OSLI Retina

May 2019

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May 2019 · Vol. 50, No. 5 269 Practical Retina Incorporating current trials and technology into clinical practice Is OCT Angiography Useful in Neurodegenerative Diseases? by Dilraj S. Grewal, MD; and Sharon Fekrat, MD Marcus Tullius Cicero, considered one of Rome's greatest orators and philoso- phers, was quoted as saying, "Ut imago est animi voltus sic indices oculi." To paraphrase, we ar- rive at the oft-used adage, "The eyes are the window to the soul." A more appropriate state- ment, given today's developments in optical coherence imaging technology, might be, "The eyes are the window to the brain." The retina is the only directly observ- able extension of the brain. The retina and brain share common embryologic origins, as well as many other molecu- lar and cellular similarities. Not surpris- ingly, neurodegenerative disorders that affect the brain on a cellular level may be evidenced in the retina. Since optical coherence tomography (OCT) provides in vivo cellular imaging on a near histo- logic scale with precision at the level of microns, the retina can act as a biomark- er for central nervous system disease. A reliable, precise, and easily accessible biomarker for neurodegenerative dis- eases is crucial to identify in order to diagnose and monitor patients, and also to help possibly develop new therapies to treat these devastating diseases. In this installment of Practical Reti- na, Dilraj S. Grewal, MD, and Sharon Fekrat, MD, both of Duke Eye Center, provide a timely update on the use of OCT imaging in the detection of neu- rodegenerative disease, including Al- zheimer's, dementia, and Parkinson's disease. Drs. Grewal and Fekrat sum- marize their cutting-edge research eval- uating the use of OCT angiography for detecting retinal microvascular changes in neurodegenerative disease. With the aging of the population and the rapid increase in prevalence of neurodegen- erative disease, this area of inquiry is gaining increasing importance in the field of retina. There is expected to be a considerable increase in the incidence of neurodegenerative diseases such as mild cognitive impairment (MCI), Alzheimer's disease (AD), and Parkinson's disease (PD). It is estimated that one-third of all people born in recent years are expected to develop some form of dementia in their lifetime. 1 Alzheimer's clinical trials thus far have failed to reach primary endpoints, and the clinical and research community recognizes that a better understanding of the pathophysiology and treating at earlier stages of these diseases are the roads forward for effective therapeutic intervention. A robust, relatively low-cost, and patient-friendly biomarker for early diagnosis of neurodegenerative diseases, perhaps even before clinical symptomatology, is therefore currently a large unmet need. AD is characterized by the progressive accumulation of extracellular amyloid beta (Aβ) plaques and intracellular neurofibrillary tangles in the brain as well as altered levels of Aβ and tau in the cerebro- spinal fluid. The retina is embryologically derived from the neural tube and is a uniquely accessible, noninvasive diag- nostic target for neurodegenerative diseases. This led to con- siderable worldwide interest in the use of optical coherence tomography (OCT) for detection of retinal structural changes in AD, where thinning in the retinal nerve fiber layer (RNFL) formed by axons of the retinal ganglion cells has been dem- onstrated both histopathologically 2 and on OCT, 3 as has cho- roidal thinning. 4 Herein, we discuss the utility of OCT angiography, which has very recently shown promise to detect microvasculature changes in the retina in neurodegenerative diseases, as well as the current limitations of OCTA technology as a diagnostic tool in these diseases. Using OCTA, Bulut et al. showed that the superficial capil- lary plexus (SCP) vessel density (VD) was lower in AD compared Dilraj S. Grewal Sharon Fekrat doi: 10.3928/23258160-20190503-02 Howard F. Fine Practical Retina Co-Editor

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