Assessment of the optic disc (optic nerve head) in glaucoma Flashcards Preview

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what is glaucoma described as

a group of diseases characterised by retinal ganglion cell dysfunction and death


the is the detection of glaucoma and it's progression based on

identification of abnormalities or changes in the optic nerve head (ONH) or the retinal nerve fibre layer (RNFL), either functional or structural

so the eye does not have glaucoma unless the ONH is damaged = optic neuropathy but does go hand in hand with other features such as raised IOP, narrow angles etc

raised IOP and narrow angles = a suspect status but unless the eye is damaged at the level of the ONH, then is actually doesn't have glaucoma


name 4 points about the relationship between glaucoma and visual fields results and what do all these points mean

- Common statement….“50% nerve fibre loss before VF (Goldman bowl perimetry) defect…” - certain amount of damage to the ONH has to occur before the defect occurs

- RG cells mapped with threshold VF data

- A 5-dB VF loss ~25% RGC loss - a 25% ON fibre loss has to occur before a repeated VF loss is detected on modern images

- Abnormal points at p less than 0.5% have a mean
RGC loss of ~29%

= Extent of nerve fibre loss overstated, therefore the ONH is something we should observe first to prevent a VF defect from forming


list 5 features of a ‘normal’ optic disc

- Neural rim - yellowish/pink

- Physiological cup - avascular and pale

- White physiological scleral rim (Elschning) - scleral rim = pale colour halo around edge of disc (is where the neural tissue actually begins, so most accurately estimate disc margin if not will over estimate the CD ratio)

- Yellow-white ‘sieve-like’ appearance of lamina cribrosa

- Rim width configuration - ISNT (but not just the only guide for glaucoma)


why is the ISNT rule rim width configuration not the only guide for detecting glaucoma

because it doesn't apply with a px who has, a tilted disc or myopic px's etc so is just a guide for detecting, but the rule can be broken with glaucoma


when considering the c/d ratio, what else do you have to consider and why

you have to consider the height of the optic disc as well because

1.2 million nerve fibres passing through a large scleral opening gives a large cup

1.2 million nerve fibres passing through a small scleral opening gives a small cup and the nerve fibres are just more stuffed together

so if the scleral opening is large then will have a large cup = doesn't mean px has glaucoma its just a physiological difference


list the 6 optic disc changes in glaucoma

- Enlargement of the optic cup (goes hand in hand with reduction in NRR tissue)

- Loss of disc rim (neural tissue)

- Vascular changes

- Increased pallor (of NRR, not the cup which is avascular)

- Peri-papillary atrophy (changes to edge of disc)

- RNFL changes


list 6 signs that can be seen in the enlargement of the optic cup in glaucoma

- Generalised: enlargement of cup is circumferential 360 deg

- Localised: if extremely localised = focal notch of NRR

- Vt-Hz disproportion: if cup is vertically elongated = suspicious as the disc is normally vertical and the cup is normally round or horizontal

- Inter-eye asymmetry: hallmark of glaucoma

- Lamina baring or
backward bowing: pore pattern is visible = deeper (but no point measuring dioptric value as deep cup can be normal)

- ‘ISNT’ and ‘notch’


how do you assess the c/d ratio correctly

do not rely on the change in cup pallor as it does not correlate with the contour of the disc

the cup begins when theres a first discernible change in contour away from the surface of the retina and that may not match with the level of the pallor (thats why a stereoscopic view of the disc is important)


what do you need to know in order to evaluate the c/d ratio

what are 2 disadvantages of assessing c/d ratio to detect glaucoma

- Need to know optic disc
size - to interpret the amount of cupping

- Poor sensitivity/specificity: won't allow us to distinguish glaucoma alone adequately, and can better discriminate with combine with other features

- Inter/intra-observer


how can the size of the optic disc be measured clinically and how can the size of the disc have an impact on your judgement of a glaucomatous disc

by using binocular indirect ophthalmoscopy - volk lens
they will have correction factors:
Superfield 1.5
90D 1.4
78D 1.1
66D 1.0

can measure height of the disc by changing the size of your slit lamp beam vertically with the upper and lower edge of the ONH ad read off the graticule when doing volk
which is the best way to do it unless your using OCT or other photographic method

multiply the size on the graticule of the SL with the correction value of the volk lens - for 66D no correction factor required

a c/d ratio of 0.5 in a small ONH is more suspicious of a c/d ratio of 0.7 in a large ONH


what is the size of a normal ONH

what size is considered a small ONH

what size is considered a large ONH

normal = 1.7-1.8mm high

small = 1.1-1.2mm height

large = 2.1mm or more in height


what is the difference between a physiological and a pathological neural rim

what is the most important this to look for when assessing neural rim

physiological: follows the ISNT rule (even if it has a large cup in a large disc)

pathological: does not follow the ISNT rule e.g. superior NRR rim is thinner than temporal

most important thing to look for is asymmetry between both eyes e.g. less cupping in one eye and a larger amount of cupping in the other eye = different c/d ratios
and asymmetry in cupping between the superior and inferior hemifields of one eye in VFs


how can you detect asymmetry of neural rim between both eyes and in one eye and how will this appear

in a VF test

will show a arcuate defect where the nrr tissue has been lost
asymmetry in the results between the lower and the upper hemifield


what are the 4 types of vascular changes that could be found in glaucoma

- Vessel configuration
Circumlinear baring

- Calibre of vessels: near optic disc is thinned (but is not a early sign)

- Collateral vessels: not leaky, but are shunt vessels

- Haemorrhage


describe the 4 different changes that can occur with vessel configuration in glaucoma

Nasalisation: major trunk vessels have shunted in the nasal region (normally they should have curved around more) seen in advanced stage

Bayonetting: can be normal in deep/steep cupping, or seen in glaucoma where can see a sharp edge to the cup and then see a BV deflecting underneath the RIM, so it emerges at the base of the cup in a different position

Flyover/overpass: vessel crossing the central part of the disc and its lost contact support with the disc tissue underneath

Circumlinear baring: vessel follows a course/curved pattern with an area of pallor above that BV which tends to imply that cupping has increased but that BV has been beared/exposed as theres cupping above an below it


what type of sign in glaucoma is disc haemorrhaging and where is it mainly located

what does it indicate

which type of glaucoma can it be commonly seen in

what is the difference in outcome compared to someone who has glaucoma and no disc haemorrhaging

what is the ddx of disc haemorrhaging in glaucoma

an active sign of progression seen more commonly infer-temporally (which correlates with supers-nasal vf defect)

it indicates the glaucoma is not controlled and needs to be closely monitored

commonly seen in normal tension glaucoma

haemorrhage in glaucoma will show larger progression of VF loss compared to px with glaucoma and no disc haemorrhage

ddx - disc haemorrhaging can also happen in PVD


what is peri-papillary atrophy

what type of feature is it

which type of peri-papillary atrophy is uncommon in normals and hence seen in glaucoma

what outcome is it associated with

thinning of the retina and choroid around the edge of the disc

is a second order feature = can be acquired due to glaucoma

a-zone and b-zone
b-zone uncommon in normals, so rare in patients who don't have a pathology and hence may be seen in glaucoma

it is visible sclera b zone = closer to the disc and a bad form of NRR loss (if inferiorly will form a superior arcuate VF loss)
NRR and VF loss


what are all the 8 questions you will want in your optic disc checklist

- Is the vertical C/D ratio more than 0.5?

- Is the C/D ratio consistent with disc size?

- Is the cup more vertically oval than the disc?

- Does rim configuration differ from ‘ISNT’?

- Are there any notches or pallor regions in the nrr?

- Are there any disc haemorrhages?

- Is the inter-eye C/D ratio asymmetry more than 0.2?

- Has there been a more than 0.15 change in C/D ratio?


when can a c/d ratio asymmetry of more than 0.2 be regarded as normal

when the size and the height of the disc between the 2 eyes is different. so account for that


how should you record your assessment of the optic disc

if theres a fundus machine then take a picture

if there isn't then draw it

write the c/d ratio

describe the appearance of the ONH and any pathology seen

record which volk lens was used and the correction factor when measuring the height of the disc


what is the name of a scale that can be used to assess a optic disc in glaucoma

what does it incorporate

what is a advantage to this scale

disc damage likelihood scale

Incorporates into a grading scale:
- The effect of disc size
- Focal rim width

- Advantage: Highly reproducible - correlates with VF loss


what is the method of using the disc damage likelihood scale

- Measure disc size/height and correct for Volk lens used

- discs categorised as 1 of these 3 categories:
S less than 1.5mm
M 1.5 – 2.0mm
L more than 2.0mm

- Measure width of thinnest part of the rim - Rim:Disc ratio

- If no rim present at thinnest part value = 0, if rim as thick as possible (no cup) value = 0.5

- Extent of rim absence is measured in degrees

- It estimates the likelihood of a px having glaucoma e.g. over a 5 year period


which 2 places can optic disc observer variability occur

what are the 2 sources of measurement error and what is the difference in variability between both

Valid and reliable measures are needed, occurs in:
- General glaucoma clinic monitoring
- Co-management/shared care schemes

2 sources of measurement error:
- Intra-observer variability (within) i.e. yourself = has a tighter level of agreement than inter

- Inter-observer variability (between) i.e. 2 colleagues = better level of agreement


what is the criteria for change in c/d ratio which brings suspicion of glaucoma

and what system is there a benefit of using

- C/D ratio has to change by equal/more than 0.15 (within/intra)

- C/D ratio has to change by equal/more than 0.25 (between/inter)

- Benefits of using a 20 point scale*
(i.e 0.0-1.0 in 0.05 steps)


how can you do a RNFL assessment and what signs show a defect in the RNFL

what is the appearance of a pseudo defect

can only detect with monochromatic light i.e. red free (green filter on SL or OCT)

a dark wedge shaped defect which can reach the optic disc = thinning of RNFL

pseudo defect = less than a vessels width


list 3 optic nerve head imaging systems that can be used

- Heidelberg Retina Tomograph (HRT II)


- Optical Coherence Tomography (OCT)


how is sensitivity and specificity related to glaucoma

sensitivity = about detecting diseased individuals

specificity = about normals

so if trying to discriminate between glaucoma and normals = need good sensitivity and specificity

can be:
- Technique employed
- Competence/experience


list 6 congenital disc anomalies that can mimic the appearance of glaucoma and hence be a ddx

- Coloboma
- Optic disc pit
- Tilted disc
- Drusen
- Myelinated fibres
- ‘Myopic’ disc


list 5 other conditions apart from glaucoma that have nerve fibre bundle defects, paracentral, arcuate and nasal step

Can also arise due to:

- Optic nerve head drusen

- Congenital optic nerve head pits

- Coloboma of optic nerve

- Anterior ischaemic optic neuropathy

- Tilted disc


what is the NICE key implementation point (what 5 tests you should offer) for a px who has diagnosis

At diagnosis offer all people who have COAG,
who are suspected of having COAG or who have OHT all of the following tests:

- IOP measurement using GAT

- central corneal thickness (CCT) measurement

- peripheral anterior chamber configuration and depth assessments
using gonioscopy

- visual field measurement using standard automated perimetry (central thresholding test)

- optic nerve assessment, with dilatation, using stereoscopic slit
lamp biomicroscopy with fundus examination