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Enhanced Screening for Refractive Candidates based on Corneal Tomography and Biomechanics

Enhanced Screening for Refractive Candidates based on Corneal Tomography and Biomechanics. Renato Ambrósio Jr., MD, PhD Ruiz Alonso, MD; Daniela Jardim, MD; Frederico xxx, MD Marcella Salomão, MD; Simone Boghossian, MD; Bruno Fontes, MD. Rio de Janeiro - Brazil.

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Enhanced Screening for Refractive Candidates based on Corneal Tomography and Biomechanics

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  1. Enhanced Screening for Refractive Candidates based on Corneal Tomography and Biomechanics Renato Ambrósio Jr., MD, PhD Ruiz Alonso, MD; Daniela Jardim, MD; Frederico xxx, MD Marcella Salomão, MD; Simone Boghossian, MD; Bruno Fontes, MD Rio de Janeiro - Brazil

  2. Screening Refractive Candidates • Ultrasonic Pachymetry (US-CCT) and Placido Corneal Topography have been considered the “gold standard” • Unexplained ectasia may occur in cases considered as good candidates based on CCT and Placido´s topography • Enhanced screening with corneal tomography and biomechanics provides more sensitivity and specificity for determining candidacy for LASIK

  3. Clinical Example 1: LASIK Candidate? • 32 years old, female • MRx OD: • -6.00 = -1.00 x 180º, 20/15 • US-CCT: 528 µm Clinical Example 2: LASIK Candidate? • 21 years old, male • MRx OS: • -1,00 - 0,50 x 126, 20/15 • US- CCT: 531 µm

  4. Example 1: “unexplained” ectasia after LASIK OS Example 2: “unilateral” keratoconus OD

  5. Screening Refractive Candidates • US-CCT and Placido Corneal Topography would qualify cases 1 (OD) and 2 (OS) for LASIK • Case 1 had similar condition in OD when presented for LASIK, which resulted in “unexplained” ectasia • Either cases would not be considered as a good candidates for LASIK if considering topography from the contra-lateral eye • But a bilateral presentation as in the “normal” eyes may be the reason for many cases with ectasia after LASIK with no identifiable risk factors • Purpose: To present novel criteria based on corneal tomography (CTm) and biomechanical measurements to screen for ectasia (and for ectasia susceptibility)

  6. Ectasia Susceptibility: Conreal Tomography and Biomechanics Example 1: “unexplained” ectasia after LASIK OS • CTSP and PIT: Abnormal S shape • CRF: 8.1 mmHg Example 2: “unilateral” keratoconus OD • CTSP and PIT: Tangent to 95% CI • Ave PI=1.2 • CRF: 7.1 mmHg

  7. Corneal Tomography: Corneal Thickness Profiles • Average of the thickness values along twenty-two imaginary circles centered on the thinnest point TP with increased diameters at 0,4mm-steps - CTSP • PTI - Percentage of increase from the thinnest point of each of the circles • (CT@x - TP) / TP • Data is presented in a Graph with 95%CI from a normal population • Progression Index: average, min and max • Thinnest Point Value, Position and Distance from the Apex

  8. Corneal Tomography: Enhanced Elevation (Belin) • New reference sphere (new-BFS) that best fits to the peripheral corneal area excluding the central area with 4mm in diameter centered on the thinnest point • The elevation map considering the new-BFS was subtracted from the elevation map with the standard BFS that best fits the total corneal area. • The highest difference between the elevation maps in the central 4mm area was noted for anterior and posterior cornea New-BFS enhances the cone Standard-BFS may “hide” the cone Anterior - green is below 6 yellow is between 6 - 12, red is > 12 Posterior: green is < 8 yellow is between 8 - 20, red is > 20

  9. Belin-Ambrósio Enhanced Ectasia Display • Enhanced Elevation and Pachymetric Profiles are complementary to increase sensitivity and specificity!

  10. Asymmetric Keratoconus Study • Patients with keratoconus in one eye and normal axial (surface) topography in the contra-lateral eye were collected from different centers • All cases: 25 patients (20 ♂) had Pentacam exam • 12 patients (8 ♂) had additional biomechanical measureemnts (ORA - Reichert) • Average age: 30.2 (From 16 to 58) • 88% had at least one abnormal finding on the Belin/Ambrósio Enhanced Ectasia] • CRF (ORA) was lower than 8.5 mmHg in 84% of cases • Hysteresis (ORA) was lower than 8.8 mmHg in 75% of cases • Newer metrics from the ORA are under study

  11. Enhanced Elevation and Pachy Profiles are Complementary • Combination of Enhanced Elevation and Pachymetric Profiles add to each other in sensitivity and specificity

  12. Conclusions: Enhanced Screening for Refractive Candidates • New diagnostic parameters based on Corneal Tomography (Enhanced Elevation and Pachy Profiles) and Corneal Biomechanics (Hysteresis, CRF and new metrics from ORA signals) add to Ultrasonic Pachymetry (US-CCT) and Placido Corneal Topography to enhance screening for refractive candidates • These new parameters increase sensitivity and specificity for the screening process and should be considered Rio de Janeiro Corneal Tomograhy and Biomechanics Study Group

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