Lecture 31, 32 & 34
Lecture 31, 32 & 34 Vision 1 •
•
Properties of light o Visible light is what we see o Visible light=400-700nm (wavelength) o In vacuum, light travels in straight line, most of what we see is reflected and scattered from objects Structure of the eye o Extrinsic ocular (Extraocular) muscles Superior rectus (upwards; into nose)= CNIII Inferior rectus (down)= CNIII Lateral rectus (away from nose)= CNVI Medial rectus (into nose)= CNIII Superior oblique (torsion of eye; down, in, out)= CNIV Inferior oblique (torsion; keep gaze stable)= CNIII o Pupil= allows light to enter eye (controlled by size of iris o Iris (sphincter pupillae)= Muscles that control size of pupil Radial=dilate; Circular=constrict o Lens= curvature controlled by ciliary muscle (PSNS fibres via ciliary ganglion) o Aqueous humour= Between anterior and posterior chamber Feeds lens and cornea (no BVs) Replaced every 60 mins Excess production=glaucoma (carbonic anhydrase inhibitors) o Vitreous humour o Choroid layer= Vascular layer of eye containing connective tissue. Between retina & sclera Dark melanin choroid pigment helps limit uncontrolled reflection of light (clearer vision) In night animals, melanin partially absent (Tapetum lucidum) collects light reflecting it in controlled manner. Maximises light capture BUT less visual acuity o Retinal landmarks Optic disk/Optic papilla (blind spot) • Axons of ganglion cells exit and enter optic nerve Macula (yellow disk) • Central area of retina in line with visual axis Fovea • Depression in centre of macula • Visual acuity greatest here • Slightly darker because light passes through easily • Extremely thin- cells in front of photoreceptors swept aside • No rods in fovea, only cones MACULA DEGENERATION (2 types: wet or dry)
•
RETINITIS PIGMENTOSA (night vision and peripheral vision loss)
Image formation in the eye o
Pupils and papillary light reflex
Change amount of light in eye •
•
o
Dilated o
Lots of light
o
Light spread over large area
o
Low visual acuity
Contricted o
Light beams more focused
o
Higher visual acuity
Pupillary light reflex
Lens
Transparent biconvex structure behind iris
Considerably flexible (deteriorates with age- PRESBYOPIA)
•
Properties of light o Visible light is what we see o Visible light=400-700nm (wavelength) o In vacuum, light travels in straight line, most of what we see is reflected and scattered from objects Structure of the eye o Extrinsic ocular (Extraocular) muscles Superior rectus (upwards; into nose)= CNIII Inferior rectus (down)= CNIII Lateral rectus (away from nose)= CNVI Medial rectus (into nose)= CNIII Superior oblique (torsion of eye; down, in, out)= CNIV Inferior oblique (torsion; keep gaze stable)= CNIII o Pupil= allows light to enter eye (controlled by size of iris o Iris (sphincter pupillae)= Muscles that control size of pupil Radial=dilate; Circular=constrict o Lens= curvature controlled by ciliary muscle (PSNS fibres via ciliary ganglion) o Aqueous humour= Between anterior and posterior chamber Feeds lens and cornea (no BVs) Replaced every 60 mins Excess production=glaucoma (carbonic anhydrase inhibitors) o Vitreous humour o Choroid layer= Vascular layer of eye containing connective tissue. Between retina & sclera Dark melanin choroid pigment helps limit uncontrolled reflection of light (clearer vision) In night animals, melanin partially absent (Tapetum lucidum) collects light reflecting it in controlled manner. Maximises light capture BUT less visual acuity o Retinal landmarks Optic disk/Optic papilla (blind spot) • Axons of ganglion cells exit and enter optic nerve Macula (yellow disk) • Central area of retina in line with visual axis Fovea • Depression in centre of macula • Visual acuity greatest here • Slightly darker because light passes through easily • Extremely thin- cells in front of photoreceptors swept aside • No rods in fovea, only cones MACULA DEGENERATION (2 types: wet or dry)
•
RETINITIS PIGMENTOSA (night vision and peripheral vision loss)
Image formation in the eye o
Pupils and papillary light reflex
Change amount of light in eye •
•
o
Dilated o
Lots of light
o
Light spread over large area
o
Low visual acuity
Contricted o
Light beams more focused
o
Higher visual acuity
Pupillary light reflex
Lens
Transparent biconvex structure behind iris
Considerably flexible (deteriorates with age- PRESBYOPIA)
