Flashcards in Visual Defects Deck (33):
What are symptoms of visual loss?
-Blurred/out of focus
-Things look pale
Describe blurred vision
-Out of focus/not sharp
-Refractive problems (cornea, lens, shape of eye)
-Difficulty seeing in bright light (low sun, driving at night, fluorescent light)
-Corneal/lens problem (cataracts)
Describe distorted vision
-Lines not straight
-Condition affecting retina (wet macular degeneration, macular hole/pucker, retinal detachement)
Why do things look pale?
-Optic nerve disease (optic neuritis, compressive optic nerve disease)
-Condition affecting retina (wet macular degeneration, central serous retinopathy)
What is a floater?
-Opacity in vitreous
-Posterior vitreous detachment
What are cataracts?
-Opacity of the lens
-Blurred vision, glare, change in refraction
What does RPE (retinal pigment epithelium) do?
-Removes waste products from cones & rods
-Reduced function leads to drusen
What are signs of dry ARMD?
-Signs: Drusen, RPE pigmentation, RPE atrophy
-Affects reading vision: loss of small area leads to severe visual loss
-Sudden = wet ARMD
What are risk factors for carotid artery disease?
What are the differential diagnoses for distorted vision/metamorphosia?
-Wet macular degeneration
What is wet ARMD?
-Choroidal neovascular membrane: abnormal blood vessels form underneath the macula & damage cells
-Common rapid loss of vision
What are causes of central retinal artery occlusion?
-Heart disease (valve disease)
-Carotid artery disease (most common)
How does giant cell arteritis cause visual loss?
-Central retinal artery occlusion
-Anterior Ischemic Optic Neuropathy
-If one eye effected high risk to other eye
How are Choroidal Neovascular Membranes treated?
-Intravitreal injection of antiVEGF
-Binds to VEGF & prevents it acting on CNM
-Visual loss can be reversed
What causes a macular hole?
Natural movement of eyes
What is the fovea?
Point of highest visual acuity in the retina, light reaches photoreceptors directly
Which parts of the eye refract light?
-Lens: to produce sharp image, mainly for close up objects (book), lens changes shape-accommodation
How does the lens change shape?
-Rounding of the lens increases refractive power
-Due to natural elasticity
-Contraction of ciliary muscles receiving tension on zonule fibres
How does an 'emmetropic' eye correct vision?
-Focuses parallel light rays on retina
-No need for accommodation
How does a 'hyperopia' eye correct vision?
-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)
How does a 'myopia' eye correct vision?
-Eyeball is too long
-Rays converge before the retina
Where is the pigment epithelium of the eye found and what is its function?
-Behind the retina
-Cells filled with melanin to absorb light not absorbed by the retina
What do ON & OFF bipolar cells respond to? What is direct & indirect input?
-ON= depolarise in response to light
-OFF= depolarise in response to dark
-Direct= input from receptive field centre
-indirect=input from receptive field surround
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
In photoreceptors, where does absorption occur?
-Contain stack of discs containing light sensitive photopigments
-Rods= long cylindrical outer segment many discs, cones= short tapering outer segment few membranous discs
What is the pigment in rods called?
-Each cone opsin has different spectral sensitivity
-Colour perception determined by relative contribution of blue, green, red cones on retina
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
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
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
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)
What are ganglion cells mainly responsive to?
Differences in illumination that occur within their receptive fields