Post-LASIK Intraocular Lens Power Adjustment Nomogram

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Post-LASIK Intraocular Lens Power Adjustment
Nomogram

• Joseph Diehl
• jdiehl_at_ucla.edu
• Kevin Miller, MD
• Jules Stein Eye Institute,
• David Geffen School of Medicine at UCLA
• --No Disclosures--

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Whats the problem?

• Cataract surgery normally gives a good refractive
  result, BUT
• LASIK surgery on the rise
• Changes to corneal power from LASIK are not
  adequately detected by corneal topography
• With inaccurate corneal power measurements, IOL
  calculations are inaccurate as well
• and cataract patients have an unsatisfactory
  refractive result

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How do we solve it?

• Investigate the relationship between the
  LASIK-induced correction in manifest spherical
  refraction equivalent (MSRE) and post-cataract
  MSRE (the post-operative error)
• Retrospective, chart-based study of consecutive
  patients having cataract surgery after LASIK
• Requires pre- and post-LASIK surgical records

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Methods

• Plot LASIK correction in MSRE (in Diopters) vs
  predicted (based on K values from corneal
  topography) post-cataract MSRE (D)
• On same graph, plot the actual post-cataract MSRE
• The difference between the predicted and actual
  post-cataract MSRE is the post-operative error
  the surgeon should target to achieve emmetropia
  for the given LASIK correction in MSRE
• Graph the LASIK correction against this
  difference to determine if a relationship exists

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Patient Demographics

• 32 suitable eyes from 23 patients
• Average age 59 years (range 45-74)
• 60 female, 40 male
• 25 myopic LASIK, 7 hyperopic LASIK
• MSRE (D) mean std dev (range)
• Pre-LASIK -5.9 /- 4.9 (-14.8 to 3.4)
• Post-LASIK -1.0 /- 1.5 (-4.8 to 1.6)

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RESULTS

• post-cataract MSRE (D) Mean /- Std Dev
  (Range)
• Predicted error -2.0 /- 1.8 (-6.3
  to 0.7)
• Actual error -0.3 /- 0.7 (-1.8
  to 0.8)
• Absolute error 0.5 /- 0.5 (0.0
  to 1.8)

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-2
Arrows demonstrate a single patient with a LASIK
correction of -5 D. Implanted IOL had a
predicted post-op MSRE of -3 diopters, but an
actual post-op MSRE of only -1. Difference of -2,
so this patient will be -5, -2 on following graph.
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(No Transcript)
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Outcomes Deviation from equation
56
41
3
Less than 0.5 D
0.5 to 1.0 D
More than 1.0 D
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Statistically Speaking

• Deviation from trendline (D)
• Mean /- Std Dev (Range)
• -0.1 /- 0.6 (-1.1 to
  0.8)
• ABSOLUTE deviation from trendline (D)
• Mean /- Std Dev (Range)
  
• 0.5 /- 0.3 (0.0
  to 1.1)
• STANDARD (statistically predicted) ERROR
• Mean of 0.65 D (0.64 to 0.71)

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Post-LASIK IOL Power Adjustment Nomogram

• LASIK correction (D) target MSRE (D)
• -12 -4.9
• -11 -4.3
• -10 -3.8
• -9 -3.2
• -8 -2.7
• -7 -2.3
• -6 -1.9
• -5 -1.5
• -4 -1.1
• -3 -0.8
• -2 -0.5
• -1 -0.3
• 1 0.1
• 2 0.3
• 3 0.4
• 4 0.5

Target error (D) for emmetropia -0.0177(L)20.1
92(L)-0.0624 LLASIK correction (D)
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Discussion

• Mathematical relationship clearly evident between
  LASIK correction and post-cataract refractive
  error
• Cataract surgeon selects IOL with predicted
  post-operative MSRE that correlates in nomogram
  with LASIK correction
• Post-LASIK and post-cataract MSRE measurements
  done at inconsistent intervals, because patients
  didnt return for follow-up, however, cornea can
  take months to stabilize
• Inconsistencies in measurement of MSRE (measured
  by technician, physician, or machine)
• No method yet that consistently produces results
  equal to eyes without refractive surgery
• Necessary to have complete LASIK records
• Imperative that patients return for all scheduled
  LASIK post-operative examinations to get accurate
  and stable MSRE
• Prospective use of nomogram necessary to further
  refine graph and determine predictive value