Boris Gramatikov, Ph.D.
I am a member of the Hopkins faculty since 1996, and am currently Assistant Professor in the Division of Pediatric Ophthalmology and Adult Strabismus at The Wilmer Eye Institute. I am a biomedical engineer with expertise in medical instrumentation and signal processing. My present research interests are in focus detection and retinal birefringence scanning, including transition from the laboratory bench to clinical settings. The main goal is to identify and treat children with strabismus (misaligned eyes) or anisometropia (unequal refractive error) before irreversible amblyopia (functional monocular blindness) results. Click here for more on Clinical Technology Development at the Division.
Please click here for my web page at the Wilmer Eye Institute.
I have chaired the Baltimore Chapter of the IEEE-EMBS (Institute of Electrical and Electronics Engineers, Engineering in Medicine and Biology Society), which is a part of the Baltimore Section of the IEEE. I chaired the Section in 2006, and am presently an ExCom member and Director for Educational Activities and Continuing EE Education.
Current projects
Determination of ocular defocus using the double-pass blur image
of a point source of light
The double-pass blur image of a point source is used to determine the quality of
focus of the human eye. This project is based on earlier work by Dr.
David Guyton, Dr. David Hunter and Nainesh Gandhi. An apparatus that can
determine a threshold of defocus was devised using a circle/annulus (bulls-eye)
photodiode that can distinguish focused from defocused light. A monochromatic
near-infrared light source (laser diode) is employed. The light reflected from
the fundus of the eye is projected by a beamsplitter onto the bulls-eye
detector, which is optically conjugate to the laser diode. The photodetector
signal obtained is a function of the amount of defocus caused by the
double-pass point spread reflected from the retina. The signal is affected by
refractive error, incomplete accommodation, media opacities, and abnormalities
of retinal reflection. One of the major risk factors for amblyopia is
refractive error, or, more accurately, the degree of defocus the eye
experiences. The defocus is perhaps best quantified by measuring the size of
the retinal blur circle. Such defocus detection can be combined with
eye-fixation monitoring to be used as a screening tool to detect risk factors
for amblyopia. (Click here for a
figure)
Retinal Birefringence Scanning
utilizes the optical polarization properties of the human retina. This method
was originally developed by Dr.
David Guyton and Dr. David Hunter ("Automated detection of eye
fixation by use of retinal birefringence scanning", Applied Optics
38,OT&BO:1273-9, March 1999; Retinal
Birefringence Scanner – very first prototype), and is related to the
Haidinger brush phenomenon - a bow-tie or propeller-like pattern that appears
to rotate about the fixation point when a polarizing filter is placed over the
eye and rotated. This phenomenon reflects the retinal nerve fiber axon
arrangement about the fovea and can be utilized in a variety of useful
applications. In our settings, foveal fixation is monitored in human
subjects remotely and continuously by use of a noninvasive retinal scan.
Polarized near-infrared light is imaged onto the retina and scanned in a 3-deg
annulus at frequency f .
Reflections are analyzed by differential polarization detection. The detected
signal is predominantly 2f during
central fixation, and f during
paracentral fixation. Phase shift at f correlates with the
direction of eye displacement. Mathematical modeling of birefringence in
retinal birefringence scanning has confirmed the experimental and
clinical results. Potential applications of this technique include screening
for eye disease, eye position monitoring during clinical procedures, and use of
eye fixation to operate devices. Considering that the structure of the fovea is
the basis of the retinal birefringence scan signal, the experience gained from
bringing retinal birefringence scanning to the clinic will also increase our
understanding of foveal structure in health and other forms of disease. I am
involved in the development of a portable Bilateral Retinal Birefringence
Scanner (BRBS) with improved noise performance, to be used as a pediatric
vision screener. The new design incorporates binocular foveal
birefringence scanning, and separate channels for binocular focus detection.
This combination of focus and alignment detection should identify over 95% of
all children at risk for amblyopia. Some of this work was performed in
collaboration with AURA (Association of Universities for Research in Astronomy,
Inc.), the Space
Telescope Science Institute and the Instrument
Development Group (IDG) at the Department of
Physics and Astronomy at the Johns Hopkins
University.
The Pediatric Vision Screener – early
prototype
Current
work on the Pediatric Vision Screener
Using computer modeling, optical technologies, modern electronic hardware, novel signal processing and optimization methods, we are presently redesigning and reconstructing the Pediatric Vision Screener, with the goal of making it a clinically relevant, market-oriented and competitive product.
Some spin-off products: a vision scanner using non-moving parts, a biometric (security) scanner using the birefringent properties of the retina, and others (please see publications).
More about me:
This page was last updated on Dec 7, 2009