Visual Defects Flashcards
1
Q
What are symptoms of visual loss?
A
- Blurred/out of focus
- Glare
- Distorted vision
- Shadow
- Floater
- Things look pale
2
Q
Describe blurred vision
A
- Out of focus/not sharp
- No distortion
- Macular problem
- Refractive problems (cornea, lens, shape of eye)
3
Q
Describe glare
A
- Difficulty seeing in bright light (low sun, driving at night, fluorescent light)
- Corneal/lens problem (cataracts)
4
Q
Describe distorted vision
A
- Lines not straight
- Wavy/jumbled up
- Condition affecting retina (wet macular degeneration, macular hole/pucker, retinal detachement)
5
Q
Why do things look pale?
A
- Optic nerve disease (optic neuritis, compressive optic nerve disease)
- Condition affecting retina (wet macular degeneration, central serous retinopathy)
6
Q
What is a floater?
A
- Opacity in vitreous
- Vitreous syneresis
- Posterior vitreous detachment
- Vitreous haemorrhage
7
Q
What are cataracts?
A
- Opacity of the lens
- Common ageing
- Gradual onset
- Blurred vision, glare, change in refraction
8
Q
What does RPE (retinal pigment epithelium) do?
A
- Removes waste products from cones & rods
- Reduced function leads to drusen
9
Q
What are signs of dry ARMD?
A
- Signs: Drusen, RPE pigmentation, RPE atrophy
- Gradual deterioration
- Affects reading vision: loss of small area leads to severe visual loss
- Sudden = wet ARMD
10
Q
What are risk factors for carotid artery disease?
A
- Hypertension
- Smoking
- Diabetes
- High Cholesterol
11
Q
What are the differential diagnoses for distorted vision/metamorphosia?
A
- Wet macular degeneration
- Macular hole/pucker
- Retinal detachment
12
Q
What is wet ARMD?
A
- Choroidal neovascular membrane: abnormal blood vessels form underneath the macula & damage cells
- Common rapid loss of vision
13
Q
What are causes of central retinal artery occlusion?
A
- Embolic
- Heart disease (valve disease)
- Carotid artery disease (most common)
14
Q
How does giant cell arteritis cause visual loss?
A
- Central retinal artery occlusion
- Anterior Ischemic Optic Neuropathy
- Not treatable
- If one eye effected high risk to other eye
15
Q
How are Choroidal Neovascular Membranes treated?
A
- Intravitreal injection of antiVEGF
- Binds to VEGF & prevents it acting on CNM
- Visual loss can be reversed
16
Q
What causes a macular hole?
A
Natural movement of eyes
17
Q
What is the fovea?
A
Point of highest visual acuity in the retina, light reaches photoreceptors directly
18
Q
Which parts of the eye refract light?
A
- Cornea
- Lens: to produce sharp image, mainly for close up objects (book), lens changes shape-accommodation
19
Q
How does the lens change shape?
A
- Rounding of the lens increases refractive power
- Due to natural elasticity
- Contraction of ciliary muscles receiving tension on zonule fibres
20
Q
How does an ‘emmetropic’ eye correct vision?
A
- Normal eye
- Focuses parallel light rays on retina
- No need for accommodation
21
Q
How does a ‘hyperopia’ eye correct vision?
A
- Farsightedness
- Eyeball is too short
- Rays are focused behind the retina
- Result= blurry circle
- Accommodation needed for distant objects so near objects not in focus (convex lens)
22
Q
How does a ‘myopia’ eye correct vision?
A
- Nearsightedness
- Eyeball is too long
- Rays converge before the retina
- Concave lens
23
Q
Where is the pigment epithelium of the eye found and what is its function?
A
- Behind the retina
- Cells filled with melanin to absorb light not absorbed by the retina
24
Q
What do ON & OFF bipolar cells respond to? What is direct & indirect input?
A
- ON= depolarise in response to light
- OFF= depolarise in response to dark
- Direct= input from receptive field centre
- indirect=input from receptive field surround
25
What are the 3 types of retinal ganglion cells?
- Magnocellular: M-type, large cell type, large receptive field, detect stimulus movement
- Parvocellular: P-type, smaller cell type, sensitive to stimulus form & fine detail, colour opponent cells
- Non-M, Non-P: K-type, medium cell type
26
In photoreceptors, where does absorption occur?
- Outer segments
- Contain stack of discs containing light sensitive photopigments
- Rods= long cylindrical outer segment many discs, cones= short tapering outer segment few membranous discs
27
What is the pigment in rods called?
- Rhodopsin
- Each cone opsin has different spectral sensitivity
- Colour perception determined by relative contribution of blue, green, red cones on retina
28
What are the components of the retina that send information to the brain?
- Photoreceptors= convert light energy to neural activity
- Bipolar cells= create direct pathway from photoreceptors to ganglion cells. Receives input from 1 photoreceptor, receptive field centre makes direct contact
- Horizontal/amacrine cells= indirect pathway, modulators, receptive field surround makes contact with bipolar cells via these cells
- Retinal ganglion cells= axons leave eye forming optic nerve
29
What is the mechanism for ON centre bipolar cells?
1) light in centre
2) photoreceptor hyperpolarised
3) less glutamate released from photoreceptor
4) mGluR6 on ON bipolar cell surface less active allowing Na channel to open= depolarisation
30
What is the mechanism for ON centre bipolar cells for surroundings?
1) light in surround, dark in centre
2) centre photoreceptor depolarised, surround photoreceptor hyperpolarised
3) more glutamate released from centre photoreceptor, less glutamate released from surround photoreceptors making horizontal cells hyperpolarised
4) mGluR6 on ON bipolar cell surface more active closing Na channel= centre hyperpolarisation
5) Reduction in GABA release from horizontal cells depolarises central receptor producing more bipolar hyperpolarisation
31
What are the 3 types of retinal ganglion cells?
- Magnocellular (m-type)= large, large receptive field, detection of stimulus movement
- Parvocellular (p-type)= small, sensitive to stimulus form & fine detail & differences in wavelength of light(colour opponent cells), most common
- Non-M non-P (k-type)= medium, sensitive to differences in wavelengths of light (colour opponent cells)
32
What are ganglion cells mainly responsive to?
Differences in illumination that occur within their receptive fields
33
What is visual processing?
- M channel= analysis of object motion
- P-IB channel= analysis of object shape
- Blobs= analysis of object colour
- Orientation columns- simplex & complex cells in layers
- Ocular dominance columns= monocular-info from R or L eye
