Reference to the eye being a window into our soul has dated back to the 1st century BC. While this nebulous concept has been difficult to study, we do know that the retina manifests changes in many brain disorders, and as such is a “window into the brain”. This seems logical since the retina is an embryological extension of the CNS and shares anatomical, functional and physiological similarities to the brain itself. With evolving technology, we now have the ability to obtain detailed three-dimensional images from within the retina using optical coherence tomography (OCT).
Wang and colleagues examined whether strokes are associated with retinal nerve fiber layer defects (RNFLDs) using OCT. They studied 154 patients with acute ischemic stroke, and 2890 subjects from a population-based group (Beijing Eye Study) in whom OCTs were performed and history of previous stroke was available. After adjusting for risk factors, they found that acute stroke and history of previous stroke was significantly associated with RNFLDs. Conversely, presence of RNFLDs was also significantly associated with acute or previous stroke.
The authors suggest that RNFLDs be added to list of ophthalmological findings present in stroke patients. Previously, a number of retinal microvascular abnormalities such as arterio-venous nicking and arteriolar thinning have been shown to be associated with stroke and hypertension. However, these findings have also been found in normal subjects. In contrast, RNFLDs seem to have a higher diagnostic specificity although it is not pathognomonic. In addition, the RNFLDs remain a permanent marker on the retina compared to vascular abnormalities that may reverse.
The RNFLDs seen on OCT allows us to visualize these “retinal microinfarcts” that may be a harbinger of eventual cerebral stroke. The detection of these by ophthalmologists should perhaps prompt assessment and optimization of cardiovascular risk factors to prevent further sequellae.