1. Glaucoma and OCT – Are
Macula Scans More Valuable
than Disc Scans?
Jason Higginbotham Bsc (Hons) MCOptom FBDO

2. Glaucoma and OCT – Are Macula Scans More
Valuable than Disc Scans?
Glaucoma clinic – lets go back 25 years!
Look for the following:
1. Raised Intra Ocular Pressure (IOP)
2. Glaucomatous Field Loss
3. High CD Ratio, disc Pallor, deep cups, nasal shift of vessels,
bayonetting and so on
4. Px symptoms and family history
5. Narrow angles
6. Secondary markers (E.g. Krukenberg’s spindles)

3. A Classic View?
Open angle glaucoma

5. Do we measure IOP?
IOP is still considered the biggest risk factor for Glaucoma.
Do we measure it?
NO!? We estimate it. Often we are a long way off. Only two devices
measure actual IOP – The Reichert Ocular Response Analyser and the
Oculus Corvis ST.
OCT has shown a much higher rate of normal and low tension
glaucoma cases. IOP is important still, but how relevant?

6. Oculus Corvis

7. Are Fields reliable?
I’d like to say yes, but the subjective nature of these tests and the
affects of tilted discs and optic disc drusen (for example) can possibly
affect the results – as can happen on OCT disc scans.
What about pre-perimetric glaucoma?
What are RNFL fibres?
In glaucoma, up to 50% of retinal nerve
fibres are lost before a visual field defect
becomes manifest with full threshold
automated static perimetry (Quigley et al
1989)

8. Definition of Glaucoma
Glaucoma: a group of diseases of the optic nerve which result in a
loss of retinal ganglion cells in a characteristic pattern of optic
neuropathy
Glaucoma is a group of eye diseases that cause progressive damage
of the optic nerve at the point where it leaves the eye to carry visual
information to the brain. - World Glaucoma Association
The American Academy of Ophthalmology now defines glaucoma as
“a group of diseases with certain features including an intraocular
pressure that is too high for the continued health of the eye.”

9. What actually occurs in Glaucoma and where?
Studies have shown that the actual process at play is RGC (Retinal
Ganglion Cell) body shrinkage followed by RGC body death taking
place.
This has been shown to be due to cellular apoptosis caused either by
ischaemia or by excitotoxicity (glutamate in the vitreous). IOP may
cause release of glutamate as a traumatic response and glutamate is
toxic to RGC’s.
However, papers also suggest bringing down the IOP in normal
tension glaucoma patients is effective at slowing progress of the
disease.

10. Theories of Damage
What actually occurs in Glaucoma and where?

11. What actually occurs in Glaucoma and where?
We now have two main theories:
Selective Damage Theory versus
Reduced Redundancy Theory
It’s probable that a ‘bit of both’ are at play!
However, it’s the RGC that dies off in all cases. But the axonal death
may bring about the RGC death, or does it?

12. The Ganglion Cell Complex
The Ganglion Cell Complex (GCC) is the innermost five layers of the
retina (ILM, RNFL, GCL, IPL and INL).
Easier to measure as a whole than just the GCL or GCL and IPL.
GCC tends to shrink before obvious change at the disc, but there are
cases where this doesn’t occur.
Lots of evidence to suggest that ganglion cell body shrinkage takes
place first. Does axonal damage occur later – if so, the RNFL may be
intact or appear so for longer and might not manifest on eye
examination.

13. Normal GCC
GCC thinner in Glaucoma

14. The Ganglion Cell Complex
With the added ‘G Chart’,
Ganglion Cell Complex
thickness can be assessed
against the normative data.
Notice that now the scale
only represents half a bell
curve. Where the GCC is
thicker, this is represented
in white as there is no
known pathology of GCC
hyperplasia.
G Chart

15. The Ganglion Cell Complex
Normative Scales

16. Disc scans – RNFL measurement
Disc RNFL Analysis

17. Macula Scans versus Disc Scans
It is well known that Macula scans are more repeatable, accurate
and reliable than Disc scans.
Macula scans are easier to repeat and compare due to greater
fixation stability and ease of scan overlay.
Disc scans are more prone to subtle positioning errors, fixation loss
and opto-kinetic nystagmus.
Disc Drusen, Tilted Disc, Peripapillary ERM’s and papilloedema all
affect the accuracy and repeatability of disc scans.

18. Progression analysis
• Spotting Glaucoma early is one of the most
important uses of OCT and is certainly one area
where Optometrists come into their own within
Primary care and also in Community
Ophthalmology and Secondary care.
• We can use the software to analyse if there is
any progression in loss of Ganglion Cell Complex
(GCC) at the Macula or Retinal Near Fibre Layer
(RNFL) thickness at the Optic Nerve Head (ONH).
• Superior / Inferior step analysis as well as R/L
comparison are always important too.

19. GCC Progression R Eye

20. RNFL Progression R Eye ONH

21. This 44 year old patient
attended a clinic. They had
evident disc cupping in both
eyes with some palour.
Our suspicions would already be
aroused by the discs, but the
IOP’s were not raised.
A Late Stage Example. Case 1.

22. • The right visual
field shows an
arcuate scotoma,
with blind spot
enlargement in
the left eye.

23. The field loss becomes more obvious when we look at the RNFL layer
thickness deviation maps against the normative data.
You can see the evidence of loss of RNFL particularly in the Right Eye
which corresponds perfectly with the field plot on the previous page.
R L

24. The ETDRS chart
shows minor
thinning of the retina
inferior to the
Macula in the right
eye.
The G Chart, however, shows considerable inferior thinning and loss of
the Ganglion Cell Complex across the inferior Macula. The shape from
the deviation map is typically arcuate and matches the field loss very
closely. Note the nasal step and the horizontal mid line.

25. Example Case 2
84 Year Old Female
Drop in vision RE. Family history of Glaucoma.
IOP’s RE 17 mmHg LE 20 mmHg. CCT 512 microns.
Visual Fields inconclusive, poor compliance.
VA RE 6/24 distorted. LE 6/9 .
OH – Bilat IOL’s. FOH – Mother Glaucoma. GH – Good.
Arthritis. Meds – Anti inflammatories. FMH – Nil.
No headaches or other Sx. Driver. Retired, but does
voluntary work part time!

34. Example Case 3
61 Year Old Male
No visual complaints.
IOP’s RE 19 mmHg LE 18 mmHg. Corrected IOP’s.
Visual Fields show minor initial loss of sensitivity RE.
VA RE 6/6 LE 6/6 OH – No Ops. FOH – None
GH – Good. Meds – None. FMH – Nil.
No headaches or other Sx. Driver. Accountant.
Uses PC a lot. Plays golf and goes to the gym.

40. Example Case 4
65 Year Old Female
Noticed poor vision LE. A few headaches. No eye ache.
No haloes. Reading difficult.
Corrected IOP’s RE 22 mmHg LE 23 mmHg.
Visual Fields RE: Full 26 dB, LE: Early inferior arcuate
loss 24 dB. Slightly narrow angles OU.
VA RE 6/6- LE 6/9
OH – Good. No Ops. FOH – Sister Glaucoma.
GH – Hypertension. Meds – Anti hypertensives and
statins. FMH – Father heart attack.
Driver. Retired.

47. Example Case 5
72 Year Old Female
Night driving difficult. No headaches. No pain or other
ocular symptoms.
IOP’s RE 13 mmHg LE 13 mmHg.
Visual Fields full right and left. 24-2 screening.
VA RE 6/6- LE 6/6-
OH – Early lens opacities. No Ops. FOH – Mother went
blind; AMD. GH – Arthritis and IBS Meds – Anti
inflammatories. FMH – Nil. Driver. Retired. Uses PC and
likes to read.

53. Potential Errors with Macula Scans
There are circumstances where the reliability and accuracy of
Macula scans is slightly reduced. These include:
• High myopes. Some cases show overall retinal thinning, whereas
occasionally, the GCC alone seems thinned in some myopes.
• Epi retinal membranes (ERM’s) can affect the overall retinal
thickness and make accurate assessment of GCC difficult.
• Presence of over underlying pathology, particularly where a
large regional increase in overall retinal thickness occurs, such as
CSR (central serous retinopathy).

54. Potential for the future
As higher resolution devices become available with longer
wavelength infra red lasers and greater tissue penetration, then it
will be likely that better repeatability of scans will occur and more
effective scan imaging even with dense lens opacities might
become possible.
As whole eye OCT is being developed, it may not be too long before
such device can offer assessment of more eye parameters in one
full glaucoma plot.
Many devices have software which can or will incorporate visual
field plots and other test results.

55. Earliest Glaucoma detection
There is no doubt that OCT can detect glaucomatous damage much
earlier than visual fields and other older techniques.
However, it is possible to detect even earlier changes that OCT’s
might not.
Modern ERG / VEP tests can detect extremely subtle alterations in
the speed of response in the visual system and the speed of
depolarisation in the process of ‘seeing’.
There is a new device which makes these tests much quicker and
easier than before.

56. The Diopsys Nova and Argos systems
Tabletop
Cart

57. ERG and VEP for early glaucoma detection
Structure
Fundus Photograph
(Subjective)
Function
Visual Field
(Subjective)

58. ERG and VEP for early glaucoma detection
Structure Function
Optical Coherence Tomography
(Objective)
ERG
(Objective)

59. ERG and VEP for early glaucoma detection
Electrical activity of the retina
ERG
Pattern ERG
Flash ERG • Objective/functional assessment for early to
moderate disease patients
• First technology to assess cell sickness, not cell
death
• Early diagnosis = early treatment
• Additional information to assist the doctor to make
a more informed decision to either treat or follow
the patient
• Assists the doctor in determining whether
treatment is working or not
• Like OCT, Electrophysiology is a multi faceted
technology which offers clinical benefits for
glaucoma, retina, and anterior segment

60. • Glaucoma
• Multiple Sclerosis
• Ischemic Optic Neuropathy
• Traumatic Brain Injury
• Amblyopia
• Other Neuropathies
MAIN INDICATIONS
Visual Evoked Potential (VEP)
ERG and VEP for early glaucoma detection

61. Age (years): 75
Gender: Male
Complaint: Blurry vision, OD<OS
Personal History: Hypertension, COAG
(Dorzolamide, Timolol)
Family History: CVA
Allergies: No known allergies
Uncorrected VA OD: 20/50
Uncorrected VA OS: 20/50
Refraction OD: -1.50 x 94
Refraction OS: +1.00 -0.50 x 92
BCVA OD: 20/20
BCVA OS: 20/20
Case 1: ERG correlates with visual fields and RNFL
assessment

62. IOP OD (mmHg): 19
IOP OS (mmHg): 17
Pupil OD: PERRL, negative APD
Pupil OS: PERRL, negative APD
Anterior Segment OD: Pseudophakic
Anterior Segment OS: Pseudophakic
Fundus Exam OD: CD ratio 0.6
Fundus Exam OS: CD ratio 0.6
Diagnosis: COAG

63. Visual Fields: Outside normal limits (OS worse then OD)

64. RNFL thickness: outside normal
limits OS worse then OD
PERG: outside normal limits
OS worse then OD

65. PERG correlates with visual field and RNFL
assessment
When used in conjunction with other diagnostic
modalities PERG can offer another valuable tool
to help the doctor treat or follow a patient.
Case 1 Conclusion

66. Case 2: VEP
Glaucoma Suspect
Reason for test:
Standard test are unreliable
Patient Work-Up
Gender Male
Age 70
Ethnicity White
Complaints/Symptoms None
Family History Mother & Grandmother glaucoma
IOP (mmHg) OD 23
IOP (mmHg) OS 21
Pachymetry (µm) OD 506
Pachymetry (µm) OS 507
Refraction OD Plano
Refraction OS Plano
BCVA OD 20/25
BCVA OS 20/25
Preliminary Diagnosis Glaucoma Suspect

67. Visual Field Results
Humphrey 24-2 shows a slight depression in the inferior Blind Spot OD, and
borderline GHT findings although this field was somewhat unreliable. OS
without defect.

68. HRT Result

69. VEP Result
Shows increased latency in
low & high contrast OD,
and normal amplitude &
latency OS.

70. Diagnosis and Treatment:
“Having the ability to obtain a new objective measurement of optic nerve function by
performing a VEP has helped significantly in the decision to treat this patient for early POAG.”
Dr. Farrell Tyson
Initiated treatment with Lumigan 0.01 % OU
Follow up visit one month later, IOP’s were 18 and 16 (acceptable level for patient)
Will follow at quarterly intervals
Conclusion: VEP Aids in Decision To Treat

71. In summary
We must use ALL the information available to us to hopefully
produce more effective and early diagnosis of glaucoma.
As well as the ‘usual’ information, OCT provides massively useful
data, especially the macula scans and the GCC progression.
New versions of old technology, like ERG/VEP can aid in the earliest
diagnoses, in differential diagnosis and in follow up / treatment
analysis.

72. In summary
Be aware of the potential limitations of devices.
Consider follow up examinations where immediate referral might
not be necessary.
Each piece of data or scan results are pieces in a diagnostic jigsaw
puzzle.

73. Thank you for Listening.

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