KERATOREFRACTIVE SURGERIES

DR. KISHORE KHADEModerated 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 fibrils.

• 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.

HISTORY

• In 1978 bore,myers & cowden were first in USA to perform radial keratotomy & report there results.

• Lamellar surgery were evolving simultaneously, Jose Barraquer was the first to correct refractive error through lamellar surgery.

CLASSIFICATION OF KERATOREFRACTIVE Sx

LOCATION ADDITION SUBTRACTION RELAXATION COMPRESSION

SUPERFICIAL EPIKERATOPHAKIA

1.PRK2. LASEK

---------- CORNEAL MOLDING

INTRASTOMAL 1.KERATOPHAKIA2.INTRACORNEAL LENSES3.PINHOLE APERTURES

1.LASIK LAMELLAR KERATOPLASTY

PERIPHERAL INTRACORNEAL STROMAL RING

WEDGE RESECTION

RADIAL KERATOTOMY.

1.THERMOKERATOPLASTY.2.COMPRESSION SUTURES

INDICATIONSINDICATIONS

• MYOPIA : Photorefractive karatoplasty. LASEK. LASIK.HYPERMETROPIA : PRK/ LASEK 2-3D LASIK upto 4D Conductive keratoplasty Laser thermal keratoplasty

INDICATIONSINDICATIONS

• ASTIGMATISM : Limbal relaxation/ arcuate PRK/LASEK upto 3D LASIK upto 5D Conductive keratoplasty• PRESBYOPIA : Conductive keratoplasty

Preoperative evaluationPreoperative evaluation

• MOTIVATION• CYCLOPLEGIC REFRACTION• SLIT-LAMP BIOMICROSCOPY.• PUPIL SIZE.• CORNEAL TOPOGRAPHY• PACHYMETRY• WAVEFRONT

Clinical significance of corneal Clinical significance of corneal topographytopography

• Indispensable tool for refractive surgeons– Preoperative screening– Surgical planning – Assessment of surgical outcomes– Detection and management of complications– Refinement and development of surgical

techniques

Principles of Corneal TopographyPrinciples of Corneal Topography

• Placido disc system• Non-Placido disc system

– Scanning slit– Rasterstereography – Laser Holographic interferometry

FIGURE 2-17 BASIC CHARACTERISTICS OF AN AXIAL MAP

Simulatedkeratometerand astigma-tism indicator

Statistical index indicators

Pupil sizeindicator

Dioptric power and radius indicators

Vertex and pupil distance and location indicators

1mm x 1mmgrid indicators

Center of map(vertex) andcenter of pupilmarkers

Pupil marker

KeratometryKeratometry

• Advantages• Accessibility• Ease of use• Precision is good• Low cost• Adequate for most contact lens fitting

• Limitations• Small area measured: periphery and apex not measured.• Assumes that the cornea is a spherical surface: accuracy is

questionable• Irregular topography not described specifically and sometimes

undetected

WAVEFRONT

• Discovered nearly 400 years ago by christopher scheiner.

• 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 retina.

• 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, and axis.

Wavefront Technology

Diagnostic devices :

1. higher-order aberrations :

field curvature, distortion, diffraction, spherical aberration, chromatic aberration, coma

2. refraction vs. wavefront refraction (refractive map)

cf. keratometry vs. topographic map Wavefront-guided refractive surgery

Types of aberrometer

• Hartmann shack system outgoing reflection aberrometry)

• 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 irregularity

of horizontal and vertical alignment of the spots of this eye with significant aberration.

EPIKERATOPHAKIA

• 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 corneaq opaque.

• Werblin and kauffman later devised using lathe cut donor corneal lenticule mainly in peadiatric aphakic patients.

• With planopower lenticule was developed to treat keratoconus like onlay lammellar keratoplasty.

EPIKERATOPHAKIA

• 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 to 0.3mm.

• Rehydrated epikeartophakia lenticule is sutured into the host cornea.

*

ALLOPLASTIC REFRACTIVE KERATOPLASTY

• 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 stroma.

• Shape of lenticule is concave or convex depends on refractive status of eye ie: myope/ hypermetrope

KERATOPHAKIA

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

the lenticule.Corneal decompensation may lead to postop

opacification, perforation & flattening of Ac may occur. PK may require for the complication.

EXCIMER

• Trokel, srinivasan & barren first suggested the use of excimer for corneal surgery.

• Excimer derived from term excited dimer of inert gases.

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 abalation.

Photo refractive keratoplasty

• Patients selections; motivation age >18years refraction stability Ocular pathology systemic condition

ocularKeratoconusAdvanced keratitis siccaLagophthalmosCorneal vascularisationPathological changes in retina & lensHerpesdepressed Corneal scarProgressive myopia.

SystemicCollagen vascular diseaseImmunodeficiencyKeloid formationDmPregnancy & lactation

PREOPERATIVE EVALUATION

• 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

PRK

• Laser caliberation & prechecks• Ppd & topical anesthesia • Determination of optical centre.• Removal of epithelium• Stromal ablation• Postop medication• Placement of soft contact lens• ***

COMPLICATIONS

• Intra OP: Error in laser programming. Incompelete epithelial removal Decentered ablation.Post OP :

EarlyDelayed wound healingInfectionNSAIDS infiltratesAB precipitatesCORNEAL melts

INTERMED 2wk-6 mnthOver/under corrRegressionStreep corneal islands ScarsSteriod induced complicationss

LATE >6 monthsSteriods inducedScarsHalos/ glaresVisual fluctuationsCorneal haze

LASEK

• Laser subepithelial keratomileusis (LASEK) is a relatively new refractive surgical technique that purportedly combines the advantages of laser in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).

• 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

• 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.

LASEK

• 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 sweep.

• A therapeutic soft contact lens is placed onto the cornea.

LASIK

• Initially described by Pallikaris in1990.• Preoperative consideration; Patient selection. Stability of refraction. Fundus Corneal thickness/ conus Patients anxiety/ sedation.

LASIK procedure

• Anesthesia : topical with 1% proparacaine or 4% xylocaine.

• 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 not saline.

Microkeratome is slide over surface to raise the epithelial flap.

• Excimer laser reshapes the cornea by removing a pre-determined precise amount of tissue.

• The corneal flap is repositioned iris sweep – no stitch required.

• Fluence test.• ***

CORNEAL BIOMECHANICS

• Layered corneal is permanently severed following surgery.

• This reduces the tension in the remaining peripheral segments allowing expansion of peripheral layers.

• Peripheral expansion results in higher order aberrations.

• 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

patient’s need Anatomical customization Optical customization

Customized Refractive Surgery

Functional customization based on pt’s need

1. age

2. presbyopia

3. occupational and recreational needs

4. refraction

5. psychological tolerance

Customized Refractive Surgery

Anatomical customization

1. corneal diameter and thickness

2. pupil size

3. anterior chamber depth

4. anterior and posterior lens shape

5. axial length

Customized Refractive Surgery

Optical customization

1. customization based on corneal topography

2. customization based on wavefront measurement

Customized refractive surgery

1}SCANNING SPOT: spot size of 1mm or lesser to treat 4th order aberrations with optical zone diameter of 6mm.

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

ablation profile.3}SCANNING SPOT RATE: small spots utilise 200Hz

energy.

4} SPOT PLACEMENT: spot is best when it is non-sequential such that one spot is not placed next to the precedding spot.

EYE TRACKING: 1) SAMPLING RATE. 2)LATENCY. 3) TRACKER TYPE. 4) CLOSE-LOOP VERSUS OPEN LOOP TRACKING.

Wavefront-Guided Refractive Surgery

“ 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 : 40 %

Adding wavefront informations is helpful in cases within 0.25 D of the intended correction.

FEMTOSECOND LASER

• 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 corneal endothelium.

FEMTOSECOND LASER

• 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).

FEMTOSECOND LASIK

• Femto laser has been devised to raise LASIK flaps

MECHANICAL FEMTOLASER

Mechanism Cut from side to side with globe pressure

Creates an interface cut at predetermined depth

Flap Meniscus flap Planar flaps

Flap thickness Depends on suction ring thickness,corneal diameter & curvature

Independent of any such parameters

Size & shape Makes an D shape flap Well centered flap is created

Complications Free flap, button hole are common

Light sensitivity, photophobia common but self limiting

FEMTOSECOND DISADVANTAGES

• Longer suction time• More flap manipulation• Opaque bubble layer may interfere with excimer

ablation

• Bubbles in the anterior chamber may interfere with tracking and registration

• Increased overall treatment time

FEMTOSECOND DISADVANTAGES

• 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/

RA.• Infections.• Severe dry eye.• RD• 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

• Corneal Haze• Epithelial Sloughing or Defects• Striae• Traumatic Flap Dislocation• Diffuse Lamellar Keratitis

LASIK

1 Faster visual recovery – 1 day

2 No Post operative pain3 Good for low and high

myopes4 Predictable and stable5 Not good for contact

sports

LASEK/PRK

1 Visual recovery – 1 week2 Mild to Moderate post

op pain3 Low myopia, thin

corneas4 Less predictable,

modulation5 Contact sports, military

EPI-LASIK

• Surface ablation in which a viable epithelial flap is raised.

• 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 cells.

• ****

CORNEAL RINGSCORNEAL RINGS

• In cases like keratoconus structural integrity is increased by :

INTACS C3R

INTACSINTACS

• 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 CROSS CORNEAL 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 corneal stroma.

• RIBOFLAVIN drops are placed every 2 mins, 30 mins prior to UV-A radiation.

• After the procedure bandage contact lens is used.

C3RC3R• ADVTG: increase intigrity & progression reduce astigmatism & myopia enhance contact lens fitting

C/I : keratometry >60D pachymetry < 400 m infection/ corneal opacity (central) <12 yrs or >40 yrs

Laser thermal keratoplasty

• Thermal tissue necrosis gives rise to enhanced corneal remodelling, thereby limiting effect & causing regression.

• Ho: YAG laser uses wavelength of 2.13mm ,pulse duration of 200-300ms laser is used to create paracentral corneal coagulation & shrinkage in the controlled manner

• Contact mode : fibr-optic probe to deliver laser pulses to premarked points on the cornea.

• NON- Contact mode: A slit lamp delivery system is used to deliver pulses in an octagonal pattern on the cornea simultaneously.

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 KERATOTOMY

• 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

RADIAL KERATOTOMY

Limbal Relaxing Incisions

• Limbal Relaxing Incisions (LRI) are a refractive surgical procedure to correct minor astigmatism in the eye.

• 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 keratectomy.

Over view

EPIKERATOPHAKIA

RADIAL KERATOTOMY

Limbal Relaxing Incisions

THERMOKERATOPLASTY

INTRACORNEAL STROMAL RINGPRKLASEKLASIK

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