Faculty > Ravi

Nathan Ravi, M.S., Ph.D., M.D., F.A.A.O.

Professor, Ophthalmology and Visual Sciences
Professor, Energy, Environmental and Chemical Engineering
Washington University in St. Louis MO

Lab: (314)747-4474

Chief of Staff
Department of Veterans Affairs Medical Centers (John Cochran and Jefferson Barracks)
St. Louis, MO

Executive Suite: (314)289-6470

Education:

B.S. Chemistry, University of Bombay, India (1972)

M.S. Physical Chemistry, University of Bombay, India (1975)

Ph.D. Polymer Science, Virginia Tech (VPI and SU) (1980)

M.D. University of Miami (1988)

Intern, Internal Medicine, Albany Medical Center (1988-1989)

Resident, Ophthalmology, Albany Medical Center (1989-1992)

Clinical Area:

Comprehensive Ophthalmology

Research Interests:

Ocular biomechanics, biomimetic prosthesis, nanomedicine, drug delivery

Artificial lens:

Research in Dr. Ravi's laboratory is directed toward understanding the pathophysiology of presbyopia and developing medical or surgical treatments for this condition. Presbyobia, which means "aging eye," results in an inability to see clearly at near distances. Although this condition is not vision threatening, it affects all of us. The current treatment for this condition is bifocals, which provides good vision at only two focal planes. Benjamin Franklin first created bifocals more than 200 years ago. Our research lab is investigating the lens-based causes of presbyopia by quantifying the biomechanical behaviors of the lens. We use these measurements to reverse engineer potential lens prostheses by designing novel polymeric. A key challenge is to identify materials that not only match the human lens in physical, optical, and mechanical properties, but that also exhibit biocompatibility and long term stability. These substances should also be introduced into the eye by a minimally invasive surgery. We have identified copolymers that can potentially be injected into a pre-evacuated lens capsular bag, wherein they can spontaneously form a gel.

Artificial vitreous:

The vitreous body is the clear "jelly" in the middle of the eye behind the lens. It is approximately 99% water by weight, with the remainder primarily crosslinked type II collagen fibrils and hyaluronic acid. It acts as a viscoelastic damper during eye movements, thus ensuring retinal attachment to choroid. With advancing age, the vitreous undergoes a non-uniform transition from a formed gel to a phase separated fluid in an elderly adult, leading to the appearance of "floaters.” A number of vision-threatening phenomena such as macular holes, retinal detachments, and vitreous hemorrhage are associated with this transition. Clinically, silicones and perflorocarbons are used as temporary vitreous substitutes. However, we have designed, synthesized, and characterized water soluble copolymers that, upon injection within the vitreous cavity, spontaneously form a hydrogel under certain physiological conditions. The formed hydrogel is optically clear, contains more than 95% water, matches the viscoelastic properties of the natural vitreous, and exhibits minimum toxicity in both tissue culture and rabbits. Various polymers are being synthesized and tested for improved properties as a vitreous substitute.

Nanomedicine:

The perception of vision and the ability to dynamically focus are excellent examples of how nature exploits nanoscience. The cornea, lens, and vitreous efficiently utilize nanoscience 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 (RI). We are also investigating the role of quantum dots for use as artificial retina.

Ocular Drug Delivery:

We have developed techniques of making nanoparticles using block-copolymers that have tissue adhesive properties. Pilocarpine was used as a prototypic drug. Thermodynamic polymer-drug interaction calculations are also performed.

Research Facilities:

To accomplish these goals, we use chemical computational software that identifies potential polymeric structures with desired properties. This dramatically reduces the time required to identify a suitable polymer for the application. The laboratory is a modern polymer synthesis and characterization facility. It features a dynamic mechanical analyzer, a microvolume capillary rheometer for rheometry, and gas permeation chromatography (GPC) with viscosity, refractive index, and light scattering detectors in tandem. Additionally, we have developed custom instrumentation including a robotic eight-arm equibiaxial stretcher, a novel microindentation device, a dynamic light scattering instrument, and a slit lamp for small animal examination. The facility also includes an animal surgery lab equipped with modern surgical instruments and lasers. The research team consists of polymer and nanoparticle chemists, biologist, and chemical engineers and has extensive collaborations throughout Washington University’s Schools of Medicine and Engineering. Graduate students from the School of Engineering are needed to continue advancing these important projects.

Press Releases:

Publications:

(Dr. Ravi has over 100 publications, including papers, abstracts and 4 book chapters. He holds 8 patents and has delivered over 50 invited lectures. A few current and relevant publications are listed below.)

Mortimer K, Mitchel N, Williams K, Day E, Gordon M, Hall B, Rodin E, Ravi N, September, 2008: Effect of resident experience on procedure length in cataract surgery. Mayo Clinic Conference: Systems Engineering & Operations Research in Health Care, Rochester Minnesota.
Carpenter G, King J, Kroupa L, Kymers S, Williams K, Hovmand P, Ravi N, September, 2008: Decreasing appointment no-shows. Mayo Clinic Conference: Systems Engineering & Operations Research in Health Care, Rochester Minnesota.
King J, Day TE, Carpenter G, Kroupa L, Rodin EY, Ravi N, September, 2008: Simulation of an emergency department. Mayo Clinic Conference: Systems Engineering & Operations Research in Health Care, Rochester Minnesota.
Andley U, Hamilton PD, Ravi N, 2008. Mechanism of Insolubilization by a Single point Mutation in αA-Crystallin Linked with Hereditary Human Cataract. Biochemistry, 47 (36): 9697–9706.
Reilly M, Hamilton PD, Perry G, Ravi N, 2008: Comparison of the Behavior of Natural and Refilled Porcine Lenses in a Robotic Lens Stretcher: Accepted, Experimental Eye Research.
Reilly M.A., Ravi N, 2008: Microindentation of the Young Porcine Ocular Lens. Accepted, Journal of Biomechanical Engineering.
Reilly M.A., Perry G., Ravi N., A Dynamic Microindentation Device with Electrical Contact Detection. Accepted, Review of Scientific Instruments, 2008.
Swindle KE, Hamilton PD, Ravi N, 2008: In situ formation of hydrogels as vitreous substitutes: viscoelastic comparison to porcine vitreous. Journal of Biomedical Materials Research Part A. 87A-3, 656-665.
Reilly MA, Rapp B, Hamilton PD, Shen AQ, Ravi N, 2008: Material Characterization of Porcine Lenticular Soluble Proteins. Biomacromolecules, 9(6), 1519-1526.
Reilly MA, Hamilton PD and Ravi N, 2008: Novel Dynamic Multi-Arm Radial Lens Stretcher: A Mechanical Analog of the Ciliary Body. Experimental Eye Research, 86:157-164.
Zhang D, Hamilton PD, Kao J, Venkataraman S, Wooley K, Ravi N, 2007: Formation of nanogel aggregates by an amphiphilic cholesteryl-poly(amidoamine) dendrimer in aqueous media. Journal of Polymer Science Part A: Polymer Chemistry 45:2569-2575.
Swindle KE, Ravi N, 2007: Recent Advances in Polymeric Vitreous Substitutes. Expert Review of Ophthalmology, 2(2):255-266.
Ravi N, 2007: New horizons in intra-ocular lens. Federal Practitioner, February Supplemental Issue
Ravi N, Wan KT, Swindle K, Hamilton PD, Duan G, 2006: Development of techniques to compare mechanical properties of reversible hydrogels with spherical, square columnar and ocular lens geometry. Polymer. 47: 4203-4209.
Swindle KE, Hamilton PD, Ravi N, 2006: Advances in the development of artificial vitreous humor utilizing polyacrylamide copolymers with disulfide crosslinkers. Polymer Preprint, 47:64.
Foster WJ, Aliyar HA, Hamilton PD, and Ravi N, 2006: Internal Osmotic Pressure as a Mechanism of Retinal Attachment in a Vitreous Substitute. Journal of Bioactive and Compatible Polymers, 21(3):221-235.
Ravi N, Aliyar H, Hamilton PD, 2005: Hydrogel nanocomposite as a synthetic intra-ocular lens capable of accommodation, Macromolecular Symposia, 227(1):191-202.