Normal Fundus 1 - CSB Flashcards
Define the Fundus
The back portion of the interior of the globe as seen through the pupil via an ophthalmoscope.
[key to note that you know the fundus isn’t just the retina - it’s everything you can see at the back of the eye including but not limited to structures such as vessels and the choroid.]
What is the limit of the fundus? (i.e. where the retina joins the ciliary body)
Ora serrata
Which components of the eye join at the ora serrata?
Retina joins the ciliary body at the equator of the eye
What is the maximum percent of the fundus an ophthalmoscope allow us to see?
65-70%
[if you are really skilled and the patient has a decent sized pupil]
What technique allows for a full (100%) view of the fundus?
Scleral indentation (can see all the way around into the periphery). Here an instrument is pressed onto the side of the eyeball thus pushing the fundus into view of the direct ophthalmoscope.
Which two things does the orange/red background of the fundus as seen from the pupil arise from?
- Light directly being reflected off choroidal blood vessels/blood in the choroidal circulation
- Light that is reflected back from the sclera and transmitted through choroidal blood vessels
What is the choriocapillaris?
The dense network of choroidal capillaries. [It provides blood supply to retina].
What two things does the amount of light directly reflected from the choroidal blood vessels and transmitted through the choroidal blood vessels depend on? (i.e. what does the brightness of the fundus background depend on?)
- degree of pigmentation of the retina - degree of pigmentation of the choroid (basically RPE - retinal pigment epithelium which is present in the retina and choroid absorbs light thus where there is more RPE the fundus background will look less bright)
[Important to note fundus background is highly variable]
What type of appearance does a fundus have if there is a lot of pigment in the choroid?
Brown and dim
What is a property of most of the fundus/retinal layers in a healthy eye?
That they are transparent and thus do not contribute to the fundus appearance all. All we see is the blood vessels in the retina and layers behind the retina.
What retinal layer does contribute to a typical fundus appearance?
The internal limiting membrane = between the retina and vitreous
What appearance does the internal limiting membrane layer of the retina have?
Appearance of ‘‘watered silk’‘/shiny especially in younger people, as although its transparent it reflects the ophthalmoscope beam.
What are the three different types of normal fundus which are just present due to physiological differences between people?
- uniform stippled
- tesselated (tigroid)
- albinotic
what are the three types of uniform stippled types of fundus appearance
- dark or negroid
- medium or caucasian
- light or blonde
what does a uniform stippled fundus look like
like its made up of lots of little dots or coloured, looking speckled
What are the two reasons for a dark or negroid appearance of a fundus?
- heavily pigmented RPE
- heavily pigmented choroid
What are the two reasons for a medium or Caucasian fundus appearance?
- normally pigmented RPE
- normally pigmented choroid
What are the two reasons for a light or blonde fundus appearance?
- lightly pigmented RPE
- lightly pigmented choroid
What does the light pigmentation of the RPE and choroid in a light or blonde fundus result in, in regards to its appearance?
- A bright glow from choroid resulting in the ability to see individual choroidal blood vessels.
What are the two reasons for a tessellated or tigroid fundus appearance?
- lightly pigmented RPE
- normal to heavily pigmented choroid so can see through the RPE as it hasn’t got much pigment, but the choroid underneath has lots of pigment so you can’t see choroidal vessels. (This gives a stripy appearance hence the term tigeroid - ‘tigery’).
What is the reason for an albinotic fundus appearance?
Virtually no pigment in RPE or choroid, so can see through layers of the choroid and RPE thus blood vessels of underlying choroidal circulation can be seen too.
What 4 things does the degree of pigmentation in the retina depend on and explain whether the degree of pigmentation is uniform across the whole retina
- age (as you age you lose pigment- so fundus becomes slightly dimmer) - race
- hereditary
- metabolic
[you can have more than one type of fundus background in the same eye, degree of pigmentation of retina and choroid don’t always run parallel- e.g. can have a highly pigmented retina but low pigmented choroid]
Define the optic disc
The ophthalmoscopic view of the optic nerve head
What are the 8 main features of the optic disc you assess?
- size
- shape (is it more vertically oval or horizontally oval?)
- colour (healthy pink or pale white?)
- margins
- level of cupping and cup depth
- neuroretinal rim ( the part around the cup)
- vessels
- surroundings
What 2 things does the colour of the optic disc depend on?
- the white lamina cribrosa and myelinated nerve fibres behind the lamina - the red blood (around the optic disc rim) in capillaries supplying the disc
Why is it harder to detect glaucoma in a small optic disc?
As a small disc has a small cup to disc ratio therefore the RGC (retinal ganglion cells) axons are more bunched up (usually a big cup to disc ratio is expected to be seen in a glaucomatous patient).
What does a pink rim around the disc indicate?
a healthy optic disc as there are lots of tiny capillaries giving a good blood supply
what does a deeper cup visually look like?
A deeper cup looks visually more pale- as you are looking more into the lamina cribrosa
why is the cup in the centre of the disc more pale?
This is because you are looking at a more deeper level in the optic nerve head (so more towards the back) , seeing through to the lamina cribrosa and myelinated nerve fibres underneath,
What do disc margins of disc look like in a healthy eye?
There is a relative blurring of margins on nasal 2/3rds of the disc due to distribution of nerve fibres.
What can sharp clear margins on the nasal side of the disc indicate
Optic atrophy
What can very blurred margins on the temporal side of the optic disc indicate?
Oedema (swelling of the disc) - which may be a sign of raised intracranial pressure
What can be the causes of a swollen disc/papilloedoema and how does it appear in volk and direct ophthalmoscopy?
Causes of a swollen optic disc arise from raised intracranial pressure which can be caused by the following:
- aneurysm
- haemorrhage
- space occupying tumour.
In a volk lens- disc looks raised and swollen
I
What can be the causes of a swollen disc/papilloedema?
raised intracranial pressure from:
- aneurysm
- haemorrhage
- space occupying tumour
What % of eyes have a flat disc (as in no measurable cup)?
15%
How can the level of cupping be measured
By recording the VERTICAL C/D ratio
What does a cup depth which goes more deep overtime indicate?
Glaucoma as they are losing RGC’s (retinal ganglion cells) overtime e.g. if 0.2 CD ratio in 20’s then 0.5 CD ratio in 50’s = pathological
What cup to disc ratio is susceptible to glaucoma (primary/chronic open angle)?
0.6 CD ratio
What does a cup depth which goes more deep overtime indicate?
Glaucoma as they are losing RGC’s (retinal ganglion cells) overtime
What is visible in people who have a deep cup?
The lamina cribrosa
How does the lamina cribrosa appear in very deep cup?
As a granular structure - resembling the appearance of rice pudding
what can be observed at the boundaries of the cup when assessing the cup depth?
- look at colour change
- the small bv’s skirt around the edge of the cup
Explain which 3 ways you can detect level of cup depth with a handheld direct ophthalmoscope?
-
quantitative:
- the difference in the lens required for focusing Steps: First focus on the neuroretinal rim then make a note of the power. Then move across and focus on the bottom of the cup and make a note of this power. Subtract the two powers to find the depth of the cup. e.g. if the edge of the disc was clear with plano, but the bottom of the cup was first clear with a -3D lens, you would record depth of cup as 3D.
- a shallow cup will be at the same level as the rim, so don’t need to change lens power as much - parallax (qualitative)
You are looking to see relative movement. - when moving the ophthalmoscope beam - areas at different levels move at different speeds - deep cup = more movement experienced at cup. The less movement there is the shallower the cup. 3. Pallor - This method involves inspecting degree of paleness of the optic disc. Increased pallor is associated with increased depth due to visibility of the lamina cribrosa and underlying myelinated fibres.
Which 2 blood vessels branch out from optic nerve head?
- central retinal vein
- central retinal artery
Describe the central retinal artery
CRA has all characteristics of a true artery, but after branching soon becomes an arteriole
Describe the central retinal vein
CRV has all characteristics of a true vein but after branching soon becomes a venue
What is the usual pressure of the central retinal vein?
2mmHg higher than mean IOP
Explain why and how spontaneous pulsation of the central retinal vein occurs
- CRV pressure is usually constant - 2mmHG higher than mean IOP - during cycle of variation of IOP = the IOP will become greater than the CRV pressure - this leads to partial collapse of the vein, which will not recover until IOP falls back below that in the CRV
What causes characteristic surroundings of the optic disc?
Certain layers of the fundus stopping short of the disc
List 3 characteristic surroundings of the optic disc
- A scleral ring
- A choroidal crescent
- Pigment spots
How does a scleral ring occur?
RPE and choroid stop short of the disc and only the sclera reaches the optic nerve head which results in the appearance of pale ring around disc. (when recording this use clock numbers to say where thickest and whether it goes all around in a ring)
[look at what arrows on fundus photo are pointing out]
What can a scleral ring cause visually and why?
A Larger blind spot as px has no rods or cones here
How does a choroidal crescent occur?
RPE stops short of the disc causing a pigmented ring around the disc (a little away from the disc itself) and the sclera and choroid reach/go to the disc. (It creates a sort of dim moon shape)
Which group of people can a scleral ring occur in?
Myopic patients who have large axial lengths
How/Why do pigment spots occur around the optic disc?
A build up of more than the usual amount of pigment at the edge of the disc
Where does the cilio-retinal artery come from?
It is not a branch of the CRA, but is derived from blood vessels supplying the choroid, i.e. from underlying choroidal circulation
How large is the cilio-retinal artery
varies in size, but can be as large as a principle arteriole
What does the cilio retinal artery supply
significant area of the retina
How is having a cilio-retinal artery beneficial
If you get a central retinal artery occlusion, you won’t go blind as the cilio-retinal artery will supply the retina and you will still have an island of vision left
What happens in ocular albinism?
The fundus and iris lack pigment thus reflected light from ophthalmoscope glows back through the iris
What would optic atrophy look like in terms of colour of the optic disc?
The optic disc would be a pale colour because surrounding vessels have died so there is a limited blood supply.
What is a swollen optic disc referred to as?
Papilloedema
Is it suspicious if someone’s had a cup to disk ratio of 0.6 their whole life?
No
Is it suspicious if someones CD ratio increases?
Yes
Is asymmetry between a CD ratio in two eyes suspicious?
Yes (if beyond >0.1)
Is there general variation in cup depth across the population?
Yes, there are physiological differences.
What is the neuroretinal rim?
The part around the cup.
What is the ISNT rule in regards to the neuroretinal rim?
Healthy eye usually follows ISNT rule i.e.neuroretinal rim is thickest inferiorly, then superiorly, then nasally, then temporally.Next
What can the ISNT rule not being followed be evidence of?
Suspected evidence of glaucoma. With glaucoma you begin to see vertical thinning, with atrophy along the inferior and superior rims. Thus, when optic nerves don’t follow the ISNT rule, they may have had glaucomatous damage.
Tell me about myelinated nerve fibres as a surrounding to the optic disc.
Nerve Fibres are not normally myelinated until level of lamina cribrosa (so anything anterior to this will not normally be myelinated)
Sometimes NFs retain their myelin sheath on the disc or the retina ( this is a congential condition)
Normally nerve fibres appear transparent however myelinated nerve fibres appear a brilliant white against the fundus background.
It is Non progressive condition.
What is associated with an area of myelinated nerve fibre on the fundus?
A corresponding blind spot/scotoma in that area of the visual field.
[because patients are born with it they don’t tend to notice it]
How can you tell apart a myelinated nerve fibre area from a white lesion on the retina?
The myelinated nerve fibre area shall obscure blood vessels on the retina (the nerve fibres are infront of the blood vessels).
