Retinal vascular biomarkers for early detection and monitoring of Alzheimer's disease

The earliest detectable change in Alzheimer''s disease (AD) is the buildup of amyloid plaque in the brain. Early detection of AD, prior to irreversible neurological damage, is important for the efficacy of current interventions as well as for the development of new treatments. Although PiB-PET imaging and CSF amyloid are the gold standards for early AD diagnosis, there are practical limitations for population screening. AD-related pathology occurs primarily in the brain, but some of the hallmarks of the disease have also been shown to occur in other tissues, including the retina, which is more accessible for imaging. Retinal vascular changes and degeneration have previously been reported in AD using optical coherence tomography and laser Doppler techniques. This report presents results from analysis of retinal photographs from AD and healthy control participants from the Australian Imaging, Biomarkers and Lifestyle (AIBL) Flagship Study of Ageing. This is the first study to investigate retinal blood vessel changes with respect to amyloid plaque burden in the brain. We demonstrate relationships between retinal vascular parameters, neocortical brain amyloid plaque burden and AD. A number of RVPs were found to be different in AD. Two of these RVPs, venular branching asymmetry factor and arteriolar length-to-diameter ratio, were also higher in healthy individuals with high plaque burden (P=0.01 and P=0.02 respectively, after false discovery rate adjustment). Retinal photographic analysis shows potential as an adjunct for early detection of AD or monitoring of AD-progression or response to treatments.     

Methods and limits of digital image compression of retinal images for telemedicine

PURPOSE: To investigate image compression of digital retinal images and the effect of various levels of compression on the quality of the images. METHODS: JPEG (Joint Photographic Experts Group) and Wavelet image compression techniques were applied in five different levels to 11 eyes with subtle retinal abnormalities and to 4 normal eyes. Image quality was assessed by four different methods: calculation of the root mean square (RMS) error between the original and compressed image, determining the level of arteriole branching, identification of retinal abnormalities by experienced observers, and a subjective assessment of overall image quality. To verify the techniques used and findings, a second set of retinal images was assessed by calculation of RMS error and overall image quality. RESULTS: Plots and tabulations of the data as a function of the final image size showed that when the original image size of 1.5 MB was reduced to 29 KB using JPEG compression, there was no serious degradation in quality. The smallest Wavelet compressed images in this study (15 KB) were generally still of acceptable quality. CONCLUSIONS: For situations where digital image transmission time and costs should be minimized, Wavelet image compression to 15 KB is recommended, although there is a slight cost of computational time. Where computational time should be minimized, and to remain compatible with other imaging systems, the use of JPEG compression to 29 KB is an excellent alternative.     

Neuroretinal rim measurement error using PC-based stereo software

The neuroretinal rims of a set of glaucoma patients were measured using digitized stereo photographs, to determine the reproducibility of computerized stereo measurements of the neuroretinal rim. Each rim was measured five times at 18 locations, with measurement error (ME) defined as the mean of standard deviations of each set of measurements. The following ME were determined: (i) inter-sessional variability (n = 27 right and 24 left eyes, at t1 and t2); (ii) inter-assessor variability (n = 9, 2 assessors); and (iii) variability after colour adjustment algorithms were applied (n = 15). The results were as follows: (i) inter-sessional variability was 3.41+/-1.08 for t1 and 3.22+/-0.84 for t2; (ii) there was a significant difference between the two assessors, although the ME was still low; and (iii) there was no significant differences between the ME of unadjusted and adjusted images. With a measurement error of up to 11% of rim width, these results show that lowcost rim measurements can be made using PC-based software.     

Telemedicine Screening for Diabetic Retinopathy

Diabetic eye disease is the most common cause of new cases of blindness in the Western world. If the disease is detected early then proper treatment can be provided to prevent loss of vision. Regular screening can reduce the incidence and prevalence of blindness due to diabetic retinopathy. Health personnel, optometrists and primary care providers can perform the screening using digital nonmydriatic fundus cameras. Digital data can be archived, stored, manipulated and sent via telecommunication networks, e.g. the Internet, to ophthalmologists for diagnosis and second opinions.Easy-to-operate, low cost and portable digital fundus cameras and intuitive software are necessary to perform cost-effective screening of rural, remote and underserved communities using trained lay personnel. Several feasibility studies of telemedicine screening for diabetic retinopathy have been reported. These studies demonstrate the enormous usefulness of this technology for communities living in rural and remote areas. Further studies are needed to prove the cost benefit of telemedicine technology for diabetic retinopathy screening.     

Computer-assisted planimetry associated with Sturge-Weber syndrome

Photographs of the optic nerve head (optic disc) in the eye are used for the clinical assessment of the disease glaucoma. These images are usually subjectively assessed by a clinician. A case of Sturge-Weber Syndrome which includes glaucoma as a symptom, is presented here. Narrowing of the rim of the optic disc was measured using custom-made measurement software confirming glaucomatous progression. To maximize the information obtained from optic disc images, low cost software can assist with quantifying disc parameters aiding clinical interpretation.     

Diabetic retinopathy screening: can the viewing monitor influence the reading and grading outcomes

Purpose

To evaluate the accuracy of different viewing monitors for image reading and grading of diabetic retinopathy (DR).

Design

Single-centre, experimental case series—evaluation of reading devices for DR screening.

Method

A total of 100 sets of three-field (optic disc, macula, and temporal views) colour retinal still images (50 normal and 50 with DR) captured by FF 450 plus (Carl Zeiss) were interpreted on 27-inch iMac, 15-inch MacBook Pro, and 9.7-inch iPad. All images were interpreted by a retinal specialist and a medical officer. We calculated the sensitivity and specificity of 15-inch MacBook Pro and 9.7-inch iPad in detection of DR signs and grades with reference to the reading outcomes obtained using a 27-inch iMac reading monitor.

Results

In detection of any grade of DR, the 15-inch MacBook Pro had sensitivity and specificity of 96% (95% confidence interval (CI): 85.1–99.3) and 96% (95% CI: 85.1–99.3), respectively, for retinal specialist and 91.5% (95% CI: 78.7–97.2) and 94.3% (95% CI: 83.3–98.5), respectively, for medical officer, whereas for 9.7-inch iPad, they were 91.8% (95% CI: 79.5–97.4) and 94.1% (95% CI: 82.8–98.5), respectively, for retinal specialist and 91.3% (95% CI: 78.3–97.1) and 92.6% (95% CI: 81.3–97.6), respectively, for medical officer.

Conclusion

The 15-inch MacBook Pro and 9.7-inch iPad had excellent sensitivity and specificity in detecting DR and hence, both screen sizes can be utilized to effectively interpret colour retinal still images for DR remotely in a routine, mobile or tele-ophthalmology setting. Future studies could explore the use of more economical devices with smaller viewing resolutions to reduce cost implementation of DR screening services.