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Enhanced Screening for Refractive Candidates based on Corneal Tomography and Biomechanics

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Marcella Salom o, MD; Simone Boghossian, MD; Bruno Fontes, MD. Rio de Janeiro - Brazil ... Ultrasonic Pachymetry (US-CCT) and Placido Corneal Topography have been ... – PowerPoint PPT presentation

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Title: Enhanced Screening for Refractive Candidates based on Corneal Tomography and Biomechanics


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 Placidos
    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 PI1.2
  • 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_at_x - TP) / TP
  • Data is presented in a Graph with 95CI 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 gt 12 Posterior green is lt 8
yellow is between 8 - 20, red is gt 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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