SCHÄFER Bhavapriya

Evaluation of Retinal Morphology and Blood Flow in Diabetic and Non-Diabetic Animals Using Optical Methods

Diabetes mellitus (DM) is a major public health problem in industrialized and newly industrialized countries and a major financial burden on health care systems and patient’s quality of life. The disease’s main characteristic - chronic hyperglycaemia - is associated with long-term impairment of the eye such as diabetic retinopathy (DR). Often the disease is not diagnosed until the patient’s vision is already impaired and retinal neurons are irreparably damaged. To develop treatment options that can intervene early into the progression of the disease, more knowledge has to be gained about the early pathogenesis. One of the main aspects, alterations in retinal blood flow, can be targeted for diagnostic purposes.

The proposed study aims to measure retinal blood flow in animals that present a diabetic phenotype in order to establish a suitable model for investigating alterations of ocular blood flow caused by DM. By means of a high-resolution dual-beam Doppler optical coherence tomography (DOCT) system and a Dynamic vessel analyzer (DVA) changes in retinal blood flow and retinal morphology will be evaluated. Ocular blood flow data will be assessed in two groups, a diabetic rat model and a wildtype phenotype. A total of eight measurements will be performed before and after diabetes induction. The first measurement will be performed one to five days prior to diabetes induction and serve as a baseline value for later comparison. The following three measurements will be performed after one, two and three weeks respectively. The last four measurements will be performed five to 10 weeks after diabetes induction. Measurements will be used to monitor the onset and progression of DR and data will be compared to physiological blood flow in the retinal vasculature. Besides the total retinal blood flow (TRBF), neurovascular coupling (NVC), adaptational diameter changes of the retinal vessels in response to a light stimulus and vasomotion (VM), which are spontaneous oscillations of vessel diameters, will be assessed and compared between healthy and diabetic animals.

The project will include one pilot and one main study. For all proposed experiments, Long Evans rats will be used. The first part of the pilot experiment will be performed in order to investigate the influence of different anesthetic protocols on the retinal blood flow and flicker response as well as systemic blood pressure (BP) in pigmented rats. The results of these measurements will be further used to test for repeatability within measurements. The anesthetic protocol with the smallest effect on systemic BP and retinal blood flow while upholding sustained flicker response will be applied in the second part of the pilot study and the main study.

Streptozotocin (STZ) will serve as DM inducing agent, generating a model that will represent type I diabetes (T1DM). The second part of the pilot study will be performed to induce diabetes nd to evaluate and adapt measurement techniques on a smaller sample of diabetic and nondiabetic rats. These findings will serve as the basis for sample size calculations for the main part.

The study group of the main experiment will consist of diabetic animals, while the control group will consist of healthy, age-matched wildtype rats. Output parameters will be assessed over time from all animals using DOCT and DVA. The non-invasive and contact-free nature of DOCT allows for longitudinal measurements and thus enables assessment of individual progression of the disease. This provides a much better insight into haemodynamic changes of the retina than previous methods, while using a lower number of animals. Morphological data obtained from high-resolution OCT imaging will be correlated with histological findings. Microscopy provides cellular resolution, which offers insight into subtle changes in the retinal vessels’ morphology, which can be correlated with changes in blood flow, NVC and VM. Three animals per group and time point will be sacrificed in order to assess and quantify tissue changes during DR progression.

Methods and Skills:

Optical imaging; optical coherence tomography; animal experimentation; histology

Publications:

Hinney B, Gottwald M, Moser J, Reicher B, Schäfer BJ, Schaper R, Joachim A, Künzel F. Examination of anonymous canine faecal samples provides data on endoparasite prevalence rates in dogs for comparative studies. Vet Parasitol 245: 106-115, 2017