The potential for evaluating the effects of intensified antithrombotic therapy using retinal optical coherence tomography angiography
Section snippets
Background
Oral anticoagulants are widely used in the treatment and prevention of both venous and arterial thromboembolism. They are classified into vitamin K anticoagulants (VKAs) and non-vitamin K antagonist oral anticoagulants (NOACs). Warfarin was approved by the United States Food and Drug Administration [US FDA] in 1954 [1]. It acts by inhibiting the synthesis of vitamin K-dependent clotting factors [Factors II, VII, IX, and X] via inhibition of the C1 subunit of vitamin K epoxide reductase [VKORC1]
Monitoring of oral anticoagulants
The main advantage of NOACs over VKAs is the absence of the need for continuous monitoring. For warfarin, there is a need to maintain the patient within a therapeutic window by dose adjustment. NOACs have wide therapeutic window due to their predictable pharmacokinetics and pharmacodynamics, a rapid onset and offset of action, and a short half-life.
Currently, there are few haematological methods to monitor the activity of oral anticoagulants. Activated partial thromboplastin time [aPTT] and
Optical coherence tomography [OCT] and optical coherence tomography angiography [OCTA]
The use of OCT for the human eye was first presented at the International Conference of Optics in Life Sciences in 1990 [8]. Since then, the technology has evolved tremendously. The current OCT machines are able to provide resolution details of retinal images in the order of few micrometers.
OCTA is a non-invasive imaging technique that provides angiographic information of the retinal blood vessels. Gao et al. and de Carlo et al. have discussed extensively on the history and principles of OCTA
Case study
A 75 year old gentleman with chronic atrial fibrillation was on maintenance therapy apixaban 5 mg twice daily. He was admitted for left acute brachial artery thrombosis. The condition was successfully treated with intravenous alteplase, which was then continued with subcutaneous enoxaparin 50 mg twice daily. While on the above treatment, he experienced amaurosis fugax. Retinal emboli were detected (Fig. 1). OCTA showed a poorly defined parafoveal capillary network (Fig. 2). The patient was
Discussion
Routine coagulation profile [PT/INR/aPPT] was performed but was of limited use as the patient was treated with NOACs and anti-platelet therapy. In this particular situation, OCTA provided a very useful guide to the clinicians as to adjustment of the dosage of these medications. A well-defined parafoveal capillary network (Fig. 4) after treatment can be translated clinically into a significant improvement of retinal blood flow and more importantly therapeutic efficacy.
The quantification of flow
Future research
Further studies using double-blinded randomised controlled trials are needed to confirm the above observation. Besides vessel density and flow index, researchers should develop new or novel parameters to measure the effects of anticoagulants on the parafoveal capillary network.
Conclusion
Retinal OCTA has great potential. Further research and development will extend its use beyond the realm of ophthalmology.
Conflict of interest statement
The author declared that he has no competing interests.
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