Eye is the Window to the Brain Pathology
Department of Ophthalmology, Stanford University, School of Medicine, Stanford, CA, USA
*Corresponding author: Varun Kumar, Department of Ophthalmology, Stanford University, School of Medicine, Stanford, CA, USA, Tel: +1 2047871927; E-mail: firstname.lastname@example.org
Citation: Kumar V (2017) Eye is the Window to the Brain Pathology. Curr Adv Ophthalmol 2017: 3-4. doi:https://doi.org/10.29199/CAOP.101013
Received: 25 September, 2017; Accepted: 31 October, 2017; Published: 15 November, 2017
In many neurological diseases, retina is affected leading to partial or complete vision loss, which further depends upon the severity of the disease. For example, majority of the stroke victims suffer vision loss due to stroke-induced retinal damage [1,2]. Similarly, there is an aggregation of toxic huntingtin protein , intra retinal amyloid deposition , and loss of retinal dopaminergic neurons  in mouse model of Huntington, Alzheimer and Parkinson’s disease respectively. These studies strongly suggest the association between brain and the eye. However, questions remain how important is the pathophysiological responses of the retina of the eye in understanding these neurological diseases? This has not been well investigated. Moreover, why eye is the mirror/window to the brain pathology? Part of the reason is the retina being a structure of the brain, which projects out of the diencephalon, have similar embryonic origin as brain, shares similar brain vasculature, blood barriers as well as pathophysiology. Moreover, earlier changes necessary to understand the pathophysiology of specific neurological diseases is easily demonstrated in the retina of the eye as described above.
Understanding the metabolic changes in the retina can be used not only as a biomarker for eye diseases but some prominent fatal diseases as well. For example, detection of homocysteine in the retina is a biomarker for age-related macular degeneration  but also, for cardiac diseases . Proteomic analysis of the ocular fluid such as vitreous humor has provided exciting results for biomarkers to be used for detection or progression of many neurodegenerative diseases such as Alzheimer’s disease , glaucoma  etc. However, if we further understand the retina, questions remain how accurately earlier retinal changes can be used as biomarkers for predicting different neurological diseases? This is a very complex question and hard to answer because different diseases might have mixed effects on the retina. At this stage, it will be difficult to differentiate specific diseases associated changes in the retina.
However, there are some neurological diseases such as stroke, which greatly co-relates with retinal changes. For example, De Silva et al., demonstrated that patients with severe focal retinal arteriolar narrowing were highly susceptible to recurrent cerebrovascular events (stroke) as compared to those without arteriolar narrowing . Moreover, retinal examination can also be useful for stroke risk stratification as well. For example, McGeechan et al., demonstrated that wider retinal venular caliber increases the risk of stroke in humans whereas the caliber of retinal arterioles was not associated with stroke . They further put emphasis on considering inclusion of retinal venular caliber in prediction models containing stroke risk factors, which can reassign intermediate risk stroke category to lower risk. All the above studies strongly suggest that it will be worth understanding and imaging retina for early detection of pathophysiological changes after stroke. Similarly, Alzheimer’s disease is associated with significant loss of retinal ganglion cells, thinning of the retinal nerve fiber layer as well as optic nerve degeneration . Using laser Doppler imaging device, Berisha et al., demonstrated a significant narrowing of the retinal veins and reduced venous blood flow in Alzheimer’s disease compared to healthy people . Therefore, retinal vascular abnormality can be used as biomarker for Alzheimer’s disease. As evident, Alzheimer’s disease is characterized by b amyloid deposition. Using hyperspectral imaging, b amyloid having a unique hyperspectral signature, can be easily visualized in the retina, which can predict the occurrence of Alzheimer’s disease .
In conclusion, eye is one such organ of brain, which is easily accessible and shares similar vasculature, anatomy and physiology to the brain. Therefore, therapeutics effective in other neurological diseases might be used to reduce retinal damage and vice versa. Moreover, vision loss after many neurological diseases should not be neglected. In fact, the molecular changes in the retina can be used as a biomarker of neurological diseases such as Alzheimer’s and stroke, if tested appropriately.