chapter 17 Image formation of the eye

Refraction of light rays

(a) Refraction is the bending of light rays at the junction of two transparent substances with different densities. (b) The cornea and lens refract light rays from distant objects so the image is focused on the retina. (c) In accommodation, the lens becomes more spherical, which increases the refraction of light.

convex

A surface that curves outward is said to be _____. When the surface of a lens is _____, that lens will refract incoming light rays toward each other, so that they eventually intersect.

retina

As light rays enter the eye, they are refracted at the anterior and posterior surfaces of the cornea. Both surfaces of the lens of the eye further refract the light rays so they come into exact focus on the ___.

concave

If the surface of a lens curves inward, the lens is said to be ____ and causes light rays to refract away from each other.

hyperopia; hypermetropia

In ____ or farsightedness, also known as _____ , individuals can see distant objects clearly, but not close ones.

blurred vision

Light rays entering at the periphery would not be brought to focus on the retina and would result in _____________.

oculomotor (III) nerve

Parasympathetic fibers of the ______ innervate the ciliary muscle of the ciliary body and, therefore, mediate the process of accommodation.

near point of vision

The _______ is the minimum distance from the eye that an object can be clearly focused with maximum accommodation. This distance is about 10 cm (4 in.) in a young adult.

photopigment

The first step in visual transduction is absorption of light by a_____(visual pigment), a colored protein that undergoes structural changes when it absorbs light, in the outer segment of a photoreceptor. Light absorption initiates the events that lead to the production of a receptor potential.

central fovea

The lens must bend these parallel rays just enough so that they fall exactly focused on the ________, where vision is sharpest.

anterior and posterior surfaces

The lens of the eye is convex on both its ___ & ____, and its focusing power increases as its curvature becomes greater.

rhodopsin

The single type of photopigment in rods is ____

refraction

When light rays traveling through a transparent substance (such as air) pass into a second transparent substance with a different density (such as water), they bend at the junction between the two substances. This bending is called _____.

curved

When the eye is focusing on a close object, the lens becomes more ____, causing greater refraction of the light rays.

relaxed

When you are viewing distant objects, the ciliary muscle of the ciliary body is ____and the lens is flatter because it is stretched in all directions by taut zonular fibers

image formation

___ involves.... (1) the refraction or bending of light by the lens and cornea (2) accommodation, the change in shape of the lens (3) constriction or narrowing of the pupil

Myopic

_____ individuals can see close objects clearly, but not distant objects. (nearsightedness)

convergence

_____ is the medial movement of the two eyeballs so that both are directed toward the object being viewed ex: tracking a pencil moving toward your eyes. The nearer the object, the greater the degree of _____ needed to maintain binocular vision. The coordinated action of the extrinsic eye muscles brings about _____.

Binocular vision

________ occurs when light rays from an object strike corresponding points on the two retinas. - When we stare straight ahead at a distant object, the incoming light rays are aimed directly at both pupils and are refracted to comparable spots on the retinas of both eyes. As we move closer to an object, however, the eyes must rotate medially if the light rays from the object are to strike the same points on both retinas.

circular muscles of the iris

constriction of the pupil is a narrowing of the diameter of the hole through which light enters the eye due to the contraction of the _____

inverted

images focused on the retina are _____(upside down) They also undergo right-to-left reversal; that is, light from the right side of an object strikes the left side of the retina, and vice versa. The reason the world does not look inverted and reversed is that the brain "learns" early in life to coordinate visual images with the orientations of objects.

accommodation

increase in the curvature of the lens for near vision is called _____

night blindness

prolonged vitamin A deficiency and resulting below - normal amount of rhodopsin may cause ______ or nyctalopia an inability to see well at low light levels

color blindness

results in lack of deficiency of one of the 3 cones . Most common is red and green cones are missing and people have the tenancy not being able to distinguish red from green

contracts

the ciliary muscle of the ciliary body is relaxed and the lens is flatter because it is stretched in all directions by taut zonular fibers. When you view a close object, the ciliary muscle _______, which pulls the ciliary process and choroid forward toward the lens. This action releases tension on the lens and zonular fibers. Because it is elastic, the lens becomes more spherical (more convex), which increases its focusing power and causes greater convergence of the light rays

astigmatism

the cornea or the lens has an irregular curvature. As a result, parts of the image are out of focus, and thus vision is blurred or distorted.

emmetropic eye

the normal eye, known as an ______, can sufficiently refract light rays from an object 6 m (20 ft) away so that a clear image is focused on the retina.