This document discusses recent advances in diagnosis of glaucoma. It describes various techniques used to measure intraocular pressure such as Goldmann applanation tonometry and new rebound and contour tonometers. It also discusses anterior chamber angle assessment tools like gonioscopy, ultrasound biomicroscopy, and anterior segment optical coherence tomography. Imaging techniques for evaluating the optic disc and retinal nerve fiber layer are discussed, including confocal scanning laser ophthalmoscopy, scanning laser polarimetry, and optical coherence tomography.

1. Recent Advances in Diagnosis of
Glaucoma
Dr Harpreet Kaur
Dept of Ophthalmology
Govt Medical College
Amritsar

2. • Chronic, progressive optic neuropathy
characterised by optic disc retinal nerve fibre
layer changes with corresponding visual field
defects and IOP as a major risk factor.
• It is the second leading cause of blindness
globally, so early diagnosis has become a
necessity to treat this preventable cause of
blindness.

3. Tonometry
• GAT (Goldmann
Applanation Tonomtery)
– Still the gold standard

5. • Many devices are coming up for measurement
of IOP
– Rebound Tonometer
– Dynamic Contour Tonometer
• Indentation tonometry: highly dependent on
rigidity of ocular tissue
– Hard cornea: high readings, soft: low readings
• Newer techniques don’t influence corneal
biomechanical properties

8. Advantages-
• Requires a short training period
• Useful in children as
– No anaesthesia is required
– Better tolerated than GAT

9. • Corneal thickness independent tonometry
– Dynamic Contour Tonometer
– Ocular Response Analyzer

10. DCT
• Measures IOP & OPA
(Ocular Pulse Amplitude)
• Principle: when the
contours of the cornea
and tonometer match,
then the pressure
measured at the surface
of the eye equals the
pressure inside the eye

12. Ocular Response Analyser(ORA)
• Provides IOP measurement free from
influence of corneal biochemical
properties
• It measures corneal hysteresis & corneal
resistance factor & thus overcomes the
demerits of GAT to some extent

13. Ocular Response Analyzer
It directs the air jet against the cornea and measures not one but two
pressures at which applanation occurs
• 1) when the air jet flattens the cornea as the cornea is bent inward
and 2) as the air jet lessens in force and the cornea recovers.

14. Ocular response analyser
• The first is the resting intraocular pressure.
• The difference between the first and the second
applanation pressure is called corneal hysteresis
• Corneal hysteresis is a measure of the viscous
dampening and, hence, the biomechanical properties
of the cornea.
• The biomechanical properties of the cornea are related
to corneal thickness and include elastic and viscous
dampening attributes.

15. • IOP correlate well with Goldmann tonometry but, on average,
measure a few millimeters higher.
• Further , while IOP varies over the 24-hour day, hysteresis
seems to be stable.
• Congdon et al found that a ‘low’ hysteresis reading with the
ORA correlates with progression of glaucoma, whereas thin
central corneal thickness correlates with glaucoma damage.
• It has practical value in the management of glaucoma.

16. Anterior Chamber Angle Assessment
• Gonioscopy
• Imaging Techniques
– Anterior Segment Optical Coherence Tomography
(ASOCT)
– Ultrasound Biomicroscopy (UBM)
– Pentacam
– Scanning Peripheral Anterior Chamber Depth
Analyzer (SPAC)

17. Optical coherence tomography
• Optical Coherence Tomography, or OCT, is a
noncontact, noninvasive imaging technique used to
obtain high resolution cross-sectional images of the
retina and anterior segment.
• Three-dimensional imaging technique with ultrahigh
spatial resolution
• Measures reflected light from tissue discontinuities
• Based on interferometry
– involves interference between reflected light and
a reference beam.

18. Optical coherence tomography-The process is
similar to that of ultrasonography, except that light is used instead of
sound waves.
Analog to
ultrasound

19. Anterior segment optical coherence
tomography (OCT)
• High-speed anterior segment optical
coherence tomography (OCT) offers a non-
contact method for high resolution cross-
sectional and three-dimensional imaging of
the cornea and the anterior segment of the
eye.
•Anterior Segment Optical Coherence Tomography
enhances surgical planning and postoperative care
for a variety of anterior segment applications by
expertly explaining how abnormalities in the anterior
chamber angle, cornea, iris, and lens can be
identified and evaluated

20. Applications in Glaucoma
• Angle Imaging
• Screening for angle closure
• Studying the effect of Peripheral Iridotomy
• Imaging of blebs
• Analysis of tube position in implant surgeries
• Pachymetry

21. Advantages
• Non-contact
– No possibility of indentation, so no corneal
abrasion or punctate epithelial erosion as seen in
UBM
• Shorter imaging time
• Rapid image acquisition
• More physiological as pt is sitting upright

22. Limitations
• Not able to penetrate pigmented iris
epithelium
• Ciliary body, zonules not visualised clearly

23. Image shows an anterior-chamber angle as viewed
with gonioscopy and the OCT
The latter replaces subjective evaluation with objective
measurement.

24. A narrow angle is apparent with OCT imaging, in
this case 9.5°.

25. With the increase in popularity of anterior
chamber imaging, and anterior segment
OCT proving to be the best tool for high
resolution biometry, Anterior Segment
Optical Coherence Tomography is a must-
have for anterior segment, refractive,
cornea, and glaucoma surgeons.

26. Scanning Peripheral AC Depth Analyser
(SPAC)
• Takes consecutive slit lamp images from
optical axis of the eye to the limbus
• Images are captured on a charge-coupled
device camera by the computer
• Total of 21 images are taken of AC depth at 0.4
mm intervals & converted into numerical and
categorical grades by comparison with
normative database

28. PENTACAM
• Rotating Scheimpflug camera
images the ant segment from
cornea to post surface of lens
in 3 dimensions
• Limitations
– As the angle recess can’t be
directly visualised, does not
allow any angle assessment in
detail.
– AC angle width is extrapolated
from corneal endothelium & ant
iris surface

29. Imaging Techniques for optic Disc
and RNFL evaluation in glaucoma
• 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 )

30. Heidelberg Retina Tomography (HRT)
• Diagnostic procedure
• Allows three-dimensional
topographic analysis of optic
disk and retina
• Provides rapid and reproducible
measurements of optic disk
topography on a pixel-by-pixel
basis, as well as a reproducible
analysis of various optic disk
parameters.
• Disc area, Rim area, Cup area

31. Why HRT ????
• Functional and Structural Diagnosis
• Glaucoma diagnosis in clinical practice has
been traditionally based on IOP, visual fields
and subjective assessment of optic disc, but
these methods have many limitations

32. • IOP
■ Large overlap between healthy and
glaucomatous eyes
■ Corneal thickness affects accuracy (thicker
cornea have high IOP & thinner have LOW
IOP)
■ IOP fluctuates
■ Many glaucoma patients have normal IOP

33. • Visual Fields
■ Poor sensitivity for early detection
■ Highly variable (affetced by age , media
opacity)
■ In fact, OHTS reports that 86 % of visual field
abnormalities were not replicated on retesting
■ Subjective---(handicapped pt unable to
perform)

34. Subjective Assessment of the
Optic Disc
■ Poor agreement on interpretation , even
among experts
■ Progression missed in up to 50 % of time by
experts
■ Time consuming
■ Subjective

35. • Therefore, an objective structural
assessment of optic disc is necessary.
• HRT is proven to be as good or better than
expert readers of optic disc photographs
and provides fast, objective assessment of
complete optic nerve head structure
including retinal nerve fiber layer.
• In addition, HRT provides an objective
validated statistical analysis to show
glaucomatous progression

36. Early Detection: Optic Disc Changes
First
Ocular Hypertension Treatment
Study (OHTS), analyzed
glaucoma diagnosis and
treatment of ocular hypertensive
patients. Study showed 55 % of
glaucoma patients optic disc
changes could be measured
first,35 % VF changes could be
detected first. Results
demonstrate analysis of optic
nerve head structure is a pivotal
aspect of glaucoma diagnosis,

37. • HRT enables quantitative evaluation of all
relevant anatomical structures – cup, rim
and RNFL (retinal nerve fiber layer). With
highest spatial resolution of any imaging
device for glaucoma diagnosis, HRT provides
comprehensive data for glaucoma detection
and follow-up assessment

38. Complete ONH Assessment
HRT checks all vital structure of optic nerve head:
CUP
■ C/D Ratio
■ Shape
■ Asymmetry
RIM
■ Area & Volume
■ Asymmetry
RNFL
■ Height Variation Contour
■ Thickness
■ Asymmetry

39. HRT II Printout

40. Topography Image
• False color image
• Similar to gray scale of VF printout
• Provides size shape,and location of cup
• Elevated area typically appear darker
• Lighter color represent
depressed regions

41. • Topography image and is classified as
• small (disc sizes less than 1.6 mm2)
• Average (1.6 mm2–2.6 mm2)
• Large (greater than 2.6 mm2)
• This section also provides two Cup-related
parameters, Cup/Disc Area Ratio and Cup Shape
Measure
• Along with actual parameter measurements, a
symmetry measure between eyes is also given
• This is ratio expressed as a percentage of OD/OS

42. Normative Stereometric Parameters
PARAMETER NORMAL EARLY MODERATE ADVANCED
Disc Area
(mm2)
2.257 ± 0.563 2.345 ± 0.569 2.310 ± 0.554 2.261 ± 0.461
Cup Area
(mm2)
0.768 ± 0.505 0.953 ± 0.594 1.051 ± 0.647 1.445 ± 0.562
Rim Area
(mm2)
1.489 ± 0.291 1.3 93 ±0.340 1.260 ± 0.415 0.817 ± 0.334
Cup Volume
(mm3)
0.240 ± 0.245 0.294 ± 0.270 0.334 ± 0.318 0.543 ± 0.425
Rim Volume
(mm3)
0.362 ± 0.124 0.323 ± 0.156 0.262 ± 0.139 0.128 ± 0.096
Cup/Disc Area
Ratio
0.314 ± 0.152 0.380 ± 0.179 0.430 ± 0.203 0.621 ± 0.189

43. PARAMETER NORMAL EARLY MODERATE ADVANCED
Mean Cup
Depth (mm)
0.262 ± 0.118 0.279 ± 0.115 0.289 ± 0.130 0.366 ± 0.182
Maximum Cup
Depth (mm)
0.679 ± 0.223 0.680 ± 0.210 0.674 ± 0.249 0.720 ± 0.276
Cup Shape
Measure
-0.181 ± 0.092 -0.147 ± 0.098 -0.122 ± 0.095 -0.036 ± 0.096
Height
Variation
Contour (mm)
0.384 ± 0.087 0.364 ± 0.100 0.330 ± 0.108 0.256 ± 0.090
Mean RNFL
Thickness
(mm)
0.384 ± 0.063 0.217 ± 0.076 0.182 ± 0.086 0.130 ± 0.061
RNFL Cross-
Sectional
Area (mm2)
1.282 ± 0.328 1.155 ± 0.396 0.957 ± 0.440 0.679 ± 0.302

44. OU QUICKVIEW New Print Report
• All parameter values
automatically adjusted for
age-related changes, and
also for their correlation
with optic disc size.
• Results in greatly reduced
normative range for each
parameter , making
comparisons to normative
database using ethnic-
specific which more
sensitive for detecting
abnormalities.

45. • Classification symbol also based on the p
value
• If the parameter within the 95% normal
range (p>.05), Green√ -- within normal
range
• Between 5th &0.1 percentile of normal
distribution (p<.05 &>0 .001), yellow !
point -- borderline
• p value < 0.1 percentile of normal
distribution, red X -- outside normal limits--
means that < 0.1% (1 out of 1,000) of all
normal from the database have values this
low, indicate high probability of abnormality

46. • Contour height graph presented with 95%
normative range superimposed in green
• Lightly colored solid line gives average value for
specific age , optic disc size & ethnicity
• Yellow area represents values between 5th and
0.1 percentile of normal distribution (p< .05
and greater than .001) indicating a borderline
classification
• Red area represents < 0.1 percentile of normal
distribution outside normal limits.

47. • Mean RNFL thickness, &inter-eye symmetry
• Inter-eye symmetry is r value of Pearson
Product Correlation coefficient obtained by
correlating right and left eyes point by point
along this graph.
• Two contour height graphs plotted together
Solid black line gives OD profile & dashed
line gives OS profile.

48. Scanning Laser Polarimetry
• Glaucoma is characterized by loss of retinal
ganglion cells and their axons i.e. retinal nerve
fiber layer (RNFL).
• Several studies have shown that changes in
optic nerve head (ONH) and retinal nerve fiber
layer (RNFL) precede the visual field loss by
several years.
• Thus, RNFL examination helps in early
diagnosis of glaucoma.

49. Principle
• Scanning laser polarimetry (SLP) is designed to
quantitatively assess the thickness of the
peripapillary RNFL.
• It is based on the measurement of a physical
property called retardation of an illuminating
laser beam passing through the birefringent
RNFL.
• Birefringence in the nerve fiber layer arises
from the parallel arrangement of microtubules
within the axons of this layer.

50. • A 780-nm diode confocal scanning laser with
an integrated polarimeter is focused on the
retina.
• The backscattered light that doubly passes
through the RNFL shows retardation that is
measured by a polarization detection unit.
• The total data acquisition takes 0.7 seconds.
• Three images of each eye are obtained. Each
image measures 20 × 20 degrees and contains
(256 × 256) pixels.
• A reflectance image of the scanned image is
produced.

51. • These are displayed in a color-coded
map. Areas of high retardation are
displayed in yellow and areas of low
retardation displayed in blue.
• The operator outlines the optic disc
margin and retardation values are
automatically generated along a 10
pixel-wide ellipse, concentric with
and 1.75 times larger than the disc
diameter.
• The thickness values along the
perimeter of the ellipse are then
plotted as a cross-sectional graph
(TSNIT).

53. • Patient’s identification data
• Image quality score : Scores of 7 or higher
are considered to be of good quality,
while scores less than 7 should be
interpreted with caution.

54. Fundus Image
• The Fundus Image is a
reflectance image depicting
a 20° x 20° image of the posterior pole.
• The GDx utilizes more than 16,000 data points from
the scan area to produce and display the Fundus
Image showing the optic nerve head.
• This image allows the initial quality evaluation of the
scan to determine if it is adequate for further analysis
and is used for centering the ONH ellipse

55. Nerve Fiber Layer Map
• The Nerve Fiber Layer Map is a color map
depicting the different RNFL levels in the 20° x
20° area surrounding the optic nerve head
(ONH).
• This image presents the phase shift generated
by RNFL thickness and its structural
organization.
• RNFL is represented using a color scale, with
dark blue representing smaller RNFL values
(smaller phase shift) and generally bright red
representing larger RNFL values (greater phase
shift).

56. • A typical normal pattern is characterized by
bright yellows and reds (thicker) in the superior
and inferior sectors, and greens and blues
(thinner) in the nasal and temporal sectors.

57. • Symmetry Analysis report, the TSNIT
(Temporal-Superior-Nasal-Inferior-Temporal)
nerve fiber layer graph displays the normal
range (shaded area) and patient’s values of
RNFL developed from the measurement data
obtained along the Calculation Circle.

58. • The green plot displays the right
eye (OD), and the purple plot
displays the left eye (OS).
• The left side of the graph starts
the plot from the Calculation
Circle, beginning at the temporal
side of the retina.
• As the map progresses to the right
it plots the RNFL values obtained
by tracing around the Calculation
Circle, passing through the
Temporal, Superior, Nasal, Inferior,
and then back to the Temporal
positions.

59. Parameters Table
• It presents parameters
computed from the
Calculation Circle and they are
compared to values
from the normative database.
• Values are color- coded to
indicate deviation from
normal, as in the Deviation
Map.

60. • TSNIT Average :This parameter evaluates the
average RNFL (μm) in the Calculation Circle.
( Normal 46 -68 μm)
• Superior Average: This is the average of all
pixels (μm) in the superior 120 degrees of the
Calculation Circle. ( Normal 55 - 85 μm)

61. • Inferior Average : This is the average of all pixels
(μm) in the inferior 120 degrees of the
Calculation Circle.
( Normal 40 - 75 μm)
• TSNIT Std. Dev. (Standard Deviation) : This
number represents the standard deviation of the
values contained in the Calculation Circle. The
higher the number, the greater the modulation
of the double-hump pattern.

62. Inter-Eye Symmetry
• This is the correlation of corresponding points in
the TSNIT data for right and left eyes.
• The closer the ratio is to 1.0, the more symmetric
the nerve fiber layer.
• If only one eye is evaluated, this value is not
shown.

63. • The Nerve Fiber Indicator (NFI)
for GDx is an algorithm that
analyzes the entire RNFL profile.
• The NFI is an indicates the
likelihood that the polarimetric
retinal nerve fiber layer map is
abnormal.
• A higher number is more likely to
be related to abnormality, but is
not definitive NFI (Nerve Fiber
Indicator)

65. Advantages
• Easy to operate
• Does not require pupillary dilation
• Comparison with age matched normative
database
• Good reproducibility
• Does not require a reference plane.

66. Limitations
• Affected by anterior and posterior segment
pathologies.
• Does not measure actual RNFL thickness
• Limited use in moderate/advanced glaucoma.
• Difficult in nystagmus, very small pupil and media
opacities.
• Requires wider database for Indian population.
• Young patients database not available.
• Backward compatibility not present.

67. OCT
• Objectively measures RNFL thickness & optic
disc parameters
• Helps in diagnosis of glaucoma and also to
assess the progression of the disease

68. Glaucoma Scans
When evaluating the glaucoma suspect or the
glaucoma patient, two parameters that the
ophthalmologist is interested in are the
characteristics of the optic nerve cup and the
thickness of the nerve fiber layer surrounding
the optic nerve head
• The Fast Optic Disc scan
• The Fast RNFL Thickness scan

69. The Fast Optic Disc scan
The optic cup profile can be evaluated by capturing a
"Fast Optic Disc" scan
The patient fixes on the target, which is automatically
placed at the edge of the scan window so that the
optic nerve is viewed toward the center of the video
window. The operator then moves the scan so that
the star pattern is centered on the optic nerve
head. Centering can be aided by clicking on the scan
window to view the white centering lines.

71. The optic nerve scan can be analyzed with the
"optic nerve head analysis" protocol

72. Advantages
• Measures RNFL thickness without the need for
a reference plane or magnification correction
• RNFL, Optic Disc and Macula scans are
available in one instrument

73. The Fast RNFL Thickness scan
Nerve fiber layer thickness can be evaluated with the
"Fast RNFL Thickness" scan. This is a circular scan
that requires the operator to place the circle so that
the center of the circle is centered on the optic nerve
head.

74. The analysis software places lines on the top and
bottom of the nerve fiber layer and the distance
between the two lines is interpreted to be the
thickness of the nerve fiber layer

75. Care must be take to make sure that the image is
captured with the circle centered on the optic nerve
The placement of the circle can make a big difference
in the analysis of the nerve fiber layer thickness

76. These two scans (OD) are of a normal eye. The scan in
the first analysis is well centered and the RNFL
thickness falls within the normal range. The scan in
the second analysis is of the same eye (OD), but the
scan is not well centered. The analysis is abnormal
(black arrows).