2. Eye’s refractive power determined by 3
variables - 1. Power of the cornea
2. Power of the lens
3. Length of the eye
EMMETROPIA
- Optically normal
eye
- Image of the object
being viewed is
focused on retina
- Resulting in clear &
sharp vision
3. AMMETROPIA – A condition of refractive
error
- Causes blurred vision as
image is
not focused on retina
1. Myopia
- Near-sightedness
Image is focused
in front of retina
2. Hyperopia
- Far-sightedness
- Image is focused
behind retina
4. 3. Astigmatism – Refraction varies in different
meridia
- Rays of light entering eye
can’t converge to
a point focus but form focal
lines
4. Presbyopia – Eye sight of old age
- Physiological insufficiency of
accomodation
leading to progressive fall in near
vision
- Mechanism :
1. Senile lens hardening
5. PUPIL SIZE & CENTRATION OF
REFRACTIVE PROCEDURES
Rays of light from a point source are
refracted by the area of cornea overlying
the entrance pupil . This area is c/a the
corneal optical zone .
Entrance pupil - Virtual image of
anatomical pupil formed by magnifying
effect of the cornea – larger & closer to
cornea.
Optical zone in a keratorefractive procedure
: “The area of central cornea that bears the
refractive change caused by the surgery”.
6. FACTORS DETERMINING
CENTRATION OF
KERATOREFRACTIVE PROCEDURES
Foveal photoreceptors
orient themselves towards
centre of the pupil (StilesCrawford effect), even if
entrance pupil becomes
eccentric.
Pupillary dilatation
under mesopic & scotopic
conditions, beyond the
edge of the optical zone
causes edge glare & haloes
=> Favour the centration of
KR procedures on the
7. CLASSIFICATION OF REFRACTIVE
PROCEDURES
REFRACTIVE SURGERIES
CORNEA BASED
R.K.
PRK
LASIK
EPILASIK
LASEK
Conductive
Keratoplasty
Corneal Inlays
and rings
LENTICULAR BASED
Clear Lens
extraction for
myopia
Phakic IOL
Prelex Clear
Lens
Extraction with
use of
Multifocal
IOL’s
COMBINED(BIOPTICS)
•
Combination
of the two
19. Astigmatic Keratotomy (AK)
For astigmatism only
1-2 tranverse relaxing mid-peripheral
corneal incisions
Arcuate or straight fashion
Perpendicular to the steep meridian
Localized ectasia of peripheral cornea
& central flattening of the incised
meridian
22. Cataract surgery - Limbal Relaxing
Incisions have gained popularity- more
comfortable for patient than arcuate or
transverse mid-peripheral incisions
24. PHOTOREFRACTIVE
KERATECTOMY
Outer layer of cornea is removed then
laser is applied
vision improves as surface heals after
4 to 7 days
discomfort present during healing
can cause corneal scarring
27. LASIK (Laser-assisted in situ
keratomileusis)
Most commonly performed
refractive surgery
Combines lamellar corneal
surgery with accuracy of
the excimer laser
Excimer laser ablation of
corneal stroma beneath a
hinged corneal flap that
is created with a
mechanical femtosecond
laser microkeratome
28. HISTORICAL REVIEW
Barraquer first described lamellar refractive
surgery in 1949
Dr. Ruiz introduced microtome propelled by gears
& keratomiluesis in situ in early 1980s
Dr. Leo Bores performed 1 st keratomiluesis in situ
in 1987 in the US
Burrato reported use of excimer laser in situ after
a cap of corneal tissue was removed
Pallikaris – idea of combining precision of
excimer laser with lamellar corneal surgery
LASIK was introduced & developed at the Univ. of
Crete, Greece
Wavefront-guided LASIK became available in the
US in 2003
29. Types of lasers used
Excimer
: for corneal stromal
ablation
Non-Excimer solid state lasers : for
flap creation
30. EXCIMER LASERS
Excited
dimer of two atoms
-an inert gas(Argon)
-a Halide(Fluoride)
releases ultraviolet energy at193nm
Reshapes corneal surface by removing
anterior stromal tissue
Process – Non-thermal
Ablative
Photodecomposition
31. Laser delivery patterns :
1) Broad-beam lasers - deliver a large diameter
beam of laser – starts small & expands as the laser
is delivered
ADV. Less operative time
DISADV. Creation of central islands ( difficulty to
maintain
uniform consistency over a larger diameter beam)
32. 2) Scanning excimer lasers:
- Scanning-slit laser
- Flying spot laser
Provide smoother ablation than the old
broad-beam lasers
33.
Advantage of Non-Excimer solid state
lasers No
toxic excimer gases
Wavelength closer to absorption peak of
corneal collagen—less thermal and
collateral damage
Better pulse to pulse stability
Not absorbed by air,water,tear fluid-so
less sensitive to humidity or room
temperature
No purging with inert gases required.
34. Patient selection
Patients need to be fully informed about
potential risks,benefits and realistic
expectations
Age should be above 18 years
Refractive status should have been stable
for at least 1 year.
Current FDA approval
Myopia-upto -15D
Hyperopia –upto +6D
Astigmatism-upto 6D
35.
CCT such that minimum safe bed thickness
left(250-270µ).Post op Corneal thickness
should not be <410µ.
Extreme keratometric values ( flatter than
41.00 or steeper than 47.00) avoided
Videokeratoghic clues to a KC suspect:
K value > 47.2 D,
Inferior steepening of > 1.4 D,
difference of > 1.9 between K values of
both eyes
Contact lens free period before
examination :
3-4 wks for rigid contact lens wearers
2 wks for soft contact lens wearers
36. BASIC MECHANISM
Normal cornea – prolate shape ( greater
curvature centrally )
Myopic correction – create an oblate shape
by central corneal laser ablation
Hyperopia - Excimer laser ablation at midperiphery steepening of central cornea
Mixed astigmatism –
1)Bitoric LASIK technique – flattening
the steep meridian with paracentral
ablation over the flat meridian
2)Cross-cylinder technique – dividing
cylinder power into 2 symmetrical parts –
half of the correction is treated on the
positive meridian & half on the negative
37. MUNNERLYN EQUATION
Roughly defines the depth of ablation
required to achieve a specific amount of
correction
For 1 D correction depth of ablation
required (in microns) one-third of the
square of diameter (in mm)
So each spherical equivalent diopter of
myopic correction performed at a 6mm
optical zone will ablate 12 microns of
tissue
38. OPERATIVE PROCEDURE
5mg Diazepam 5-10 min before procedure
Verification of entered computer data before
starting procedure
Topical anasthesia-Proparacaine 0.5%,
Lignocaine 4%.
Surgical Painting and draping
Lid speculum with aspiration
Proper centration over pupil & maintenance
by the aid of Tracking systems & iris
registration
C/L eye taped shut to prevent cross-fixation
39. 1 st step - Creation of flap
Corneal marking
with ink
Adequate placement
of suction ring
using bimanual
technique
Suction
engagement by foot
control
40. Adequate IOP (>65mmHg) which is
necessary for the microkeratome to
create a pass and resect the corneal
flap.
verified by BARRAQUER
TONOMETER
confirmed by patient – temporary
loss of visualization of fixation light
41. 2nd step - Resection of corneal
flap
Artficial tear drops instilled
MICROKERATOMES
1) Steel Microkeratome
-Uses Disposable blades
-Blade Plate can be set at 120µ,140µ,160µ
and180µ.
-Nasal or superiorly hinge flaps can be
created.
-Eg.Hansatome,ACS,Carriazo Barraquer,
Moria.
2) Waterjet Keratome
-Less debris & collateral damage than blade
42. 3) Laser Keratome (IntraLase)
-
Solid-state laser
1053 nm wavelength
3 µm spot size- high precision
Uses brief Femtosecond laser pulses to
cause disruption in a lamellar plane
- Needs lower vacuum & any hinge can be
made
- Can make flaps as thin as 100µ(Sub
Bowmans
Keratomileusis)
43. - Flap has vertical edges –so reduced
epithelial ingrowth.
- Steel Microkeratome flap thicker in
periphery and thinner in the centre. Not so
with Intralase(Planar).
44. 3 rd Step-Delivery of Laser After
flap is lifted,assessment of
residual corneal bed thickness usin USG
pachymetry
laser is applied to the stroma according
to the ablation profile calculated by the
machine.
Excimer Laser beam is delivered by the
following ways depending on the
machineBeam Delivery
Broad Beam
Scanning Slit Beam
Flying Spot
45.
Most machines employ a flying spot
to deliver laser with the help of
incorporated eye tracker or iris
registration.
46. 4 th step-Reposition Of the Flap After
irrigating interface ,flap reposited
Sweeping movements with a wet cellulose
sponge
From the hinge towards the periphery of
flap
Adhesion verified – stretching the flap
towards gutter
Topical antibiotic, steroid & lubricant
instillation transparent plastic
shields
47. WAVEFRONT-GUIDED
(CUSTOMIZED) EXCIMER LASER
REFRACTIVE SURGERY
To correct higher-order aberrations in addition to
lower- order sphero-cylinder corrections
- LOWER ORDER Nearsightedness
Farsightedness
Astigmatism
- HIGHER ORDER Spherical aberration
Chromatic aberration
Diffraction
Curvature of field
Coma
Trefoils
Quadrifoils
48.
Higher order aberrations occur in
visually significant manner in 1015% of population
Cannot be corrected with
spherocylinder lens or conventional
laser refractive surgery
Correction – Hard contact lenses
- Wavefront-guided
customized
49. MEASUREMENT OF WAVEFRONT
ABERRATIONS (ABERROMETRY)
ABERROMETER
OUTGOING ABERROMETERS
Analyze outgoing light that emerges
From retina & passes through the
Optical system of eye
Hartmann-Shack Aberrometer
(most commonly used)
INGOING ABERROMETERS
Analyze ingoing light that forms an
image on the retina
Tscherning Aberrometer
Ray Tracing Aberrometer
Scanning Slit Refractometer
50. ANALYSIS & DECOMPOSITION OF
WAVEFRONT ABERRATIONS INTO
COMPONENTS
ANALYSIS OF ABERRATIONS
ZERNIKE POLYNOMIALS
(most commonly used)
FOURIER ANALYSIS
51. CUSTOMIZATION OF ABLATION
PROFILE
TYPES OF CUSTOMIZATION
TOPOGRAPHY-GUIDED ABLATION
(Conventional laser surgery)
WAVEFRONT-GUIDED ABLATION
(Customized laser surgery)
52.
Conversion of wavefront measurement
data to an ablation profile
Imported to an excimer laser
Precise registration of these patterns
on cornea by eye trcking & iris
registration technology
Precise wavefront-guided ablation
during LASIK is achieved
53. CUSTOMIZED ABLATION
PLATFORMS
1) Nidek Advanced
Vision
EXcimer Laser
system
OPD-Scan optical path
difference scanning
system (combines
measurement of
corneal topography &
aberrometry)
Develops customized
ablation profile
EC-5000CX II excimer
56. 4)Bausch and Lomb
Zyoptix System
Diagnostic part :
- Zywave aberrometer –
a Hartmann-Shack
sensor
- ORBSCAN – 3D
information about
cornea
Truncated Gaussian
beam laser – 2 sizes –
2mm – corrects
majority of refractive
error in short time
1mm – more specific
ablation pattern on
58. COMPLICATIONS
INTRAOPERATIVE
COMPLICATIONS
1) Incomplete flap
– premature termination of microkeratome
advancement
- inadequate globe exposure
- loss of suction during pass
Never reverse microtome & then go
forward
penetration to a deeper level than initial pass
59. 2) Thin flap
- due to poor suction
- difficult to reposition
& likely to wrinkle
3) Buttonholed flap
- If K > 50 D
- Ablation should not be
performed, flap
repositioned
4) Full thickness
resection
60. 5) Free cap – flat/ small
cornea, poor suction
- Small / decentered :
procedure aborted
- Adequate size/ well
centered : placed on
conjunctiva with
epithelial side down &
procedure completed
6) Epithelial defects –
prevented by adequate
lubrication
61. ABLATION COMPLICATIONS
1) Central islands – small central elevations
a) abnormal beam profile (broad beam lasers)
b) particulate matter blocking subsequent laser
pulses
c) increased hydration
2) Decentration – current lasres with incorporated
eye-tracking & iris registration systems
3) Under/ Over-correction
- excessive hydration : undercorrection
- desiccation : overcorrection & haze
62. POSTOPERATIVE
COMPLICATIONS meibomian gland
1) Interface debris – mostly
material – cleaning of interface with BSS
2) Flap displacement – first 24 hrs
- lifted & repositioned
3) Night vision disturbances – haloes / glare
4) Post Lasik Dry eye
Fluctuating vision,SPK
Temporary neuropathic cornea
Confocal microscopy-90% reduction in corneal
nerve fibres-regeneration by 1 year.
Rx-Preservative Free lubricants
63. 5) Punctate epithelial keratopathy – pre-existing dry
eye / blepharitis
- tt frequent lubrication , punctal plugs
6) Diffuse lamellar
keratitis (Sands of
Sahara syn)
- non-infective interface
inflammation
- 1 st week after LASIK
- fine granular sand-like
infiltrate in the interface
periphery
- if not treated corneal
scarring
64. Grade
1Focal involvement
- Normal V/A.
- Rx Intensive topical
steroids.
Grade
II –
Diffuse involvement
– Normal V/A.
- Rx-Add systemic
steroids.
65. Grade
III –
Diffuse confluent
granular deposits
- Reduced V/A.No AC
reaction.
- Rx-Same as
above+Antibiotics
Grade
IV –
Diffuse confluent
granular deposits
+intense central striae.
- Marked Reduced V/A
- Rx-Interface
irrigation + above
67. 7) Flap striae & microstriae
Flap undulations
Macrostriae -Linear
lines in clusters,seen
on retroillumination
Causes-Incorrect
position of flap
-Movement of flap
after LASIK
Rx-Lift flap
-Rehydrate and
float it back
-Check for flap
adhesion
68. Microstriae -Flap in
position but fine
wrinkles seen
superficially
-Due to large myopic
ablation
-Rx- Observe.They
resolve
spontaneously
70. Classification GRADE
1-Faint white line <2mm
from flap edge
GRADE 2-Opaque cells <2mm from
flap edge with rolled flap edge
GRADE 3-Grey to white fine opaque
line extending >2mm from flap edge.
GRADE 4-If ingrowth >2mm from
edge with documented progression
Rx flap lifted epithelium scraped at
stroma & under flap repositioned.
Mitomycin-C can be used
72. 10) Keractasia
- Ablation beyond 250 µm of posterior
corneal stroma
- LASIK performed on unrecognized KC
suspects
- tt – RGP lenses, corneal transplant
11) Post op Glaucoma(Pseudo DLK) -Steroid
induced.
12) Vitreoretinal Complications Increased risk of RD due to alteration of
anterior vitreous by suction ring-Risk
0.08%.
73. LASEK & Epi-LASIK
Corneal surface ablative refractive
procedures
Anterior stroma of cornea (ant. 1/3
rd)
has stronger interlamellar
connections than post. 2/3 rd .
So surface ablation preserves the
structural integrity better than
LASIK especially in the correction of
74. LASEK
Creating an epithelial flap with
dilute alcohol (18%) applied for 25-35
seconds & repositioning this flap
after laser ablation
Plane of cleavage Hemidesmosomal
attachments in the most superficial
part of lamina lucida of BM
75. Epi-LASIK
Use of a motorized epithelial
separator with oscillating blade, to
mechanically separate a 60-80µ
corneal epithelial flap from stroma &
repositioning this flap after laser
ablation
Plane of cleavage Not within but
underneath the Basement Membrane
76. HISTORY
1 st LASEK 1996 by Dr. Azar
Cimberle & Camellin independently
coined the term LASEK
Epi-LASIK a recent development in
refractive surgery technology
77. ADVANTAGES OVER PRK
Greater post-operative comfort
Faster visual recovery allows
bilateral simultaneous surgery
Reduced risk of corneal haze
78. ADVANTAGES OVER LASIK
Flap related complications are
eliminated in LASEK
If microkeratome related
complications occur during EpiLASIK, procedure can be easily
converted to PRK & completed
Absence of corneal lamellar flap in
both procedures, reduces risk of
keractasia
79. COMPLICATIONS
INTRAOPERATIVE
LASEK related
1) Alcohol leakage
problems:
during surgery
2) Incomplete
flap
epithelial detachment
(insufficient alcohol
exposure)
Epi-LASIK related
Flap-related
- free flap
- incomplete
- buttonholing
81. Laser Thermo-Keratoplasty
(LTK)
FDA approval Jan 2000
Ho:YAG (Holmium:yttrium-aluminiumgarnet) laser – deliver laser energy to
periphery of cornea
For Hyperopia (0.75 to 2.5 D)
Takes months to stabilize
In time, the effect wears off in a
substantial number of cases
83. CONDUCTIVE
KERATOPLASTY
Application of low-energy, high
frequency radiofrequency current to
heat & shrink peripheral & paracentral
stromal collagen resulting in
steepening of central cornea
Used for hyperopia (1 – 2.25D),
hyperopic astigmatism and
presbyopia
FDA approved 2002
Provides better stability than the
previously used procedure Laser
84.
CORNEAL RESPONSE TO HEAT
55 – 58 ˚C collagen shrinkage
(disruption of
H bonds of tertiary collagen
structure)
65 – 78 ˚C collagen relaxation
> 78 ˚C collagen necrosis
85.
Hyperopia
Lower corrections : 8 spots at 6mm optical
zone
& 8 spots at 7mm
optical zone
Greater corrections : 24 spots applied ( 8
additional
(+2 to +2.50D )
spots at 8mm optical
zone)
Even greater corrections : 32 spots
Hyperopic astigmatism
Peripheral heat spots along a single
(flatter) meridian
87. SCLERAL EXPANSION
BANDS
Designed to treat
presbyopia
Not FDA approved
Theory: Presbyopia
is due to
slackening of
fibers attached to
the lens.
Figure : Implanted scleral
expansion band (full circular
band model)
88. Intrastromal Corneal Ring
Segments
(Intacs)
PMMA arcuate segments placed
within peripheral cornea to correct
myopia
FDA Approved 1999
< 3.0 D myopia , < 1.0D
Astigmatism
Emerging role as an adjunct for
keratoconus & corneal ectasia
89.
1 st generation ICRS : 360˚ ICRS
Current design: 2 PMMA
segments,150˚ arc length
Hexagonal cross section
Fixed inner diam. 6.8 mm
Fixed outer diam. 8.1 mm
90. Refractive effect directly related to
thickness
INTACS THICKNESS
(mm)
0.25
RECOMMENDED PRESCRIBING RANGE (D)
0.30
-1.75 to -2.25
0.35
-2.38 to -3.00
-1.00 to -1.63
91.
92. SURGICAL TECHNIQUE
ICRS channel
formation at 2/3 rd
corneal depth,
outside central
optical zone
Insertion of
segment
Suturing of entry
site
Adv
Reversibility
Hyperacuitty
93. PHAKIC INTRAOCULAR
LENSES
Artificial lenses implanted in the anterior
or posterior chamber in the presence of the
natural crystalline lens to correct
refractive errors
Intraoperative iridectomy or preoperative
Nd:YAG laser iridotomies – necessary to
avoid post-op pupillary block glaucoma
95. AC angle-supported AC iris-fixated
NuVita (Bausch &
Lomb)
Vivarte (Ciba vision)
Kelman Duet
I-CARE
Acrysof AC
Verisyse/ Artisan
(AMO/Ophtec)
Artiflex/ Veriflex
PC sulcus-supported
Implantable Contact
Lens (ICL)
Phakic Refractive Lens
(PRL)
Sticklens
96. GENERAL CRITERIA FOR
IMPLANTING PHAKIC IOLs
Age above 18 years
Stable refraction (< 0.5D change for 6 months)
Ammetropia not suitable for Excimer laser
surgery (high powers or thin cornea)
AC depth >= 3.2mm for iris-claw lens
>= 2.5mm for pc PIOLs
Minimum endothelial cell density
> 3500 cells/mm² at 21 yrs age
> 2800 cells/mm² at 31 yrs age
> 2200 cells/mm² at 41 yrs age
> 2000 cells/mm² at 45 yrs age
No other ocular pathology (corneal disorders,
glaucoma, uveitis, cataract)
97. Indications
High Myopia
December 2004, FDA approved 1 st PIOL :
Verisyse/ Artisan ‘iris-claw’ lens
Myopia -5 to -20 D
Astigmatism upto 2.5 D
December 2005, FDA approved a 2 nd PIOL :
Visian ICL(Implantable Contact Lens)
Myopia -3 to -20 D
Astigmatism upto 2.5 D
High Hyperopia
Upto +3.0 D
98. Ancillary tests
IOL power calculation
AC PIOL
- Power calculation is independent of axial
length of eye
- Depends on : 1)Central corneal curvaturekeratometry (k)
2) ACD
3) Preoperative spherical
equivalent
PC PIOL
- Corneal thickness & axial length also taken
into consideration
99. AC DIMENSIONS & SIZING OF
PIOL
Most of the complications arise due to
inaccurate sizin of PIOLs
External measurement from limbus-tolimbus( white-to-white dist.)
Gives approx estimation of AC diameter
- Measured b/w 3 & 9 o’clock meridians with
calipers
- ORBSCAN
- Videokeratoscopes
- High frequency UBM
100. Diam of lens = w-w dist + 0.5 to 1.0
mm
(For both angle & sulcus-supported
PIOLs)
106. ADVANTAGES
Most stable & predictable refractive
method
Newer designs – improved safety &
efficacy
Reversible
Significant gain of postoperative
BCVA in myopia – reduction in
image minification
No loss of contrast sensitivity (as
seen in LASIK)
109. BIOPTICS
Concept of first implanting a phakic
IOL to reduce the amount of myopia,
then fine tuning the residual
correction with LASIK
I/Cs –extremely high myopia
- high astigmatism
- lens power not available
Combination has expanded the limits
of refractive surgery
