Khairun Nisa Berawi, dr., Mkes., AIFO

SPECIAL SENSES

1. Vision

2. Hearing and Equilibrium

3. Smell

4. Taste

ANATOMY

LENS AND CILIARY MUSCLE

THE RETINA

THE ROD AND CONE

•Rhodopsin

•Retinal (11-cis retinal)

•Opsin :

-Scotopsin in rods

-Photopsin in cones

•Nyctalopia

ACCESSORY STRUCTURES OF THE EYE

1. Orbit

2. Eyelids, eye lashes, eyebrows

3. Conjunctiva

4. Lacrimal apparatus

5. Muscle of the eye and eyelid

Please re-read by yourself !!!

PHYSIOLOGY OF VISION

1. Refraction of the light rays entering the eye

2. Focusing of images on the retina by accommodation of the lens and convergence of the images

3. Conversion of light waves by photochemical activity into neural impulses

4. Processing of neural activity in the retina and transmission of coded impulses through the optic nerve

5. Processing in the brain, culminating in perception – the object is “seen”

1. REFRACTION OF LIGHT RAYS

1st Medium

2nd MEDIUM

There is a different density between 1st medium and 2nd medium the light is bended

The bending is called refraction

REFRACTION IN NORMAL EYE

In normal eye (emmetropia), light rays come to focal exactly on the retina

Refraction

REFRACTION IN MYOPIA

In myopia (nearsighted eye), the focal point falls in front of the retina

REFRACTION IN HYPERMETROPIA

In hypermetropia (farsighted eye), the focal point falls behind the retina

2. ACCOMMODATION

The role of the adjustable lens

A reflex process

Bring images into perfect focus on the retina

Nearby Object

Distant Object

The lens becomes round

The lens becomes flattened

1. Ciliary muscle contract

2. Ciliary body pull forward and inward

3. Tension on suspensory ligaments of lens reduced

4. Lens becomes thicker (rounder) due to its elasticity

MKING IT POSSIBLE TO FOCUS A NEARBY OBJECT

TO FOCUS ON NEARBY OBJECT

TO FOCUS ON A DISTANT OBJECT

1. Ciliary muscle relax

2. Ciliary body returns to resting satae

3. Tension on suspensory ligaments of the lens increased

4. Lens becomes thinner (flatter)

MAKING IT POSSIBLE TO FOCUS ON A DISTANT

OBJECT

PURKINYE IMAGES

Object

IIIIII

Accommodation

Cornea

Lens

Phacoscope

To see Purkinye II and III through the pupil

Pupil

CONVERGENCE

Near Object

•Binocular visionPerceive on image

Distance

Depth

Three – dimensionality

•Stereoscopic vision

The two eyeballs turn slightly inward

3. CONVERSION OF LIGHT WAVES BY PHOTOCHEMICAL ACTIVITY INTO

NEURAL IMPULSES

1. Photochemical activity in rods

2. Photochemical activity in cones

PHOTOCHEMICAL ACTIVITY IN RODS

11-cis retinal in rhodopsin

absorb a photon

11-cis retinal converted into all-trans retinal, which

activates scotopsin to act as an enzyme

Transducin is produced, and activate

phosphodiesterase

Phosphodiestarease hydrolysis cGMP

Plasma membrane channel close, Na+ are prevented from

entering rod, and hyperpolarization occurs

11-cis retinal and scotopsin combine to synthesis rhodopsin

Neural signals are processed by bipolar, amacrine, horizontal,

and ganglion cells

Action potentials of ganglion cells are

conveyed to brain via optic nerve

Light is perceived as visual images

PhotonRhodopsin molecule

(11-cis retinal + scotopsin

BLEACHING AND REGENERATION OF

PHOTOPIGMENT

What is the conversion of cis- to trans-retinal called ?.

PHOTOCHEMICAL ACTIVITY IN CONE

The Events of Visual Excitation is Similar as in Rod

Rods contain : Scotopsin

Cones contain : Photopsin

3 types of cones: Red, Green, and Blue Cones

Color perception depend on which cones are stimulated and their combinations

The same retinal absorbs a different frequency of light•Red cones: the long wave

•Green cones: the middle wave

•Blue cones: the short wave

VISUAL ADAPTATION

Bright light “bleaches” rhodopsin

The light-sensitive rods become overloaded

Rods are no more sensitive

Light adaptation occurs when eyes adjust to bright light

Dark adaptation occurs as eyes adapt slowly to darkness

Light adaptationEnter darkened room

Resynthesize rhodopsin Dark adaptation

(5 minutes)

(20 – 30 minutes)

Rods become more senstive

NEURAL PATHWAYS FOR VISION

LIGHT REFLEX

(PUPIL REFLEX)

LIGHT RETINA IMPULS N. OPTICUS CHIASMA OPTICUS

TRACTUS OPTICUS

CORPUS GENICULATUM

LATERALE

COLLICULUS SUPERIORN. III

GANGLION CILIARIS

N. CILIARISM. CIRCULARIS

IRIDIS

PUPIL CONSTRICT