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)
3.
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.
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
10.
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
Bluesloping 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
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.
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.
32.
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.
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
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
46.
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
48.
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%.
50.
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
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
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
Notas do Editor
This laser, which is not powerful enough to harm the eye, is first focused on the surface of the optic nerve and captures that image. Then it is focused on the layer just below the surface and captures that image. The HRT continues to take images of deeper and deeper layers until the desired depth has been reached. Finally, the instrument takes all these pictures of the layers and puts them together to form a 3-dimentional image of the entire optic nerve.
Any ONH that is determined to be “outside normal limits” is not necessarily glaucomatous but is statistically outside the normal ranges
for the group of eyes in the normative database. The decision as to whether “outside normal limits” represents “glaucoma” is a clinical judgment made by considering all
clinical information together.
MRA makes use of the relationship between log neuroretinal rim area and optic disc area to define the normal ranges.
Figure 3.2 illustrates the linear regression line between log neuroretinal rim area and optic disc area (marked “50%”). This is the “average” or “predicted” relationship between log neuroretinal rim area and optic disc area. The lower three lines represent the lower 95.0%, 99.0%, and 99.9% prediction intervals for the same relationship. Thus, for the 95.0% prediction interval, 95.0% of normal eyes would be expected to have a neuroretinal rim area above that interval line. The same reasoning applies to the 99.0% and 99.9% prediction intervals. These intervals are calculated for the ONH as a whole and for each of the six predefined sectors.
The prediction intervals for neuroretinal rim areashould be regarded in the same way as theprobability smbols for abnormality in the reportsfrom automated perimeters. The closer the top ofthe green bar gets to the lower prediction intervals,the greater the probability that the rim area isabnormal.The MRA Report given in the HRTIIsoftwareenables a visual inspection of where the neuroretinal rim area lies in relation to thenormal ranges .