Introducing Dr. Ravi
Nathan Ravi reached the USA in 1976, after graduating from the University of Bombay, India, with a BS (’73) and MS (’75) in physical chemistry. He pursued an advanced degree in polymer science at the Virginia Polytechnic Institute, earning his PhD in 1980. During his doctoral studies, he designed high-temperature thermoplastics that were tested by NASA as adhesives to prevent thermal insulating tiles from falling off space shuttles during re-entry. He worked in industry afterward, researching the use of polymers in biotechnology, then returned to academia six years later. Dr. Ravi joined the University of Miami’s accelerated PhD – MD program and received his MD two years later, in 1988. He completed his internship in internal medicine (’89) and residency in ophthalmology (’92) at the Albany Medical Center in New York. Later in 1992, he joined the Department of Ophthalmology and Visual Sciences at Washington University and was Board Certified in 1995. Dr. Ravi is a Fellow of the American Academy of Ophthalmology. In 2010, he also earned an MBA from Washington University.
Dr. Ravi is a Professor in the Department of Ophthalmology and Visual Sciences (DOVS) and Energy, Environmental & Chemical Engineering (EECE), and a Faculty Scholar at the Institute of Public Health. Dr. Ravi is also a full-time VA physician, currently serving at the St. Louis VA Medical Center – John Cochran Division, where he was the Chief of Staff between 2006 – 2010. During his tenure at WU and the VA, he has mentored numerous undergraduate, graduate, and post-graduate students along with a number of junior faculty in both ophthalmology and engineering. In 1999, he was the recipient of the “Ophthalmology Teacher of the Year Award” award.
Dr. Ravi has delivered numerous lectures as a keynote speaker and visiting professor. He has over 150 publications, including peer-reviewed articles, book chapters, and patents. Competitive federal funds over the last 20 years have enabled him to explore his interests in the development of visual intra-ocular lens prostheses that can be injected via minimally invasive surgery and will auto-focus, thus eliminating the need for glasses and contact lenses. Most recently, motivated by the maladies of his VA patients, he has become passionately involved in understanding the pathophysiology of toxic military burn pit aerosols.
Dr. Ravi served as the President of the Association of Veterans Affairs Ophthalmologists and has been actively involved in the American Academy of Ophthalmology’s federal and international divisions. He has served on research panels for the VA, review panels of the NIH, and advisory panels for the FDA. At the national level, he served on several VA eye-care committees, improving the quality and efficiency of eye care. He received the “Secretariat Award” from the American Academy of Ophthalmology both in 2005 and 2007 in recognition for his work at the VA hospitals and his role in international ophthalmology. In 2016, he received the “Ophthalmology Teacher of the Year Award” from Washington University’s School of Medicine. The St. Louis Veterans Affairs Medical Center recognized Dr. Ravi’s contributions to science with the “Lifetime Achievement Award” in 2017.
Areas of Expertise and Research
Directed towards understanding the pathophysiology of presbyopia and developing medical or surgical treatments for this condition, this research seeks to quantify the biomechanical behavior(s) of the lens. Presbyopia, or aging of the eye, results in an inability to see clearly at near distances. Although this condition does not threaten loss of vision, it eventually affects everyone. Current treatment uses bifocals, first created by Benjamin Franklin, which provide good vision at only two focal distances. Our work uses measurements to reverse engineer potential lens prostheses that employ new polymers or polymeric substances. Key challenges include identifying materials that mimic the human lens in terms of its physical and optical properties, long term stability, and biocompatibility, and that require only minimally invasive surgery to implement. We have identified copolymers that can potentially be injected into a pre-evacuated lens capsular bag, where they will spontaneously gelate.
The vitreous body is the clear ‘jelly’ in the center of the eye behind the lens. While it is ~99 wt-% water, cross linked Type II collagen fibrils and hyaluronic acid give it consistency. The fibrils act as viscoelastic dampers during extreme eye movements, preventing the retina from detaching from the choroid. With age, the vitreous undergoes a non-uniform transition to phase-separated fluids, leading to the appearance of ‘floaters’. Several other vision-threatening phenomena may result: macular holes, retinal detachments, and vitreous hemorrhage. Clinically, silicones and perfluorocarbons are used as temporary vitreous substitutes. In our lab, we have designed, synthesized, and characterized water soluble co-polymers that, upon injection within the vitreous cavity, spontaneously form a hydrogel under favorable physiological conditions. Our hydrogel is optically clear, contains >95 wt-% water, matches the viscoelastic properties of the natural vitreous, and exhibits minimal toxicity in rabbits. We are now synthesizing and testing polymers with improved properties as vitreous substitutes.
Visual perception and dynamic focusing are excellent examples of how nature exploits the properties of nanoparticles. The cornea, lens, and vitreous efficiently utilize nanoscale components and phenomena to perform their functions. We have designed and synthesized nanogels to mimic the properties of globular lens proteins called crystallins. These nanogels closely match the crystallins’ size, viscoelasticity, and refractive index. At present, we are investigating the use of quantum dots in manufacturing artificial retinae.
Ocular Drug Delivery and Engineered Nanoparticles
Using ‘block co-polymers’ that have tissue adhesive properties, we developed a technique to manufacture nanoparticles. We tested these alongside our manufacturing of gold nanoparticles and carbon dots. We show the biocompatibility of gold nanoparticles with retinal pigmented epithelial (RPE) cells as well as its enhanched biocompatibility with hyaluronate.
Adverse Health Effects of Burn Pit Emissions
We built a one-of-a-kind burn pit simulator capable of reproducing carbonaceous aerosols with differing properties on demand. These will be used to study their toxicity on ocular, lung, and dermal cells.