Vision Notes

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This is an extract of our Vision document, which we sell as part of our Neurology Notes collection written by the top tier of Bristol University students.

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Lecture 31, 32 & 34 Vision 1

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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

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Change amount of light in eye

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Dilated o

Lots of light

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Light spread over large area

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Low visual acuity

Contricted o

Light beams more focused

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Higher visual acuity

Pupillary light reflex

LensTransparent biconvex structure behind irisConsiderably flexible (deteriorates with age- PRESBYOPIA)

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