Sherman W. Reeves, MD, MPH1,3,4; Jacob A. Kozisek, OD1,2; Noumia Cloutier-Gill, OD1,2; David R. Hardten, MD1,2,3,4

1
Sherman W. Reeves, MD, MPH1,3,4 Jacob A.
Kozisek, OD1,2 Noumia Cloutier-Gill, OD1,2
David R. Hardten, MD1,2,3,4

• Accuracy of Scheimpflug Imaging Holladay
  Equivalent Keratometry Values for IOL Power
  Calculation in Post Laser Keratorefractive
  Surgery Eyes

1 Minnesota Eye Consultants, Minneapolis,
Minnesota 2 Illinois College of Optometry,
Chicago, Illinois3 Department of Ophthalmology,
University of Minnesota, Minneapolis, Minnesota4
Department of Ophthalmology, Regions Medical
Center, St. Paul, Minnesota
Financial disclosures DRH prior speaker for
Oculus and Zeiss-Humphery Minnesota Eye
Consultants has received research funding from
BauschLomb for unrelated studies
2
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
  systems 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

3
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.

4
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.

5
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.

6
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.

7
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

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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
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 2.98
Subset Eyes s/p myopic lasik with monofocal IOL
(n 16)
9
Results ALL Eyes (n30)
10
Results Myopic LASIK/ Monofocal IOL
Subset (n16)
Difference between means -2.29 1.83 (plt0.001)
11
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.

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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 199716517-524.
2. Hamilton DR, Hardten DR. Cataract surgery in
   patients with prior refractive surgery. Curr Opin
   Ophthalmol. 20031444-53.
3. Holladay JT, Hill WE, Steinmueller A. Corneal
   power measurements using Scheimpflug imaging in
   eyes with prior corneal refractive surgery. J
   Refract Surg 2009 25862868.
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
   3511981203
5. Randleman JB, Loupe DN, Song D, Waring GO,
   Stulting RD. Intraocular Lens Power Calculations
   After Laser In Situ Keratomileusis. Cornea 2002
   21(8) 751755.