The Eye Flashcards
Label the eye
can you do this?
What is the macula and what is it function?
centre of the retina, with fovea at centre of macula
functional vision, not peripheral vision
What is the functional purpose of the retinal pigment epithelium?
Actively transports water from retina to choroid, with the flow of water causing pressure gradient to keep retina attached
Describe the photoreceptor variations and their distribution
Rod cells - black and white - more of these
Cone cells for colour vision - mainly in fovea as for detailed (connect multiple to one bipolar cell for ease of overcoming thereshold)
Physiology of vision
- In darkness retinal is bent (cis-retinal) and therefore fits in opsin
- Light causes isomerisation of retinal part into trans-retinal, causing the production of a receptor potential
- Trans-retinal is separated from opsin - bleaching
- Retinal isomerase converts back to cis-retinal
- cis-retinal binds to opsin - regeneration
- cycle continues
What inhibitory neurotransmitter is released in dakrness and turned off by light, allowing vision?
Glutamate
Which signal cascade controls vision?
cGMP
What is AMD?
Age related macular degeneration :
- Exudative AMD - neovascularisation occurs under retina from choroid, damaging the macula
- Atrophic AMD - atrophy of outer retina with loss of retinal pigment epithelium
Which type of AMD will cause blindness? and which blurred vision?
Blindness - exudative AMD
Blurred vision - both (atrophic wotn lead to blindness)
What is metamorphosia?
Distorted vision but visual acuity still ok
How does AMD affect vision and cause blindness?
- blood vessels and scar tissue grow under retina which as they are abnormal, leak, causing retina oedema
- This separate photoreceptors from retina
- Also blocks transport of oxygen and nutrients from choroid and blocks waste removal
- Results in eventual scarring and causes destruction of photoreceptors
What is drusen?
The end accumulation of pigment which is produced from photoreceptors and migrated to tip next to retinal epithelium
In what gene are polymorphisms closely associated with AMD?
Complement factor H
How can AMD be treated?
VEGF inhibitors - Ranibizumab
Bevacizumab is as effective and cheaper but licensed for cancer and wont change due to drug companies
What is bitemporal hemianopia and how is it cause?
Loss of peripheral vision
Compression of optic chiasm - e.g. pituitary tumour
