Today the filed of refractive surgery has evolved to include many modalities for the treatment of different refractive errors.
Motivation: detailed information, procedure xplained to the pt anxiety levels xplained. REFRACTION: stability of the refraction last 1 year is checked, >0.5D change accounts for unpredictable long term result. PUPIL SIZE: PUPIL SIZRE BOTH IN LIGHT & DARK should be measured,pupillometer can be used to measure pupil size, pts with larger pupil should be unstd glare & haloes Corneal thickness: topography to rule out keratoconus, its C/I in LASIK due to central corneal thinning, 250mm be left beneath a lamellar keractectomy in order tp prevent ectasia
Hartmann: small light projected to retina and reflected back and focused by lenselet arrey this recorded by video sensor and compared with theoritical aberration free sysytem.
For myopia conves portion is removed and for correction of hyperopia concave portion is removed
Refraction 0.5 spherical chnage / 0.25 cylindrical change / < 20 degree axis change in one year
The well is filled with 20% ethyl alcohol solution for 30 to 50 seconds. Longer times are recommended for young men, postmenopausal women, and long-time contact lens users, because the epithelial flaps in these groups of patients are generally more difficult to lift. At the end of the allotted time, an absorbent cellulose surgical spear is used to soak up the alcohol in the well.
Sampling rate: Rate refers to how frequently the tracker measures the eye position.varies from 60 Hz to 400 Hz Latency: time required to determined eye’s location, in close loop system such as laser radar based system gives continuous feedback occurs leads to zero latency. Its infrared camera based tracking systems. Tracker type: two types:::: video tracking: infrared light of iris against a dark pupildeviation of the eye is read & corrected. Laser radar: space stabilised image is maintained & eye position calculated continually. OPEN SYSTEM: new image is taken n compared with old image change in location is calculated. CLOSE: cont monitoring using a radar system.
They do not control progression of the keratokonus, just help for the fitting of the lens
Its not approved method still under trial, however riboflavin increases the absorption of the radiation & penetration to the deeper tissues, its increased structural integrity shows sucess in various studies of treating and progressing KCONUS.
Averg corneal penetration is 480-530 mm which is 80-90% of corneal thickness, effect was found to vary directly with the pulse energy & inversely with the distance from the centre of the cornea.
Error of application would be less in non contact mode, refractive stability & reproducibility is greater. Ho: YAG laser & the alignment of the burns, have shown that using more than one ring produces a greater refractive change & that applying the concentric rings. STATS: various studies shown improved vision between with 0.75 to 4.75D preoperatively of spherical, up to 3DS astigmatism less then 1DC.
80% depth of the cornea homogenously thermalenergy is deliveredless then 0.5D of difference in the manifest & cycloplegic refractions can be corrected. C/I: recent chnages in 1 yr, age <21 yr, dry eye, C dystrophies, glaucoma, herpes, keloid, keratoconus, DM, PREGnancy, autoimmue & vascular disorders.
DR. KISHORE KHADE
Moderated by DR. UGAM USGAONKAR
APPLIED ANATOMY OF CORNEA
• EPITEHLIUM: composed of non keratinized
startified squamous epithelium of 4 to 6 layers
thickness. BM (lamina densa & lamina lucida), wing
cells and flattened top cells having microvilli.
• BOWMAN’S LAYER: condensed superficial layer of
the stroma, consists of randomly dispersed collagen
• STROMA: 500m thick consists of collagen producing
fibroblasts keratocytes , matrix & collagen lamellae.
APPLIED ANATOMY OF CORNEA
• DESCEMETS MEMBRANE: strong well defined
sheet in between stroma & endothelium.
• ENDOTHELIUM: plays an major role in active
transport & maintenance of normal stroma.
• In 1978 bore,myers & cowden were first in
USA to perform radial keratotomy & report
• Lamellar surgery were evolving
simultaneously, Jose Barraquer was the first
to correct refractive error through lamellar
LOCATION ADDITION SUBTRACTION RELAXATION COMPRESSION
Clinical significance of cornealClinical significance of corneal
• Indispensable tool for refractive
– Preoperative screening
– Surgical planning
– Assessment of surgical outcomes
– Detection and management of complications
– Refinement and development of surgical
Principles of Corneal TopographyPrinciples of Corneal Topography
• Placido disc system
• Non-Placido disc system
–Laser Holographic interferometry
FIGURE 2-17 BASIC CHARACTERISTICS OF AN AXIAL MAP
1mm x 1mm
Center of map
center of pupil
• Ease of use
• Precision is good
• Low cost
• Adequate for most contact lens fitting
• Small area measured: periphery and apex not measured.
• Assumes that the cornea is a spherical surface: accuracy is
• Irregular topography not described specifically and sometimes
• Discovered nearly 400 years ago by
• He demonstrated a technique to measure the
refractive error of the eye using a device
known as Scheiner disc.
• Visual acuity measuring device takes into
consideration tear film, anterior corneal
surface, corneal stroma, posterior corneal
surface, anterior crystalline lens
• posterior crystalline lens surface, vitreous and
• Prior to the advent of wavefront-sensing
devices, clinical refraction consisted of three
data points for each eye: defocus (spherical
error, myopia, or hyperopia), astigmatism,
Diagnostic devices :
1. higher-order aberrations :
field curvature, distortion, diffraction,
spherical aberration, chromatic aberration,
2.refraction vs. wavefront refraction (refractive
cf. keratometry vs. topographic map
Wavefront-guided refractive surgery
Types of aberrometer
• Hartmann shack system outgoing reflection
• Tscherring system
• Ray tracing system.
• Ingoing adjustable refractometry.
• Double pass aberrometry.
Note the loss of dots centrally in a “moth-eaten” appearance and the overall
of horizontal and vertical alignment of the spots of this eye with significant aberration.
• Is an form of refractive surgery on the cornea for the
correction of keratoconus, aphakia & high myopes.
• Gasset and kauffman in 1968 tried with plastic lens,
glued over the cornea. Unfortunately glue made the
• Werblin and kauffman later devised using lathe cut
donor corneal lenticule mainly in peadiatric aphakic
• With planopower lenticule was developed to treat
keratoconus like onlay lammellar keratoplasty.
• Corenal epithelium is thoroughly denuded by
rubbing with cellulose sponge.
• 7mm to 7.5mm trephine is used to incise the
patient’s cornea partially to the depth of 0.2
• Rehydrated epikeartophakia lenticule is
sutured into the host cornea.
• This technique involves intrastromal implantation of
hydrogel materials with specific curvature.
• Alloplastic material like polysulphone is placed
between epikeratophakia graft & BM alters the
refractive power by changing the refractive index of
• Shape of lenticule is concave or convex depends on
refractive status of eye ie: myope/ hypermetrope
Lenticule with predetermined power is made
from the donor cornea.
This lenticule is placed over the host prepared stroma
with convex surface anteriorly.
The previously removed stromal disk is sutured over
Corneal decompensation may lead to postop
opacification, perforation & flattening of Ac may
occur. PK may require for the complication.
• Trokel, srinivasan & barren first suggested the
use of excimer for corneal surgery.
• Excimer derived from term excited dimer of
Leads to emission of high energy photon of UV
light having 6.4eV.
various excimer lasers are: argon fluoride
193nm,kypt cl 222nm, kypt fl 249, xenon cl
308, xenon fl 351.
Corneal tissue interaction
• Carbon- nitrogen bonds which forms the
peptide in proteins is broken by the highly
excited state of an inertgases.
• The photon induced molecular decomposition
results in abalative photo decomposition.
• The above mentioned process if precisely
controlled, restricted, gives optically smooth,
with minimal scarring with appro depth
• Visual acuity with cycloplegic refraction
• Complete ophthalmic & medical history.
• Keratometry / topography / pachymetry
• Pupil size and diameter in dim light.
• Applation tonometry
• Test for dry eye & lacrimal examination
• Laser caliberation & prechecks
• Ppd & topical anesthesia
• Determination of optical centre.
• Removal of epithelium
• Stromal ablation
• Postop medication
• Placement of soft contact lens
• Intra OP: Error in laser programming.
Incompelete epithelial removal
Post OP :
INTERMED 2wk-6 mnth
Streep corneal islands
LATE >6 months
• Laser subepithelial keratomileusis (LASEK) is a
relatively new refractive surgical technique that
purportedly combines the advantages of laser in-situ
keratomileusis (LASIK) and photorefractive
• In 1996, Azar [8•] performed the first LASEK
procedure, which he called “alcohol-assisted flap
PRK.” Later it was renamed LASEK by Camellin, who
popularized his own version
• LASEK is in essence a hybrid of PRK and LASIK that
may provide relatively quick visual recovery, while
eliminating virtually all flap-related complications.
• The LASEK procedure is based on chemically reducing
the corneal epithelial adhesion to the underlying
Bowman’s layer by the application of dilute ethanol.
• 8.0-mm diameter circular marker with an 80μm deep
cutting edge, designed to create a 270° superficial
punch cut in the epithelium.
• The denuded corneal surface is then ablated with the
excimer laser as in standard PRK.
• flap is gently repositioned over the central cornea
with a blunt instrument, such as a Barraquer iris
• A therapeutic soft contact lens is placed onto the
• Initially described by Pallikaris in1990.
• Preoperative consideration;
Stability of refraction.
Corneal thickness/ conus
Patients anxiety/ sedation.
• Anesthesia : topical with 1% proparacaine or
• Corneal marking: ensure proper realignment.
• Suction ring: placed on the eye & centerd over
the limbus. IOP rises over 60mm hg.
• Microkeratome: when adequate pressure is
obtained surface is lubricated with anesthesia
Microkeratome is slide over surface to raise the
• Excimer laser reshapes the cornea by
removing a pre-determined precise amount of
• The corneal flap is repositioned iris sweep –
no stitch required.
• Fluence test.
• Layered corneal is permanently severed following
• This reduces the tension in the remaining peripheral
segments allowing expansion of peripheral layers.
• Peripheral expansion results in higher order
• Topography allows to visualise actual change in
shape that occured following the ablation.
• Wavefront helps in to fully characterised shape
changes & resultant functional response.
Customized Refractive Surgery
Functional customization based on
Customized Refractive Surgery
Functional customization based on pt’s need
3. occupational and recreational needs
5. psychological tolerance
Customized Refractive Surgery
1. corneal diameter and thickness
2. pupil size
3. anterior chamber depth
4. anterior and posterior lens shape
5. axial length
Customized Refractive Surgery
1. customization based on corneal topography
2. customization based on wavefront
Customized refractive surgery
1}SCANNING SPOT: spot size of 1mm or lesser to treat
order aberrations with optical zone diameter of
2}SCANNING SPOT SHAPE:
(a) Gaussian beam shape: it allows very smooth
overlape creation of ablation zone.
(b)Top HAT: gives rise to spikes & valleys in the
3}SCANNING SPOT RATE: small spots utilise 200Hz
4} SPOT PLACEMENT: spot is best when it is non-
sequential such that one spot is not placed
next to the precedding spot.
1) SAMPLING RATE.
3) TRACKER TYPE.
4) CLOSE-LOOP VERSUS OPEN LOOP TRACKING.
“ Super Vision ” ( 20 / 10 )
Eliminating surgically induced aberrations is the
first step to super vision.
Seiler T : increase in higher-order aberrations
after standard LASIK : 144 %
after wavefront-guided LASIK :
Adding wavefront informations is helpful in cases
within 0.25 D of the intended correction.
• The femtosecond laser is a mode-locked, diode
pump,neodynium-glass laser. It operates in the
infrared wavelength range, at 1053 nm. It uses a spot
size of less than 3 μm and produces tissue disruption
(Photodisruption) at a specified and precise level
within the corneal stroma. The laser produces
cavitation bubbles consisting of water and carbon
dioxide which are ultimately absorbed through the
• A unique feature of the femtosecond laser is its
ability to produce tissue disruption at very low
energy settings. This is due to the very short pulse
width, or pulse duration, associated with the laser
(600 to 800 fs), and to the very rapid pulse
repetition, or speed, of the laser (15,000 to 60,000
pulses per second).
• Femto laser has been devised to raise LASIK
Mechanism Cut from side to side with
Creates an interface cut
at predetermined depth
Flap Meniscus flap Planar flaps
Flap thickness Depends on suction ring
diameter & curvature
Independent of any such
Size & shape Makes an D shape flap Well centered flap is
Complications Free flap, button hole are
but self limiting
• Longer suction time
• More flap manipulation
• Opaque bubble layer may interfere with excimer
• Bubbles in the anterior chamber may interfere with
tracking and registration
• Increased overall treatment time
• Difficulty lifting flap >6 months
• Increased risk of diffuse lamellar keratitis
• Increased cost
• Need to acquire new skills
• Delayed photosensitivity or good acuity plus
• photosensitivity (GAPP), which may require
• prolonged topical corticosteroid therapy
Contraindications of LASIK
• Pre existent anamolies- keratoconus.
• Inappropriate parameters; power/
pachymetry/ pupil size.
• Degenrative eye conditions: lupus/glaucoma/DR/
• Severe dry eye.
• Pregnancy/ lactating.
• AGE and change in refraction.
COMPLICATIONS OF LASIK
• Overcorrection: Myopic or hyperopic surface
ablation typically undergoes some degree of
regression for at least 3- 6 months.
• Undercorrection: Undercorrection occurs much
more commonly at higher degrees of ametropia
because ofdecreased predictability due to the
greater frequency and severity of regression.
• Central Islands: A central island appears on
computerized corneal topography as an area of
central corneal steepening
• Optical Aberrations :Some patients report optical
aberrations after surface ablat ion and LASIK,
including glare, ghost images, and halos
• Decentered Ablation
• Corticosteroid-Induced Complications
• Dry Eye and Corneal Sensation
• Infectious Keratitis
• Persistent Epithelial Defects
• Sterile Infiltrates
1 Faster visual recovery –
2 No Post operative pain
3 Good for low and high
4 Predictable and stable
5 Not good for contact
1 Visual recovery – 1
2 Mild to Moderate post
3 Low myopia, thin
4 Less predictable,
5 Contact sports, military
• Surface ablation in which a viable epithelial flap is
• The flap is raised at the level of the LAMINA DENSA,
the whole basement membrane remains attached to
the epithelium, increased survival of basal cells.
• Alcohol assited seperation occurs at the level of
lamina lucida and reduces survival of the epithelial
CORNEAL RINGSCORNEAL RINGS
• In cases like keratoconus structural
integrity is increased by :
• Intacs are small semicircular plastics rings of various
thickness inserted in the corneal stroma.
• They are used for the corrections of 1-3D.
• They work by flatting of central portion of the cornea
there by correcting myopic refractive error.
• They smoothen out corneal irregularities
which improves the quality of visison.
CORNEAL COLLAGEN CROSSCORNEAL COLLAGEN CROSS
LINKING with RIBOFLAVINLINKING with RIBOFLAVIN
• C3R is a procedure which uses RIBOFLAVIN as the
photosensitiser with UV rays of 365nm.
• UV light increases the number of collagencross
linking fibres which are the anchors within the
• RIBOFLAVIN drops are placed every 2 mins, 30 mins
prior to UV-A radiation.
• After the procedure bandage contact lens is used.
Laser thermal keratoplasty
• Thermal tissue necrosis gives rise to enhanced
corneal remodelling, thereby limiting effect &
• Ho: YAG laser uses wavelength of 2.13mm ,pulse
duration of 200-300ms laser is used to create
paracentral corneal coagulation & shrinkage in the
• Contact mode : fibr-optic probe to deliver
laser pulses to premarked points on the
• NON- Contact mode: A slit lamp delivery
system is used to deliver pulses in an
octagonal pattern on the cornea
Laser thermal keratoplasty
CONDUCTIVE KERATOPLASTYCONDUCTIVE KERATOPLASTY
• Utilises radiofrequency energy placed in the
periphery of the cornea to cause collagen shrinkage
& steepen the central cornea.
• 450 x 90 mm2 dimension tip radiofrequency is
delivered in the cornea causing thermal effect.
• +0.75 – +3.25D correction of cycloplegic refraction
with less then -0.75D of astigmatism.
• Age >40 yrs
• Radial incisions were made to modify the surface of
the cornea by Sato & his associates in 1894.
• To correct myopia, astigmatism & keratoconus.
• Radial incisions were made from periphery to the
paracentral area .
• However it was associted to many complications like
posterior extension leading to posterior keratotomy,
bullous keratopathy due to several of these
complications this procedure is rarely done now
Limbal Relaxing Incisions
• Limbal Relaxing Incisions (LRI) are a refractive
surgical procedure to correct minor astigmatism in
• Incisions are made at the opposite edges of
the cornea, following the curve of the iris, causing a
slight flattening in that direction.
• They are simpler and less expensive than laser
surgery such as LASIK or photorefractive
Limbal Relaxing Incisions
INTRACORNEAL STROMAL RING