"Pentacam" from the beginning

“Pentacam“
from the beginning
Dr. Tukezban Huseynova
9mm
Eye – Dr. Tuti

Content
Part III: Pentacam and Ectatic corneal diseases (ECDs)
Part II: Interpretation of Pentacam parameters
Part I: Introduction and understanding
Chapter 1: - Set up and screening
- Corneal power maps
- Elevation maps
Chapter 2: - Pachymetry Maps
- Thickness profiles
- Belin/Ambrosio enhanced ectasia display III
- Corneal tomography

Part I
Introduction and Understanding
Chapter 1: - Set up and screening
- Corneal power maps
- Elevation maps

Suggested Set-up and screening guidelines

ü Make sure that the patient has been discontinued contact lenses for at least 1 week
before the examination
Take into consideration
ü Tear film disturbance (treat the patient then repeat the capture)
ü Cornea opacities or previous surgeries (slitlamp examination before the capture)
ü Bad exposure to the cornea (small eyes, deep set eyes, nasal bridge, long lashes)
ü Perform the examination before any contact testing and before drops are instilled
ü Maps should be obtained from a doctor prior to dilation (for more accurate center of
pupil measurements) and prior to applanation
ü Insure that the scales and color bars remain consistent for every patient
ü The scales and color bars should be chosen to make the differentiation between
“normal” and “abnormal” as easy as possible

4 Maps Refractive
4-Maps Refractive
Is the standard map to study
Anterior elevation
Posterior elevation
Sagittal curvature
Pachymetry map
*Corneal tomography in clinical practice (Pentacam System), basics and clinical interpretation, 3rd edition (2019), Mazen M Sinjab

Recommended general settings

*Elevation based corneal topography, second edition, M.Belin, R.Ambrosio (2012)
Recommended Refractive Surgery Screening Settings

Color Scale
*Corneal tomography in clinical practice (Pentacam System), basics
and clinical interpretation, 3rd edition (2019), Mazen M Sinjab
Fine scale (0.25 D) exposes
irregularities while using coarse
scale may mask them
0.25 D 0.50 D
1.00 D

Color Scale for the curvature, pachymetry, and elevation maps

Maps Overlay
Overlay for the anterior sagittal curvature map

Maps Overlay
Clinical samples of a normal capture and captures with extrapolated data on the anterior sagittal map
Kmax symbol (red arrow) within the
center of the hot spot (normal)
A very peripheral Kmax (Artifact, red
arrow). The capture should be repeated

Maps Overlay
Clinical samples of extrapolated data
9mm

Maps Overlay
Clinical samples of extrapolated data
By every extrapolated data the capture should be repeated!

Maps Overlay
Overlay for the elevation maps
Overlay for the corneal thickness map
Red arrow – Thinnest location (TL)

Reference body shape
The standard 8mm diameter for the best fit
sphere (BFS) reference surface (RS)

Reference body shape
8mm BFS
5 mm BFS
10 mm BFS

Corneal Power Maps

ü There are several maps measuring corneal power based on 4 factors
Factor 1: The refractive Effect
Factor 2: Inclusion of the anterior and posterior corneal surfaces
Factor 3: The refractive Index (RI = 1.33)
Factor 4: Location of the principle planes (where corneal thickness contribues to corneal power)
Ø The anterior sagittal curvature map
Ø The anterior tangential curvature map
Ø The refractive power map
Ø The true net power map
Ø The equivalent K-reading power map
Ø The total corneal refractive power map
Those are also Pre-Cat.OP Maps
Corneal Power Maps
Maps measuring corneal power are:

Corneal Power Maps
The Anterior Sagittal Map
1
5mm
ü Represents anterior surface dioptric power measured
by the sagittal method
ü Steep areas are displayed in hot colours (red and
orange), while flat areas are displayed in cold colours
(green and blue)
ü The cross point of this segmentation represents apex
(anatomical center) of the cornea
ü Beside the shape of the map, parameters should be
studied particularly on the steep axis, superior (S) and
inferior (I) at the 5-mm central circle
ü Sagittal map is used to describe normal and abnormal
patterns

Principle of calculating superior inferior difference
A B
B: Simple rough method
5 mm
A: Rabinowitz Method
Corneal Power Maps

Patterns of the anterior sagittal map
*Patterns on the anterior sagital map are classified into four groups: A, B, C, D
Group A
Group B
Group C
Group D
Corneal Power Maps
Symmetric patterns
Special Shapes
Angulated patterns
Asymmetric patterns

Group A Symmetric patterns
Round pattern (R) Oval pattern (O)
Normal SB
Corneal Power Maps
Note:
ü Symmetric patterns are not always normal
ü Group A is abnormal when Km < 48D
ü Oval and Round patterns are encountered in corneas with
insignificant astigmatism, < 1D
See further about regular astigmatism
*Stepp by Step Reading Pentacam Topography: Basics and case study series, 2nd edition (2015), Mazen M Sinjab, Arthur B. Kummings

Corneal Power Maps
Regular astigmatism
Oblique Astigmatism
The SB is neither vertical nor
horizontal
Against-the-Rule (ATR)
In ATR astigmatism, the SB is
on/within 30° of the Horizontal
meridian of the cornea
With-the-Rule (WTR)
In WTR astigmatism, the SB is
on/within 30° of the vertical
meridian of the cornea

Corneal Power Maps
*Corneal tomography in clinical practice (Pentacam
System), basics and clinical interpretation, 3rd edition
(2019), Mazen M Sinjab Dr. Tukezban Huseynova
Group B Asymmetric patterns
Asymmetric bowtie/inferior
steep (AB/IS)
the I-S difference is >1.4 D
Asymmetric bowtie/
superior steep (AB/SS)
the S-I difference is >2.5 D
Superior steep pattern (SS)
Inferior Steep (IS)

Group C Angulated patterns
Corneal Power Maps
Asymmetric bowtie/skewed radial
axis index (AB/SRAX)
The angle between the axes of the
two lobes is >22° (Abnormal)
Symmetric bowtie/skewed radial axis
index (SB/SRAX)
The angle between the axes of the
two lobes is >21° (Normal ≤21° )
SRAX
SRAX

Group D Special shapes
Butterfly pattern (B) Crab -Claw pattern (C) Vertical D pattern
Smiling face pattern (SF) Vortex pattern (V)
Corneal Power Maps
*Corneal tomography in clinical practice
(Pentacam System), basics and clinical
interpretation, 3rd edition (2019), Mazen
M Sinjab
*Corneal Collagen Cross Linking, Mayen
M. Sinjab, Arthur B. Cummings (2017)

The Anterior Tangential Map
2
Morphologic patterns of ectatic disorders
Corneal Power Maps
ü This map is similar to sagittal map but more detailed using the
tangential principle in calculating the radius of curvature
ü K readings are higher by this map that’s why this map can’t be
used in IOL calculation formulas
ü Tangential map is being used to describe corneal irregularities
ü It is also useful for determining morphologic patterns of the cone in
ectatic corneal disorders
ü There are three patterns of the cone: nipple, oval and globus

The nipple cone
The oval cone
The globus cone
Patterns of the tangential map
Corneal Power Maps

The Anterior Tangential Map
ü Widely adopted
ü K readings are more precise compared
to tangential map
The Anterior Sagittal Map
ü More susceptible to local curvature
changes, because it depends on circles
ü More capable of detecting corneal
irregularities
ü Describes better the contour of zones
ü Describes better postsurgical corneas
ü Has no reference axis
ü K-readings are higher then when
measured by the sagittal map for the
same corneal surface
Sagittal Map (front) Tangential Map (front)
Corneal Power Maps

The Refractive Power Map
3
ü This map measures the power of refraction of the anterior surface based on RI
ü Can’t be used in IOL calculation formulas
ü By comparing this map with anterior sagittal map we get an idea about spherical aberration (SA)
Corneal Power Maps

Corneal Power Maps
True Net Power Map
4
ü Depends on the sagittal formula and the true RI of the cornea
ü Measures the power of anterior and posterior corneal surfaces
ü Cannot be used in IOL calculation since it depends on the true index of corneal tissue rather than
keratometric index.

Corneal Power Maps
The Equivalent K-reading (EKR) Power Map
5
ü Being used for K readings recalculation in operated and non-operated eyes
ü Within the central 4.5 mm zone presents the actual corneal power that the patient uses for distance
vision
ü EKR can be used for IOL calculation in virgin as well as in operated corneas

Corneal Power Maps
Total Corneal Refractive Power(TCRP) Map
6
ü Calculates total corneal power in terms of air, corneal tissue and aqueous humour
ü Cannot be used in the classic IOL formulas which are based on the keratometric RI (1.33)
ü This total corneal astigmatism is crucial for toric IOL or limbal relaxing incision planning
ü TCRP can be applied in regular corneas, while EKR can be applied in irregular corneas
Note:
TCRP for toric IOL power calculation:
Toric IOLs can be calculated based on
the individual SIA (surgically induced
astigmatism) and TCRP. The latter
takes the posterior corneal surface
into account, improving the accuracy
of IOL power calculation.
*https://www.pentacam.com/de/modelle/software-aoo.html

Elevation Maps

ü Points above the RS are considered elevations
and expressed in plus values, and those
below the RS are considered depressions and
expressed in minus values
ü There are several shapes of the RS, the most
important are best fit sphere (BFS) which
describes (qualifies) the shape of the
measured surface, and best fit toric ellipsoid
(BFTE) which estimates (quantifies) the
parameters of that surface
Principle of measurement and color scale
Principle of the elevation maps
ü An elevation map describes the height details
of the measured corneal surface by matching
it with a reference surface (RS)
The reference surface (RS): principle
Elevation Maps

Elevation Maps
The RS: position (float mode, nonfloat mode)
A B
float mode Non - float mode
A: RS is in neutral position (standard) B: RS will touch the apex of he cornea

Elevation Maps
The RS: position
Regular corneal astigmatism in relation with RS
ü The hourglass pattern reflects corneal astigmatism (CA)
ü Blue Colors = steep meridian (below RS)
ü The hourglass shape is only displayed when using best fit sphere (BFS)
“Hourglass” shape indicates CA

Elevation Maps
The RS: position (samples)
A B A B
elevation map sagittal map
sagittal map
elevation map
A B
WTR astigmatism
ATR astigmatism
Oblique astigmatism
*Corneal tomography in clinical practice
(Pentacam System), basics and clinical
interpretation, 3rd edition (2019), Mazen M Sinjab

Elevation Maps
The RS: Parameters
ü Each RS is defined by 2 parameters: radius and diameter
ü Choosing a larger diameter causes false positives ( sensitivity and specificity)
ü Choosing smaller diameter causes false negatives ( sensitivity and specificity)
ü Recommended standard diameter is 8mm
D = 11.94 mm
D = 9.0 mm
D = 7.0 mm

Elevation Maps
The RS: Types - best fir sphere (BFS), best fit ellipsoid (BFE), best fit
toric elipsoid (BFTE)
ü The BFS is determined by an area of the cornea that is
neither too flat nor too steep and allows easy visual
inspection for screening purposes
ü It is usually easy to obtain maps with at least 8.0 mm of
valid data (nonextrapolated)
ü Highlights CA
ü Evaluates the elevations
ü Describes and classifies corneal patterns
ü Posterior elevation map + BFS are the best map to localize
and classify cone location
ü Cone location: central (within central 3mm), paracentral
(between 3mm and 5mm central zones) or peripheral
(outside the 5mm central zone)
BFS

Elevation Maps
The RS: Types BFS
Classification of cone location by the posterior elevation map with 8mm BFS float moad
Central Paracentral Peripheral
cone
cone
cone

Elevation Maps
The RS: Types BFS
Cutoff values of elevations at the points corresponding to the thinnest location
*SD=standard deviation
Cutoff elevation values for
myopic population
Cutoff elevation values for
hyperopic population
Normal Values are:
Anterior ≤ 12 µm
Posterior ≤ 15 µm

Elevation Maps
The RS: Types BFS
Cutoff values of elevations at the points corresponding to the thinnest location
Normal corneal elevation values for myopic patients
Normal corneal elevation values for hyperopic patients

Elevation Maps
The RS: Types
BFE
ü This shape is ussualy not used
Ellipsoid
BFTE
Toric Ellipsoid
ü Rotationally symmetric
ü Because it is the closest RS to corneal shape, this
RS fits well to a normal astigmatic cornea to
display the remaining irregularities and the
related higher order aberrations (HOAs)
ü This RS is used in Holladay report to detect early
keratoconus (KC)

Elevation Maps
What is better to use in clinical practice???
BFTE
BFE
BFS

Elevation Maps
Clinical Examples
BFS BFE
BFTE (front) BFTE (back)
“island”

Elevation Maps
Clinical Examples (continue.)
BFS BFE
BFTE (front) BFTE (back)
BFE
BFS
BFTE (back)
BFTE (front)

Elevation Maps
Clinical Examples (continue.)
Markedly advanced case of keratoconus
TL = 244 microns
K values > 60 D (and significantly abnormal
indices, black square)
BFS BFTE

Elevation Maps
The RS: Elevation-based patterns
The normal “symmetric
hourglass pattern” (SHP).
Normal, SHP

Elevation Maps
The RS: Elevation-based patterns
Group B Irregular patterns Irregular patterns
Note: Neither Group A nor group B are considered
as abnormal unless values are abnormal based on
the cutoff values

Elevation Maps
The RS: Elevation-based patterns (Irregular astigmatism/Island)
Irregular cornea Keratoconus

Elevation Maps
The RS: Elevation-based patterns, Sample – Astigmatism low and high
Low Astigmatism High Astigmatism

Elevation Maps
Clinical samples from elevation maps - Mild irregular astigmatism
Mild Astigmatism

Elevation Maps
Clinical samples elevation maps – Isolated posterior

Elevation Maps
Clinical samples elevation maps – Displaced apex syndrome (inferior)

Elevation Maps
Clinical samples elevation maps – Displaced apex syndrome (superior)
Normal astigmatic cornea

Elevation Maps
Clinical samples elevation maps – Faulty location
Patient with keratoconus
„Pseudo“ cone
„Real“ cone

Pachymetry Maps

Note: The computer measures the thickness of the cornea at all points depending on the elevation
maps. The difference between the front and back surface elevations is corneal thickness.
ü The Pachymetry Map has three main landmarks: Cornea
apex, thinnest location (TL) and two opposing points (S
=superior, I =inferior) on the vertical meridian within central
5 mm circle
ü Enable the characterization of the thickness profile of the
cornea
ü The normal difference between (S) and (I) points is ≤ 30 μm
ü The normal difference between two eyes is ≤ 30 μm
ü Corneal thickness represents an important variable when planning keratorefractive
surgeries, evaluating ectatic diseases and assessing corneal endothelial function
ü Additionally, corneal thickness affects intraocular pressure measurements, and
pachymetry may be an independent risk factor for glaucoma
Pachymetry Maps

Pachymetry Maps
Patterns
The normal concentric shape

Pachymetry Maps
Patterns (abnormal)
Horizontal displacement pattern
Horizontal displacement of the TL
Dome shape
The TL is vertically displaced
Bell shape
There is a thin band in the
inferior part of the cornea (PMD)
Keratoglobus
A generalized thinning reaching
the limbus
Droplet Pattern
*Corneal tomography in clinical practice (Pentacam System), basics and clinical
interpretation, 3rd edition (2019), Mazen M Sinjab

Pachymetry Maps
Distribution of corneal pachymetry at the apex, pupil center, and
thinnest point for a normal cornea
Pachymetric asymmetry at the corneal apex, pupil center, and thinnest point

Pachymetry Maps
Note: Limitations of Pachymetry map
ü Corneal Opacities lead to artifacts
ü The area of scar is usually displayed as flat area
ü Scarred area are interpreted as thin, which is not always true
ü In case of corneal scars anterior OCT is more reliable
Flat area
Flat area
Not KC
Not KC

Pachymetry Maps
The relative pachymetry map (RPM)
Normal Cornea
Suspicious Cornea
Abnormal Cornea

Thickness profiles

The corneal thickness spatial profile (CTSP) and the percentage
thickness increase (PTI)
ü The CTSP describes the average progression
of thickness starting from the TL to corneal
periphery in relation to zones concentric with
the TL
ü The PTI describes the percentage of
progression of thickness starting from the TL
to corneal periphery in relation to zones
concentric with the TL
A normal thickness profile
The CTSP
The PTI
Thickness profiles

Thickness profiles
ü The original analysis for CTSP was performed using twenty-two circles centered on
the thinnest point with increasing diameters at 0.4 mm-steps
ü The pachymetry values along each circle are averaged and plotted to create the
corneal thickness spatial profile (CTSP) graph
22 concentric circles

Thickness profiles
Patterns
Normal pattern
*Keratokonus: Recent advances in diagnosis and treatment, Jorge L Alio (2017)

Thickness profiles
ü The CTSP and PTI graphs provide information which allows the clinician to differentiate a
normal thin cornea from one with early ectatic disease
ü And enables to detect early edema, in which the change in thickness from the center towards
the periphery is decreased (PTI graph is flattened)
flattenning
CTSP
PTI

Thickness profiles
Normal thickness progression Abnormal thickness progression

Thickness profiles
Ambrosio2 color palette suggested for use on corneal thickness maps
Mean TP 550±30 µm (Normal population)
Mean TP 450 (with a 500 µm cut off for KC)
Mean TP 600&626 the best cut off for Fuchs endothelial dystrophy

Thickness profiles
ü The pachymetric progression index (PPI) are calculated for all hemi-meridian 360°,
starting from the thinnest point. The normal PPI average is 0.8-1.1
Normal PPI < 1.2 mm (0.91 ± 0.23mm)
Note: 7% of normal eyes have average PPI between 1.2 and 1.8. In addition, 10% of the
cases with clinical keratoconus have an average PPI < 1.2 and may have a CTSP and PTI
within the normal limits
When PPI-av <0.8 =cornea is thickened (cornea guttata, Fuchs endothelial dystrophy)
When PPI-av ≥ 1.2 = abnormal cornea (may be ectatic)

Thickness profiles
Patterns (abnormal)
Quick slope
Avg = 1.5
S - Shape
Flat slope
Avg = 2.9
Avg = 0.6
Inverted slope
Avg = 0.2

Belin/Ambrosio enhanced ectasia display III
Consist of
ü Belin/Ambrosio ectasia display (BAD) – elevation based pachymetry
ü Pachymetric data and numeric values

Enhanced reference surface (or enhanced BFS)
BFS (8 mm) Enhanced BFS (4 mm)
4.0 mm

Anterior elevation map of a normal cornea

Posterior elevation map of a conical cornea
A B
Flat “cone”
cone

Elevation display interpretation
BFS
Valid data Less valid data
Enhanced BFS
BFS
Enhanced BFS
4mm
4mm
Normal Eye
Difference Maps Difference Maps

Yellow areas
represent a change between 5 and
12 µm for the front surface and 12
to 16 µm for the back surface.
These eyes fall in the suspicious or
suspect zone
The green areas
represent a change in elevation
(from the baseline to the
exclusion map) of < 5 µm on the
front surface and 12 µm on the
back surface of the cornea
Normal eyes
The Red ares
represent areas where the elevation
difference between the 2 maps is ≥ 7
µm anteriorly or ≥ 16 µm posteriorly
and are the magnitude typically seen
in eyes with known ectatic disease
Ectatic disease Suspicious eyes

A patient with early keratoconus
mild cone
no cone
*EM – elevation map
Suspicious posterior EM
Suspicious yellow flag

Pachymetric data (additional to the Information from Pachymetric map)
Deviation Parameters
Progression Index
D (normal value) < 1.45

Data summary from receiver operating characteristic curves of pachymetric
parameters in normal and keratoconic eyes
AUC = area under the receiver operating characteristic curve; SE = standard error, CI = confidence interval;
ART = Ambrósio relational thickness; Ave = average; Max = maximum; PPI = pachymetric progression indices;
CCT = central corneal thickness; TP = thinnest point

Clinical sample
OS
OD
Both eyes of the same patient
OD: Typical keratoconic
cornea on front curvature,
with BAD D > 2.5 and
ART Max < 360
BAD D =7.89
BAD D =2.06
ART Max < 360
OS: FFKC cornea with
relatively normal front
surface curvature map,
but with BAD D > 1.45 and
ART Max < 412
ART Max < 412

Corneal Topometry

ü Measures the slope of the cornea on anterior tangential map
ü There are four main pattern of corneal asphericity: spheric, aspheric oblate,
aspheric prolate or aspheric hyperprolate
ü To give the slope of the cornea a value, Q-value was calculated
(N = [–0.80 to 0.40])
ü Q-value is positive (> 0) when the cornea is oblate, negative (0 and -1) when
the cornea is prolate or hyperprolate, and when the cornea is spheric Qvalue =0.
ü In KC, Q-value is highly negative; and after high myopic photoablation, Q-value is positive.
ü Abnormal Q-value causes spherical aberrations (SA)
ü The least SA are found when Q-value = –0.27, no SA when Q-value -0.53.
Q>0
Q: 0 to -1
Corneal topometry

Corneal topometry
Corneal asphericity on the curvature maps
Spherical cornea Prolate cornea
Oblate cornea

Corneal topometry
Corneal asphericity on the elevation maps
Prolate/hyperprolate cornea
Spherical cornea
Oblate cornea

Corneal topometry
Corneal assymetry on the curvature maps
Normal corneal assymetry
Assymetry in ectatic cornea
Conic pattern in ECD

Corneal topometry
Corneal assymetry on the elevation maps
ECD – tounge-like extention
Horizontal corneal asymmetry in normal cornea
ECD – segmentary assymetry
*Corneal tomography in clinical practice (Pentacam System),
basics and clinical interpretation, 3rd edition (2019), Mazen M Sinjab

Corneal topometry
Topometric Indices
1. Index of Surface Variance (ISV): expression of corneal surface irregularities.
ISV >37 (abnormal); ISV > 41 (pathological)
2. Index of vertical asymmetry (IVA): difference between superior and inferior corneal curvature,
IVA >0.28 mm (abnormal), IVA > 0.32 mm (pathological)
3. Keratoconus Index (KI): The ratio between mean anterior radius in the upper and lower segment.
KI > 1.07 (abnormal and/or pathological)
4. Center keratoconus index (CKI): the ratio between mean anterior radius values in a peripheral
ring divided by a central ring. CKI > 1.03 abnorma/pathological
5. Index of height asymmetry (IHA): is calculated by the height data asymmetry comparison of the
superior and inferior area. IHA >19 µm (abnormal); IHA > 21 µm (pathological)
6. Index of height decentration (IHD): provides the degree of decentration in the vertical direction
in a central ring with radius 3mm. IHD >0.014 µm (abnormal); IHD > 0.016 µm (pathological)
7. Rmin: smallest radius on anterior sagittal map. Rmin < 6.71 mm (abnormal/pathological)

Part II
Interpretation of Pentacam parameters
- Factors of false findings
- Enantiomorphism
- 10 Steps of corneal parameters interpretation

Factors of false findings

ü False positives (false abnormal findings)
ü False negatives (false normal findings)
1. Contact lenses (soft)
Hot spot induced by soft contact lens
Hot spot

1. Contact lenses (rigid gas permable, RGP)
The two-difference map of a KC eye showing the flattening effect of an RGP
B
A C
A: immediately after removal of the lens
B: 16 days after removal of the lens
C: The change in curvature over the 16-day period

2. Misalignement
ü Patient error misalignment
ü Examiner‘s error misalignment
Clues of misalignment
ü QS: abnormal yellow? Red?
ü Km stability: (>0.3 D between captures)
ü Astigmatic dissociation: >1D and/or >10°
difference betwen MA and TA
ü Unusual pupil center cordinates: if X and/or Y
are ≥0.2 mm
ü Unusual TL coordinates: if X and/or Y of TL are
≥0.2 mm
ü Intereye asymmetry: ≥0.1 mm (in coordinates)
between two eyes
ü Assymetric patterns on the curvature, elevation
or pachymetry maps
QS
Km
Astig
Pupil center
Thin. location

Clinical sample
Misalignement

Possible misalignements for astigmatic cornea
Misalignement
Vertical SB
SB/SRAX
Horizontasl SB

3. Tear film disturbance
Tear film deficiency (Dry Eye)
Before the treatment After the treatment

3. Tear film disturbance
Tear film excess
Effect of excess tears on tomography
Excess tear situation Normal situation

4. Large angle Kappa or Lambda (angle K > 5°)
*nodal points (N, Nʹ), the entrance pupil (E)
and the center of rotation of the eye (C)
Shortly about eye axis and angles
Angles formed between various ocular axes
Pupillary axis
Optical axis
Visual axis Line of sight Fixation axis
α γ
λ
κ
Normal angle K is between 2-5°
5. Other factors of false findings
ü Corneal opacities and pathologies
ü Previous corneal surgeries
ü Bad exposure to the camera (anatomical features)
ü Pregnancy
*https://entokey.com/overview-of-the-eye/

Enantiomorphism

Those irregularities are:
When angle kappa is large:
- SB/SRAX
- Horizontal displacement of the TL
- Skewed hourglass
When the vertical component of angle kappa is large
- IS
- AB/IS
- Vertical displacement of the TL
- Skewed hourglass
When both components of angle kappa are large
- AB/SRAX
- Vertical-horizontal displacement of the TL
- Skewed hourglass
Enantiomorphism
ü ….is the phenomenon in which there is a mirror symmetry between the two eyes
in both tomographic shapes and values
ü This term is very important to study tomographical patterns
ü When in mirror shape cornea some irregularities exist, they may be considered as
normal

Enantiomorphism
Enantiomorphism in curvature maps Enantiomorphism in anterior elevation maps
Enantiomorphism in posterior elevation maps Enantiomorphism in pachymtery maps

Intereye corneal asymmetry score
Enantiomorphism

10 Steps of corneal parameters
interpretation

10 Steps of corneal parameters interpretation
*Simulated K (SimK): Simulated keratometry measurements
characterize corneal curvatures in the central 3-mm area
Km

Thinnest location

Astig

Anterior Sagittal Map

EM, anterior
EM, posterior
*EM = elevation map

*Simulated K (SimK): Simulated keratometry measurements
characterize corneal curvatures in the central 3-mm area

Part III
Pentacam and Ectatic corneal diseases (ECDs)
- Introduction of ECDs
- ECDs progression criteria

Introduction of ECDs

*Laser Vision Correction
Established Ectasia
ü Keratoconus (KC)
ü Pellucid marginal
degeneration (PMD)
ü Pellucid-like KC (PLK)
ü Keratoglobus
ü Post LVC* ectasia
Paraectasia
ü Forme fruste KC (FFKC)
ü Keratoconus suspect
(KCS)
Corneas with high
potentials
ü Posterior KC
ü Apparently normal corneas
(positive Family history)
ü Unclassified abnormal
Ectatic Corneal Diseases

Keratoconus (KC)
ü It is characterized by a combination of an abnormal anterior curvature map and
abnormal posterior elevation map.
ü KC may be also in thick corneas
ü Thin corneas don‘t have necessarily KC
Established Ectasia
Normal thin cornea (TL = 472 µm)
Curvature map Elevation map (front)
Pachymetry map Elevation map (back)
KC with normal thickness (TL = 570 µm)
Curvature map
Pachymetry map
Elevation map (front)
Elevation map (back)
570 µm 472 µm

PMD
ü It is characterized by a combination of a crab-clow pattern on the anterior curvature
map and an abnormal posterior elevation map
ü „Bell sign“ on the pachymetry map is the hallmark of PMD
Established Ectasia
Curvature map
Pachymetry map
Curvature map
Pachymetry map
„Bell sign“
„crab-clow“
„Bell sign“
„crab-clow“

PLK
ü It is characterized by a combination of a crab-clow pattern on the anterior
curvature map and an abnormal posterior elevation map
ü Not associated with „Bell sign“ on the pachymetry map
ü PLK should be monitored as it can be progressed to PMD
Established Ectasia
*Corneal Collagen Cross Linking, Mayen M. Sinjab, Arthur B. Cummings (2017)
Curvature map
Pachymetry map
Curvature map
Pachymetry map
NO „Bell sign“
„crab-clow“
„crab-clow“
„kissing -birds“
„kissing -birds“
NO „Bell sign“

Comparison between inferior keratoconus/pellucid-like keratoconus (PLK)
and pellucid marginal degeneration (PMD)

Keratoglobus
ü It is characterized by a generalized steepenning in the anterior curvature map and
generalized thinning extending from limbus to limbus
Established Ectasia
Curvature map
Pachymetry map

Differentiation of keratoconus (KC), pellucid marginal degeneration
(PMD), and keratoglobus (KG)

Note:
ü PMD is characterized by inferior band of thinning and bell sign on the pachymetry map
ü Neither crab-claw pattern nor kissing-birds sign is a hallmark of PMD as they can be seen
in the inferior type of KC
ü In advanced cases of PMD, there is an extrapolation in corneal tomography with a
limited analyzed area, which makes decision-making difficult in some management
modalities
ü Superior type of PMD has been also reported
ü KG is usually congenital and rarely acquired
ü Nothing specific in tomography in KG except for the generalized thinning extending from
limbus to limbus
ü KG, in its moderate forms, should be differentiated from KC and PMD

Post LVC ectasia
ü It usually occurs post LASIK and rarely post-PRK
ü Can have a pattern of any ECDs
Established Ectasia
Pachymetry map
Curvature map

FFKC and KCS
ü Can be described by abnormal anterior curvature map with a normal posterior
elevation map
ü BAD cannot detect FFKC and KCS
Paraectasia
Paraectasia with a normal BAD display
BAD
Curvature map
Pachymetry map
FFKC
D = 1.96

Posterior KC (KC posticus/“subclinical KC“)
ü It is characterized by thinning of the posterior cornea without ectasia of the
anterior cornea
ü It can be also acquired as a result of corneal trauma
ü „Subclinical“ KC can be unilateral or asymmetric bilateral and progresses if
untreated
Corneas with high potential
Apparently normal corneas
ü Eyes of tomographically normal corneas with positive family history of an ECDs
Unclassified abnormal corneas
ü Abnormal corneas which do not meet the criteria of ECDs

ECDs Progression Criteria
Note: Kmax is being used to detect or document ectatic progression and is regularly used as an indicator efficacy or failure. There is still no
normative data for Kmax yet, it‘s location is important
Parameters used in the literature to define progression of ECDs

Thank you
Eye_dr_tuti
Eye_dr_tuti

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