S20 Visual defects 2 Flashcards
What is the function of the vitreous humour of the eye?
Lies between lens and retina, keeps eye spherical.
Which parts of the eye refract light?
Cornea (does most of it).
Lens.
How does lens accommodation occur?
Ciliary muscle contraction relieves tension on zone fibres, allowing lens to become rounder due to natural elasticity.
Define emmetropic eye.
A normal eye that can focus parallel light rays on the retina without the need for accommodation.
Differentiate between hyperopia and myopia.
Lens fix?
Hyperopia: farsighted - can’t see near objects. Fix: convex lens.
Myopia: shortsighted. Fix: concave lens.
What is the function of the pigmented epithelium of the eye?
Filled with melanin which absorbs any light not absorbed by the retina.
Differentiate between rods and cones.
Cones: colour - daylight, high temporal resolution. Trichromatic with high acuity concentrated in fovea.
Rods: no colour - low light, slow resolution Achromatic (one pigment) with low acuity.
Where does light absorption take place in the eye?
Membranous disks in the outer segments of the photoreceptors of the eye.
Define scotopic, mesopic and photopic.
Scotopic: night time.
Mesozoic: twilight.
Photopic: daytime.
What is trichromat and dichromat?
Tri: normal colour vision.
Dichromat: colour blindness.
How does signal transduction occur in photoreceptors?
Light of the correct wavelength leads to a decrease in the amount of neurotransmitter.
What are the three types of retinal ganglion cells?
What do they sense?
Magnocellular (M-type). Stimulus mvmt.
Parvocellular (P-type). 90% pop. Stimulus form + fine detail.
Non-M Non-P (K-type).
What does the magnocellular pathway carry information about?
Motion.
What does the blob pathway carry information about?
Colour.
What does the parvo-interblob pathway carry information about?
Shape.
