Unit 2 Exam Lab 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
What is being described below?
- 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 fovea
What two things describe the site where the optic nerve and blood vessels leave the retina?
- It is the blind spot
- It 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 (air:aqueous solution, air:glass, aqueous solution:glass, water:aqueous solution, etc.)
The interface which produces the most refraction of light in the normal eye is
air - cornea
What are the four components of the refractive system of the eye in order from the air to the retina?
1.cornea
2. aqueous humor
3. lens
4. vitreous humor
CALV
Which of the four components of the eye’s refractive system is not fixed and can change its refractive power as needed?
Lens
Point at which light converges behind a lens
Focal Point
Distance between the lens and the focal point
Focal Length
Lens that causes light rays to converge
Convex Lens
Lens that causes light rays to diverge
Concave Lens
Convex:
Converging or Diverging
+ or - diopters
Converging
+ diopters
Cancave:
Converging or Diverging
+ or - diopters
Diverging
- diopters
True or false:
The largest lens would have the shortest focal length if distance of light source is kept constant
True
If an eye’s refractive system has a focal length of 17.3 millimeters, calculate its refractive power in diopters.
Show the steps to calculate
17.3/1000=0.0173
1/0.0173=57.8
Meters are equal to Diopters
If a lens has a refractive power of of + 57 diopters, its focal length would be____ meters.
Show the steps to calculate
1/57=0.0175
About 0.018
Meters are equal to Diopters
Which of the following are associated with emmetropia?
- Focal point is on the retina
- Focal length=17 m
- Refractory power=59 d
What three reflexes are associated with the near response?
- accommodation reflex
- pupillary reflex
- convergence reflex
Does the accommodation reflex increase or decrease the refractive power of the eye lens?
Increase
Why is the accommodation reflex necessary to focus the image of a near object on the retina? Near light rays are _____ and require a ______ refractive power to focus on the retina.
Diverging; greater
In the accommodation reflex, the ciliary muscle _______, which ______ the tension on the suspensory ligaments, and _____ the refractive power of the lens.
Contracts
Decreases
Increases
What is the contraction of the ciliary muscle is the result of?
Increased parasympathetic
What is the relaxation of the ciliary muscle is the result of?
Decreased parasympathetic
What type of muscle is the ciliary muscle?
Muti-unit smooth muscle
Eye drops containing atropine, a cholinergic antagonist, are routinely administered before cataract surgery. What effect do these drops have on the ciliary muscle and the lens of the patient’s eye?
block ciliary muscle contraction; keeps lens flat
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.
Relaxes
Contracts
The near point of vision (increases or decreases) with age and changes has the lens (loses or gains) elasticity?
Increases
Loses
Where is the focal point for near vision (with respect to the retina) in uncorrected presbyopia?
behind the retina
What type of lens corrects presbyopia?
convex spherical
What are the phrases below describing?
- is part 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.
The pupillary reflex
What Autonomic Nervous System activity is responsible for active pupillary dilation?
Increased sympatetic
What Autonomic Nervous System activity is responsible for active pupillary constriction?
Increased parasympathetic
What type of muscle is found in the iris?
Multi-unit smooth muscle
What type of reflex is being described below?
- assists with near vision by moving the eyeballs inward to achieve a single image when viewing near objects
- focuses the image on the fovea of both eyes
- prevents double vision
- controlled by somatic nervous system
The convergence reflex
Which of the following are associated with hyperopia?
-Focal point behind the eye
-Focal length >17 mm
-Refractive power of lens system
-Corrected with convex/+ diopters 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
Which of the following are associated with myopia?
-Focal point in front of retina
-Focal length
-Refractory power >59 d
-Corrected with concave/- diopters lens
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
What are two characteristics of the The Snellen eye chart?
- Was created by Hermann Snellen, a 19th century ophthalmologist
- Sets a standard of visual acuity for people standing 20 feet from the chart.
In 20/20 vision, what does the first 20 represent?
Subject’s vision
What does 20/10 vision mean?
Better than normal acuity:
subject see at 20 feet what someone with 20/20 vision could see at 10 feet.
What does 20/200 vision mean?
Poor visual acuity:
subject must stand at 20 feet to see what someone with 20/20 vision sees at 200 feet.
What is an astigmatism 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
If one observes an astigmatism chart and sees a blurred lines in the 2-8 axis, they can conclude what two things?
- They have astigmatism.
- The refraction of light in the 2-8 axis is different than in the other axes.
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 axis; one axis
What two types of lens can be used to correct astigmatism?
- Cylindrical concave
- Cylindrical convex
Which of the following statements concerning contact lenses is/are true?
-Hard, but not standard soft contact lenses be used to correct astigmatism.
-Hard lenses conform to the cornea duplicating any defects that may exist.
-The tear layer between a hard lens and a cornea with an irregular surface helps correct the refractive defects.
-A special soft lens called toric lenses can be used for astigmatic eyes.
-Hard, but not standard soft contact lenses be used to correct astigmatism.
-The tear layer between a hard lens and a cornea with an irregular surface helps correct the refractive defects.
-A special soft lens called toric lenses can be used for astigmatic eyes.
