Retinal and Choroidal Thickness in an
Indigenous Population from Ghana
Comparison with Individuals with European or African
Ancestry
Moussa A. Zouache, PhD,1 Caitlin D. Faust, BS,1 Vittorio Silvestri, HND,2 Stephen Akafo, FRCOphth,3
Seth Lartey, FWACS, FGCPS,4 Rajnikant Mehta, MSc, PCAP,5 Joseph Carroll, PhD,6
Giuliana Silvestri, FRCOphth, MD,7 Gregory S. Hageman, PhD,1 Winfried M. Amoaku, FRCOphth, PhD8
Purpose: To evaluate the thickness of the macular retina and central choroid in an indigenous population
from Ghana, Africa and to compare them with those measured among individuals with European or African
ancestry.
Design: Cross-sectional study, systematic review, and meta-analyses.
Participants: Forty-two healthy Ghanaians, 37 healthy individuals with European ancestry, and an additional
1427 healthy subjects with African ancestry from previously published studies.
Methods: Macular retinal thickness in the fovea, parafovea, and perifovea and central choroidal thickness
were extracted from OCT volume scans. Associations with ethnicity, age, and sex were assessed using mixed-
effect regression models. Monte Carlo simulations were performed to determine the sensitivity of significant
associations to additional potential confounders. Pooled estimates of retinal thickness among other groups with
African ancestry were generated through systematic review and meta-analyses.
Main Outcome Measures: Macular retinal thickness and central choroidal thickness and their association
with ethnicity, age, and sex.
Results: When adjusted for age and sex, the macular retina and central choroid of Ghanaians are signifi-
cantly thinner as compared with subjects with European ancestry (P < 0.001). A reduction in retinal and choroidal
thickness is observed with age, although this effect is independent of ethnicity. Meta-analyses indicate that retinal
thickness among Ghanaians differs markedly from that of African Americans and other previously reported
indigenous African populations.
Conclusions: The thickness of the retina among Ghanaians differs not only from those measured among
individuals with European ancestry, but also from those obtained from African Americans. Normative retinal and
choroidal parameters determined among individuals with African or European ancestry may not be sufficient to
describe indigenous African populations.
Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclo-
sures at the end of this article. Ophthalmology Science 2024;4:100386 ª 2023 by the American Academy of
Ophthalmology. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/
4.0/).
Supplemental material available at www.ophthalmologyscience.org.Despite possessing more genetic variation than any other
region,1e3 Africa is under-represented in scienti c studies,4,5fi
including in ophthalmology.6 Because of this, the way in
which genetic and environmental variation within the
continent and divergence from groups from other
geographical locations (such as Europe or Asia) influence
the prevalence and/or clinical presentation of ocular
diseases among indigenous African populations is poorly
characterized.7 Evidence points towards significant
differences between individuals of African and Europeanª 2023 by the American Academy of Ophthalmology
This is an open access article under the CC BY license (http://creativecommons.
org/licenses/by/4.0/). Published by Elsevier Inc.descent. African Americans are 15 times more likely to
develop glaucoma, the second leading cause of blindness
worldwide, and are 7 times more likely to suffer permanent
vision loss from it.8,9 They are on average 4 times more
likely to be afflicted by diabetic retinopathy.10,11 Retinal
vein occlusion is more common among African Americans
than individuals with European ancestry.12 The early stage
of age-related macular degeneration (AMD) affects a larger
proportion of Europeans (11.2%) thanAfricans (7.1%).13 The
late stages of the disease are almost twice as prevalenthttps://doi.org/10.1016/j.xops.2023.100386 1
ISSN 2666-9145/23
Ophthalmology Science Volume 4, Number 2, April 2024amongst Europeans as compared to Africans (0.5% vs. 0.3%,
respectively).13 Phenotypically, drusen and focal
hyperpigmentation, 2 features that are characteristic of early
and intermediate AMD, are more common amongst
Europeans compared with individuals with African
ancestry.14,15 Non-neovascular AMD features such as
geographic atrophy are more common outside the macula
among African Americans patients.15 Certain diseases of the
choroid such as polypoidal choroidal vasculopathy have clear
ethnic predispositions among individuals with African
ancestry.16,17 While presumed to be more common in
European populations, central serous chorioretinopathy
appears to be more aggressive among African American
patients.18
While valuable, these observations are limited by the fact
that subjects of African descent considered in these studies
only account for a small proportion of the genetic diversity
characteristic of Africa. For instance, the ancestry of African
Americans is predominantly from the Niger-Kordofanian re-
gion (w71%) and European populations (w13%), with levels
of admixture varying considerably between individuals.3
Additional determinants of visual impairments including
environmental and socioeconomic factors such as education
level, income, employment, and distance to care facilities also
contribute to the variability in susceptibility to ocular diseases
and are likely to vary between African, African American,
and European populations.7,19e21 Findings established among
African Americans and individuals of European descent may
therefore not be entirely translatable to indigenous African
populations. Considering this, it is necessary to establish
normative comparisons between indigenous African pop-
ulations and individuals of African and European ancestry.
Systematic comparisons between these different groups
would ensure that biomarkers specific to indigenous pop-
ulations may be identified, so that disease risk and prognosis
may be accurately assessed. This is a decisive step toward
improved clinical care and precision medicine.22
This study was undertaken to evaluate macular retinal
thickness and central choroidal thickness in a healthy indig-
enous African population from Ghana, and to compare them
with those measured among individuals with European
ancestry and previously reported populations of African
descent. The thickness of the retina and choroid are
commonly used to diagnose, monitor, and estimate the risk of
progression of many vitreoretinal disorders.23e28 These
measures rely on OCT, an established and widely available
imaging technique that allows for 3-dimensional re-
constructions of regions of the macula and posterior pole.
Existing databases for normative OCT measurements,
including retinal and choroidal thickness, have mostly been
established using individuals with European descent and
often overlook baseline differences in retinal and choroidal
anatomy between ethnic groups.29 Previous studies have,
however, shown that ethnicity influenced retinal and
choroidal thickness significantly, including among African
Americans30e36 and Afro-Caribbeans.37,38 Indigenous
African populations without ocular diseases have been
considered in a limited number of studies only,34,39,40 with
macular retinal thickness being the main feature examined.
Ghanaians included in this study were recruited from 22
locations, the capital Accra and Kumasi in the Ashanti
region. While the fine-scale genetic structure within west
Africa is complex, previous studies indicate that these par-
ticipants have a close genetic relationship within the Niger-
Congo area, which is part of the larger Niger-Kordofanian
region.41,42
Methods
Subjects
Ghanaian subjects were recruited as part of a prospective study
carried out at 2 teaching hospitals in Ghana, the Korle-Bu Hospital
in Accra and the Komfo Anokye Teaching Hospital in Kumasi.
The aims and details of the study were explained to all subjects
with the help of interpreters (if necessary) and information leaflets,
and written consent was obtained from all patients. A questionnaire
detailing the Ghanaian patients’ ophthalmic and medical histories
was completed by the local ophthalmic nursing staff. Best cor-
rected Snellen visual acuity corrected by glasses or pinhole was
assessed for all participants. Individuals with self-reported Euro-
pean ancestry were recruited from local communities surrounding
the Medical College of Wisconsin (Milwaukee, WI).43 To ensure
consistency in age representation between the Ghanaian and
European groups, all Ghanaians participants younger than 40 (2
subjects) were excluded from analyses. The research adhered to
the tenets of the Declaration of Helsinki and the protocol was
approved by the ethics review boards of both the Korle-Bu Hos-
pital (University of Ghana Medical School Protocol ID No: MS-Et/
M.4-P./2008/2009) and the Komfo Anokye Teaching Hospital
(KNUST Reference: CHRPE/32/10) for Ghanaian participants and
by the institutional review board at the Medical College of Wis-
consin for individuals with European ancestry.
Imaging and Screening for Retinal Diseases
The same imaging protocol was applied for all Ghanaians and
participants of European descent. All patients were dilated prior to
imaging using tropicamide 1% and phenylephrine 2.5%. Each
patient underwent a slit lamp biomicroscopy and fundus exami-
nation performed by a retina specialist in addition to an OCT scan
in both eyes when possible. A Zeiss Cirrus high-definition (HD)-
OCT (Carl Zeiss Meditec) was employed for capture in all study
sites. This device does not rely on the patient’s ability to fixate, and
it allows for post-hoc repositioning of the scan to the center of the
fovea. Volumes acquired in all participants were nominally 6 
 6
mm and consisted of  128 B-scans (512 A-scans/B-scans). The
signal strength for all scans was  7.44,45 Screening of the images
for vitreoretinal and choroidal disorders was performed by G.S.,
W.A., and G.S.H. using fundus and OCT images. Eyes
presenting with a history of vision-limiting ocular diseases or
clinical marker of any vitreoretinal disorder including AMD, dia-
betic retinopathy, retinal vascular diseases, epiretinal membranes,
vitreomacular traction, intraretinal cysts, hereditary macular dis-
ease, or macular holes were excluded. Eyes with myopia of more
than 4.00 diopters (D) were also excluded from these analyses.
Axial length (AL) was measured among subjects with European
ancestry only using the IOLMaster ocular biometer (Carl Zeiss
Meditec).
Image Segmentation
Both macular retinal and choroidal thicknesses were measured
using the Cirrus HD-OCT proprietary software.46 All OCT B-scans
were manually inspected to ensure that the inner limiting
Zouache et al  Retinal and Choroidal Thickness Among Ghanaiansmembrane and retinal pigment epithelium layers were accurately
segmented, and that the hyporeflective border between choroid
and sclera was visible; see Figure 1. For the retina, the Cirrus
HD-OCT software generates false color 2- and 3-dimensional
thickness maps presented in 9 segments corresponding to the
quadrants of the ETDRS.47 The inner (3 mm) and outer (6 mm)
rings of the map, which corresponded to the parafoveal and
perifoveal regions, respectively, were divided into superior,
inferior, nasal, and temporal quadrants. The central 1 mm
diameter region corresponded to the central foveal area. Central
choroidal thickness was measured at the thinnest center point of
the fovea manually from "5-Line Raster" high-definition images
using the "Ruler" tool.48 These measurements were undertaken by
2 observers (J.S. and V.S.). A third observer (W.A.) adjudicated if
there was any disparity (defined as a difference > 10% between
observers) in measurements.
Systematic Review
The objective of the systematic review was to determine typical
retinal and choroidal thickness values among individuals with
African ancestry. Searches were undertaken on PubMed, Google
Scholar, and Scopus from their inception to August 31st, 2022. The
terms "retina," "retinal thickness," "macular thickness," "retinal
macular thickness," "choroid," "choroidal thickness," "central
choroidal thickness," "subfoveal choroidal thickness," and "optical
coherence tomography," were searched individually and then
combined with "race," "ethnicity," "African," "Africa," or "African
American." Reference lists were hand-searched and relevant cita-
tions screened for additional sources. Conference abstracts were
included. Studies were eligible for inclusion if they reported
measurements in any quadrant of the ETDRS map, specified the
imaging modality used, and provided a mean or median and
standard deviation with sample size, 95% confidence interval (CI),
or standard error for each measurement. Studies that did not report
information on the age of participants (mean or median) were
excluded. In studies considering differences between multiple
ethnic groups, only measurements and information collected
among subjects with African ancestry were recorded. Within each
study, if measurements were reported for both left and right eye, 1
eye was randomly selected for inclusion in the meta-analysis. Only
measurements made among healthy individuals were included in
the meta-analysis.
Sensitivity to Additional Confounders
We sought to determine how large the effect of confounders not
considered in our study would have to be to affect the significance
of the association with ethnicity that we report. We did so using
Monte Carlo simulations (n ¼ 5.05 
 106). Each simulation
introduced a random error, ranging from 0% to 100% of the
original measurement, to the retinal or central choroidal thickness
measured in each eye. A P value (here denoted Psim) for association
with ethnicity while adjusting for age and sex was computed for
each simulation. The association was assumed to remain significant
if the proportion of Psim < 0.05 was > 95% or 99%. Convergence
analyses were carried out to determine the minimum number of
Monte Carlo simulations to run.
Statistical Analyses
Statistical analyses were carried out using R (The R Foundation,
software version 4.2.0).49 The level of significance for all tests was
set at a ¼ 0.05. All P values provided are 2-tailed and adjusted for
multiple comparisons using Bonferroni corrections. Bland-Altman
plots50 and Pearson’s correlation coefficient (denoted r) and its CI
were used to identify correlations between retinal thicknessmeasured in the left and right eyes of the same individual.
Associations between ethnicity, age, sex, and retinal or choroidal
thickness were assessed by using mixed-effect linear regression
models implemented in the R package lme4.51 Dependencies
between measurements made in the left and right eye of the
same subject were accounted for by including a random effect
term of the form (1 | Subject). Power calculations for multiple
regressions were performed by assuming that the proportion of
variance explained by ethnicity, age, and sex was between 20%
and 30%.43 Sample sizes in this study ensured that regression
models including 3 covariates (age, sex, and ethnicity) had a
power > 85%. Post hoc power analyses were performed using
the R package simr52 to determine the power associated with
each regression model. Outputs from the mixed-effect models
were visualized and plotted using the R packages ggplot253 and
sjPlot.54 Meta-analyses were performed using the R package
metafor55 and random-effect linear regression models. Forest plots
were used to visualize thicknesses estimated in each study identi-
fied through systematic review. Heterogeneity between published
investigations was assessed using Cochran’s Q statistic56 and the I2
metric.57
Results
Patient Demographics
A total of 992 eyes of 496 subjects were examined during 3
visits to Ghana (128 individuals on the first visit, 204 on the
second visit, and 164 on the third visit). Color fundus images
were available from 990 (98.8%) eyes, and OCT scans were
captured in 493 eyes (49.7%). OCT scans from 69 eyes (7%)
were ungradable due to medial opacity. A total of 424 OCT
volume scans were of sufficient quality to allow for seg-
mentation. Of these, 78 scans captured in 42 Ghanaians met
the inclusion criteria and were processed for further analyses
(see Fig 1). Fundus images and OCT volume scans were
available and of sufficient quality for segmentation for all
eyes from the European group, which consisted of 37
individuals (see Table 1). Fifty-seven percent (27 partici-
pants) of Ghanaians were women; this proportion did not
differ significantly from that of the European group (76%, 28
subjects, P ¼ 0.4). The median age for all participants was
59.5 years old, with an interquartile range (IQR) of 12.5
years. The median age of Ghanaians (60, IQR 8.5) did not
differ significantly from that of subjects with European
ancestry (58.0, IQR 20.0, P ¼ 0.7). Measurements made in
the left and right eye of the same patient were dependent and
strongly correlated in all regions of the retina and choroid
sampled (0.60  r  0.95; P < 0.001 for all regions). Me-
dian AL among participants with European ancestry was 23.4
(IQR 1.3). Axial length was not measured among Ghanaian
subjects.
Retinal Thickness among Ghanaians and
Subjects with European Ancestry
Retinal thickness was investigated using mixed-effect linear
regression models including age, sex, and ethnicity as
covariates. When adjusted for ethnicity and age, the retina of
females was on average thinner than that of males within the
parafoveal region (see Fig 2A). This difference was
statistically significant in the central foveal region (P ¼3
Ophthalmology Science Volume 4, Number 2, April 2024
Figure 1. OCT scans recorded in the right (A, B) and left (C, D) eyes of a 50-year-old Ghanaian male. In (A) and (C) the segmentation of the inner
limiting membrane and retinal pigment epithelium layer is shown. The quantification of the thickness of the central choroid is shown in (B) and (D).0.004). In contrast, the retina of females was on average
thicker in the perifoveal region, although this difference
did not reach statistical significance in any of the ETDRS
quadrants (P > 0.07).
When adjusted for age and sex, the retina of Ghanaians
was on average significantly thinner than that of participants
with European ancestry in every region of the macula (P <
0.001; Fig 2B). The largest difference in thickness between
the 2 groups was observed at the fovea (mean difference
45.3 mm, 95% CI [36.48; 54.12], P < 0.001). The
amplitude of this difference decreased radially with
distance from the foveal region, ranging from 30.07 mmTable 1. Baseline Demographics of Ghanaians and Partici
Demographic White (n [ 37)
Sex
Females 28
Males 9
Age
Median (IQR) 58 (20)
Range 41e85
Eyes (included in analysis)
OD 37
OS 37
IQR ¼ interquartile range; OD ¼ right eye; OS ¼ left eye.
*Chi-square test, c2 ¼ 0.73.
yWilcoxon rank sum test, W ¼ 820.5.
4
(95% CI [22.31; 37.83]) to 32.17 mm (95% CI [24.43;
39.91]) in the parafovea to 14.93 mm (95% CI [8.44;
21.42]) to 19.23 mm (95% CI [12.12; 26.34]) in the
perifovea.
We observed a reduction in retinal thickness with
age in all regions of the retina (Fig S3) independent of
sex or ethnicity. This decrease was statistically
significant in the superior (b ¼ 6.8mm/decade, P ¼
0.001), nasal (b ¼ 5.2mm/decade, P ¼ 0.01) and
inferior (b ¼ 4.9mm/decade, P ¼ 0.02) regions of
the parafovea, and in the superior (b ¼ 4.4mm/
decade, P ¼ 0.008) perifovea.
pants with European Ancestry Included in This Study
Ghanaians (n [ 42) P Value for Differences
27 0.4*
15
60 (8.5) 0.7y
45e82 -
40 -
38
Zouache et al  Retinal and Choroidal Thickness Among Ghanaians
Figure 2. Differences in retinal thickness between (A) females and males and (B) participants with European ancestry and Ghanaians, plotted for each
quadrant of the ETDRS map using the right eye as a template. In (A), thickness measured among females was used as a reference. In (B), thickness measured
among the European group was used as reference. In both (A) and (B), estimates were determined using mixed-effect linear regression models generated
independently for the 9 sectors of the ETDRS map and include 95% confidence intervals and associated P values. Estimates in (A) are adjusted for age and
ethnicity. Estimates in (B) are adjusted for age and sex.Central Choroidal Thickness Among Ghanaians
and Subjects with European Ancestry
Central choroidal thickness was investigated using mixed-
effect linear regression models including age, sex, and
ethnicity as covariates. The central choroid was thinner
among males compared with females (mean difference
14.87 mm, 95% CI [6.4; 36.14]); however, this difference
was not significant (P ¼ 0.17); see Figure 4A. The central
choroid was thinner among Ghanaians compared with
subjects with European ancestry (mean difference
60.28 mm, 95% CI [41.01; 79.55], P < 0.001); see
Figure 4B. When adjusted for ethnicity and sex, age was
associated with a reduction of the choroidal thickness by
6.7mm/decade on average (Fig 4C). This decrease was,
however, not statistically significant (P ¼ 0.18).
Sensitivity to Additional Confounders
We sought to assess the sensitivity of the differences that we
observed between Ghanaians and individuals with European
ancestry to potential confounders not accounted for in our
regression models. These include genetic and environmental
factors, but also potential differences in ocular parameters
between these 2 groups. To do so, we performed Monte
Carlo simulations to simulate the effect of an added error in
measurement caused by potential confounders. Each simu-
lation introduced a random error, ranging from 0% to 100%
of the original measurement, to the retinal or central
choroidal thickness measured in each eye of Ghanaian
participants. A P value (here denoted Psim) for association
with ethnicity (adjusted for age and sex) was then computed
for each simulation. Based on these analyses, we observed
that the association in the temporal perifovea was the most
sensitive to uncertainties in measurements. The most robustassociation with ethnicity was that found with central
choroidal thickness. We estimated that this association
remained significant (threshold for Psim set at 99%) if errors
in measurements remained below 52%. If the threshold for
Psim is set at 95%, then measurement errors would have to
be smaller than 62% (see Fig S5).Comparison with Previous Studies
No studies assessing central choroidal thickness among
subjects with African ancestry were identified through the
systematic literature search. An approximate average cen-
tral choroidal thickness of 375 mm was reported among a
group of overseas students and foreign residents in central
China (mean age 26.9).58 We identified 10 studies that
examined variations in macular retinal thickness among
individuals with African ancestry, 7 of which satisfied the
inclusion criteria. Five of these studies30e32,34,35 were
performed in the United States and reported
measurements made among African Americans. Only 1
eligible study was carried out on the African continent
(South Africa).59 Moderate to high levels of
heterogeneity were observed among retinal measurements
reported for African Americans in all regions of macula
(52.9%  I2  92.5%, P < 0.07). To reduce this
heterogeneity, we grouped studies based on the mean age
of the subjects considered before generating pooled
estimates. Two studies31,35 reported a mean age among
participants lying between 20 and 30 years (21 and 28.9
years, respectively). Two investigations30,34 considered
subjects between 40 and 50 years of age on average
(47.7 and 49, respectively). The remaining study32
comprised individuals 30e40 years of age on average
(mean 36.2); see Table S2.5
Ophthalmology Science Volume 4, Number 2, April 2024
Figure 4. Variation of the choroidal thickness with (A) sex, (B) ethnicity, and (C) age. Estimates and 95% confidence intervals were determined using
mixed-effect linear regression models including age, sex, and ethnicity as covariates. In (C), the 95% confidence interval is shown for the slope of each
regression. (***P < 0.001).Estimates pooled among African Americans, mean
retinal thickness reported among black South Africans, and
those generated for Ghanaians and subjects with European
ancestry considered in this study are plotted by age group in
Figure 6. For consistency with the methodology applied for
the meta-analysis, estimates plotted for Ghanaians and in-
dividuals of European descent were not adjusted for age or
sex. We observed marked differences in retinal thickness
between ethnic groups. The retina of Ghanaians was thinner
than that of black South Africans in all quadrants of the
ETDRS map. The amplitude of these differences ranged
from 2.8 mm in the temporal parafovea to 35.3 mm in the
superior perifovea. Among African Americans, we observed
a reduction in pooled retinal thickness estimates with
increasing age group in all regions of the macula. Retinal
thickness measured among Ghanaians was thinner than that
obtained from African Americans in the 20e30 age group in
all ETDRS quadrants, with differences ranging from 9.3 mm
in the inferior perifovea to 30.3 mm in the superior parafo-
vea. It was on average thicker than that among African
Americans from the 30e40 and 40e50 age groups. The
amplitude of these differences ranged from 18.6 mm in the
superior perifovea to 44.6 mm in the temporal perifovea.Discussion
Macular retinal thickness among Ghanaians differs mark-
edly from that of individuals with European ancestry, Af-
rican Americans, and other previously reported indigenous
African populations. The retina in all regions of the macula
is on average significantly thinner among Ghanaians as
compared to individual of European descent. This difference
is independent of age and sex; it is largest within the central
1 mm foveal region and decreases in amplitude radially with
distance from the foveal center. Systematic review and
meta-analyses of previous reports indicate that macular
retinal thickness differs markedly between Ghanaians, black
South Africans, and African Americans, and that some of
these differences may be partly driven by age. Central6
choroidal thickness is also significantly thinner among
Ghanaians as compared to subjects with European ancestry.
Previous studies have been consistent in reporting that
the retina of African Americans30e36 was on average thinner
than that of individuals with European ancestry. The
reduction in pooled retinal thickness estimates with age that
we observed among African Americans in all quadrants of
the ETDRS map indicates that age should be carefully
considered when comparing retinal features between pop-
ulations. This finding is reinforced by the fact that, when
compared to the group of individuals with European
ancestry that we considered, macular retinal thickness was
smaller among African Americans in the 30e40 years and
40e50 years age groups in all quadrants of the ETDRS map
but was generally thicker in the outer quadrants among
African Americans from the 20e30 years age groups. The
lack of adjustment for age could explain why the mean
central macular thickness among black South Africans was
previously found to be higher than averages from African
Americans and European subjects.59 A reduction in retinal
thickness with age has been demonstrated among
individuals with European ancestry,60 a pattern that we
also observed among Ghanaians. A previous study
performed among individuals with predominantly
European ancestry found that foveal, perifoveal, and
peripheral macular thicknesses decreased in patients > 60
years of age; however, it was predicted to increase with
age in younger individuals in some regions of the
macula.61 These findings highlight the need for further
investigations to elucidate the contribution of age to
macular retinal thickness and its differential effect on both
genetically mixed and indigenous groups.
We previously reported that the foveal pit of Ghanaians
was significantly wider and larger in volume as compared to
that of a group composed of individuals with European
ancestry.43 This variation may partly explain why the
amplitude of the differences in retinal thickness between
Ghanaians and subjects of European descent is maximal at
the fovea and within the parafoveal belt of the macula and
decreases radially with distance from its center. Significant
Zouache et al  Retinal and Choroidal Thickness Among Ghanaians
Figure 6. Estimates of retinal thickness among African Americans, black South Africans, Ghanaians, and a group of individuals with European ancestry, by
age group, with associated 95% confidence intervals. The age group was determined based on the mean age of subjects reported by each study and is
indicated between parentheses. Estimates for African Americans from the 20e30 and 40e50 age group were pooled through meta-analysis. For consistency
with the methodology applied for this analysis, estimates plotted for Ghanaians and subjects of European descent are not adjusted for age or sex.
7
Ophthalmology Science Volume 4, Number 2, April 2024differences in the morphology of the foveal depression and
in their pattern of variation with age between Ghanaians and
individuals with European ancestry may be important
drivers of the dissimilarities in retinal thickness that we
observed. Future studies will seek to determine
longitudinal changes in the shape of the foveal pit and
how they may influence retinal thickness among subjects
with African or European ancestry. While our study
measured total retinal thickness only, future studies will
be directed toward investigating associations with specific
retinal sublayers and their blood supply to gain a better
understanding of mechanistic differences underlying ethnic
differences. Retinal layers, including the outer nuclear
layer, the outer plexiform layer, the inner nuclear layer,
the inner plexiform layer, and the ganglion cell layer each
serve a unique function in the visual process60,62 and may
vary in their structure with ethnicity. Previously reported
differences in the vascular density of the superior,
intermediate, and deep retinal capillary plexuses within the
fovea and parafovea among healthy subjects with African
ancestry compared with subjects of European descent63,64
may also be key factors to consider.60
The central choroid was found to be significantly
thinner among Ghanaians compared with participants of
European descent. This finding is consistent with a previ-
ous study carried out among overseas students and foreign
residents in central China, which found that the subfoveal
choroid was thinner among participants of African descent
compared with individuals with European ancestry.58 The
significance of this finding is unclear. The main function
of the choroid is to support the metabolic requirements of
the outer retina, which includes the photoreceptor cells.
The choroid plays an essential part in the delivery of
oxygen and nutrients to the outer retina and the clearance
of fluids and metabolism byproducts from the subretinal
space.60,65e67 How these functions relate choroidal thick-
ness is unknown, mainly because this feature has mainly
been investigated in the context of retinal diseases.
Reduced choroidal thickness has been reported in eyes
presenting large drusen or reticular pseudodrusen,68,69
pigmentary abnormalities,70 and in late stage AMD
(neovascular AMD and/or geographic atrophy).24,708
While choroidal vascularity also varies over the course of
AMD71 and between populations with European and
African ancestry,63,64 its association with choroidal
thickness remains to be clari ed.72fi
The main limitation of this study was that only a small
number of confounders were considered. We evaluated the
significance of this shortcoming by performing sensitivity
analyses for associations between retinal or choroidal
thickness and ethnicity. Our sample size was too small to
effectively assess the contribution of weakly associated
factors such as body mass index,59 lens thickness,73 or
smoking70 on retinal or choroidal thickness. Axial length
has been associated with thin inner and outer macula, but
not central macula.59 While previous studies indicate that
AL is unlikely to have a strong effect on retinal thickness
measurements,45 it has been shown to be an important
confounder for choroidal thickness.58,59,70,71 Mean AL
among our European group lied within a range similar to
that of participants from studies included in our meta-
analyses (see Table S2). Since we did not have access to
AL measurements among Ghanaians, we estimated the
expected range of errors introduced by variations in AL on
choroidal thickness measurements from a previous study.58
Based on this investigation, the largest error introduced by
AL is approximately 42%, which is below the 52% error in
measurements necessary to affect the significance of
differences in choroidal thickness (see Fig S5).
Therefore, the lack of correction for AL is unlikely to
affect the observed association between choroidal
thickness and ethnicity among our participants. The
imbalance between the number of males and females
among Ghanaians and individuals with European
ancestry in our study did not allow us to effectively
investigate associations between sex and retinal and
choroidal thickness. Retinal thickness was on average
smaller within the fovea and parafovea among females,
in agreement with previous investigations,31,34,39,59,74 but
not in the perifovea, which is inconsistent with previous
reports.35,75e77 Future studies will include a larger num-
ber of participants and systematically investigate the effect
of additional genetic and environmental confounders on
retinal and choroidal parameters.Footnotes and DisclosuresOriginally received: February 6, 2023.
Final revision: July 17, 2023.
Accepted: August 14, 2023.
Available online: August 21, 2023. Manuscript no. XOPS-D-23-00029.
1 Sharon Eccles Steele Center for Translational Medicine, John A. Moran
Eye Center, Department of Ophthalmology & Visual Sciences, University
of Utah, Salt Lake City, Utah.
2 NICRN, Belfast Health and Social Care Trust, Belfast, UK.
3 Unit of Ophthalmology, Department of Surgery, University of Ghana
Medical School, Accra, Ghana.
4 Eye Unit, Eye Ear Nose and Throat Department, Komfo Anokye Teaching
Hospital and Kwame Nkrumah University of Science and Technology,
Kumasi, Ghana.5 Research Design Service, East Midlands (RDS EM), University of Not-
tingham, Nottingham, UK.
6 Department of Ophthalmology & Visual Sciences, Medical College of
Wisconsin Eye Institute, Milwaukee, Wisconsin.
7 Ophthalmology Department, Belfast Health and Social Care Trust, Bel-
fast, UK.
8 Academic Ophthalmology and Visual Sciences, Mental Health & Clinical
Neurosciences (Academic Unit 1), University Hospital, QMC, Nottingham,
UK.
Disclosure(s):
All authors have completed and submitted the ICMJE disclosures form.
The authors made the following disclosures: G.S.H. is a shareholder,
consultant and co-founder of Perceive Biotherapeutics Inc.
Zouache et al  Retinal and Choroidal Thickness Among GhanaiansThis work was supported in part by the National Eye Institute of the
National Institutes of Health under award numbers R01EY033580
(J.C.) and R24EY017404 (G.S.H.). The content is solely the re-
sponsibility of the authors and does not necessarily represent the
official views of the National Institutes of Health. Additional support
from an Unrestricted Grant from Research to Prevent Blindness, New
York, NY, to the Department of Ophthalmology & Visual Sciences,
University of Utah (MAZ & GSH).
HUMAN SUBJECTS: Human subjects were included in this study.
The research adhered to the tenets of the Declaration of Helsinki and
the protocol was approved by the ethics review boards of both KBTH
(University of Ghana Medical School Protocol ID No: MS-Et/M.4-P./
2008/2009) and KATH (KNUST Reference: CHRPE/32/10) for Gha-
naian participants and by the institutional review board at the Medical
College of Wisconsin for individuals with European descent. The aims
and details of the study were explained to all subjects with the help
of interpreters (if necessary) and information leaflets, and written
consent was obtained from all patients.Author Contributions:
Conception and design: Zouache, Carroll, Silvestri, Hageman, Amoaku
Data Collection: Zouache, Silvestri, Akafo, Lartey, Carroll, Silvestri,
Hageman, Amoaku
Analysis and interpretation: Zouache, Faust, Mehta, Carroll
Obtained funding: N/A
Overall responsibility: Zouache, Faust
Abbreviations and Acronyms:
AL ¼ axial length; AMD ¼ age-related macular degeneration;
CI ¼ confidence interval; IQR ¼ interquartile range.
Keywords:
Africans, African-Americans, Choroid, OCT.
Correspondence:
Moussa A. Zouache, PhD, John A. Moran Eye Center, Department of
Ophthalmology & Visual Sciences, University of Utah, 65 N Mario
Capecchi Drive, Salt Lake City, UT 84132. E-mail: moussa.zouache@hsc.
utah.edu; Winfried M. Amoaku, FRCOphth, PhD. E-mail: winfried.
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