This document discusses newer tests for diagnosing glaucoma, including dynamic contour tonometry, ocular response analyzer, rebound tonometry, anterior segment optical coherence tomography, and various imaging techniques and tests for assessing the optic nerve, retinal nerve fiber layer, visual fields, and detection of apoptosing retinal cells. These newer tests aim to detect glaucoma earlier and more accurately than traditional tests like Goldmann applanation tonometry.

1. NEWER TESTS FOR GLAUCOMA
By Dr.Shruthy Vaishali
Moderator – Prof. Dr.K.N.Jha
Dr.A.R.Rajalakshmi

2. • Glaucoma is one of the leading causes of
blindness worldwide. Early diagnosis of
glaucoma is critical to prevent permanent
structural damage and irreversible vision loss.
• Chronic, progressive optic neuropathy
characterised by optic disc and retinal nerve
fibre layer changes with corresponding visual
field defects and with raised IOP

3. The assessment of glaucoma is done with these
following parameters:
• IOP Measurement
• Status of anterior chamber angle
• Optic nerve head changes
• Abnormalities in visual field.

4. IOP Measurement
• Goldmann Applanation tonometry – Gold
standard.
Other newer types are:
• Dynamic contour tonometry
• Ocular Response Analyser
• Rebound Tonometry

5. Dynamic Contour Tonometry
• 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

6. • It is not affected by central corneal thickness.
• It has a disposable tip which prevents
contamination.
• Numerical display of result .
• No need for calibration.
• It is superior to Goldmann applanation
tonometry.

7. Ocular Response Analyser

8. 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.

9. • 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

10. Rebound Tonometry
• A 1.8mm diameter plastic ball on a stainless
steel wire is held in place by an
electromagnetic field in a handheld battery-
powered device.
• When the ball hits the cornea, the ball and
wire decelerate; the deceleration is more
rapid if the IOP is high and slower if the IOP is
low. The speed of deceleration is measured
and is converted by the device into IOP.

11. • Influenced by central corneal thickness
• Affected by other biomechanical properties of
the cornea, including corneal hysteresis and
corneal resistance factor.

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

13. Ultrasound Biomicroscopy
• In the principle of ultrasonography, the depth of
tissue structures is determined by directly
measuring the time delay of returning ultrasound
signal
• Requires contact with the eye, and a coupling
medium is necessary such that scanning must be
performed through an immersion bath.
• Operates at 50 MHz
• Tissue penetration is approximately 4 to 5 mm

14. • Standard measurements include: 1) Angle
opening distance (AOD). 2) Angle recess area
(ARA)

15. • Advantages: Can assess angle through opaque
media.
• Limitations: longer image acquisition times,
and the need for a skilled operator

16. Anterior Segment 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.
Priciples:
• Interferometry
• Low coherence light in near infra-red range

17. A low coherence infrared light (820nm) is projected on
the beam splitter
One beam is directed through the ocular media (Probe
beam) and the other beam is focused on to a reference
mirror at known variable position (Reference beam)
Probe beam is reflected back from the boundaries
between the retinal microstructures and is scattered
differently from tissues with different optical
properties
The distance between the beam-splitter and the
reference mirror varies continuously and when equal,
the light reflected from the retinal tissue and the
reference mirror interacts to produce an interface
pattern (interference)
Detected by a camera detector and processed into a
signal

19. 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

20. • Non-contact
– No possibility of indentation, so no corneal
abrasion or punctate epithelial erosion as seen in
UBM
• Shorter imaging time
• Rapid image acquisition

23. 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

26. EyeCam
• The EyeCam is a new technology originally
designed to yield wide-field photographs of
the pediatric fundus for the diagnosis and
management of posterior segment
diseases.With modifications in the optical
technique and the inclusion of a 130 degree
lens, the device can be used to visualize angle
structures in a manner similar to direct
gonioscopy.

28. Limitations
• Unable to provide quantitative measurements
• takes longer than gonioscopy (about 5–10 min
per eye).
• more expensive and additional space is
required for supine examination.
• It is not known if supine positioning would
widen the angle due to the effect of gravity on
the lens–iris diaphragm

29. Imaging Techniques for optic Disc and
RNFL evaluation in glaucoma
• Confocal scanning laser ophthalmoscopy
(HRT ; Heidelberg Retinal Tomography )
• Scanning Laser polarimetry (GDx )
• Optical Coherence Tomography

30. Confocal scanning laser
ophthalmoscopy
• Confocal = conjugate + focal
• i.e. the focal plane of the retina and the focal plane of
the image sensor are located at conjugate positions
• Confocality achieved by placing pinholes in front of the
detector which is conjugate to the laser focus
• Spatial filters (pin holes) are used to eliminate out-of-
focus light or flare
• Size of the pin hole – determines degree of confocality
• Smaller pin hole – highly confocal image

31. • 670-nm diode laser beam focused in the x-axis and y-
axis (horizontal and vertical dimensions) of the ONH,
perpendicular to the z-axis (axis along the optic nerve)
• Reflected image from this plane is captured as a 2-
dimensional scan
• Successive equidistant images are obtained (64 in total)
• 3-dimensional construct of the ONH region
• Topographic map
• Calculation of cup-to-disc (C/D) ratio
• Rim area
• Other optic disc parameters

32. CUP
■ C/D Ratio
■ Shape
■ Asymmetry
RIM
■ Area & Volume
■ Asymmetry
RNFL
■ Height Variation Contour
■ Thickness
■ Asymmetry

33. Topography Image
• False color image
• Similar to gray scale of VF printout
• Provides size, shape and location of cup

36. Scanning Laser Polarimetry
• 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.

37. • Form birefringence
• Splitting of a light wave by a polar material into two
components
• Two components travel at different velocities and creates a
relative phase shift (retardation)
• The amount of retardation is proportional to thickness of
polar tissue (RNFL)
• The RNFL behaves as a polar tissue because of the
microtubules (with diameter smaller than the wavelength
of light)
• The greater the number of microtubules, the greater the
retardation.The greater the retardation the greater is the
tissue thickness

38. • 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.
• A reflectance image of the scanned image is
produced.

40. 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).
• 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).

41. • 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.

42. • 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)
• Inferior Average : This is the average
of all pixels (μm) in the inferior 120
degrees of the Calculation Circle. (
Normal 40 - 75 μm)
• The Nerve Fiber Indicator (NFI) for
GDx is an algorithm that analyzes the
entire RNFL profile.

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

44. Limitations
• Does not measure actual RNFL thickness
• Limited use in moderate/advanced glaucoma.
• Difficult in very small pupil and media
opacities.
• Requires wider database for Indian
population.
• Young patients database not available.

45. OCT Glaucoma Scans
• The Fast Optic Disc scan
• The Fast RNFL Thickness scan

46. 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.

47. • "optic nerve head analysis" protocol

48. 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.

49. • 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

51. • Ganglion cell analysis
• The ganglion cell layer is thickest in the
perimacular region and decreased total
macular thickness has been observed in
glaucomatous eyes likely due to thinning of
the ganglion cell layer in this region.

52. Perimetry
• Standard automated perimetry detects a
visual field defect when about 40% of retinal
ganglion cells are lost.
• So it is preferable to detect damage at earlier
stages given the irreversible nature of vision
loss in glaucoma.

53. Recent advances in perimetry
• SWAP-Short wave-length automated perimetry
• FDT-Frequency Doubling Technology perimetry
• HPRP-High Pass resolution perimetry
• High Spatial Resolution perimetry
• Motion Detection Perimetry
• Heidelberg Edge perimetry
• RareBit perimetry

54. Short Wavelenght Automated
Perimetry
• Also know as Blue-on-Yellow perimetry
• Here yellow backgroud light(530nm) at a
luminance of 100cd/m2 suppresses the red
and green cones.
• The blue cones are stimulated by a Goldmann
Size V(1.7˚) light with a narrow band short
wavelenght interference filter (440nm) with a
duration of 200 millisecond.

55. Advantages:
• Very high sensitivity and specificity.
• Detects glaucomatous changes earlier than
standard automated perimetry
Disadvantages
• Increased patient fatigue
• Long adaptation time
• Bright yellow background is very intense and
the blue stimuli are hard to perceive

56. Frequency Doubling Technology
perimetry
• Frequency doubling technology (FDT) essentially
creates an image that appears double its actual
spatial frequency, in which approximately twice
as many light and dark bars are usually present .
• This perimetry test does not depend on the
appearance of the target but rather the minimum
contrast needed to detect the stimulus at
different locations in the visual field.

57. • The first generation Frequency Doubling
Technology
• In the first generation FDT perimeter, each
target is displayed as a 10-degree-diameter
square, the central stimulus which is
presented as a 5-degree-diameter circle.

58. The second generation Humphrey
Matrix
• The ability to monitor eye fixation.
• Threshold testing on the Humphrey Matrix
uses smaller targets that are presented along
a grid. In addition, greater spatial resolution is
available with 24-2, 30-2, 10-2, and macular
threshold tests.
• 54 targets

59. • High sensitivity and specificity.
• Detecting early visual field loss compared to SAP
• It is comparatively faster
• FDT has been reported to have both lower intra-
and inter-test variability compared to SAP, which
suggests it may be a useful test to monitor long-
term progression of visual field loss.
• Relatively inexpensive, efficient, and non-
operator dependent nature of the test.
• The FDT machines are relatively portable and
thus may lend itself to use in community
screenings for glaucoma.

61. Heidelberg Edge Perimetry
• It uses a unique stimulus called Flicker Defined
Form.
• A round stimulus is created by reversing the
phase of flickering black and white dots, thereby
forming illusory outlines. The test uses randomly
flickering points in medium illumination (50
cd/m²).
• The background remains the same during the
whole test. Background luminance is 50 cd/m2,
the marker showing time is 400 ms, and the
frequency is 15 Hz.

62. High Pass Resolution Perimetry
• In this method along with detection, the resolving
thresholds are also measured.
• The test target consists of bright circular cores
surrounded by dark borders.
• It tests 50 targets in 30˚central visual field.
• Main advantages are shorter test time and the
strong preference by patients .
• The sensitivity and specificity better than
conventional perimetry. A minor disadvantage
was its slightly less precise spatial definition of
field defects.

63. Rarebit Perimetry
• RareBit Perimetry depends on minute stimuli
("rare" bits or "microdots") .
• 24 rectangular test areas .

64. High Spatial Resolution Automated
Perimetry
• High spatial resolution perimetry was performed
using a Humphrey automated perimeter by
measuring luminance sensitivity across a 9 by 9
degree custom grid of 100 test locations with a
separation between adjacent locations of 1
degree
• in glaucomatous eyes fine luminance sensitivity
loss was present .
• Limitation : high intratest variability.

65. Motion Detection Perimetry
• It measures the patients ability to detect a
coherent shift in position of dots in a circular
area against a background of non-moving
dots.
• Its sensitivity is superior to conventional
automated perimetry.

66. OCT angiography
• Using OCT angiography, reduced peripapillary
retinal perfusion in glaucomatous eyes can be
visualized as focal defects and quantified as
peripapillary flow index and peripapillary
vessel density, with high repeatability and
reproducibility. Quantitative OCT angiography
may have value in future studies to determine
its potential usefulness in glaucoma
evaluation.

68. Detection of Apoptosing Retinal Cells
• The DARC Technology (Detection of
Apoptosing Retinal Cells) is an innovative
technique that uses the unique optical
properties of the eye to allow direct
visualization of nerve cells dying through
apoptosis, identified by fluorescent-labeled
annexin V.

70. • Thank you