Senses III.

Vision Vision

Focus of the light on a light-sensitive surface using lens and an aperture and opening = camera

Process in which light reflected from the objects is translated into mental image Light entering in the eye, lens focus, light on retina Light energy transduced into electrical signal Neural pathways and brain processes the electrocity into visual images Light

Visible light Electromagnetic radiation with wavelength of 360 nm (violet) and 760 nm (red)

Basic colors Red Green Blue Cornea

It forms about 1/5 of eye bulb surface

Colorless, transparent, richly innervated Highest No. of nociceptors/area

Light enters the anterior surface of the eye

Reflex – after stimulation - eyewink Pupil

Light pass into the interior of the eye

Black spot in the middle of the pigmented layer

Organ that can increase its size up to 10x Iris

Around the pupil

Composed of pigment and muscle cells narrowing = myosis; dilatating = mydriasis regulates the amount of light coming to retina

Pupilar reflex – can be evoked by changing light intensity Lens

Without vessels

Transparent

Diameter 9 mm; thickness 3,7 mm

Optical magnification 20 D

Focuses light rays Corpus ciliare

Thickened choroid – smooth muscle for the lens

It allows eye accomodation Sclera

It forms about 4/5 of eye bulb surface

White connective tissue membrane

Helps to maintain the shape of the eye bulb Vitreus humour

Inside the eye bulb behind lens

Transparent gelatine substance

FUNCTION – maintains eye pressure: 3,3 – 4 kPa (25 – 30 torr) and eyeball shape Chorioidea

A lot of vessels and pigment cells

Absorbs light rays and prevents its reflextion Other eye structures

Orbita Muscles of eye bulb Eyelid, eyebrows Conjuctiva Aqueous humor Lacrimal organs (gland, punct, sac, duct) Optical apparatus of the eye

Cornea, aqueous humour, lens, vitrous humour, retinal layers

Refractice power: cornea 43D lens 16D other 1D Total 60D

- accomodation

Optical axis = bulb length

Picture on retina: smaller, real, upside down

Optical axis disorders

Emetropic eye – if refractory power is proportional to the lenght of optical axis; the picture is created directly on retina

Ametropic eye – blurred picture • hyperopia (far vision) – the sharp picture is created behind retina • myopia (near vision) – sharp picture is created in front of retina • Astigmatism • irregular curvation of cornea Retina

Thin transparent Blind spot – site of membrane entering n. opticus 130 milion of cells Fovea centralis – Rods (respond to site of clearest vision eye intesity, black&white vision) Cones (respond to various walength – color vision) Retina composition Pigment layer

Rods

Cones

Horizontal cells Bipolar cells Amacrine cells

Ganglion cells Rods & cones compositon

Outer segment (discoid lamelas) Containing pigment, the active center Inner segment organels Basis nucleus Pediculus Synapse with neurotransmitter (glutamate) Pigments and cell activation

Summary Transducin 3 subunits, activates GDP to GTP and so allowing the phosphodiesterase to be active Metarhodopsin II Activates transducin by splitting into betagama and alpha subunits Phosphodiesterase Changes cGMP to GMP and thus closes the Ca/Na channel Phosducin Binds betagama subunit of transducin in condition of too much light, preventing transducin to recover. Arrestin Breaks opsin and retinal acid, so the rhodopsin molecule can regenerate Retinal convergence Visual fields

• On bipolar cells • Off bipolar cells Further retinal image processing

Rather contrast than light itself stimulates ganglion cell!!! CNS pathway Practicals Visual acuity Visual acuity – ability to see objects with details sharply; ability of retina to distinguish two near points as separate Fovea centralis; visual angle for details is 1min., for whole object 5 dg. Visual acuity

5/ x

The „x“ to be found Ophthalmoscopy Examination of retina

Apparatus: ophthalmoscop-light source that refract light through prism into eye

Direct ophthalmoscopy- non accomodated eye of examinee; short distance; direct and enlarged picture.

Indirect ophthalmoscopy- convex lens is laid in front of eye – inverted and smaller picture is created – larger part of retina is covered Retina – n. opticus with the blood vessles, fovea centralis Ophthalmoscopy Purkyňe pictures

Part of light rays is reflected from cornea, anterior and posterior part of the lens

1. Purkyňe picture – reflection from cornea. Picture will be smaller, direct, sharp

2. Purkyňe picture – reflection from the anterior part of the lens. Picture will be direct, bigger, blurred.

3. Purkyňe picture – reflection from posterior part of the lens; picture will be sharp, very small and inverted. Keratoscopy

Detection of irregular shape of the cornea Perimetry

Examination of visual field Visual field – sum of all points that we can see when fixing our eye at another one point Monocular/Binocular visual field Perimetry – identification of scotoma The only physiological scotoma is the blind spot Perimetry Senses IV. PHYSIOLOGY OF VISION II. Light adaptation Light adaptation

1. Pupilary reflex 2. Neurotransmiter 3. Spatial sumation 4. Temporal sumation 5. Succesive contrast (afterimages) Adaptation examples

Physical characteristics of light hue – wavelenght, color as we detect it color – color as we percept it by brain saturation – level of light reflection; how bright do we percept the object according to object lightness/brightness – level of light reflection; how bright do we percept the object according to environment Simultaneous contrast

Color vision

3 types of basic colors: red, green, blue, because there are 3 types of cones

3 types of cones: sensitive to short (S), middle (M) & long (L) wavelenghts. (S): 430 nm = blue (M): 530 nm = green (L): 560 nm =red Additive mixing of colors with Maxwell circles and monochromatic filters The white color:

All 3 types of cones are stimulated by the same intensity

With concomitant stimulation of one color and supplemental/additive color with the same intensity Helmholz triangle Examination of colors with pseudoisochromatic tables

•Anomal trichromats- 3 types of cones but only of two groups weakened sensitivity to green or red

•Dichromats- 2 types of cones deuteranopy- inability to detect green Protanopy – inability to detect red •Monochromats- 1 type of cones – general inability to see colors Pseudochromatic tables Pseudochromatic tables Lateral inhibition

Ability of excited neuron to inhibit activity of neighbouring neurons

Stereoscopic vision

3D vision Basis: binocular vision Both eys are fixed on same object and we see it as one even two object are created The contemporary stimulation of corresponding points on retina – have the same cortical projection + corresponding points projected to space – horopter space Stereoscopic vision Stereoscopic vision

Binocular keys convergency accomodation stereopsy – disparat points on retina – do not have the same cortical projection; two pictures are formed, which if not too distant, create the plastic reality Movement of eyes must be coordinated, so the pictures fall on the identical points on retina. Otherwise diplopia results. Stereoscopic/deep vision Monocular keys movement paralax – positional change of object to background; distant objects move slowly kinetic perception of depth – movement of object from observer makes the object smaller color vision – correct color interpretation and mainly brightness helps to detect shape and position interposition perspective & size – characteristics of parallel lines to converge in distance can help us to percept environment characteristics

Stereoscopic/deep vision Air perspective – object in distance are blurred Periphery vision – outer segment of periphery vision, parallel lines are round

Stereoscopic vision? Optical ilussions

Based on the imperfect perception Physiologic illusions („afterimages“) Cognitive illusions double-meaning (Rubin vase) distortion (Cafe wall, Zollner illusion) paradox (penrose triangle, waterfall, stairs) fictive (halucinogens, schizophrenia)

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