phacoemulsification some basic ideas…
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Khalid M. Al-Arfaj, MD. Phacoemulsification some Basic Ideas…. Dammam University . 1-Quiz …. 2- lecture …. 3-Vedio …. Basic Phaco Settings. Basic Phaco Settings. Sculpting. 60 / 80 / 24 US, Vac, Asp . Quadrant Removal/Burst. 45 / 400 / 37 BW 50 - 120. Quadrant Removal/Pulse. - PowerPoint PPT PresentationTRANSCRIPT
Phacoemulsification some Basic Ideas…
Khalid M. Al-Arfaj, MDDammam University
3-Vedio …
1-Quiz …
2- lecture …
Basic Phaco Settings
US Vacuum Aspiration Pulse Rate Burst WidthPhaco/Sculpt 60 80 24
Pulse/Quad 45 376 35 6
Burst/Quad 45 400 37 50 - 120
60 / 80 / 24 US, Vac, Asp.
Basic Phaco Settings Sculpting
Quadrant Removal/Burst
45 / 400 / 37 BW 50 - 120
Quadrant Removal/Pulse
45 / 376 / 35 PR 6
Horizontal Choping
Vertical Choping
Courtesy of David Chang, MD
Evolution of IOL Calculation Formulas
Clinical History FormulaUsed before 1975Simple formula to calculate IOL powerP = 18 + (1.25 x Ref)Poor accuracy
>50% had >1D error“9 D surprise” – some huge errors due to the inaccuracy of calculating refractive error prior to cataract formation
Formulas and Their
DerivationsRegression Formulas
Derived from retrospective computer analysis of postoperative data from a large number of patients
SRK FormulaP = A – 2.5L – 0.9KDerived by Sanders, Retzlaff and Kraff1
Required measurementsL – Axial length (mm)K – Corneal power (D)A – A Constant
1 Sanders DR, Retzlaff J, Kraff MC. Arch Ophthalmol 1983;101:965-967
Formulas and Their
Derivations SRK and early Theoretical formulas fairly accurate for eyes of moderate lengthInaccuracies occurred at extremes of axial length
Modern Theoretical Formulas
Most important concept is postop Anterior Chamber Depth is related to IOL placement in the eye, not to preop ACDAll have a personalizable factor to improve accuracy of calculationsHolladay/Holladay 2
S factor – personalized surgeon factorSRK/T
A constant – based on multiple variables (IOL manufacturer, implant style, surgeon’s technique, etc.)
Hoffer QPersonalized ACD value
All based on Thin Lens Optics
Modern Theoretical Formulas
Modern Theoretical Formulas
Found to be more accurate than older formulasAll basically the same in predicting IOL power in average eyesDifferences occur at extremes of AL and K’sPersonalized factors based on optimal cases (PCIOL, intact capsule)
Must change when surgical plan changes (Sulcus PCIOL or ACIOL)
Modern Theoretical Formulas
Axial Length Measurement
Current methodsContact A Scan BiometryOptical Biometry
Partial Coherence Interferometry
A Scan Biometry
Use of A scan ultrasound to measure axial length
Contact
Normal Phakic Contact A
Scan C1 – Anterior surface of CorneaC2 – Posterior surface of CorneaL1 – Anterior surface of LensL2 – Posterior surface of LensR – Retina
Optical Coherence BiometerIOL Master
Fine beam of infrared laser used to measure axial length
ultrasound vs. optical
biometry
Ultrasound A-Scan10MHz sound wave IOLMaster
780nm laser beam
ILM
RPE
averaging across foveal cup reflection at Bruch's membrane
• Foveal thickness is about 150µ (±20) from ages 10 to 80 years.• The parafoveal area is between 0.10 mm and 0.16 mm thicker.
alignment precision:
ultrasound vs. optical
IOLMaster780nm laser beam
IOLMaster uses a point fixation light, measures along visual axis to the RPE at foveal center and then adds back the foveal thickness.
fixation point
A-scan US does not measure to the exact center of the fovea, but samples an area around it due to the broad angle of the U/S beam and fixation light.
Ultrasound A-Scan10MHz sound wave
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fixation blob
Comparison of three methods
90%80%70%60%50%40%30%20%10%
90%80%70%60%50%40%30%20%10%
myopia hyperopia
applanation A-scanfalsely short axial lengthvariable corneal
compressioncorneal micro-abrasionshighly operator dependentsource of IOL power errors
-2.0 -1.0 0.0 1.0 2.0
myopia hyperopia
partial coherence interferometrynon-contact laser devicephakic, pseudophakic, phakic IOLsposterior staphyloma, silicone oilnot limited by wavelengthor retinal thickness variations
-0.5 0.0 0.5 spherical equivalent prediction error (D) Data courtesy of Warren E. Hill, MD, FACS
Pearls and PitfallsMeasure axial length of both eyes
Take multiple readings of each to assure accuracyCompare eyes
Shouldn’t be a significant disparity in axial lengths unless a significant difference in refraction
Axial Lengthmeasure too short - myopic surprisemeasure too long - hyperopic surpriseNormal Eye: 1.0 mm error 2.5 to 3.0 D surpriseShort Eye: 1.0 mm error 7.5 D surprise
Keratometry1D curvature error 1D surprise
IOL Power Selection
What is your target postop refraction?
Examine patient dataDiscuss with patient
Match other eye?Monovision?Binocular distance?Binocular near?
IOL Choices
How do you choose IOL?Material
SiliconeAcrylicPMMA
ConfigurationOne pieceThree piece
Delivery systemFold vs. Inject
Basic IOL Design Features
Haptic
Edge
Optic
Haptic1-piece3-piecediameter
Edge
Optic
Basic IOL Design Features
Haptic Design
13.0
1
Basic IOL Design Features
Haptic
Edgesquarerounded
Optic
Edge Design
Squarereduced PCOdysphotopsias?
Rounded anteriorreduced PCOreduced internal reflections
Optic Design
MaterialRigid
PMMAFoldable
acrylicsiliconecollamer
Focality/Sphericity
Monofocalspherictoricwavefrontaspheric
Multifocalaccomodativepseudoaccomodative
Diameter5.0 to 7.0 mm
6.0
Which lens?
Consider matching IOL design features with individual patient needs
Lens choice
High myopia
Considerations: IOL size, powerlonger haptic span, larger optic diameterlow power
Lens choice
High hyperopia
Considerations: IOL size, powersmaller haptic span, smaller optic diameterhigh power IOL
Lens choice
Presbyopia
Considerations: spectacle independence
multifocal IOL (accomodative, pseudoaccomodative)monovision using two monofocal IOLs
Lens choice
Astigmatism (corneal)
Considerations: correct corneal astigmatism
Toric IOL
Lens choice
Improved functional vision
Considerations: maximize contrast sensitivity
aspheric
Lens choice
Macular degeneration
Considerations: block toxic UV lightblue blocking chromophore
Lens choice
Pseudoexfoliation
Considerations: Long term zonular stability
avoid silicone material (capsular phimosis)
Crystalens
“ Accommodating” Lens –single optic
Crystalens
Crystalens
The Multifocals
ReZoom & ReSTORThe good Less capsule issues
Known material Good near vision
The Bad: Unwanted photopsia Contrast sensitivity
ReZoom
AcrySof® ReSTOR® Apodized Diffractive IOL
Anatomy of the Apodized Diffractive IOL
Step heights decrease peripherally from 1.3 – 0.2 microns
A +4.0 add at lens plane equaling +3.2 at spectacle plane
Central 3.6 mm diffractive structure
Patient Selection
Pre-operative Exclusion Criteria
Subjective ExclusionHypercritical patientsPatients with unrealistic expectationsOccupational night drivers
Medical Exclusion>1.0 D of corneal astigmatism?Pre-existing ocular pathologyPrevious refractive patients
Patient Satisfaction
Crystalens, ReZoom, and ReSTOR all have clinical studies extolling the level of spectacle independence, excellent near, intermediate, and far vision of patients with these lenses.
Future Technology
The HumanOptics IOL ( 1CU) is a single optic accommodative lens continuing in clinical trials in Europe.
(Image courtesy of HumanOptics, Ophthal Clinics of N. Amer. March 2006.)
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Future Technology
Accommodative intraocular lenses with two optics. Gross photographs showing the injection of the Synchrony lens (Visiogen).
Source: Liliana Werner, M.D., Ph.D. and Nick Mamalis,M.D.
Sarfarazi Lens
The Sarfarazi IOL, currently licensed by Bausch & Lomb, is comprised of a minus-powered optic positioned posteriorly to a positive-powered optic joined by compressible bridges.
Reproduced from Ophthal Clinics of N. Amer. March 2006 courtesy of Bausch & Lomb
Other Technology
Lens replacement with flexible polymers injected into the capsular bag.
