In structured illumination microscopy, an object is
illuminated by sinusoidally patterned light, rather than conventional uniform
illumination, and digital image processing is done to obtain axial sectioning
(3D imaging) and super-resolution (imaging at frequencies beyond the normal
diffraction cutoff of the optical system).
The technique can be used in microscopes for imaging
both fluorescent and non-fluorescent objects, such as tissues, cells and
micro-structures such as semiconductor chips, in both in vitro and in
A key in vivo application is retinal imaging of
the human eye. Retinal imaging is used to diagnose retinal disease, such
as diabetic macular edema, retinitis pigmentosa, age-related macular
degeneration (AMD) and glaucoma.
Structured illumination imaging has been used before in
in vitro fluorescent microscopy to obtain super resolution but this is
the first time this is being done in vivo on a constantly moving subject,
such as a living human eye, and for non-fluorescent objects.
Applied to the human eye, this technology enables the
imaging of individual cells and retinal structures smaller than 2 microns, such
as rods, foveal cones, fine blood capillaries and ganglion cell axions, which
are difficult to resolve in vivo because the patient?s pupil, which is
the limiting aperture in the optical system, cannot typically be dilated beyond
6 to 8 mm. Our technology includes image processing for image
registration to address the motion of the eye and the reduction of the speckle
defect related to coherent laser illumination. It does not require
that the cells be made fluorescent. The technique is compatible with
adaptive optics used to correct for the aberrations of the eye. Current
ophthalmoscopes and fundus cameras used by doctors for examining the retina have
low resolution and can only detect disease when it is at an advanced
stage. This technology takes the resolution to the cellular level below 2
microns and is expected to enable diagnosis at an early stage for more effective
treatment. Current confocal imaging techniques also provide axial
sectioning (3D imaging) through the different layers of the retina, but these
confocal systems are complex and expensive compared to this structured
illumination / digital signal processing technique.
Applied to in vitro microscopy, the technique will
provide axial sectioning, and super-resolution for both fluorescent and
non-fluorescent objects. Current microscopes with structured
illumination require fluorescent objects and only perform axial sectioning, and
do not provide lateral super-resolution.