Jesse B. Schallek, Ph.D.
Assistant Professor - Department of Ophthalmology (SMD)
Assistant Professor - Department of Neuroscience (SMD)
Assistant Professor - Center for Visual Science (RC)
PhD | Neuroscience | SUNY Upstate Medical University
The neural cells that line the back of our eyes are sensitive to light and initiate our ability to see. These cells are among the most metabolically active tissues in the human body and are nourished by a dense network of capillaries that circulate blood to deliver nutrients and remove waste products from these hard-working cells. However, dysfunction of this neural-vascular system associates with a variety of retinal diseases and collectively gives rise to the leading cause of blindness in the developed world.
Our lab investigates blood flow in the living eye by using a specialized camera called an Adaptive Optics Scanning Light Ophthalmoscope (AOSLO) to correct for small imperfections of the optics of the eye. Once corrected, we can image the microscopic integrity of the smallest vessels that are ten-times thinner than a human hair. Additionally, capturing videos of this tissue enables study of the movement of single blood cells flowing within this network. We are developing and applying this cutting-edge technology to study blood flow in the retina in conditions of health and disease.
single AOSLO field
Blood Flow Imaging
In our lab, we have the capability to observe individual red blood cells in the smallest capillaries in the retina. This provides a unique opportunity to study the retinal vasculature with a resolution that was not possible before. With the goal of studying vascular abnormalities in the eye in diseases like diabetes, our lab has developed a novel way of non-invasively tracking the total volumetric flow rate of blood in the living mouse retina using adaptive optics scanning light ophthalmoscopy (AOSLO). This technique automatically determines blood cell velocity (Radon transform) from space-time images of individual erythrocytes as they pass by a fast 30 kHz point-scan, which rapidly scans across a first-order blood vessel close to the optic disc. Using sodium fluorescein contrast, we can accurately determine vessel diameters. The blood cell velocity and vessel diameter together give volumetric blood flow, using the well-known equations of Poiseuille’s law.
In-vivo determination of total blood flow in a C57BL/ 6J mouse retina
A great number of retinal neurons are translucent, making them difficult to detect using standard imaging techniques. Split-detector imaging provides contrast enhancement noninvasively and expands our capabilities to image both retinal neurons and the vasculature non-invasively.
Enhanced contrast of vessels imaged with split-detection
Imaging individual red blood cells in single capillaries without contrast agents
The basic constituents of blood can be greatly affected in the case of disease. We are strengthening our ability to quantify these differences without a blood draw by instead using the natural transparency that the eye provides as a window to look at the retinal vasculature.Adaptive optics scanning laser ophthalmoscope (AOSLO) imaging has recently provided counts of red blood cells (RBCs) in capillaries of the living mouse retina without the use of contrast agents (Schallek et al. ARVO 2015). However, white blood cells (WBCs) are far rarer, accounting for only one in every 3400 RBCs in the healthy mouse (Jackson Labs), making their quantification more challenging. In our lab, we use AOSLO to image label-free RBCs and WBCs labeled with acridine orange (AO) to compute their ratio in the living mouse, with the goal of providing an in vivo complete blood count (CBC) - a physiological marker of systemic health. Future work will look at identifying biomarkers that differentiate WBCs from RBCs in label free strategies that image multiple scattering of light in the retina, such as split-detection.
AOSLO imaging of the four major constituents of blood
Detection of white blood cells in single capillaries
Retinal vasculature damage during the progression of diabetes
Diabetic retinopathy is a serious complication that can develop over time in diabetes patients, causing impairments or even loss of vision. We are studying structural abnormalities in the vasculature of the retina over time in a mouse model of diabetes. By injecting mice with streptozotocin, an antibiotic that has pancreatic β-cell cytotoxic effects, we have been able to induce type 1 diabetes mellitus. In our lab, we are using retinal angiography, optical coherence tomography (OCT), and adaptive optics scanning laser ophthalmoscopy (AOSLO) to track changes in the density of retinal pericyte cells and the thickness of the retinal layers over time.
Retinal angiography image of pericytes in a healthy mouse
OCT image showing the thickness of the retina in a healthy mouse
Guevara-Torres A, Williams DR, and Schallek JB (2015). Imaging translucent cell bodies in the living mouse retina without contrast agents. Biomed. Opt. Express 6, 2106-2119.
Aby Joseph, Andres Guevara-Torres, David R Williams, Jesse B Schallek. “Measurement of blood flow in the largest vessels and smallest capillaries in the living mouse retina using an adaptive optics scanning light ophthalmoscope”. Invest. Ophthalmol. Vis. Sci. 2015; 56(7):3323.
Schallek JB, Geng Y, Nguyen H, Williams DR. "Morphology and topography of retinal pericytes in the living mouse retina using in vivo adaptive optics imaging and ex vivo characterization." Investigative ophthalmology & visual science. 2013 54(13):8237-50. Epub 2013 Dec 19.
Schallek JB, McLellan GJ, Viswanathan S, Ts'o DY. "Retinal intrinsic optical signals in a cat model of primary congenital glaucoma." Investigative ophthalmology & visual science. 2012 Apr; 53(4):1971-81. Epub 2012 Apr 18.
Schallek JB, Ts'o D. "Blood contrast agents enhance intrinsic signals in the retina: evidence for an underlying blood volume component." Investigative ophthalmology & visual science. 2011 Mar; 52(3):1325-35. Epub 2011 Mar 10.