#10. Light perception. Adaptation. Methods of examination. Disturbancies of adaptation. Flashcards
What is the FUNCTION of the RETINA?
- LIGHT PERCEPTION is the MAIN Function of the Retina
What are the LIGHT SENSITIVE CELLS?
Light rays cause CHEMICAL CANGES in PHOTOSENSITIVE PIGMENTS in these cells, EMITTING Nerve Impulse VIA OCCIPITAL LOBES (Cerebrum) VIA Optic Nerves
1) RODS
- MORE Sensitive than Cones
- STIMULATED in LOW Intensity / DIM Light
- MORE in N.O at PERIPHERY of RETINA
- RHODOPSIN (Photosensitive Pigment) here
2) CONES
- SENSITIVE to BRIGHT Light
- Colour ONLY BE SEEN in Daylight
- DIFFERENT WAVELENGTHS stimulate Photosensitive Pigments, PERCEIVING DIFFERENT Colours
What are VISUAL PERCEPTIONS?
They are SUBJECTIVE VISUAL SENSATIONS
- CAUSED by the ACTION of Light ON THE Visual System
What are the 4 TYPES of VISUAL PERCEPTION?
1) LIGHT SENSE = Ability to PERCEIVE light in ALL GRADES of Intensity
2) FORM SENSE
- Ability to PERCEIVE the SHAPE of OBJECTS
- E.g. Visual Acuity
- USING the SNELLEN CHART / LOGMAR CHART
3) COLOUR SENSE
- Is what helps us DISTINGUISH BTW DIFFERENT Colours
- 3 Factors INFLUENCE
a. Colour Tone (Hue) = Determined by WAVELENGTH
b. Saturation = Determined by QUANITY of WHITE LIGHT ADDED to MAIN Tone
c. Brightness = Determined by LIGHT INTENSITY
4) SENSE OF CONTRAST
- Ability to PERCEIVE SLIGHT Changes in LUMINANCE
- BETWEEN REGIONS that are NOT Separated by Borders
What are the METHODS OF EXAMINING the VISUAL ADAPTION?
1) ORIENTING RESPONSE
- Organism’s IMMEDIATE Response to LIGHT CHANGES in ENVIRONMENT
2) ADAPTOMETRY
- Evaluating LIGHT SENSITIVITY by an APPARATUS
a. ADAPTOMETER of FORSTER
b. ADAPTOMETER of KRAKOW-WISHNEWSKI
What are the 2 DISTURBANCES of ADAPTATION?
1) HEMERALOPIA = Disturbance of ADAPTATION to DARKNESS
a. Essential - Alimentary / Hepatic Diseases / Metabolic Diseases / Toxic Damage VIA Metals
b. Symptomatic
- Pigment Retinal Degeneration
- HIGH Myopia
- Glaucoma
- Retinal Detachment
2) NICTALOPIA = Disturbance of ADAPTATION to BRIGHTNESS
