The document discusses two imaging techniques used to detect glaucoma - HRT (Heidelberg Retinal Tomography) and GDx (scanning laser polarimetry). HRT uses confocal scanning laser ophthalmoscopy to generate a 3D topographic image of the optic disc and retinal nerve fiber layer. GDx measures the retinal nerve fiber layer thickness around the optic disc using scanning laser polarimetry, which analyzes the polarization of light passing through the birefringent retinal nerve fiber layer. Both provide objective measures of the optic disc and retinal nerve fiber layer but have limitations such as dependency on accurate contour line placement for HRT.

1. HRT and GDx
SIVATEJA CHALLA

2. INTRODUCTION
Normal methods of detecting glaucoma:
1. IOP measurement
2. Optic disc observation
3. Functional assessment : Visual field assessment
4. Structural assessment : Assess the structure of optic nerve and/or RNFL: By
Imaging :
 Confocal scanning laser ophthalmoscopy ( HRT ; Heidelberg Retinal
Tomography ;Heidelberg Engineering, Heidelberg, Germany )
 Scanning Laser polarimetry(GDx ; Carl Zeiss Meditec , Dublin , California , USA
)
 Optical Coherence Tomography ( OCT ; Carl Zeiss Meditec)

4.  Changes in RNFL and optic nerve head may precede the VFD.
 ONH can be scanned with HRT and OCT
 The nerve fiber layer can be scanned with GDX and OCT
 macula can be scanned with OCT
 In advanced glaucoma:
1- Scanning computerized ophthalmic diagnostic imaging play a least
prominent role.
2– VF testing is more appropriate to assess disease progression.

5. HRT

6. LAYOUT
 Introduction
 Principle
 How to read print and Different parameters
 Limitations

7. INTRODUCTION
 Non quantitative methods like disc photography, measurement of CDR
require subjective physician interpretation and can be difficult and time-
consuming in a busy clinical practice.and also observer dependent
 Have to provide a more objective method to detect changes and
progression

8.  The culmination of these efforts has resulted in the development of
confocal scanning laser ophthalmoscopy, which provides rapid,
noninvasive, non contact imaging of the disc.
 Provides three-dimensional topographic analysis of optic disk

9. PRINCIPLE
 Confocal scanning laser ophthalmoscopy
 Uses laser light instead of a bright flash of white
light to illuminate the retina (670 nm diode laser)
 Laser is used as light source & beam focused to
one point of examined object
 Reflected light go same way back through optics &
separated from incident laser beam by beam splitter
&deflected to detector
 This allow to measure reflected light only at one
individual point of object

11. What the HRT does
 Once the patient is positioned, HRT II automatically performs a pre-scan
through the optic disc to determine the depth of the individual’s optic nerve.
 Next, it determines the number of imaging planes to use (range of scan
depth 1-4mm)
 Each successive scan plane is set to measure 0.0625 mm deeper
 Automatically obtains three scans for analysis.
 Aligns and averages the scans to create the mean topography image

12.  A series of 32 confocal images, each 256 X 256
pixels, is obtained in a duration of 1.6 seconds.
 Computer converts 32 confocal images to a single
topographic image in approximately 90 seconds

13. Print out
A. PATIENT DATA
B.TOPOGRAPHY
C.HORIZONTAL
HEIGHT PROFILE
D.VERICAL
HEIGHT PROFILE
E.REFELCTION IMAGE
H.TOP FIVE PARAMETERS
F.MEAN HEIGHT
CONTOUR GRAPH
G.MOORFIELDS
REGRESSION
ANALYSIS

14. A.Patient data
 Provides information on exam type (baseline or
follow-up), patient demographic information
(patient name , age, gender, ethnicity, etc.), and
basic image information including image focus
position, and whether astigmatic lenses were used
during acquisition.

15. B.Topography image
 HRT draws a color-coded map.
 give an overview of the disc.
 Red  cup
 Green or Blue  NRR tissue
Bluesloping rim Green nonsloping rim tissue

16. Also gives disc size
small (sizes less than 1.6 mm2) Average (1.6 mm–2.6 mm2) Large (greater than 2.6 mm2)

17. C.HORIZONTAL HEIGHT PROFILE
 Height profile along the white horizontal line in the topography image.
 The subjacent reference line (red) indicates the location of the reference
plane (separation between cup and neuroretinal rim).
 The two black lines perpendicular to the
height profile denote the borders
of the disc as defined by the contour line.

18. D.VERTICAL HEIGHT PROFILE
 Height profile along the white vertical line in the topography image.
 The subjacent reference line (red) indicates the location of the reference
plane (separation between cup and neuroretinal rim).
 The two black lines perpendicular to the height profile denote the borders
of the disc as defined by the contour line.

19. E.REFELCTION IMAGE
 False-color image that appears similar to a
photograph of the optic disc
 Darker areas are regions of decreased overall
reflectance, whereas lighter areas, such as the base
of the cup, are areas of the greatest reflectance
 Valuable in locating and drawing the contour line
around the disc margin
 In the reflection image the optic nerve head is divided
into 6 sectors.
 Depending on this patient’s age and overall disc size the
eye is then statistically classified as.

20. F.MEAN CONTOUR HEIGHT GRAPH
 After the contour line is drawn around the border of the optic disc, the
software automatically places a reference plane parallel to the peripapillary
retinal surface located 50 μm below the retinal surface
 The reference plane is used to calculate the thickness and cross-sectional
area of the retinal nerve fiber layer
 The parameters of area and volume of the neuroretinal rim and optic cup
are also calculated based on the location of the reference plane. cup 
area of the image that falls below the reference plane, neuroretinal rim 
above the reference plane

21.  Green contour line should never go below red reference plane . If it does,
then contour line is likely not in proper position
 The graph depicts, from left to right: the thicknesses of the temporal (T);
temporal-superior (TS); nasal-superior (NS); nasal (N); nasal-inferior (NI);
temporalinferior(TI); and temporal (T) sectors.
 the thickness of the normal retina is irregular, the contour line will appear
as what is known as the ‘double-hump.’ The hills or ‘humps’
correspond to the superior and inferior nerve fiber layer, which are
normally thicker than the rest of the areas.
Reference line
Retinal surface height profile

22. G.MOORFIELDS REGRESSION ANALYSIS

23. H.Stereometric analysis
If the SD is greater than 40 µm, the test should be
repeated to improve reproducibility or the results
should be interpreted with caution.

25. Difference in follow up report

26. Normal values of the HRT II
stereometric parameters

27. So…

28. Patient information
Quality score
C/D Ratio
Cup shape measurement
Rim area
Rim volume
TSNIT graph

29. Follow-Up Report
 Baseline exam, and length of time in months
between reports compared
 Topography image red indicate worse area
and green indicate improved area

30. Glaucoma Probability Score (GPS)
 new software included in the HRT 3 generation allows calculation of the
GPS
 MRA is replaced by GPS.
 Shows the probability of damage
 Fast, simple interpretation
 Based on the 3-D shape of the optic disc and RNFL
 Utilizes large, ethnic-selectable databases
 Employs artificial intelligence: Relevance Vector Machine
 No drawing a contour line or relying on a reference plane
 Reduced dependency on operator skill

31.  unlike the MRA, the GPS utilizes the
whole topographic image of the optic
disc, including the cup size, cup depth,
rim steepness, and horizontal/vertical
RNFL curvature whereas the MRA uses
only a logarithmic relationship between
the neuroretinal rim and optic disc areas.

33. Limitations
 The contour line (which is a subjective determination of the edge of the
disc) and the reference plane set by the device to delineate cup from
rim, are the two main sources of error in this technology.
 Because these determinations may be incorrect, this makes the HRT II not
a good on-the-spot diagnostic device. However, in sequential analyses,
these sources of error remain constant and the device is good to measure
change over time.

34.  Moorfields Regression Analysis Can Discriminate Glaucomatous Nerves
From Normals With 84.3% Sensitivity And 96.3% Specificity.
 How Ever These Problems Were Solved In Hrt3 Where Gpa Software Is
Used.
 The HRT Will Occasionally Call A Severely Damaged Optic Nerve Normal
Or A Normal Optic Nerve Abnormal.
 Heidelberg Retina Tomography Tends To Overestimate Rim Area In
Small Optic Nerves And To Underestimate Rim Area In Large Nerves.
So On Either Extreme Of Disc Size Range, Care Should Be Taken When
Analyzing These Scans.

35. GDx VCC

36. INTRODUCTION
 GDX evaluates the site of damage before the patients experience any vision
loss
 GDX is:
- Simple to use and easy for both the patient and operator.
- Near infra-red wavelength(780 nm)
- Measurement time is 0.7 seconds.
- Total chair time less than 3 minutes for both eyes.
- Undilated pupils work best.
- Painless procedure.
- Doesn’t require any drops.
- Completely safe.

37.  The GDx :
- maps the RNFL and compares them to a database of healthy,glaucoma-free patients.
- Analyses the RNFL thickness around the optic disc
 Sensitivity of 89% and a specificity of 98%.
 GDx VCC should be added to the standard clinical examination to
compliment the information from these other methods

38. PRINCIPLE - scanning laser polarimetry
 Scanning laser polarimetry is an imaging technology that is utilized to measure
peripapillary RNFL thickness
 based on the principle of birefringence
 main birefringent intraocular tissues are the cornea, lens and the retina
 In the retina, the parallel arrangement of the microtubules in retinal ganglion cell
axons causes a change in the polarization of light passing through them.
 The change in the polarization of light is called retardation
 The retardation value is proportionate to the thickness of the RNFL

39.  Light polarized in one plane travels
more slowly through the birefringent
RNFL than light polarized
perpendicularly to it.
 This difference in speed causes a
phase shift (retardation) between the
perpendicular light beams.

40.  VCC stands for variable corneal
compensator, which was created to
account for the variable corneal
birefringence in patients
 Uses the birefringence of Henle’s
layer in the macula as a control for
measurement of corneal
birefringence

41. GDx VCC

42. GDx print out

43. A.Patients information
 Patient data and quality score: the patient’s name,
date of birth, gender and ethnicity are reported. An
ideal quality score is from 7 to 10

44. B.FUNDUS IMAGE
 The fundus image is useful to check for image quality:
 Every image has a Q score representing the overall quality of the scan
 The Q ranges from 1-10, with values 8-10 representing acceptable quality.
 This score is based on a number of factors including :
-Well focused,
- Evenly illuminated,
- Optic disc is well centered,
- Ellipse is properly placed around the ONH.

45.  The Operator Centers The Ellipse Over The
ONH In This Image
 The Ellipse Size Is Defaulted To A Small
Setting But Manipulating The Calculation
Circle Can Change The Size Of The Ellipse
 The Calculation Circle Is The Area Found
Between The Two Concentric Circles, Which
Measure The Temporal-superiornasal-inferior-
temporal (TSNIT) And Nerve Fiber Indicator
(NFI) Parameters
 By Resizing The Calculation Circle And
Ellipse, The Operator Is Able To Measure
Beyond A Large Peripapillary Atrophy Area

47. C.RNFL thickness map
 The thickness map shows the RNFL thickness in a color-coded format from blue to
red.
 Hot colors like red and yellow mean high retardation or thicker RNFL
 cool colors like blue and green mean low retardation / thinner RNFL
 A healthy eye has yellow and red colors in the superior and inferior regions
representing thick RNFL regions and blue and green areas nasally and temporally
representing thinner RNFL areas.
 In glaucoma, RNFL loss will result in a more uniform blue appearance

49. D.Deviation maps
 The deviation map reveals the location and magnitude of RNFL defects
over the entire thickness map
 RNFL thickness of patient is compared to the age-matched normative
database
 Dark blue squares RNFL thickness is below the 5th percentile of the
normative database
 Light blue squares deviation below the 2% level
 Yellow deviation below 1%
 Red deviation below 0.05%.

51. E.TSNIT map
 TSNIT stands for Temporal-Superior-Nasal-Inferior-Temporal
 TSNIT displays the RNFL thickness values along the calculation circle
 In a normal eye the TSNIT plot follows the typical ‘double hump’ pattern,
with thick RNFL measures superiorly and inferiorly and thin RNFL values
nasally and temporally
 In a healthy eye, the TSNIT curve will fall within the shaded area which
represents the 95% normal range for that age
 When there is RNFL loss, the TSNIT curve will fall below this shaded area,
especially in the superior and inferior regions

52.  In the center of the printout at the bottom, the TSNIT graphs for both eyes are
displayed together.
 healthy eye there is good symmetry between the TSNIT graphs of the two eyes
and the two curves will overlap
 in glaucoma, one eye often has more advanced RNFL loss and therefore the two
curves will have less overlap

53. F.Parameters table
 The TSNIT parameters are summary measures
based on RNFL thickness values within the
calculation circle
 Normal parameter values are displayed in green
 abnormal values are color-coded based on their
probability of normality.colours are similar to
deviation maps.

54.  TSNIT Average: The average RNFL thickness around the entire calculation circle
 Superior Average: The average RNFL thickness in the superior 120° region of the
calculation circle
 Inferior Average: The average RNFL thickness in the inferior 120° region of the
calculation circle
 TSNIT SD
 Inter-eye Symmetry Values range from –1 to 1, Normal eyes have good symmetry with
values around 0.9

55. The Nerve Fiber Indicator (NFI)
 Global measure based on the entire RNFL thickness map
 Calculated using an advanced form of neural network, called
a Support Vector Machine (SVM)
 Not colour coded
 Output values range from 1 –100
 1-30 -> low likelihood of glaucoma
 31-50 -> glaucoma suspect
 51+ -> high likelihood of glaucoma
Clinical research has shown that the NFI is
the best parameter for discriminating normal
from glaucoma

56. Serial Analysis
Detecting RNFL Change Over Time
 Serial Analysis can compare up
to four exams
 The Deviation from Reference
Map displays the RNFL
difference, pixel by pixel, of the
followup exam compared to the
baseline exam

57. LIMITATIONS
 Eyes with macular pathology may show wrong RNFL values due to
improper anterior segment birefringence (ASB) compensation at macula
 ASB may get altered after refractive surgery,so do fresh macular scan to
compensate for changes
 Large disc,large areas of PPA,affect RNFL,so use large scan circle

58. Early Glaucoma Example moderate Glaucoma Example advanced Glaucoma Example

60. CONCLUSIONS
 The ability to detect early glaucomatous structural changes has great potential
value in delaying and avoiding progression of the disease
 the most difficult optic discs to interpret in terms of glaucomatous changes–
specifically highly myopic and tilted optic discs – are also those discs which
optic nerve imaging devices have the greatest limitations in discriminating
abnormality from pathology
 should not be regarded as replacing the skilled ophthalmologist’s capacity to
evaluate all aspects of the patient’s diagnosis.
 but they can definitely aid in the complicated decision-making process

61. THANK YOU

62. Topographic Change Analysis (TCA)
 Statistically-based progression algorithm that accurately detects structural
change over time by comparing variability between examinations and
providing a statistical indicator of change.
 Aligns subsequent images with the baseline examination, providing a
point-by-point analysis of the optic disc and peripapillary RNFL