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Pentacam Screening forPentacam Screening for
KeratoconusKeratoconus
with special attention towith special attention to
Bel...
Reading The Pentacam’s Maps For Detecting
Keratoconus
Standard Approach
 The key to successfully screening patients with the Pentacam is
to create a standardized template that...
4 Map
4 Map
4 Map Curvature map and keratoconus
 Curvature measurements are reference based, meaning the
curvature map will change ba...
4 Map Curvature map and keratoconus
 It is important to realize that we cannot rely on corneal
curvature to diagnose kera...
4 Map Curvature map and keratoconus
4 Map Curvature map and keratoconus or PMD
4 Map Elevation and keratoconus
 Use best-fit sphere and float and a scale that is ±75μm
 we suggest front elevation fir...
4 Map Elevation and keratoconus
Keratoconus Map
Keratoconus Map
•ISV =. Gives the deviation of individual corneal radii from the mean value. Elevated
in all types of irregularity of the ...
Pachymetry Map and Kertaoconus
Keratoconus Map
 Keratoconus is a noninflammatory pathologic condition
characterized by pr...
Pachymetry Map and Kertaoconus
Keratoconus Map
 Interestingly, there were some cases with early keratoconus
evident on th...
Pachymetry Map and Kertaoconus
Keratoconus Map
OD(mmHg) OS(mmHg) Normal
Corneal hysteresis 9.8 9.1 11.9 ± 1.97
Corneal res...
Holladay Report (6 Maps)
Holladay Report and Keratoconus
 The strategy is that when the ‘hot spot’ on the
tangential Map, relative pachymetry map ...
Holladay Report and Keratoconus
Holladay Report and Keratoconus
Belin /Ambrosio Enhanced Ectasia Display
Introduction
 While measurements such as aberrometry and
curvature can be used in evaluating a patient for
ectatic diseas...
 In about 5% of the cases, there is significant
asymmetry in that the less involved eye initially
presents with a normal ...
 Actual raw elevation data lacks enough surface
variability for an easy qualitative inspection that
would allow the clini...
Elevation Subtraction Map
 By subtracting a known shape the
differences or variance become highlighted
or exaggerated
 T...
Enhanced Reference Surface
 For most clinical situations using a best-fit-sphere gives
the most useful qualitative map (i...
Enhanced Reference Surface
Best Fit Sphere vs Toric Ellipse
Enhanced Reference Surface
 While the Best-Fit-Sphere (BFS) is qualitatively
useful, the clinician typically assumes that...
Role of Cone on BFS
 In the case of keratoconus or ectasia, the
cone or apical protrusion will have the effect
of steepen...
Exclusion Zone
 New screening display of Belin / Ambrósio Enhanced Ectasia
Display try to eliminate this problem.
 Their...
Centering & size of Exclusion Zone?
 Earlier investigations looked at centering the
exclusion zone on the apex and also t...
Best Exclusion Size
 A 4 mm exclusion zone appeared to balance the
need for sensitivity without significant false
positiv...
Standard BFS vs Enhanced BFS
Standard BFS vs Enhanced BFS
Normal Cornea
Standard BFS vs Enhanced BFS
Ectatic Cornea
Average Change In Elevation
BFS vs Modified Shape
Average Change In Elevation
BFS vs Enhanced BFS
 The average changes in corneal elevation (when going
from standard to en...
Elevation Display Interpretation
Baseline Elevation Maps
 The first two elevation maps
 front surface (left map)
 back surface (right map)
 Above each ...
Exclusion Maps
 Immediately below the standard
elevation maps are
 The anterior exclusion map
 The posterior exclusion ...
Difference Map
 The bottom 2 maps are
 relative change in elevation from the baseline
elevation map to the exclusion map...
Pachymetric Evaluation
.
 The pachymetric portion of the display
includes
 The pachymetry map (Corneal Thickness),
 The...
Pachymetric Evaluation
 In only about 12% of normal corneas, the pachymetric
difference between the TP and the apex is > ...
Pachymetric Evaluation
 The CTSP displays the average
thickness measurements along
twenty-two concentric circles
centered...
Pachymetric Evaluation
 The second graph (percentage of
thickness increase (PTI)) is
calculated using a simple formula:
(...
Pachymetric Evaluation
 keratoconus patients have thinner corneas and a
faster and more abrupt increase of the CTSP and
P...
Pachymetric Evaluation
 Normal corneas typically have an
Average progression index < 1.2 and a CTSP and
PTI lines withi...
Conclusion
 The Pentacam is improving ophthalmic
diagnostics by providing valuable
information in screening for keratocon...
Pentacam
Pentacam
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Pentacam

One step forward in corneal imaging

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Pentacam

  1. 1. Pentacam Screening forPentacam Screening for KeratoconusKeratoconus with special attention towith special attention to Belin / Ambrósio EnhancedBelin / Ambrósio Enhanced Ectasia DisplayEctasia Display M.Khanlari, MDM.Khanlari, MD
  2. 2. Reading The Pentacam’s Maps For Detecting Keratoconus
  3. 3. Standard Approach  The key to successfully screening patients with the Pentacam is to create a standardized template that always displays the same maps in the same order using consistent colors and scales  Routinely we use the Pentacam’s Four-map composite report which includes ○ sagittal curvature maps ○ anterior elevation (front) ○ posterior elevation (back) ○ pachymetry or corneal thickness Keratoconus Map Holladay Report Belin /Ambrosio Enhanced Ectasia Display
  4. 4. 4 Map
  5. 5. 4 Map
  6. 6. 4 Map Curvature map and keratoconus  Curvature measurements are reference based, meaning the curvature map will change based on the reference axis. Typically, the reference axis is neither the corneal apex nor the line of sight but some arbitrary axis made by the normal line that the keratoscope makes with the corneal surface.  In some images the difference between the topographer’s reference axis, the line of sight, and the corneal apex lead to curvature patterns that may be interpreted as abnormal (eg, asymmetric bowtie astigmatism, inferior steepening)
  7. 7. 4 Map Curvature map and keratoconus  It is important to realize that we cannot rely on corneal curvature to diagnose keratoconus. Curvature is a reference-based measurement that changes with the angle of evaluation.  A decentered apex will always lead to focal areas of curvature steepening (when no true abnormality exists). True elevation maps do not make these assumptions and are independent of the reference axis  Therefore, we suggest examining an eye’s elevation and pachymetry maps first and the curvature map last.
  8. 8. 4 Map Curvature map and keratoconus
  9. 9. 4 Map Curvature map and keratoconus or PMD
  10. 10. 4 Map Elevation and keratoconus  Use best-fit sphere and float and a scale that is ±75μm  we suggest front elevation first and Look at back elevation and pachymetry next and at curvature last  Normal values for front elevation are less than +12μm.  Differences greater than +15μm typically indicate keratoconus  Between +12 and +15μm are suspicious.  Normal values for posterior elevation are approximately 5μm higher than those for front elevation,
  11. 11. 4 Map Elevation and keratoconus
  12. 12. Keratoconus Map
  13. 13. Keratoconus Map
  14. 14. •ISV =. Gives the deviation of individual corneal radii from the mean value. Elevated in all types of irregularity of the corneal surface (scars, astigmatism, deformities caused by contact lenses, keratoconus etc.). •IVA = Index of Vertical Asymmetry. Gives the degree of symmetry of the corneal radii with respect to horizontal meridian as axis of reflection . Elevated in cases of oblique axes of astigmatism, in keratoconus or in limbal ecstasies. KI = Keratoconus-Index. Elevated especially in keratoconus •CKI = Center Keratoconus-Index. Elevated especially in central keratoconus. •RMin = Radii minimum Gives the smallest radius of curvature in the entire field of measurement. Elevated in keratoconus. •IHA = Index of Height Asymmetry. Gives the degree of symmetry of height data with respect to the horizontal meridian as axis of reflection. Analogous to IVA, though sometimes more sensitive. •IHD = Index of Height Decentration. This index is calculated from Fourier analysis of height and gives the degree of vertical decentration. Steeper in keratoconus. •ABR = Aberration coefficient.Calculated on the basis of Zernike analysis. If there are no abnormal corneal aberrations, ABR is 0.0, otherwise ABR becomes 1.0 or greater, depending on the degree of aberration Indices and Keratoconus Level Keratoconus Map
  15. 15. Pachymetry Map and Kertaoconus Keratoconus Map  Keratoconus is a noninflammatory pathologic condition characterized by progressive thinning and protrusion of the cornea.  The thinning process occurs in one particular area so that the surrounding area remains disproportionately thicker.  Physiologically, the normal cornea is thinner in its center and thicker in the periphery.  The gradual increase of the corneal thickness from the center toward the periphery in healthy eyes falls within a normal range and that this characteristic could lead to a criterion for identifying pathology such as ectasia.
  16. 16. Pachymetry Map and Kertaoconus Keratoconus Map  Interestingly, there were some cases with early keratoconus evident on the anterior corneal maps that had normal posterior elevation maps.  Thus in this situation pachymetric progression data could provide information to identify ectasia and add to the surgeon’s armamentarium in the preoperative screening process.
  17. 17. Pachymetry Map and Kertaoconus Keratoconus Map OD(mmHg) OS(mmHg) Normal Corneal hysteresis 9.8 9.1 11.9 ± 1.97 Corneal resistance Factor 7.74 7.23 11.4 ± 2.07
  18. 18. Holladay Report (6 Maps)
  19. 19. Holladay Report and Keratoconus  The strategy is that when the ‘hot spot’ on the tangential Map, relative pachymetry map and back elevation map using the toric Ellipsoid are all at the same point, the diagnosis of Forme Fruste Keratoconus is confirmed. Relative Pachymetry :Measurements that exceed -3.0% Back Elevation Map :Elevations above 15 microns above the Toric Ellipsoid Tangential map : red nipple and usually above 48 D..
  20. 20. Holladay Report and Keratoconus
  21. 21. Holladay Report and Keratoconus
  22. 22. Belin /Ambrosio Enhanced Ectasia Display
  23. 23. Introduction  While measurements such as aberrometry and curvature can be used in evaluating a patient for ectatic disease, they are derivatives of elevation.  With subclinical disease, anterior curvature alone may not provide enough information to detect an early corneal abnormality.  The goal of the Belin / Ambrósio Enhanced Ectasia Display is to combine elevation based and pachymetric corneal evaluation in an all inclusive display
  24. 24.  In about 5% of the cases, there is significant asymmetry in that the less involved eye initially presents with a normal curvature map.  Longitudinal studies have found that about 50% of such cases progress to clinical keratoconus.  The new elevation based approach has increased sensitivity to 75% in eyes from patients previously diagnosed with unilateral keratoconus (Salomão and Ambrósio,). Role of Elevation Based Approach
  25. 25.  Actual raw elevation data lacks enough surface variability for an easy qualitative inspection that would allow the clinician to separate normal from abnormal corneas. Fault of Raw Elevation Data
  26. 26. Elevation Subtraction Map  By subtracting a known shape the differences or variance become highlighted or exaggerated  The term “Elevation Maps” while ingrained are technically incorrect. A better term would be an “Elevation Subtraction Map” since we do not look at the actual elevation data, but only the data after subtracting out some reference shape
  27. 27. Enhanced Reference Surface  For most clinical situations using a best-fit-sphere gives the most useful qualitative map (i.e. easiest to read and understand).  Since the normal eye is an aspherical prolate surface the central 8 – 9 mm zone yields a reference surface that allows for subtle identification of both ectatic disorders and astigmatism.  Larger zones would typically yield a flatter BFS and smaller zones a steeper BFS. While other shapes may have some clinical utility, shapes that more closely approximate a cone (e.g. toric ellipsoid) will actually mask the cone as the best-fit-toric ellipsoid more closely matches the cone contour
  28. 28. Enhanced Reference Surface
  29. 29. Best Fit Sphere vs Toric Ellipse
  30. 30. Enhanced Reference Surface  While the Best-Fit-Sphere (BFS) is qualitatively useful, the clinician typically assumes that the reference surface (the shape being subtracted) closely approximates a “normal” cornea.  The problem here is that there is such variability in corneal shape that the “normal” or “average” shape does not represent a clinically useful reference surface for individual corneal evaluation.  What is typically not appreciated is that the BFS will be influenced by any abnormal portion of the cornea.
  31. 31. Role of Cone on BFS  In the case of keratoconus or ectasia, the cone or apical protrusion will have the effect of steepening the BFS. This stepened BFS will actually minimize the elevation difference between the apex of the cone and the BFS
  32. 32. Exclusion Zone  New screening display of Belin / Ambrósio Enhanced Ectasia Display try to eliminate this problem.  Their goal is to design a reference surface that more closely approximates the individual’s normal cornea after excluding the conical or ectatic region.  To do this, they identify a 4.0 mm optical zone centered on the thinnest portion of the cornea and excluded it from the reference shape calculation (exclusion zone).  They calculate the new “enhanced BFS” by utilizing all the valid elevation data from within the 8.0 mm central cornea, and outside the exclusion zone
  33. 33. Centering & size of Exclusion Zone?  Earlier investigations looked at centering the exclusion zone on the apex and also the zone of minimal radius of tangential curvature, but the thinnest region turned out to be the most reliable.  They also looked at different optical zone sizes. Larger zones increased sensitivity at the expense of specificity, while smaller zones did the opposite.
  34. 34. Best Exclusion Size  A 4 mm exclusion zone appeared to balance the need for sensitivity without significant false positives.  The elevation difference between using a standard BFS and the new “enhanced” BFS will be significant for a conical cornea, while the difference is minimal in a normal cornea
  35. 35. Standard BFS vs Enhanced BFS
  36. 36. Standard BFS vs Enhanced BFS Normal Cornea
  37. 37. Standard BFS vs Enhanced BFS Ectatic Cornea
  38. 38. Average Change In Elevation BFS vs Modified Shape
  39. 39. Average Change In Elevation BFS vs Enhanced BFS  The average changes in corneal elevation (when going from standard to enhanced BFS) were as follows: Anteriorly ○ Normal eyes showed an average change in apex and maximum elevation of 1.86±1.9μm and 1.63±1.4μm. ○ Keratoconus eyes showed anterior apex and maximum elevation changes of 20.4±23.1μm and 20.9±21.9μm. (P<.0001). Posteriorly, ○ Normal eyes showed an average change in apex and maximum elevation of 2.86±1.9μm and 2.27±1.1μm. ○ Keratoconus eys showed posterior apex and maximum elevation changes of 39.9±38.1μm and 45.7±35.9μm. (P<.0001).
  40. 40. Elevation Display Interpretation
  41. 41. Baseline Elevation Maps  The first two elevation maps  front surface (left map)  back surface (right map)  Above each map  The radius of curvature of the BFS in mm  The diameter of the zone used to compute the BFS  The diameter of the circle (in mm) centered on the corneal apex inside  In this sample map  The radius of curvature of the BFS for the front surface is 8.17mm  The radius of curvature of the BFS for the back surface is 6.63 m
  42. 42. Exclusion Maps  Immediately below the standard elevation maps are  The anterior exclusion map  The posterior exclusion map  for the front of the cornea  Baseline BFS is 8.17 mm,  Enhanced BFS is 8.18mm. ○ The size of the BFS changed very little, as did the elevation map, when going from the baseline to the exclusion map.  For the back of the cornea  Baseline elevation was 6.63mm.  Enhanced BFS was 6.84mm
  43. 43. Difference Map  The bottom 2 maps are  relative change in elevation from the baseline elevation map to the exclusion map.  The bottom maps contain only 3 colors,  The green represents a change in elevation of ○ Less than 6 microns on the front and ○ Less than 8 microns on the back surface of the cornea and are ○ Typically within the range seen in normal eyes.  The red represents areas where the difference is ○ 12 microns anteriorly or ○ 20 microns posteriorly and ○ The magnitude typically seen in eyes with known keratoconus.  The yellow areas represent a change ○ Between 6 and 12 microns for the front surface and ○ Between 8 to 20 microns for the back surface
  44. 44. Pachymetric Evaluation .  The pachymetric portion of the display includes  The pachymetry map (Corneal Thickness),  The two graphs and  The pachymetric indices.  It identifies  the corneal thickness at the apex (center of the exam),  the thinnest point (TP) and the location and distance of the thinnest point relative to the apex.  The direction of the TP is displayed as temporal (T), nasal (N), superior (S) and inferior (I) or intermediate (e.g. IT inferio- temporal). 
  45. 45. Pachymetric Evaluation  In only about 12% of normal corneas, the pachymetric difference between the TP and the apex is > 10μm.  They also found a positive correlation (r2 = 0.61) comparing the distance difference and the pachymetric difference between the apex and thinnest point (TP).  In eyes with keratoconic the distance between the apex and the thinnest point is significantly higher (1.52 ± 0.58mm) than normals (0.9 ± 0.23mm) (p<0.05).  Along with the thinnest point evaluation, the pachymetric display evaluates the thickness profile of the cornea
  46. 46. Pachymetric Evaluation  The CTSP displays the average thickness measurements along twenty-two concentric circles centered on the thinnest point with increasing diameters of 0.4mm steps  In addition to the average values, the standard deviations of the pachymetry along each circle are calculated.
  47. 47. Pachymetric Evaluation  The second graph (percentage of thickness increase (PTI)) is calculated using a simple formula: (CT@x - TP)/TP, where x represents the diameter of the imaginary circle centered on the TP with increased diameters as provided by the CTSP.  Each graph displays the examined eye data in red and three broken dark lines, which represent the upper and lower double standard deviation (95% - confidence interval) and the average values from a normal population
  48. 48. Pachymetric Evaluation  keratoconus patients have thinner corneas and a faster and more abrupt increase of the CTSP and PTI than normal corneas.  CTSP and PTI graphs were designed to enable the rapid identification of very early forms of ectasia, increasing sensitivity and specificity for screening candidates for refractive surgery.  The thickness profile also enables clinical differentiation of a normal thin cornea from an ectatic cornea, and a normal thick cornea from an edematous cornea.
  49. 49. Pachymetric Evaluation  Normal corneas typically have an Average progression index < 1.2 and a CTSP and PTI lines within the 95% CI limits.  However there is some overlap between normal and keratoconic eyes. About 7% of normal eyes have ○ 1.2 < average progression index <1.8 ○ Current hypothesis is that these cases may have higher susceptibility to develop ectasia if stressed such as intensive eye rubbing and/or subjected to lamellar refractive surgery. In addition, 11% of the cases with clinical keratoconus have ○ average progression index < 1.2 and ○ CTSP and PTI within the normal limits. ○ It's also hypothesize that these cases have lower odds for ectasia progression and, in some conditions, may benefit from advanced customized surface ablation procedures.
  50. 50. Conclusion  The Pentacam is improving ophthalmic diagnostics by providing valuable information in screening for keratoconus.  These improvements will help achieve better surgical outcomes and enhance patient satisfaction

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