Title: Enhanced Screening for Refractive Candidates based on Corneal Tomography and Biomechanics
1Enhanced 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
2Screening 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
3Clinical 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
4Example 1 unexplained ectasia after LASIK OS
Example 2 unilateral keratoconus OD
5Screening 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)
6Ectasia 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
7Corneal 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
8Corneal 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
9Belin-Ambrósio Enhanced Ectasia Display
- Enhanced Elevation and Pachymetric Profiles are
complementary to increase sensitivity and
specificity!
10Asymmetric 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
11Enhanced Elevation and Pachy Profiles are
Complementary
- Combination of Enhanced Elevation and
Pachymetric Profiles add to each other in
sensitivity and specificity
12Conclusions 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