topography & tomography course handout color nov07.pdf

Topography/Tomography Course 2008

Jack T. Holladay, MD, MSEE, FACS Page 1 of 12

Jack T. Holladay, MD, MSEE, FACS # 1

Jack T. Holladay, MD, MSEE, FACSJack T. Holladay, MD, MSEE, FACS

Clinical Professor of OphthalmologyClinical Professor of OphthalmologyBaylor College of MedicineBaylor College of Medicine

Houston, TexasHouston, Texas

www.docholladay.comwww.docholladay.com

CornealTopography and Tomography


CORNEAL CORNEAL TOPOGRAPHYTOPOGRAPHY

nn Refractive Power MapsRefractive Power Mapsoo Local Radius of Curvature MapsLocal Radius of Curvature Mapspp Profile Difference or Height MapsProfile Difference or Height Mapsqq Distortion MapsDistortion Mapsrr PachymetryPachymetry MapsMapsss Corneal Parameters (15)Corneal Parameters (15)

Jack T. Holladay, MD, MSEE, FACS # 4 Jack T. Holladay, MD, MSEE, FACS # 5


POWER MAPSPOWER MAPS

Steel Ball Steel Ball ---- StandardStandard

7.5 mm radius = 45 D7.5 mm radius = 45 D


APPROXIMATEAPPROXIMATECONVERSION CONVERSION

FORMULAFORMULA

DPowermm

Power

rNNPower

455.7

0.000,15.337,1

12

=

=

=

@ all points@ all points




EXACTEXACTCONVERSION CONVERSION

FORMULAFORMULASnellSnells Laws Law

Central Power = 45 DCentral Power = 45 DPeripheral Power = 45 D to 48 DPeripheral Power = 45 D to 48 D

N i N ri r*sin *sin=



Asphericity (Q)AsphericityAsphericity (Q)(Q)

Q = 0Q = 0++

++-- --QQ

OblateOblate

SphericalSpherical

Pro

late

Pro

late

EllipticalElliptical




Asphericity (Q)AsphericityAsphericity (Q)(Q)Q = Q = --2.002.00 Severe KSevere K--ConusConus, +5 D PRK, +5 D PRKQ = Q = --1.001.00 Mild KMild K--ConusConus, + 2 D PRK, + 2 D PRKQ = Q = --0.520.52 No Spherical AberrationNo Spherical Aberration

Q = Q = --0.260.26 NormalNormalQ = 0.00Q = 0.00 SphericalSphericalQ = +1.00Q = +1.00 8 cut RK, 8 cut RK, --5 D PRK5 D PRKQ = +2.00Q = +2.00 16 cut RK, 16 cut RK, --12 D PRK12 D PRK







36

Tomography

OculusPentacam

Measuring Corneal PowerPost Corneal Refractive Surgery 3711/5/2007 JTH 11/5/2007 JTH 3737

zz OrbscanOrbscan allows posterior allows posterior curvature measurement curvature measurement but but not accuratenot accuratezz PentacamPentacam ((ScheimflugScheimflug) from ) from

Oculus and Oculus and ArtemusArtemus (High (High Frequency Digital U/S under Frequency Digital U/S under investigationinvestigation

Corneal Power MeasurementCorneal Power Measurement

3811/5/2007 JTH 11/5/2007 JTH 3838 3911/5/2007 JTH 11/5/2007 JTH 3939



4011/5/2007 JTH 11/5/2007 JTH 4040 4111/5/2007 JTH 11/5/2007 JTH 4141

4211/5/2007 JTH 11/5/2007 JTH 4242 4311/5/2007 JTH 11/5/2007 JTH 4343

4411/5/2007 JTH 11/5/2007 JTH 4444 4611/5/2007 JTH 11/5/2007 JTH 4646



4711/5/2007 JTH 11/5/2007 JTH 4747

Why are Ks & Topography Inaccurate ?

Why are Ks & Topography Inaccurate ?

nn Data is from Data is from PARACENTRALPARACENTRALRegion Region NOT CENTRALNOT CENTRAL

oo Actual Power of Actual Power of PosteriorPosteriorCorneaCornea is is UNKNOWNUNKNOWN

zz Posterior Corneal Radius is Posterior Corneal Radius is assumed to be 82% of Frontassumed to be 82% of Front

for IOL Calculationsfor IOL Calculations 4811/5/2007 JTH 11/5/2007 JTH 4848

11/5/2007 JTH 11/5/2007 JTH 4949

1. Calculation from Prior Data(Pre K & MR known)1. Calculation from Prior Data(Pre K & MR known)

Pre KR Mean K Pre KR Mean K = = 44.00 D44.00 D

Change in SEQ RefChange in SEQ Ref == --4.50 D4.50 D

Calc Mean KCalc Mean K = = 39.50 D39.50 D5011/5/2007 JTH 11/5/2007 JTH 5050

Frequency Distribution of 'Optimal Pupil' Size

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

Optimal Sample Zone Diameters (mm)

Freq

uenc

y (%

)

LASIK EYES RK EYES

5111/5/2007 JTH 11/5/2007 JTH 5151

EKR 4.5 mm vs. Backcalculated K (Post RK-eyes)

R2 = 0.8909

32.0

33.0

34.0

35.0

36.0

37.0

38.0

39.0

40.0

41.0

42.0

43.0

44.0

45.0

46.0

32.0 33.0 34.0 35.0 36.0 37.0 38.0 39.0 40.0 41.0 42.0 43.0 44.0 45.0 46.0

EKR @ 4.5 mm zone (D)

Back

-cal

cula

ted

K-re

adin

g (D

)

5211/5/2007 JTH 11/5/2007 JTH 5252

EKR 4.5 mm vs Historical Method K (Post LASIK eyes)

R2 = 0.9741

35.0

36.0

37.0

38.0

39.0

40.0

41.0

42.0

43.0

44.0

45.0

46.0

47.0

48.0

49.0

35.0 36.0 37.0 38.0 39.0 40.0 41.0 42.0 43.0 44.0 45.0 46.0 47.0 48.0 49.0

EKR @ 4.5 mm zone (D)

His

toric

al M

etho

d K

-read

ing

(D)



5311/5/2007 JTH 11/5/2007 JTH 5353

EKR 4.5mm vs Post LASIK+Post RK eyes

R2 = 0.9681

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

5411/5/2007 JTH 11/5/2007 JTH 5454

Accuracy of EKRAccuracy of EKR

0.540.54ALLALL

0.940.94RKRK

0.42 0.42 LASIKLASIK

STD 4.5STD 4.5(D)(D)

PriorPriorSxSx

5511/5/2007 JTH 11/5/2007 JTH 5555 5611/5/2007 JTH 11/5/2007 JTH 5656

5711/5/2007 JTH 11/5/2007 JTH 5757 5811/5/2007 JTH 11/5/2007 JTH 5858



5911/5/2007 JTH 11/5/2007 JTH 5959Holladay Report Holladay Report Equivalent Equivalent KeratometricKeratometric PowerPower 6011/5/2007 JTH 11/5/2007 JTH 6060

6111/5/2007 JTH 11/5/2007 JTH 6161 6211/5/2007 JTH 11/5/2007 JTH 6262

6311/5/2007 JTH 11/5/2007 JTH 6363 6411/5/2007 JTH 11/5/2007 JTH 6464



6511/5/2007 JTH 11/5/2007 JTH 6565

SummarySummaryzz Optimal ZoneOptimal Zonezz LASIK: 4.5 mmLASIK: 4.5 mmzz RK: 5.0 mmRK: 5.0 mmzz Customize for small/large pupilsCustomize for small/large pupils

zz AccuracyAccuracyzz LASIK: LASIK: 0.42 D0.42 Dzz RK: RK: 0.94 D0.94 D

zz Error on MYOPIC sideError on MYOPIC side 11/5/2007 JTH 11/5/2007 JTH 6666

Corneal EctasiaCorneal Ectasiazz By definition is a By definition is a thinningthinning with anterior movementwith anterior movement

zz KK--conusconus:: posterior surface 1posterior surface 1stst detectable movedetectable move, , because because epithelium thins and epithelium thins and masksmasks anterior anterior movement of Bowmanmovement of Bowmans Membranes Membrane

zz PPosterior surface float is more sensitive IF osterior surface float is more sensitive IF ACCURATE ACCURATE NOT ARTIFACT!NOT ARTIFACT!

zz Most prior reports are artifact due to Posterior Most prior reports are artifact due to Posterior Surface is VIRTUAL IMAGE seen through Surface is VIRTUAL IMAGE seen through Anterior Surface and is distorted by Refractive Anterior Surface and is distorted by Refractive Surgery Surgery oblate, blend zone, etc.oblate, blend zone, etc.

6711/5/2007 JTH 11/5/2007 JTH 6767 6811/5/2007 JTH 11/5/2007 JTH 6868

6911/5/2007 JTH 11/5/2007 JTH 6969

RELATIVE PACHYMETRY MAPRELATIVE PACHYMETRY MAP SHOWS RELATIVE THICKNESS AT EVERY POINTSHOWS RELATIVE THICKNESS AT EVERY POINT

7011/5/2007 JTH 11/5/2007 JTH 7070



7111/5/2007 JTH 11/5/2007 JTH 7171

DO NOT USE Best Fit Spherefor Prolate Cornea

DO NOT USE Best Fit Spherefor Prolate CorneaProlateProlate CorneaCornea

Best Fit SphereBest Fit Sphere

Always Above BFSAlways Above BFSin centerin center

Always Below BFSAlways Below BFSin peripheryin periphery

Amount dependsAmount dependsOn On AsphericityAsphericity

Of CorneaOf Cornea

7211/5/2007 JTH 11/5/2007 JTH 7272

USE Best Fit Toric Ellipsoideto Prolate Cornea

USE Best Fit Toric Ellipsoideto Prolate CorneaProlateProlate CorneaCornea

WithWithEctasiaEctasia

Best Fit Best Fit ToricToric EllipsoidEllipsoid

Only detectsOnly detectsIrregularitiesIrregularitiesFrom From ProlateProlate

SurfaceSurface

7311/5/2007 JTH 11/5/2007 JTH 7373 7411/5/2007 JTH 11/5/2007 JTH 7474

7511/5/2007 JTH 11/5/2007 JTH 7575 7611/5/2007 JTH 11/5/2007 JTH 7676



7711/5/2007 JTH 11/5/2007 JTH 7777

ConclusionConclusionzz PentacamPentacam ScheimpflugScheimpflug very very

sensitive detection of thinning sensitive detection of thinning disorders (disorders (Cone,PellucidCone,Pellucid), if use ), if use zzTangential (local radius) MapTangential (local radius) Map to to

determine determine nipplenipple on fronton frontzzToricToric Ellipsoid Float Ellipsoid Float ((not BFS) with not BFS) with

Elevation MapsElevation Maps to determine location to determine location of protrusions in back and front of protrusions in back and front surfacesurfacezz RELATIVERELATIVE PachymetryPachymetry Map to Map to

determine Thinnest determine Thinnest RelativeRelative PointPoint11/5/2007 JTH 11/5/2007 JTH 7878

!Thank You!!Thank You!

topography & tomography course handout color nov07.pdf

Documents

facs page

d prk5 d prkq

d prk12 d prkjack

dperipheral power

dcentral power

cut rk

height mapsprofile difference

zz orbscanorbscan