Abstract
Purpose
To demonstrate the three-dimensional choroidal volume distribution in healthy subjects using enhanced depth imaging (EDI) spectral-domain optical coherence tomography (SD-OCT) and to evaluate its association with age, sex, and axial length.
Design
Retrospective case series.
Participants
One hundred and seventy six eyes from 114 subjects with no retinal or choroidal disease.
Methods
EDI SD-OCT imaging studies for healthy patients who had undergone a 31-raster scanning protocol on a commercial SD-OCT device were reviewed. Manual segmentation of the choroid was performed by two retinal specialists. Macular choroidal volume map and three-dimensional topography were automatically created by the built-in software of the device. Mean choroidal volume was calculated for each Early Treatment Diabetic Retinopathy Study (ETDRS) subfield. Regression analyses were used to evaluate the correlation between macular choroidal volume and age, sex, and axial length.
Main Outcome Measures
Three-dimensional topography and ETDRS-style volume map of the choroid.
Results
Three-dimensional topography of the choroid and volume map was obtained in all cases. The mean choroidal volume was 0.228 ± 0.077 mm3 for the center ring and 7.374 ± 2.181 mm3 for the total ETDRS grid. The nasal quadrant showed the lowest choroidal volume, and the superior quadrant the highest. The temporal and inferior quadrants did not show different choroidal volume values. Choroidal volume in all the EDTRS rings was significantly correlated with axial length after adjustment for age (P<0.0001), with age after adjustment for axial length (P<0.0001) and with sex after adjustment for axial length (P<0.05). Choroidal volume decreases by 0.54 mm3 (7.32%) for every decade and by 0.56 mm3 (7.59%) for every mm of axial length. Males have a 7.37% greater choroidal volume compared to that of females.
Conclusions
EDI SD-OCT is non-invasive and well-tolerated procedure with an excellent ability to visualize three-dimensional topography of the choroid and to measure choroidal volume at the posterior pole using manual segmentation. Age and axial length are inversely correlated with choroidal volume, most likely leading to changes in retinal metabolic support in old and high myopic patients. Sexual differences should be considered when interpreting an EDI SD-OCT scan of the choroid.
Introduction
The choroid has various valuable functions in the eye, including metabolic support of the retinal pigment epithelium (RPE) and the retina1 and blood supply to the outer retinal layers. However, it is also involved in the pathogenesis of several vision-threatening diseases, such as age-related macular degeneration (AMD)2, polypoidal choroidal vasculopathy (PCV)3, central serous chorioretinopathy (CSR)4, Vogt–Koyanagi–Harada (VKH) disease5, and high myopia-related chorioretinopathy.6
Visualization of the choroid by indirect ophthalmoscopy and fluorescein angiography is difficult since pigment in the RPE and choroid obstructs the view. Indocyanine green angiography allows for visualization of choroidal vessel perfusion but does not provide three-dimensional anatomical and quantitative evaluations. Recently, Spaide et al., by using a spectral-domain optical coherence tomography (SD-OCT) device, developed the enhanced depth imaging (EDI) technique, which enables in-vivo imaging and measurement of the choroid.7 Since then, many investigators have performed a bi-dimensional detailed analysis of the choroid among healthy patients8–12 as well as patients with chorio-retinal pathologies,13–27 using the EDI technique on various SD-OCT devices. Since automated choroidal segmentation software remains unavailable, choroidal thickness measurements were performed manually, and choroidal thickness was measured only at selected points along a single, horizontal and/or vertical SD-OCT B-scan passing through the fovea. As a result, exhaustive information about the real volume of the choroid using a SD-OCT is limited.
Previous studies have reported choroidal thickness measurements at the fovea and selected points of the choroid in healthy eyes.8,26,28–30 However, the choroidal thickness measurements in these studies differ from each other, possibly due to limited sample size, different image acquisition techniques and inconsistencies in choosing the locations for repeated measurement. Moreover, the irregularity of the inner chorio-scleral border influences the measurement at few sampling points.26,27 To overcome this problem, evaluation of the choroid over the entire posterior pole would be a better tool to evaluate chorio-retinal diseases.
Recently, choroidal thickness mapping has been reported by Sadda et al31, in which they utilized an EDI SD-OCT and used manual segmentation. Choroidal volume mapping was introduced by Yoshimura et al.32 using an experimental swept-source OCT (SS-OCT) at 1050 nm, which is not commercially available. In a recent study33, Shin et al. calculated an interpolated choroidal volume measurement using a 6-radial scan protocol on a conventional SD-OCT (3D OCT-2000, Topcon, Tokyo, Japan). However, the chorio-scleral boundary was not detected in all the cases because of scattering and low penetration of the used wavelength through the RPE. Moreover, inadequate averaging (eight images) and disproportionate interpolation due to few (six) scans used may have compromised the validity of the measurements.
In a previous report by our group34, we devised an innovative method of choroidal volume measurement using the built-in software for retinal volume measurement of an EDI SD-OCT after manual choroidal segmentation on a 31-raster scan protocol. Inter-observer and intra-observer reproducibility and repeatability of this method were excellent.34
The aim of the present study was to perform a three-dimensional topographic visualization of the choroidal volume of the posterior pole in a large sample of healthy subjects and to assess correlation of the volume with age, sex and axial length.
Methods
Study population
Starting in July 2011, all patients undergoing SD-OCT scans at the Jacobs Retina Center at Shiley Eye Center, University of California San Diego (La Jolla, CA) underwent choroidal imaging as part of their evaluation. A raster scan of the macula using a SD-OCT device in EDI-mode (Heidelberg Spectralis HRA2; Heidelberg Engineering, Carlsbad, CA) was used to study the choroid. The raster scan required approximately thirty seconds of additional time and was therefore incorporated into the standard scanning protocol. After approval by the Institutional Review Board of the University of California at San Diego for chart review and data analysis, we retrospectively reviewed charts and images of 176 healthy eyes from 114 patients who underwent multimodal examination to rule out retinal pathologies or to document floaters and posterior vitreous detachment over a three-month period (July 2011 to September 2011). To be considered eligible for data and image analysis as part of this study, patients’ eyes must have had no pathology other than floaters and posterior vitreous detachment. We excluded eyes/patients with any systemic or local disease that could affect the choroid including uncontrolled hypertension, diabetes, coagulopathies, AMD, PCV, CSR, VKH disease, or other conditions that have been shown to affect the choroid.
Patients underwent ophthalmic evaluation including best-corrected visual acuity (BCVA), slit lamp biomicroscopy, axial length measurement using ocular biometry (IOLMaster; Carl Zeiss Meditec, Jena, Germany), and a raster scan of the macula using the SD-OCT device in EDI-mode without pupillary dilation. The study was conducted in adherence with the tenets of the Declaration of Helsinki.
Choroidal volume scanning protocol
The scanning protocol included thirty-one high-resolution B-scans centered at the fovea, associated to a simultaneous near-infrared image with undilated pupils. An internal fixation light was used to center the scanning area on the fovea. Each scan was approximately 9.3 mm in length and spaced 240 microns apart. All thirty-one B-scans were acquired in a continuous, automated sequence and covered a 30×25 degrees area centered on the fovea. A minimum of twenty-five frames were automatically averaged and used to obtain a good-quality choroidal image using the built-in TruTrack™ Active Eye Tracking software of the device (Heidelberg Engineering, Carlsbad, CA).
Choroidal volume image analysis
Two retinal specialists manually performed the choroidal segmentation, applying a previously described method.34 A 6mm diameter choroidal volume map, centered on the fovea, was automatically generated by the built-in software of the device, by applying the grid used by the Early Treatment Diabetic Retinopathy Study (ETDRS).35 The ETDRS grid divides the macula into three concentric rings (center, inner and outer), the inner ring measuring 1 to 3 mm and the outer ring measuring 3 to 6 mm from the center (referring to a ring with a diameter of 1 mm centered on the fovea). The grid further divides inner and outer rings into four quadrants (superior, inferior, temporal, and nasal); thus, the ETDRS grid divides the macula into nine subfields. After generating thickness and volume maps, three-dimensional topography of the choroid was obtained using the same built-in software of the device, and color-coded thickness map was superimposed on the inner surface of the choroid in the topographic image using Photoshop CS3 (Adobe, San Jose, CA).
Choroidal volume maps were grouped by axial length, age and sex to facilitate the clinical applications of our findings. To determine the axial length, we judged the eyes’ refraction to be myopic (axial length ≥ 24.5 mm), emmetropic (24.5 > axial ≥ 23.4 mm), or hyperopic (axial length < 23.4 mm), on the basis of a normal axial length variation with refraction and age found in the literature.36,37 Eyes were divided into three age groups: eyes of patients ≤ 40 years old, 41 to 60, and ≥ 61 years old.
Statistical analysis
Statistical analysis was performed using SPSS statistical software version 20 (SPSS Inc., Chicago, IL). All values are presented as a mean ± the standard deviation (SD). Fisher’s Least Significant Difference test was used to compare the choroidal volume at different ETDRS subfields. Pearson’s correlation, independent samples t-test, and partial correlation were calculated to assess the relationship of the choroidal volume in the three ETDRS rings of the macula35 with three independent factors, including age, axial length, and sex. Multiple linear regression analysis was used to evaluate the correlation between choroidal volume of each ring and the same grouped factors, dividing eyes by age, axial length and sex of the patients. A p-value of <0.05 was considered to be statistically significant.
Results
One hundred and seventy six eyes of 114 healthy subjects (51 men and 63 women), with a mean age of 50 years (range 14 to 89 years), were included in the study. Ethnic distribution included 75 Caucasians subjects, 20 Asians subjects, 18 Hispanics subjects and 1 Black subject. One hundred and sixty eyes were phakic and 16 were pseudophakic. BCVA ranged from 20/63 to 20/20 (Snellen equivalent). Axial length measurement was available in 146 out of 176 eyes (83%): the mean axial length was 24.6 ± 1.6 mm (range: 21.03–31.56 mm).
Using high-resolution B-scans and a minimum averaging of twenty-five frames, the choroidal borders were clearly detected in all cases; no eye was excluded because of poor-quality choroidal images. The basement membrane of the RPE appeared as a regular hyper-reflective line, with a concave aspect toward the choroid. Differently, the chorio-scleral interface (outer border of the choroid) appeared irregular and corrugated, following the course of the deepest choroidal vessels (Figure 1, available at http://aaojournal.org). Three-dimensional choroidal topography and volume map were obtained in all eyes (Figure 2). In none of the cases did the built-in software fail to reconstruct the map or topography.
Figure 1.
Example of enhanced depth imaging of the choroid on a horizontal B-scan passing through the fovea in a left eye, before (A) and after (B) manual segmentation. The basement membrane of the retinal pigment epithelium (inner border of the choroid) appeared as a regular hyper-reflective line, with a concave aspect towards the choroid. Differently, the chorio-scleral interface (outer border of the choroid) appeared irregular and corrugated, following the course of the deepest choroidal vessels.
Figure 2.
A three-dimensional topographic visualization of the choroid with superimposed color-coded choroidal thickness map (microns) in an eye with axial length of 23.2 mm (A–D) and in an eye with axial length of 26.5 mm (E–H). The superior quadrant of the macula appears thicker than the other quadrants, while the nasal quadrant is the thinnest.
Table 1 (available at http://aaojournal.org) shows the mean choroidal volume in each area of the ETDRS map. The mean choroidal volume of the fovea was 0.228 ± 0.077 mm3; the inner ring choroidal volume was 1.748 ± 0.558 mm3 while for the outer ring the choroidal volume was 5.398 ± 1.566 mm3. The choroidal volume in the nasal quadrant was significantly lower than all the other quadrants (p<0.0001), while the superior quadrant had a significantly higher choroidal volume than all the others. No differences were noted in choroidal volume between the inferior and temporal quadrants. The mean choroidal volume of the total ETDRS map was 7.374 ± 2.181 mm3.
Table 1.
Choroidal volume measurements (mm3) for each ETDRS area.
| Mean | Standard Deviation | Median | |
|---|---|---|---|
| Subfields | |||
| Center | 0.228 | 0.077 | 0.220 |
| Inner Superior | 0.458° | 0.141 | 0.465 |
| Inner Nasal | 0.411 | 0.149 | 0.390 |
| Inner Inferior | 0.431 | 0.149 | 0.420 |
| Inner Temporal | 0.448 | 0.142 | 0.450 |
| Outer Superior | 1.535ࠤ | 0.434 | 1.550 |
| Outer Nasal | 1.082 | 0.419 | 1.000 |
| Outer Inferior | 1.382‡ | 0.442 | 1.345 |
| Outer Temporal | 1.398‡ | 0.401 | 1.385 |
| Rings | |||
| Center | 0.228 | 0.077 | 0.220 |
| Inner | 1.748 | 0.558 | 1.690 |
| Outer | 5.398 | 1.566 | 5.290 |
| Quadrants | |||
| Superior | 1.994 | 0.568 | 2.010 |
| Nasal | 1.493* | 0.561 | 1.385 |
| Inferior | 1.813** | 0.584 | 1.780 |
| Temporal | 1.846*** | 0.537 | 1.835 |
| Total ETDRS map | |||
| 7.374 | 2.181 | 7.145 | |
ETDRS, Early Treatment Diabetic Retinopathy Study
P<0.05 compared to values of inner nasal subfield.
P<0.0001 compared to values of outer nasal subfield.
P<0.01 compared to values of outer inferior subfield.
P<0.05 compared to values of outer temporal subfield.
P<0.001 compared to values of other quadrants.
P<0.01 compared to superior quadrant.
P<0.05 if compared to superior quadrant
Table 2 (available at http://aaojournal.org) shows correlation analysis between mean choroidal volume of each ring, age, axial length, and sex. The mean choroidal volume showed a negative correlation with age (p<0.01) and with axial length (p<0.01) in the fovea, inner and outer rings (Pearson’s correlation). Considering the total macular area, a low-grade correlation was found with age (p<0.01, r= −0.387) and axial length (p<0.01, r= −0.349). No correlation with sex was noted (independent samples t-test). After adjustment for axial length using partial correlation analysis, the mean choroidal volume correlated significantly with age (p<0.0001) and also with sex (p<0.05) in all the rings. After adjustment for age, the mean choroidal volume in all the rings highly correlated with axial length (p<0.0001).
Table 2.
Correlation analysis between mean choroidal volume and age, axial length, and sex for each ETDRS ring.
| Pearson’s Correlation Coefficient |
P | Partial Correlation Coefficient |
P | |
|---|---|---|---|---|
| Fovea | ||||
| Age (y) | −0.297 | <0.01 | −0.340 | <0.0001 (adjusted for AXL) |
| Axial length (mm) | −0.389 | <0.01 | −0.429 | <0.0001 (adjusted for age) |
| Sex | n/a | >0.05* | −0.170 | <0.05 (adjusted for AXL) |
| Inner ring | ||||
| Age (y) | −0.325 | <0.01 | −0.376 | <0.0001 (adjusted for AXL) |
| Axial length (mm) | −0.374 | <0.01 | −0.420 | <0.0001 (adjusted for age) |
| Sex | n/a | >0.05* | −0.164 | <0.05 (adjusted for AXL) |
| Outer ring | ||||
| Age (y) | −0.409 | <0.01 | −0.453 | <0.0001 (adjusted for AXL) |
| Axial length (mm) | −0.333 | <0.01 | −0.396 | <0.0001 (adjusted for age) |
| Sex | n/a | >0.05* | −0.213 | <0.05 (adjusted for AXL) |
| Total macular area | ||||
| Age (y) | −0.387 | <0.01 | −0.434 | <0.0001 (adjusted for AXL) |
| Axial length (mm) | −0.349 | <0.01 | −0.408 | <0.0001 (adjusted for age) |
| Sex | n/a | >0.05* | −0.202 | <0.05 (adjusted for AXL) |
y, years; AXL, axial length; D, diopters; ETDRS, Early Treatment Diabetic Retinopathy Study; n/a, not applicable.
Independent samples t-test
Table 3 shows results of the multiple linear regression analysis for mean choroidal volume of the fovea, inner ring, outer ring and total macula. A stepwise method was used to determine the most unexpected factors. The model determined by age, axial length and sex had the best regression. The model showed a good coefficient of determination, which was 0.568 (R2 = 0.323) for the total macular choroidal volume.
Table 3.
Multiple linear regression analysis for choroidal volume of the macula by age, axial length and sex for each ETDRS ring.
| Factor | Coefficient | Standard Error |
R2 | P |
|---|---|---|---|---|
| Center | ||||
| Intercept | 0.861 | 0.094 | 0.275 | <0.0001 |
| Age | −0.001 | 0.000 | 0.275 | <0.0001 |
| Axial length | −0.021 | 0.003 | 0.275 | <0.0001 |
| Sex | −0.025 | 0.011 | 0.275 | <0.05 |
| Inner circle | ||||
| Intercept | 6.346 | 0.693 | 0.285 | <0.0001 |
| Age | −0.011 | 0.002 | 0.285 | <0.0001 |
| Axial length | −0.153 | 0.026 | 0.285 | <0.0001 |
| Sex | −0.180 | 0.084 | 0.285 | <0.05 |
| Outer circle | ||||
| Intercept | 18.300 | 1.866 | 0.334 | <0.0001 |
| Age | −0.038 | 0.006 | 0.334 | <0.0001 |
| Axial length | −0.405 | 0.069 | 0.334 | <0.0001 |
| Sex | −0.664 | 0.226 | 0.334 | <0.01 |
| Total ETDRS map | ||||
| Intercept | 25.507 | 2.621 | 0.323 | <0.0001 |
| Age | −0.051 | 0.009 | 0.323 | <0.0001 |
| Axial length | −0.579 | 0.097 | 0.323 | <0.0001 |
| Sex | −0.869 | 0.317 | 0.323 | <0.01 |
ETDRS, Early Treatment Diabetic Retinopathy Study
The mean choroidal volume of the total macula (Table 4) was 8.311 ± 2.199 mm3 in patients ≤ 40yo, 7.258 ± 1.886 mm3 in patients ranging in age between 41 and 60yo, 6.526 ± 2.108 mm3 in patients ≥ 61yo (Figure 3, A–C). Dividing the eyes by axial length, it was 8.355 ± 2.243 mm3 in hyperopic eyes, 7.645 ± 2.186 mm3 in emmetropic eyes, 6.761 ± 2.005 mm3 in myopic eyes (Figure 3, D–F). Males presented a mean macular choroidal volume of 7.664 ± 2.283 mm3, while females 7.138 ± 2.077 mm3.
Table 4.
Choroidal volume measurements for ETDRS rings dividing by age, axial length, and sex.
| Center | Inner Ring | Outer Ring | Total ETDRS map | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Mean (mm3) |
SD | Mean (mm3) |
SD | Mean (mm3) |
SD | Mean (mm3) |
SD | P | |
| Age | |||||||||
| <40 y (n=59) | 0.255 | 0.080 | 1.950 | 0.576 | 6.106 | 1.561 | 8.311 | 2.199 | |
| 41–60 y (n=60) | 0.222 | 0.067 | 1.714 | 0.491 | 5.322 | 1.346 | 7.258 | 1.886 | <0.001 |
| >61 y (n=57) | 0.206 | 0.076 | 1.576 | 0.550 | 4.744 | 1.504 | 6.526 | 2.108 | |
| Axial length* | |||||||||
| Hyperopic (n=35) | 0.273 | 0.076 | 2.052 | 0.564 | 6.030 | 1.623 | 8.355 | 2.243 | |
| Emmetropic (n=42) | 0.237 | 0.073 | 1.810 | 0.550 | 5.599 | 1.593 | 7.645 | 2.186 | <0.01 |
| Myopic (n=69) | 0.202 | 0.068 | 1.570 | 0.510 | 4.989 | 1.442 | 6.761 | 2.005 | |
| Sex | |||||||||
| Males (n=79) | 0.235 | 0.080 | 1.802 | 0.587 | 5.627 | 1.636 | 7.664 | 2.283 | <0.05 |
| Females (n=97) | 0.222 | 0.073 | 1.705 | 0.533 | 5.211 | 1.489 | 7.138 | 2.077 | |
Data are available for 146 eyes
SD, standard deviation; ETDRS, Early Treatment Diabetic Retinopathy Study; y, years.
Figure 3.
Effect of age (A–C) and axial length (D–F) on color-coded choroidal thickness map and mean choroidal volume of each subfield of the Early Treatment Diabetic Retinopathy Study (ETDRS) grid. (A) Right eye of a 30 years old patient: total choroidal volume is 8.53 mm3; (B) Right eye of a 50 years old patient: total choroidal volume is 7.39 mm3; (C) Right eye of a 70 years old patient: total choroidal volume is 6.36 mm3; (D) Hyperopic eye (axial length = 22.5 mm): total choroidal volume is 8.61 mm3; (E) Emmetropic eye (axial length = 24.5 mm): total choroidal volume is 7.47 mm3; (F) Myopic eye (axial length = 26.5 mm): total choroidal volume is 6.54 mm3.
Figure 4 (available at http://aaojournal.org) shows a significant (p<0.01) negative correlation between the total choroidal volume in the ETDRS map and the axial length (R2 = 0.122). Univariate regression analysis showed an approximate decrease in choroidal volume of 0.56 mm3 (7.59%) for every mm of axial length. Age tended to have a negative correlation of high significance (p<0.01, R2 = 0.150, Figure 4, available at http://aaojournal.org). Univariate regression analysis showed an approximate decrease in choroidal volume of 0.54 mm3 (7.32%) every 10 years.
Figure 4.
Left: scatterplot of axial length (AXL) and macular choroidal volume of all subjects shows a significant negative correlation (P<0.01; R2=0.122). Right: scatterplot of age and macular choroidal volume of all subjects shows a significant negative correlation (P<0.01; R2=0.150).
Discussion
In the present study, a three-dimensional visualization of the choroid of the macular area in a large sample of healthy eyes was performed using an EDI SD-OCT, and allowed a comprehensive analysis of the choroidal anatomy. Manual segmentation of the choroidal borders was performed following a well-reproducible method described in a previous report by our group.34 Volume of the analyzed choroid was automatically calculated by the built-in software of the SD-OCT.
So far, no previous report has provided in-vivo data regarding volume of the choroid in normal eyes using EDI SD-OCT. Yoshimura et al.32 recently reported measurement of the choroidal volume of the macula using a prototype of SS-OCT, which is not yet available commercially. In that report, mean choroidal volume of the center ring (within the 1.0-mm diameter ETDRS circle) was 0.159 ± 0.066 mm3, 1.412 ± 0.567 mm3 within the ETDRS inner ring, and 5.411 ± 2.097 mm3 within the ETDRS outer ring. In our study, results of the choroidal volume measurement are higher: mean choroidal volume of the center ring was 0.228 ± 0.077 mm3, 1.976 ± 0.634 mm3 within the ETDRS inner ring and 7.374 ± 2.181 mm3 within the ETDRS outer ring. Explanations for this difference may be the smaller sample size (31 eyes) or the older mean age (64 years) of the population studied by Yoshimura32; moreover, we cannot exclude ethnic variations in the choroidal volume. However, they did not analyze the correlation between macular choroidal volume and age, axial length, and sex. In our study, results of multiple regression analysis showed a good coefficient of determination for the macular choroidal volume in the model determined by age, axial length and sex (R2 = 0.323).
By stepwise analysis, we found that age was highly associated with choroidal volume in each ETDRS ring. Univariate regression analysis showed an approximate decrease in volume of 0.54 mm3 (7.32%) for every 10 years. Although the reductions were similar, the R2 value was low (0.150), suggesting great inter-individual variations. With the increasing age and the regressing choroidal volume, the ability of the choroid to supply sufficient levels of oxygen and other metabolites to the RPE and outer retina may decrease7, contributing to the onset of AMD in elderly people.
We also found a significant negative correlation with axial length in all ETDRS rings. Univariate regression analysis showed an approximate decrease in volume of 0.56 mm3 (7.59%) for every mm of axial length. Similar to the regression of the age, the R2 was low (0.122), suggesting great inter-individual variations. Choroidal thinning appears to be prominent in highly myopic eyes; this may play a role in the pathophysiologic features of vision loss in high myopia, such as a relative ischemia of the outer retina, RPE and the choroid itself.13
Moreover, our study is the first to report inter-sexual differences in choroidal volume in healthy subjects: males have a significantly greater choroidal volume than females (7.37% greater than females). The influence of sex in choroidal thickness and volume was not assessed in previous reports.7,9,13,29,31–33 Clinic-based studies have previously documented that the retina is thicker in men than in women38–41; thus, we can speculate a similar finding for the choroid. However, a longitudinal follow-up study is needed to address the clinical significance of this finding.
The present study also showed that nasal choroid volume in the inner ring was significantly lower than the superior choroid; similarly, nasal choroidal volume of the outer ring was significantly lower than the one of all the other outer-ring quadrants. This loss of choroidal tissue in the nasal quadrant could be a contributing cause for the development of peripapillary atrophy and may play a role in glaucoma, as previously speculated by Margolis and Spaide.7
Our study has some limitations. First, it is retrospective in nature; however, we carefully excluded eyes/patients with conditions that have been suggested to affect the choroid, and we included only normal eyes and eyes with only floaters and posterior vitreous detachment in this study. Second, we performed manual segmentation of choroidal borders on SD-OCT B-scans because reliable software to perform automated choroidal segmentation is not available. Although manual segmentation may at first appear to be less reliable, we did show in a previous report that our manual technique is highly reproducible.34 In the future, automated choroidal segmentation software may reduce the risk of errors of the manual segmentation still further. Third, we did not study the potential effect of ethnicity, diurnal variation, blood pressure, hydration status, and other systemic or genetic factors on macular choroidal volume; further studies are warranted to evaluate those factors.
In conclusion, our study shows that EDI SD-OCT is a non-invasive and well-tolerated procedure with an excellent ability to visualize choroidal anatomy and to measure choroidal volume at the posterior pole using manual segmentation without pupillary dilation. Age, axial length and sex are highly associated with choroidal volume in normal patients, most likely leading to insufficient metabolic supplements for the macula especially in elderly high-myopic patients. Our study provides a normative database for choroidal volume, which may be useful for future choroidal analysis studies in various chorio-retinal diseases. A larger, prospective, multi-center study would help to evaluate variations of macular choroidal volume related to ethnicity and other systemic or genetic factors. Assessment of choroidal volume may provide an innovative way to understand their patho-physiology and to evaluate their clinical course.
Supplementary Material
Acknowledgments
Financial support: Supported by NIH grants R01EY007366 and R01EY018589 (WRF), R01EY016323 (DUB) and R01EY020617 (LC), "RPB incorporated and unrestricted funds from Jacobs Retina Center". The funding organizations had no role in the design or conduct of this research.
Footnotes
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Financial disclosure: None of the authors have any financial interests to disclose.
This article contains online-only material. The following should appear online-only: Table 1, Table 2, Figure 1, Figure 4.
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