Flashcards in 15 - Retinal Physiology Deck (24):
What is visible light?
Electromagnetic radiation between the wavelengths of 400 nm (blue) and 750 nm (red)
What do the lacrimal glands secrete? And what stimulates the secretion of this?
Parasympathetic stimulation via the facial nerve
What do tears contain? Where do they enter and exit the eye and then drain into?
Antibodies, lysozyme to prevent bacterial growth
Enter - excretory ducts
Exit - lacrimal punctum
Drain - into nasolacrimal duct
What are the 3 layers of the eye?
Cornea and sclera
Iris, ciliary body and choroid
What is vitreous humour and its function?
Watery gel produced by glia cell in retina
Holds the shape of the eye to maintain focussing
What is the function of the cornea and 2 major features?
Main refractive surface
Richly supplied with nerve fibres
What is intraocular pressure?
Difference between the formation and drainage of aqueous humour produces the intraocular pressure
It helps to keep the cornea a spherical surface
What is normal intraocular pressure?
10 - 21mmHg
Where is visual acuity the highest in the eye?
Fovea - lots of cone cells
Where is the blind spot in the eye and why is this a blind spot?
Where the visual axons leave the eye to form the optic nerve
There are no photoreceptors here
What is aqueous humour? Where is it formed?
Protein free filtrate, formed in the posterior chamber by the ciliary body
What is glaucoma?
Damage in the retina die to an increase in intraocular pressure as the drainage of the aqueous fluid is blocked - damages optic nerve and blood vessels
What is the difference between open angle glaucoma and primary angle glaucoma?
Open angle glaucoma - slow and progressive, trabecular meshwork becomes blocked and the angle between the cornea and iris is normal (40degrees)
Angle closure glaucoma - rapid increase in pressure, extreme pain and sudden vision loss. angle between the cornea and iris is reduced, the flow of fluid inside the eye cannot pass through the CANAL OF SCHLEMM
What is the treatment for glaucoma?
Surgery - incision at the cornea-sclera junction allowing for aqueous fluid to drain out
Drugs - reduce formation of aqueous humour or increase drainage
Prostaglandin analogs increase outflow of aqueous humor through canal of Schlemm
Beta-adrenergic receptor antagonists decrease aqueous humor production
Alpha2-adrenergic agonists work by a dual mechanism, decreasing aqueous production and increasing outflow.
Parasympathomimetic agonists and anticholinesterases work by contraction of the ciliary muscle, which opens the canal.
Carbonic anhydrase inhibitors lower secretion of aqueous humor by inhibiting carbonic anhydrase in the ciliary body.
What is cataracts? What causes cataracts?
Due to proteins forming in the lens
Old age due to too much UV light exposure
Aqueous humour usually protects
What conditions can cause cataracts and why?
Diabetes and hypertension
Reduce the levels of antioxidants
Other risk factors - exposure to excess UV light or infrared light
What are the 2 types of photoreceptors? What is the difference between them?
Cone Cells - see detail, active in daylight, red, green and blue types
Rod Cells - only one type, sensitive to light, active in the dark, rhodopsin photopigment
What stops tonic glutamate release?
Light which hyperpolarizes the cell
Why does the eye require high amounts of oxygen?
Photoreceptors are one of the most metabolically active cells in the body
Constant inward leak of sodium in the dark -
What are the 3 main neurones that form the path from the photoreceptor to the optic nerve?
What are interneurons also known as?
Where do the axons of ganglion cells project into?
The optic nerve
What is the blood supply to photoreceptors?
Choroid (network of capillaries supplied by the ciliary arteries)