Exercise 24 Special Senses: Visual Tests and Experiments

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Explain why vision is lost when lights hits the blind spot?

There are no photoreceptors present, therefore vision is lost when light hits this spot (the blind spot)



light bending



ability to focus for close (less than 20 feet) vision



normal vision



inability to focus well on close objects (farsightedness)






blurred vision due to unequal curvatures of the lens or cornea



medial movement of the eyes during focusing on close objects


In farsightedness, light is focused __1__ the retina. The lens required to treat myopia is a __2__ lens. the "near point" increases with are because __3__ of the lens decreases as we get older. A convex lens, like that of the eye, produces an image that is upside down and reversed from left to right. Such an image is called a __4__ image.

1. behind

2. concave

3. flexibility

4. real


During distance vision, the ciliary muscle is __1__, the ciliary zonule is __2__, the convexity of the lens is __3__
and light refraction is __4__.

1. relaxed

2. taut

3. decreased

4. decreased


During close vision, the ciliary muscle is __1__, the ciliary zonule is __2__, lens convexity is __3__, and light refraction is __4__.

1. contracted

2. relaxed

3. increased

4. increased


Normal vision

being able to see at 20 feet what a person with normal vision can see at 20 feet


Explain why each eye is tested separately when using the Snellen eye chart.

because both eyes could have different vision


20/40 vision

person can see at 20 feet what a person with normal vision can see at 40 feet. less than normal vision.


20/10 vision

person can see at 20 feet what a person with normal vision can see at 10 feet. better than normal vision.



irregularities in the curvatures of the lens and/or the cornea lead to a blurred vision problem

- corrected by cylindrically ground lenses with opposite curvature gradation



degeneration of the accommodation power of the eye associated with aging

- caused by when the lens become sclerotic and less flexible


wavelengths of light three cone types of the retina respond maximally

blue pigments, green pigments, red pigments


How can you explain the fact that we see a great range of colors even though only three cone types exist?

Interpretation of the intermediate colors of the visible light spectrum is a result of overlapping input from more than one cone type


Explain the difference between binocular and panoramic vision.

Binocular vision, there is a overlap between the visual fields of the left and right eye. Panoramic vision, the left and right eyes see in two different directions resulting in a panoramic field of view.


Advantage of binocular vision

provides 3-dimensional vision and an accurate means of locating objects in space, known as depth perception


What factors are responsible for binocular vision?

the eyes are in the front of the head and the ability of visual cortex to resolve two different views into a single image.


Convergence reflex, what happened to the position of the eyeballs as the object was moved closer to the eyes?

What extrinsic eye muscles control the movement of the eyes during this reflex?

Value of this reflex?

- medial eye movements; both eyes are directed toward the near object viewed

- medial, superior, inferior rectus muscles

- Helps maintain and is responsible for keeping the eyes aligned and focused on an object


Photopupillary reflex, what happened to the pupil of the eye exposed to light?

What happened to the pupil of the nonilluminated eye?


- it constricted

- it dilated

- light exposed to the pupil will constrict as a protective response to prevent damage to photoreceptor cells


Why is the ophthalmoscopic examination an important diagnostic tool?

it can determine if a person has pathological conditions or degenerative changes in optic nerve or retina


Why is it more of a strain on the extrinsic and intrinsic eye muscles to look at close objects than at far objects?

when looking at near objects your eyes constantly need to converge and accommodate. Using these muscles will constantly cause strain. But looking at far objects don't need to converge and accommodate so you don't use these muscles making less strain on the eyes.

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