This thesis explores how retinal Optical Coherence Tomography Angiography (OCTA) can advance our understanding of the systemic effect of COVID-19. Over two years since the first case was detected in the UK, researchers are still discovering the long-term effect of the virus. There are more than 80 NHS-run post-COVID-19 clinics in the UK, and around 1 in 10 who test positive for COVID-19 will develop post-covid-19 syndrome (PCS) or 'long COVID'. These patients suffer ongoing breathlessness, fatigue, memory, and concentration problems, amongst other life-impacting symptoms. This has severely impacted lives, with many out of work and their activities of daily living majorly affected. It has been postulated that many of the systemic effects of COVID-19 are associated with microvasculature damage. The eye provides us with a window into this microvasculature. Via retinal OCTA, we have a non-invasive opportunity to visualise the circulation in vivo - in many systemic disorders such as diabetes, hypertension and other cardiovascular; abnormalities are visible in retinal tissue. While many studies incorporating OCTA have found retinal microvascular changes in the acute phases or just after the acute phase of patients hospitalised with COVID-19, few examine longer-term effects in different patient sub-groups. In particular, the existence or absence of microvascular disease in patients with long COVID-19 or those with severe COVID-19 disease could be of substantial relevance. There is currently no standard test for PCS. OCTA is a rapid, non-invasive imaging device that could act as a non-invasive biomarker in assessing microvascular dysfunction associated with COVID-19. This, in turn, could aid physicians in diagnosing and thus personalising treatment of this often-disabling condition. Alternatively, if there are no retinal microvascular changes, sufferers could be reassured that changes do not persist in the long-term post-COVID-19. It could also help our understanding of the disease as its long-term effect is yet unknown. In this study, we clinically evaluate participant OCTA scans and apply in-house designed image processing and analysis techniques to scrutinise the images further. The software for this automated analysis had been previously validated and published to detect subclinical microvascular changes in OCT-A in systemic diseases such as diabetes but only on a relatively small 4x4mm scan. For this study, we analyse 4x4 images and each participant's wider, 10x10mm OCTA images. We present evidence for the validity and reliability of these algorithms. Unfortunately, the interpretation of OCTA imaging is not without limitations. Therefore, our in-house image-analysis programme addresses OCTA limitations such as image artefacts. We apply these algorithms to key groups of patients who have had COVID-19. Firstly, patients suffering from PCS. Secondly, patients post hospitalisation for COVID-19 with no underlying comorbidities, and thirdly patients post-COVID-19 infection who did have comorbidities. Our findings were that no changes were seen in the PCS cohort or the posthospitalisation with no co-morbidity's cohort. There were changes seen in the group postCOVID-19 infection who did have co-morbidities. Despite its limitations, our study is reassuring for those suffering ongoing symptoms post COVID-19. Studies suggest that OCTA parameters may reflect the microvascular changes occurring elsewhere in less-accessible organs such as the lungs or the kidneys. The virus does not appear to cause retinal microvascular changes in the long term. Therefore, this study can offer reassurance to sufferers of PCS.
|Date of Award
|31 Dec 2022
- The University of Manchester
|Jane Ashworth (Supervisor) & Tariq Aslam (Supervisor)