Phacoemulsification some Basic Ideas…

transcript

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

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)

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

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

fixation blob

Comparison of three methods

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

Haptic1-piece3-piecediameter

Haptic Design

Haptic

Edgesquarerounded

Edge Design

Squarereduced PCOdysphotopsias?

Rounded anteriorreduced PCOreduced internal reflections

Optic Design

MaterialRigid

PMMAFoldable

acrylicsiliconecollamer

Focality/Sphericity

Monofocalspherictoricwavefrontaspheric

Multifocalaccomodativepseudoaccomodative

Diameter5.0 to 7.0 mm

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

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.

Phacoemulsification some Basic Ideas…

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