Week 4 Vision Objective 1 Flashcards
Refraction
light bends as it moves across an angulated surface of a transparent material
What happens when light hits a perfectly perpendicular surface?
It keeps traveling unaffected
Degree of refraction is called the
ratio of two refractive indices of the two transparent media
Refractive index
velocity of light in a vac / light traveling in a substance
Refractive power
measures how much light bends light, measured in diopters
1 diopter
1 meter divided by the focal length of a lens
Focal point and length
the point through which all light will travel after passing through each part of the lens
distance from the center of the lens to the focal point
Depth of focus will increase as
pupillary diameter decreases
Emmetropia
normal eye sight, normal depth of focus and
parallel light rays are in sharp focus on the retina
all objects are seen clearly
Hypertropia
Farsightedness
eye is too short
lens system is too weak
image forms behind eyeball
all distant objects can be seen clearly
Myopia
nearsightedness
ciliary muscle is completely relaxed, light rays are focused in front of the retina
image forms in front of the retina
usually due to too long an eyeball
Visual acuity
measure of the resolving power of the eye
Visual acuity averages
Light from a distant source will create a “spot” that is around 11 micrometers, and whose center is brighter than periphery
average diameter of a cone in the retina is 1.5 micrometers
therefore, visual acuity for a two point source of light is 1.5 to 2 mm
Formation of fluid in the eye
aqueous humor in the eye is formed by ciliary bodies
produced by ciliary body cells in the posterior chamber via osmosis
Na is pumped into space along with Cl and bicarbonate
Flow of fluid in the eye
fluid flows from the anterior chamber into the canal of schlemm and from there into aqueous veins in the sclera
a tonometer is used to measure the intraocular pressure
normal pressure is 15 mm Hg
