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Biometry andIOL Calculations for Refractive Cataract SurgerySaturday, September 22, 2018Vienna

Rhonda G WaldronMMSc, COMT, CRA, ROUB, CDOS

Diagnostic Echographer, Senior Associate in OphthalmologyEmory Eye Center

Atlanta GAOwner, Eye Scan Consultingrhondawaldron@comcast.net

Thank you!!!

This educational activity is jointly sponsored through unrestricted educational grants from:

Improving Surgical Outcomes

Most common causes for post-op surprises:

• Axial eye length error was #1 in past

• Erroneous K-readings was #2

• Today it is IOL position – primarily capsulorrhexis dependent

• Per Warren Hill, MD, the biggest error today is prediction of lens position

Standardizing Protocol

• If you standardize your protocol, you will standardize your outcomes

• Preoperative measurements must be standardized

• Surgery must be standardized as much as possible

• One perfect component will not lead to perfect outcomes, but one bad component can cause refractive surprise

First Things First• What is it that we’re trying to do here?

Determine where the IOL will sit, and therefore what power it needs to be to bend light to a focus on the retina

Bringing Light to Focuswith IOLs

• The shorter the eye, the closer the retina is to the IOL so stronger power needed

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IOL Position (PC vs AC)

• PC IOL’s sit closer to the retina than AC IOL’s so need more power to bend light to focus on the retina

Posterior chamber IOL Anterior chamber IOL

IOL Position (Sulcus)

• If IOL placed in sulcus, subtract power from IOL power if original power more than +9.0 D

• Subtract -0.50 if original IOL +9.50 - +17.0 D

• Subtract -1.00 if original IOL +17.5 - +28.0 D

• Subtract -1.50 if original IOL more than +28.0

IOL positioned in bag IOL positioned in sulcus

IOL Position in Bag• For every 0.1 mm a 20D PC IOL is displaced,

0.19 D post-op surprise, so 1.0 mm = ~2.0 D

• The stronger the IOL the bigger the surprise

• Implants sitting too far forward induce myopia

• Implants sitting too far back induce hyperopia

IOL Position in Bag• Capsulorhexis allows precise estimation of IOL

position, or post-op ACD – should be round, centered, and smaller than the IOL optic

• Too large causes anterior displacement of IOL

• Too small causes posterior displacement

IOL Position in Bag

• For a 6.0 mm optic, a well-centered, 360°overlapping capsulorhexis of 5.5 mm achieves the gold-standard scenario in most cases

• Believed to also deter epithelial cells from proliferating, preventing posterior capsular opacification

• Capsulotomies too large have a PCO rate above 50%

• Capsular overlap locks in the final effective lens position

“The Perfectly Sized Capsulorhexis”, Raviv, T., Cataract & Refr Surgery Today, June 2009

IOL Position in Bag

• Capsular overlap provides stabilization of refractive outcomes

• As capsular forces and fibrosis stiffen the posterior capsule the IOL will be pushed forward if not stabilized by anterior overlap

• 360° overlap provides standardization of ELP and thus the A-constant for calculations

• Sizing the capsulorhexis becomes the single most critical surgeon variable in achieving consistency in IOL calculations

“The Perfectly Sized Capsulorhexis”, Raviv, T., Cataract & Refr Surgery Today, June 2009

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IOL Position in Bag

Per Jack Holladay MD, other things during surgery that affect lens position are:

• How much lens is rotated after insertion

• Technique for inserting lens

• How viscoelastic is removed

All make it mandatory to personalize lens constants

Lens Constants

• Implants made from different materials

• Haptics are different and at different angles

• Situate at different planes within the bag, so manufacturers assign a “constant” indicating approximately where it will sit

• The higher the constant, the further back the implant sits by design

• The further back it sits, the higher the power needed

Types of Lens ConstantVaries by Formula Used

• A-Constant (SRK/T):

Anticipated positionwithin the eye

• Effective Lens Position (Holladay II, Hoffer Q): Distance from corneal vertex to principal plane of thin IOL

• Surgeon Factor(Holladay I, Barrett U2 LF similar):Distance from iris plane to IOL plane

A-Constant ELP SF116.0 3.75 0.09117.3 4.50 0.83117.8 4.85 1.11118.5 5.25 1.51119.2 5.75 1.90119.8 6.00 2.24120.8 6.75 2.81

IOL Calculation PrintoutNote Lens Constants and Powers

Measuring ALP(Actual Lens Position)

• Immersion, IOLM 700, or LenStar post-operatively

• Measure ACD and add 0.5 mm for thickness of IOL and compare to manufacturers ELP

• Don’t use IOL Master 500 or older for this – doesn’t measure ACD accurately in pseudophakic eyes

• Contact A-scan also produces inaccurate ACD due to corneal compression

A-Constant ELP SF116.0 3.75 0.09117.3 4.50 0.83117.8 4.85 1.11118.5 5.25 1.51119.2 5.75 1.90119.8 6.00 2.24120.8 6.75 2.81

Personalization of Constants

• Constant on IOL packet rarely correct• Must be increased for non-contact

biometry methods • Immersion and optical biometry need

same constant (if same method used for K’s), not so for contact biometry

• Must be refined for each surgeon and each IOL

• Personalization has to do with precise surgical technique as well as pre-op measurement techniques

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Personalization Techniques

• ULIB (Users Group for Laser Interference Biometry) great starting place for optical and immersion if optical K’s used

• Some programs available for personalization (Holladay II, many biometers)

• You must track your outcomes!

• If post-ops are too myopic, the constant needs to be decreased

• If post-ops are too hyperopic, the constant needs to be increased

ULIB for Optical Biometry• Use “A SRKT” column for A-constants

• Use “Hoff pACD” column for Holladay II or Hoffer Q

• Use “”Holl-1 sf” column for Barrett Universal II or Holladay I

• All three Haigis constants are listed

• NEVER use “nominal A” – that is what is on IOL packaging

What About the Lens Constants Between Immersion

and Optical Biometry?• Dr. Haigis: “It may be noted that for

immersion ultrasound – since it had served as a basis to calibrate PCI biometry – the same IOL constants may be used as for optical biometry.”

• Only applies if same method of keratometry is being used for both groups!

Keep Lens Constants Consistent

• If unable to get axial length with optical, proceed with the K’s if that’s what you normally use

• Then do immersion ultrasound and type that measurement into the optical biometer and run calculations with same formula as is normal practice

• Constant now stays the same!

Calculation FormulaSelection

History of Formula Selection• SRK: P = A - 2.5L - 0.9K

Inaccurate for long or short eyes

• SRK II: Correction factors for long and short

Considered inaccurate & obsolete as stated by Dr. Retzlaff since 1992

• These were regression formulas (back-calculated based on actual retrospective analysis of patient post-op data)

• Theoretical (based on geometric optics as applied to eye models) considered more accurate, so regression were abandoned

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History of Formula Selection

• Two-Variable Theoretical Formulas (Axial length and Ks only being considered):

SRK/T, Holladay I, & Hoffer Q• How did we use them?

< 22.0 mm = Hoffer Q

22.1 – 25.9 mm = Holladay I or SRK/T

> 26.0 mm = SRK/T

• These should now be abandoned

Problem with Two-Variable Formulas

• They falsely assume that as the eye gets shorter or longer, the anterior segment size also gets shorter or longer in proportion

• In normal length eyes, 96% have normal anterior segment size, so rare to have small or large ant seg

• In short eyes, 80% have normal ant seg size, just short vitreous cavity, so only 20% have smaller ant seg

• In long eyes, 90% have normal ant seg size, just long vitreous cavity, so only 10% have large ant seg

Multi-Variable Formulas

• Haigis has three variables: axial length, K’s, ACD with three constants tied to each variable

• Holladay II has six variables: axial length, K’s, horizontal white-to-white, ACD, lens thickness, age (we now know performs best when refractive error not entered)

Horizontal “White-to-White”

• Should measure even if not for Holladay II

• Average = 11.7 mm + 0.46 mm

• Estimate of bag size, some say add 0.5 mm, others say add 1.0 mm to HWTW for sizing IOL haptic edge to haptic edge

• Prevents inferior decentration of IOL

• If large HWTW, will need a larger diameter implant! May need to special order!

• Large HWTW may not be a good candidate for a premium lens due to rotation or decentration risks

Horizontal “White-to-White”

• Helps to determine where IOL will sit within eye

• Gives information regarding anterior segment size, which affects lens position

• If over 12.0 mm, anterior segment is large and lens sits deeper

• If 10.5 mm or less, anterior segment is small and lens sits more anterior

Holladay II in IOL Master• Holladay II formula (not complete HICSOAP software) is

in later versions of the IOL Master• If using Holladay II on IOL Master 700, leave refractive

error blank• The software will show a pop-up that you’ve left it blank

and you must then click to allow “default” values of zeroes in the refraction

• Verified with Zeiss that “plano” is not actually being used, but rather the refraction is being left out completely when predicting lens postion, which is accurate

• Also check your software version of 500 – you may need to enter a value in “vertex distance” to get Holladay II to run (default value is 12 mm, and some software versions enter this automatically, some don’t)

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Holladay IOL Consultant

• Holladay software asks you to enter axial length in “Ultrasound” or “Optical” box

• The constant automatically decreases when type into “Ultrasound” box, so for use with applanation A-scan biometry or manual K’s

• Per Jack Holladay: If using optical K’s in Holladay II but an immersion A-scan, enter length in “Optical” box - has more to do with K’s than axial length

• So if always use optical K’s in combination with optical or immersion axial length, you will ALWAYS enter value in “Optical” box

|_____|_____|____|_____|_____|_____|_____|__|_____|_____|_____|_____|_____|_____|_____|_____|____|

<17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 >34

Axial Length in mm

SRK / T

H Q

Holladay 1

Polypseudophakia Holladay 2 Minus Power Lenses

HaigisOptimized Optimized

< - - Normal - - > < - - - - - - - - - - - Long - - - - - - - - - >< - - Short - - >< - - - Extreme - - - > < - - - - - - Extreme - - - - - >|||||||||||||||||||||||||||||||

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IOL power calculation ~2011 Warren Hill, MD

Which IOL formula should I use? hill@doctor-hill.com

Warren E. Hill, MD, FACS

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Newer Multivariable Formulas• Olsen Formula uses ray tracing, six variables: AL,

Ks, ACD, LT, age, CCT, only available on LenStarcurrently or by purchasing software (BAD without LT, so can’t use with IOL Master v.500 or older!)

• Barrett Universal II Formula five variables: AL, Ks, ACD, LT, HWTW, available on line or on LenStar or in Barrett Suite on IOL Master 700

• First formulas based on optical biometers (do internal adjustments to axial lengths for better accuracy)

• Fine to enter immersion axial lengths into formulas when necessary due to dense cataracts (personally verified with Drs. Olsen and Barrett –RW)

Formula RankingWarren Hill MD, ASCRS 2015

“Comparison of 9 Intraocular Lens Power Calculation Formulas”

Cooke DL, Cooke TL, JCRS, Vol 42, Issue 8, Aug 2016, pp 1157-1164

Key Points:

• For LenStar, Olsen best for all eyes followed closely by Barrett Universal II

• For IOLM 500 or older, on line Barrett U2 best followed by Haigis (Olsen terrible because no lens thickness)

• IOLM 700 not included in study

• Holladay II performed better when preoperative refraction was excluded, even if had true pre-cataract refraction

Hill-RBF CalculatorWarren Hill MD, ASCRS 2018

• Mathworks Laboratory working with Dr. Hill on RBF (Radial Basis Functions) Calculator

• Utilizes mathematics (highly complex algorithms, pattern recognition, and artificial intelligence)

• Three variables: AL, Ks, ACD (optical only)

• Now programmed only in the LenStar, but is available on line through the generosity of Haag-Streit

www.RBFCalculator.com

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Retrospective study 3,212 cases of 13 surgeons from 8 countriesWeighted mean = 95% within 0.5D C

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of W

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. Hill

Original RBF Performance Hill-RBF Performance

The vast majority of surgeons achieve 78% of their cases within +/-0.5D

Only 6% of surgeons achieve 84% of their cases within +/-0.5D

Only 1% of surgeons achieve 92% of their cases within +/-0.5D

In the validation set all 13 participating surgeons would have achieved more than93% of their cases within +/-0.5D

Version 2 now available with more eye lengths accepted and more target refractions

ASCRS 2017• Per Stephen Scoper, MD (VA Eye Consultants),

% of patients within 0.5 D:

Version 2 RBF Orig RBF Barrett

All (n=288) 94.8% 91.5% 94.3%

Short (n=87) 88.5% 83.3% 87.4%

Long (n=60) 98.3% 96.9% 91.7%

Avg (n=141) 97.2% 96.3% 97.2%

ASCRS 2018

Hill-RBF Version 2 results from MUSC, Charleston:

• + 0.25 D = 82%

• + 0.50 D = 98%

• + 1.00 D = 100%

Of Note:

• Mathematical models don’t work well for keratoconus, post-refractive eyes, or Chinese eye anatomy

Hill-RBF Version 2:

Standardizing Keratometry

Standardizing Keratometry• Choose a method and use it only, and personalize

your constant accordingly!• How radius correlates with power, not the actual

corneal power, so none are truly accurate• Different keratometers give different answers

because they are measuring different zones• Topography is NOT keratometry, algorithm for Sim K

can be misleading• Consistency is key -- choose the method that no

matter who does it, they get the same answer!• More devices = more confusion!!!!!

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Standardizing Keratometry• K’s must never be measured after an eye

examination - tonometry, gonio exams, proparacaine, dilating drops, etc. can cause erroneous K-readings!

• Presented by Cynthia Matossian , MD (Hawaiian Eye 2014): K’s off by 1D, axis off by 10 degrees following eye exam

• Best to bring all patients back for pre-op measurements on another day if they expect spectacle independence!

• Leave SCLs out for one week prior, gas-perm CLs out until K’s are stable!

Standardizing Keratometry• Per Jack Holladay:• Artificial tears and saline cause epithelial

edema and result in steep K readings!• They also reduce astigmatism!• Lots of quick blinks should be used

instead of artificial tears, then obtain readings within one second!

• If impossible to obtain, treat the dry eye for at least six weeks!!!

Measuring K’s with IOL Master

• 500 = 1 zone (2.5 mm), 6 points • 700 = 3 zones (1.5mm, 2.5 mm, 3.5 mm), 18 points

Total Keratometry with IOL Master 700

• Total Keratometry (TK) now available with Barrett Suite

• Swept source technology can measure posterior corneal surface and utilize actual measurement, not a nomogram, for both toric(Barrett TK Toric Formula) and non-toric (Barrett TK Universal II Formula) calculations

• Uses three values (anterior curvature, corneal thickness and proprietary calibrated posterior corneal curvature), adds the refractive indices of air, the cornea and the aqueous humour in the thick lens formula as described by Gullstrand to calculate Total Keratometry (TK)

Total Keratometry with IOL Master 700

Measuring K’s with LenStar

• 32 reference points oriented in two circles at 2.3 mm and 1.65 mm optical zones, very accurate for axis

• Validation Criteria:

< + 0.20 D power in each meridian

< + 3.5° axis in each meridian

• If there is <0.75 D of cylinder it can be difficult to have all less than 3.5 ° of standard deviation on axis - still acceptable because patient is not a toric IOL candidate

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Measuring K’s with LenStar

• These standard deviations are visible below the measurements as you’re scanning!

Toric Calculations:What is Astigmatism?

• The normal cornea without astigmatism will be a perfect half-circle (or spherical, or round)

• The astigmatic cornea is shaped more like a football, with one meridian being significantly more steeply curved than the meridian perpendicular to it

• Causes light to have two focal points in the back of the eye rather than one (either in front of the retina, behind the retina, or both) with blurring or distortion at all distances

• The steepest and flattest meridians are called the “principal meridians”

Toric Calculations:Types of Astigmatism

• “With-the-Rule” astigmatism is steeper vertically

• “Against-the-Rule” astigmatism is steeper horizontally

• “Oblique” astigmatism is at any other axis

Toric Calculations:Role of Topography

• Identifies the principal meridians by assigning false colors to represent curvature (“hotter” = steeper)

• Must determine if the astigmatism is “regular” or “irregular” to know if patient is a good toric candidate (standard keratometersautomatically position the measurements 90 degrees from each other so cannot make this determination)

• “Regular” astigmatism = principle meridians 90 degrees away from each other

• “Irregular” astigmatism = axes not 90 degrees apart

Toric IOL CalculationsPer Warren Hill, MD: • Calculate sphere with usual axial lengths and keratometry • Determine steep meridian by drawing a line manually

through steepest axis of central 3.5 mm of a topographic map

• Use multiple instruments for K’s (manual, auto, IOLM, LenStar)

• The instrument that got the axis correct and in agreement with observed axis is the one to use for power

• “The instrument in agreement with what we know to be correct is the one most likely to be correct. The instrument in disagreement with what we know to be correct is the one most likely to be incorrect!”

Toric IOL CalculationsExample from Warren Hill, MD: • Readings on same eye from IOLM, LS, Auto K, Sim K

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Toric IOL CalculationsExample from Warren Hill, MD: • Observed axis drawn on topo:

Toric IOL CalculationsExample from Warren Hill, MD: • Readings on same eye from IOLM, LS, Auto K, Sim K

Toric IOL Calculations

Example #2 from Warren Hill, MD: • Two different readings, observed axis:

Toric IOL CalculationsExample #2 from Warren Hill, MD: • Two different readings, resulting calcs:

Toric IOL CalculationsExample #2 from Warren Hill, MD: • Two different readings, post-op results:

Toric IOL Calculations• www.SIA-Calculator.com is available to determine

surgeon’s surgically induced astigmatism, but does vary from patient to patient based on incision location and architecture as well as corneal radius, thickness and rigidity, so recommended to use 0.12 D if using small, temporal incision < 2.4 mm (if nasal incision, more induced cylinder so must study to determine SIA)

• www.astigmatismfix.com will determine how much to rotate a lens post-op

• Because we now know posterior corneal astigmatism exists, calculators now adjust for this based on theoretical models

• As of ASCRS 2018, using total corneal power not as accurate as using anterior corneal measurements and current calculators, but close (this may likely change, since we have new formulas like Barrett TK Toric in IOL Master 700 – no peer reviewed results yet)

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Toric IOL Calculations• Alcon calculator uses the Barrett

Toric Algorithm to account for PCA• J&J calculator has option for PCA

for WTR, ATR, and oblique astigmatism using their own nomogram working with Drs. Koch and Ma based on Tecnis Toricoutcomes (can opt not to include PCA if entering total corneal power)

• Barrett Toric Calculator uses Barrett’s algorithm theoretical model

• Abulafia-Koch uses regression model for PCA and can be used with Hill-RBF in LenStar

• Holladay’s toric calculator currently does not account for PCA

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Toric IOL CalculationsWhat we’ve learned in recent years:• Calculate sphere as per normal protocol• Verify axis manally with topography (don’t

always trust a single instrument)• Don’t ignore posterior corneal astigmatism

in calculations (theoretical models vs. actual measurements currently being developed)

• Use 0.12 D for SIA (centroid value) for small, temporal incisions

• WTR astig will drift into ATR as we age, so leave 0.25 - 0.5 D WTR to compensate

• Flip the axis if needed to get least amount of cylinder

Adjusting K’safter Refractive Surgery

The Post-Refractive Surgery Keratometry Challenge

• Central cornea flattened for myopic correction, steepened for hyperopic correction

• Using standard keratometry readings results in over-estimation of corneal curvature in the previous myope due to reading a larger area than desired, resulting in a hyperopic surprise (+3.0 D to + 6.0 D)

• In the previous hyperope, results in an under-estimation due to reading a smaller area, and a myopic surprise, though not on the order of the previous myope

The Most Reliable Methods Today

Shammas Methods*Shammas, et al AJO 2003; 136:426-32

• For Myopic LASIK patients: Measure K’s today (optical), average, then adjust

K = 1.14 (K post-op) - 6.8

• For Hyperopic LASIK patients: Measure K’s today (optical), average, then adjust

Shammas, et al J Cataract Ref Surg 2013; 39:739-744

K = 1.0457 (K post-op) – 1.9538

* In LenStar

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Masket Method*Masket S, Masket SE. JCRS 2006; 32:430-434

• For PRK and LASIK patients (not RK!)

• Must know amount of correction from history (LSE = spherical equivalent of change after laser vision correction)

IOL Adjustment = LSE x (-.326) + 0.101

• Adjust final power, not measurements

• Use optical K’s and Biometry and run calcs, then adjust implant power

• No need to determine corneal power

• Mean outcome -0.15 D, 28 out of 30 eyes within 0.5 D of target

* In LenStar

Haigis L*• For both myopic and hyperopic LASIK on recent

versions of IOLM (older versions have neither, semi-older versions have myopic only)

• Measure patient on IOLM like always, but choose Haigis L myopic or hyperopic formula

• No history required

• For myopia, Haigis L has a correction function for IOL Master keratometry plus a correction factor for the ACD change (0.5 mm steeper since part of cornea removed) due to ablation

• For hyperopia, since no ablation, has correction function for K’s only

* In IOL Master

Barrett True K Method*Barrett GD. True-K formula: New Approach to biometry

after LASIK. Presented at ASCRS 2009

• For myopic LASIK, hyperopic LASIK, and RK

• Based on Barrett Universal II formula

• Calculates a modified K value for post-refractive patients

• Requires optical Ks as measured and the pre-and post-refractive surgery refractions for maximum accuracy

• Can also be run with no history available

* In LenStar and IOL Master 700 Barrett Suite

ASCRSPost-Refractive Surgery

IOL Calculatorwww.ASCRS.org

Run in addition to embedded methods in optical biometer

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Prior Myopic LASIK/PRK Prior Myopic LASIK/PRK

• Best results from Barrett True K, Haigis-L, Shammas, and Masket

Prior Hyperopic LASIK/PRK Prior Hyperopic LASIK/PRK

• Best results from Barrett True K, Haigis-L, Shammas, and Masket

Prior RK Prior RK

• Best results probably Barrett True K, IOL Master/Lenstar (using K’s as measured) , Atlas 1-4

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RK Patients

• Measure them in morning rather than afternoon – K’s flatter in the am, steeper in pm (make them plano in the am, myopic in pm – not hyperopic am, plano pm!)

• Aim for -0.75 or -1.00 in post-RK patients because of hyperopic shift over several years

• Don’t want them to drift into hyperopia - drift into plano instead

• After RK, many patients have a hyperopic surprise that will settle out over time (if not gone by 2 months post-op, IOL exchange)

Other Problems

• How many patients had RK and LASIK? No calculator for that!

• How many patients had enhancements?

• How do we know if the first procedure under- or over-corrected? Did they have flattening or steepening from the enhancement?

Patient Unsure• Patient had LASIK OU, wasn’t sure what type

• Asked if she was nearsighted or farsighted beforehand

• Her answer was “both”

Patient Unsure• Patient had LASIK OS only for monovision purposes

• Was plano OU beforehand

• Would that be myopic or hyperopic LASIK?

Patient Unsure• Patient had LASIK OU for monovision purposes

• Was it myopic or hyperopic based on measurements?

• Which eye was near eye?Standardizing Axial

Eye Length Measurements

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Standard Dimensions

• Avg AEL = 23.5 mm

• Normal Range = 22.0 mm - 24.5 mm

• All readings on same eye within 0.1 mm

• OD and OS within 0.3 mm of each other

• What can justify a difference of more than 0.3 mm by patient’s history?-Anisometropia, amblyopia, scleral buckle

Importance of Accuracy

• 0.1 mm error = ~0.25 D post-op surprise in average length eyes (1 mm = 2.5 D)

• In longer eyes (30 mm) 1.0 mm = 1.75 D

• In short eyes (20 mm) 1.0 mm = 3.75 D

• In extremely short eyes, 0.1 mm error as much 0.75 D post-op!

Standardizing Biometry

MUST use non-contact methods only

• Optical biometry

• Immersion ultrasound biometry

• B-Scan biometry needed at times

Importance of Accuracy

• If the measurement is too short, the post-op error = myopic direction

• If the measurement is too long, the post-op error = hyperopic direction

Contact Method:No Longer an Option!

• Not accurate enough for today’s patients• Studies from 1980’s verified 0.14 – 0.36 mm

error due to corneal compression• Uncontrollable variables: biometrist and IOP

dependent• Takes longer to do than immersion!• “Of historical interest only”

With Contact TechniqueVisual Axis Not Enough!

AEL 25.18 LT 4.41 ACD 2.87 AEL 25.80 LT 4.41 ACD 3.49

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Measuring Axial Length with Light

Optical Biometry: IOL MasterZeiss

• Axial Length

• K’s

• ACD

• HWTW

• Eccentricity of visual axis

• Measurement range 14-38 mm

Optical Biometry: IOL Master 700

Zeiss

3-Zone Keratometry Fixation Check

• Swept source OCT technology, measures axial length, CCT, ACD, LT, HWTW, K’s, pupil size, eccentricity of visual axis

• Penetrates dense cataracts better than previous opticalmeans

Optical Biometry: Lenstar LS 900Haag-Streit

• Corneal thickness (CCT)• Anterior chamber depth (ACD)• Corneal curvature• Lens thickness (LT)• Axial length (AL)• White to white• Pupillometry• Eccentricity of the visual

optical line• Measurement range 14-32 mm

Multifocals andPupil Barycenter

• Per Jack Holladay MD, pay attention to the pupil barycenter (eccentricity of visual axis) information from IOL Master and LenStar

• Add x and y together, and make sure the number is 0.6 or less (ignore + and – signs)

• If 0.7 or higher, not a good candidate for a multifocal because fixation too eccentric –will likely have halos and glare!

• Karhanova M, Maresova K, Pluhacek F, Mlcak P, Vlacil O, Sin M. Cesk Slov Oftalmol. The importance of angle kappa for centration of multifocal intraocular lenses. 2013 Jun; 69(2): 64-8. (Article in Czech)

• Prakash G, Prakash DR, Agarwal A, Kumar DA, Agarwal A, Jacob S. Predictive factor and kappa angle analysis for visual satisfactions in patients with multifocal IOL implantation. Eye (2011) 25, 1187-1193.

Multifocals andPupil Barycenter

• Good candidate for multifocal:

• Bad candidate for multifocal:

Must be < 0.6 when add x and y together!

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How Does Optical Biometry Compare with Immersion?

Per Dr. Haigis:

“Partial coherence interferometry is a non-contact, user- and patient-friendly method for axial length determination and IOL planning with an accuracy comparable to that of high-precision immersion ultrasound.”

“Its accuracy is superior to that of the commonly used applanation method and is directly comparable to that of high-precision immersion ultrasound.”

Graefe’s Arch Clin Exp Ophthalmol (2000) 238:765-773

How Does Optical Biometry Compare with Immersion?

• Ultrasound measures across foveal cup

• Optical biometers measure to RPE at foveal center

• Foveal thickness about 150 microns, depending on AEL

How Does Optical Biometry Compare with Immersion?

• Formulas based on ultrasound measurement at ILM interface

• Optical biometers calculate RPE to ILM distance proportional to axial length

• This distance is subtracted from measurement to RPE

• Result displayed is the “ILM adjusted” measurement, and should coincide with immersion ultrasound within 0.1 mm

How Does Optical Biometry Compare with Immersion?

• Optical biometers programmed with an algorithm in order to calibrate it to immersion ultrasound by Dr. Haigis, comparing 600 eyes

• AL IOLM = 1.0006 X AL IUS + 0.0337

• Example:

Immersion meas = 23.45 mm

IOL Master = 1.0006 (23.45) + 0.0337

= 23.49777

Difference = 0.04777

Optical and Immersion

• The “marriage” of the two is the best case scenario

• Beware false statements of one being more “accurate” than the other

• Differences are clinically insignificant when both are of high quality with the exception of long eyes

• Sometimes neither one works and B-scan must be used!

Refractive Lensectomy Patient

23.90

23.94

23.80

23.79

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2+ NSC, 2+ PSC OU

23.51

23.61

24.02

24.07

2+ NSC, 2+ PSC OD3+ NSC, 3+ PSC OS

23.30

23.34

23.38

23.43

3+ NSC, Hx of Anterior Uveitis

Error 24.42

IOL Master Waveform

• The primary maxima represents the layer the light reflected from (RPE)

IOL Master Waveform

• What’s the blue circle?

• The caliper!

• Programmed to land on the highest peak it “sees”

• Can be moved by right-clicking and dragging it if in wrong position

Data Page Verification• Data page documents the number of readings, spike

pattern, SNR, double peaks, etc

• Must not ever delete readings! Do not falsify the document!

• Don’t delete error messages, outliers, red numbers, double peaks!

• Must have true record of reliability!

• Hit the “print” button after completing measurements, prior to going to calculation screen

19

Double Peaks

• Double peaks are caused when there is a reflection of the light from another layer or source, indicating probable macular pathology

• First find out the cause, verify with A or B

• Then go through the measurements and move the caliper if necessary

Double PeaksDouble Peak on IOLM

Poor retinal spike on A

Varying #’s on both

ERM on OCT (not seen by MD)

B = 24.70 mm

Macular Disease and IOL Master 700 Macular Disease and IOL Master 700

LENSTAR LS 900

• Measurements obtained with eye in same position

• All measurements obtained allow for operator validation

• All calipers can be adjusted as deemed necessary

• Separate computer allows for input of Holladay II with autopopulation and links to websites (ASCRS, ULIB, etc)

Measuring Axial Lengthwith LenStar

• Scan pattern similar to A-scan biometry• Can see cornea, lens echoes, retinal ILM

and RPE (rather than retina and sclera)

20

LenStar Data Page LenStar Final Step

• After “finishing” EVERY exam, click on axial length to check calipers, then click on K’s to check for bad readings, then click on HWTW to likely move calipers

Macular Disease and LenStar

• Retinal spikes do not align on top of each other or are too far apart

• Ex: epiretinal membrane (ERM)

Optical Biometry Can’t be utilized in 100% of patients, so

immersion must still be used when:

• Mature cataracts, strong PSC• Fixation difficulties• Tremor/nystagmus• Significant corneal or vitreal opacity• RPE defects• Pigment epithelial detachment • Physical disabilities preventing

access

Cases that Should be Verified with Immersion Ultrasound

• Borderline measurements or unable to measure• Two eyes measuring more than 0.3 mm different

in length• Eyes 25.0 mm or longer: Optical most often

measures long eyes too long, causing hyperopic surprises - perform immersion and B-scan biometry to verify if not using Olsen or Barrett Universal II formulas

Long Eye:Optical vs. Ultrasound

Post-op using Imm:OD: -0.75 +1.25 X 140 (SE = -0.125)OS: -0.50 + 0.50 X 008 (SE = -0.25)

28.51 mm 28.37 mm28.10 mm 28.09mm

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Wang Koch Equations• There are two assumptions these equations make that are

not always true:

1. That optical ALWAYS gets the measurement wrong in long eyes (definitely not true!)

2. The longer the eye the greater the error (most definitely not true – the error is NOT proportional to axial length!)

• In the super-long eye, these equations over-adjust (by as much as 2.0 mm!) leading to myopic surprises

• Best practice is to use ultrasound (immersion and B-biometry) for higher accuracy and to determine if optical correct or not , OR

• Use Olsen or Barrett formulas with optical measurements with internal corrections

Courtesy Carl Zeiss Meditec

Optical vs. Ultrasound vs. Wang Koch in Long Eyes

• Optical: 37.34 mm OD

37.07 mm OS

• Immersion & B: 36.83 mm OD

36.81 mm OS

• Wang-Koch: 35.78 mm OD

35.54 mm OS

Used US meas: targeted -2.25, post-op = -2.00 OU

Measuring Axial Length with Sound

How Does A-Scan Work?• As a thin, high frequency sound

beam passes through the eye, each time it strikes interface (a change in density) part of the sound beam is reflected back into probe, referred to as the “echo”, and is represented as a spike arising from baseline

• The greater the change in density, the higher the spike

• An Amplitude scan• When aligned along visual axis,

will have five tall spikes: Cornea, anterior lens, posterior lens, retina, sclera

What caused these spikes?

• Multiple spikes within the lens

• Caused from changes in density within the nucleus

• Dense nuclear sclerotic cataracts

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What caused these spikes?

• Small blips along vitreous baseline

• Slightly more highly reflective spike to the left of the retinal spike

What caused these spikes?

What caused these spikes? Sometimes it’s a Missing Spike

Perpendicularity is Crucial

• Must be perpendicular to all interfaces

• Sound is reflected and refracted, just like light rays

Perpendicularity Evident on Scan

• Five high spikes after probe spike

• Retinal spike as steeply rising as possible

23

Errors in Immersion Biometry• Gain too high (cannot split retina and sclera into separate spikes)

• Not perpendicular to macula = crooked retinal spike

• Not going through center of lens = shortened posterior lens spike

Perpendicular to Optic Disc rather than Macula

• No sclera at optic nerve, therefore no scleral spike present on display

• To correct, direct sound beam more temporal to find macula

Perpendicular to Optic Disc rather than Macula24.22 23.90

Immersion Technique

• Probe immersed in shell of saline

• Most accurate/no corneal compression (0.015 - 0.05 mm depending on manufacturer)

• The method to which optical was calibrated in its development

Infusion Shell Multiple Technician Biometry Study of One Eye

M. Bryan Waldron, CCOA, ROUB

• 87 technicians from USA and Europe obtained five readings on same eye of one subject with Accutome Accusonic

• Skill levels varied: certified/non-certified, most with no immersion experience, some no biometry experience, MDs, ODs, nurses

• Total of 435 measurements of OD• Average 24.54 mm, std deviation 0.03 mm• OCB: 24.56 mm

24

Challenging Eyes

The High Myope• Can’t get quality retinal

spike because macula sloped

• Perpendicularity impossible

• Measurements long and very variable

• Optical problematic in these eyes if not using Olsen or Barrett formulas, so must get accurate measurement

The High Myope

Normal globe

Ovoid Myopic globe Staphyloma Double Staphyloma

B-Scan Biometry • Align B-scan with “HMAC”

position (probe on corneal vertex, marker nasal) with 4 or 5 mm of gel on probe tip

• Corneal vertex and posterior lens surface centered on left, macula centered on right inferior to optic nerve

• Macula ~4.5 mm down from center of optic disc

• Place one caliper on macula, move the other to the center of the anterior corneal vertex

If you can’t see the cornea, you’re not using enough gel!

B-Biometry Technique• Measures total axial length on B-scan from anterior

corneal surface to macula

• Find corneal echoes within artifacts – small double-line

• If not visible, not enough gel on probe tip or probe too deep in gel!

• Some machines send measurements into their A-scan software for calculations

23.78 on A-scan 23.80 on B-scan

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B-biometry = 30.34mm

A-scan = 30.03, 30.26, 30.0, 30.20, 30.15, 29.98

High MyopeOD: 28.34, 28.66, 28.62, 28.85 OS: 28.56, 28.46, 28.28, 28.65

28.66 28.28

28.68 28.29

Confirming Axial Length Difference

23.57 24.78

23.54 24.71

Extremely Long Eye

• -30.0 CTL’s OU with -3.00 specs

• OD cc: 20/30 OS cc: HM brunescent NSC

• Retinal spike so far to right, off the screen!

Extremely Long Eye

• Used B-scan to measure vitreous length

• ACD and LT from biometry

Vitreous OD: 33.91 mm OS: 34.89 mm

Extremely Long Eye

Total length:

OD: 41.17 mm OS: 42.03 mm

-10.0 D IOL highest power available

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Extremely Long Eye

Post-Op Results:

• OD sc: 20/70, with -3.00 specs = 20/30+

• OS sc: 20/70, with -3.00 specs = 20/30+

Longest Eye Ever?

OD: -38.0

BCVA: 20/80

1+ NSC, 3+ Cortical

OS: NLP from recurrent RD

Tried v. 5 IOL Master

Longest Eye Ever?

Contact A-scan:

Immersion A-scan:

Longest Eye Ever!?

Vitreous length from B-scan = 36.58 mm

Adding all together: 2.63 + 5.59 + 36.58 = 44.80 mm!

Post-op outcome: -3.00 +0.25 X 160 = 20/60

Macular Disease and Ultrasound

• Sound beam perpendicular to flat surface reflects back easily

• If convex, part of the sound will be diverted resulting in low-quality spike

• If irregular or coarse surface, more scattering with compromised spike

Macular Disease and Ultrasound

• If unable to get quality retinal spike, review chart for macular pathology

• Alert surgeon/get OCT

• B-scan if poor view of fundus

27

Macular Edema

*Best way to measure when CME? Optical and B-scan(Immersion would measure too short)

Macular Pathology

*Best way to measure when ERM? Optical (B-Scan and Immersion would measure too short)

Macular Pathology Macular Pathology

*Best way to measure when PED? B-Scan(Optical and Immersion would measure too short)

Macular Pathology

*Best way to measure when VMT? Optical and B-scan(Immersion would measure too short)

Protocol for Bad Retinal Spike

1. Is it a long eye? If not, review chart for noted macular pathology

2. If none noted, do OCT!

3. If view in poor, do B-Scan!

4. Once pathology determined, decide the best way to measure

5. If none discovered, it was misalignment all along

6. You MUST find the problem!

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Case Presentation• Patient seen 5 weeks prior for cataract evaluation

• BCVA 20/50 OD, 20/40 OS

• Exam unremarkable except for cataracts and mac drusen

Case Presentation• No history to support axial length difference

• Immersion performed to verify – measurements same

Case Presentation

• B-scan performed to further verify axial length difference

• Eye that measured shorter has visible macular elevation

• Rechecked vision OD, now 20/300

Case Presentation• OCT and FA performed to further investigate

• Submacular hemorrhage OD

• Case cancelled, patient transferred to retina clinic for immediate evaluation and treatment

ALL Patients Deserve Highest Quality Care

• Expectations and demands have changed

• We have to practice the highest standard of care

• Only optical or immersion axial lengths (B-biometry when needed) – No contact biometry

• Do not measures K’s after an eye exam or after tears and always use the same zone

• Use the best formula (they all require good data in!)

• Standardize your measurements, formulas, and surgery and you’ll standardize your outcomes

The End

Thank you so much for your kind attention!To contact speaker: rhondawaldron@comcast.net