The Eye and Visual Pathways Flashcards
Which part of the eye is non-stretchy?
Where is the Aqueous humour found? What does it do?
What maintains the level of aqueous humour in the eye?
Where is the Vitreous humour? What is it?
What is the function of the Cornea?
What is the lens kept in place by? What is its function?
What is the Iris and its function?
- Sclera, Cornea
- In front of lens; keeps eye pressure constant
- Produced by Ciliary body and drained out at the angle of the eye at an equal rate
- Behind lens - jelly, transparent substance
- Focuses light rays; refracts light
- By Ciliary body and Suspensory ligaments; changes shape to focus on objects of varying distances
- Coloured part of eye; forms pupil and controls amount of light entering
Retinal layers:
What is the first layer?
What is the Neural Retina? Which cell type does it contain? What do the cells do?
What are the 2 types of photoreceptors? What is each used for?
What are the last 2 inner layers?
- Retinal Pigment Epithelium
- An extension of the Optic nerve; retinal ganglion cells lay on the inner side of the retina and bundle together to form the optic nerve
o Has Photoreceptors for transduction of light into an electric signal - Rod (night vision), Cone (day vision)
- Inner nuclear layer, and then a Ganglion cell layer
Peripheral vision:
What do the cone cells do here?
Central vision:
Where are the retinal blood vessels?
What is the structure of the central retina?
Why doesn’t it have any image blur?
How does it have high resolution? Which cell type is most abundant here?
- Cone photoreceptors are widely spaced out and send impulses to the Ganglion cells via Bipolar cells
o Cone cells converge input on to single ganglion cell to increase “pixel” size; Receptive field Centre - LOW RESOLUTION
- Retinal Blood vessels radiating away from optic nerve head towards centre
- Centre is the Fovea Centralis, surrounded by the Macula Lucida
- No overlying vessels, and only has a Photoreceptor layer - No image blur as light doesn’t have to pass through as many layers
- High (Red and Green) CONE cell density - no convergence, so resolution stays high
Pupil constriction:
Which muscle is used? What innervates it?
Pupillary Light Responses:
What process occurs when light is shone directly into one eye to cause pupil constriction?
What is the CN III vulnerable to be affected by? What will this cause?
Pupil dilation:
Which muscle is used? What innervates it?
What is special about these nerves?
Accommodation Reflex:
What occurs during it?
- By SPHINCTER Pupillae (circular muscle on inner edge of Iris); Driven by parasympathetic (ACh) SHORT CILIARY NERVES
- Retinal ganglion cells send impulses along the Optic nerve to the Pretectal Nucleus
o Pretectal Nucleus then activates BOTH Edinger-Westphal Nuclei, which sends parasympathetic impulses along CN III (Oculomotor) to the Ciliary Ganglions = Pupil constriction by SHORT CILIARY NERVES in BOTH EYES - Vulnerable to ↑Intracranial Pressure = Pupil dilation
- By DILATOR Pupillae muscles; Driven by sympathetic (NA) LONG CILIARY NERVES
- Nerves not affected by light
- Parasympathetic Short ciliary nerves contract Ciliary muscles = Relaxation of Suspensory Ligaments = Lens becomes fatter
Eye defects:
What is Myopia?
What is Hypermetropia?
Ageing eye:
What happens with Presbyopia?
What happens with Cataracts?
What happens in Vitreous Degeneration? What can it lead to?
- Optics too strong for the eye (Short-sighted)
- Optics too weak for the eye (Long-sighted)
- Lens proteins degenerate, Lens become stiff, Focus is fixed
- Lens proteins become opaque
- Vitreous proteins clump together; vitreous jelly can shrink away and tear the retina = Retinal Detachment
Primary Visual Pathway:
What path does the optic nerve take? What are the 2 branches? What does each path control?
What happens when the LGN cells are activated?
How is an image processed by the eye?
- Behind Optic Chiasm, the Optic Tracts travel up into the brain, branching into 2 parts:
o One branches off into Brainstem; controls Intraocular and Extraocular muscles
o Other branches off into Lateral Geniculate Nucleus/LGN (in thalamus) - LGN cells send impulses along axons in the Optic Radiation, terminating in the Primary Visual Cortex of the occipital lobe
- Left side of image goes to right side of both eye retina; axons from both retinae go to the right side of the brain
Visual field:
What is the blind spot? Why is it there?
What maps the Nasal and Temporal retina?
What is Monocular Scotoma?
What is Hemianopia?
What is Quandrantanopia?
- Optic nerve head, where nothing overlaps it
- Temporal Hemifield maps Nasal retina, Nasal Hemifield maps Temporal retina
- Blind patch in part of field due to retinal damage
- Loss of a Hemifield
- Loss of a quadrant
Lesions:
How is an image mapped?
What do Homonoymous defects mean? Where must the damage be?
Where must the lesion be to cause Monocular Blindness?
Where must the lesion be to cause Homonymous Hemianopia?
Where must the lesion be to cause Homonymous Superior Quadrantanopia?
- Left mapped to right, Down mapped to Up
- Matching defects in both eye; damage behind chiasm
- Lesion in one Optic nerve side
- Lesion in one side of LGN
- Lesion in lower half of posterior pathway
