You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: A Review on the Extraction of Quantitative Retinal Microvascular Image Feature 
Chapter Title:  Microaneurysm Detection. 
1. Abstract of Cited Paper (BIB001):  BACKGROUND AND PURPOSE ::: The retinal and cerebral vasculature share similar anatomic, physiological, and embryological characteristics. We reviewed the literature, focusing particularly on recent population-based studies, to examine the relationship between retinal signs and stroke. Summary of Review- Hypertensive retinopathy signs (eg, focal retinal arteriolar narrowing, arterio-venous nicking) were associated with prevalent stroke, incident stroke, and stroke mortality, independent of blood pressure and other cerebrovascular risk factors. Diabetic retinopathy signs (eg, microaneurysms, hard exudates) were similarly associated with incident stroke and stroke mortality. Retinal arteriolar emboli were associated with stroke mortality but not incident stroke. There were fewer studies on the association of other retinal signs such as retinal vein occlusion and age-related macular degeneration with stroke, and the results were less consistent. ::: ::: ::: CONCLUSIONS ::: Many retinal conditions are associated with stroke, reflecting possible concomitant pathophysiological processes affecting both the eye and the brain. However, the incremental value of a retinal examination for prediction of future stroke risk remains to be determined. 
2. Abstract of Cited Paper (BIB002):  Purpose: To examine the relationship between microaneurysm turnover (formation rate), using a new semi-automatic method (MA-Tracker) based on color fundus photographs, and diabetic 
3. Abstract of Cited Paper (BIB003):  BACKGROUND AND PURPOSE ::: Small vessel disease plays a role in cerebral events. We aimed to investigate the prevalence and patterns of retinal microvascular signs (surrogates for cerebral small vessel disease) among patients with transient ischemic attack (TIA) or acute stroke and population control subjects. ::: ::: ::: METHODS ::: Patients with TIA or acute stroke aged ≥49 years admitted to hospitals in Melbourne and Sydney, Australia, were recruited to the Multi-Centre Retina and Stroke Study (n=693, 2005 to 2007). Control subjects were Blue Mountains Eye Study participants aged ≥49 years without TIAs or stroke (n=3384, 1992 to 1994, west of Sydney). TIA, ischemic stroke, or primary intracerebral hemorrhage was classified using standardized neurological assessments, including neuroimaging. Retinal microvascular signs (retinopathy, focal arteriolar narrowing, arteriovenous nicking, enhanced arteriolar light reflex) were assessed from retinal photographs masked to clinical information. ::: ::: ::: RESULTS ::: Patients with TIA or acute stroke were older than control subjects and more likely to have stroke risk factors. After adjustment for study site and known risk factors, all retinal microvascular signs were more common in patients with TIA or acute stroke than in control subjects (OR, 1.9 to 8.7; P<0.001). Patients with TIA and those with ischemic stroke had similar prevalences of nondiabetic retinopathy (26.9% versus 29.5%; OR, 0.8; 95% CI, 0.5 to 1.6), diabetic retinopathy (55.5% versus 50.0%; OR, 1.3; 95% CI, 0.4 to 3.6), focal arteriolar narrowing (15.6% versus 18.4%; OR, 0.8; 95% CI, 0.4 to 1.5), and arteriovenous nicking (23.0% versus 17.8%; OR, 1.4; 95% CI, 0.7 to 2.7). ::: ::: ::: CONCLUSIONS ::: Patients with TIA and acute stroke may share similar risk factors or pathogenic mechanisms. 
4. Abstract of Cited Paper (BIB004):  Microaneurysm in the retina is one of the signs of simple diabetic retinopathy. We have been investigating a computerized method for the detection of microaneurysms on retinal fundus images. In this study, the computerized scheme was developed by using twenty five cases. After image preprocessing, candidate regions for microaneurysms were detected using a double-ring filter. Any potential false positives located in the regions corresponding to blood vessels were removed by automatic extraction of blood vessels from the images. One hundred twenty six image features were determined, and 28 components were selected by using principal component analysis, and the candidate lesions were classified into microaneurysms or false positives using the rule-based method and an artificial neural network. The true positive rate of the proposed method was 68% at 15 false positives per image. 
5. Abstract of Cited Paper (BIB005):  The damage to the retina of the eye caused by high blood pressure is known as hypertensive retinopathy (HR). The advancement in automatic retinal image analysis has made it possible to detect & diagnose this disease at an early stage. To indicate the presence and severity of Hypertensive Retinopathy, Arterio-Venous ratio (AVR) is an important measurement. For the calculation of AVR (the ratio of retinal arterioles to venuoles), classification of vessels into arteries and veins is an essential step. This paper proposes a novel technique for classifying the vessels into arteries and veins. The proposed system uses binary vessel mask and optic disc (OD) center localization to extract Region of Interest (ROI) around OD. Feature extraction modules extract a number of intensity based features followed by classification which classifies vessels as arteries and veins. The features are extracted by focusing on the visual difference between the arteries and veins in different color spaces. The proposed system is tested on a locally gather fundus image dataset. An accuracy of 81.3% is achieved.

Literature Review:
Generally, microaneurysm is a specific small area that is seen in the microvasculature of fundus eye image which looks like a swelled balloon. Microaneurysm is recognized as the biomarker of diabetic retinopathy as well as the presign of ischemic stroke or acute stroke that is generally observed in the fundus retinal images after analyzing the eye images BIB002 BIB004 . Figure 3 shows retinal fundus image with microaneurysm (inside the white square). An automated microaneurysm detection method was investigated in BIB005 which was applied on the 50 training cases from Retinopathy Online Challenge (ROC) dataset and they came out with 45% sensitivity with their proposed method when false positive rate per image was 27. Authors of BIB003 used MA-Tracker, a semiautomated method, to observe the relation between the state of diabetic retinopathy and BIB006 . microaneurysm and they experienced that the formation rate of microaneurysm is a better bioindicator of the development of diabetic retinopathy to clinically significant macular edema (CSME) among the patients of type 2 diabetes with Nonproliferative Diabetic Retinopathy. Authors of BIB001 developed an automated algorithm that can count the microaneurysm and detect the turnover of microaneurysm from a digital Fluorescein angiogram repeatedly which dealt with 64 images of diabetes patient and they observed that this algorithm showed 82% sensitivity along with 2.0 false positive rate per image.