Imaging Diseased Eyes

inversely

magnification & FOV are _____ proportional

smaller

the greater the magnification of the imaging system, the ______ the FOV

resolution

ability to distinguish between 2 very close objects; smallest size of the object that can be seen by the imaging system

smaller

the ______ the wavelength the better the resolution

larger

the ______ the numerical aperture the better the resolution

smaller

the better the resolution, the ______ the r value

high, high

a combo of _____ mag & ____ resolution is desired for seeing tiny details of the object

independent

magnification & resolution are _____

lower

the _________ the wavelength of light, the better the resolution

contrast

difference in luminance &/or color that makes an object (or its representation in an image or display) distinguishable

brightness

the overall lightness of the image

backward scattered light

imaging in the eye is made possible primarily through ______ _______ ________ from different tissues

scatter

deviation in multiple directions as may be produced by cells or cellular features of the eye w/ which light interacts

exacerbated

scattering can be ______ by diseased tissues

invisible range (near-infrared)

which range of light is beneficial for surgery & imaging of the eye?

reflected, refracted, absorbed, scattered

what can light transmitted through the eye do?

1. intensity/energy

2. wavelength

3. coherence

4. polarization

what are the 4 fundamental properties of light?

1. frequency of the photon

2. number of photons emitted at a given frequency

3. energy carried by individual photons

4. refractive index of tissue

5. wavelength of light

what things does the backscattering of light in any direction depend on?

total energy

for a scatter producing multiple frequencies of radiation, this is the sum of energies produced at individual frequencies

wide field illumination

• illumination type

• pros:

  • provide the fastest enface view of the tissue, captured in a single shot

  • large FOV

• cons:

  • low image contrast

  • cross-sectional view is only possible by montaging images of different depths

slit illumination

• illumination type

• pros:

  • provide a fast cross-sectional view of the tissue, captured in a single shot

  • improved image contrast in 1 axis

• cons:

  • the enface view can be obtained by scanning across the tissue (slow)

point-scanning illumination

• illumination type

• pros:

  • improved image contrast in both axes

• cons:

  • slow for capturing the 3D image of the tissue

  • small FOV depending on the resolution of the image (Nyquist limit)

slit lamp

illumination by a thin slice of light, provides:

• reflection off desired surface (ant seg, post seg)

• scattered light portion of the image

Scheimpflug principle

orientation of the plane of focus is not parallel to the image plane

scheimpflug imaging

rotates the electronic camera in order to create a sharp image at all depths in the anterior chamber of the eye, increases the depth of focus, allows for more detailed & accurate imaging, contributing to better diagnostics & measurements of the anterior segment

BIO

• flood illumination or flashed illumination of the retina

• imaging formed on the observer’s retina

fundus camera

• flood illumination or flashed illumination of the retina

• imaging (digital) formed on a charged coupled device or complementary metal oxide semiconductor

degraded contrast due to backscattered light rays from different parts of the eye crossing over

what is the con of wide-field imaging, why does this occur?

rejects

confocal aperture _______ the out of focus light from other layers

point scanning laser ophthalmoscopy (SLO)

• sequential point illumination of the retina

• imaging (digital) formed on a point detector

• illuminates 1 point of the retina at a time, removing the contribution of backscattered light from other parts of the retina, thereby, improving the contrast of the retinal image

confocal SLO

SLO that performs even better by eliminating out-of-focus backscattered light from other depths of the retina

faster, wider, more, higher

while fundus imaging is ______ & provides a _____ FOV of the retina, SLO provides a ______ contrasted & ______ detailed view of the retina

line SLO

midground b/t wide-field illumination & point-scanning illumination, enabling faster imaging & detailed view of a wide field retina

interference

describes a unique case of superposition of 2+ individual waves, resulting in a standing wave; occurs under strict conditions: wavelength, coherence, polarization

interference, Michelson interferometer

OCT uses _________ realized w/ a ________ to measure the time of flight of light into & out of the eye

ultrasound

OCT is the optical analogy of _______

axial length

Zeiss IOLMaster uses time-domain OCT to determine the _________ of the eye

better

the broader the bandwidth of the source, the _______ the axial resolution

cornea

birefringence due to regular arrangement of collagen fibrils, most birefringent tissue in the eye

lens

no birefringence due to regular arrangement of fibers along the direction of light propagation

nerve fiber layer

birefringence due to oriented cylindrical structures w/in the ganglion cell axons

fibers of henle

birefringence due to oriented cylindrical structures w/in photoreceptor axons

RPE & sclera

depolarization caused by multiply-scattering of light

perpendicular

tissues made of fibers that are _______ to light are generally birefringent, they exhibit a refractive index along the fibers that is different from the refractive index across the fibers

ultra-widefield retinal image w/ integrated OCT

what 2 things does Optos give?

adaptive optics SLO

corrects the aberration of the eye, thereby enabling high contrast images of different layers of the retina w/ SLO

low, 10-20um, 1-10mm

OCT typically operates at a ____ numerical aperture w/ a corresponding lateral resolution in the order of _____, which enables a long depth of imaging in the other of _____ at the expensive of lateral resolution

2um

optical coherence microscopy achieves a ____ lateral resolution

weaker

fluoresced light is usually a ____ signal compared to the reflected light from the same target, or structures b/t the target & the camera/eye

air-tear film interface

what is the most powerful refractive surface of the eye?

less

fuch’s endothelial corneal dystrophy makes the cornea ____ transparent due to increased scattering & stromal edema

less

cataracts make the lens ____ transparent due to increased scattering

retina

what is the most sensitive & highly metabolic tissue of the eye?