Automated quantification of retinal vessel morphometry in the UK Biobank Cohort

The following topics are dealt with: feature extraction; learning (artificial intelligence); image classification; image segmentation; computer vision; object detection; feedforward neural nets; image colour analysis; image representation; medical image processing

Summarising the retinal vascular calibres in healthy, diabetic and diabetic retinopathy eyes

Retinal vessel calibre has been found to be an important biomarker of several retinal diseases, including diabetic retinopathy (DR). Quantifying the retinal vessel calibres is an important step for estimating the central retinal artery and vein equivalents. In this study, an alternative method to the already estab- lished branching coefficient(BC) is proposed for summarising the vessel calibres in retinal junctions. This new method combines the mean diameter ratio with an alternative to Murray’s cube law exponent, derived by the fractal dimen- sion,experimentally, and the branch exponent of cerebral vessels, as has been suggested in previous studies with blood flow modelling. For the above calcu- lations, retinal images from healthy, diabetic and DR subjects were used. In addition, the above method was compared with the BC and was also applied to the evaluation of arteriovenous ratio as a biomarker of progression from diabetes to DR in four consecutive years, i.e. three/two/one years before the onset of DR and the first year of DR. Moreover, the retinal arteries and veins around the optic nerve head were also evaluated. The new approach quantifies the vessels more accurately. The decrease in terms of the mean absolute percentage error was between 0.24% and 0.49%, extending at the same time the quantification beyond healthy subjects

Automated retinal image quality assessment on the UK Biobank dataset for epidemiological studies.

Morphological changes in the retinal vascular network are associated with future risk of many systemic and vascular diseases. However, uncertainty over the presence and nature of some of these associations exists. Analysis of data from large population based studies will help to resolve these uncertainties. The QUARTZ (QUantitative Analysis of Retinal vessel Topology and siZe) retinal image analysis system allows automated processing of large numbers of retinal images. However, an image quality assessment module is needed to achieve full automation. In this paper, we propose such an algorithm, which uses the segmented vessel map to determine the suitability of retinal images for use in the creation of vessel morphometric data suitable for epidemiological studies. This includes an effective 3-dimensional feature set and support vector machine classification. A random subset of 800 retinal images from UK Biobank (a large prospective study of 500,000 middle aged adults; where 68,151 underwent retinal imaging) was used to examine the performance of the image quality algorithm. The algorithm achieved a sensitivity of 95.33% and a specificity of 91.13% for the detection of inadequate images. The strong performance of this image quality algorithm will make rapid automated analysis of vascular morphometry feasible on the entire UK Biobank dataset (and other large retinal datasets), with minimal operator involvement, and at low cost

Retinal characteristics of myopic eyes in a semi-rural UK population

All levels of myopia are associated with an increased risk of ocular diseases such as glaucoma, and retinal detachment. The prevalence of myopia is increasing at an alarming rate across the globe so an increase in ocular morbidity would be expected unless action is taken. The studies in this thesis were carried out to investigate how the retina, and optic nerve head change in appearance at different levels of myopia. Identification of signs indicating future progression would allow targeting of interventions to minimise the ultimate degree of myopia. This thesis describes four community-based studies investigating retinal appearance in myopic eyes. A mixture of retrospective cross-sectional and longitudinal assessments using previously obtained digital fundus images are presented, along with a prospective cross-sectional study of the peripheral retina. The participants had myopia ≤-0.50 D and were mainly of white European ethnicity. Crescent width was found to increase with both age and level of myopia. Those with inferior-temporally located crescents had the highest levels of myopia. Tilted discs were associated with higher levels of myopia and smaller optic discs. Upon longitudinal assessment of disc measures, the optic cup measures, and crescent width were found to increase. Peripheral retinal lesions were observed in 27 % of eyes. Pigmentary degeneration was the most frequently observed and was associated with increasing age and the widest crescents. White without pressure was found in 5.8 % of eyes and was associated with a higher magnitude of myopia. Static retinal vessel analysis showed no significant relationships between retinal vessel calibre summary measures and myopia, age, or optic nerve head measures. The position of the myopic crescent is a possible predictor of future myopic progression. Further longitudinal study is needed to investigate this. The vertical disc diameter remained constant justifying the use of the quotient of the maximum crescent width to vertical disc diameter to determine crescent width change without the need for magnification correction

Suitability of UK biobank retinal images for automatic analysis of morphometric properties of the vasculature

To assess the suitability of retinal images held in the UK Biobank--the largest retinal data repository in a prospective population-based cohort--for computer assisted vascular morphometry, generating measures that are commonly investigated as candidate biomarkers of systemic disease.Non-mydriatic fundus images from both eyes of 2,690 participants--people with a self-reported history of myocardial infarction (n=1,345) and a matched control group (n=1,345)--were analysed using VAMPIRE software. These images were drawn from those of 68,554 UK Biobank participants who underwent retinal imaging at recruitment. Four operators were trained in the use of the software to measure retinal vascular tortuosity and bifurcation geometry.Total operator time was approximately 360 hours (4 minutes per image). 2,252 (84%) of participants had at least one image of sufficient quality for the software to process, i.e. there was sufficient detection of retinal vessels in the image by the software to attempt the measurement of the target parameters. 1,604 (60%) of participants had an image of at least one eye that was adequately analysed by the software, i.e. the measurement protocol was successfully completed. Increasing age was associated with a reduced proportion of images that could be processed (p=0.0004) and analysed (p<0.0001). Cases exhibited more acute arteriolar branching angles (p=0.02) as well as lower arteriolar and venular tortuosity (p<0.0001).A proportion of the retinal images in UK Biobank are of insufficient quality for automated analysis. However, the large size of the UK Biobank means that tens of thousands of images are available and suitable for computational analysis. Parametric information measured from the retinas of participants with suspected cardiovascular disease was significantly different to that measured from a matched control group