Orbscan & topo

an overview of topography and orbscan

2. CoCornrneal eal ToTopopogrgrapaphyhy
andand
OOrrbbssccaann IIII
M.Khanlari,MDM.Khanlari,MD
Noor Vision Correction CenterNoor Vision Correction Center

3. ►Topography refers to determining Topography refers to determining
and describing the features of a and describing the features of a
surfacesurface

4. Description of Corneal surfaceDescription of Corneal surface
 Corneal surface elevationCorneal surface elevation
 Corneal surface slopeCorneal surface slope
 Corneal surface radius of Corneal surface radius of
curvaturecurvature
 Corneal powerCorneal power

5. Methods of MeasurementMethods of Measurement
►Reflection-based methodsReflection-based methods
measure the measure the slopeslope and use this to calculate and use this to calculate
radius of curvatureradius of curvature and and powerpower. .
However, corneal However, corneal elevationelevation can’t be calculated can’t be calculated
from measurements of slope alone.from measurements of slope alone.
►Projection-based methodsProjection-based methods
measure the measure the elevation elevation and use this to calculate and use this to calculate
slopeslope, , curvaturecurvature, and , and powerpower

6. Methods of MeasurementMethods of Measurement
A.A.Reflection-based methodsReflection-based methods
A.A.KeratometryKeratometry
A.A.ManualManual
B.B.AutomatedAutomated
B.B.KeratoscopyKeratoscopy
A.A.PhotokeratoscopyPhotokeratoscopy
B.B.VideokeratoscopyVideokeratoscopy
B.B.Projection-based methodsProjection-based methods
A.A.Slit PhotographySlit Photography
B.B.RasterstereographyRasterstereography
C.C.Moire InterferenceMoire Interference
D.D.Laser interferometryLaser interferometry

7. Curvature Based Placido Disc VideokeratographyCurvature Based Placido Disc Videokeratography
Measures Slopes & Curvatures Measures Slopes & Curvatures
DirectlyDirectly
Specular Reflection of an illuminated Specular Reflection of an illuminated
conical Placido disk with 16 to 32 ringsconical Placido disk with 16 to 32 rings
Maximum corneal diameter that is Maximum corneal diameter that is
mapped is 8 to 10 mmmapped is 8 to 10 mm
One imageOne image
One surfaceOne surface

8. Elevation Based Slit Scanning VideokeratographyElevation Based Slit Scanning Videokeratography
Measures Elevation DirectlyMeasures Elevation Directly
A series of slit lamp beams are A series of slit lamp beams are
compiled across the cornea to create a compiled across the cornea to create a
profile of the corneaprofile of the cornea
Multiple ImagesMultiple Images
Multiple SurfacesMultiple Surfaces

9. CoCornrneal eal ToTopopogrgrapaphyhy
Normal CorneaNormal Cornea

10. Reading the MapsReading the Maps

11. System for studying topographic mapSystem for studying topographic map
►Check Check
►NameName
►DateDate
►EyeEye
►ScaleScale
►RangeRange
►StepStep interval (normalized, absolute) interval (normalized, absolute)
►TypeType of measuremnt (curvature, power , of measuremnt (curvature, power ,heightheight))
►MapMap
►AxialAxial
►TangentialTangential
►RefractiveRefractive
►ElevationElevation
►Statistical information Statistical information
►cursor boxcursor box
►IndicesIndices
►Compare previous maps of the same eyeCompare previous maps of the same eye
►Compare with topography of the other eyeCompare with topography of the other eye

12. Check Check NameName
DateDate
EyeEye

13. Absolute ScaleAbsolute Scale (standardized)(standardized)
Same dioptric step power on every mapSame dioptric step power on every map
Allow direct comparison of 2 different mapsAllow direct comparison of 2 different maps
AdvantagesAdvantages: Rapid pattern recognition of topographic maps: Rapid pattern recognition of topographic maps
DisadvantageDisadvantage: Because the large steps do not show subtle : Because the large steps do not show subtle
changeschanges
Should be used for routine clinical analysisShould be used for routine clinical analysis

14. Normalized ScaleNormalized Scale (relative)(relative)
Dioptric power steps based on the patients corneaDioptric power steps based on the patients cornea
AdvantageAdvantage:Dioptric steps is smaller and show more detailed changes:Dioptric steps is smaller and show more detailed changes
DisadvantageDisadvantage: 2 different maps can not be compared directly: 2 different maps can not be compared directly
More sensitive and useful for researchMore sensitive and useful for research

15. Color Scale for Surface CurvatureColor Scale for Surface Curvature
•sharp
•fast bend
•short radius
•Higher power
•flat
•slow bend
•long radius
•Lower power
(+ +)
(+)
Red
BlueMin
Max
G ree nG ree n a nd a nd ye llo w ye llo w re p res en t p o wers ch a rac rteristic of n orma l c orn e a re p res en t p o wers ch a rac rteristic of n orma l c orn e a

16. Absolute scale Absolute scale
with with
1.5 D step interval1.5 D step interval
Normalized scale Normalized scale
with with
0.5 D step interval0.5 D step interval

17. Topographic MapsTopographic Maps
Axial MapAxial Map
Tangential MapTangential Map
Refractive Map Refractive Map
Elevation MapElevation Map

18. Axial Map (Axial Map (power map, sagital map)power map, sagital map)
►Axial power: Axial power: A fixed A fixed
center of curvature is used center of curvature is used
for calculating the power for calculating the power
at all pointsat all points
very simple map and very simple map and
values directly values directly
comparable to comparable to
keratometrykeratometry
Paxial = (n' – 1) / raxial

20. Tangential Map Tangential Map (( Inst Instantaneous ,local, true , meridional)antaneous ,local, true , meridional)
►Tangential power: Tangential power: A floating A floating
center of curvature is used by center of curvature is used by
means of a standard formula for means of a standard formula for
calculating powercalculating power
►Measures the power at a certain Measures the power at a certain
point in meridional direction point in meridional direction
relative to the other points on the relative to the other points on the
particular ringparticular ring
►More sensitive for local curvature More sensitive for local curvature
changechange
►Most useful in following trend in Most useful in following trend in
the post surgical or pathologic the post surgical or pathologic
eyes.eyes.
Pinst = (n' – 1) / rinst

22. Refractive Map (paraaxial )Refractive Map (paraaxial )
►Paraxial power: Paraxial power: used for central used for central
paraxial rays where the paraxial rays where the sagittal depthsagittal depth
is approximately proportional to the is approximately proportional to the
curvaturecurvature
►Applies snellen’s law to describe the Applies snellen’s law to describe the
cornea’s actual refractive powercornea’s actual refractive power
►Evaluate visual performance in post- Evaluate visual performance in post-
refractive surgery patientrefractive surgery patient
►Identifies Identifies central islandcentral island who have who have
undergone PRK or LASIKundergone PRK or LASIK
Pref = n/f
f = z + y/ tan (θi - θr)

23. Quantitative IndicesQuantitative Indices
Quantitative reference points to guide and Quantitative reference points to guide and
asses the effect of therapyasses the effect of therapy
Common indices include :Common indices include :
Simulated keratometry values (Sim K)Simulated keratometry values (Sim K)
Surface Asymmetry index (SAI)Surface Asymmetry index (SAI)
Surface Regularity Index (SRI)Surface Regularity Index (SRI)

24. Quantitative IndicesQuantitative Indices
►
Simulated keratometry valuesSimulated keratometry values (Sim K) (Sim K)
Obtained from data points on mires Obtained from data points on mires 77, , 88 and and 99
Provide the power and location of the steepest meridian Provide the power and location of the steepest meridian
and flattest meridianand flattest meridian
Analogous toAnalogous to keratometerkeratometer
Good correlationGood correlation with with refractive cylinderrefractive cylinder

25. Quantitative IndicesQuantitative Indices
►Surface Asymmetry indexSurface Asymmetry index (SAI)(SAI)
Centrally weighted summation of differences in Centrally weighted summation of differences in
corneal power between corresponding points corneal power between corresponding points 180180
degrees apart on degrees apart on 128128 equally spaced meridians equally spaced meridians
crossing all the mirescrossing all the mires
Theoretically is Theoretically is zerozero for for
perfect sphere perfect sphere ,,perfectly spherocylinderical perfectly spherocylinderical
regular regular astigmatism astigmatism andand a surface with a power a surface with a power
that is radially that is radially symmetricalsymmetrical
Is sensitive to paracentral keratoconus Is sensitive to paracentral keratoconus

26. Quantitative IndicesQuantitative Indices
►Surface Regularity IndexSurface Regularity Index (SRI)(SRI)
Summation of local fluctuations in power among 256 Summation of local fluctuations in power among 256
equally spaced hemimeridians on the 10 central miresequally spaced hemimeridians on the 10 central mires
Approach 0 for a normally smooth corneal surfaceApproach 0 for a normally smooth corneal surface
It increases with increasing irregular astigmatismIt increases with increasing irregular astigmatism
High correlationHigh correlation with with best BSCVAbest BSCVA
Can predict the optical performance of a normal corneaCan predict the optical performance of a normal cornea

27. Kcn Map indices in PentacamKcn Map indices in Pentacam
ISV = Index of Surface Variance.
IVA = Index of Vertical Asymmetry.
KI = Keratoconus Index.
CKI = Central Keratoconus Index.
Rmin= the smallest radius of curvature
IHA = Index of Height Asymmetry.
IHD = Index of Height Decentration.
ABR = Aberration Coefficient.
KKS = Keratoconus Stage.
AA = Analysed Area.

28. Watch for the BumpsWatch for the Bumps

29. Watch for the BumpsWatch for the Bumps
A bump on the inferior cornea, associated with A bump on the inferior cornea, associated with
thinning, is almost always diagnostic of thinning, is almost always diagnostic of “KCN”“KCN”
A “smile”- shaped rather than round bump, exactly A “smile”- shaped rather than round bump, exactly
at 6 o’clock at 3mm below the center, no more at 6 o’clock at 3mm below the center, no more
than 25 than 25 μμm thinner than 3 mm above the center, m thinner than 3 mm above the center,
suggestive of suggestive of “contact lens“contact lens warpagewarpage””

31. Normal CorneaNormal Cornea
Flattens progressively from the center to the periphery by 2 Flattens progressively from the center to the periphery by 2
to 4 D, as to 4 D, as
Nasal hemimeridians flattening more than the temporal Nasal hemimeridians flattening more than the temporal
hemimeridians hemimeridians
Two corneas at one individual normally exhibit non super Two corneas at one individual normally exhibit non super
imposable mirror- image symmetry(imposable mirror- image symmetry(EnantiomorphismEnantiomorphism))
The normal cornea exhibits relative smoothness and The normal cornea exhibits relative smoothness and
absence of significant irregular astigmatism.absence of significant irregular astigmatism.

33. Normal corneaNormal cornea
►Naturally occurring corneal topographic Naturally occurring corneal topographic
patterns are classified by shape aspatterns are classified by shape as
((Bogan´s studyBogan´s study) )
 Round (22.6%)Round (22.6%)
 Oval (20.8%)Oval (20.8%)
 Symmetrical bowtie (17.5%)Symmetrical bowtie (17.5%)
 Asymmetrical bowtie (32.1%)Asymmetrical bowtie (32.1%)
 Irregular (7%)Irregular (7%)

34. 20.8%17.5%32.1%7.1%22.6%
Pattern AnalysisPattern Analysis
►SphericalSpherical
►OvalOval
►BowtieBowtie
SymmetricalSymmetrical
AsymmetricalAsymmetrical
►IrregularIrregular

35. Regular AstigmatismRegular Astigmatism
Most common naturally deviation from the normal Most common naturally deviation from the normal
corneacornea
Usually with the ruleUsually with the rule
As a symmetrical bowtie of high powerAs a symmetrical bowtie of high power

36. Irregular AstigmatismIrregular Astigmatism
Every deviation from a pure ellipsoidal shape can Every deviation from a pure ellipsoidal shape can
be devastating to vision when is centrally within be devastating to vision when is centrally within
the pupillary areathe pupillary area
Functionally, is that component of astigmatism that Functionally, is that component of astigmatism that
can not be corrected with spectaclecan not be corrected with spectacle
Common causes: dry eye, corneal scars , ectatic Common causes: dry eye, corneal scars , ectatic
corneal degeneration, ptrygium, contact lens corneal degeneration, ptrygium, contact lens
warpage or over wear, trauma ,surgery (cataract, warpage or over wear, trauma ,surgery (cataract,
PK and refractive surgery)PK and refractive surgery)

37. Corneal topography is particularly mandatory for Corneal topography is particularly mandatory for
these corneal conditionsthese corneal conditions
Advanced keratoconusAdvanced keratoconus
Post-penetrating keratoplastyPost-penetrating keratoplasty
Post RK or LASIKPost RK or LASIK

38. CoCornrneal eal ToTopopogrgrapaphyhy
KeKerratatoococonnusus

39. Rabinowitz and McDonnell CriteriaRabinowitz and McDonnell Criteria
►Central corneal power Central corneal power >47>47
►A difference of A difference of 3 D or more3 D or more in corneal power in corneal power
comparing points 3 mm comparing points 3 mm IInferior to the center nferior to the center
to points 3 mm to points 3 mm ssuperior to the center (uperior to the center (II--SS))
►Asymmetry between central corneal power Asymmetry between central corneal power
of fellow eyes of fellow eyes in excess of 1Din excess of 1D

40. Keratoconus detection overviewKeratoconus detection overview
►Topographic characteristicTopographic characteristic
High irregular astigmatism High irregular astigmatism
(SRI>1) (CU index<80%) (IAI) (PVA) (PCA) (Tot Astig(SRI>1) (CU index<80%) (IAI) (PVA) (PCA) (Tot Astig))
High central corneal power High central corneal power
(Sim K>50 D) (CSI) (DSI) (Eff RP)(Sim K>50 D) (CSI) (DSI) (Eff RP)
Inferior cornea, steeper than superior cornea Inferior cornea, steeper than superior cornea
(IS value>1.4) (SAI>0.5) (OSI)(IS value>1.4) (SAI>0.5) (OSI)
Large difference between the apex and the peripheryLarge difference between the apex and the periphery
(AA) (HRT)(AA) (HRT)
Disparity in the central power between the two eyes Disparity in the central power between the two eyes
(>1 D)(>1 D)

41. OOrrbbssccaann IIII

42. Elevation Based Slit Scanning VideokeratographyElevation Based Slit Scanning Videokeratography
•Measures Elevation DirectlyMeasures Elevation Directly
•A series of slit lamp beams are compiled A series of slit lamp beams are compiled
across the cornea to create a profile of the across the cornea to create a profile of the
corneacornea
•Calculates the Full Pachymetry & CurvaturesCalculates the Full Pachymetry & Curvatures
•Multiple ImagesMultiple Images
•Multiple SurfacesMultiple Surfaces
•Evaluates the Shape of the CorneaEvaluates the Shape of the Cornea

43. Terrain TopographyTerrain Topography
Highlands
Lowlands
Color-coded Map
Sea Level

44. Close-Fitting Reference Surfaces
• Corneal topography differs from terrestrial topography in that
the reference surface is not some fixed “mean sea-level”, but is
movable.
Higher (Red)
Lower (Blue)
Sea Level (Green)
Sea Level (Green)

45. 1.20 Slits from Left to Right
2.20 Slits from Right to Left
3.Each slit per 0.7 second
4.Elimination of saccadic
movements by eyetracking
5.Large face plate Placido Disc
ORBSCAN IIORBSCAN II

46. Reading the MapReading the Map

47. Color-coded mapsColor-coded maps
►ColorsColors
►Warm colorsWarm colors
►Cool colorsCool colors
►ScalesScales
►RangeRange
►StepsSteps
►OverlaysOverlays
►PupilPupil
►CircularCircular
►GridGrid
►RadialRadial
►Thinnest pointThinnest point
►K-labels & linesK-labels & lines
►NumericalNumerical

48. Color-coded mapsColor-coded maps
►DisplaysDisplays
►ProfileProfile
►Two-dimensionalTwo-dimensional
►3-dimensional3-dimensional
►DualDual
►Difference mapDifference map
►Quad mapsQuad maps
►MeasurementsMeasurements
►ElevationElevation
►CurvatureCurvature
►PowerPower
►PachymetryPachymetry
►Anterior chamber Anterior chamber
depthdepth

49. ColorsColors

50. Color Scale for Relative ElevationColor Scale for Relative Elevation
•high
•anterior to the
reference surface
•low
•posterior to the
reference surface
reference

(+)
(-)
anterior
posterior
Red
BlueMin
Max

51. Colors: ElevationColors: Elevation
•Profile @ 180°
•Profile @ 90°
•Points above the
best fit sphere
•Points below the
best fit sphere
•Warm Colors
•Cool Colors

52. Color Scale for Surface CurvatureColor Scale for Surface Curvature
•sharp
•fast bend
•short radius
•flat
•slow bend
•long radius
(+ +)
(+)
Red
BlueMin
Max

53. Colors: Axial PowerColors: Axial Power
•Warmer Colors
•Higher Power
•Cooler Colors
•Lower Power

54. Color Scale for PachymetryColor Scale for Pachymetry
•thick
•thin
Blue
RedMin
Max

55. Colors: PachymetryColors: Pachymetry
•Cooler Colors
•Thicker Areas
•Warmer Colors
•Thinner Areas

56. Colors: PachymetryColors: Pachymetry
•Thicker Areas
•Thinner Areas

57. OverlaysOverlays

58. Overlays: ElevationOverlays: Elevation

59. Overlays: ElevationOverlays: Elevation

60. Overlays: PowerOverlays: Power

61. Overlays: PowerOverlays: Power

62. Overlays: PowerOverlays: Power

63. Overlays: PachymetryOverlays: Pachymetry

64. Overlays: PachymetryOverlays: Pachymetry

65. Overlays: PachymetryOverlays: Pachymetry

66. ScalesScales

67. Scale: PowerScale: Power
►By changing the steps, the range of the By changing the steps, the range of the
scale can be adjusted:scale can be adjusted:
25 – 58 D25 – 58 D
with 1D stepswith 1D steps
33 – 50 D33 – 50 D
with 0.5 D stepswith 0.5 D steps
37 – 46 D37 – 46 D
with 0.25 D stepswith 0.25 D steps

68. Scale: ElevationScale: Elevation

69. Scale: ElevationScale: Elevation

70. Scale: ElevationScale: Elevation

71. MeasurementsMeasurements

72. MeasurementsMeasurements
►Anterior corneal elevation and curvature Anterior corneal elevation and curvature
►Posterior corneal elevation and curvature Posterior corneal elevation and curvature
►Full corneal pachymetry Full corneal pachymetry
►Simulated keratometry Simulated keratometry
►White-to-white diameter White-to-white diameter
►Pupil size (mesopic) Pupil size (mesopic)
►Anterior chamber depth Anterior chamber depth
►Angle kappa Angle kappa
►Irregularity index Irregularity index

73. Mean PowerMean Power

74. Tangential PowerTangential Power

75. Astigmatic PowerAstigmatic Power

76. Optical PowerOptical Power

77. Anterior ChamberAnterior Chamber

78. DisplaysDisplays

79. DisplaysDisplays
•Profile
•Topographic
•3-dimensional

80. Displays: DualDisplays: Dual
Axial Power Map Anterior Elevation
Flatter areas stand above the best fit sphere
Steeper areas fall below the best fit sphere

81. Displays: DifferenceDisplays: Difference
Preop
Pachymetry
Postop
Pachymetry
Amount of
ablation

82. Display: Quad MapDisplay: Quad Map

83. OOrrbbssccaann IIII
KeKerratatoococonnusus

84. KCN CRITERIA IN POWER KCN CRITERIA IN POWER
MAPSMAPS
►““Broken bow-tie” appearanceBroken bow-tie” appearance
►Central power Central power > 47 D> 47 D
►> 3 D> 3 D difference in the 3 mm zone difference in the 3 mm zone
►> 1 D> 1 D greater power than the greater power than the
fellow eyefellow eye

85. BROKEN BOW-TIEBROKEN BOW-TIE

86. KCN CRITERIA IN ELEVATION KCN CRITERIA IN ELEVATION
MAPSMAPS
1.1.Maximum elevation Maximum elevation > 50 µm> 50 µm
2.2.Posterior best fit sphere in diopter Posterior best fit sphere in diopter > 55 D> 55 D
3.3.R anterior BFS / R posterior BFS (mm): R anterior BFS / R posterior BFS (mm):
"££1.211.21 okok
"³³1.21 and 1.21 and ££ 1.27 1.27 suspectsuspect
"³³ 1.271.27 suggestivesuggestive
4.4.Roush criterionRoush criterion: the relative elevation difference : the relative elevation difference
between close between close maxima maxima andand minima minima > 100µm> 100µm
5.5.More than More than threethree colors on colors on 1010µm (µm (antant) and) and
2020 µm ( µm (postpost) in the ) in the central 3 mm zonecentral 3 mm zone

87. ANTERIOR ELEVATIONANTERIOR ELEVATION
The maximum elevation measured is 65 µm (>55µm)

88. POSTERIOR ELEVATIONPOSTERIOR ELEVATION
59.5 D
Maximum elevation= 124 µm

89. ANTERIOR & POSTERIOR ANTERIOR & POSTERIOR
ELEVATIONELEVATION
R anterior BSF /R posterior BSF > 1.21 - 1.27
R anterior BFS /R posterior BFS (mm) = 1.26
7.41 5.86

90. ROUSH CRITERIONROUSH CRITERION
Roush criterion: the relative elevation difference between close
maxima and minima = 130 µm (>100µm)
130 µm

91. COLORS IN ANT CENTRAL 3 COLORS IN ANT CENTRAL 3
MM ZONEMM ZONE
Seven colors can be counted in the central 3 mm zone with a
10µm step scale (>3 colors)

92. COLORS IN POST CENTRAL COLORS IN POST CENTRAL
3MM ZONE3MM ZONE
Seven colors can be counted in the central 3 mm zone with a
20µm step scale (>3 colors)

93. RELATION BETWEEN 4 MAPSRELATION BETWEEN 4 MAPS
Three step rule:Three step rule:
►OneOne abnormal mapabnormal map: : CautionCaution
►TwoTwo abnormal mapsabnormal maps: : ConcernConcern
►ThreeThree abnormal mapsabnormal maps: : ContraindicationContraindication

94. 1 1 ABNORMAL MAPABNORMAL MAP: CAUTION: CAUTION

95. 2 2 ABNORMAL MAPSABNORMAL MAPS : CONCERN: CONCERN

96. 3 3 ABNORMAL MAPSABNORMAL MAPS : :
CONTRAINDICATIONCONTRAINDICATION

97. RELATION BETWEEN 4 MAPSRELATION BETWEEN 4 MAPS
►The posterior “high point” correlates The posterior “high point” correlates
well withwell with
the the anterior anterior stesteepestepest point point
the the anterior anterior hhigheighestst p poioinnt, t, aanndd
the the thinnestthinnest spot on the cornea spot on the cornea

98. RECOMMENDED QUAD MAPRECOMMENDED QUAD MAP

100. Corneal TopographyCorneal Topography
Corneal PathologyCorneal Pathology

101. Computer-Assisted VideokeratographyComputer-Assisted Videokeratography
►CapturingCapturing of an image of the cornea after of an image of the cornea after
reflection a target off the corneal surfacereflection a target off the corneal surface
►AnalyzingAnalyzing of the image and converting data to of the image and converting data to
curvature values using computer software by curvature values using computer software by
complex algorithmscomplex algorithms
►DisplayingDisplaying of color topographical images by of color topographical images by
using pre-determined color scalesusing pre-determined color scales
►ManipulationManipulation of data creation various displays of data creation various displays

102. Corneal Surface ElevationCorneal Surface Elevation
►Data measured in terms of Data measured in terms of
height or elevation (or height or elevation (or
sometimes depth) from a sometimes depth) from a
reference plane describe the reference plane describe the
true shape of the corneal true shape of the corneal
surface.surface.
►Once the true shape has Once the true shape has
been measured, slope, been measured, slope,
curvature, and power can be curvature, and power can be
calculated from it.calculated from it.

103. Corneal Surface SlopeCorneal Surface Slope
►The gradient of the tangent at a The gradient of the tangent at a
particular point on a curved particular point on a curved
surfacesurface
►Mathematically, the slope is the Mathematically, the slope is the
first differential of a curve. first differential of a curve.
Therefore, it is a more sensitive Therefore, it is a more sensitive
way of demonstrating small way of demonstrating small
changes in height between two changes in height between two
points on a surface.points on a surface.

104. Radius of CurvatureRadius of Curvature
►Slope (Slope (αα) can be converted to ) can be converted to
radius of curvature (radius of curvature (r)r): : r = r =
d/cos d/cos αα
where where d d is the distance from is the distance from
the corneal centerthe corneal center
►Corneas with a steep Corneas with a steep
surface slope have a small surface slope have a small
radius of curvature while radius of curvature while
those which are flatter have those which are flatter have
a relatively large radius of a relatively large radius of
curvaturecurvature

105. Corneal PowerCorneal Power
►A measure of the A measure of the
refractive effect of a refractive effect of a
lenslens
►P=(nP=(n
22 – n – n
11) / r) / r

106. Normal CorneaNormal Cornea
►Asphericity Asphericity
►Eccentricity (Prolate and oblate)Eccentricity (Prolate and oblate)
►Toricity ( Regular and Irregular)Toricity ( Regular and Irregular)
►Symmetry (vs Asymmetry)Symmetry (vs Asymmetry)

107. Corneal GeographyCorneal Geography
►The corneal surface can be divided into The corneal surface can be divided into
four anatomic zones. four anatomic zones.
• The central zoneThe central zone
• The paracentral zoneThe paracentral zone
• The peripheral zoneThe peripheral zone
• The limbal zone The limbal zone

109. Normal CorneaNormal Cornea

110. Corneal MeasurementCorneal Measurement

111. Best Fit SphereBest Fit Sphere
•Anterior Corneal Surface
•Best Fit Sphere

112. Best Fit SphereBest Fit Sphere

113. Raw ImageRaw Image

114. Raw Placido ImageRaw Placido Image

115. Raw Placido ImageRaw Placido Image

118. Triangulation locates points in spaceTriangulation locates points in space
triangulated
space point
complex object
S
c
h
e
i
m
p
f
l
u
g
s
l
i
t
-
b
e
a
m
p
r
o
j
e
c
t
o
r Video
Camera
calibrated
slit-beam
surface diffusely
reflected
camera ray

119. Terrain TopographyTerrain Topography

120. Terrain TopographyTerrain Topography

121. Hybrid Technology of ORBSCAN II
3. Unify triangulated and reflective data to obtain
accurate surfaces in elevation, slope, and curvature.
1. Measure surface elevation directly by triangulation
of backscattered
slit-beam.
2. Measure surface
slope directly using
specular reflection,
supplemented with
triangulated elevation.

125. Colors: ElevationColors: Elevation
Topographic or two dimensional view

126. Scale: PowerScale: Power
1.0 D
0.5 D
.25 D

127. Data Available by One Exam
•Four ocular surfaces: Anterior Cornea, Posterior
Cornea, Anterior Iris, Anterior Lens
•Geometry and shape maps: Relative Elevation,
Inclination, Surface Curvature
•Distance maps between surfaces: Full Corneal
Pachymetry, Anterior Chamber Depth
•Optical function maps: Optical Power
•Clinical tools: Surgical Planning, Contact Lens
Fitting