Vision Flashcards
Illuminance
The amount of light received by an object per unit area (lux).
Lux
The degree of illumination of a surface 1m from a source of 1 candela radiating uniformly in all directions.
What is the illuminance of full sunlight?
100 000 lux
Luminance
The amount of light emitted by an object per unit area (candelas per m^2)
Light adaptation
Retinal ability to decrease sensitivity to bright light. Results in eye having weaker responses to increasing increments of light intensity when light is v. bright
Chromatic abberation
Lens aberration where different colours of light are each refracted at different angles due to different wavelengths. Result = defected images with coloured fringes.
Spherical abberation
Defect in lens shape - becomes spherical rather than ellipsoid. Results in blurred image thus reduced visual acuity.
Glare
When small particles in optical media scatter light in all directions. Reduces contrast.
Tritanopia
- Lack of blue cones
- Blue-yellow colour blindness
- Blue appears green
- Yellow appears violet
Presbyopia
Reduction in accomodation power due to decrease in lens elasticity.
Visual acuity
.
Diffraction
When light waves spread out when they pass through a small aperture.
Effect of diffraction on image quality.
Causes the image of a point source to be a blurred circle known as the pointspread function.
How does pupil size affect lens aberrations?
As the pupil dilates, lens aberrations become more significant and the pointspread function broadens.
What is the difference btw refractive errors and aberrations?
Aberrations involve the lens and refractive errors involve the shape of the eye.
Emmetropic
When an object at infinity is sharply focused. If not, eye is ametropic
Hypermetropia
Long-sightedness - image forms behind the retina (eye squashed inwards)
Myopia
Short-sightedness - image forms in front of retina.
Accommodation
When the focal length of the lens changes to focus on objects at different distances.
Describe the near reflex.
Simultaneous constriction of the pupli to improve depth of focus and convergence of two eyes to fixate on new target.
What overall system controls pupil diameter?
The ANS
What muscles does the parasympathetic system control?
Sphincter
What muscles does the sympathetic system control?
Diator
Which muscle primarily controls pupil diameter?
The sphincter
Describe a test used to test intact brainstem function in unconscious patients.
.
Dark adaptation
The adjustment of the eye to low light intensities. Involves dilation of the pupils and activation of rod cells.
