D - Open Angle Glaucoma 1 & 2 - Week 3 Flashcards
Define Glaucoma (in specific terms. What is lost?)
A disease of the optic nerve with progressive loss of RGC and RNFL with typical functional loss (arcuate VF loss) and no other cause
can occur with or without high iop
OAG is often a presumptive diagnosis based on which 4 factors?
Risk factors
Appearance of RNFL
Appearance of NRR
Typical VF loss
What 4 assessments are needed to determine the level of risk of glaucoma? (i.e. the assessments that will define management)
IOP
Ant. chamber + angle
Fundus: RNFL and NRR
Visual Field
What should a patient present with for us to classify them as a glaucoma patient?
Concomitant presence of RNFL, ON, VF loss
List 5 high risk factors for glaucoma
myopia
RVO
eye injury
iris degeneration
papilledema
List 4 low risk factors for glaucoma
female
diabetes
migraine
sleep apnea
Is IOP a risk factor for glaucoma? Explain
OAG can be IOP independent below 18mmHg (=LTG). However, high IOP is a risk factor for one form of OAG (high pressure OAG)
What assessment do you need to specifically diagnose low tension glaucoma? Why? How can you perform this assessment?
Need the diurnal curve of IOP in all LTG cases to dismiss IOP spikes.
Get patient to come in on multiple days at multiple times to measure IOP.
Alternatively, the ICare tonometer allows the patient to self monitor their IOP (get them to check at 9am, noon, 6pm)
What is considered a higher risk for glaucoma when measuring diurnal IOP?
Any isolated reading >21 or a spike >4mmHg = Higher risk
By how much will corneal thicknes (CCT) modify IOP readings?
Increase in 1mmHg for every 25 micron increase in corneal thickness and vice-versa
What MUST you do if you find an IOP reading >29mmHg? (2)
Evaluate angle for closure and measure CCT
What should you consider if you find an IOP reading <6mmHg?
Consider hypotony or very low CCT/abnormality.
NB: Hypotony = break in cornea with fluid leaking out (an eye can’t survive too long in this condition)
Is a thicker or thinner cornea a higher risk for OAG?
Thin cornea
List 8 risk factors for OAG
Family hx
African-american
DM, migraine, sleep apnea
High BP: aggressive BP lowering
Steroid use
Eye or iris injury/surgery
Myopia
RVO, past papilledema
List 7 risk factors for LTG
Family hx
Japanese
DM, migraine, sleep apnea
Aggressive BP medication
Age >65yo
High myopia
Cardio-vascular disease
What is the purpose of anterior chamber assessment in glaucoma detection? (3)
Assess the angle
Assess to exclude 2ndary OAG (e.g. PXG, PDG, AAU)
Ensure OAG Dx
What is angle closure determined by? (2)
AC depth (shadow test)
TM patent: angle open if VH >0.25.
Need both (and gonio) to diagnose PAC (primary angle closure)
What findings in gonioscopy are necessary for diagnosing PAC? (2)
Angle open to only ATM over >180deg
Angle unimpeded (no pigment, blood or other, congenital malformation)
What disc features should be evaluated for glaucoma? (3)
papillary crescents
NRR thickness
Other signs - haemorrhage
What does a disc cup shape represent?
large disc + surface defect = steep profile for edge
What does a disc saucer shape represent?
small disc + deep defect = shallow profile/’tenting’ (NRR hard to see edge with saucer disc)
In general, what disc shape is associated with glaucoma?
A cup. However do note that saucers can have glaucoma too. Can use visual field results and presence of PPA to help diagnose
What VF defect is associated with surface fibre loss?
Proximal VF defect (Bjerrum)
What VF defect is associated with deeper fibre loss?
Distal VF defect (nasal step)
If a disc with a saucer shape turned out they had glaucoma, what would the likely VF defect be if present?
distal/nasal step
What is an abnormal CDR? Is CDR a reliable tool for glaucoma diagnosis?
CDR>0.7. or abnormal asymmetry >0.2 b/w eyes
No, not reliable b/c CDR varies greatly.
What change in NRR thickness do you expect to see with glaucoma?
Thinning at the inferior and superior poles. This means that the inferior/superior poles become same or less thickness as nasal (I>S>N>T no longer follows)
Does NRR show pallor in early OAG?
No. NRR never shows pallor in early OAG
What is the relationship between the size of the optic disc and the NRR?
In very large discs expect thin NRR everywhere. Vice-versa for small discs.
How thick do you expect the NRR to be in large discs?
> /1.25 BV widths or >/= 0.1 disc diameter
What should you use for diagnosis of glaucoma in small discs? (2)
Look for PPA and RNFL loss
How do you measure size of the optic disc with an ophthalmoscope? What represents a small ON? What about a large ON?
Use medium aperture and look at vertical extent of ON.
Small ON < 0.75 of aperture
Large On > 1.25 of aperture (cup inside aperture)
What is the normal ON size when measured with OCT?
1200-2200 microns (1.2-2.2mm)
What blood related changes might you expect in the fundus of a patient with glaucoma? (2)
Drance (ON) haemorrhage
Peri-papillary crescents (or atrophy, PPA)
How do Drance (ON) haemorrhages occur?
due to loss of glial support leading to vascular compromise/haemorrhage
Define drance haemorrhage. Can they precede VF and RNFL loss?
Any haemorrhage up to 1 DD away from the disc
Can precede VF and RNFL loss by 2-5 years
Provide a very common cause for drance haemorrhages
high systemic BP
How do peri-papillary crescents occur?
Loss of deep choroidal blood flow gives overlying atrophy
What is the benefit for using OCT in glaucoma patients?
OCT gives excellent spatial and depth resolution for detection RNFL defect & patient management. OCT can also define NRR and GCC.
What is the most useful clinical OCT procedure for glaucoma assessment?
Generally, RNFL > GCC > NRR
However, ON/NRR may be useful in highly myopic eyes since RNFL and GCC give a high false positive rate for those eyes.
In general, what makes assessment of GCC less useful in glaucoma assessment than RNFL?
While GCC is useful at the macula (b/c half of the ganglion cells are there). The other half of the ganglion cells are elsewhere, meaning you can still have the disease without it showing up in GCC assessment
Which of the 3 methods (RNFL, Mac GCC, ON/NRR) should be used for glaucoma detection?
All three methods + visual field testing
What mean deviation (MD) in VF testing represents a mild OAG defect?
MD >-6dB OR any central points 15-25dB
(NB: > means greater than. or in this case more positive than)
What mean deviation (MD) in VF testing represents a moderate OAG defect?
MD
What mean deviation (MD) in VF testing represents an advanced OAG defect?
MD
What should you consider good criterion for abnormal VF for clinical application? (2)
2 repeated VF tests where same 3-point (1 can be edge pt) cluster is abnormal (>10dB loss) or 1 pt p=0.01 and 2 pts p = 0.05
Repeat VF tests @ 1 month if abnormal
What is RED disease and what is a likely cause?
Low RNFL that is marked as abnormal compared to model data but is actually still normal. Can happen to myopes.
Describe SOAP for POAG
S: none, reduced VF
O: normal ON colour z loss in NRR or RNFL defect; typical VF defect; open un-occluded angle; IOP >21 at some stages
A: identify risk; disc+NFL; VF; Gonio; IOP
P: Tx+monitor: lower IOP, sx or meds
Describe SOAP for LTG
S: none, reduced VF
O: optic neuropathy consisting of: NRR loss/RNFL defect, usual VF defect, open un-occluded angle, IOP <22, vascular cause likely
A: risk factors; disc+NFL; VF; Gonio: IOP (diurnal)
P: Tx or monitor. Neuroprotectants and/or vasoactive meds?
List 3 glaucoma masqueraders
Congenital On anomalies
Vascular conditions at ON or in retinal NFL
Tumours or masses along NFL, nerve or pathway
Can you use beta blockers to treat LTG?
No. NEVER!
