Glaucoma Flashcards
What are the 3 broad types of glaucoma?
-open angle
-closed angle
-secondary
what are the 4 types of open angle glaucoma?
-Primary open angle glaucoma (POAG)
-Low tension glaucoma (LTG)/ normal tension glaucoma (NTG)
-Pigment dispersion
-Pseudoexfoliation
what is the biggest risk factor for glaucoma?
age as its a disease of the ageing visual system
why is migraine a risk factor for POAG?
because constricting your peripheral digital arteriole causes similar constriction of the optic nerve which can cause it to become damaged
how does aqueous production and movement in the eye work?
- The ciliary epithelium produces aqueous at 3 ml per minute
- It flows around the iris from the posterior to anterior chamber and then drains through the trabecular meshwork. 3. This is at an angle between the cornea and the iris.
- Then goes into the canal of schlemm to exit the eye.
- The higher the resistance in the trabecular meshwork, the greater the pressure of the eye will be.
in angle closure, the iris itself blocks off the trabecular meshwork
what are some causes of secondary glaucoma?
-uveitis
-trauma
what are the risk factors for primary open angle glaucoma?
-elevated IOP
-older age
-black race
-family history of glaucoma
-myopia
-migraine and vasospasm
what is non conventional outflow?
where aqueous can also exit below the trabecular meshwork in uveal scleral flow (UVA).
how does open angle glaucoma come about?
when there’s a gradual increase in resistance of the trabecular meshwork and so IOP gradually builds causing a slow onset POAG. as IOP builds, the optic disk becomes deeper hence increased CD ratio and cupping.
what is the rim of the optic disk?
where the retinal ganglion cells line the inside of the depression of the optic nerve (like a hole in the back of the eye) and the optic disk is where they dont line the cup.
what is BMO?
bruchs membrane opening, determines the edge of the optic disk as its the end of bruch’s membrane
what happens to the lamina cribrosa of a glaucomatous optic nerve
its depth increases
how does the optic nerve/ disk change in glaucoma?
-increased cupping
-increased CD ratio
-optic nerve starts to go pale
-tilted disk
why does tilted optic disk increase risk of glaucoma?
as if it tilts down, the forces acting on the disk cause injury to the axons of the retinal ganglion cells
what are the predisposing factors for developing angle closure glaucoma?
-Headaches
-Halos around bright lights
-Shallow anterior chamber (<1.5mm) (smaller van herrick grade)
-Females
-People with smaller eyes (east asians)
-Convex lens iris diaphragm (where the iris is pushed forward by the aqueous trapped in the anterior chamber which gives it a convex appearance)
what is the grading system used by ophthalmologists to grade glaucoma?
Shaeffer Kanski system
-0 is closed
I shwalbe’s top of Tm
II is where you can see the trabecular meshwork
III is where you can see the scleral spur
IV is where you can see everything so top of scleral body and scleral space
why is anterior segment OCT starting to be done more than gonioscopy?
as it gives you a quantitative view of the corneal angle without being uncomfortable and coming with risk of infection
What is axenfeld anomaly?
an example of an angle issue due to additional tissue forming in the cornea periphery in this case posterior embryotoxon. Can cause a risk of glaucoma as it affects the trabecular meshwork and possibly block it
what is a sign of congenital glaucoma?
a child rubbing their eyes alot due to the wateriness
what is aniridia and how is it linked to glaucoma?
where there is no iris and this can increase risk of glaucoma as it can mean trabecular meshwork also does not properly form.
what is chronic angle closure glaucoma?
where the patient presents with no other symptoms other than somewhat high IOP.
what is a sign of acute primary angle closure?
corneal oedema
what are the signs/ symptoms of congenital glaucoma?
-corneal oedema
-lacrimation
-photophobia
what are the treatment options for glaucoma?
-IOP lowering drops e.g. prostaglandins
-Selective laser trabeculoplasty (SLT) - gold standard of glaucoma surgery
(usually patients have a choice between these two and most will go with drops as they are more familiar)
-Otherwise surgery - a hole is made in the eye to allow excess aqueous to drain but not too much otherwise IOP becomes too low (target pressure is 10mmHg)
what is SLT?
selective laser keratoplasty - where the trabecular meshwork gets heated to a point so it can break and hence allow the aqueous to flow through and lower the IOP. It seems to lower the patient’s risk of developing glaucoma in the future.
what are the negatives of IOP lowering drops?
-they come with side effects:
Lower lid scarring (severe)
Fat atrophy
Red eye
Discomfort
Shadows around eyes
-the patient has to be compliant
what is cycloiodide laser?
a more invasive glaucoma treatment than SLT where the ciliary body itself is lasered
what is a complication of SLT? How can it be avoided?
cystic blebs. This can be avoided using mitomycin C (MMC) which is an antimetabolite (an anti cancer drug) which prevents the formation of fibroblasts.
what kind of patients may not be suitable for laser treatment for glaucoma and what may they undergo instead?
patients with uveitis or previous retinal procedures
instead could undergo filtration surgery:
1.small flap is created under the upper eyelid in the sclera
2. mini shunt is inserted under the flap to allow fluid to drain from inside the eye
3. fluid collects in a filtering bleb (area around the implant so the fluid can be gradually absorbed into the body)
how can you diagnose glaucoma?
Assessment of the optic nerve
Angle assessment
IOP measurement
Visual fields
In someone suspected with glaucoma with high IOPs what should you do before referring them?
redo their IOPs with goldmann and you may what to redo visual fields
why are sita fast and faster better than full threshold?
because in full threshold its so long alot of patients lose focus so we dont get accurate results from them
why is suprathreshold not recommended for patients with glaucoma?
because as the defect increases, the variability increases and causing you to be more likely to miss localised defects produced by glaucoma
how can you tell which eye is which on a VF plot?
when the blindspot is on the left its the left eye and when the blindspot is on the right its the right eye.
what are the most common used algorithms in static perimetry?
full threshold strategy and SITA (swedish interactive threshold algorithm)
what are the advantages to sita standard compared to full threshold algorithm?
-saves approximately 35-50% of the examination time
-has increased specificity due to reduced test duration
-reduced fatigue effect and false positive response
by what percentage of the sita standard algorithm does sita fast reduce the test time?
~84%
how does threshold strategy work?
uses a staircase to estimate the threshold at any given location:
1. the luminance of a constant in size projected stimulus is changed in predetermined steps
2. accuracy of the measured threshold increased with the use of smaller steps
where is the blind spot in the visual field?
15 degrees temporally
where does a normal visual field extend?
100 degrees temporally, 60 degrees nasally, 60 degrees superiorly and 70 degrees inferiorly
how big is the average blindspot and where is it in relation to the horizontal meridian?
average blindspot is 7.5 degrees in diameter and vertically centered 1.5 degrees below the horizontal meridian
what three programmes threshold perimetry be performed in with Humphrey field analyser (HFA)?
- The 30-2 programme
- The 24-2 programme
- The 10-2 programme
for the 30-2 programme in static threshold perimetry, how many stimulus locations are there and how does the grid work?
76 stimulus locations, based
upon a square grid with an inter-stimulus separation of 6°, within the central 27° radius of the visual field, which
represents about two-thirds of the nerve fibres on a background luminance of 31.5 asb
how many locations does the 10-2 program have in threshold perimetry and how are they separated?
10-2 program comprises 68 locations based upon a square grid with an inter-
stimulus separation of 2°, within the central 9° radius of the visual field and is useful for increasing the spatial resolution of paracentral defects and for end-stage disease
know each threshold test and what diseases you can apply it to
check ss
what does the grayscale plot on VFs show you?
the estimated values of sensitivity across the field where each shade of gray reoresents a range of 5dB
why is the grayscale plot on VFs not very reliable
-not age corrected
-not corrected in terms of eccentricity
this means it can easily miss or misinterpret defects
what do negative total deviation vales mean?
an estimated sensitivity worse than the estimate in the normal eye of an
equivalent age
what does a negative pattern deviation value mean?
A negative sign indicates an estimated sensitivity worse than the estimate in the
normal eye of an equivalent age
what does a total deviation plot test?
how much the height of your vision has been reduced by the potential defect.
what side of the VF, temporal or nasal does the 24- sita fast and faster have more locations?
on the nasal as the nasal side of the VF is going to be more affected by glaucoma
what does pattern deviation show you?
the localised component of the defect instead of total deviation which shows the diffuse defect. This is the plot you should look at first for glaucomatous defects
what does mean deviation tell you?
Mean deviation gives you a gross idea of how much diffuse loss the patient has.
what are the negatives of mean deviation?
-affected by cataract and refractive defocus
what are the visual field indices?
- The Mean Deviation (MD)
- The Pattern Standard Deviation (PSD)
- The Visual Field Index (VFI)
what mean deviation is functional blindness associated with?
an MD of approximately -25dB
how does PSD reflect the magnitude of field loss?
normal value is approx 1dB and as the area of loss increases, the the PSD becomes increasingly positive
how is pattern standard deviation limited?
because it only increases to a certain degree of visual field loss and and after which the localised loss cannot be differentiated from the generalised loss to the psd goes back to 1 hence is limited by the lack of dynamic range of the perimeter
why can the visual field index (VFI) make it difficult to determine early stages of glaucoma?
because you need at least 30% to 40% RGC loss before the visual field can detect a defect
What is the glaucoma hemifield test?
compares the symmetry in the
presence and the magnitude of the Pattern Deviation probability levels in
five predetermined mirrored zones selected in the superior field to that in
the inferior field based on the normal anatomy of the retinal nerve fibre layer to detect field loss symmetric around the horizontal meridian
what are the qualitative classifications for GHT?
- ‘Outside Normal Limits’, where one or more of the zones in the superior
field are significantly different from the corresponding inferior zone(s) - ‘Borderline’, where one or more of the zones in the superior field may be
different from the corresponding inferior zone(s) - ‘General Depression of Sensitivity’; where all zones are equally adversely
affected - ‘Abnormally High Sensitivity’ where the threshold estimate at the stimulus
locations in the zones are abnormally high - ‘Within Normal Limits’ where the threshold estimate at the stimulus
locations is within the normal range
what is fixation stability evaluated by?
the Heijl-Krakau blind spot technique and by gaze tracking.
what is the upper limit for the proportion of acceptable fixation losses?
20%
how can you interpret fixation stability in VFs?
- Any deviation in the eye movement from 10° is recorded
- Upward spikes on the gaze graph manifest an eye movement
- Downward spikes indicate a blink
what is the difference between relative scotomas and absolute scotomas?
relative are formed from retinal areas with reduced light intensity and absolute are formed from retinal areas with no light intensity
what visual symptoms do patients report when they have glaucoma?
most dont report tunnel vision and instead they have blurred parts or scotomas or otherwise seem to think their vision is not affected
where are glaucoma lesions?
pre chiasmic
look at the classifications of defects in VFs ss
ok
in visual fields, what is the Bjerrum area?
An arcuate zone that expands from the blind spot nasally around the fixation point or to the nasal field of vision
or both. An enlargement of paracentral scotomas signifies a continuous area of focal loss
what is a centrocaecal scotoma?
a continuous scotoma from the blind spot that originates from the papillomacular nerve fibre bundle region
how might arcuate scotomas be different in myopic patients?
they may develop closer to fixation than in other patients
in an arcuate scotoma why is the temporal portion of the field narrow?
because all the retinal
nerve fibers from that region are funneling together to form the optic
nerve
what does the visual field look like during the onset of glaucoma?
a mild, diffuse depression and/or localized visual field defects are
observed
what does a visual field look like in early glaucoma?
paracentral defects in the Bjerrum area
and/ or a nasal step
what are the signs of advanced glaucoma in VFs
-arcuate scotomas involve the blind spot
-arcuate scotomas are found superiorly inferiorly to form a double arcuate scotoma
what are the signs of late glaucoma in VFs?
-only a ring around the fixation point in the paracentral region and a temporal island in the mid peripheral region remain unaffected
what approaches can be used to identify glaucoma progression?
- Empirical clinical judgement
- Event-based analysis
- Trend-analysis
- Defect classification systems
whats wrong with empirical clinical judgement to assess glaucoma progression?
- its open to inter and intra observer variability
- only gives qualitative info which can be more difficult to compare/ interpret by someone else
what is event analysis?
a way to compare the sensitivity at a given location of the measured VF of the pattern deviation map in two examinations.
(resistant to the effect of progressive catarcat)
what are the negatives of event analysis?
-cant determine the rate of change of the progression
-its influenced by the inbetween test variability which is high especially in extensively depressed stimulus locations
in event analysis, whats the difference between possible visual field progression and likely visual field progression?
possible is where 3 or more locations exhibit a statistically significant reduction in the estimated sensitivity compared to that derived at the two baseline examinations, which lies outside that for stable glaucoma, on two successive examinations whereas likely is on three or more successive examinations
what is trend analysis?
where the progressive loss in a series of visual fields over months/ years is plotted and a linear relationship between a given VF outcome and the tine to follow up is quantified to give an estimation of the rate of progression
what are the limitations to trend analysis?
- The necessity to have five or more examinations to plot the slope
- The frequency of examinations
- The levels of within- and between-examination variability
- The position of the examination within the time series
- The lack of agreement over the magnitude of the slope for the identification of progression
- The lack of separation of the normal age-decline in sensitivity; the overestimation of a patient due to the
normal age-decline in sensitivity (which you can overcome with the use of the pattern deviation values) - The analysis of global indices does not provide spatial information as for the observed defect; thus, is not sensitive for the early detection of glaucoma, but provides information about the global range, fact that is suitable for the longitudinal observation of the patient
