ARMD Flashcards
1
Q
Describe the layers of the retina?
A
- Differs from anatomy at fovea and macula
- Most posterior (from choroid) to anterior:
o Choroid provides some blood flow to retinal structures
o Retinal Pigment Epithelium (RPE) – 2 main functions:
To provide vitamin A to photoreceptors
Heavily pigmented to prevent scatter of light from photons (which are not incident on photoreceptors themselves
o Rods/Cones:
Away from macula have mixture of rods & cones with more rods further out in periphery and more cones present centrally on retina
o Outer nuclear layer:
Contains cell bodies of horizontal and bipolar cells
When photon hits one of rods or cones it causes a transformation in the opsin proteins within the rods/cones – start of the nerve impulse travelling from rods and cones - Start of the journey for photons creating an impulse which can then be decoded within brain as visual signal
Once opsin has been transformed and signal transmits to horizontal and bipolar cells – first to cell bodies
o Outer plexiform layer:
Contains axons of horizontal and bipolar cells
o Inner nuclear layer:
Contains amacrine cells
o Inner plexiform layer:
Contains axons of bipolar and amacrine cells – as they then go onto synapse with ganglion cells
o Ganglion cell layer:
Contains ganglion cells
o Retinal nerve fibre layer:
Takes nerve fibres (axons of ganglion cells) to optic nerve
o Inner limiting membrane:
Most anterior structure in retina
2
Q
Describe the macula?
A
- One of key differences between macula and peripheral retina is proportion of cone cells to rod cells
- In periphery, much higher proportion of rod cells
- In central macula, densely populated area in central 0.15mm of retina (foveola) of cone cells
- As move away from central foveola, start to get a sharp decline in number of cone cells
o & at same time, an increase in number of rod cells - Trend continues out into far periphery
- In central foveola, absolutely no rod cells – only cone cells in that area
o Cones important for detailed and colour vision
Macula is AVASCULAR -> supplied solely by choroid (another reason for excellent vision as retinal BVs do not disrupt vision in this area at all)
3
Q
Describe the fovea?
A
- Distribution of photoreceptors in macula is quite different to surrounding retinal tissues
- Other differences too
- Macula lutea extends across from fovea into parafoveal region - ~2.5mm in diameter
- Fovea is ~1.5mm in diameter – encircling central foveola
o Foveal pit of foveola is 0.15mm in diameter
o Foveal pit quite different to rest of retina and even rest of macula – as it is almost devoid of the other layers of the retina aside from cone photoreceptors & RPE
o At edge of foveal pit, start to see other cell layers appearing – some cell bodies (horizontal and bipolar cells) and some amacrine cell processes - As go further out into macula area - ~0.35mm encircling foveola, start to see the first ganglion cell bodies
4
Q
Describe the foveola/foveal pit?
A
- Devoid of a lot of other layers you would expect in surrounding retina
- Concentrated density of cone photoreceptors – allows for really detailed vision and good colour vision in this area
- No rods
- When look at fovea, cone cells are extremely well packed – packed in hexagonal mosaic
o Allows for detailed vision with high resolution and detailed colour vision
5
Q
Describe the fovea cellular structure?
A
- How the cone photoreceptors are packed within central foveola
- Regimented hexagonal pattern
- Majority of cone photoreceptors in this area are red and green photoreceptors
- Slightly larger cone photoreceptors highlighted with arrows (IN IMAGE) are the blue cone photoreceptors
- Allows for extremely detailed vision
o High resolution of images which are projected onto fovea
o Detailed colour vision
6
Q
What are the key features of the macula?
A
- Densely packed cone photoreceptors
- An absence of rods at the fovea
o Rods are more important for night vision and not as important for detailed vision - Fovea is avascular and in this area the retina is supplied with oxygen which diffuses from the choroid to the foveal retina
- Fovea 1.5mm across
- Foveola (foveal pit) 0.15mm diameter – cones most densely packed in this area
- Avascular zone (supplied purely by choroid – centred on foveola) 0.5mm diameter
- Half of the retinal nerves in the optic nerve serve the fovea
- Retina is thinnest at the fovea as retinal cell bodies and structures are displaced concentrically to the edge of the fovea to allow
7
Q
What is AMD and how many people have it in UK?
A
- AMD: long-term degenerative condition
- Leading cause of visual impairment in the UK
- ~600,000 people diagnosed (UK)
- AMD is relevant to optometrists as loss of sight can have impact on quality of life and emotional health
8
Q
What are the statistics for AMD (50 yos, 65 yos, 80 yos)?
A
- Prevalence estimates for UK by age groups (all types of AMD):
- 50+ y: 2.4 %
- 65+ y: 4.8 %
- 80+ y: 12.2 %
- Number of people with AMD predicted to rise
- 26,000 new cases each year (NICE estimate)
- Key reasons: aging population, increase in life expectancy
- Workload implications for HES
9
Q
How many people in UK are visually impaired from AMD?
A
- Visual impairment (6/18 or worse) from AMD affects
o 4% of UK population > 75 years
o 14% of UK population > 90 years
o 1.6% have VA < 6/60 in population > 75 years - ^Bilateral VA
10
Q
What are the Risk Factors for AMD from Nice Guidance?
A
- Diet low in omega 3 and 6 and carotenoids and minerals are a risk of AMD
- Lack of exercise
- Smoking – biggest modifiable risk factor
- Older age
- Hypertension
- Family history of AMD
- BMI of 30 kg/m2 or higher
- Presence of AMD in the other eye – monitor these pxs really carefully
- High fat diet
11
Q
What is dry AMD? Is it more or less common? How fast does it progress?
A
- More common presentation
- Slowly progressing
- No sudden loss of vision
- Managed by Optometrists in most cases
Larger drusen more associated with disease progression
12
Q
A
13
Q
Describe NICE Classification of dry AMD (normal eyes, early AMD (low, medium, high risk of progression), late AMD)
A
- Normal eyes
o No signs of AMD.
o Small (hard) drusen (<63 micrometres (1/2 a vein width (look at central vein))) only. - Early AMD
o Low risk of progression:
Medium drusen (≥63 but <125 micrometres), or
Pigmentary abnormalities.
o Medium risk of progression:
Large drusen (≥125 micrometres), or
Reticular drusen, or
Medium drusen with pigmentary abnormalities.
o High risk of progression:
Large drusen (≥125 micrometres) with pigmentary abnormalities, or
Reticular drusen with pigmentary abnormalities, or
Vitelliform lesion without significant visual loss (best-corrected acuity better than 6/18), or
Atrophy <175 micrometres and not involving the fovea. - Late AMD (dry)
o Geographic atrophy (in the absence of neovascular AMD).
o Significant visual loss (6/18 or worse) associated with:
Dense or confluent drusen, or
Advanced pigmentary changes and/or atrophy, or
Vitelliform lesion.
63um is half a vein width in diameter
13
Q
Describe reticular drusen (dry AMD)?
A
- Drusen are sub retinal pigment epithelium deposits of extracellular debris composed of lipids and proteins which sit just below the RPE, or between the RPE and bruchs membrane
- Reticular drusen are also known as pseudo-drusen or subretinal drusenoid deposits. Contrary to the drusen which lie below the retinal pigment epithelium (RPE), reticular drusen are located superficial to the RPE. They are yellowish subretinal lesions arranged in a network and indicate a greater risk of AMD progression
Due to position, reticular drusen are much more strongly linked with progression of RPE
14
Q
Describe vitelliform lesion (dry AMD)?
A
- Accumulation of lipofuscin within the subretinal space
- Lipofuscin and extracellular deposit accumulation in drusen is below the RPE. Lipofuscin is is a heterogeneous material composed of a mixture of lipids, proteins, and different fluorescent compounds, the main fluorophore of which has recently been identified as a derivative of vitamin A
- Clinical course of patient 3.
o (A) Vitelliform lesion in the left eye.
o (B) FA showing staining and leakage of the vitelliform lesion without evidence of CNV.
o (C) Vitelliform lesion in the left eye with associated SRF. Given the appearance of VM, the patient was observed without injection. Two years later
o (D), the vitelliform lesion coalesced and the SRF resolved spontaneously.
o (E) Five years after from presentation, the vitelliform lesion spontaneously collapsed
15
Q
Describe atrophy (dry AMD)?
A
- In early stages, may just have small patches of atrophy
- Geographic atrophy - loss of cells in the fovea - RPE and outer retina (rods and cones are lost)
- Geographic atrophy - Complete loss or RPE and outer retina if is at least 250 microns wide (2 vein widths in diameter - can be seen on any OCT- standard research definition
o On OCT: when there is atrophy, start to lose form of RPE and start to lose some of the layers as the outer segments of the rods and cones start to decay