2. • Refractive surgery encompasses a range of procedures aimed at
changing the refraction of the eye by altering the cornea or lens, the
principal refracting components.
• Myopia, hypermetropia (hyperopia) and astigmatism can all be
addressed, though correction of presbyopia is yet to be achieved on a
consistently satisfactory basis .
3. Techniques
• Excimer laser
ablation is done
under a partial-
thickness lamellar
corneal flap.
• Laser-assisted in situ
Keratomileusis (LASIK)
• Refractive Lenticule
Extraction (ReLEx):
ReLEx "FLEx"
(Femtosecond Lenticule
Extraction)
ReLEx "SMILE" (Small
Incision Lenticule
Extraction)
FLAP BASED PROCEDURES
The excimer laser is used to
ablate the most anterior
portion of the corneal stroma.
These procedures do not
require a partial thickness cut
into the stroma. Surface
ablation methods differ only in
the way the epithelial layer is
handled.
• Photorefractive keratectomy
(PRK)
• Transepithelial
photorefractive keratectomy
(TransPRK)
• Laser Assisted Sub-
Epithelium
Keratomileusis(LASEK)
• EPI-LASIK
SURFACE PROCEDURES
CORNEAL INCISIONAL
PROCEDURES
OTHERS
• Radial keratotomy
• Arcuate keratotomy
• Limbal relaxing
incisions
• Laser thermal
keratoplasty (LTK)
• Intrastromal
corneal ring
segments (Intacs)
• Phakic intraocular
lens (PIOL)
implantation
6. LASERS USED FOR REFRACTIVE CORNEAL
PROCEDURES
• EXCIMER LASER
• SOLID STATE UV LASER
• INFRARED FEMTOSECOND LASER
7. EXCIMER LASER
• EXCIMER is “excited dimer”
• Dimer of inert gas example
Argon or Xenon bound with a
halogen eg. Fluorine or Chloride
• combination of gases Arf of
wavelength 193nm is
appropriate as longer
wavelength of more than 280nm
causes endothelial damage
• Arf : has the ability to remove
minute amount of corneal tissue
(0.2 -0.3 nm ) with no thermal
damage .
The femtosecond lasers have
the property to emit ultrashort
pulses with high crest power
from low energy pulse
• Based on photodisruption :
focused laser pulses divide
the tissue at molecular level
• Infra red wave (1053nm)
Advantage :
It makes it possible to focus
the beam very accurately
much deeper than excimer
No heat damage of
surrounding tissue
SOLID STATE U-V LASER FEMTOSECOND LASER
10. PROCEDURE
• Patient selection :
-patient motivation
-Age : above 18 years of age with stable refractive error for atleast 1 year . There is no
upper age limit . How ever , patient older ta 45 years should be operated sparingly because
: there is a greater risk of over correction and need for using presbyopic glasses
- Occupation : RK avoided in jobs requiring night driving because of chance of trouble
some glare , sportsperson , security person ( more chances of globe trauma )
- Ocular abnormalities :
ABSOLUTE : keratoconus , chronic steroid and antimetabolite use for immunosuppression ,
glaucoma , herpes simplex , connective tissue disorder
RELATIVE : Blepharitis , dry eye , uveitis , chronic eye rubbing , diabetes mellitus , other
ocular surface disorders
11. • PRE OPERATIVE EVALUATION
- SLT LAMP EXAMINATION
- Cycloplegic refraction
- Measurement of pupil size : is essential as the optical function is influenced
by the diameter of the pupil . Pupil size should be measured under low light
conditiond preferably with an infrared pupillometer .
IDEALLY , THE ABLATION ZONE SHOULD NOT BE LESS THAN THE DIAMETER OF
DARK ADAPTED PUPIL (6mm ) to prevent post operative glare and halos
- IOP : rule out glaucoma
- Posterior segment evaluation
- Keratometry , corneal topography measurements , pachymetry
12. Surface corneal laser ablation procedures
• Corneal surface ablation in form of
PRK is the oldest technique of laser
vision correction .
• It became unpopular with advent of
LASIK which is interstromal ablation
• Recently there is resurgence of
Advanced surface ablation
procedures : utility in thinner
corneas , no flap related
complications , less haze and
regression because of adjuvant of
mitomycin C .
13. PHOTOREFRACTORY KERTECTOMY
• employs excimer laser ablation to reshape the cornea.
• correct myopia up to 6 D (sometimes higher)
• astigmatism up to around 3 D
• low–moderate hypermetropia.
• Advantage : no flap related complications , procedure of choice for patients
at higher than average occupational or leisure-related risk of eye injury.
• Residual refractive error : post cataract surgery , post LASIK or post any
other refractive surgery
• Preferred procedure when LASIK is contraindicated
14. Technique
• corneal epithelium is removed prior to
ablation by an automated brush (Amoils
epithelial scrubber) and alcohol.
• Ablation of the Bowman layer and anterior
stroma is performed, generally taking 30–
60 seconds.
• sophisticated tracking mechanisms adjust
laser targeting with eye movement, and will
pause the procedure if the eye is
significantly decentered.
• The epithelium usually heals within 48–72
hours.
• A bandage contact lens is generally used to
minimize discomfort.
• Subepithelial haze invariably develops
within 2 weeks and commonly persists for
several weeks to months.
• Intraoperative application of mitomycin C
(mitomycinLASEK or M-LASEK) may reduce
haze.
15. Complications
• slowly healing epithelial defects
• corneal haze with blurring and
haloes
• poor night vision and regression of
refractive correction.
• Uncommon problems include
decentred ablation, scarring,
abnormal epithelial healing,
irregular astigmatism, infection and
acute corneal necrosis.
16. ADVANCED SURFACE ABLATION PROCEDURES
• Advanced PRK : Epithelium is removed mechanically with a beaver knife or a spatula or specialized brush
• LASEK : Epithelium flap is created with help of alcohol . A pre-incision is made with micro trephine . 30%
alcohol is applied for 20 sec . The alcohol is absorbed with a merocele sponge . Excess alcohol is irrigated
away with BSS . Flap is raised and repositioned / removed at the end of surgery .
• Epi-LasiK : Epithelial flap is created with the help of a blunt epi keratome and repositioned at the end of
surgery . Preferred over LASEK as avoids toxic effects from alcohol .
• Transepithelial PRK :Epithelium is removed by the laser in Photoablative de-epithelialization mode followed
by laser reshaping the stroma in PRK mode
Epi-lasik
17. INDICATIONS
• Myopia upto 6D
• Astigmatism upto 4D
• Hyperopia upto 3D
• Residual refractive error : post cataract surgery , post LASIK or post
any other refractive surgery
• Preferred procedure when LASIK is contraindicated
18. LASER SUBEPITHELIAL KERATOMILEUSIS(LASEK)
• Combined features PRK and LASIK
• Epithelial flap is removed by alcohol
Procedure
• Anaesthesia
• Trephining
• Alcohol(20%) treatment for 1 min
• Separation of epithelium
• Stromal ablation with excimer laser
• Reposition of epithelial flap
• BCL over flap
19. LASIK : Laser (or laser-assisted) in situ
keratomileusis (LASIK)
• The excimer laser advantage :
can ablate tissue to a precise depth , negligible disruption of surrounding
areas ,used to reshape corneal stroma exposed by the creation of a
superficial flap;
• the flap remains attached by a hinge to facilitate accurate and secure
repositioning.
Myopia is corrected by central ablative flattening, and hypermetropia by
ablation of the periphery so that the centre becomes steeper.
• LASIK can generally be used to treat higher refractive errors than surface
ablation techniques (see below): hypermetropia up to 4 D, astigmatism up
to 5 D and myopia up to 12 D depending on initial corneal thickness.
20. • Patient selection :
Important consideration for lasik
A CORNEA WITH CENTRAL THICKNESS OF LESS THAN 450 MICRON IS
CONTRAINDICATED IN LASIK
-IOP, pupil size , contact lens use , visual acuity , refraction , slit lamp biomicroscopic
examination , posterior segment evaluation
CORNEAL TOPOGRAPHY AND PACHYMETERY ARE MOST ESSENTIAL BEFORE
PERFORMING LASIK
- Most important is to rule out sub epithelial ectactic disorders .
-Adequate globe exposure : patient with sunken eye balls and small apertures pose a problem as it is
mandatory for application of suction ring and microkeratome to pass
-Corneal thickness : at least be 450microns in the centre . An adequate handling thickness of 500 micron
provides about 90 micron for ablation since 180 micron is the thickness of the flap and 250 micron stromal base is to
be left behind .
21.
22. Flap
• Ideal flap : 130 -160 micron in thickness , before starting the
procedure , it should be noted for patient with myopia of 25 D or
more or when cct is less than 530 micron , a thinner flap 130 micron
or shallower ablation or both are required
• Speed of the pass : A rapid pass produces a thin cut while a slow pass
produces a thicker corneal flap
• Oscillation of the blade affects the flap
• Iop : 60 -65 mmhg
23. Femtosecond laser over
microkeratome :
• Reduced symptoms of dry eye
• Gentle approach with minimal or no transient
visual loss( black out period )
• Suction needed here is much less compared to
a vacuum created by mechanical device
• The laser beam can be focused at any depth so
that a wide range of flap thickness can be
obtained
• There are greater option in flap diameter , side
cut angle , hinge position and hinge length
• The chances for epithelial in growth are less
since cells are not carried in by the blade
24. Post operative care
• Antibiotics and corticosteroid therapy
• tear supplements
• follow up : 1 day, 1 wk., 3wks, 3 months, 6months
• Avoid water in eyes - first 2wks
• Wear protective gear in any contact sports
• Avoid eye rubbing => dislocation of flap
• 3-6 months later = adequate stabilization of flap
25.
26. CUSTOM LASER IN SITU KERATOMILEUSIS
• C-LASIK, also called 'customized ablation LASlK', is a revolution in
photorefractive procedures.
• Custom ablation is an ablation pattern that attempts to optimize the
eye's optical system using a variety of spherical, cylindrical,aspherical
and asymmetrical treatments based on the individual eye's optic and
anatomy as well as the patient's needs
• The exact assessment of individual eye's optics is made by corneal
topography and aberrometry
27. Types :
• Corneal topography-guided ablation
• wavefront-guided ablation
Corneal topography-guided ablation takes care of the ocular aberrations
detected by corneal topography and treats the irregularities as ntegrated
part of the laser treatment plan.
Wavefront-guided ablation treats the aberrations of the entire human optical
system that are measured by a variety of wavefront measurement devices.
28. LASIK OVER PRK : Less pain , early recovery , les post opp
haze
LASEK OVER LASIK :
- Corneal ectasia is less as residual bed thickness is more
- Flap related complications are not known
- Additional correction of myopia up to 5 D more than
LASIK ia possible as another 90 micron of corneal stroma
is available for ablation
- Better for thin cornea . An individual with ct of 490
micron may still have an option of 6 D myopia correction
- Increase in high order aberrations noted with LASIK
- POST op chances of dry eye are less as the corneal nerves
are not severed as with LASIK
- Large zone treatment is possible with LASEK . In LASIK ,
the flap size is restricting factor to the size of the
treatment zone
- Disadvantage : Pain more , delayed recovery
EPI-LASIK over LASEK : No alchol side effect ,
less pain , faster healing and leass haze
EPI LASIK vs Lasek VS lasik present status :
- EPI – LASIK has replaced LASEK
- LASEK is good alternative where latter is
handicaped i.e. myopia >8D and thin cornea
- But not preferred due to complications .
29. NEWER LAMELLAR CORNEAL REFRACTIVE
PROCEDURES
• REFRACTIVE LENTICULE EXTRACTION : refractive lamellar corneal surgery which attempts to
remove ,add or modify the corneal stroma so that the radius of curvature of anterior corneal
surface is altered as desired .
• Approaches :
- FLEX (FEMTOSECOND LASER LENTICULE EXTRACTION )
- SMILE ( SMALL INCISION LENTICULE EXTRACTION)
30. Surgical steps of relex
1. Creation of intrastromal lenticule: the Intrastrornal refractive lenticule of
calculated parameters is created by four femtosecond Incisions (photodisruption
plane) as follows:
• First photodisruption plane is created along the Posterior surface by applying
laser pulses from Periphery to the center of the proposed intra- stromal lenticule
(usually 6-7 mm optic zone
• Second photodisruption plane is a 360° vertical Side cut along the periphery of
the proposed Lenticule
• Third photodisruption plane is made along the Anterior surface of the lenticule
starting from Centre to the periphery and extending 0.5-1 mm beyond the
vertical side cut of the lenticule.
• Fourth photodisraption plane is a vertical cut in the anterior corneal flap (anterior
side cut). The extent of this cut varies depending Upon the approach
31.
32. 2. Removal of Ienticule and reposition of anterior corneal flap . The
technique of removal of created lenticule is different in Flex and SMILE
In Flex approach, the steps are as follows;
- The hinged anterior corneal flap is separated from
the anterior surface of the lenticule with the help of a
specially designed ReLEx Manipulator.
- The anterior corneal flap is then lifted to the side as
in standard LASIK.
- The intrastromal lenticule is then separated all along
its peripheral edge and separated posteriorly from
the bed with the help of ReLEx manipulator.
- The freed lenticule is then removed away with the
help of a forceps
- A drop of irrigating fluid is placed on the bed and
the anterior corneal flap is repositioned gently as in
standard LASIK.
In Smile approach, the anterior surface, peripheral
margins (360°) and posterior surface of the
lenticule is separated from the surrounding tissue
with the help of ReLEx manipulator inserted
through the 40-60° cut made in the anterior cornea
A 21-gauge forceps is then introduced through the
smile incision, the edge of the lenticule is firmly
grasped and the lenticule is gently pulled out of the
incision .
The anterior corneal surface is gently pressed to
snugly oppose the anterior and posterior raw
surfaces of the intrastromal tunnel.
33.
34. Additional Advantages of Smile ReLEx
• Flip-related complications gone.
• Healing is much faster.
• Lower potential for dry eye as fewer
corneal nerves cut.
• As flap is not made, so better long-term
stability of cornea
• Further, reduced risk of corneal ectasia
Advantages of Flex over Femto-LASlK/
conventional LASIK
• Excimer laser-related complications are
eliminated.
• Microkeratome-related complications
eliminated (of. conventional LASIK).
• Refractive results more accurate especially in
myopia of to 10 D.
• Potential for stroll drying is less.
• Induction of optical aberration is minimized.
• Reduction of the effective optical zone does
not occur.
• Low potential for flap misalignment error.
• Risk of corneal ectasia is less.
