exam 2 study guide #6 Flashcards
Which photoreceptor is responsible for night (low acuity, low light threshold) vision?
Rods
Which photoreceptor is responsible for color (high acuity, high light threshold) vision?
Cones
The relative concentrations of cones is greater in the _____ than the _____ of the retina.
fovea; periphery
The relative concentrations of rods is greater in the _____ than the _____ of the retina.
periphery; fovea
The fovea:
-provides the area of greatest acuity
-is where we direct our focus when trying to view an object
-is the area where the four layers of accessory neurons and blood vessels are “pulled to the side”
-allows light to directly stimulate the cones
The site where the optic nerve and blood vessels leave the retina:
-is the blind spot
-has no photoreceptors
What two factors determine the refractive power of a lens?
-the angle at which light enters a lens
-the difference in the refractive indices of the two media
The interface which produces the most refraction of light in the normal eye is
air-cornea
List the four components of the refractive system of the eye in order from the air to the retina.
-cornea
-aqueous humor
-lens
-vitreous humor
Which of the four components of the eye’s refractive system is not fixed and can change its refractive power as needed?
lens
focal point
point at which light converges behind a lens
focal length
distance between the lens and the focal point
convex lens
-lens that causes light rays to converge
-positive diopter
concave lens
-lens that causes light rays to diverge
-negative diopter
calculating refractive power in diopters
take 1000 and divide by focal length
Which of the following are associated with emmetropia?
-focal point on the retina
-focal length = 17mm
-refractive power of lens system = 59 diopters
What three reflexes are associated with the near response?
-accommodation
-pupillary
-convergence
What does the accommodation reflex do to the refractive power of the eye lens?
increase
Contraction of the ciliary muscle is the result of
increased PANS`
Relaxation of the ciliary muscle is the result of
decreased PANS
What type of muscle is the ciliary muscle?
multi-unit smooth
Light rays entering the eye from a distant source are____, while light rays from near sources are _____.
parallel; diverging
Ciliary muscles _____ for distant vision, and _____ for near vision.
relax, contract
The near point of vision
-increases with advancing age
-changes as the lens loses elasticity
Where is the focal point for near vision (with respect to the retina) in uncorrected presbyopia?
behind the retina
Where is the focal point for near vision (with respect to the retina) in uncorrected presbyopia?
convex spherical
The pupillary reflex is:
-apart of the near response
-involves pupillary constriction occurring simultaneously with the accommodation reflex.
-helps improve the acuity of near vision by reducing the divergent light rays from the near source.
What Autonomic Nervous System activity is responsible for active pupillary dilation?
increased SANS
What Autonomic Nervous System activity is responsible for active pupillary constriction?
increased PANS
What type of muscle is found in the iris?
multi-unit smooth muscle
The convergence reflex:
-focuses the image on the fovea of both eyes
-prevents double vision
Which of the following are associated with hyperopia?
-focal point behind the retina
-focal length> 17mm
-refractive power of lens system
-corrected with positive diopter lens
-corrected with convex lens
Which of the following are associated with myopia?
-focal point in front of the retina
-focal length
-refractive power of lens system> 59 diopters
-corrected with negative diopter lens
-corrected with concave lens
How is correction of hyperopia accomplished?
by adding to the refractive power of the eye’s refractive system therefore shortening the focal length so the focal point falls on the retina
How is correction of myopia accomplished?
by reducing the refractive power of the eye’s refractive system therefore extending the focal length so that the focal point falls on the retina
Astigmatism is the result of:
a difference in refractive power in one or more axes of the refractive system
What are two potential causes of astigmatism?
-irregularly shaped cornea
-irregularly shaped lens
A spherical lens has a _____focus, while the cylindrical lens has a _____ focus.
point; line
A spherical lens focuses light in _____, while the cylindrical lens focuses light in____.
all axes; one axis
