CoCornrneal eal ToTopopogrgrapaphyhy andand

OOrrbbssccaann IIIIM.Khanlari,MDM.Khanlari,MD

Noor Vision Correction CenterNoor Vision Correction Center

►Topography refers to Topography refers to determining and describing the determining and describing the features of a surfacefeatures of a surface

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

Methods of MeasurementMethods of Measurement►Reflection-based methodsReflection-based methods

measure the measure the slopeslope and use this to and use this to calculate calculate radius of curvatureradius of curvature and and powerpower. .

However, corneal However, corneal elevationelevation can’t be can’t be calculated from measurements of slope calculated from measurements of slope alone.alone.

►Projection-based methodsProjection-based methods measure the measure the elevation elevation and use this to and use this to

calculate calculate slopeslope, , curvaturecurvature, and , and powerpower

Methods of MeasurementMethods of MeasurementA.A. Reflection-based methodsReflection-based methods

A.A. KeratometryKeratometryA.A. ManualManualB.B. AutomatedAutomated

B.B. KeratoscopyKeratoscopyA.A. PhotokeratoscopyPhotokeratoscopyB.B. VideokeratoscopyVideokeratoscopy

B.B. Projection-based methodsProjection-based methodsA.A. Slit PhotographySlit PhotographyB.B. RasterstereographyRasterstereographyC.C. Moire InterferenceMoire InterferenceD.D. Laser interferometryLaser interferometry

Curvature Based Placido Disc Curvature Based Placido Disc VideokeratographyVideokeratography Measures Slopes & Curvatures Measures Slopes & Curvatures

DirectlyDirectly Specular Reflection of an Specular Reflection of an

illuminated conical Placido disk illuminated conical Placido disk with 16 to 32 ringswith 16 to 32 rings

Maximum corneal diameter that Maximum corneal diameter that is mapped is 8 to 10 mmis mapped is 8 to 10 mm

One imageOne image One surfaceOne surface

Elevation Based Slit Scanning Elevation Based Slit Scanning VideokeratographyVideokeratography

Measures Elevation DirectlyMeasures Elevation DirectlyA series of slit lamp beams are A series of slit lamp beams are

compiled across the cornea to compiled across the cornea to create a profile of the corneacreate a profile of the cornea

Multiple ImagesMultiple ImagesMultiple SurfacesMultiple Surfaces

CoCornrneal eal ToTopopogrgrapaphyhy Normal CorneaNormal Cornea

Reading the MapsReading the Maps

System for studying topographic System for studying topographic mapmap► 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

Check Check NameNameDateDateEyeEye

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 : Rapid pattern recognition of topographic mapsmaps

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

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 :Dioptric steps is smaller and show more detailed changeschanges

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

Color Scale for Surface Color Scale for Surface CurvatureCurvature

• sharp• fast bend• short radius• Higher power

• flat• slow bend• long radius• Lower power

(+ +)

(+)

Red

BlueMin

Max

GreenGreen and and yellow yellow represent powers characrteristic of normal cornea represent powers characrteristic of normal cornea

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

Topographic MapsTopographic Maps

Axial MapAxial Map Tangential MapTangential Map Refractive Map Refractive Map Elevation MapElevation Map

Axial Map (Axial Map (power map, sagital power map, sagital map)map)

► Axial power: Axial power: A fixed A fixed center of curvature is center of curvature is used for calculating the used for calculating the power at all pointspower at all points

very simple map and very simple map and values directly values directly comparable to comparable to keratometrykeratometry

Paxial = (n' – 1) / raxial

Tangential Map Tangential Map (( Inst Instantaneous ,local, true , antaneous ,local, true , meridional)meridional)

► Tangential power: Tangential power: A A floating center of curvature is floating center of curvature is used by means of a standard used by means of a standard formula for calculating powerformula for calculating power

► Measures the power at a Measures the power at a certain point in meridional certain point in meridional direction relative to the other direction relative to the other points on the particular ringpoints on the particular ring

► More sensitive for local More sensitive for local curvature changecurvature change

► Most useful in following trend Most useful in following trend in the post surgical or in the post surgical or pathologic eyes.pathologic eyes.

Pinst = (n' – 1) / rinst

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 sagittal depthdepth is approximately is approximately proportional to the curvatureproportional to the curvature

► Applies snellen’s law to describe Applies snellen’s law to describe the cornea’s actual refractive the cornea’s actual refractive powerpower

► Evaluate visual performance in Evaluate visual performance in post- refractive surgery patientpost- refractive 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)

Quantitative IndicesQuantitative Indices Quantitative reference points to guide Quantitative reference points to guide

and asses the effect of therapyand asses 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)

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 Provide the power and location of the steepest

meridian and flattest meridianmeridian and flattest meridian Analogous toAnalogous to keratometerkeratometer Good correlationGood correlation with with refractive cylinderrefractive cylinder

Quantitative IndicesQuantitative Indices► Surface Asymmetry indexSurface Asymmetry index (SAI)(SAI)

Centrally weighted summation of differences Centrally weighted summation of differences in corneal power between corresponding in corneal power between corresponding points points 180180 degrees apart on degrees apart on 128128 equally equally spaced meridians crossing all the miresspaced meridians crossing 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 a surface with a power that is radially power that is radially symmetricalsymmetrical

Is sensitive to paracentral keratoconus Is sensitive to paracentral keratoconus

Quantitative IndicesQuantitative Indices► Surface Regularity IndexSurface Regularity Index (SRI)(SRI)

Summation of local fluctuations in power among Summation of local fluctuations in power among 256 equally spaced hemimeridians on the 10 256 equally spaced hemimeridians on the 10 central mirescentral 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 Can predict the optical performance of a normal

corneacornea

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.

Watch for the BumpsWatch for the Bumps

Watch for the BumpsWatch for the Bumps A bump on the inferior cornea, associated A bump on the inferior cornea, associated

with thinning, is almost always diagnostic of with thinning, is almost always diagnostic of “KCN”“KCN”

A “smile”- shaped rather than round bump, A “smile”- shaped rather than round bump, exactly at 6 o’clock at 3mm below the exactly at 6 o’clock at 3mm below the center, no more than 25 center, no more than 25 μμm thinner than 3 m thinner than 3 mm above the center, suggestive of mm above the center, suggestive of “contact lens“contact lens warpagewarpage””

Normal CorneaNormal Cornea Flattens progressively from the center to the Flattens progressively from the center to the

periphery by 2 to 4 D, as periphery by 2 to 4 D, as Nasal hemimeridians flattening more than the Nasal hemimeridians flattening more than the

temporal hemimeridians temporal hemimeridians Two corneas at one individual normally exhibit non Two corneas at one individual normally exhibit non

super imposable mirror- image super imposable mirror- image symmetry(symmetry(EnantiomorphismEnantiomorphism))

The normal cornea exhibits relative smoothness The normal cornea exhibits relative smoothness and absence of significant irregular astigmatism.and absence of significant irregular astigmatism.

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%)

20.8%17.5%32.1%7.1%22.6%

Pattern AnalysisPattern Analysis►SphericalSpherical►OvalOval►BowtieBowtie

SymmetricalSymmetrical AsymmetricalAsymmetrical

► IrregularIrregular

Regular AstigmatismRegular Astigmatism Most common naturally deviation from the Most common naturally deviation from the

normal corneanormal cornea Usually with the ruleUsually with the rule As a symmetrical bowtie of high powerAs a symmetrical bowtie of high power

Irregular AstigmatismIrregular Astigmatism Every deviation from a pure ellipsoidal shape Every deviation from a pure ellipsoidal shape

can be devastating to vision when is centrally can be devastating to vision when is centrally within the pupillary areawithin the pupillary area

Functionally, is that component of astigmatism Functionally, is that component of astigmatism that can not be corrected with spectaclethat can not be corrected with spectacle

Common causes: dry eye, corneal scars , Common causes: dry eye, corneal scars , ectatic corneal degeneration, ptrygium, ectatic corneal degeneration, ptrygium, contact lens warpage or over wear, contact lens warpage or over wear, trauma ,surgery (cataract, PK and refractive trauma ,surgery (cataract, PK and refractive surgery)surgery)

Corneal topography is particularly Corneal topography is particularly mandatory for these corneal conditionsmandatory for these corneal conditions

Advanced keratoconusAdvanced keratoconus Post-penetrating keratoplastyPost-penetrating keratoplasty Post RK or LASIKPost RK or LASIK

CoCornrneal eal ToTopopogrgrapaphyhy KeKerratatoococonnusus

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 in corneal

power comparing points 3 mm power comparing points 3 mm IInferior nferior to the center to points 3 mm to the center to points 3 mm ssuperior uperior to the center (to the center (II--SS))

►Asymmetry between central corneal Asymmetry between central corneal power of fellow eyes power of fellow eyes in excess of 1Din excess of 1D

Keratoconus detection Keratoconus detection overviewoverview

► 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)

OOrrbbssccaann IIII

Elevation Based Slit Scanning Elevation Based Slit Scanning VideokeratographyVideokeratography

• 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 across the cornea to create a profile of the corneathe cornea

• Calculates the Full Pachymetry & Calculates the Full Pachymetry & CurvaturesCurvatures

• Multiple ImagesMultiple Images• Multiple SurfacesMultiple Surfaces• Evaluates the Shape of the CorneaEvaluates the Shape of the Cornea

Terrain TopographyTerrain TopographyHighlands

Lowlands

Color-coded Map

Sea Level

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)

1. 20 Slits from Left to Right2. 20 Slits from Right to Left3. Each slit per 0.7 second4. Elimination of saccadic

movements by eyetracking5. Large face plate Placido Disc

ORBSCAN IIORBSCAN II

Reading the MapReading the Map

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

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 Anterior

chamber depthchamber depth

ColorsColors

Color Scale for Relative Color Scale for Relative ElevationElevation

• high• anterior to the

reference surface

• low• posterior to the

reference surface

reference

(+)

(-)

anterior

posterior

Red

BlueMin

Max

Colors: ElevationColors: Elevation

• Profile @ 180°

• Profile @ 90°

• Points above the best fit sphere

• Points below the best fit sphere

• Warm Colors

• Cool Colors

Color Scale for Surface Color Scale for Surface CurvatureCurvature

• sharp• fast bend• short radius

• flat• slow bend• long radius

(+ +)

(+)

Red

BlueMin

Max

Colors: Axial PowerColors: Axial Power• Warmer Colors• Higher Power

• Cooler Colors• Lower Power

Color Scale for PachymetryColor Scale for Pachymetry

• thick

• thin

Blue

RedMin

Max

Colors: PachymetryColors: Pachymetry• Cooler Colors• Thicker Areas

• Warmer Colors• Thinner Areas

Colors: PachymetryColors: Pachymetry• Thicker Areas

• Thinner Areas

OverlaysOverlays

Overlays: ElevationOverlays: Elevation

Overlays: ElevationOverlays: Elevation

Overlays: PowerOverlays: Power

Overlays: PowerOverlays: Power

Overlays: PowerOverlays: Power

Overlays: PachymetryOverlays: Pachymetry

Overlays: PachymetryOverlays: Pachymetry

Overlays: PachymetryOverlays: Pachymetry

ScalesScales

Scale: PowerScale: Power►By changing the steps, the range of By changing the steps, the range of the scale can be adjusted:the 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

Scale: ElevationScale: Elevation

Scale: ElevationScale: Elevation

Scale: ElevationScale: Elevation

MeasurementsMeasurements

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

Mean PowerMean Power

Tangential PowerTangential Power

Astigmatic PowerAstigmatic Power

Optical PowerOptical Power

Anterior ChamberAnterior Chamber

DisplaysDisplays

DisplaysDisplays

• Profile

• Topographic

• 3-dimensional

Displays: DualDisplays: DualAxial Power Map Anterior Elevation

Flatter areas stand above the best fit sphere

Steeper areas fall below the best fit sphere

Displays: DifferenceDisplays: Difference

Preop Pachymetry

Postop Pachymetry

Amount of ablation

Display: Quad MapDisplay: Quad Map

OOrrbbssccaann IIII KeKerratatoococonnusus

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 difference in the 3 mm

zonezone►> 1 D> 1 D greater power than the greater power than the

fellow eyefellow eye

BROKEN BOW-TIEBROKEN BOW-TIE

KCN CRITERIA IN ELEVATION KCN CRITERIA IN ELEVATION MAPSMAPS

1.1. Maximum elevation Maximum elevation > 50 µm> 50 µm2.2. Posterior best fit sphere in diopter Posterior best fit sphere in diopter > 55 D> 55 D3.3. R anterior BFS / R posterior BFS (mm): R anterior BFS / R posterior BFS (mm):

1.211.21 okok 1.21 and 1.21 and 1.27 1.27 suspectsuspect 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) and2020 µm ( µm (postpost) in the ) in the central 3 mm zonecentral 3 mm zone

ANTERIOR ELEVATIONANTERIOR ELEVATION

The maximum elevation measured is 65 µm (>55µm)

POSTERIOR ELEVATIONPOSTERIOR ELEVATION59.5 D

Maximum elevation= 124 µm

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

ROUSH CRITERIONROUSH CRITERION

Roush criterion: the relative elevation difference between close maxima and minima = 130 µm (>100µm)

130 µm

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)

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)

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

1 1 ABNORMAL MAPABNORMAL MAP: CAUTION: CAUTION

2 2 ABNORMAL MAPSABNORMAL MAPS: CONCERN: CONCERN

3 3 ABNORMAL MAPSABNORMAL MAPS: : CONTRAINDICATIONCONTRAINDICATION

RELATION BETWEEN 4 MAPSRELATION BETWEEN 4 MAPS

►The posterior “high point” The posterior “high point” correlates well withcorrelates well 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

RECOMMENDED QUAD MAPRECOMMENDED QUAD MAP

Corneal TopographyCorneal TopographyCorneal PathologyCorneal Pathology

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 of the image and converting

data to curvature values using computer data to curvature values using computer software by complex algorithmssoftware by complex algorithms

►DisplayingDisplaying of color topographical images of color topographical images by using pre-determined color scalesby using pre-determined color scales

►ManipulationManipulation of data creation various of data creation various displaysdisplays

Corneal Surface ElevationCorneal Surface Elevation►Data measured in terms Data measured in terms

of height or elevation (or of height or elevation (or sometimes depth) from a sometimes depth) from a reference plane describe reference plane describe the true shape of the the true shape of the corneal surface.corneal surface.

►Once the true shape has Once the true shape has been measured, slope, been measured, slope, curvature, and power curvature, and power can be calculated from it.can be calculated from it.

Corneal Surface SlopeCorneal Surface Slope► The gradient of the tangent at The gradient of the tangent at

a particular point on a curved a particular point on a curved surfacesurface

► Mathematically, the slope is Mathematically, the slope is the first differential of a curve. the first differential of a curve. Therefore, it is a more Therefore, it is a more sensitive way of demonstrating sensitive way of demonstrating small changes in height small changes in height between two points on a between two points on a surface.surface.

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 ααwhere 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 those which are flatter have a relatively large have a relatively large radius of curvatureradius of curvature

Corneal PowerCorneal Power

► A measure of the A measure of the refractive effect of refractive effect of a lensa lens

► P=(nP=(n22 – n – n11) / r) / r

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)

Corneal GeographyCorneal Geography►The corneal surface can be divided The corneal surface can be divided

into four anatomic zones. into four anatomic zones. • The central zoneThe central zone• The paracentral zoneThe paracentral zone• The peripheral zoneThe peripheral zone• The limbal zone The limbal zone

Normal CorneaNormal Cornea

Corneal MeasurementCorneal Measurement

Best Fit SphereBest Fit Sphere

• Anterior Corneal Surface

• Best Fit Sphere

Best Fit SphereBest Fit Sphere

Raw ImageRaw Image

Raw Placido ImageRaw Placido Image

Raw Placido ImageRaw Placido Image

Triangulation locates points in Triangulation locates points in spacespace

triangulatedspace point complex object

Scheimpflug

slit-beamprojector Video

Camera

calibrated slit-beamsurface diffusely

reflectedcamera ray

Terrain TopographyTerrain Topography

Terrain TopographyTerrain Topography

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 backscatteredslit-beam.

2. Measure surface slope directly using specular reflection, supplemented with triangulated elevation.

Colors: ElevationColors: Elevation

Topographic or two dimensional view

Scale: PowerScale: Power

1.0 D

0.5 D

.25 D

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