Transcript Dr. Richard Lindstrom

Accuracy of Scheimpflug Imaging Holladay
Equivalent Keratometry Values for IOL
Power Calculation in Post Laser
Keratorefractive Surgery Eyes
Sherman W. Reeves, MD, MPH1,3,4; Jacob A. Kozisek, OD1,2;
Noumia Cloutier-Gill, OD1,2; David R. Hardten, MD1,2,3,4
Minnesota Eye Consultants, Minneapolis, Minnesota
2 Illinois College of Optometry, Chicago, Illinois
Department of Ophthalmology, University of Minnesota, Minneapolis, Minnesota
4 Department of Ophthalmology, Regions Medical Center, St. Paul, Minnesota
1
3
**Financial disclosures: DRH – prior speaker for Oculus and ZeissHumphery; Minnesota Eye Consultants has received research funding
from Bausch+Lomb for unrelated studies**
Background
• Traditional keratometry measurements, such as manual
keratometry, inadequately measure corneal refractive power
in eyes that have undergone prior laser keratorefactive
surgery (LKS) such as laser in situ keratomileusis (LASIK) or
photorefractive keratectomy (PRK).1,2
• Holladay Equivalent Keratometry Readings (EKR), available
with the Pentacam Scheimpflug imaging system’s Holladay
Report software package, are purported to provide accurate
keratometry measurements in post LKS eyes.3
• Analysis of corneal power across a 4.5mm optical zone is the
default measurement of the EKR software.
• A recent study suggested that EKR measurements at 4.5 mm
zone may overestimate the true keratometric power in post
LKS eyes.4
Minnesota Eye Consultants
www.mneye.com
Purpose
To determine the accuracy of Pentacam
Scheimpflug system Holladay Equivalent
Keratometry Values for intraocular lens
calculation prior to cataract extraction in eyes
that have previously undergone excimer laser
corneal refractive surgery.
Minnesota Eye Consultants
www.mneye.com
Methods
•
Design
– Retrospective cohort
– IRB approval granted by Chesapeake Research Review, Inc.
•
Setting
– Minnesota Eye Consultants (MEC), a private group practice with a
large cataract and refractive surgery patient base.
•
Subjects
– Identified through a search of computerized billing database.
– Eligibility:
• Eyes with prior hyperopic or myopic LASIK or PRK that
subsequently underwent cataract surgery at MEC from Jan. 2006
to Dec. 2009 and with Pentacam measurements obtained
preoperatively for cataract surgery.
– Exclusions:
• Presence of visually significant ocular pathology unrelated to
cataract.
• Eyes with intraoperative complications during cataract extraction.
Minnesota Eye Consultants
www.mneye.com
Methods
• Chart Review
– Clinical data collected
• Preoperative
– Axial length
– Manual keratometry values
– Pentacam EKR values
» Extrapolated at 4.5mm, 3.0mm and 2.0mm
optical zones
• Power and model of intraocular lens implanted
• Postoperative
– Stable spherical equivalent refractive error obtained
between 2 to 12 weeks after cataract extraction.
Minnesota Eye Consultants
www.mneye.com
Methods
• Analysis
– The back-calculated keratometry value (BackCalc K) was
generated for each patient with the Holladay IOL Consultant
program, Version 2.50.3129a (Holladay Consulting, Inc. Bellaire,
TX), using the postoperative refraction, axial length, lens power
and lens constant of the lens implanted.
• The BackCalc K represents the “ideal” keratometry value for an eye which, if
entered into the IOL calculation formula preoperatively, would have generated
and emmetropic spherical equivalent postoperative refractive outcome.5
– Manual keratometry and Pentacam EKRs at the 4.5mm, 3.0mm,
and 2.0mm zones obtained immediately prior to cataract
extraction were then compared to the BackCalc K values for each
patient.
– Paired t-tests were use to compare the BackCalc K to manual and
EKR Ks
– Subset analysis was performed on eyes status post myopic laser
with a monofocal IOL implanted. Wilcoxan rank-sum testing was
used for subset comparisons due to small group numbers.
Minnesota Eye Consultants
www.mneye.com
Results
• Population
– 30 eyes of 25 patients met the inclusion & exclusion
criteria
– 29 eyes status post Lasik
• 23 eyes post myopic LASIK
• 6 eyes post hyperopic LASIK
– 1 eye status post PRK
• Unknown prior refractive error
– IOL models implanted included
•
•
•
•
•
Tecnis Z9002 and Z9003
AR40e
Clariflex
Crystalens AT-45, 5.0 and HD
ReZoom
– 16 eyes status post myopic LASIK with a monofocal IOL
implanted
Minnesota Eye Consultants
www.mneye.com
Results
Measure
Mean
(D)
SD
(D)
BackCalc K
40.52
+ 4.48
Manual K
42.05
+ 2.80
EKR 4.5mm
41.75
+ 3.09
EKR 3.0mm
41.13
+ 3.33
EKR 2.0mm
40.85
+ 3.43
Subset: Eyes s/p
myopic lasik
with monofocal
IOL (n = 16)
Minnesota Eye Consultants
ALL Eyes
(n = 30)
Measure
Mean
(D)
SD
(D)
BackCalc K
39.01
+3.33
Manual K
41.30
+2.23
EKR 4.5mm
40.9
+2.66
EKR 3.0mm
40.1
+2.86
EKR 2.0mm
39.8
www.mneye.com
+2.98
Results – ALL Eyes (n=30)
BackCalc K - Km 4.5mm
5.00
5.0
3.00
3.0
1.00
1.0
-1.00
1
3
5
7
9 11 13 15 17 19 21 23 25 27 29
-3.00
-5.00
Difference between means =
-1.53D ± 2.15D (p<0.001)
-7.00
-9.00
Patient
Diopters
Diopters
BackCalc K - Man K
-1.0
1
3
5
-5.0
Difference between means =
-1.23D ± 1.77D (p<0.001)
-7.0
-9.0
Patient
5.0
3.0
3.0
1.0
1.0
3
5
7
9 11 13 15 17 19 21 23 25 27 29
-3.0
-5.0
-7.0
-9.0
Differences between means =
-0.61D ± 1.69D (p=0.06)
Minnesota Eye Consultants
Patient
Diopters
Diopters
BackCalc K - Km 2.0mm
5.0
1
9 11 13 15 17 19 21 23 25 27 29
-3.0
BackCalc K - Km 3.0mm
-1.0
7
-1.0
1
3
5
7
9 11 13 15 17 19 21 23 25 27 29
-3.0
-5.0
-7.0
-9.0
Difference between means =
-0.33D ± 1.72D (p=0.3)
Patient
www.mneye.com
Results
– Myopic LASIK/ Monofocal IOL Subset
(n=16)
BackCalc K - Man K
1.0
1.00
-3.00
-5.00
-1.0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Difference between means =
-2.29 ± 1.83 (p<0.001)
Diopters
Diopters
-1.00
-9.00
-3.0
-5.0
Patients
-9.0
1.0
Patients
1.0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
-3.0
Difference between means =
-1.1 ± 1.0 (p = 0.004)
Minnesota Eye Consultants
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
-3.0
-5.0
Difference between means =
-0.8 ± 1.1 (p=0.03)
-7.0
-7.0
-9.0
-1.0
Diopters
Diopters
Difference between means =
-1.9 ± 1.0 (p<0.001)
BackCalc K - Km 2.0mm
BackCalc K - Km 3.0mm
-5.0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
-7.0
-7.00
-1.0
BackCalc K - Km 4.5mm
-9.0
Patients
Patients
www.mneye.com
Conclusions
• Pentacam Equivalent Keratometry Readings in the 4.5mm
zone overestimate the keratometry value in post LASIK
and PRK eyes undergoing cataract extraction when
compared to an ideal K based on post surgical outcomes
data.
• Shrinking the EKR optical zone produced flatter EKRs,
which at the 3.0mm and 2.0mm zones were statistically
indistinguishable from the ideal K when all eyes in the
study were considered.
• A 2.0mm EKR gave a more accurate estimate of the actual
keratometry than larger zones in the subset of eyes status
post myopic LASIK and with a monofocal IOL implanted.
• Use of the Pentacam EKR measurements in the 2.0mm
and/or 3.0mm zones may provide improved accuracy of
Pentacam Equivalent K measurements in these eyes.
Minnesota Eye Consultants
www.mneye.com
References
1. Maeda N, Klyce SD, Smolek MK, McDonald MB. Disparity between
keratometry-style readings and corneal power within the pupil after
refractive surgery for myopia. Cornea 1997;16:517-524.
2. Hamilton DR, Hardten DR. Cataract surgery in patients with prior
refractive surgery. Curr Opin Ophthalmol. 2003;14:44-53.
3. Holladay JT, Hill WE, Steinmueller A. Corneal power measurements
using Scheimpflug imaging in eyes with prior corneal refractive
surgery. J Refract Surg 2009; 25:862–868.
4. Tang Q, MD, Hoffer KJ, Olson MD, Miller KM. Accuracy of Scheimpflug
Holladay equivalent keratometry readings after corneal refractive
surgery. J Cataract Refract Surg 2009; 35:1198–1203
5. Randleman JB, Loupe DN, Song D, Waring GO, Stulting RD.
Intraocular Lens Power Calculations After Laser In Situ
Keratomileusis. Cornea 2002; 21(8): 751–755.
Minnesota Eye Consultants
www.mneye.com