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CORNEAL REFRACTIVE SURGERY
Major m kashif hanif DOMS.FCPS Cl. eye splt AFIO RWP
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Sequence of presentation
Brief overview of anatomy of cornea Brief overview of physiology of
cornea Corneal refractive surgery
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Gross anatomy of cornea
11.5mm horizontal diameter 10.5mm vertical diameter 1 mm thick periphery 0.5mm thick centrally Anterior surface radius 7.7mm Posterior surface radius 6.8mm
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Microscopic anatomy
Epithelium 5-6 layers thick Stratified squamous ,
nonkeratinised Superficial cells have
microvilli Basement membrane
strongly attached to Bowman’s layer
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Bowman’s layer 8-12 microns Acellular interwoven collagen
fibrils Incapable of
regeneration Ends abruptly at
limbus
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Stroma 90% of cornea thickness 400microns centrally 80% water Glycosaminoglycans
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Descemet’s membrane 10microns thick Type IV collagen fibrils Basement membrane of
the endothelium Secreted and
regenerated by endothelial cells
Terminates abruptly at limbus (Schwalbes line)
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Endothelium Single layer,
polygonal, cuboidal cells
Tight junctions Incapable of
regeneration Lines passages of
trabecular meshwork
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Physiology of cornea 3 main functions Light transmission Light refraction Protection
Corneal metabolism Energy needed for maintenance of
transparency and dehydration Glucose Oxygen
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Ametropia
A refractive error (ametropia) is a disorder that occurs when parallel rays of light entering the non-accommodating eye are not focused on the retina
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Normal Eye Myopia
Hypermetropia Astigmatism
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Aim Of Refractive Surgery
Alter refractive state of eye , enable patients to see without visual aids
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refractive surgery divided into four major areas: 1. INCISIONAL TECHNIQUES 2. INTRASTROMAL CORNEAL RINGS
(INTACS) 3. THERMAL TECHNIQUES 4. LAMELLAR PROCEDURES
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INCISIONAL TECHNIQUES
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Radial Keratotomy
Sato,1939 radial cuts pattern : spokes of a
bicycle wheel 4-16 incisions Extra-pupillary region
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Complications
Glare, star bursts Fluctuation of vision Regression, progression of
refractive effect Corneal perforation into the
anterior chamber Infectious keratitis and
endophthalmitis
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Incisional Astigmatic Keratotomy
Incision in the cornea flattens the meridian in which it is made and steepens the meridian 90 degrees away.
Single or paired Optical zone between
6.0 mm and 7.0 mm
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Relaxing incisions may be combined with compression sutures placed 90° away from them to reduce large degrees of corneal astigmatism
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INTRASTROMAL CORNEAL RINGS
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Intrastromal Corneal Rings
The ring segments flatten cornea similarly to the way you can flatten the top of a tent by pushing on the sides.
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Intrastromal corneal Rings
Indicated for low myopia (1-3D) and min astigmatism < 1.00D
Advantage: reversible, natural corneal physiology maintained, no use of lasers , no removal of tissue
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Complications
Fluctuation of vision Under- or over-correction Induced regular or irregular
astigmatism Glare , haloes Corneal perforation Pain Infectious keratitis
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THERMAL PROCEDURES
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Thermokeratoplasty
Hypermetropia +0.75 D to +3.25 D
Astigmatism less than or equal to 0.75 D
Spherical equivalent +0.75 D to +3.00 D
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This technique modifies the central corneal curvature by heat-induced shrinkage of collagen fibers in the midperiphery of the cornea.
Noncontact Technique Holmium laser
thermokeratoplasty (LTK) Conductive
Keratoplasty contact probe
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LAMELLAR PROCEDURES
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Lamellar Procedures
Laser in situ keratomileusis Laser Epithelial Keratomileusis Epithelial LASIK
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What is Laser?
Light Amplification by Stimulated Emission of Radiation (LASER)
Ground state Pumping Atoms in the excited state are unstable
and their electrons tend to spontaneously return to the ground state by emitting light energy
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What Is An Excimer Laser?
EXCIMER= “excited dimer” Argon or Xenon bound with a
halogen eg. Fluorine or Chloride diatomic gas halide - temporary
excited state
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Excimer Laser
During decay emits UV of 193nm Remove controlled amounts of tissue
with extreme precision
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Photorefractive keratectomy
Indication myopia up to 6D astigmatism up to 3D Hypermetropia up to 3D
Myopia 10um of ablation = 1D of
myopia Hypermetropia
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Photorefractive Keratectomy
Technique
The visual axis is marked and the corneal epithelium removed
The patient fixates on the aiming beam of the laser The laser is applied to ablate only bowmans layer and
anterior stroma
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30-60 seconds
Bandage contact lens
The cornea usually heals within 48-72
hours
Subepithelial haze
Post-op period
Topical steroids and NSAIDs.
Antibiotics
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Complications
Slow healing epithelial defects Corneal haze Haloes Dry eyes Decentred ablations Scarring Abnormal epithelial healing Irregular astigmatism Hypoaesthesia Sterile infiltrates Infection
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LASER EPITELIAL KERATOMILEUSIS
(LASEK)
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Laser Epitelial Keratomileusis
Indication Myopia 8D Hypermetropia 3D Astigmatism 3D
LASEK works well for patients who are unsuitable for LASIK such as those with very thin cornea
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Alchol 20% is applied for 30-40 seconds and an epithelial sheet is cleaved at the basement membrane
Laser is applied
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Comlpications
Pain Corneal haze Over / undercorrection Loss of sharpness of vision Infection
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Epithelial Lasik
Instead of using alcohol to loosen the epithelium, an epikeratome is used
Instead of using an oscillating sharp blade to incise the cornea beneath Bowman’s membrane, the epikeratome uses a blunt oscillating separator
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LASER IN-SITU KERATOMILEUSIS (LASIK)
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LASER ASSISTED IN-SITU KERATOMILEUSIS (LASIK)
Concept first intro by Jose Barraquer, 1964
founder : Dr Ionas Pallikaris- first to use microkeratome and laser
KERATOMILEUSIS = “to shape cornea” IN-SITU = “ in place” LASIK = “to shape cornea in place”
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Principles Of Lasik
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Principles Of Lasik
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Principles Of Lasik
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Myopia : 1-15D Hypermetropia : 1-4D Astigmatism : up to 5D Adequate corneal thickness >
45O m
Inclusion Criteria
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Inclusion Criteria
Age: > 21 years old, no max age.
stable refraction over past 24 months
Central K’s: > 39D - < 47D
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Exclusion Criteria
Immunocompromise Corneal irregularities Pachymetry < 450m Ocular herpes within the last
year Progressive myopia
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Ideal Candidate
Be at least 18 years of age Stable vision for at least one year Adequate thickness of the cornea Healthy eyes
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Under L/A, cornea is marked
Suction ring applied (65mmHg)
Microkeratome cut hinged flap
Flap folded to expose stromal bedStromal ablatedFlap repositioned
Basic Lasik Procedure2 3
4
56
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Antibiotics and corticosteroid therapy(4-6wk tapered course), tear supplements
Followup on 1 day, 1 wk, 3wks, 3 months, 6months
Avoid water in eyes - no shower, hot tub or swimming- first 2wks
Avoid eye rubbing dislocation of flap
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Complications
INTRAOPERATIVE: free flap, loss of corneal flap, wrinkling of flap , perforated or thin flap, corneal perforation, bleeding from neovessels
POSTOPERATIVE: displaced flaps, corneal infection, diffuse lamellar keratitis , dry eyes , Subepithelial haze , Epithelial defects , ectasia
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Complications
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Blurred vision
Corneal haze
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Complications
Epithelial ingrowth
Diffuse lamellar keratitis
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Complications
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Corneal hypoesthesia
Dry eyes:
Complications
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Night vision problems
starbursts
Haloes
Complications
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Discomfort
Photophobia
Conjunctival haemorrhage
Complications
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ComparisonPRK LASIK LASEK
Myopia 6D 15D 8D
Hypermetropia 3D 4D 3D
Astigmatism 3D 5D 3D
Flap thickness The epithelium and stroma are cut to a thickness of 100-180 microns
The epithelium and stroma are cut to a thickness of 100-180 microns
The epithelium is cut to a thickness of 50 microns
Procedure Uses a microkeratome knife and excimer laser
Uses a microkeratome knife and excimer laser
Uses a alcohol , trephine and excimer laser
Pain From epithelial defect
Minimal Minimal
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PRK LASIK LASEK
Visual rehabilitation
Prolonged (upto 1week)
Rapid 2 days Rapid 4-7 days
Cornel haze Upto 10% Minimal Minimal
Asigmatism 1% 3-10% 1%
Advantages Better choice for poor LASIK candidates including people with lessCorneal tissue
Appropriate for people who have more corneal tissue, lessDiscomfort than LASEK, almost no pain, 6/6vision or better isTypically achieved, corneal haze very rare, immediate clear vision,Follow -up enhancements are easier if needed.
Better choice for people with lessCorneal tissue, fewer haze outcomes than LASIK, no complications of stromal flap as inLASIK, less risk of dry eye than LASIK. Lost LASEK flap less risky than a lost LASIK flap, lowers risk of DLK
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PRK LASIK LASEK
Disadvantages More discomfort than LASIK, more corneal haze , takes longer to heal than LASIK
Those with thinner corneas may suffer less than ideal results, flap may dislodge with trauma, uneven flap edges may lead to astigmatism, flap may result in scars
More discomfort than LASIK, takes longer to heal than LASIK,Trauma, such as being hit in the eye may cause flap to dislodge, uneven flap edgesLeading to astigmatism
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Femtosecond Lenticule Extraction (FLEx)
The surgeon makes a flap in the anterior cornea similar to the flap created in LASIK
The flap is lifted and the lenticule is removed and discarded
The flap is repositioned, as in LASIK The removal of the lenticule reduces
the curvature of the cornea, thereby reducing myopia
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