A brief view of how to read a pentacam scans

1. Pentacam Analysis
Dr Nikhil R P
MBBS, MS, DNB, (FPRS)

2. QUAD MAP ANALYSIS
PARAMETERS:
1. QS : OK ( Abnormal: Data gaps/ Fix / Model )
2. Q- value: Normal  -1 to 0 ( ideal is -0.26- Least spherical
ablation, myopic photoablation, after RK )
• 0 Sphere
• >0 Oblate cornea
• <-1 Hyperprolate /prolate ( KC, Hyperopic phototablation
3. K1 ( kf) K flat. Normal- >34D , measured in 3mm zone
4. K2( Ks) Steep K. Normal <49D
5. Km ( K- Avg) Mean curvature of ant surface
• Km< 40 D  Free Flap complication may occur
• Km> 46 D  Button hole complication may occur
6. Kmax  Maximum curvature power of whole anterior surface
• Normal 49D
• Kmax difference b/w 2 eyes  <2D
• Kmax-K2 diff in same eye <1D
• If difference >1D, Kmax to be used instead of K2
7. Astigmatism SimK ( K2-K1) within 3mm zone
• To be compared with Manifest Refraction
8. Pachy apex(.) : Thickness at corneal apex. “x” & “y” co-
ordinates are there for location
9. Pupil centre(+): Corneal thickness corresponding to pupil centre
• Normal: “x” is < 200µm ( or <5 deg)
• Important to evaluate ANGLE KAPPA.
10. Pupil Diameter : Photopic, Mesopic, Scotopic size.
11. Thinnest Location(TL) (o):
• Thickness & location of thinnest point of cornea
• < 470µm in normal & < 500µm in abnormal topo
• Normal diff b/w both eyes < 30 µm
• Diff b/w TL & Pachy apex  < 10 µm
• “y” co-ordinate: Normal : <-0.5mm
• ABNORMAL : <0.5/0.5 to 1/>1mm
• “-” sign indicates Inferior displacement of TL
Safe parameters for ICL :
• Anterior chamber depth (ACD)> 3mm
• Anterior chamber Angle ( ACA)> 30 deg
• Anterior chamber volume( ACV)> 100mm3
• ACD<24 deg, ACD <2.1mm, ACV < 100mm3
Risk of angle closure glaucoma.

3. QUAD MAP ANALYSIS
ANTERIOR SAGITTAL MAP:
• Anterior surface dioptric power
• Steep areas  HOT colors – RED/ ORANGE
• Flat areas COLD Colors – GREEN/ BLUE
• Parameters to be read on 5mm circle
• Normal pattern is Symmetric bowtie (SB)
• Normal I-S difference < 1.5D. Inferior ( higher value than
superior)
• SB- REGULAR ASTIGMATISM ( WTR / ATR ) +/- 15 degree
of vertical/ horizontal meridian.
• Qblique astigmatism SB is neither vertical or horizontal
• ABNORMAL PATTERNS:
• AB/SRAX > 22 ( angle between two lobes)
• AB/SS: SS- IS> 2.5D
• AB/IS: IS- SS> 1.5D
• Butterfly and Claw pattern : PMD
• Enantiomorphism:
• Sagittal map appears mirror shaped of that in other eye

4. QUAD MAP ANALYSIS
ELEVATION MAPS :
• The patient’s cornea is compared to normative age related
data base and the elevation/depressions are calculated in
both ANTERIOR (A) and POSTERIOR (B) surface.
• Reference surface ( RS ) : 8mm IDEAL
• ELEVATIONS (+) , DEPRESSIONS (-)
• Best Fit Sphere ( BFS )  Quantifies the shape measured
• Best Fit Toric Ellipsoid ( BFTE )  Quantifies parameters of
that surface
SHAPE: (BFS FLOAT Mode) :
• Normal : Symmetric hour glass ( WTR ) – Regular
astigmatism
• ABNORMAL :
• Skewed hour glass: Seen in large angle kappa, Misalignment
during capture, distorted cornea
• Tongue- Like extention & Irregular hourglass : distorted
cornea
• Isolated Island : Distorted cornea
PARAMETERS ( BFTE Mode): Highest plus within 5mm zone
Cone Location :
• Can be central ( 3mm)/ paracentral ( 3-5mm)/ peripheral (
>5mm)
• If cone is peripheral  KISSING BIRDS SIGN
A
B
µm Anterior Posterior
BFTE >12 >15
BFS: Myopic 7.7 17.7
BFS: Hyperopic 6.5 27.8
Hour Glass Skewed hour glass Isolated Island KISSING BIRDS SIGN

5. QUAD MAP ANALYSIS
PACHYMETRY MAPS:
• Corneal apex (+)
• Thinnest Location (o)
• Difference b/w Sup & Inf points ( < 30 µm )
• Normal map : Concentric shape
• ABNORMAL pattern:
• Horizontal displacement of TL
• Dome Shaped: Vertically displaced TL
• Bell Shaped : Thin band of cornea inferiorly (PMD).
• Keratoglobus : Generalized thinning
Horizontal displacement of TL Vertical displacement of TL Bell Shaped : PMD Keratoglobus
Quick Slope S Shape Flat curve
Inverted shape
Details of CTSP & PTI in
other slide

6. INDICES Helps in differentiating normal corneas from KC.
HIGHLY SENSITIVE
1. Index of Surface Variance ( ISV ):
• Measured as standard deviation of individual sagittal radii from
mean curvature
• ISV > 37 YELLOW  ABNORMAL
• ISV> 41 RED  PATHOLOGICAL
2. Index of Vertical Symmetry ( IVA ): “mm”
• Mean difference b/w Superior & Inferior curvature
• IVA >0.28 ABNORMAL
• IVA >0.32 PATHOLOGICAL
3. Keratoconus Index ( KI ):
• Ratio b/w mean radius values in upper half & Lower half of
cornea
• KI > 1.07 ABNORMAL
4. Central Keratoconus Index ( CKI ) :
• Ratio b/w mean radius of curvature in a peripheral placido ring &
mean radius of curvature of central ring
• CKI > 1.03 ABNORMAL
5. Index of Height Asymmetry ( IHA ): “µm”
• Mean difference b/w corneal elevation in superior hemisphere &
inferior hemisphere in horizontal meridian
• IHA > 19  ABNORMAL
• IHA > 21  PATHOLOGICAL
6. Index of Height Decenteration ( IHD ) : “µm”
• Measures vertical decenteration of elevation data on a ring with
radius of 3mm
• IHD> 0.014 ABNORMAL
• IHD > 0.016 PATHOLOGICAL
REFRACTIVE ANALYSIS
8. Topographic Keratoconus Index ( TKC ):
• Negative- 0
• Possible- 0.5
• Positive- 1
• Abnormal- 2
• Post – surgery- 3
7. R min:
• Denotes max steepness of cone
• Smallest radius of sagittal/ axial corneal curvature
• Rmin< 6.71mm ABNORMAL

7. BELIN AMBROSIO DISPLAY
BAD_D
A
• Elevation maps
• Enhanced/ Exclusion
maps
• Difference maps
B
• CTSP
• PTI
• Kmax, Q
value, QS
• PPI, ART max
C
• Parameters:
• Df, Db, Dp, Dt, Da
• Final D
• Multivariate Index
• Integrates Anterior Elevation,
Posterior Elevation, Pachymetry
Data
• Complete Overview of corneal
shape
• Quick screening tool
• Standard Elevation maps: (A)
• Radius of BFS is noted eg: r= 7.7 float
• Diameter of zone used to complete the BFS dia=8mm
• Represents Anterior and Posterior elevation data relative
to standard BFS
• Enhanced / Exclusion maps: (B)
• Anterior and Posterior elevation data relative to BFS
located outside 4mm circle is calculated with EXCLUSION
of central 4mm zone.
• This zone cant be modified.
• Exclusion zone is determined by the magnitude of
astigmatism
• Difference maps: (C)
• Diff b/w standard & Exclusion map
µm Anterior Posterior
GREEN <6 <8 Normal
YELLOW 6-12 8-20 Suspicious
RED >12 >20 KC
A
B
C

8. BELIN AMBROSIO DISPLAY
• Df : Front Elevation
• Db : Back Elevation
• Dp : Pachymetry Progression
• Dt : Corneal thickness at thinnest location
• Da : Corneal thinnest displacement
• Final D : is calculated considering all 5 parameters.
• These parameters denote the STANDARD DEVIATION from the mean of
normative database.
• Individual parameter may be RED/ YELLOW & the “final D” can be normal.
D values (SD)
< 1.6 SD WHITE Normal
1.6- 2.6 SD YELLOW Suspicious
>2.6 SD RED KC
• Corneal thickness spatial profile ( CTSP ) : (A)
• Average progression from thinnest point to periphery
• NORMAL: Av: 0.8- 1.1
• ABNORMALS:
• Quick slope : Red line leaves before 6mm . Avg > 1.1 ( FFKC )
• S- Shape: Red curve has SHARP “S”. Avg > 1.1 ( FFKC )
• Flat curve: Red curve takes straight curve. Avg <0.8 ( edematous
cornea, Fuch’s dystrophy)
• Inverted curve: Red curve follows upward course. Avg <0.8 & minus
value might be there. ( few cases of PMD)
• Percentage thickness increase ( PTI ) : (B)
• Percentage thickness index . It denoted % of progression
• Normal Avg: 0.8- 1.1
• Avg α Fast transition
• Pachymetric Progression Index ( PPI ):
• Calculates change in corneal thickness overall 360 deg of cornea
• Progression value at each meridian from the thinnest point is
defined as progression index
• PPI – Max: Meridian with Max pachymetric increase (0.85±0.18)
• PPI - Min : Meridian with Min pachymetric increase (0.58±0.30)
• PPI- Avg : Avg of all meridians (0.13±0.33)
• Ambrosio relational thickness :
• Ratio b/w thinnest point & PPI
• Distinguishes KC eyes from normal eyes
• ART Max, ART Min, ART Avg
• ART Max < 412 µm  KC
A
B

9. 13 POINT ALGORITHM :
• Point No. 1: The quality specification of the capture (QS);
• Point No. 2: The maximum keratometry (K) value;
• Point No. 3: The corneal thickness at the thinnest location;
• Point No. 4: The y (vertical) coordinate of the thinnest location;
• Point No. 5: The corneal asphericity at the 6-mm optical zone (Q-value);
• Point No. 6: The shape and value of the anterior sagittal curvature map;
• Point No. 7: The shape and values of the anterior elevation map;
• Point No. 8: The shape and values of the posterior elevation map;
• Point No. 9: The shape and value of the pachymetry map;
• Point No. 10: The shape of the corneal thickness spatial profile (CTSP) and
the average of thickness progression;
• Point No. 11: The amount and axis of topographic astigmatism measured
by the total corneal refractive power and compared with the manifest
astigmatism; and
• Point No 12: A comparison between the patient’s two eyes
• Point No 13: BAD Display, BAD parameters, PPI, ARTmax *Sinjab M, Step by Step, Reading Pentacam Topography

10. SUMMARY
*Sinjab M, Step by Step, Reading Pentacam Topography

11. µm Anterior Posterior
GREEN <6 <8 Normal
YELLOW 6-12 8-20 Suspicious
RED >12 >20 KC
BAD_D Difference Maps
D values (SD)
< 1.6 SD WHITE Normal
1.6- 2.6 SD YELLOW Suspicious
>2.6 SD RED KC
BAD_D PARAMETERS including Final D
Yellow-
Abnormal
Red-
Pathological
ISV (SD) >37 >41
IVA (mm) >0.28 >0.32
IHA (µm) >19 >21
IHD (µm) >0.014 >0.016
KI >1.07 Abnormal
CKI >1.03 Abnormal
Rmin <6.71mm Abnormal
PPI- Avg 0.13±0.33
PPI- Min 0.58±0.30
PPI- Max 0.85±0.18
ART Max < 412µm KC
SUMMARY
*Sinjab M, Step by Step, Reading Pentacam Topography

13. CBI- Corvis Biomechanical Index
• Comprehensive biomechanical screening and keratoconus detection
• Based on corneal thickness profile and deformation parameters
• Developed by Riccardo and Paolo Vinciguerra from Italy
• Normal <0.5
• Advantages:
o A higher safety, as patients at risk for developing ectasia after LASIK can be excluded
o A higher efficiency, as surgery can be performed when patients have a stiff and stable cornea
* Vinciguerra, et al., J Refract Surg. 2016

14. TBI – Tomographic Biomechanical Index
• Integration of Pentacam data for a combined tomographic and biomechanical analysis
• TBI is calculated using an artificial intelligence approach to optimize ectasia detection
• By combining tomographic data with biomechanical data, one can further improve sensitivity and
specificity in the detection of patients with a significant risk for developing ectasia after refractive
surgery
• Normal < 0.29

15. Cut off values for border line cases/KC
• I-S >1.4
• BAD-D >1.6
• CBI >0.5
• TBI >0.29
• CCT<480µm
*Vinciguerra, et al., J Refract Surg. 2016
* Ambrosio et al., J Refract Surg. 2017

16. A simplified algorithm to aid in decision making regarding
suitability for combined refractive surgery with CXL
*Brar S, Gautam M, Sute SS, Ganesh S. Refractive surgery with simultaneous collagen cross-linking for
borderline corneas - A review of different techniques, their protocols and clinical outcomes. Indian J
Ophthalmol. 2020 Dec;68(12):2744-2756. doi: 10.4103/ijo.IJO_1709_20. PMID: 33229650.

17. Classification systems for KC
• Severity : Mild, Moderate, Severe based on K- readings.
• Cone: Round or nipple, Oval , Globus
• Amsler Krumeich et al., : Stage 1, 2, 3, 4
• Rabinowitz/Rasheed’s KISA % : KISA %= Central K x I-S Asymmetry x AST (degree of regular
corneal astigmatism) x SRAX x 100/300.
• Normal : <50 %
• KC Suspect: 60-100%
• KC: >100%
• Belin ABCD classification system/ Progression Display: A,B & C- are autogenerated.
• A: Anterior Radius of curvature in 3 mm
• B: Posterior Radius of curvature in 3mm
• C: Thinnest pachymetry in microns
• D : Distance Best Corrected Visual Acuity ( to be entered )

18. Amsler Krumeich Staging

19. *Belin MW, Kundu G, Shetty N, Gupta K, Mullick R, Thakur P. ABCD: A new classification for keratoconus. Indian J Ophthalmol 2020;68:2831-4

20. Thank you