A comparative study between fundus imaging and optical coherence tomography for the early diagnosis of Alzheimer’s disease

Alzheimer’s disease (AD) is a progressive disorder of the brain as well as retina that causes cognitive impairment. This leads to permanent memory loss and disrupt the daily routine activities [16]. The two important hallmarks of AD are amyloid beta protein, extracellular and tau protein, intracellular that accumulate near the neurons which blocks the signals from brain to neuron and viceversa [7]. These two proteins affects the entorhinal cortex and hippocampal regions as well as the internal layers of the retina that leads to change or degradation in cerebrospinal fluid (CSF) levels [8]. There are different types of tests for diagnosing AD. Some of them are illustrated below. Initially we can screen AD with some neuropsychological tests like Mini Mental State Examination, memory clock drawing etc to find the memory impairment [9]. The most important imaging modalities which are used for diagnosing AD are Computed tomography (CT) scan, magnetic resonance imaging (MRI), Positron Emission Tomograhy (PET) and Single Photon Emission CT Scanning (SPECT), in which CT and MRI are non invasive. Although powerful invasive techniques such as PET and SPECT can be used for early diagnosis, but it may results some side effects also. These modalities will help to figure out irregularities in the brain structure and brain tissues due to normal ageing or other previous accidents or diseases in connection with brain such as tumor, hydrocephalus, history of strokes, and white matter disease which are the reason for memory impairment. MRI and CT are non invasive, the predecessor is more sensitive than CT to find out irregularities in the brain region [10-13]. Cerebrospinal fluid (CSF) examination which was done earlier is now not a part of the routine examination of AD [14]. We know that the dementia of Alzheimer’s type is a brain related disease, but investigations and reports made on AD shows that there is evidence of visual problems such as reading, finding or seeing or moving objects and difficulty in recognizing color features [15]. The study on AD shows that there is visual cortex defects. But the recently made investigations show that anterior visual pathways, degeneration of nerves in optics and retinal ganglion cells loss are also connected with AD [16,17]. The main reason in the visual disabilities is due to the deposits of amyloid beta (Aß) protein and acetylcholine has been found in the retina [16,18]. The starting of AD pathology may occur in the visual association area [19]. AD shows loss of visual properties early in the disease and functional losses correlate with cognitive losses. The losses of visual function in AD have different aspects that are usual with neuronal losses affecting the eye, such as age-related macular degeneration and glaucoma [20]. In normal cases without memory impairment there was an absence of such pathology in the hippocampus area where the symptoms of AD begins, which processes memory. The loss of visual function other than acuteness may be the initial significant indication of AD. Age-related macular degeneration degrades all frequencies of contrast sensitivity; demonstrate color disorders across all wavelengths, and decrease in foveal detection of motion [21-23]. The researchers are stating that instead of starting in the brain’s regions that process memory, such as the hippocampus, AD may actually start in the portion of the brain that integrates Volume 1 Issue 6 2017