants was conducted between January 2011 and December 2013.15 For this study, we consecutively recruited 478 subjects from SiMES participants who attended the follow-up examination from February 2012 to July 2013. Written informed consent was obtained from all participants after explanation of the nature and possible consequences of the study. The study adhered to the tenets of the Declaration of Helsinki, and ethics approval was obtained from the Singapore Eye Research Institute Institutional Review Board.
OCULAR EXAMINATIONS:
Each study participant underwent a standard ophthalmic examination including measurement of refraction and visual acuity, slit-lamp biomicroscopy, tonometry, pachymetry, perimetry, ocular biometry, fundus examination, and SD OCT imaging. Refraction and corneal curvature were measured using an autokeratorefractometer (Canon RK 5 Auto RefKeratometer; Canon Inc Ltd, Tochigiken, Japan). Spherical equivalent (SE) was calculated as the sum of the spherical power and half of the cylinder power. Best-corrected visual acuity (BCVA) was measured monocularly using a logarithm of the minimal angle of resolution (logMAR) chart (Lighthouse International, New York, New York, USA) at a distance of 4 m. Central corneal thickness was measured using an ultrasound pachymeter (Advent; Mentor O & O Inc, Norwell, Massachusetts, USA). Ocular biometry, including axial length (AL), was measured using noncontact partial coherence interferometry (IOL Master V3.01; Carl Zeiss Meditec AG, Jena, Germany). Intraocular pressure (IOP) was measured using Goldmann applanation tonometry (Haag-Streit, Bern, Switzerland) before pupil dilation. Standardized visual field testing was performed with static automated white-on-white threshold perimetry (SITA Fast 24-2, Humphrey Field Analyzer II;
2
Standardized visual field testing was performed with static automated perimetry (Swedish Interactive Threshold Algorithm standard 24-2, Humphery Field Analyzer II; Carl Zeiss Meditec, Dublin, California, USA). A visual field was defined as reliable when fixation losses were less than 20%, and falsepositive and false-negative rates were less than 33%. A glaucomatous visual field defect was defined as the presence of 3 or more significant (P < .05) nonedge continuous points with at least 1 at the P < .01 level on the same side of the horizontal meridian in the pattern deviation plot, and classified as ‘‘outside normal limits’’ on the Glaucoma Hemifield Test, confirmed on 2 consecutive visual field examinations. SiMES is part of the Singapore Epidemiology Eye Diseases (SEED) study.17 For the purpose of conformity between other studies in SEED, we have used Cirrus HDOCT for RNFL thickness measurements and Spectralis SD OCT with EDI for choroidal measurements. In addition, we believe that the use of 2 SD OCT machines has its own advantages, as systematic measurement error in 1 machine, if existing, could lead to a biased association between peripapillary choroidal thickness and RNFL thickness, whereas this could be taken care of by the use of 2 machines.
RETINAL NERVE FIBER LAYER IMAGING AND MEASUREMENT: Cirrus HD-OCT (software version 6.0; Carl Zeiss
Meditec, Inc, Dublin, California, USA) was used to measure peripapillary RNFL. After pupil dilation, RNFL scan acquisitions were performed for each participant using an optic disc cube 200 3 200 scan protocol, which generates a cube of data in a 6 mm 3 6 mm grid with 200 3 200 axial measurements. In brief, the subject’s pupil was first centered and focused in an iris viewing camera on the acquire screen, and the line scanning ophthalmoscope (LSO) with ‘‘auto focus’’ mode was then used to optimize the view of the retina. The ‘‘center’’ and ‘‘enhance’’ modes were used to optimize the Z-offset and scan polarization, respectively, for the OCT scan to maximize the OCT signal. Rescanning was performed if a motion artifact or saccades through the calculation circle (3.46 mm diameter around the ONH) were detected. The OCT scans were excluded if there was the presence of RNFL or ONH
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algorithm segmentation failure. All the OCT scans included in the study had signal strength of at least 6, which is considered as acceptable quality. RNFL thicknesses (average, clock hours, and quadrants) were derived automatically from a single scan using the in-built automated software for segmentation and parameter measurements without manual operator adjustment.
ness and peripapillary choroidal thickness were excluded. Of the 478 total subjects (947 eyes) examined, 104 eyes were excluded (5 eyes with best-corrected logMAR visual acuity >0.30, 14 eyes with SE greater than -6 diopter, 42 eyes with a diagnosis of glaucoma, and 43 eyes with poor OCT image quality), leaving 843 nonglaucomatous eyes for final analysis.
PERIPAPILLARY CHOROIDAL THICKNESS IMAGING AND MEASUREMENT: Peripapillary choroid was imaged using
STATISTICAL ANALYSIS:
the EDI mode of the Spectralis SD OCT. EDI is a method that improves resolution of choroidal details as the zerodelay line with the highest sensitivity is closer to the choroid, and more accurate image acquisition is possible in comparison with those of standard retinal SD OCT methods.18 Following the Spectralis user manual guidelines, subjects’ keratometry readings and the refraction data were entered into the machine to estimate optical magnification and, therefore, to allow for more accurate comparisons across individuals. The peripapillary region was scanned using a 360 degree, 3.4-mm-diameter circle that was centered on the optic disc, each comprising 100 averaged scans (using the proprietary automatic averaging and eye tracking features of the device). Scans were centered using an internal fixation and centering was confirmed by a scanning laser ophthalmoscope integrated into the instrument. In our study, the Bruch membrane and choroidal-scleral interface were delineated with the automatic segmentation algorithm developed by Tian and associates.14 This algorithm demonstrated good consistency with the manual measurements of choroidal thickness (the average of the Dice coefficients over 45 tested images was 90.5% with standard deviation of 3%).14 The peripapillary choroidal thickness in the optic disc region was automatically measured as the perpendicular distance between the outer portion of the hyperreflective line corresponding to the RPE and the hyporeflective line or margin corresponding to the choroidal-scleral interface at the 12 discrete locations (30 degrees apart) and the 4 quadrants. In our recently published paper19 using automated choroidal segmentation software we have demonstrated excellent intrasession repeatability (intraclass correlation coefficient ranging from 0.9998 to 0.999) of peripapillary choroidal thickness measurement at all 4 quadrants. EXCLUSION CRITERIA:
For our analyses, we excluded subjects based on the following criteria: best-corrected logMAR visual acuity >0.30, SE greater than 6 diopter, and clinical features compatible with a diagnosis of glaucoma. The quality of the SD OCT image was assessed prior to the analysis, and images that had motion artifacts or were of insufficient quality (signal strength of <6 for Cirrus OCT and a quality index of <25 decibels for Spectralis OCT, as suggested by the manufacturer, for the image quality assurance) for a reliable determination of RNFL thickVOL. -, NO. -
Mean and standard deviation (SD) of both peripapillary choroidal thickness and RNFL thickness was calculated in all subjects for clock hours and 4 quadrants. Associations of peripapillary choroidal thickness (independent variable of interest) with RNFL thicknesses (dependent variable) were assessed using linear regression. Generalized estimating equations (exchangeable correlation matrix) were used to account for the correlation between pairs of eyes for each individual. Factors such as age, sex, AL, IOP, diabetic retinopathy, and agerelated macular degeneration were included in the multivariate model to adjust for potential confounding. Statistical significance was set at P < .05 unless otherwise indicated. The data were analyzed with MedCalc version 12.3 (Medcalc Software, Ostend, Belgium) and SPSS version 20.0 (SPSS, Inc, Chicago, Illinois, USA).
RESULTS A TOTAL OF 843 EYES FROM 424 SUBJECTS WERE INCLUDED IN
the study. Of the 424 subjects, 363 (85.6%) did not have any eye diseases; the remaining 61 (14.4%) had eye diseases including diabetic retinopathy (8.5%) and early (5.2%) and late (0.6%) age-related macular degeneration. The included participants’ mean age was 66.74 6 10.44 years and 258 (60.9%) participants were female. The clinical characteristics of the included and excluded eyes are shown in Table 1. Compared to the eyes included in the analysis, excluded eyes were more myopic and had poor BCVA. Table 2 presents the distribution of mean peripapillary choroidal thickness and RNFL thickness measured at 12 clock hours and 4 quadrants (superior, nasal, inferior, and temporal). The average peripapillary choroidal thickness was 135.59 6 56.74 mm and the average RFNL thickness was 92.92 611.41 mm. There are variations in the topographic profile of peripapillary choroidal thickness and RNFL thickness among clock hours and different quadrants. Peripapillary choroid was thickest (150.04 6 59.72 mm) at the superior quadrant and thinnest (110.71 6 51.61) at the inferior quadrant, whereas RNFL was thickest (118.60 6 19.83 mm) at the inferior and thinnest (67.36 6 11.36) at the temporal quadrant. Table 3 shows the linear regression analyses of the associations of peripapillary choroidal thickness (exposure variable of interest) by locations evaluated against RNFL thicknesses (dependent variable) from the same location
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TABLE 1. Comparison of Ocular Characteristics of Included and Excluded Eyes in Evaluating the Relationship Between Peripapillary Choroid and Retinal Nerve Fiber Layer Thickness Included (n ¼ 843 Eyes)
Characteristics
Axial length, mm Anterior chamber depth, mm Corneal curvature, mm Spherical equivalent, D BCVA, logMAR Central corneal thickness, mm Intraocular pressure, mm Hg Average RNFL thickness, mm
Excluded (n ¼ 61 Eyes)
P Valuea
23.56 (0.98) 3.14 (0.38)
24.27 (1.92) 3.00 (0.42)
.198 .185
7.67 (0.25) 0.23 (1.57) 0.28 (0.45) 539.72 (32.64)
7.64 (0.24) 3.19 (5.54) 0.55 (0.78) 536.10 (32.16)
.876 .002 .028 .063
14.30 (3.17)
15.48 (4.92)
.150
92.92 (11.41)
93.11 (11.09)
.923
BCVA ¼ best-corrected visual acuity; D ¼ diopter; logMAR ¼ logarithm of the minimal angle of resolution; RNFL ¼ retinal nerve fiber layer. Data presented are means (standard deviations). a P value was obtained with generalized estimating equation.
(Figure) to calculate regression coefficients (b). In Model 1, including age, sex, and AL, we found that thinner peripapillary choroidal thickness was independently associated with thinner RNFL thickness globally (b ¼ 1.364 mm for per-SD decrease in peripapillary choroidal thickness, P ¼ .002) and in the inferior (b ¼ 2.539, P ¼ .001) and superior (b ¼ 2.492, P ¼ .001) quadrants. In Model 2, including age, sex, AL, IOP, diabetic retinopathy, and age-related macular degeneration, thinner peripapillary choroidal thickness was independently associated with thinner RNFL thickness globally (b ¼ 1.329 mm for per-SD decrease in peripapillary choroidal thickness, P ¼ .003) and in the inferior (b ¼ 2.566, P < .001) and superior (b ¼ 2.348, P ¼ .001) quadrants. In order to control for potential confounding effect from OCT signal strengths, we further included signal strength from both Cirrus and Spectralis OCT in our regression analyses. The results remained similar after further adjustment for signal strength (Model 3 in Table 3). However, in all models, the association was not present in the temporal quadrant.
DISCUSSION OUR STUDY PROVIDES THE POPULATION-BASED DATA ON
the quantitative relationship between peripapillary choroidal thickness and RNFL thickness measured by SD OCT in nonglaucomatous subjects. We found that thinner 4
TABLE 2. Distribution of Peripapillary Choroid and Retinal Nerve Fiber Layer Thickness in Nonglaucomatous Eyes at Clock-Hour Sectors (30 Degrees Apart) and 4 Quadrants, With 360-Degree, 3.4-mm-Diameter Peripapillary Circle Scans (N ¼ 843 Eyes)
Measurement Location
Clock hours 1 2 3 4 5 6 7 8 9 10 11 12 Quadrants Superior Nasal Inferior Temporal Average thickness
Peripapillary Choroidal
Retinal Nerve Fiber Layer
Thickness (mm)
Thickness (mm)
Mean (SD)
Mean (SD)
138.61 (77.01) 147.09 (70.88) 148.38 (65.03) 150.46 (62.21) 151.06 (59.39) 151.68 (61.06) 145.17 (61.97) 133.58 (58.49) 115.32 (53.67) 102.01 (51.07) 113.25 (57.11) 129.24 (68.31)
56.95 (11.08) 81.10 (16.00) 115.72 (23.97) 116.95 (26.79) 115.26 (24.91) 81.07 (16.87) 57.38 (11.06) 67.01 (14.72) 113.61 (30.65) 127.30 (28.03) 115.00 (30.08) 67.53 (14.04)
150.04 (59.72) 143.12 (58.46) 110.71 (51.61) 138.47 (68.65) 135.59 (56.74)
116.05 (18.42) 69.69 (11.28) 118.60 (19.83) 67.36 (11.36) 92.92 (11.41)
SD ¼ standard deviation. One o’clock corresponded to the temporal region, 4 o’clock to the superior, 7 o’clock to the nasal, and 10 o’clock to the inferior.
peripapillary choroidal thickness was independently associated with thinner RNFL thickness globally, in the inferior and superior quadrants, even after adjusting for relevant confounders. The results of this study provide evidence that thinning of the peripapillary choroid is associated with corresponding RNFL thinning. In terms of topographic profile, the peripapillary choroid was thickest at the superior and thinnest at the inferior quadrants, whereas RNFL was thickest at the inferior and thinnest at the temporal quadrants. Thinnest peripapillary choroid in the inferior quadrant may explain the susceptibility of the inferior optic nerve region to glaucoma. To date, none of the studies has thoroughly investigated the quantitative relationship between peripapillary choroidal thickness and RNFL thickness in normal subjects, particularly in the general population. Only a few studies,20,21 when analyzing RNFL as one of the covariates associated with peripapillary choroidal thickness, reported no significant correlation, a finding contrary to our results. Similarly, Maul and associates in a cross-sectional study of 74 suspects and glaucoma patients reported no significant association of peripapillary choroidal thickness with either degree of glaucoma damage
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TABLE 3. The Associations of Peripapillary Choroidal Thickness With Retinal Nerve Fiber Layer Thickness in a Population-Based Sample of Nonglaucomatous Eyes (N ¼ 843) Using Generalized Estimating Equation
Average peripapillary choroidal thickness Inferior peripapillary choroidal thickness Superior peripapillary choroidal thickness
Model 1a
Model 2b
Model 3c
Retinal Nerve Fiber Layer Thickness
Retinal Nerve Fiber Layer Thickness
Retinal Nerve Fiber Layer Thickness
Beta (95% CI)
P Value
Beta (95% CI)
P Value
Beta (95% CI)
P Value
1.364 (0.497, 2.232) 2.539 (1.099, 3.979) 2.492 (1.086, 3.898)
.002 .001 .001
1.329 (0.463, 2.196) 2.566 (1.124, 4.009) 2.348 (0.937, 3.760)
.003 <.001 .001
1.334 (0.464, 2.205) 2.565 (1.119, 4.010) 2.340 (0.923, 3.757)
.003 .001 .001
CI ¼ confidence interval. Average, inferior, and superior peripapillary choroidal thickness was regressed with average, inferior, and superior retinal nerve fiber layer thickness, respectively. Average, inferior, and superior peripapillary choroidal thicknesses were analyzed per standard deviation decrease. a Adjusted for age, sex, and axial length. b Adjusted for age, sex, axial length, intraocular pressure, diabetic retinopathy, and age-related macular degeneration. c Adjusted for age, sex, axial length, intraocular pressure, diabetic retinopathy, age-related macular degeneration, and signal strength from Cirrus and Spectralis optical coherence tomography.
FIGURE. Scatterplot showing positive correlation of (Left) average retinal nerve fiber layer (RNFL) thickness with average peripapillary choroidal thickness, (Middle) inferior RNFL thickness with inferior peripapillary choroidal thickness, and (Right) superior RNFL thickness with superior peripapillary choroidal thickness.
or RNFL thickness.22 There are several reasons for this. First, their peripapillary choroidal thickness measurements were not automated but involved manual delineation of the choroidal boundaries, making it not only time consuming, but also prone to measurement errors. Second, these studies were performed in clinic-based settings with a potential selection bias and involved smaller sample sizes (36 and 76 normal subjects in studies by Ho and associates and Huang and associates, respectively).20,21 To address these issues, we therefore developed and used a novel technique of automated choroidal segmentation14,19 to objectively and efficiently obtain the thickness of the peripapillary choroid and investigate its association with RNFL thickness in a population-based sample. Interestingly, our results demonstrate significant positive association between inferior, superior, and average peripapillary choroidal thickness and RNFL thickness (ie, VOL. -, NO. -
thinner peripapillary choroid in these quadrants was associated with thinner RNFL). A possible reason for the positive association between these structural features could be because both ONH and peripapillary choroid shares the common source of blood supply via the short posterior ciliary arteries.10–13 Our study supports the hypothesis that since glaucomatous neurodegeneration occurs at the ONH,23 it is likely that concurrent choroidal changes would also occur in the peripapillary region underlying areas of RNFL thinning. It is also interesting to note that although the association between peripapillary choroidal thickness and RNFL in the temporal region was significant in the univariate analysis, it was abolished after incorporating age, sex, and AL. We believe that the association in the temporal region is primarily driven by AL, given that the temporal region is most influenced by AL measurements compared to the other regions.
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In terms of topographic profile of peripapillary choroid and RNFL thicknesses, our results confirmed the asymmetric distribution of both the peripapillary choroid and RNFL thicknesses.19,24–26 The mean peripapillary choroidal thickness and RNFL thickness measurements showed regional differences, peripapillary choroid being thickest superiorly and thinnest inferiorly, whereas RNFL was thickest inferiorly and thinnest temporally. Our observations of the distribution of peripapillary choroidal thickness are similar to the results of previous EDI-OCT studies in normal eyes, which have consistently shown the inferior region to be the thinnest, compared to other regions.19–21,27,28 Although it remains unclear why the inferior choroid demonstrates such prominent thinning, we favor the theory that both the vascular watershed zone and the embryonic location of the optic fissure closure may be responsible.29 As the optic fissure is located in the inferior aspect of the optic cup and is the last part of the globe to close,30 this regional difference in ocular development may contribute to the thinner choroid found in the inferior region. Therefore, development of the ONH and peripapillary choroid needs to be considered to explain the spatial distribution of peripapillary choroidal thickness at different sectors. Despite RNFL being thickest in the inferior quadrant, this region is most vulnerable to glaucomatous damage. Selective and predominant inferior RNFL loss in early glaucoma is multifactorial. One of the known reasons for the vulnerability of the inferior region is that the lamina cribrosa of the inferior pole has larger pores and thinner connective tissue and glial support for passing retinal ganglion cell axons.31–33 Based on our findings, this could also possibly be because of the thinnest peripapillary choroid in the inferior region. We speculate that thinnest peripapillary choroid in the inferior quadrant, which represents an area of lower blood supply, may predispose the inferior region of the optic nerve to glaucomatous ischemic damage, suggesting a possible explanation for the observation that glaucoma typically affects the inferior optic nerve region first. Peripapillary choroidal thickness as a surrogate to vascular supply12,13 found a mild to moderate association, more so with inferior RNFL thickness, in our study of nonglaucomatous eyes. The magnitude of association is weak, thus again suggesting involvement of multiple factors related to inferior RNFL susceptibility in glaucoma pathogenesis. Further examination in glaucoma patients would be needed to confirm this association and to see whether such association is stronger in glaucomatous eyes.
The strengths of this study include its population-based design and a relatively large sample size with a single common ethnicity. Hence, our findings were unlikely to be confounded by ethnic heterogeneity. Unlike other studies, which involved manual delineation of choroidal boundaries, we used an automated choroidal segmentation technique to objectively obtain the thickness of the peripapillary choroid. Therefore, our measurements of peripapillary choroidal thickness are less prone to measurement errors. The relationship between peripapillary choroidal thickness and RNFL was confirmed after adjusting for potential clinical factors. Nevertheless, this study has a few limitations. First, recent studies have reported diurnal fluctuations in choroidal thickness in the macular region.34–36 To the best of our knowledge, there are no data on the association between diurnal variation and choroidal thickness in the peripapillary region. Our subjects were examined only at a single time point, and thus we are not able to take account of any diurnal variation of peripapillary choroidal thickness. However, the peripapillary choroidal thickness measurements in our study were not performed at the same time of the day; each participant underwent the OCT examination in a randomized manner with respect to when the readings were obtained. It seems unlikely that circadian changes may have influenced the results of our investigation. Second, owing to the cross-sectional nature of our study we could identify a structural relationship between peripapillary choroidal thickness and RNFL thickness, but cannot address the temporal relationship between these structures. More longitudinal data are needed to clarify this relationship. Last, our investigation included consecutive participating subjects from a population-based study and thus some of them had eye diseases. Therefore, the distribution of peripapillary choroidal thickness and RNFL thickness determined in this study may represent the thickness not in healthy eyes but in the general adult and elderly populations. However, this would not affect the observed associations, because in the multiple regression analysis models we have adjusted for the potential ocular diseases in elderly people that might influence peripapillary choroidal thickness. In conclusion, the current study demonstrates significant positive associations between peripapillary choroid and RNFL thicknesses and examines this structure-structure relationship. Understanding of the relationship between these structural parameters may be useful clinically for assessment of ONH damage in glaucoma. However, this relationship needs to be explored further in glaucomatous eyes of varying severity before it is applied in clinical settings.
FUNDING/SUPPORT: THIS STUDY WAS SUPPORTED BY A GRANT FROM NATIONAL MEDICAL RESEARCH COUNCIL (SINGAPORE) and National Research Foundation University Fund (Singapore). The sponsor or funding organization had no role in the design or conduct of this research. Financial Disclosures: C.Y. Cheung: received grant support from National Medical Research Council (NMRC) and Biomedical Research Council, Singapore directed to Singapore Eye Research Institute; T.A.: received grant support from National Medical Research Council (NMRC) and Biomedical Research Council, Singapore directed to Singapore Eye Research Institute; T.Y.W.: received grant support from National Medical Research Council
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(NMRC) and Biomedical Research Council, Singapore directed to Singapore Eye Research Institute; Advisory Board member for Abbot, Novartis, Pfizer, Allergan, and Bayer; independent consultant for Abbot, Novartis, Pfizer, Allergan, and Bayer; C.Y. Cheng: received grant support from National Medical Research Council (NMRC) and Biomedical Research Council, Singapore directed to Singapore Eye Research Institute. All authors attest that they meet the current ICMJE requirements to qualify as authors.
REFERENCES 1. Sommer A, Katz J, Quigley HA, et al. Clinically detectable nerve fiber atrophy precedes the onset of glaucomatous field loss. Arch Ophthalmol 1991;109(1):77–83. 2. Tuulonen A, Lehtola J, Airaksinen PJ. Nerve fiber layer defects with normal visual fields. Do normal optic disc and normal visual field indicate absence of glaucomatous abnormality? Ophthalmology 1993;100(5):587–597. 3. Bowd C, Weinreb RN, Williams JM, Zangwill LM. The retinal nerve fiber layer thickness in ocular hypertensive, normal, and glaucomatous eyes with optical coherence tomography. Arch Ophthalmol 2000;118(1):22–26. 4. Schuman JS, Hee MR, Puliafito CA, et al. Quantification of nerve fiber layer thickness in normal and glaucomatous eyes using optical coherence tomography. Arch Ophthalmol 1995; 113(5):586–596. 5. Zangwill LM, Williams J, Berry CC, Knauer S, Weinreb RN. A comparison of optical coherence tomography and retinal nerve fiber layer photography for detection of nerve fiber layer damage in glaucoma. Ophthalmology 2000;107(7): 1309–1315. 6. Chen FK, Yeoh J, Rahman W, Patel PJ, Tufail A, Da Cruz L. Topographic variation and interocular symmetry of macular choroidal thickness using enhanced depth imaging optical coherence tomography. Invest Ophthalmol Vis Sci 2012; 53(2):975–985. 7. Horecky J, Baciak L, Kasparova S, Pacheco G, Aliev G, Vancova O. Minimally invasive surgical approach for threevessel occlusion as a model of vascular dementia in the ratbrain bioenergetics assay. J Neurol Sci 2009;283(1-2): 178–181. 8. Hayreh SS. Blood supply of the optic nerve head and its role in optic atrophy, glaucoma, and oedema of the optic disc. Br J Ophthalmol 1969;53(11):721–748. 9. Nicolela MT, Hnik P, Drance SM. Scanning laser Doppler flowmeter study of retinal and optic disk blood flow in glaucomatous patients. Am J Ophthalmol 1996;122(6): 775–783. 10. Duijm HF, van den Berg TJ, Greve EL. Choroidal haemodynamics in glaucoma. Br J Ophthalmol 1997;81(9):735–742. 11. Flammer J, Orgul S, Costa VP, et al. The impact of ocular blood flow in glaucoma. Prog Retin Eye Res 2002;21(4): 359–393. 12. Hayreh SS. The blood supply of the optic nerve head and the evaluation of it - myth and reality. Prog Retin Eye Res 2001; 20(5):563–593. 13. Hayreh SS. The 1994 Von Sallman Lecture. The optic nerve head circulation in health and disease. Exp Eye Res 1995; 61(3):259–272. 14. Tian J, Marziliano P, Baskaran M, et al. Automatic segmentation of the choroid in enhanced depth imaging optical coherence tomography images. Biomed Opt Express 2013; 4(3):397–411.
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15. Rosman M, Zheng Y, Wong W, et al. Singapore Malay Eye Study: rationale and methodology of 6-year follow-up study (SiMES-2). Clin Experiment Ophthalmol 2012;40(6): 557–568. 16. Foster PJ, Buhrmann R, Quigley HA, Johnson GJ. The definition and classification of glaucoma in prevalence surveys. Br J Ophthalmol 2002;86(2):238–242. 17. Chua J, Tham YC, Liao J, et al. Ethnic differences of intraocular pressure and central corneal thickness: the Singapore Epidemiology of Eye Diseases study. Ophthalmology 2014; 121(10):2013–2022. 18. Spaide RF, Koizumi H, Pozzoni MC. Enhanced depth imaging spectral-domain optical coherence tomography. Am J Ophthalmol 2008;146(4):496–500. 19. Gupta P, Jing T, Marziliano P, et al. Peripapillary choroidal thickness assessed using automated choroidal segmentation software in an Asian population. Br J Ophthalmol 2015;99(7):920–926. 20. Ho J, Branchini L, Regatieri C, Krishnan C, Fujimoto JG, Duker JS. Analysis of normal peripapillary choroidal thickness via spectral domain optical coherence tomography. Ophthalmology 2011;118(10):2001–2007. 21. Huang W, Wang W, Zhou M, et al. Peripapillary choroidal thickness in healthy Chinese subjects. BMC Ophthalmol 2013;13:23. 22. Maul EA, Friedman DS, Chang DS, et al. Choroidal thickness measured by spectral domain optical coherence tomography: factors affecting thickness in glaucoma patients. Ophthalmology 2011;118(8):1571–1579. 23. Jonas JB, Budde WM, Panda-Jonas S. Ophthalmoscopic evaluation of the optic nerve head. Surv Ophthalmol 1999;43(4): 293–320. 24. Wang YX, Pan Z, Zhao L, You QS, Xu L, Jonas JB. Retinal nerve fiber layer thickness. The Beijing Eye Study 2011. PLoS One 2013;8(6):e66763. 25. Zhao L, Wang Y, Chen CX, Xu L, Jonas JB. Retinal nerve fibre layer thickness measured by Spectralis spectral-domain optical coherence tomography: The Beijing Eye Study. Acta Ophthalmol 2014;92(1):e35–e41. 26. Cheung CY, Chen D, Wong TY, et al. Determinants of quantitative optic nerve measurements using spectral domain optical coherence tomography in a population-based sample of non-glaucomatous subjects. Invest Ophthalmol Vis Sci 2011; 52(13):9629–9635. 27. Tanabe H, Ito Y, Terasaki H. Choroid is thinner in inferior region of optic disks of normal eyes. Retina 2012;32(1): 134–139. 28. Ouyang Y, Heussen FM, Mokwa N, et al. Spatial distribution of posterior pole choroidal thickness by spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci 2011; 52(9):7019–7026. 29. Ikuno Y, Kawaguchi K, Nouchi T, Yasuno Y. Choroidal thickness in healthy Japanese subjects. Invest Ophthalmol Vis Sci 2010;51(4):2173–2176.
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30. Schoenwolf G, Bleyl S, Brauer P, Francis-West P. Larsen’s Human Embrology. Philadelphia: Elsevier; 2009:602– 616. 31. Jonas JB, Mardin CY, Schlotzer-Schrehardt U, Naumann GO. Morphometry of the human lamina cribrosa surface. Invest Ophthalmol Vis Sci 1991;32(2):401–405. 32. Quigley HA, Addicks EM. Regional differences in the structure of the lamina cribrosa and their relation to glaucomatous optic nerve damage. Arch Ophthalmol 1981;99(1): 137–143. 33. Radius RL, Gonzales M. Anatomy of the lamina cribrosa in human eyes. Arch Ophthalmol 1981;99(12):2159–2162.
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34. Chakraborty R, Read SA, Collins MJ. Diurnal variations in axial length, choroidal thickness, intraocular pressure, and ocular biometrics. Invest Ophthalmol Vis Sci 2011;52(8): 5121–5129. 35. Tan CS, Ouyang Y, Ruiz H, Sadda SR. Diurnal variation of choroidal thickness in normal, healthy subjects measured by spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci 2012;53(1):261–266. 36. Usui S, Ikuno Y, Akiba M, et al. Circadian changes in subfoveal choroidal thickness and the relationship with circulatory factors in healthy subjects. Invest Ophthalmol Vis Sci 2012; 53(4):2300–2307.
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Biosketch Preeti Gupta graduated with masters in Optometry from Queensland University of Technology, Australia in 2008. She then joined the Ocular Epidemiology Research Group at Singapore Eye Research Institute, Singapore, where she conducts and coordinates epidemiological and population-based projects under the Singapore Epidemiology of Eye Disease programme. Her area of interest includes epidemiology of major eye diseases and ocular imaging using novel image processing techniques.
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Biosketch Ching-Yu Cheng leads Ocular Epidemiology Research group at Singapore Eye Research Institute and co-directs the Singapore Epidemiology of Eye Diseases (SEED) program. His primary research interests are related to epidemiology and genetics of major eye diseases. His current work involves a variety of epidemiological, clinical, and image research on glaucoma; and identification of susceptibility genes for complex ocular diseases, such as glaucoma, macular degeneration and cataract, using both genome-wide association approaches and next-generation sequencing technology.
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