Faculty > Ravi

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

Associate Professor, Ophthalmology and Visual Sciences
Affiliate Professor of Chemical Engineering
Washington University in St. Louis MO
(314) 747-4458

& Chief of Ophthalmology
Veterans Affairs Medical Center
St. Louis , MO

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 biomaterials, nanomedicine, drug delivery

Ocular biomaterials:

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" in Greek - 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 150 years ago! Our research lab is investigating the lens-based causes of presbyopia by determining the biomechanics of the lens. We are "engineering" novel polymeric substitutes that resemble a young lens and which can ultimately be implanted as an artificial human lens. 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. Presently, our lab has identified copolymers that can potentially be injected into a pre-evacuated lens capsular bag, wherein they can spontaneously form a gel-the artificial lens.

Artificial vitreous:

The vitreous body is simply the clear "jelly" in the middle of the eye, posterior to the lens. It is made up primarily of non- crosslinked type II collagen fibrils and hyaluronic acid and is approximately 99% water by weight. 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 and may appear as "floaters". A number of vision-threatening phenomena such as macular holes, retinal detachments, and vitreous hemorrhage are associated with this transition. Currently, 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, has a modulus of ~100 pascal , a stress relaxation time of few seconds, and minimum toxicity in tissue culture. Various polymers are being synthesized and tested for improved properties as a vitreous substitute.

Nanomedicine:

The perception of vision and the ability to auto focus is an excellent example 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 the lens crystallins , particularly their size, viscoelasticity, and refractive index (RI). We are also investigating the role of quantum dots for use as artificial retina.

Ocular Drug delivery: Ravi lab has developed techniques of making nanoparticles using block-copolymers that have tissue adhesive properties. Pilocarpine was used as a prototypic drug. Thermodynamic polymer-drug interactions are also performed.

Research Facilities:

To accomplish these goals, the Ravi laboratory uses chemical computational software that enables them to identify potential polymeric structures with desired properties and perform What if? experiments in- silico. The laboratory is a modern polymer synthesis and characterization facility. It features a dynamic mechanical analyzer, a microvolume capillary rheometer for nanorheology characterization, and GPC with viscosity refractive index and light scattering detectors in tandem. Additionally, a dynamic eight-arm radial stretcher, a dynamic light scattering instrument, and a slit lamp for small animal examination were custom-designed for ophthalmic research. The facility also includes an animal surgery lab equipped with modern surgical instruments and lasers. The research team consists of an organic chemist, a protein chemist, a molecular biologist, a neuroscientist, and polymer chemists. Graduate students from Chemical and Biomedical Engineering also conduct small projects.

Press-Releases:

Publications:

(Dr. Ravi has written approximately 35 papers, 30 abstracts, 3 book chapters; holds 8 patents; and has spoken at over 40 invited lectures. A few current and relevant publications are listed below.)

  1. Aliyar H, Hamilton PD, Ravi N. Hybrid hydrogels as artificial human lens . Polymer Preprints2004 45 (2).
  2. Aliyar H, Hamilton PD, Ravi N. Preparation and characterization of polymeric proteo-mimitics . Polymer Preprints 2004 45 (2).
  3. Fetsch MF, Aliyar H, Hamilton PD, Ravi N. Synthesis and characterization of hydrophobically modified hydrogels as artificial human lens substitutes . Polymeric Materials Science and Engineering 2003 88:899.
  4. Ravi N, Mitra A, Hamilton PD, Horkay F. Characterization of the network properties of poly( ethylene glycol)- acrylate hydrogels prepared by variations in the ethanol-water solvent composition during crosslinking copolymerization . Journal of Polymer Science, Part B: Polymer Physics 2002 40:2677-2684.
  5. Murthy KS, Ravi N. Hydrogels and potential probes for investigating the mechanism of presbyopia. Current Eye Research 200122(5):384-93.


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