Key words
pediatric COVID-19 - retinal neurodegeneration - swept-source - optical coherence
tomography
Schlüsselwörter
pädiatrisches COVID-19 - Netzhautneurodegeneration - Swept-Source-optische Kohärenztomografie
Introduction
The World Health Organization accepted the coronavirus disease 2019 (COVID-19), raised
from China in December 2019, as a global pandemic in March 2020 due to its quick spread
and possible
serious sequels and fatal results [1]. The pathogen is an enveloped RNA virus of the beta coronavirus family and is called
severe acute respiratory syndrome
coronavirus 2 (SARS-CoV-2) [2], [3]. Human-to-human transmission of the COVID-19 has been reported via the spread of
respiratory droplets
[4]. COVID-19 mainly causes respiratory tract infections [5], [6]. However, COVID-19 has a wide clinical
spectrum from mild to severe manifestations including cough, fever, myalgia, fatigue,
dyspnea, anosmia, diarrhea, pneumonia, severe acute respiratory syndrome, septic shock,
multi-organ
failure, and even death [7], [8], [9], [10].
The mechanism of the SARS-CoV-2 infection is thought to be the angiotensin-converting
enzyme (ACE) 2 receptors located on the host cells [11], [12], [13]. COVID-19 might result in hypercoagulability and exacerbated systemic inflammation
by the ACE 2 receptors expressed almost in all
major organs, properly on the endothelial cells [5], [14]. The endothelial cells have important functions to prevent ischemia, tissue
edema, vasoconstriction, and coagulation [14]. The involvement of endothelial cells can lead to impaired microvasculature function
with increased inflammatory
marker responses (fibrinogen, D-dimer, C-reactive protein, etc.) in COVID-19 patients
[14].
Previous reports have demonstrated the presence of viral RNA in tears of adult COVID-19
patients [15], [16]. Conjunctival hyperemia,
epiphora, and chemosis have been reported as anterior segment findings in adult
COVID-19 patients [17], [18]. Meanwhile,
microhemorrhages, cotton wool spots, and hyperreflective lesions have been documented
as retinal findings in adult COVID-19 patients [17]. The existence of viral
RNA has also been demonstrated in the conjunctiva and tear secretions of pediatric
patients [19]. It has been postulated that pediatric COVID-19 patients have a
better prognosis, shorter disease duration, and lower disease prevalence than
adult patients [20], [21]. There are limited studies about
ocular involvement of the COVID-19 in the pediatric population. Moreover, to the
best of our knowledge, no reports have been documented regarding optical coherence
tomography (OCT) findings in
the COVID-19 children. In the present study, we intended to compare early covid
swept-source (SS) OCT measurements between pediatric COVID-19 patients and healthy
children to assess retinal
neurodegeneration and choroidal thickness (ChT) alterations.
Methods
The present study was designed cross-sectionally and conducted in adherence to the
tenets of the Declaration of Helsinki. The institutional review board approved the
study. All parents of the
children signed the informed consent before study enrollment.
Pediatric Subjects
A total of 46 children with regular controls (7 – 18 years old) were randomly circuited
in the study between April 2020 and October 2020. Only the right eyes of the participants
were
enrolled in the study. Twenty-four eyes of 24 early post-COVID-19 (Alpha variant)
children were included in the COVID-19 group. These patients were enrolled in the
study 4 weeks (28 days)
after they completed COVID-19 treatment to investigate early covid posterior
segment measurements. The patients did not have any COVID-19 symptoms at the time
of examination. Twenty-two eyes
of age- and gender-matched 22 healthy children with negative COVID-19 antibody
blood test results served as the control group. Clinical, laboratory, and radiologic
findings were evaluated
for COVID-19 prediagnosis. The blood tests for inflammatory markers were performed
at the time of admission to the hospital (just prior to the hospitalization). The
confirmation of the Alpha
variant COVID-19 diagnosis was performed by the polymerase chain reaction (PCR)
test. All children in the COVID-19 group had positive PCR test results for SARS-CoV-2.
All children cooperated
with ophthalmic examination and OCT measurements. All children in the COVID-19
group required hospitalization for some lung involvement. Fortunately, none of the
children had oxygen
saturation lower than 90%, so no one was intubated. The COVID-19 group completed
oral combined treatment of ampicillin/sulbactam and azithromycin for 7 days. All children
had a detailed
ocular examination including best-corrected visual acuity (BCVA, in logMAR),
intraocular pressure (IOP, mmHg, with a pneumatic tonometry-Topcon, Tokyo Japan),
spheric equivalent (SE,
Diopter), axial length (AxL, mm), biomicroscopic anterior segment (no signs of
conjunctivitis, clear cornea, no cells in the anterior chamber, normal iris, symmetric
pupil, and crystalline
phakic lens) and fundus assessment as well as SS-OCT measurements. The children
with IOP greater than 21 mmHg, refractive error > ± 1.00, ΑxL of 22 – 24 mm, history
of an ocular disorder
(corneal opacity, cataract, ocular inflammation, choroidal or retinal diseases,
etc.), previous ophthalmic surgery, and systemic disease were not included in the
study.
Optical Coherence Tomography Measurement System
All scans were taken by the same experienced and masked researcher and all OCT parameters
were measured during the morning shift to inhibit diurnal effects. The scans with
poor quality
(< 60/100) were excluded and repeated images were taken up to get high-quality
results. The scans were performed using a deep range imaging Triton model SS-OCT (Topcon,
Tokyo, Japan) with
the 3D wide protocol (12.0 × 9.0 mm) measuring on the peripapillary area and
macula. The central macular thickness (CMT, um) was measured between the inner limiting
membrane (ILM) and
retinal pigment epithelium (RPE) under the fovea. The retinal nerve fiber layer
(RNFL) thickness measurement was performed from the ILM to the ganglion cell layer
(GCL) borders at the
temporal, superior, nasal, and inferior peripapillary quadrants. The GCL thickness
was measured from two different layers and in six sectors of the macula (superior,
temporal-inferior,
temporal-superior, inferior, nasal-inferior, and nasal-superior). The GCL+ thickness
was measured from the RNFL and the inner nuclear layer (INL). The GCL++ thickness
was measured from the
ILM to the INL borders. The ChT measurements were performed between the Bruch
membrane and the sclera-choroidal interface at five different points (subfovea, 500
microns nasal and temporal
points from the fovea, 1500 microns nasal and temporal points from the fovea;
[Fig. 1]).
Fig. 1 Central macula, retinal nerve fiber layer, and ganglion cell layer thickness measurements
performed by swept-source optical coherence tomography.
Statistical Analysis
The SPSS software version 21.0 (IBM Corp., Armonk, NY, USA) was used for the statistical
analysis of the study. Continuous variables were described as mean ± standard deviation.
The
detection of normal distribution was analyzed by the Shapiro-Wilk test. The BCVA,
IOP, and SS-OCT measurements were compared between the groups. The chi-square test
was used for the analysis
of categorical parameters. A p value of < 0.05 was accepted as significant. Since
the Studentʼs t-test cannot be employed for comparing many different OCT parameters
between the groups,
the ANOVA test was used for statistical analysis, and the Bonferroni correction
was employed for multiple testing. Correlations of inflammation markers with OCT parameters
were similarly
analyzed with correction. For these parameters, the statistical significance
was accepted if a p value of < 0.002 was obtained.
Results
The mean age of the children in the COVID-19 group was 13.29 ± 2.91 (8 – 17) years
and the mean age of the children in the control group was 13.09 ± 2.88 (7 – 17) years
(p = 0.759). The
similarity was noted between the gender numbers of the COVID-19 (13 female, 11
male) and control (12 female, 10 male) groups (p = 0.412). The mean BCVA value was
0.02 ± 0.01 logMAR in the
COVID-19 group, which was similar to the control groupʼs value (0.01 ± 0.01 logMAR),
(p = 0.341). The mean IOP value in the COVID-19 group (13.88 ± 2.83 mmHg) was also
similar to the control
groupʼs mean IOP value (13.47 ± 2.45 mmHg), (p = 0.372). The mean SE and AxL values
were also similar in the COVID-19 (SE = + 0.52 ± 0.04, ΑxL = 22.85 ± 4.22) and control
groups
(SE = + 0.48 ± 0.05, ΑxL = 22.92 ± 5.06) (p = 0.216 and p = 0.302, respectively).
None of the patients in the COVID-19 group showed any signs of retinopathy in the
biomicroscopic fundus assessment. Approximately 70.8% (17) of the children presented
with fever, 37.5% (9)
with cough, 16.7% (4) with weakness, 12.5% (3) with diarrhea, 8.3% with a sore
throat (2) and vomiting (2), and 4.2% with shortness of breath (1), headache (1),
chest pain (1), and joint pain
(1) in the COVID-19 group. The mean hospitalization duration was 4.8 ± 2.3 days
(3 – 8 days). The time since the positive PCR test results was 28 days + hospitalization
duration (4.8 ± 2.3
days [3 – 8 days]) and time since the first symptoms was plus 2 days (the positive-resulted
PCR tests were performed 2 days before the hospitalization). The mean levels of fibrinogen,
D-dimer,
white blood cell (WBC) count, erythrocyte sedimentation rate (ESR), and C-reactive
protein (CRP) in the COVID-19 group are presented in [Table 1].
Table 1 The mean concentrations of the proinflammatory markers in the COVID-19 group.
|
Parameters (mean ± SD)
|
COVID-19 group
|
Normal range
|
|
SD: standard deviation, COVID-19: coronavirus disease 2019, WBC: white blood cell,
ESR: erythrocyte sedimentation rate, CRP: C-reactive protein
|
|
Fibrinogen (mg/L)
|
297.79 ± 78.63 (210 – 492)
|
200 – 400
|
|
D-dimer (µg/mL)
|
1.34 ± 0.80 (0.19 – 2.98)
|
< 0.5
|
|
WBC count (per mcL)
|
8682.50 ± 5749.86 (3300 – 26 300)
|
5000 – 10 000
|
|
ESR (mm/hour)
|
23.54 ± 12.11 (5 – 52)
|
0 – 10
|
|
CRP (mg/L)
|
10.39 ± 12.19 (3 – 49)
|
0 – 5
|
The mean CMT values of the children in the COVID-19 group (227.48 ± 15.85 µ) and the
healthy individuals in the control group (225.68 ± 16.96 µ) were similar (p = 0.601).
The mean RNFL
thickness measurements in the overall and peripapillary quadrants including the
temporal, superior, nasal, and inferior areas are presented in [Table 2]. All RNFL
thickness measurements were thicker in the COVID-19 group. Statistically significant
differences were noted in the global and nasal RNFL quadrant thickness measurements
between the COVID-19
and control groups (p < 0.002 for both). The mean GCL+ and GCL++ thickness measurements
in the superior, temporal-inferior, temporal-superior, inferior, nasal-inferior, and
nasal-superior
sectors are presented in [Table 3]. All GCL thickness measurements were thinner in the COVID-19 group. However, statistically
significant outcomes were observed
only in the nasal-inferior sectors of the GCL+ and GCL++ between the COVID-19
and control groups (p < 0.05 for all). The mean thickness measurements performed at
five different choroidal
points (subfovea, 500 µ, and 1500 µ far away from the subfovea at temporal and
nasal sides) are presented in [Table 4]. All ChT measurements were thinner in the
COVID-19 group. However, results very close to statistical significance were noted
in the locations of temporal 500 µ, 1500 µ, and nasal 500 µ from the subfovea between
the COVID-19 and
control groups (p = 0.002 for all).
Table 2 Assessment of the mean RNFL thickness measurements in the COVID-19 and control groups.
|
Thickness measurements (µm)
|
COVID-19 group (n = 48)
|
Control group (n = 44)
|
p*
|
|
RNFL: retinal nerve fiber layer, COVID-19: coronavirus disease 2019, *statistical
analysis was calculated by the ANOVA test, **statistically significant
|
|
RNFL_Global
|
109.79 ± 9.77
|
100.72 ± 9.64
|
0.001**
|
|
RNFL_Temporal
|
77.37 ± 10.67
|
74.77 ± 8.58
|
0.104
|
|
RNFL_Superior
|
137.25 ± 15.74
|
131.18 ± 15.15
|
0.045
|
|
RNFL_Nasal
|
84.76 ± 10.28
|
72.98 ± 15.09
|
< 0.001**
|
|
RNFL_Inferior
|
142.05 ± 11.51
|
136.64 ± 15.09
|
0.009
|
Table 3 Comparison of the mean GCL+ and GCL++ thickness measurements between the COVID-19
and control groups.
|
Thickness measurements (µm)
|
COVID-19 group (n = 48)
|
Control group (n = 44)
|
p*
|
|
GCL: ganglion cell layer, COVID-19: coronavirus disease 2019, **statistical analysis
was calculated by the ANOVA test, GCL+/++_S: ganglion cell layer in the superior sector,
GCL+/++_Ti: ganglion cell layer in the temporal-inferior sector, GCL+/++_Ts:
ganglion cell layer in the temporal-superior sector, GCL+/++_I: ganglion cell layer
in the inferior
sector, GCL+/++_Ni: ganglion cell layer in the nasal-inferior sector, GCL+/++_Ns:
ganglion cell layer in the nasal-superior sector, **statistically significant
|
|
GCL+_S
|
72.45 ± 9.19
|
73.24 ± 4.52
|
0.422
|
|
GCL+_Ti
|
72.24 ± 6.78
|
73.82 ± 4.27
|
0.603
|
|
GCL+_Ts
|
72.67 ± 7.38
|
73.08 ± 4.38
|
0.588
|
|
GCL+_I
|
70.83 ± 8.44
|
78.86 ± 4.27
|
0.012
|
|
GCL+_Ni
|
72.35 ± 10.47
|
79.80 ± 5.01
|
< 0.001**
|
|
GCL+_Ns
|
73.62 ± 11.29
|
79.48 ± 4.77
|
0.016
|
|
GCL++_S
|
105.52 ± 10.11
|
109.16 ± 7.05
|
0.034
|
|
GCL++_Ti
|
97.07 ± 8.01
|
98.22 ± 5.16
|
0.212
|
|
GCL++_Ts
|
93.76 ± 8.08
|
96.74 ± 5.67
|
0.024
|
|
GCL++_I
|
100.54 ± 9.85
|
109.52 ± 7.22
|
0.010
|
|
GCL++_Ni
|
113.40 ± 11.95
|
123.12 ± 17.50
|
0.001**
|
|
GCL++_Ns
|
116.95 ± 11.04
|
121.76 ± 7.08
|
0.006
|
Table 4 Evaluation of the mean ChT measurements in the COVID-19 and control groups.
|
ChT Measurements (µm)
|
COVID-19 group (n = 48)
|
Control group (n = 44)
|
p*
|
|
ChT: choroidal thickness, COVID-19: coronavirus disease 2019, *statistical analysis
was calculated by the ANOVA test, **statistically significant
|
|
Subfovea
|
340.02 ± 78.10
|
371.50 ± 86.14
|
0.035
|
|
Temporal_500
|
330.33 ± 79.94
|
368.40 ± 81.97
|
0.002
|
|
Temporal_1500
|
313.90 ± 71.57
|
345.80 ± 81.98
|
0.002
|
|
Nasal_500
|
321.45 ± 74.49
|
356.60 ± 87.95
|
0.002
|
|
Nasal_1500
|
280.90 ± 85.74
|
308.28 ± 85.13
|
0.016
|
The correlations of inflammation markers with the OCT parameters that were different
between COVID-19 and control groups were investigated. The mean initial inflammatory
markers in the
COVID-19 group were correlated with some SS-OCT measurements. The mean fibrinogen
level demonstrated a statistically significant positive correlation with the mean
nasal RNFL thickness
measurement (r = + 0.512, p < 0.001). The mean D-dimer level in the COVID-19 group
resulted in negative significant correlations with the mean GCL+ thickness measurement
in the
nasal-inferior sector (r = − 0.442, p = 0.001). The mean ESR concentration showed
statistically significant positive correlations with mean RNFL thickness measurements
in an overall assessment
(r = + 0.436, p = 0.001). The mean ESR concentration showed a weak negative correlation
with the mean GCL++ thickness measurements in the nasal-inferior (r = + 0.398, p = 0.002)
sector.
Discussion
SS-OCT is a noninvasive tool enabling repeatable and high-resolution images of the
retina and even the choroid, which is a deeper layer. OCT measurements can provide
a comprehensive
evaluation of retinal neurodegeneration, structural changes in the peripapillary
area, macula, choroid, and optic nerve head related to many ocular or systemic disorders.
In this study, SS-OCT
was used to investigate the effect of SARS-CoV-2 neurotropism on the OCT thickness
measurements and retinal neurodegeneration in early post-COVID-19 pediatric patients.
No significant
differences were observed between the mean CMT measurements of the two groups.
Significant RNFL thickening was noted in the nasal quadrant and overall assessment,
significant thinning was
observed in the nasal-inferior GCL sectors, and weak choroidal thinning was observed
in the temporal and nasal choroidal locations of the COVID-19 group. Some significant
correlations were
also found between the mean values of inflammatory markers and SS-OCT measurements.
Symptomatic anterior segment ocular involvement of SARS-CoV-2 has been reported in
both adult and pediatric COVID-19 patients [18], [22]. However, to the best of our knowledge, very limited studies have been reported
regarding OCT analysis of the retina or choroid in pediatric COVID-19 patients. Posterior
segment
findings in adult COVID-19 patients have been documented, such as acute macular
neuroretinopathy papillophlebitis, retinitis, and optic neuritis [23], [24]. In addition, fine cotton wool spots accompanied by retinal microhemorrhages and
focal hyperreflective spots in the GCL and IPL layers of OCT scans have also been
reported in the adult COVID-19 patients [25]. Similarly, a case report also demonstrated a hyperreflective band, sparing the
outer retina, at the levels of GCL and
IPL in an SS-OCT image of an adult COVID-19 patient [26]. No vascular leakage or exudation and no hypo- or hyperautofluorescence were noted
in this hyperreflective
band [26]. A cohort observational study revealed that mean CMT and GCL values were similar
in post-COVID-19 adult patients and healthy controls [27]. Retinal cotton wool spots (9 cases), vitreous fibrillary degeneration (10 cases),
and papillary focal retinal hemorrhage (1 case) were examined in these adult
COVID-19 patients [27]. Macular hole and epiretinal membrane had similar prevalence in both groups [27]. In contrast, it has been also
postulated that these hyperreflective dots could be normal retinal vessels, and
the cotton wool spots could be associated with myelinated nerve fibers or other pathological
conditions [28].
Supporting our results, a cohort study in pediatric COVID-19 patients concluded that
children with recent COVID-19 had RNFL thickening when compared to healthy children
[29]. In contrast to our results, this study reported GCL thickening [29]. Similar to our study, another study showed RNFL thickening and GCL thinning in
adult patients [30]. Moreover, the authors observed that this thickening of the RNFL was more prominent
in the adult COVID-19 cases with cotton wool spots than the
adult COVID-19 patients without cotton wool spots [30]. Similarly, a report concluded thickening of the RNFL in the adult COVID-19 patients,
which might be due to
COVID-19-related hypoxia and inflammation [31]. Another recent study reported that adult COVID-19 patients showed RNFL thickening
in the overall assessment and in
the nasal peripapillary quadrants, which was similar to our results, representing
nasal RNFL thickening [32]. However, in contrast to our results, the authors noted
that adult COVID-19 patients presented GCL thickening in the superior outer, nasal
outer, and inferior outer sectors [32]. Interestingly, adult COVID-19 patients
with anosmia and ageusia demonstrated a thicker peripapillary RNFL and macular
GCL than the patients without these symptoms [32]. In contrast to this study and
previously mentioned reports, a study reported no change in the mean RNFL thickness
measurement of adult COVID-19 patients [33], and another study documented no
differences in the mean RNFL, GCL, and ChT measurements of adult COVID-19 patients
compared to healthy controls [34]. It is warranted to investigate if these RNFL
and GCL thickness alterations are temporary or permanent results of COVID-19.
RNFL thickening in the present study might be assumed by the initial effect of inflammation
in the short-term
period [35]. Unlike RNFL thickening, short-term GCL and weak choroidal thinning in this study
may be explained by earlier neurodegeneration of the ganglion cells in
the GCL than the axonal loss in the RNFL and preceding of retinal neurodegeneration
than the vascular processes [35], [36].
The choroid is a highly vascularized tissue, which makes it more suspectable to inflammation
and ischemia-associated systemic disorders. A reduction in ChT following exercise
might be related
to an exercise-induced decrease in the flow of the internal carotid artery [37]. Regarding weakly significant results of this study, it can be postulated that
temporal and partial nasal choroidal thinning in the pediatric COVID-19 patients
may be related to blood flow reduction due to SARS-CoV-2 caused hypercoagulability
and vasculitis [38].
COVID-19 patients usually demonstrate elevated laboratory abnormalities in fibrinogen,
D-dimer, WBC count, sedimentation, and CRP concentrations [39]. An elevated
D-dimer level can be used as a biomarker for thrombus formation and as an independent
predictor for hospital mortality [40]. A study reported that adult COVID-19
patients with elevated D-dimer concentrations presented with retinal vascular
abnormalities [41]. The results of the present study have shown that pediatric
COVID-19 patients with elevated D-dimer concentrations demonstrated nasal-inferior
GCL+ thinning following the recovery of the SARS-CoV-2 infection. This offers the
hypothesis that COVID-19
might lead to subclinical neurodegenerative alterations at the level of GCL, and
the underlying physiopathology might be due to retinal vascular hemodynamic changes
related to SARS-CoV-2
infection-induced effects and potential microangiopathy and a prothrombotic state.
The correlations of inflammatory markers with altered SS-OCT measurements showed coherent
results with the alterations of thickness measurements representing RNFL thickening
and GCL thinning.
According to the literature review, no studies have been reported about the RNFL
thickness analysis, neurodegenerative alterations in the GCL, or ChT changes in the
early post-COVID-19
pediatric patients. Thus, this study may be among the first reports in the literature
examining these OCT parameter changes associated with the COVID-19 infection in the
pediatric population.
However, the study has some limitations, including a relatively small sample size,
lack of disease severity (none of the patients had a respiratory failure or were intubated),
and short-term
OCT measurements. Regarding these limitations, new studies with larger sample
sizes, the presence of the disease severity, and long-term OCT measurements are warranted
to be conducted in the
future.
In conclusion, the present study compared SS-OCT measurements in early post-COVID-19
children and healthy controls. The outcomes of the study demonstrated retinal neurodegenerative
alterations in the COVID-19 children and some significant differences in SS-OCT
measurements between the pediatric COVID-19 and control groups. The clinical relevance
of this study is that the
neurodegenerative effect of SARS-CoV-2 in the retina and ChT alterations might
be possible in pediatric patients without apparent ocular involvement as well as adult
patients. Nonetheless,
these changes may be secondary to the poor general condition of the affected pediatric
patients, but not directly correlated to the outcomes of COVID-19.
