Systematic approach to toric IOL power calculation...
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4/9/2016 1 Corneal astigmatism measurements Methods of calculation Corneal surgically induced astigmatism (SIA) Toric IOL misalignment Sources of Unexpected residual astigmatism! & 180 Single-angle vs. double-angle plots for astigmatism data ATR ATR WTR WTR ATR Toric IOL cylinder power at the corneal plane is calculated by using a fixed ratio: Alcon Oculentis PhysIOL Commercial Toric IOL calculators
Transcript of Systematic approach to toric IOL power calculation...
4/9/2016
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Corneal astigmatism measurements
Methods of calculation
Corneal surgically induced astigmatism (SIA)
Toric IOL misalignment
Sources of
Unexpected residual astigmatism!
& 180
Single-angle vs. double-angle plots for astigmatism data
ATR ATR
WTR
WTR ATR
Toric IOL cylinder power at the corneal plane is
calculated by using a fixed ratio:
Alcon
Oculentis
PhysIOL
Commercial Toric IOL calculators
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Toric IOL cylinder power at the corneal plane is
calculated by using the estimated ELP.
AMO
Medicontur
Rayner
Zeiss
Holladay, ASSORT, Barrett
Commercial Toric IOL calculators
Toric IOL cylinder power at the corneal plane is
calculated by using the estimated ELP.
AMO
Medicontur
Rayner
Zeiss
Holladay, ASSORT, Barrett
Commercial Toric IOL calculators
0.7 D difference
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81 eyes
LEI
IOLMaster2
68 eyes
Ein-Tal
Lenstar1
Errors in Predicted Residual Astigmatism
1. Abulafia et al, J Cataract Refract Surg 2015; 41:936-9442. Abulafia et al, J Refract Surg 2015; accepted for publication
Commercial Toric IOL calculators
Q: Does the ELP make a difference?
A: Yes, but…mostly for extreme cases
81 eyes
LEI
IOLMaster2
68 eyes
Ein-Tal
Lenstar1
Errors in Predicted Residual Astigmatism
1. Abulafia et al, J Cataract Refract Surg 2015; 41:936-9442. Abulafia et al, J Refract Surg 2015; accepted for publication
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Standard keratometric and topography machines
tend to yield inaccurate results in assessing the net
corneal astigmatic power
Posterior Corneal Astigmatism
Posterior Corneal Astigmatism
Koch et al, J Cataract Refract Surg 2012;38:2080-2087
715 eyes of 434 patients
Posterior Corneal Astigmatism
Koch et al, J Cataract Refract Surg 2012;38:2080-2087
WTR
ATR
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Most posterior corneas are steep vertically
The posterior cornea acts like a negative lens
It creates a net plus power along the horizontalmeridian
ATR astigmatism
What is the effect of the posterior corneal astigmatism?
Koch et al, J Cataract Refract Surg 2012;38:2080-2087
81 eyes
LEI
IOLMaster2
68 eyes
Ein-Tal
Lenstar1
Errors in Predicted Residual Astigmatism
1. Abulafia et al, J Cataract Refract Surg 2015; 41:936-9442. Abulafia et al, J Refract Surg 2015; accepted for publication
Intraoperative aberrometry
Standard toric IOL calculators + Nomogram (Baylor)
Barrett Toric IOL calculator
Standard toric IOL calculators
+ Direct measurements of the PCA (Scheimpflug, OCT,
Cassini)
Standard toric IOL calculators + AK (Abulafia-Koch) formula
Solutions:
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Baylor Nomogram:
Koch et al, J Cataract Refract Surg 2013;39:1803-1809
The Barrett Toric Calculator
SEq Universal II formula
ELP IOL cylinder power correction at the corneal plane
Mathematical model Net corneal astigmatism !
P< .001 (J0)
Each ring = 0.50 D
99 eyes
LEI
IOLMaster & Holladay
Pentacam & Holladay
IOLM-Pentacam & Holladay
IOLMaster & Barrett
Errors in Predicted Residual Astigmatism
Abulafia et al, J Refract Surg 2015; accepted for publication
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The Abulafia-Koch (AK) formula
Abulafia et al, Barcelona, ESCRS 2015
J0: Regression of estimated net corneal astigmatism by measured corneal astigmatism (R²=0.986)
J45: Regression of estimated net corneal astigmatism by measured corneal astigmatism (R²=0.963)
AK Formula – ATR astigmatism
The AK formula calculates the estimated net corneal astigmatism, by using anterior corneal based measurements!
AK Formula – WTR astigmatism
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AK Formula – oblique astigmatism
Centroid Error in Predicted Residual Astigmatism
WTR ATR
Each ring = 0.50 D
(P< .0001 [J0]; P= .986 [J45])
Abulafia et al, accepted as an abstract, Barcelona, ESCRS 2015
Centroid Error in Predicted Residual Astigmatism
WTR ATR
Each ring = 0.50 D
(P= .986 [J0]; P= .990 [J45])
Abulafia et al, accepted as an abstract, Barcelona, ESCRS 2015
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61 years old female
Ref: -7.75, -0.75x161°
AL = 27.21mm, mean K = 43.02 D, ACD = 3.19 mm
Example: WTR Astigmatism
Primary instrument
Axial power map
Steep meridian: 87°
Supporting instruments
IOLMaster
Steep K: 89°
Lenstar
Steep K: 86°
Primary and secondary supporting instrumentsdetermining the steep meridian
Use primary and secondary supporting instrumentspower difference between meridians
Primary instrument
Lenstar KeratometryPower difference
Pentacam front power map: 2.4 D
Supporting instruments
IOLMaster Keratometry: 2.21 D
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Toric IOL Calculation
+ AK
Toric IOL Calculation
+ AK
Toric IOL Calculation
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Error in predicted residual astigmatism
LE uneventful cataract extraction, SN6AT4, 11.5 D
Post op refraction (cyl): 0.25D x 155° cyl
Alcon: 0.61 D x 167° ; Holladay: 0.68 D x 168°
Holladay (pentacam) TCRP: 0.80 D x 166°
Posterior astigmatism: 0.53 D x 167°
Alcon + AK: 0.14 D x 114°
Holladay + AK: 0.14 D x 133°
Barrett: 0.16 D x 142°
The outcome of toric IOL implantation can be optimized by using ‐
Appropriate methods of calculation
Summary
+ AK + AK
