Optical Coherence Tomography Laser therapy for Diabetic Retinopathy Vitrectomy

1. OPTICAL COHERENCE
TOMOGRAPHY
LASER THERAPY FOR DIABETIC
RETINOPATHY
VITRECTOMY
PREPARED & PRESENTED BY-
AL AMIN
JYOTISHMOY BORAH
MADHURJYAMOI TALUKDAR
MIHIR GHOSH
NILIMESH SARMA
RUHUL AMIN BARBHUIYA
B.OPTOMETRY 3rd YEAR, 2021-22

2. OPTICAL COHERENCE
TOMOGRAPHY(OCT)
INTRODUCTION
 OCT is a non-contact, noninvasive imaging
diagnostic tool that can perform crossectional
images of biological tissues within less than 10µ
axial resolution using light waves.
 It is specially suited for retinal disorders as retina
is easily accessible to external light.

3. BASIC PRINCIPLE
 Combination of low-coherence
interferometry with a special
Broadband width light in near
Infrared range(810nm).
 A broadband width near-IR light
beam is projected. The beam is
split to the tissue of interest called
as probe beam and to a
reference mirror at a known
variable position.
 The light is reflected back from
the boundaries between the micro structures and
is also scattered differently from tissues with
different optical properties .
 The echo time delay of the light reflected from
various layers of the retina is compared with echo
time delay of light reflected from the reference
mirror.

4.  A positive interference is produced when light
reflected from the retina and reference mirror
arrives simultaneously or within short coherence
length of each other.
 This interference is measured by a photodetector
which finally produces a range of time delays for
comparison.
 The interferometer integrates several data points
over 2mm of depth to construct a tomogram of
retinal structures.
 It is a real-time tomogram using false colour
scale. Different colours represent light
backscattering from different depths of the
retina.
 The low-coherence light source determines the
axial resolution which is 10µ for OCT1 & OCT2 ,
and 7-8µ for OCT3. The transverse resolution
depends on the probe beam diameter and is 20µ.

5. THE OCT MACHINE
The OCT system comprises of the following:-
 Fundus viewing unit.
 Interferometric unit.
 Computer display.
 Control panel.
 Colour inkjet printer.
Generations of commercially available OCT
machine:-
 OCT 1- 1st generation OCT machine.
 OCT 2- 2nd generation OCT machine.
 Both OCT 1 & OCT 2.
 OCT 3- 3rd generation OCT unit.

6. Fig: The OCT Machine

7. PROCEDURE OF OCT
 Activation of the machine and entering of patient data
is the first step.
 Patient position- the patient’s are dilated and patient
is asked to look into the internal fixation target light in
the ocular lens.
 Protocols for scan acquisition is selected as per the
case requirement. The scanning beam is placed on the
area of interest and scans are obtained. The Zeiss
Stratus OCT machine provides 19 scans acquisition
protocols designed for examination of retina and ONH.
 Production & display image- On z axis, 1024 points
are captured over a 2mm depth to create a tissue
density profile, with resolution of 10µ. On x-y axis,
tissue density profile is repeated upto 512 times every
5-60µ to generate a cross-sectional image. Several
data points over 2mm of depth are integrated by the
interferometer to construct a tomogram of retinal
structures. Images thus produced has an axial
resolution of 10µ and a transverse resolution of 20µ.
The tomogram is displayed in either gray scale or
false colour on a high resolution computer screen.

8. NORMAL OCT SCAN OF RETINA
The OCT scan of retina allows cross-sectional study of
the macular, peripapillary region including RNFL, &
ONH region.
COLOUR CODING IN OCT SCAN
 Red-yellow represent areas of maximal optical
reflection and backscattering.
 Blue-black represent areas of minimal signals.
INTERPRETATION OF RETINAL SCAN
 Vitreous anterior to the retina is non-reflective and is
seen as a dark space.
 Vitreo-retinal interface is well defined due to the
contrast between the non-reflective and the back
scattering retina.
 Different intermediate layers of neurosensory retina
betweeen the dark layer of photoreceptor and red
layer of RNFL are seen an alternating layers of
moderate and low reflectivity.

9. THE MACULAR SCAN
 Line Scan-It gives an option of acquiring multiple
line scan without returning to main window.
 Radial line-It consists of 6-24 equally spaced line
scan that pass through a central common axis.
 Macular Thickness-This is same as radial line
except the aiming circle as a fixed diameter of
6mm.

10. OPTIC DISC SCAN
Characteristic description of an optic disc scan is
shown below-
 Optic disc boundaries and diameters:The point at
which choriocapillaries terminates at lamina
cribrosa determines the disc boundaries.
 Optic cup is determined by the points at which
the nerve fibre layer terminates.

11. CLINICAL APPLICATION OF OCT SCAN
 MACULAR DISORDERS:
OCT pictures of some of the important macular lesions is
as below-
1.Macuar hole-OCT allows confirmation of diagnosis of
macular hole and differentiates it from the clinically
stimulating condition such as lamellar hole, course of
disease & response to surgical intervention.
2.Macular oedema-In OCT scan, the macular oedema is
characterised by the intraretinal areas of decreased
reflectivity and retinal thickening.
3.ARMD-Morphological changes in the nonexudative
ARMD. As well as subretinal fluid, intraretinal thickening
& choroidal neovascularization in exudative ARMD.
4.Central serous chorioretinopathy-In OCT scan, the
central serous chorioretinopathy is characterized by an
area of decreased reflectivity between two highly
reflective layers- the neurosensory retina & RPE.
5.Epiretinal membrane is diagnosed on OCT by the
presence of a highly reflective diaphanous membrane
over surface of retina.

12.  OCT IN GLAUCOMA
-Glaucoma diagnosis. Optic disc scan is
very useful in diagnosing & monitering
glaucomatous change.
-Useful in evaluating the RNFL for early
glaucoma detection.
-Evaluation of cystoid macular oedema
after combined cataract & glaucoma
surgery.

13. LIMITATIONS OF OCT
 Being purely dependent on optical principles, it
requires a minimal pupillary diameter of 4mm to
obtain a high quality image.
 OCT has limited applications in patients with poor
media clarity due to corneal oedema, dence
cataracts, vitreous haemorrhages and asteriod
hyalosis.
 High astigmatism, decentred IOL can
compromise quality of OCT scan.
 Limited transverse sampling.

14. OCT FOR ANTERIOR SEGMENT IMAGING &
BIOMETRY
 Anterior segment imaging- The anterior segment
can be evaluated & measured pre &
postoperatively after image acquisition, using the
analysis mode of system’s software.
 Corneal imaging & pachymetry –The OCT provies
high-resolution corneal images and
documentation for the anterior segment
specialist to support the evaluation of optical
health.
 New LASIK information- In addition to providing
a full-thickness pachymetry map prior to laser
surgery,OCT is the non-contact device to
image,measure and document both corneal flap
thickness and residual stromal thickness
immediately following LASIK surgery.

15.  IOL and implant imaging-OCT may also aid
postoperative evaluation by allowing imaging and
visualization of IOLs and implants in the eye.

17. LASER THERAPY FOR DIABETIC
RETINOPATHY
 Diabetic retinopathy refers to retinal changes
seen in patients with Diabetes mellitus.
 With increase in the life expectancy of
diabetics,the incidence of diabetic retinopathy
has increased.
 Diabetic retinopathy is a leading cause of
blindness.
TREATMENT OF DIABETIC RETINOPATHY
 Intravitreal anti-VEGF drugs
 Intravitreal steroids
 LASER therapy
 Surgical treatment

18. LASER THERAPY
 ETDRS had recommended focal laser for focal
DME and GRID laser for diffuse DME.
 Laser helps possibly by stimulating the RPE
pump mechanism and by inhibiting VEGF release.
 Before the advert of Anti-VEGFs,which only
stabilises the vision,was the mainstay
in the treatment of DME.
 However with the introduction of anti-VEGF
drugs which also improves vision,the role of
Laser therapy has become limited.
 Laser therapy is performed using double
frequency YAG laser 532nm or argon green laser
or diode laser.

19.  Present indicate on protocols for laser
therapy are shown below-
1.Macular photocoagulation:
It is of 2 types-
a)Focal photocoagulation:It is the
treatment of choice for focal
DME not involving the
centre of fovea.

20. b)Grid photocoagulation:It is no more the
treatment of choice for focal DME.It may
be considered only for recalcitrant cases
not responding to anti-VEGF and intra-
vitreal steroids

21.  2.Panretinal photocoagulation(PRP)or scatter
laser consist of 1200-1600 spots,each 500
micrometre in size and 0.1 sec duration.
 Laser burns are applied outside the temporal
arcades and on nasal side one disc diameter
from the disc upto the equator.
 The burns should one
burn width apart.
 In PRP inferior quadrant of retina is first
coagulated. PRP produces destruction of
hypoxic retina which is responsible for the
production vesoformative factors.

24. VITRECTOMY
 Vitrectomy is the surgical removal of
vitreous.
 Common terms used in vitrectomy are :
Anterior vitrectomy :It refers to removal
of anterior part of vitreous.
Core vitrectomy : It refers to removal f
central bulk of vitreous.
Subtotal and total vitrectomy : In this
almost whole of the vitreous is removed.

25. TECHNIQUES OF VITRECTOMY
 Anterior vitrectomy:limbal approach
This technique is employed to perform only
anterior vitrectomy.
 Indications :
Vitreous loss during catract extraction
Aphakic keratoplasty
Anterior chamber reconstruction after perforating
trauma with vitreous loss
Subluxated and anteriorly dislocated lens

26. Pars plana vitrectomy :
Pars plana approach is employed to perform
anterior vitrectomy, core vitrectomy, subtotal
and total vitrectomy.
Pars plana vitrectomy (PPV) is a commonly
employed technique in vitreoretinal surgery that
enables access to the posterior segment for
treating conditions such as retinal detachments,
vitreous hemorrhage, endophthalmitis, and
macular holes in a controlled, closed system.
Indication :
 Endophthalmitis with vitreous abscess.
 Vitreous haemorrhages.
 Proliferative retinopathies such as those
associated with diabetes, eales’s disease,
retinopathy of prematurity and retinitis
proliferans.

27.  Complicated cases of retinal detachment such as
those associated with giant retinal tears, retinal
dialysis and massive vitreous traction. Presetly,
even simple cases of rhegmatogenous, retinal
detachment are managed with this technique.
 Removal of intra ocular foreign bodies.
 Removal of dropped nucleus or IOL from the
vitreous cavity.
 Persistent primary hyperplasty vitreous.
 Vitreous membranes and bands.
 Macular pathology like macular hole and epi-
retinal membrane.

29. PROCEDURE OF PARS PLANA VITRECTOMY
(PPV) :
Basic Setup
The basic components of a vitrectomy setup
include the following elements:
 Vitrectomy machine (e.g., Alcon Constellation,
DORC EVA, Bausch + Lomb Stellaris PC).
 Surgical microscope and wide-angle viewing
system (e.g., Zeiss RESIGHT, Oculus BIOM, AVI).
 Infusion cannula which maintain IOP set by the
vitrectomy machine.
 Endoillumination light source for visualization of
the posterior segment including vitreous and
retina.
 Vitrectomy cutter (or vitrector): for vitreous
removal, aspiration, and peeling and cutting
membranes among other functions.

30. Gauges
 The gauge refers to the
size of the instruments with
higher numbers corresponding
to smaller instruments.
 Endophthalmitis rates twelve to
twenty-eight times higher with
25-gauge vitrectomy compared
to 20-gauge vitrectomy although
endophthalmitis rates were low
in both groups. However,subsequent
studies have found similar rates of
endophthalmitis with 20-gauge and 25-gauge
vitrectomy.
 There are numerous advantages of small-gauge
vitrectomy, including:
Increased patient comfort.
Decreased corneal astigmatism.
Decreased operative times.
Decreased conjunctival scaring.

31. Dyes
The following four dyes are the
most commonly used in vitreoretinal
surgery:
 Triamcinolone acetonide: available
In non-preservative-free formulation
Called Kenalog and preservative-free
formulation called Triescence,
Triamcinolone is particularly useful for
staining the vitreous gel. Injection of triamcinolone
during pars plana vitrectomy
 Trypan blue: a hydrophilic dye also used for staining the
anterior capsule during phacoemulsification surgery. It
is used in vitreoretinal surgery to stain the ERM and ILM
and is FDA approved for use in ERM removal cases.
 Brilliant blue: commonly used worldwide and recently
approved by the FDA in 2019, it is used primarily for
staining the ILM with minimal toxicity.
 Indocyanine green: traditionally used for angiography,
indocyanine green also effectively stains the ILM.
However, at higher concentrations, it is toxic to the
retina and RPE.

32. Retinal Detachment
The principles of retinal detachment repair via pars plana vitrectomy are
to remove the vitreous gel and any vitreoretinal traction, locate and
laser any retinal tears, and insert an intraocular tamponade.
The basic steps are as follows:
 Insert trocars in the pars plana (3.0-4.0mm from the limbus
depending on the lens status) typically using a beveled incision
technique.
 Perform a core vitrectomy to remove the central vitreous gel. Use of
triamcinolone can aid with vitreous removal.
 Induce a posterior vitreous detachment if a natural one has not
already occurred. This is often done using the vitrectomy cutter on
the aspiration only setting (i.e., the cutter function is turned off).
 Perform a peripheral vitrectomy and release traction over the
detached retina, at the retinal tears, and any areas of lattice
degeneration. Again, triamcinolone can be helpful during this step.
 Flatten the retina by draining subretinal fluid from a pre-existing
break or a newly created drainage retinotomy while performing a
fluid-air exchange, typically using a soft tip cannula. Alternatively,
heavy liquids such as perfluorocarbons can be injected posteriorly to
push subretinal fluid anteriorly out through a pre-existing break.
 Once the retina is flattened, endolaser is then performed around the
retinal breaks.
 Insert an intraocular tamponade. SF6 (lasting 2-3 weeks) and C3F8
(lasting 6-8 weeks) gas are most commonly used although there are
indications for silicone oil (lasting permanently until it is taken out) if
longer tamponade is needed or in patients who are monocular, must
fly, or cannot position.

33. Membrane Peel
 To treat conditions such as epiretinal membranes, macular
holes, vitreomacular traction, tractional retinal
detachments, and proliferative vitreoretinopathy,
membrane peeling may be necessary. As with retinal
detachment surgery, the initial steps of inserting trocars,
performing a core vitrectomy, and inducing a posterior
vitreous detachment if not already present are similar. The
degree of peripheral vitrectomy performed may depend on
the clinical scenario.
 Next, attention is turned to the membrane itself that
requires peeling. A different set of techniques is used here
compared to retinal detachment surgery. First, a higher
magnification and resolution lens is used, which may be
the 68-degree AVI lens, the green macular lens with the
Zeiss RESIGHT, or the DORC flat vitrectomy lens.Next, a
vital dye can be instilled in the posterior segment to
improve tissue visualization. With any membrane peel, an
initial flap must be created if not naturally present,
followed by peeling of the membrane off the retinal
surface. The initial flap can be created with Maxgrip or ILM
forceps, an MVR blade, a Tano scraper, a Finesse Flex loop,
or a pick.

34. Complications of vitrectomy
 Infections.
 Excess bleeding.
 High pressure in the eye.
 New retinal detachment caused by the surgery.
 Lens damage.
 Increased rate of cataract formation.
 Problems with eye movement after surgery.
 Change in refractive error.
There is also a risk that the surgery will not
successfully repair your original problem, if this
happens , the patient will need a repeat surgery.

35. THANKYOU