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Post-LASIK Intraocular Lens Power Adjustment Nomogram

Post-LASIK Intraocular Lens Power Adjustment Nomogram. Joseph Diehl jdiehl@ucla.edu Kevin Miller, MD Jules Stein Eye Institute, David Geffen School of Medicine at UCLA --No Disclosures--. What’s the problem?. Cataract surgery normally gives a good refractive result, BUT…

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Post-LASIK Intraocular Lens Power Adjustment Nomogram

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  1. Post-LASIK Intraocular Lens Power Adjustment Nomogram Joseph Diehl jdiehl@ucla.edu Kevin Miller, MD Jules Stein Eye Institute, David Geffen School of Medicine at UCLA --No Disclosures--

  2. What’s 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

  3. 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

  4. 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

  5. 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)

  6. 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)

  7. } -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.

  8. Outcomes: Deviation from equation 56% 41 % 3% Less than 0.5 D 0.5 to 1.0 D More than 1.0 D

  9. 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)

  10. 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)^2+0.192(L)-0.0624 L=LASIK correction (D)

  11. 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 didn’t 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

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