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Lecture 2

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Matthias Niemeier

Lecture 2 - vision – Contrast than relative Optics – Light is waves – wavelength, frequency (brightness) and amplitude (color) – Polarity of light – Birds use, humans cannot – Three concepts: reflection absorption refraction (transparent surfaces) - depends on which of the two mediums denser Anatomy of the eye – Pupil, sclera, Iris, cornea, optic nerve – cornea is important for the focus of light – only the cornea cannot change shape (like the lens) which is also important for focus – Optic disk = blind spot – macula – acute (good) vision – fovea – best vision here – helpfullness of iris – you can tell if the person is looking at you or what they are looking at (difference between Iris and Sclera) – contraction of the ciliary fibers stretches the lens flat – pressure of vitreous humor gives the eye round shape Eye disorders – Strabism: one eye becomes weak and affects oculomotor so you have double vision so you pick one eye causing oculardominance and eventually that becomes blind (the week eye) (cross eyes) – Cataracts - clouding of the lens – needs to replace the lens (artificial lens) – Glaucoma – the vitreus pressure if there is too much then you get glacoma and this is usually in the blind spot so usually don't even notice – Detached retina - the retina detaches from the back of the eye- this can be lasered back to the eye – Retinitis pigmentosa - hereditary autoimmune disease where the body attacks the area right around the retina so you lose your sight starting with night vision. Spatial vision -Light that comes from a single source comes and collects at the cornea and then refracts the light – The cornea cannot change shape but the lens can – When the cilliary fibres relax, the lens stretches and thinner for far images – When the ciliary fibers contract, the lens relaxes (back to regular form) and thicker for images closer. Vision correction – Emmetropia – normal – Hyperopia – myopia – astigmatism – Cornia not being completely properly structured - not spherical The pupillary light reflex – the smaller the pupil, the more focused the vision is – the pupil controls the level of light going into the eye – consensual – both pupils should construct/relax at the same time – If the pupils are not consensual, it is a find that something is not right in the brainstem The visual field Visual acuity: the minimum distance between two dots that you can still see both dots. Anatomy of the retina Vertical pathway – photoreceptors– bipolar cells – ganglion cells Horizontal pathway Light enters from the ganglion cell layer and ends at the photoreceptor layer photoreceptors are special types of neurons Graph – 0= the fovea – the blue curve equals count of cones – red is count of rods – so in the fovea there are only cones and no rods – in the peripheral retina, the further you go, the less light there is so you see less (almost blind) – there are more rods in the retina than cones 1 photoreceptor is attached to 2 bipolar cells is attached to it 1 ganglion cell – with the more photoreceptors/ bipolar/ ganglion cells, the more you can see (sensitive) but the less acuity so sensitivity and acuity are opposite. Pit shape of fovea – more visual acuity (find out why it is pit shaped) Phototransduction of rods – Rods are in the dark – don't send out action potentials, they send out graded potentials – since it is graded potential, it is more detailed and more sensitive to how much light is there and not just the
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