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PHYSIOLOGY OF PHYSIOLOGY OF VISIONVISION
Structure of visual analyser
• Receptor part – rods & cones of the retina
• Conducting pathways- optic nerve, optic chiasm,optic tracts,lateral geniculate body
• Visual cortex – occipital lobe around calcarine fissure
Refractive mediums of the eye
• Cornea (40-43 D)• Lens (19-33 D)• Vitreous body (0 D)• Light conduction & refraction• Refractive power of the eye is 59-
73 D
Construction of image on the retina of the reduced
eye• Real• Reduced• Turned upside down
Emmetropia
Hypermetropia
Hypermetropia corrected with convex lens
Myopia
Myopia corrected with concave lens
Physiological abnormalities of
refraction• Spherical abberation• Chromatic abberation• Astigmatism
Pupillary reflex• Pupil constriction under the
influence of light• Midbrain reflex • Parasympathetic nucleus of
n.oculomotorius
Accomodation reflex• Changing the curvature of
crystaline lens for better refraction at close vision
• Common pathways with pupillary reflex
Flat lensRelaxed ciliary muscle
contractedZinnon ligament
contracted ciliary muscle
Convex lens
Eye at rest
Zinnon ligamentRelaxed Zinnon ligament
Accomodation reflex
Close & distant points of clear vision
• Close point of clear vision- min distance at which the object is clearly seen at max tension of accomodation mechanism (10 cm)
• Distant point of clear vision- min distance at which the object is clearly seen at max relaxation of accomodation mechanism (infinity)
Acuity of vision• Is determined by the least distance
between two points that the eye can distinguish
• Normal eye can distinguish 2 points subtended by an angle of 60 seconds
• Measured by Snellen’s types
Field of vision• Aggregate number of points seen
simultaneously when the eye is fixed steadily on one point
• The extent of the field of vision is measured by perimeter
Receptor department• Rods -110-125 mln• Cones -6-7 mln
Conducting pathways