2Customized LASIK & PRK will dominate in next few years Customized Corneal AblationCustomized LASIK & PRK will dominate innext few yearsSpeedy recovery, good quality of visionsatisfactory outcomeDisadvantage of conventional refractivesurgery in some patients:* Increase in HOA* Reduction in visual quality٤٩
3Wavefront Customized Visual Correction Ocular wavefront sensing: Will be increasingly employedWill become routine in visionassessmentWavefront customization is employed tooptimize any refractive surgeryprocedure٥١
25Evaluation of vision quality Compromised more at dim light during night and represented by:a) Double visionb) Ghostingc) Glared) Halose) Starburstsd) Reduced contrast sensitivity
26Quantification of magnitude of the aberration 1)Usually by RMS wavefront error2)It gives a rough estimate
27Types of aberrationsLow Order Aberration (LOA) : 1st & 2nd order aberrationHigh Order Aberration (HOA) : 3rd to 6th or 10th
28How to evaluate the quantity of optical system Root Mean Square ( RMS )The RMS is SD of height (depth) of wavefront relative to the reference at all the point in the wavefront. RMS is very useful measure of optical quality.Peak-To-Valley (PV)Distance from the highest to lowest point on the deformed wavefront relative to the reference wavefront.
29RMS1 is qualitative presentation of 1st order aberration, RMS2 is due to 2nd order and etc. RMSh represents the total RMS of HOA (including 3rd to 6th OA)RMSg represents the total RMS of HOA and LOATotal RMS increases with agingLASIK increases RMS especially in subjects with larger pupilsRMSh > 0.3 and > 20% of total RMS is clinically significant and indicative for customized ablation
30Wavefront measuring devices Hartmann-shack style devices are the most common used
32Hartmann-shack style1)A narrow beam of light is projected on to the retina and the light reflected from the fovea passes through the lens and the cornea and exists the eye
33Customization can be based on corneal topography or wavefront measurements. Corneal topography guided ablation has been attempted on patients with regular and irregular astigmatism, decentered ablations, and central islands. The irregular astigmatism group is more challenging and may benefit most from corneal topography guided ablation as the systems become more refined.
41Considering refractive lens at corneal surface Real eye with AberrationsConsidering refractive lens at corneal surfaceExcimer etching by customized ablationConverting wavefront to flat wavefrontPerfect focus on foveaIdeal eye١٢
49Zero order (no order)=axial symmetry, flat Zernike’s PolynomialsZero order (no order)=axial symmetry, flatwavefrontFirst order = linear aberration, tilting around ahorizontal (x) or vertical axis (y)Second order = focus shift,spherical defocus or astigmatismThird order = corresponding tocoma, triangular astigmatismFourth order = sphericalaberration, complex patternsFifth-10th order = Irregular aberrations,important when pupil is wide dilated.10/14/2007٧XVth Congress of Iranian Society of OphthalmologyOctober 2005
60Wavefront guided customization Goals Spherocylinder correctionTo correct the aberration that are induced by conventional laser vision correction and pre-existing aberration.
61Requirment for wavefront Efficient eye trackingGood registeration system for eyeSmall size laser spotSufficient corneal bed thickness
62Challenges to wavefront Tear film abnormalitiesMiotic pupil : If severe may be difficult to measure and provide information beyond the 3mm optical zone and therefore require pharmacological dilation.
65Wavefront map with cycloplegic or mydriatic 1) Has significant difference in pre-op refractive error compared to subjective refraction
66(Ablation profile algorithm) 1) After good aberration maps, Ablation profile algorithm is needed 2) Should be designed to make the post-op higher order aberrations as minimal as possible 3) Not only correcting the pre-op higher order aberration but also preventing the induction of new higher order aberrations.
67Conversion to Ablation Profile: Ablation profile is fundamentally inverse of wavefronterror mapGoal: Correction of refractive error and higher-orderaberrationsPupil diameter at least 0.5mmlarger than scotopicLimbal marking for cyclotorsiondetectionWavefront measurement + corneal curvature +biomechanics ablation profile complex٣٥
70RegistrationRegistration refers to the method by which a customized ablation pattern based on preoperative wavefront analysis from the aberrometer is superimposed in the same position on the eye during the laser treatment.
71LADARWave and LADARVision systems: Centration is established by the surgeon when the patient fixates on the target light. The instrument captures a video image of the eye, and the surgeon defines the pupillary ring (red) and limbus ring (yellow). These will be used by the LADARVision tracker to follow the eye during application of the customized ablation pattern.
72Torsional alignmentTorsional alignment refers to the need to compensate for the cyclotorsion of the eye that occurs when the patient lies down.The eye usually rotates less than 5 degrees, but in some patients, postural cyclotorsion can be as much as 10 to 12 degrees.
73MisalignmentA small misalignment in in the axis can have significant impact on the results of procedureA 5-7 degrees of cyclotorsion when changing from sitting position to supine position. 50% of the visual benefit of HOA is lost.
75Bausch and lomb zyolptix system has DiagnosticTreatment components for wavefront customized corneal ablation
76Diagnostic part of zioptix systems (2172 laser) In zy wave aberometer and ORBscan both machine are integrated in one workstation. It has Hartmann-shack sensor that measures up to 5th order zernike term. It measures sphere from +6.0 D to -12. D and 0 to 5 D of cylender with pupil diameter from 2.5 to 8.6 mm.
77Pupil during exam Orbscan must be performed with an undilatd pupil Wavefront meaurements are taken with a dilated pupil.
82Eye trackerThe system has 120 Hz active eye tracker with a passive automatic shut-off system corrects for intraoperative eye movement in every dimention including cyclotortion and pupil shift
83FDA investigation for outcomes for wavefront guided lasik in myopia for 3 separate laser platforms LADAR visionTechnolus 217 z for low to moderate myopiavisxConventionalWave front guided72% ………….20/2089% ……..20/20
84Environmental Conditions Control of environmental conditions during treatments is important. In previous U.S. FDA Multi-Center Clinical Trials, the room conditions were:Temperature ranged from 68ºF to 72ºF (20ºC to 22.2ºC)Relative humidity ranged from 40% to 45%Treatments performed at >24ºC were associated with less accurate outcomesStability of temperature and humidity is important
85Future of Customized Corneal AblationLASIK vs surface ablationEach microkeratome induces specific “flaponly” aberration(flap size, thickness)Considering “flap aberrations” in totaltreatment calculations٤٢
86Show promising results with use of Future of Customized Corneal Ablation …cont.Surface Ablations:Show promising results with use ofimmunomodulating agentsBetter control of cellular and biochemicalreactionsIntroduction of new drugs to better regulatewound healing and refractive outcomeGene therapy for better control of post laserkeratocyte activation and wound healing٤٣
88Presbyopia: Customized multifocal ablation Aberrations may be induced when creatingmultifocalityPotential loss of contrast sensitivity and qualityof visual functionFuture results will be improved:* Wavefront mapping, sophisticated eyetrackers and corneal registration* Preoperative simulation of postop condition٤٤
89Correction of HOA needs smaller spot delivery Laser Delivery RefinementsCorrection of HOA needssmaller spot deliveryrequires mm spot size>5th orderSmaller spot size needs faster and better eyetrackersSmaller ablation depth per pulse providesideal correction profile for higher orders٤٥
90The Human Hair (125 microns) Etched with an excimer laser Courtesy of IBM
91Effects of Laser Ablation ThermalNon-thermalYAGCO2Excimer
94Wavefront measurement devices and consequently wavefront correction ConclusionWavefront measurement devices andconsequently wavefront correctionprocedures are still in process ofevolutionAchievement of “supervision”: withadvancement in current procedureswill not be a dream in near future٥٤