The physiology of vision I. Learning objectives 96, 99.

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Protection of the eye

•Position

•Eyelids

•Tear secretion

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Eyelids

Open the eyelids M. levator palpebrae sup. (N. oculomotorius)………ptosis

Close the eyelids M. orbicularis oculi (N. facialis)………lagophtalmus

voluntary closure

blinking reflex:

touching the eyelashes

strong light, approaching objects, loud sound

sleep (increased tone of M.orbicularis)

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ptosis M. levator palpebrae sup. (N. oculomotorius)

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Eyelids

Open the eyelids M. levator palpebrae sup. (N. oculomotorius)………ptosis

Close the eyelids M. orbicularis oculi (N. facialis)………lagophtalmus

voluntary closure

blinking reflex:

touching the eyelashes

strong light, approaching objects, loud sound

sleep (increased tone of M.orbicularis)

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Tears

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• plasma ultrafiltrate, slightly hypertonic, 1 ml / day

• lubricates and protects

• rinsing out foreign objects

• lyzozym + secretory antibodies + antigenes

• emotional tool

• reflex: afferent: n. V. ------> brainstem (pons)

• efferents: n. VII----> ggl. pterygopalatinum -----> n.V. --> glands

Tears

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ggl. pterygopalatinum

Lacrimal gland

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The electromagnetic spectrum

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• the visible spectrum: 400-700 nm • importance of the reflected spectrum

• light intensity: candela (cd) • luminance: from 10-6 cd/m2 to 107 cd/m2 • normal conditions 1-40 X differences • phosphenes (deformation, migrain, electric stimuli) • importance of the contrast

Light and vison

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visible spectrum: 400-700 nm • importance of the reflected spectrum

• light intensity: candela (cd) • luminance: from 10-6 cd/m2 to 107 cd/m2 • normal conditions 1-40 X differences • phosphenes (deformation, migrain, electric stimuli) • importance of the contrast

Light and vison

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visible spectrum: 400-700 nm • importance of the reflected spectrum

• light intensity: candela (cd) • luminance: from 10-6 cd/m2 to 107 cd/m2 • normal conditions 1-40 X differences • phosphenes (deformation, migrain, electric stimuli) • importance of the contrast

Light and vison

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Liu Bolin, the invisible man

luminance, color, pattern

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Camera obscura

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Camera obscura

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Camera obscura

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Camera obscura

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Camera obscura

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Camera obscura

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upside down Small curved surface two pieces

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upside down Small curved surface two pieces

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D = 1

f (m)

0.1

0.5

Focal length (f)

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http://w.sharkdesigns.co.uk/bushcraft/bushcraft_articles_and_advice/FIRE/chaga_tinder_article.html

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24.4mm

Optical properties of the eye

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total refractory power: ~ 60 D cornea: ~ 40-43 D lens: ~ 17-20 D vitreous humor: - 4 D

Refractory index

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Refractory index is higher for blue than for red light

Dispersion

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Accommodation

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lens: flat, weak refractory power lens: thick, refractory power strong

looking far ~ parallel light rays ciliary muscles relaxed zonula fibres stretched, lens flat

looking close diverging light rays ciliary muscles contracted zonula fibres relaxed, lens thick

Accommodation

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Presbiopy

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Near point [m]

Accomodation [D]

Age

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The spatial resolution power of the eye

α

α ≥ 1’ Light rays from two separate points must have 1’ (minute of arc) angle. 1 cm from 57 cm distance is 1° (degree of arc).

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Sn

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n c

ha

rt

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Refractory errors

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Removing the old lens

Inserting the new lens

Presbiopy

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Near point [m]

Accomodation [D]

Age

Refractory errors

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Astigmatism

Refractory errors

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Ceratoscop (Placido)

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Astigmatism

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healthy astigmatism

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intraocular pressure: ~16 Hgmm, due to the aqueous humor measuring: tonometry •composition: plasma ultrafiltrate

•production: active, epithelial cells in the ciliary body

•drainage: passive, transcellular vesicular transport

role of the pupil

trabecular meshwork

Schlemm chanels

Intraocular pressure

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Circulation of the aqueous humor

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iris

lens

ciliary body

cornea

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Glaucoma

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• glaucoma

• headache (sudden onset, radiates into the orbit,

into the temporal region)

• blurred vision

• bradycardy

• painful, hard eyeballs

• nausea, vomitus

Intraocular pressure

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Eye movement

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Her laughter was historical indeed when he finally proposed to her.

Gaze tracking while reading

fixation fast, forward

fast, backwards „regression”

Eye movevements

Optical axis unchanged

(conjugated movements)

Optical axis changed

(vergence movements)

Movement

type

Fixation Rotation Saccades Pursuit

movements

Convergence Divergence

Duration max. 0.5 s

Speed up to

1000°/s

up to 60°/s

Angle 10°

compensa

tion

Distance Object close Object

far away

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Eye movements conjugated eye movements

torsion movements

converging, diverging movements

saccades short and fast with or without head movements speed = up to 500-1000 °/s (!) fixation periods 0.5 s, 10000/day pursuit movements if object, head or body moves speed = up to 60 °/s

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Eye movements

•conjugated eye movements

•torsion movements

•converging, diverging movements

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•converging, diverging movements

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Gaze

Target

Head movement

Eye movement

to right

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n. III.

n. VI.

n. III.

n. III.

n. IV.

n. III.

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Saccades

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Pursuit movements

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Optokinetic nystagmus

vertical

horizonthal

eye

gaze

head

auditory stim.

visual stim.

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