The present study is an exploratory study involving human participants, and the research was performed in accordance with the Declaration of Helsinki and was approved by the All India Institute of Medical Sciences Institutional Ethics Committee (IECPG -554/26.09.2019, RT -02/28.11.2019), New Delhi, India. The authors confirm that informed consent was obtained from all subjects included in this exploratory study and can be provided on reasonable request to the corresponding author.
This exploratory study was conducted between November 2019 and May 2021 in the Department of Neurology, Department of Neuroradiology and Department of Ophthalmology, All India Institute of Medical Sciences, New Delhi, a tertiary care hospital in India.
STUDY DESIGN AND PARTICIPANTS
Adult patients more than 18 years of age and diagnosed with symptomatic acute ischemic stroke (AIS) due to ECAD, were eligible for enrolment. AIS was classified as per Trial of Org 10172 in Acute Stroke Treatment (TOAST).9 Patients with any other cerebro-vascular co-morbidities apart from ECAD ischemic stroke , those with visual loss or visual impairment, or media opacities preventing high-quality imaging and hypertensive retinopathy more than Grade 2, and terminally ill patients on life support measures were excluded. Details of inclusion and exclusion criteria are provided in supplementary appendix.
Risk factor matched viz diabetic, hypertensive, dyslipidaemic subjects without ocular disease of any sort nor any history of previous cerebro-vascular disease were included as controls.
Visual impairment is often defined as a best corrected visual acuity of worse than either 6/12 or 6/18.10 Accordingly, both in the cases and control arms, patients with best corrected visual acuity (BCVA) worse than 6/18 were excluded from the study.
- Correlation between OCTA findings at three to six weeks and functional outcome (mRS) at three months of onset of acute ischemic stroke due to Extracranial Carotid Artery Atherosclerotic Disease (ECAD).
- Changes in retinal and optic nerve head (ONH) perfusion using OCTA in patients with ischemic stroke due to extracranial internal carotid artery atherosclerotic disease at three to six weeks of onset of stroke and at three months onset of stroke.
- Correlation between the retinal and ONH perfusion parameters obtained using OCTA and NIHSS score at the time of onset of stroke, mRS at the time of discharge, mRS at 3 months of stroke onset and change in mRS.
Screening of patients was done during hospitalization and outpatient visits. Eligible patients were enrolled into this exploratory study and their demographic details, vitals, along with the day of onset of stroke, type of stroke, CTA or MRA findings, were noted and a mRS (modified Rankin Score) at the time discharge. The criteria of modified Rankin Score (mRS) used is provided in the Supplementary appendix. The degree of carotid artery stenosis was assessed by two independent neuro-radiologists (M.K.N. and A.G.), and any disparity in results between them was resolved by A.K.P.
Sample size estimation
Satterthwaite's t test assuming unequal variances was used for sample size estimation and considering 10% loss to follow-up, a total of 44 cases and 44 controls were planned for enrolment.
The patients enrolled as cases underwent detailed ophthalmological and OCTA examination at 3-6 weeks of stroke onset using Spectral Domain Cirrus HD-OCT Model 5000 (Carl Zeiss, Meditec, Inc, 5160 Hacienda Drive, Dublin, CA 94568 USA) (Representative images acquired from a case shown in Figure S1). Thereafter, the 3-month functional outcome assessment was carried out by assessing the mRS by telephonic conversation which is validated and has been shown to have a good agreement with face-to-face assessment.11
Initially Doppler ultrasound of the bilateral carotid arteries was performed on healthy subjects who were screened for enrolment as control subject. If no stenosis was detected, the subject underwent detailed ophthalmological evaluation and if found eligible, OCTA examination was performed on him by the same ophthalmologist using the same device and enrolled in this exploratory study (Representative images acquired from a control shown in Figure S2).
All the scans of cases and controls were reviewed by two ophthalmologists (R.C. and S.P.A.) and non-qualified images were excluded. The vessel perfusion densities and ONH perfusion data from qualified images were included in the analysis. The detailed methodology of obtaining the OCTA images and the analysis of Deep macula OCTA scans using “ImageJ” software is mentioned in details in the supplementary appendix. 12
Literature search revealed that there is lack of normative data for OCTA findings in the Indian population. Moreover, since OCTA has recently been introduced into commercial use, so the protocols required for proper selection of OCTA images are also not defined yet. Also, the findings differ as per the technology used to perform OCTA. In the present study analysis of OCTA images was done by using the fovea (Central), parafovea (inner) and whole en face (full), and also the total vessel density at the level of superficial retina and total perfusion density were also analyzed.7,13,14,15
The normative data for this study was derived from the risk factors matched controls, using the mean and standard deviation (SD) of the OCTA parameters of the control subjects. The normal range thus obtained was then compared with those of the same parameters of the cases and labelled as normal if the value is was within range or abnormal if the value was outside of this normative range.13 Thereafter the proportion of patients with very good outcome (defined as patients with mRS 0-1 at three months of stroke onset) or poor outcome (defined as mRS 2-6 at three months of stroke onset) were arranged as per the normality of OCTA parameter and then analyzed.
The eye on the same side as stroke was considered as the “Ipsilateral eye” and the eye opposite to that of side of stroke was considered as the “contralateral eye.”
DATA ANALYSIS AND STATISTICS
Data management was performed using Microsoft Excel 2007 and the statistical analysis was conducted using STATA Version 13 and IBM SPSS® Statistics 22 for Windows (IBM Corporation, Somers, NY, USA). The normality of the data distribution was tested using the Kolmogorov–Smirnov test. After confirmation of the normality, the data was presented either as mean ± SD (if normally distributed) or median and interquartile range (IQR) ( if non-normally distributed). Changes at follow-up compared with baseline were assessed using paired sample t-tests or Wilcoxon signed rank test. The two treatment groups were compared using independent Student’s t-tests for normally distributed data otherwise Mann Witney U test was applied. Independent Spearman correlation was used to assess the correlation between OCT-A changes at 3 to 6 weeks and functional outcome (mRS) at 3 months, mRS at discharge, change in mRS and baseline NIHSS. Fisher Exact Test was used. All inferential statistics was intended to be exploratory, not confirmatory, and was interpreted accordingly. Statistical significance level was set to 0.05.