Report on EYE-OCT.(OPTICAL COHERANCE TOMOGRAPHY)

1. EYE-OCT.(OPTICAL
COHERANCE
TOMOGRAPHY)
Submitted by:-
SANJIBPASHI
APPLIED ELECTRONICS AND INSTRUMENTATION ENG
HALDIA INSTITUTEOF TECHNOLOGY

2. Acknowledgment
I am sincerely thankful to Mr.Priyonko Das and also
thankful to Mr.Monodipan Shaoo& Mr.Soumya Roy-
Faculty of AEIE Dept. for this report. I thank them for
their total support & UNENDING help to me during the
entire report. I am also thankful to our friends who have
helped me very much during the report for any kind of
information, data, format, etc. Last but not the least; i
am thankful to our college & its library for providing me
the needful and supporting material for my report.
.
SANJIB PASHI

3. TABLE OF CONTENTS:
 INTRODUCTION
 WHAT IS OCT?
 PRINCIPLE OF OCT
 DIFFERENT KIND OF OCT
 WHY WE NEED OCT?
 SIX WAYS MEASLES CAN AFFECT THE EYES
 OCT SCANS PROCEDURE
 IDEA ABOUT RETINA
 DIFFERENT KIND OF ANOMALOUS
 SCANNING TIPS
 CONCLUSION

4. INTRODUCTION
 Eey Optical coherence tomography (EYE-OCT)is an
established medicalimaging technique.It is a non-invasive
optical medical diagnostic imaging modality which enables in
vivo cross-sectionaltomographic visualization of the internal
microstructure in biologicalsystems.Since its invention
(pioneered in Vienna by Prof. A.F. Fercher)in the late 1980s
and early 1990s,the original conceptof OCT was to enable
non-invasive optical biopsy.OCT is based on low-coherence
interferometry.Inconventional interferometry with
long coherence length (i.e., laser interferometry), interference of
light occurs over a distance of meters. In OCT, this interference
is shortened to a distance of micrometers,owing to the use of
broad-bandwidth light sources (i.e., sources that emit light over
a broad range of frequencies).Light with broad bandwidths can
be generated by using superluminescentdiodes or lasers with
extremely short pulses (femtosecond lasers). White light is an
example of a broadband source with lower power.

5. WHAT IS OCT?
 Optical Coherence Tomography, or OCT, is a noncontact, noninvasive
imaging technique used to obtain high resolution cross-sectionalimages of
the retina and anterior segment.
 Three-dimensional imaging technique with ultrahigh spatial resolution
 Measures reflected light fromtissue discontinuities
 Based on interferometry
 involves interference between reflected light and a referencebeam.
 Optical coherence tomography obtains imaging of subsurfacemucosa with
a resolution on the order of a low power microscop

6. PRINCIPLE OF OCT
Interferometry is the technique of superimposing
(interfering ) two or more waves, to detect
differences between them.
Interferometry works because two waves with the
same frequency that have the same phase will add
each other while two waves that have opposite
phase will subtract.

7. Light from a source is directed onto a partially
reflecting mirror and is split into a reference and a
measurement beam.
The measurement beam reflected from the
specimen with different time delays according to its
internal microstructure.

8. The light in the reference beam is reflected from a
reference mirror at a variable distance which
produces a variable time delay.
The light from the specimen, consisting of multiple
echoes, and the light from the reference mirror,
consisting of a single echo at a known delay are
combined and detected.


9. DIFFERENT KIND OF OCT
1>Time domain OCT: In time domain OCT the pathlength of the
reference arm is translated longitudinally in time. A property of low
coherence interferometry is that interference, i.e. the series of dark
and bright fringes, is only achieved when the path difference lies within
the coherence length of the light source. This interference is called auto
correlation in a symmetric interferometer (both arms have the same
reflectivity), or cross-correlation in the common case. The envelope of
this modulation changes as pathlength difference is varied, where the
peak of the envelope corresponds to pathlength matching.
The interference of two partially coherent light beams can be expressed
in terms of the source intensity, , as
where represents the interferometer beam splitting
ratio, and is called the complex degree of coherence, i.e. the
interference envelope and carrier dependent on reference arm scan
or time delay , and whose recovery of interest in OCT. Due to the
coherence gating effect of OCT the complex degree of coherence is
represented as a Gaussian function expressed as[15]
where represents the spectral width of the source in the
optical frequency domain, and is the centre optical frequency
of the source

10. 2> Frequency domain OCT (FD-OCT): In frequency domain
OCT the broadband interference is acquired with spectrally separated
detectors (either by encoding the optical frequency in time with a
spectrally scanning source or with a dispersive detector, like a grating
and a linear detector array). Due to the Fourier relation (Wiener-
Khintchine theorem between the auto correlation and the spectral
power density) the depth scan can be immediately calculated by a
Fourier-transform from the acquired spectra, without movement of the
reference arm

11. 3> Spatially encoded frequency domain OCT (spectral
domain or Fourier domain OCT): SEFD-OCTextracts spectral
information by distributing different optical frequencies onto a detector stripe
(line-array CCD or CMOS) via a dispersiveelement (seeFig. 4). Thereby the
information of the full depth scan can be acquired within a single exposure.
However, the large signal to noise advantageof FD-OCTis reduced due to the
lower dynamic rangeof stripe detectors with respectto single photosensitive
diodes, resulting in an SNR (signalto noise ratio) advantage of ~10 dB at much
higher speeds. This is not much of a problemwhen working at 1300 nm, however,
since dynamic range is not a serious problemat this wavelength range.
4>Time encoded frequency domain OCT (also swept
source OCT: TEFD-OCTtries to combine someof the advantages of standard
TD and SEFD-OCT. Herethe spectral components are not encoded by spatial
separation, but they are encoded in time. The spectrumeither filtered or
generated in single successivefrequency steps and reconstructed beforeFourier-
transformation. By accommodation of a frequency scanning light source(i.e.
frequency scanning laser) the optical setup becomes simpler than SEFD, but the
problem of scanning is essentially translated fromthe TD-OCTreference-arminto
the TEFD-OCTlight source. Herethe advantagelies in the proven high SNR
detection technology, while swept laser sources achieve very smallinstantaneous
bandwidths (=linewidth) at very high frequencies (20–200 kHz).

12. WHY WE NEED OCT?
Measles infectionscan harm the front or back of the eye,
possibly causing visionloss or blindness
 For better treatment we need OCT

13. SIX WAYS MEASLES CAN AFFECT THE EYES
Retinopathy: While rare, there are documented cases where the measles
virus destroys the retina, a layer of cells in the back of the eye that convert light
energy into electrical impulses that go to the brain. Retinitis can cause
temporary and, in some cases permanent, vision loss.
 Optic neuritis: This inflammation affects the optic nerve that sends signals fromthe back
of the eye to the brain. This complication is relatively rare but can occur in measles patients
who also develop encephalitis, or brain swelling, though cases without encephalitis have
also surfaced. Acute cases may be treated with corticosteroids. Like retinitis, vision loss
from optic neuritis can be temporary or permanent.
 Conjunctivitis: Redness and watery eyes from conjunctivitis occur in nearly all
measles patients. This type of pink eye usually develops early on in the disease and is a
hallmark symptom along with fever, cough and a runny nose, often occurring before the
telltale rash. This condition usually abates on its own as the disease runs its course.

14. Keratitis: Keratitis is an infection of the cornea, the window of the eye. In comparison
with conjunctivitis, keratitis has more severe symptoms and far more dangerous
consequences. Symptoms include pain, redness, tearing and light sensitivity. It can feel
as though foreign particles are lodged in the eye. Often treated with medicated drops,
keratitis will cause temporary blurred vision, but if it leads to scarring the loss of vision
can be permanent.
 Corneal scarring: Corneal ulcers are open sores on the front of the eye that can occur
when infected, either via the measles virus or from a bacterial infection that develops
secondary to measles. Ulcers may appear as white dots on the front of the eye and are
usually treated with topical antiviral or antibiotic drops. When the ulcers heal, they can
scar over and leave opaque scar tissue that may inhibit vision and cause blindness
Blindness:Measles is a leading cause of childhood blindness in developing countries
where immunization programs for this disease are less established or often interrupted
by conflict. When compounded by malnutrition, particularly vitamin A deficiency,
measles is associated with corneal scarring from ulceration and keratitis, two of the
most likely reasons for blindness from measles. Blindness from optic neuritis has also
been noted.

15. OCT SCANNING PROCEDURE
At first eye of the
patient is
introduce before
the sensor of the
OCT Machine
After few
min. the full
scane of the
eye thus
obtained
which is
quite visible
on the OCT

16. REGIONS OF RETINA
For purposes of analysis, the OCTimage of the retina can be subdivided vertically
into four regions
I. the pre-retina
II. the epi-retina
III. the intra-retina
IV. the sub-retina
Retinal Anatomy Compared to OCT:
 The vitreous is the black space on the top of the image
 We can identify the fovea by the normal depression
 The nerve fiber layer (NFL) and the retinal pigment epithelium
(RPE) are easily identifiable layers as they are more highly
reflective than the other layers of the retina
 This higher reflectivity is represented by the "hotter" colors (red,
yellow, orange, white) in the false color representation of the
OCT.

17. DIFFERENT KIND OF ANOMALOUS
A pre-retinal membrane with traction on the fovea:
a pigment epithelial detachmentis causing the convexity:
Macular cyst:
Preretinal macular fibrosis has been
variously termed by various
investigators as surface wrinkling
retinopathy, cellophane membrane or
cellophane maculopathy, preretinal
traction membrane, macular pucker etc.
The outer segments of the photoreceptors
receive oxygen and nutrition from the
choroid. If the retina is detached from the
choroid, the photoreceptors will fail. The
fovea has no retinal blood vessels and
depends wholly on the choroid for its
oxygen, so detachment of the macula leads
to permanent damage to the cones and rods
at the posterior pole, and loss of vision.
A cyst caused by vitreous traction in the
macula, the tiny oval area made up of
millions of nerve cells located at the
center of the retina responsible for sharp,
central vision.

18. Macular hole:
Serous retinal pigment epithelial detachment (PED):
The center of the macula is the fovea.
Foveal cysts are caused by vitreous
traction. Eyes that develop foveal cysts
may remain stable, develop full-
thickness macular holes
A serous pigment epithelial detachment
occurs when the sensory retina detaches
from the pigment epithelial layer due to
inflammation, injury, or vascular
abnormalities. A serous pigment
epithelial detachment often occurs in
conjunction with central serous
chorioretinopathy. This is because of the
fluid that accumulates in the subretinal
space.

19. SCANNING TIPS
Minimize patient fatigue by keeping scan time
to a minimum. Never scan an eye for more
than 10 minutes (FDA regulation).
Keep the cornea lubricated. Use artificial tears
and have the patient blink when you are not
saving a scan pass.
Reflectivity may be further enhanced by moving
the focus knob on the side of the OCT unit.

20. CONCLUSION
Optical coherence tomography is a
potentially useful technique for high depth
resolution, cross-sectional examination of
the fundus.To demonstrate optical
coherence tomography for high-resolution,
noninvasive imaging of the human retina.
Optical coherence tomography is a new
imaging technique analogous to ultrasound
B scan that can provide cross-sectional
images of the retina with micrometer-scale
resolution.

21. References:
www.Google.com
www.Wikipedia.org
www.ncbi.nlm.nih.gov
www.classteacher.com
www.geteyesmart.org
www.macula.org