Femtosecond Laser

Femtosecond LaserFemtosecond SI unit of time ( 10-15 of a Second )Femtosecond Laser emits optical pulses with duration in the domain of femtosecondsCurrent delivery system Use Neodymium:glass 1053 wavelength lightFocus light at spot size 3 micron

Mechanism of ActionPrinciple of photodisruptionLaser energy is absorbed by tissues which result in plasma formationExpansion of plasma creates cavitation bubbles which separates the tissue plane

Micro vs Femto second laser

Femto second laser assisted cataract surgeryFemtosecond laser first FDA approved for cataract surgery in 2010. With guidance systems it is used to make-Cataract clear corneal incisions Capsulorhexis Lens fragmentation/softening

Preoperative evaluationSpecial attention toCorneal opacitiesArcus senilisPupil sizeZonular dehiscenceGrade and type of cataractPatient should be told that operating procedure may take place in two different rooms

AnaesthesiaTopical is preferredEncourage to look at fixation lightPeribulbar blocks may cause chemosis and hinder dockingGA in very young children

InstrumentationAlcon LenSxAMO CatalysTechnolas VictusLensAR

Three basic instrumentaion-Patient interfaceLaser deliveryImaging system

Patient Interface3 basic functionMaintain positional and mechanical stability of eyeCoupling device to facilitate laser deliveryPermit acquisition of imagesTwo typesApplanating ( LenSx and Victus )Small diameterSuitable in small palpebral apertureNonapplanating ( Catalys and LensAR )Cause less increase in IOPLess SCH

Imaging systemImaging system based upon-Spectral domain optical coherence tomography3-dimensional confocal structural illumination

Imaging SystemMost important step is centering the corneaCorneal incisions and capsulorhexis

CapsulorhexisIdeally centered on limbusCan be centered on pupil ( set to 5mm )

Lens fragmentation

4-8 segmentsConcentric pattern in softer cataractsGrid pattern in harder cataractsDone before making the corneal incisions

Planning StationIncisionsPosition of primary and secondary incisions according to surgeons convenienceCan be according to pre-op astigmatismFollowed by Phacoemulsification

Contraindications Small palpebral apertureInterface diameter 11.5 to 15.5mmCan be overcome by lateral canthotomyNeck and back problemOptimal docking, imaging and laser delivery need patient to lie flatNystagmus and attention deficit disorderNot able to comply instructions and fixationGlaucomaRise in IOP 10-20 mmHg

ContraindicationsCorneal opacitiesHinder in imagingSubluxated/Dislocated lensNucleus management not possibleCorneal incision can be madeLiquefied lens material hinders laser penetration and incomplete capsulorhexisSmall PupilsRelative contraindicationPupil expanding devicesNo air bubble should be in the AC

Unique ComplicationsMachine relatedErrors in software or hardwareStop/reattemptSwitch over to conventional Phaco

Loss of suctionImproper docking/excessive eye or head movementHard head rest are prefferedIf occurs during capsulorhexis , complete manually

SCHMore in applanation type

Unique ComplicationsPupillary constrictionMiosis of 2-3 mmApplanation/laser energyIncomplete capsulotomy/Anterior capsular tearCorneal folds/lens tilt/eye movements while firing laserCapsular block syndromeIntraoperative capsular block with subsequent rupture during hydrodissectionNucleus can be rotated by pneumodissection ( air bubbles produced by laser delivery )

AdvantagesIncisionsGreater stabilityCapsulotomyMore preciseBetter IOL centration

Advantages

Nucleus management and phaco energy - Reduced ultrasound energy - Reduced effective phaco timeZonular weakness - Reduced stress on zonules during capsulorhexis and nucleus choppingMild decentration capsulorhexis can be centered on lens

Posterior capsulorhexisIn infantsMacular edemaLesser edema in comparison to phaco

Disadvantages

CostTraining of staff calibrate and operate the machineOperating room shifting of patient may be inconvenienceTime two step procedure, takes longer time then phacoIncreased expectation- more expensive more expectations

Femto Second Laser Refractive SurgeryFemtosecond laser first FDA approved for LASIK flaps in 20011st released commercial device was: Intralase FS (Abbott Medical Optics, Abbott Park, Illinois);Femtec (20/10 Perfect Vision, Heidelberg, Germany);VisuMax Femtosecond System (Carl Zeiss Meditec, Jena, Germany);Femto LDV (Ziemer Group, Port, Switzerland); andWavelight FS200

Intralase Femto lasik Technique:The suction ring is centered over the pupil. The docking procedure is then initiated while keeping the suction ring parallel to the eye.

FemtoSecond laser treatment

Flap raised with blunt spatulaSuction is then released. A spatula is carefully passed across the flap starting at the hinge and sweeping inferiorly to lift the flap for excimer laser ablation.

Advantages:

Reduced incidence of flap complications like buttonholes, free caps, irregular cuts , wrinkles as seen in LASIK.Diffuse lamellar keratitis

AdvantagesDecreased incidence of Subepithelial HazeEpithelial ingrowths

Advantages

Control over flap diameter and thickness, side cut angle, hinge position and length.Increased precision with improved flap safety and better thickness predictability.Capability of cutting thinner flaps to accommodate thin corneas and high refractive errors.Stronger flap adherence. Less increase in IOP requiredLesser incidence of dry eye. Lesser hemorrhage from limbal vessels. The ability to retreat immediately if there is incomplete FS laser ablation.

Disadvantages:

Opaque bubble layer (OBL): Gas bubbles routinely accumulate in the flap interface during FSL treatmentMay dissect into the deep stromal bed(obscuring excimer laser tracker)Reach AC, or escape to subepithelial (resulting in button hole).

Patients present with extreme photophobia and good visual acuityProposed mechanism is either an inflammatory response of the surrounding tissue to the gas bubbles or biochemical response of the keratocytes to the near-infrared laser energyResolves without sequel but requires aggressive topical steroids for weeks.

Micro-irregularities on the back surface of the FSL LASIK flap can cause rainbow glare

Rainbow glare

DisadvantagesPhotodisruption-induced microscopic tissue injury and ocular surface inflammatory mediators may cause lamellar keratitis in the flap interface.

Increased difficulty in lifting the flap if retreatment is required after that (because of good adherence).

Increased cost.

Moving the patient between 2 laser instruments.

Intrastromal lenticule extraction ReLEx (refractive lenticule extraction)Performed exclusively with a femtosecond laser system, i.e., no excimer laser is needed.Steps:. The femtosecond laser is used to cut a small lens-shaped segment of tissue (lenticule)within the center of the cornea..Made in the anterior cornea with the laser similar to the flap created in LASIK.The flap is lifted and the lenticule is removed and discarded.. The flap is repositionedThe removal of the lenticule reduces the curvature of the cornea, thereby reducing myopia.

SMILE

A variation of ReLEx is another investigational procedure called small-incision lenticule extraction (SMILE). In the SMILE procedure, a corneal flap is not created. A small incision is made in the mid-periphery of the cornea with the laser, and the lenticule is removed through this self-sealing incision. The SMILE procedure has additional potential advantages. No corneal flap is created, SMILE may pose less risk for post-surgical dry eye and ectasia than ReLEx or LASIK. No risk of flap displacement from trauma to the eye after surgery.

SMILE

The promising early results of ReLEx and SMILE suggest they may someday become a popular alternative to LASIK for vision correction. However, currently it is not possible to perform these procedures for small amounts of ametropia, as typically present in enhancement surgery, because the lenticule would be too thin to manipulate safely.

Intracor