Visual Defects Flashcards
Define: Glare. What often causes it?
Difficulty seeing in bright light.
Corneal/lens problem - usually cataracts. “Cloudy when its not cloudy outside”
What is often damaged to cause distortion?
Retina > Wet macular degeneration > Macula hole > Macula pucker > Retinal detachment
What is damaged to cause colour change?
Retina or optic nerve
Field defects are caused by damage to what?
Homonymous = visual pathway Non-homonymous = Retina or nerve.
What causes a floater?
Vitreous humour opacity
How is a cataract examined?
Red reflex or slit lamp
What causes drusen?
Impairment of the retinal pigment epithelium to remove waste products of the rods and cones
Drusen, RPE pigmentation and RPE atrophy are the signs of what disease?
Dry Age Related Macular Degeneration - small area loss = severe visual loss
What is the most common cause for Central retinal artery occlusion?
Carotid artery disease
How does Giant cell arteritis cause visual loss?
Anterior Ischaemic Optic neuropathy or Central retinal artery occlusion
What is Wet ARMD?
When the choroidal neovascular membrane grows towards macula, new blood vessels can break –> damage macula –> loss of vision.
Why is Anti-VEGF the treatment for Wet ARMD?
Inhibits VEGF which causes the choroidal neovascular membrane to growth towards the macula.
What are some of the features of Rods?
> Sensitive to scattered light
Capture more light than cones
High sensitivity to light (night vision)
Low temporal resolution (slower response)
Higher amplification
What are the receptor proteins in rods and cones called?
Opsin’s
Rhodopsin in Rods
Cone opsin - Red, Bluee and green.
What determines colour perception?
Contribution of R, B and G opsins to the retinal signal.
When all the three cone types are active, according to the Young-Helmholtz trichromatic theory, what colour is made?
White
Being trichromatic gives you what vision?
Normal
What is anomalous trichomat?
When one pigment absorbs slightly different wavelength to most normal trichomats.
What condition arises due to being a dichromat?
Colour blindness
What do ON bipolar neurones depolarise in response to?
Light
Vice versa…
Direct input from photoreceptor to bipolar cell is from the….?
Receptive field CENTRE
Indirect input from the photoreceptor to horizontal cell to bipolar cell is from the…..?
Receptive field SURROUND
What is the process of an ON bipolar cell becoming depolarised from the receptive field centre?
1) Light onto centre photoreceptor
2) Photoreceptor becomes HYPERPOLARISED
3) Bipolar cell depolarises
AND VICE VERSA
What is the process of an ON bipolar cell becoming hyper polarised from the receptive field surround?
1) Light onto surround
2) Photoreceptor HYPERPOLARISED
3) Horizontal cell HYPERPOLARISED
4) Makes central photoreceptor more Depolarised
5) So bipolar cell –> more hyper polarised
