Visual Defects

Question 1

What are symptoms of visual loss?

Answer 1

• Blurred/out of focus
• Glare
• Distorted vision
• Shadow
• Floater
• Things look pale

Question 2

Describe blurred vision

Answer 2

• Out of focus/not sharp
• No distortion
• Macular problem
• Refractive problems (cornea, lens, shape of eye)

Question 3

Describe glare

Answer 3

• Difficulty seeing in bright light (low sun, driving at night, fluorescent light)
• Corneal/lens problem (cataracts)

Question 4

Describe distorted vision

Answer 4

• Lines not straight
• Wavy/jumbled up
• Condition affecting retina (wet macular degeneration, macular hole/pucker, retinal detachement)

Question 5

Why do things look pale?

Answer 5

• Optic nerve disease (optic neuritis, compressive optic nerve disease)
• Condition affecting retina (wet macular degeneration, central serous retinopathy)

Question 6

What is a floater?

Answer 6

• Opacity in vitreous
• Vitreous syneresis
• Posterior vitreous detachment
• Vitreous haemorrhage

Question 7

What are cataracts?

Answer 7

• Opacity of the lens
• Common ageing
• Gradual onset
• Blurred vision, glare, change in refraction

Question 8

What does RPE (retinal pigment epithelium) do?

Answer 8

• Removes waste products from cones & rods

- Reduced function leads to drusen

Question 9

What are signs of dry ARMD?

Answer 9

• Signs: Drusen, RPE pigmentation, RPE atrophy
• Gradual deterioration
• Affects reading vision: loss of small area leads to severe visual loss
• Sudden = wet ARMD

Question 10

What are risk factors for carotid artery disease?

Answer 10

• Hypertension
• Smoking
• Diabetes
• High Cholesterol

Question 11

What are the differential diagnoses for distorted vision/metamorphosia?

Answer 11

• Wet macular degeneration
• Macular hole/pucker
• Retinal detachment

Question 12

What is wet ARMD?

Answer 12

• Choroidal neovascular membrane: abnormal blood vessels form underneath the macula & damage cells
• Common rapid loss of vision

Question 13

What are causes of central retinal artery occlusion?

Answer 13

• Embolic
• Heart disease (valve disease)
• Carotid artery disease (most common)

Question 14

How does giant cell arteritis cause visual loss?

Answer 14

• Central retinal artery occlusion
• Anterior Ischemic Optic Neuropathy
• Not treatable
• If one eye effected high risk to other eye

Question 15

How are Choroidal Neovascular Membranes treated?

Answer 15

• Intravitreal injection of antiVEGF
• Binds to VEGF & prevents it acting on CNM
• Visual loss can be reversed

Question 16

What causes a macular hole?

Answer 16

Natural movement of eyes

Question 17

What is the fovea?

Answer 17

Point of highest visual acuity in the retina, light reaches photoreceptors directly

Question 18

Which parts of the eye refract light?

Answer 18

• Cornea

- Lens: to produce sharp image, mainly for close up objects (book), lens changes shape-accommodation

Question 19

How does the lens change shape?

Answer 19

• Rounding of the lens increases refractive power
• Due to natural elasticity
• Contraction of ciliary muscles receiving tension on zonule fibres

Question 20

How does an ‘emmetropic’ eye correct vision?

Answer 20

• Normal eye
• Focuses parallel light rays on retina
• No need for accommodation

Question 21

How does a ‘hyperopia’ eye correct vision?

Answer 21

• 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)

Question 22

How does a ‘myopia’ eye correct vision?

Answer 22

• Nearsightedness
• Eyeball is too long
• Rays converge before the retina
• Concave lens

Question 23

Where is the pigment epithelium of the eye found and what is its function?

Answer 23

• Behind the retina

- Cells filled with melanin to absorb light not absorbed by the retina

Question 24

What do ON & OFF bipolar cells respond to? What is direct & indirect input?

Answer 24

• ON= depolarise in response to light
• OFF= depolarise in response to dark
• Direct= input from receptive field centre
• indirect=input from receptive field surround

Question 25

What are the 3 types of retinal ganglion cells?

Answer 25

- 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

Question 26

In photoreceptors, where does absorption occur?

Answer 26

- 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

Question 27

What is the pigment in rods called?

Answer 27

- Rhodopsin - Each cone opsin has different spectral sensitivity - Colour perception determined by relative contribution of blue, green, red cones on retina

Question 28

What are the components of the retina that send information to the brain?

Answer 28

- 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

Question 29

What is the mechanism for ON centre bipolar cells?

Answer 29

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

Question 30

What is the mechanism for ON centre bipolar cells for surroundings?

Answer 30

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

Question 31

What are the 3 types of retinal ganglion cells?

Answer 31

- 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)

Question 32

What are ganglion cells mainly responsive to?

Answer 32

Differences in illumination that occur within their receptive fields

Question 33

What is visual processing?

Answer 33

- 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