Segmentation of Foveal Avascular Zone in Colour Fundus Images Based on Retinal Capillary Endpoints Detection

Diabetic retinopathy (DR) is one of the diabetes complications affecting the retina. It can be detected by investigating foveal avascular zone (FAZ) since there is a correlation between enlargement of FAZ and DR progression. In this research work, a method of FAZ detection is developed. Firstly, pre-processing is conducted to enhance and improve image quality. Afterwards, segmentation of FAZ is conducted using matched filter and local entropy thresholding to extract retinal vessels. FAZ area segmentation is done based on retinal capillary endpoints detection. This work is validated using retinal fundus images from Messidor and DRIVE databases. The result of FAZ segmentation has been verified by measuring the correlation coefficient of determined FAZ areas between the capillary endpoints of the proposed method and that of detected by ophthalmologists. The correlation values achieved are 0.912 and 0.802 for two aforementioned databases, respectively. These results indicate that the proposed method has successfully detected and segmented FAZ area, due to the highly significant correlation coefficient obtained between the proposed FAZ and that of the ophthalmologists

Structure function correlation in retinal ischaemia and macular oedema

Diabetic retinopathy (DR) and retinal vein occlusion (RVO) are the two most prevalent retinal vascular diseases which affect macular perfusion, altering visual function. Firstly, healthy eyes [eyes with no structural pathology identified on Optical coherence tomography (OCT) and OCT angiogram (OCTA)] were assessed for the foveal parameters to identify the reliability of structural markers before studying pathological changes. The white ethnic group had a smaller foveal avascular zone area and perimeter compared to the Asian and Afro-Caribbean (AFC) ethnic groups, respectively in our study. Retinal capillary loss is an irreversible complication of DR. We analysed patients with advanced DR and found higher parafoveal capillary vessel density (VD) at the level of superficial capillary plexus (SCP) was associated with better best corrected visual acuity (BCVA) and low luminance visual acuity (LLVA) while for radial peripapillary capillary plexus (RPCP) only VD of temporal sector was the predictor of LLVA. Disorganization of the retinal inner layers (DRIL), a potential biomarker of focal ischaemia affects LLVA more than BCVA. In a final adjusted model, the SCP density of the parafoveal area was the only parameter that most accurately ascertained BCVA and LLVA. In the next section of this thesis, functional assessment of the effect of treatment (anti-vascular endothelial growth factor [VEGF] versus laser) on active proliferative diabetic retinopathy (PDR) showed BCVA and LLVA are well correlated before and after treatment. Our findings suggest ten letters difference between BCVA-LLVA; however, this difference becomes more remarkable for a lower level of BCVA, suggesting more advanced ischaemia affects LLVA aggressively. Next analysing, OCTA changes at the macula for PDR, and central retinal vein occlusion (CRVO), I found capillary loss was more pronounced in PDR than CRVO. The final chapter of the thesis looked at the baseline demographic and morphological changes in CRVO patients to predict vision outcomes. Baseline retinal central subfield thickness (CST) up to 900 microns can be expected to improve by 2 or more lines on Early Treatment Diabetic Retinopathy Study (ETDRS) chart or achieve >70 letters visual acuity (VA) at 100 weeks of follow up and treatment. Age of the patient and vision at the time of diagnosis of CRVO and intact ellipsoid zone can predict BCVA at 100 weeks following initiation of treatment in CRVO eyes

Glaucomatous vertical vessel density asymmetry of the temporal raphe detected with optical coherence tomography angiography.

Changes in retinal vasculature and ocular circulation may play an important role in the glaucoma development and progression. We evaluated the vertical asymmetry across the temporal raphe of the deep retinal layer vessel density, using swept-source optical coherence tomography angiography (SS-OCTA), and its relationship with the central visual field (VF) loss. Thirty-four eyes of 27 patients with open-angle glaucoma were included. SS-OCTA macular scanning was performed within a 3 × 3 mm (300 × 300 pixels) volume, centred on the fovea. The relationships between the vertical asymmetrical deep retinal vessel density reduction (ADRVD) across the temporal raphe and various ocular parameters were analysed. Twenty-two glaucomatous eyes with ADRVDs had central VF loss. Contrarily, ADRVDs were not found in any of the 12 eyes without central VF loss. Thirteen eyes (59.1%) with central VF loss had ADRVDs topographically corresponding to the central VF loss and macular ganglion cell complex thinning. The glaucomatous eyes with ADRVDs exhibited inferior rather than superior central VF loss (P = 0.032). Thus, ADRVD specifically indicates the glaucomatous central visual loss. Further analysis of ADRVD may improve our understanding on glaucoma pathogenesis, offering new treatment insights

NON-INVASIVE IMAGE ENHANCEMENT OF COLOUR RETINAL FUNDUS IMAGES FOR A COMPUTERISED DIABETIC RETINOPATHY MONITORING AND GRADING SYSTEM

Diabetic Retinopathy (DR) is a sight threatening complication due to diabetes mellitus affecting the retina. The pathologies of DR can be monitored by analysing colour fundus images. However, the low and varied contrast between retinal vessels and the background in colour fundus images remains an impediment to visual analysis in particular in analysing tiny retinal vessels and capillary networks. To circumvent this problem, fundus fluorescein angiography (FF A) that improves the image contrast is used. Unfortunately, it is an invasive procedure (injection of contrast dyes) that leads to other physiological problems and in the worst case may cause death. The objective of this research is to develop a non-invasive digital Image enhancement scheme that can overcome the problem of the varied and low contrast colour fundus images in order that the contrast produced is comparable to the invasive fluorescein method, and without introducing noise or artefacts. The developed image enhancement algorithm (called RETICA) is incorporated into a newly developed computerised DR system (called RETINO) that is capable to monitor and grade DR severity using colour fundus images. RETINO grades DR severity into five stages, namely No DR, Mild Non Proliferative DR (NPDR), Moderate NPDR, Severe NPDR and Proliferative DR (PDR) by enhancing the quality of digital colour fundus image using RETICA in the macular region and analysing the enlargement of the foveal avascular zone (F AZ), a region devoid of retinal vessels in the macular region. The importance of this research is to improve image quality in order to increase the accuracy, sensitivity and specificity of DR diagnosis, and to enable DR grading through either direct observation or computer assisted diagnosis system

NON-INVASIVE IMAGE DENOISING AND CONTRAST ENHANCEMENT TECHNIQUES FOR RETINAL FUNDUS IMAGES

The analysis of retinal vasculature in digital fundus images is important for diagnosing eye related diseases. However, digital colour fundus images suffer from low and varied contrast, and are also affected by noise, requiring the use of fundus angiogram modality. The Fundus Fluorescein Angiogram (FFA) modality gives 5 to 6 time’s higher contrast. However, FFA is an invasive method that requires contrast agents to be injected and this can lead other physiological problems. A reported digital image enhancement technique named RETICA that combines Retinex and ICA (Independent Component Analysis) techniques, reduces varied contrast, and enhances the low contrast blood vessels of model fundus images

To Investigate the Foveal Avascular Zone in a Young Healthy Population Using Optical Coherence Tomography Angiography

Introduction/Aims Inflammatory diseases such as diabetes, glaucoma and age-related macular degeneration (AMD) can alter the size and shape of the foveal avascular zone (FAZ). Macular pigment (MP), a powerful antioxidant, located at the macula can protect the eye from oxidative stress damage. This study aims to investigate possible factors affecting the FAZ, such as vessel perfusion and overweight/obesity, in association with MP status in a young, healthy population. Normative values for FAZ size/shape and vascularity will also be proposed. Methods One hundred and fifty-four subjects aged 18-35 years old were recruited. Superficial FAZ area, diameter, ganglion cell layer, central macular thickness (CMT), vascular perfusion and density were measured by Optical Coherence Tomography Angiography (OCTA). FAZ area/vascularity were assessed in relation to body mass index (BMI), trunk fat % and macular pigment optical density (MPOD). Results Mean FAZ area was 0.22±0.07millimetres squared (mm2). Reduced vessel perfusion central (≤ 24%), low MPOD (≤ 0.4optical density units (OD)) and high BMI (\u3e 25kilograms (kg)/metre (m2)) were associated with a larger FAZ area on multivariate analysis. Age, vessel perfusion and CMT were all negative predictors of FAZ area. Trunk fat % was a positive predictor of FAZ area (p = 0.03) while BMI was positively correlated with FAZ area, (Pearson’s r = 0.18, p = 0.03). Conclusions Optical Coherence Tomography Angiography has potential as a screening tool aiding in the earlier detection and monitoring of eye diseases associated with oxidative stress i.e., hypertensive and diabetic retinopathy (DR), glaucoma and AMD. FAZ size in association with MPOD assessment, may be useful in detecting and advising patients at risk of retinal oxidative stress damage

Correcting magnification error in foveal avascular zone area measurements of optical coherence tomography angiography images with estimated axial length

Background To generate and validate a method to estimate axial length estimated (ALest) from spherical equivalent (SE) and corneal curvature [keratometry (K)], and to determine if this ALest can replace actual axial length (ALact) for correcting transverse magnification error in optical coherence tomography angiography (OCTA) images using the Littmann-Bennett formula. Methods Data from 1301 participants of the Raine Study Gen2-20 year follow-up were divided into two datasets to generate (n = 650) and validate (n = 651) a relationship between AL, SE, and K. The developed formula was then applied to a separate dataset of 46 participants with AL, SE, and K measurements and OCTA images to estimate and compare the performance of ALest against ALact in correcting transverse magnification error in OCTA images when measuring the foveal avascular zone area (FAZA). Results The formula for ALest yielded the equation: ALest = 2.102K − 0.4125SE + 7.268, R2 = 0.794. There was good agreement between ALest and ALact for both study cohorts. The mean difference [standard deviation (SD)] between FAZA corrected with ALest and ALact was 0.002 (0.015) mm2 with the 95% limits of agreement (LoA) of − 0.027 to 0.031 mm2. In comparison, mean difference (SD) between FAZA uncorrected and corrected with ALact was − 0.005 (0.030) mm2, with 95% LoA of − 0.064 to 0.054 mm2. Conclusions ALact is more accurate than ALest and hence should be used preferentially in magnification error correction in the clinical setting. FAZA corrected with ALest is comparable to FAZA corrected with ALact, while FAZA measurements using images corrected with ALest have a greater accuracy than measurements on uncorrected images. Hence, in the absence of ALact, clinicians should use ALest to correct for magnification error as this provides for more accurate measurements of fundus parameters than uncorrected images

ENKRIPSI CITRA FOVEA AVASCULAR ZONE (FAZ) MENGGUNAKAN KRIPTOGRAFI VIGENERE CIPHER

Kemajuan teknologi yang berkembang pesat sekali sangat memepengaruhi atas keamanan data baik data teks maupun data citra digital. Pencurian data dari tahun ke tahun mengalami peningkatan. Salah satu area yang memerlukan keamanan data yaitu keamanan data medis pasien. Keamanan data citra medis sangat perlu dilakukan untuk melindungi keamanan data medis dari pencurian data oleh pihak ketiga supaya tidak bisa mengakses data tersebut. Perkembangan Diabetic Retinopathy (DR) setiap tahunnya juga meningkat. Menentukan tingkat keparahan DR dilakukan dengan mendeteksi Fovea Avascular Zone (FAZ). Pada penelitian ini mengenkripsi plainimage FAZ menjadi cipherimage menggunakan metode Vigenere Cipher. Waktu enkripsi rata rata dari citra FAZ yang diujikan adalah 4.96 detik.Pada pengujian didapatkan semakain luas area FAZ maka waktu enkripsi nya juga semakin lama.Kemajuan teknologi yang berkembang pesat sekali sangat memepengaruhi atas keamanan data baik data teks maupun data citra digital. Pencurian data dari tahun ke tahun mengalami peningkatan. Salah satu area yang memerlukan keamanan data yaitu keamanan data medis pasien. Keamanan data citra medis sangat perlu dilakukan untuk melindungi keamanan data medis dari pencurian data oleh pihak ketiga supaya tidak bisa mengakses data tersebut. Perkembangan Diabetic Retinopathy (DR) setiap tahunnya juga meningkat. Menentukan tingkat keparahan DR dilakukan dengan mendeteksi Fovea Avascular Zone (FAZ). Pada penelitian ini mengenkripsi plainimage FAZ menjadi cipherimage menggunakan metode Vigenere Cipher. Waktu enkripsi rata rata dari citra FAZ yang diujikan adalah 4.96 detik.Pada pengujian didapatkan semakain luas area FAZ maka waktu enkripsi nya juga semakin lama