Topics in Physiology: Vision

Topics in Physiology:

Vision

By Sasha Shomshor

Anatomy of the Eye

Anatomy of the Eye

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Anatomy of the Eye

Answers

a. Superior Rectus Muscle

b. Sclera

c. Choroid

d. Retina

e. Fovea Centralis

f. Central Artery

g. Central Vein

h. Optic Nerve

i. Conjuctiva

j. Ciliary Body

k. Posterior Chamber

l. Anterior Chamber

k + l. Anterior Cavity

m. Cornea

n. Pupil

o. Lens

p. Iris

q. Zonular Fibers

r. Posterior Cavity

s. Inferior Rectus Muscle

Accommodation

Accommodation is the ability of the eyes to keep the image focused on the retina as the distance between the eyes and the object vary. 

Accommodation results from contraction of the ciliary muscle. The lens is attached to the ciliary muscle by zonular fibers. When the ciliary muscle contracts, the lens becomes rounder and thicker. When the ciliary muscle relaxes, the lens becomes flatter.

Accommodation

Accommodation

The iris has two types of muscles that help regulate light. The radially arranged smooth muscle fibers contract to open the pupil in dim light while the circularly arranged smooth muscle fibers contract to restrict the pupil in bright light.

Visual Impairments

There are many types of visual impairments. In the next few pages we will cover a few common ones.

Visual Impairments

Emmetropia

Emmetropia is known as "normal vision". The eye is not too big or too small for the lens and light rays are able to focus correctly on the retina.

Visual Impairments

Myopia

Myopia is known as "nearsightedness" or "short vision". Myopia occurs when the eye is too big for the lens and rays focus in front of the retina. To compensate for this, concave lenses are used. 

Visual Impairments

Hyperopia

Hyperopia is known as "farsightedness" or "far vision". People with hyperopia have eyes that are too small for their lens. This causes the light rays to focus behind the retina. Convex lenses are used to correct this.

Visual Impairments

Astigmatism

Astigmatisms occur when the cornea is not perfectly round, but instead irregularly shaped. This causes some of the light rays to be unable to focus on part of the retina. Uneven, or cylindrical lenses, are used to correct astigmatisms by rounding out the cornea.