2. Optical System of the eye
1. Cornea
2. Anterior and
posterior
chambers with
liquid
3. Crystalline lens
4. Vitreous body
3. Optical Power of the eye
Is about 59 D (58,6) for distant objects and
70,5 D for near objects; D – dioptre.
Reduced eye
An image in retina is affective, reduced and
inverted
Emmetropic eye is eye with normal length
(22,4mm) and normal optical power 58,6 D
4. Anomalies of ocular refraction:
1. Myopia (short-sight)
Reasons: 1. Too long eyeball: 2. Increased
optical power of the eye
Concave lenses (-D)
2. Hypermetropia (long-sight)
Reasons: 1. Eyeball is shorter than norm;
2. Decreased optical power of the eye
Biconvex lenses (+D)
3. Astigmatism; individual lenses
9. Accommodation
Optical power for near objects (nearer 5 m)
increases
Reflex arc of the accommodation reflex:
Stimulus is unclear image in retina; conduct way
is tractus opticus to visual cortex and to
midbrain (n.III Edinjer-Westfal); efferent
fibres are ciliary nerve, ciliary ganglion to
ciliary muscle. It contracts, Zinn’s ligaments
relax and lens becomes more convex because
of elasticity.
10. Near point of distinct vision is
The measure of accomodation
10 cm for young persons and 7 cm for children
Presbyopia – senile long-sightness
Correction – biconvex glasses (+D)
Field of vision
Phorster’s perimeter
13. The pupil and pupillary reflexes
Pupil 1,8 to 7,5 mm
Reflex of the pupil narrowing (at brigt light)
Receptor field is retina. Conducting way is tractus
opticus. Centre of the reflex is n.III
oculomotorius, n.Edinger-Westfal-Yacubowich.
Parasympathetic fibres to m. sphincter iridis; Ach
Reflex of the pupil dilation (at dim light)
Receptor field is retina. Conducting way is tractus
opticus. Centre is in spinal cord (C8-Th1,2).
Sympathetic nerves to m. dilatator iridis; NA
Strong emotions, fear, anger, Pain, hypoxia
22. Conducting way of visual system
1. Retina
2. n.opticus
3. upper hills of quadrigeminal body
4. lateral geniculate bodies
5. occipital cortex (f. 17,18)
23. Dark adaptation – increase of the visual system
sensitivity to light
1. Pupil’s dilation; 2a. (10 minutes) resynthesis of
iodopsine, sensitivity increases 50-80 times; 2b.
(2 hours) resynthesis of rhodopsine, sensitivity
increases 100.000-300.000 times; 3. decrease
of lateral inhibition in retina; 4. sympathetic
n.s. and brain cortex activation
Light adaptation – decrease of sensitivity to light
1. Pupil’s narrowing; 2. Intensive brake down of
visual pigments; 3. Increase of lateral inhibition
Dark and light adaptation of visual system
26. Ttichromacy (tricomponent) theory
(Lomonosov, Young, Helmholtz)
There are 3 kinds of cones in retina, they
contain visual pigments: iodopsin, clorolabe
and erythrolabe for blue, green and red
colours. Max sensitivity 440, 535 and 565 nm
Theory of opponent colours (Hering)
White-black; red-green; blue-yellow
Trichromates
Colour blindness: protanopia, deuteranopia,
tritanopia, achromasia
