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Eyes 1 & 2 (use slide pictures (Retina (Nervous layer (Light-sensitive…
Eyes 1 & 2 (use slide pictures
Use slide need pictures
Layers of eyeball
Vascular (uvea) = Middle
Fibrous = Outer
Retina = Inner
Retina
Nervous layer
Light-sensitive
Photoreceptor cells (Rods & cones) - Sit in epithelium, specialised (outer sensory segment). Epithelial cells that look like neural cells
Rod cells - Low light intensity, night, black&white
Cone cells - Colours, bright light, day
3 layers of nervous layer (inner layer):
Ganglion cells (surface)
Bipolar cells
Photoreceptor cells (deepest)
Eye is backwards.
Continuous with optic nerve
Area centralis - Area on retina of greatest clarity (at fovea, high density of cones)
Optic disc - Where optic nerve leaves eye, blind spot
Cats and dogs - 95% rods + 5% cones. See light and shade but little colour
Outer layer is epithelial cells
Rods are many to 1 synaptic contact so lower visual clarity but easier for action potential to develop.
Cones are 1:1 synaptic contact so greatest visual clarity (acuity) (high density of cones at fovea)
Development of eye
Use pictures
Neural tube region (in forebrain) starts to grow outwards forming optic cups (retina is inside facting inwards - cilia point in)
The lateral indentation deepens, reducing size of optic canal. Cup also indents ventrally to form choroid fissure. The nervous layer becoms stratified, 3 layers. The tips of the fissure fuse enclosing the optic nerve in the eye
Vascular layer
Vascular layer - Choroid (layer) + ciliary body + iris
Choroid layer continuous with ciliary body (smooth muscle) which is in turn continuous with iris
Choroid layer vessels ramify to supply retinal layer, heavily pigmented
Axons are myelinated as vision must be quick.
More axons in optic nerve than all spinal nerves combined
Myelin acquired outside eye so as to not impede vision further
Central vessels (central retinal vein + artery).
Supply bipolar and ganglion cell layers of retina.
Tapetum lucidum
Cells containing crystals lie between pigment layer of retina and choroid. Triangular area of greenish-yellow, light-reflecting, iridescent cells usually lying dorsal to optic nerve.
Crystals bounce photons back onto rods, maximises light use at night. Humans + pigs dont have.
Vitreous chamber
Not really a part of any of the layers
Jelly-like substance (vitreous humor)
Jelly helps eye retain round shape and holds retina against back of eye
Sclera
Supporting layer
Outermost layer
Continuous with cornea (made from collagen)
Sclera is white, highly fibrous and elastic. Fibres give strength in all directions helping maintain eye shape and protection
Lens
Sits behind iris
Suspended from ciliary body by extremely fine connecting tissue
Accommodation - Change in shape of lens
Distance vision - Ciliary body relaxed, lens fibres taut, lens flat
Close vision - Ciliary body contracted, fibres slack, spherical lens
Most refraction occurs at cornea and lens
Cataracts - Lens becomes cloudy due to age, genetics or diabetes
Can be accompanied by lens luxation (displacement of lens)
Treatment = Cataract removed, animal distance vision only after op. Can be restored with prosthetic lens
Aqueous humor
Humor formed by filtration of blood plasma by ciliary process (finger like projections in ciliary body)
Fluid leaks through pupil from posteria chamber into anterior chamber
Fluid returns to circulatory system via venous plexus at transition between cornea and sclera at limbus (limbus -
border
)
Glaucoma
Raised intraocular pressure (aq. humour drainage blocked at limbus but production continues)
Extreme pain. Blindness (pressure impedes circulation).
Treatment = Drugs diffuse into eye, reduce humour secretion/improve drainage
Cornea
Cell types (not sure use picture/histology lecture):
Bulbar conjuctival epithelium
Loose connective tissue
Anterior epithelium of cornea
Nerve fibre
Corneal fibrocyte
Vascularisation & keratinisation of cornea - Keratoconjunctivitis sicca ("dry eye")
Autoimmune causing failure of tear production
Treatment: artificial tears
Ulceration - Large deep wounds can leave scar tissue impeding vision. Can be transplanted or sow third eye lid shut to bring in blood supply
Conjunctivitis - Inflammation of conjunctival membranes, many causes (incl. viral + bacterial, tear production disorder, allergy)
Treatment = eye drops or ointment
Neural
Use pictures
Optic chiasm (cross) is where nerves cross over. Nerves relay in thalamus (large geniculate body)
Nasal & temporal parts of retina. Parts closest to and furthest from retina respectively. Because fibres cross left visual field processed in right visual cortex and vice versa
(nasal fibres cross temporal do not, rendering visual fields)
The more fibres cross the better 3d vision. Herbives have fewer crossing over, better monocular 360* vision
Visual field
Carnivore eyes - Frontal position, restricted monocular lateral view, large central binocular area. Good binocular vision = good depth perception
Herbivore eyes - Lateral position = Wide monocular lateral field of vision and narrow binocular area
Pupillary light reflex
Bright light - Pupil constricts as circular muscles of iris contract
Dim light - Pupil dilates as radial muscles of iris contract
If shine light in one eye both pupils should constrict in a healthy system - Pupillary light reflex (as nerves supplying muscles are part of sympathetic nervous system)