The retina is a light sensitivepart of the eye that covers about 65 percent of its interior surface andcontains photosensitive rod and cone cells efficient to convert incident lightenergy into electrical signals that are carried to brain by optic nerve (1, 2, 3, 4, 5).Macula is an oval shaped pigmented area near the centre of retina and it has asmall depression, about 1.5 mm wide called fovea or fovea centralis,responsible for maximum visual acuity. The foveal region (approximately 500 µm) is conecell enriched and it is the only blood vessel and capillary free zone in humanbody (6, 7, 8, 9).
Two arterial circulations are responsible for retinalnourishment (i) the first branch of the internal carotid artery on each side;(ii) posterior ciliary artery nourishes retinal outer plexiform layer, outernuclear layers, photoreceptors, and the retinal pigment epithelium (10). The central retinalarterial circulation emanating from posterior ciliary artery has four mainbranches corresponding to4 quadrants of the eyeball considering optic disk as reference. Retinalvasculature is very unique (11) and understanding its arterial attributes mayprovide important information in the context of elucidating pathobiologicalfeatures for ocular diseases viz.diabetic retinopathy (DR), hypertensive retinopathy, retinal vein occlusion(RVO), central retinal artery occlusion (CRAO) (12).
DiabeticRetinopathy is currently one of the most prevalent health diseases worldwidewith an incidence of 5% and 60% uncertainty in clinical diagnosis and it has aconnotation with prolonged hyperglycemia and eventually leads to blindness. Itis the sixth major cause of blindness in India and fifth worldwide (13, 14). Diabetic complications arebroadly classified as micro-vascular which include neuropathy, nephropathy, andretinopathy or macro-vascular including cardiovascular and peripheral vasculardisease. Most often,DR is asymptomatic until the damage to eyes is severe.
So, It’s challenging totake a proper dignostic measure before it approaches toward proliferative condition or permanant vision loss. Indiabetic patients, progressive micro vascular closures leads to ischemia andtissue hypoxia which triggers final retinal neo-vascularization. The symptom ofDR includes, (i) blurred vision and slow vision loss over time, (ii) floaters, (iii) shadows ormissing areas of vision, (iv) trouble in night vision (v) formation ofmicroanurysms (Small bulging of blood vessels) (vi) leaky deposits (soft andhard exudates) and (vii) deposition oflipofuscin granules in RPE membrane. There are twobroad stages of DR: Non-proliferative Diabetic Retinopathy (NPDR),Proliferative Diabetic Retinopathy (PDR).Klienet al. in 2003 devised a new method for describing distributions retinalvascular features and their correlation in people with type 1 diabetes (15). Tortuosity is among thefirst variations in the retinal vessel network to appear in retinopathies underpathologies like hypertension, diabetes (16).
In thiswork we extracted features (i.e. vascular bifurcation pattern, bifurcationangle, tortuosity and curvature) from the colour fundus images to highlightarteriolar abnormalities observed in diabetes affected individuals throughsemi-automated processes. Parallelly, we also extracted venular thickness and intensityfeatures in discriminating DR from all study groups.DR associated retinalneurodegeneration occurs before any microcirculatory abnormalities can bedetected in ophthalmoscopic examination. In other words, retinalneurodegeneration is an early event in the pathogenesis of DR which antedatesand contributes in the microcirculatory anomalies that occur in DR (17).Therefore, development of an integrated assessment method for detectingneuroretinal degeneration is necessary using quantitative imaging biomarkersfor early diagnosis of DR.
The conventional imaging diagnostictechniques available for the detection of diabetic retinopathy are colorfundoscopy, fluorescence angiography (FA) and Optical Coherence Tomography(OCT) (18). Fundoscopy or color fundus retinal photography uses a fundus camerato grab color images of the interior surface of the eye for documenting thepresence of disorders and monitor their change over time (19). A fluoresceinangiography is a widely used medical procedure in which a fluorescent dye isinjected into the bloodstream. The dye highlights the ocular blood vessels inthe back of the eye so they can be photographed (20).
OCT delivers real-time,high-resolution, sub-surface images of up to 2 mm tissue depth (21). OCT ismainly used to monitor morphological changes in the retina over time, which hasturned out to be appreciable, particularly due to the latest perception of”disease modulation” associated with new treatment modalities. ‘Lucidity’ isone of the optical intensity descriptors used for OCT images. It tends to varywith different regions of layered body structures like skin wounds, cancerouslesions and specific retinal layers of the retina (e.g. Ganglion Cell layer(GCL) and Inner Plexiform layer (IPL)).
Specially, lucidity of the retinallayers tends to vary simultaneously with the thinning of brain tissues andconsequent atrophy. Recently Quantitative Imaging Biomarkers (QIBs) have becomewidely accepted as well-defined “image characteristics to objectively measure andassess the indicators for normal physiological processes, pathogenic progressionsor responses to therapeutic interferences (22). A recent study has implementedautomated classification of early neurodegenerative changes in DR induced mousemodel using textural features extracted from OCT (23). The concepts of QIBsfurther aided in assuming that, if biochemical and spectral characterization ofthe serum samples can be performed, then selected OCT features of retinallayers could be correlated to justify extracted QIBs. Support Vector Machine(SVM) was used here for disease classification, since it can classify thediseases with high prognostic accuracy and speed, as shown in a previous study(24). Gold nanoparticles have a number of physical properties that make them attractivechoice for medical applications.
It has significant implications in biomedical fields, but currentlythese multifunctional gold nanoparticles are used for various methods, such asconcurrent diagnosis and therapy or so-called theranostics (25, 26). A large number of reports areavailable in the literature in which the spectral change in plasmon band ofgold nanoparticle in presence of biomolecules is used as a diagnostic tool (27).Here we exploit the change in self similarity in the fractal structure, formedby gold nanoparticles in presence of serum samples, under study, todifferentiate the NOM, DM and DR.