Eye anatomy and the visual pathway 1

Which layer of the eyeball would be the first to be affected by deficient tear production?

• Sclera

• Choroid

• Retina

A condition, called night blindness, dangerously impairs our ability to drive safely at night. Its most common cause is prolonged vitamin A deficiency, which eventually causes the neural retina to deteriorate. Vitamin A supplements will restore function if taken before degenerative changes in the neural retina occur. Which component of the eye is defected in this condition?

One of the most common forms of colour blindness are the two varieties of red-green colour blindness. In people who have red or green colour blindness, red and green are seen as the same colour. Many colour-blind people are unaware of their condition because they have learned to rely on other cues—such as differences in intensities of the same colour—to distinguish green from red, for example, on traffic signals. Which component of the eye is possibly defected in this condition?

Glaucoma is a condition in which the pressure within the eye may increase to dangerous levels and compress the delicate retina and optic nerve. It can lead to blindness unless detected early. Glaucoma is a common cause of blindness in the elderly. Glaucoma is caused by blockage of the drainage of the ……………………… (Fill in the blank)

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NGSS.HS-LS1-3

Near-sightedness, or myopia (“short vision”), occurs when the parallel light rays from distant objects fail to reach the retina and instead are focused in front of it; see part (b) in the figure. Another way to think of this is the focal point of a myopic eye falls short of the retina. Therefore, distant objects appear blurry to myopic people. Nearby objects are in focus, however, because the lens “accommodates” (bulges) to focus the image properly on the retina. Correction requires concave corrective lenses that diverge the light rays before they enter the eye, so that they converge farther back on the retinal surface. In other words, near-sighted people see near objects clearly and need corrective lenses to focus on distant objects.

Which of the following is NOT the cause of myopia?

• The eyeball is too long

• The lens is too curved

• The cornea is too curved

• The ciliary muscle is too relaxed

Far-sightedness, or hyperopia (“far vision”), occurs when the parallel light rays from distant objects are focused behind the retina—at least in the resting eye; see part (c) in the figure. People with hyperopia see distant objects clearly because their ciliary muscles contract continuously to increase the light-bending power of the lens, which moves the focal point forward onto the retina. However, the diverging rays from nearby objects are focused so far behind the retina that even at full “bulge,” the lens cannot focus the image on the retina. Therefore, nearby objects appear blurry, and hyperopic individuals are subject to eyestrain as their endlessly contracting ciliary muscles tire from overwork. Correction of hyperopia requires convex corrective lenses that converge the light rays before they enter the eye. Thus, farsighted people can see faraway objects clearly and require corrective lenses to focus on nearby objects.

Which of the following is NOT the cause of hyperopia?

• The eyeball is too short

• The lens is too flat

• The cornea is too flat

• The proportion of rods/cones is abnormal

Why is using dioptres (1/f ) convenient?

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As an object moves closer, do the ciliary muscles contract, or relax to keep the object in focus?

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Given the three parameters (d_o, d_i and f), how does the human eye keep the world in focus?

• Changing f

• Keep a suitable ratio of d_o and d_i

• Keep f as constant

Which eye structure determines a person’s eye color?