REFRACTIVE SURGERIES Dr.Jyoti Shetty Medical Director, Bangalore West Lions Superspeciality Eye Hospital
CLASSIFICATION -R.K. -PRK -LASIK -EPILASIK -LASEK -Conductive Keratoplasty -Corneal Inlays and rings -Clear Lens extraction for myopia -Phakic IOL - Prelex Clear Lens Extraction with use of Multifocal IOL’s Combination of the two
LASIK(Laser Assisted In Situ Keratomileusis) • Procedure using laser to ablate the tissue from the corneal stroma to change the refractive power of the cornea
Types of lasers used- • Excimer-Excited dimer of two atoms -an inert gas(Argon) -Halide(Fluoride) which releases ultraviolet energy at193nm for corneal ablation
Non-Excimer solid state lasers- • 210nm Q switched diode pumped laser (laser off) • 213 nm Q switched diode pumped laser(Pulsar)
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.
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 -12D • Hyperopia –upto +6D • Astigmatism-upto 7D
CCT such that minimum safe bed thickness left(250-270µ).Post op Corneal thickness should not be <410µ. • Cornea not too flat or steep.<36D or>49D(Poor Optics).
CONTRAINDICATIONS • Systemic factors- • Poorly controlled IDDM • Pregnancy/lactation • Autoimmune / connective tissue disorders(RA,SLE,PAN etc) • Clinically significant Atopy,Immunosuppressed patients • Keloid tendency(esp PPK) • Slow wound healing-Marfans,Ehler-Danlos • Systemic Infection-(HIV,TB) • Drugs-Azathioprene,Steroids(Slow wound healing)
CONTRAINDICATIONS • Ocular Factors- • Glaucoma,RP(Suction Pressure-ON damage,Blebs) • Previous h/o RD or f/h of RD. • One eyed individual • Pre-existing dry eye,Keratoconus.pellucid marginal degeneration,Superficial corneal dystrophy,RCE,Uveitis,early Lenticular changes • h/o Herpetic Keratitis(one year prior to surgery)
PREOPERATIVE EVALUATION PRIOR TO LASIK • Record UCVA and BCVA Snellens V/a • Dry and wet manifest refraction(with 1% cyclopentolate) • Pupillometry-Infrared Pupillometer -Aberrometer • Large pupil-Increased HOA perceived so increased glare -Can change Optic Zone
Slit Lamp Examination- • Rule out blepharitis, miebomianitis, pingecula, Pterygium,corneal neovascularization • Other contraindications for LASIK. • IOP by applanation • Dilated Fundus Examination to role out holes ,tears.
Tear film asessment-Schirmers,TBUT and Lissamine staining • Blink Rate-(Normal---3-7/min) • Corneal Topography- • Scanning slit/placido disc • Stop RGP lenses 2 weeks prior and soft lenses I wk prior • To rule out early Keratoconus and other ectasias • For mean K values
Pachymetry -For CCT (Ultrasound/Optical) • Contrast Sensitivity testing for pre-operative baseline.
BASIC STEPS AND MACHINE SPECIFICATIONS • Topical anasthesia-Proparacaine 0.5%, Lignocaine 4%. • Surgical Painting and draping(Lint Free). • Lid speculum with aspiration. • Corneal marking-Orientation of free cap
Creation of flap- • 1st Step-Creation of suction by suction pump to raise the IOP to 65 mm Hg which is necessary for the microkeratome to create a pass and resect the corneal flap. • This is crosschecked with Barraquers tonometer.
2nd step-Resection of corneal flap Microkeratome Femtosecond Laser (Intralase)
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.
Femtosecond Laser for Flap- • Creates photodisruption using femtosecond solid state laser with wavelength of 1053nm. • Needs lower vacum. • Very short pulse with spot size of 3µ-High precision cutting device. • Any hinge can be made • Can make flaps as thin as 100µ(Sub Bowmanns Keratomileusis)
Flap has vertical edges –so reduced epithelial ingrowth. • Microkeratome flap thicker in periphery and thinner in the centre.Not so with Intralase(Planar).
3rd Step-Delivery of Laser- • After flap is lifted, laser is applied to the stroma according to the ablation profile calculated by the machine. • Laser beam is delivered by the following ways depending on the machine-
Most machines employ a flying spot to deliver laser with the help of incorporated eye tracker.
4th step-Reposition Of the Flap- • After irrigating interface ,flap reposited • Adhesion test-Striae test
ABLATION PROFILES • Wavefront Guided or customized ablation-to improve quality of vision by correcting higher order aberrations. -Wavefront analysis on entire eye done by –Hartmann Shack -Tracy
ABLATION PROFILES • Aspheric Ablation-Normal LASIK converts prolate cornea to oblate structure.(Central flattening,steep in periphery.) which induces higher order aberrations. • To reduce this and preserve the prolate structure,’Q’ value is calculated and altered to give a more aspheric ablation.
COMPLICATIONS OF LASIK • Under/over correction and regression (over time). • Post –op Keratectasia • Presents 1-12 months • Progressive regression • Treatment-RGP,Corneal transplant. • Prevention- Leave residual stromal bed -Do surface ablation -Don’t violatecorneal topography diagnosis of forme-fruste keratoconus
COMPLICATIONS OF LASIK • Night vision disturbances-Haloes/Glare • Decenteration and central islands. • 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
COMPLICATIONS OF LASIK • Post op Glaucoma(Pseudo DLK)-Steroid induced. • Vitreoretinal Complications- • Increased risk of RD due to alteration of anterior vitreous by suction ring-Risk 0.08%. • PVD(0.1% Risk) • Macular Hemorrage(0.1% Risk)
COMPLICATIONS OF LASIK • Flap Complications- • Button Hole-If K>50D,due to central corneal buckling. • .
Irregular thin flap-Inadequate suction/old blade • Short Flap-Hinge encroaches on visual axis-Due to jamming of microkeratome with hair/FB SHORT FLAP
.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 MACROSTRIAE
Microstriae-Flap in position but fine wrinkles seen superficially -Due to large myopic ablation -Rx- Observe.They resolve spontaneously MICROSTRIAE
Bleeding during flap cutting due to corneal neovascularization in contact lens users
Interface Inflammation(Sands Of sahara/DLK)-Non-Infective inflammation at the interface seen in 1st week after LASIK. • Diffuse,confluent,white granular material at the interface 1-7 days after LASIK. • Slight CCC • No AC reaction • Reduced Visual acuity
Grade 1- Focal involvement - Normal V/A. Rx Intensive topical steroids.
II – Diffuse involvement –Normal V/A. Rx-Add systemic steroids.
III – Diffuse confluent granular deposits- Reduced V/A.No AC reaction. Rx-Same as above+Antibiotics • IV - Diffuse confluent granular deposits +intense central striae. Marked Reduced V/A Rx-Interface irrigation + above
Causes-Proposed Theory • Bacterial cell wall endotoxin • Cleaning solution toxicity • Talc from gloves • Miebomian secretions
Epithelial ingrowth-Presents 1-3 months after LASIK. • Causes-Epithelial cells trapped under flap • Risk factors-Peripheral epithelial defects -Poor flap adhesion -Buttonholed flaps -Repeat LASIK
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—Lift flap and remove the sheets of epithelium.Can use MMC.
EPILASIK / LASEK • Anterior stroma of cornea (ant. 1/3 rd) has stronger interlamellar connections than post. 2/3rd. So surface ablation preserves the structural integrity better than LASIK especially in the correction of moderate to high myopia.
LASEK-Camellins Technique- • 20% absolute alcohol used for 20-35s. To raise epithelial flap. • Flap reposited after ablation
EPILASIK- Epithelial keratome used to lift epithelial flap of about 60-80µ thick. • Epithelial keratomes use - PMMA blades -Metal Epithelial Separator
CONDUCTIVE KERATOPLASTY • Uses mild heat from radiofreqoency waves to shrink collagen in the periphery of the cornea---This steepens the paracentral cornea. • Used for hyperopia (1 – 2.25D) and presbyopia. • C.K. spots are applied with a probe in rings with a dia. Of 6/7/8 mm. • 8 spots are given in each diameter ring.
7 6 5mm
Drawbacks- • Regression and retreatment in 100% cases after 6 months. • Induced cylinder >1D reported in many cases. • Usually done in one eye—Many have intolerance to monovision.
CORNEAL INLAYS • Increase the depth of focus by using pinhole optics. • Inlays have 1.6mm centre with 3.6mm surround. • Near vision improves by 1.5D with no loss of distant vision. • Used in the non –dominant eye. • These are hydrogel based.Placed in a tunnel 200-400 µ deep in centre of cornea.