Section 0.1.3

Question 1

Describe pupillary constriction

Answer 1

Pupillary constriction is caused by parasympathetic stimulation. One set of muscles is organized in a
circular fashion (around the pupil) and these muscles constrict to make the pupil smaller (i.e. less light goes through)

Question 2

Describe pupillary dilation

Answer 2

Pupillary dilation is caused by sympathetic stimulation. One set of muscles is organized in a radial
fashion (from the pupil to the edge of the iris) and these muscles contract to dilate the pupil to allow more light to go through.

Question 3

Why do light rays need to be bent so that they can enter the eye?

Answer 3

Light rays are made of photons that travel in a wave-like pattern. These waves can vary in
wavelength* and intensity* Light waves, however, radiate outwards from their source and in order
for vision to occur, these light waves need to be bent so that they can enter the eye and allow the eye to focus them for processing.

Question 4

What happens when light passes through a transparent media with a density different from air?

Answer 4

When light passes through a transparent media with a density different from air, two things happen:
* the wavelength decreases; and
* unless it enters the media perpendicularly, its direction will change. This property is called
refraction* (The eye has two refractive structures, the cornea and the lens)

Question 5

What is the cornea

Answer 5

This structure contributes the most to the refractive ability of the eye because of the large density
difference at the air-cornea boundary. The refractive ability of the cornea remains constant as the curve of the cornea cannot be altered.

However, in some persons, the surface of the cornea is uneven, which results in the uneven refraction of light known as astigmatism.

Question 6

What is the lens?

Answer 6

This is the convex structure located behind the pupil. Because of its shape it has the ability to further focus light rays on the retina. Unlike the cornea, however, the lens is adjustable

Question 7

Wavelength: the distance between the peaks of a wave.

Intensity: the amplitude of the peak.

Refraction: the bending of light when it passes from one medium to another

Question 8

What is accommodation and what is it controlled by?

Answer 8

It is the eye’s ability to adjust the lens to maintain focus on something.

It is controlled by the ciliary muscle and suspensory ligaments.

When this muscle is relaxed, the ligaments pull the
lens into a flatter, less convex shape. When the muscle contracts, it reduces the tension of the ligaments and the lens becomes more convex.

Ciliary muscle contraction is also under control of the ANS, with sympathetic stimulation causing relaxation and parasympathetic stimulation causing contraction

Question 9

Why does the location of the light source affect accomodation?

Answer 9

The location of the light source is an important factor in accommodation. When the light source is close, a stronger or more convex lens is required to bring the light into focu

Question 10

Describe the difference in how light rays enter the lens and focus depending on their distance from the light source.

Answer 10

Once light rays have moved more than 6 m from their source, the light rays are parallel to each other when they enter the eye

If the light source is closer than 6m then light rays are still diverging or moving apart from each other when they enter the eye. In this case, the eye accommodates to make a lens with a greater ability to bend light so that the eye can focus

Question 11

What happens when accommodation is not sufficient to create clear vision?

Answer 11

Corrective lenses, such as glasses or contacts, are needed

Question 12

What is the ultimate goal of the lens?

Answer 12

The ultimate goal of the lens is to focus light rays onto the retina to convert the light energy into
electrical signals sent to the CNS

Question 13

Describe the retina.

Answer 13

The retina is actually an extension of the CNS with a direct connection through the optic nerve. Each retina has over one million nerve fibres bringing information to the brain.

The retina can be divided into three layers of excitable cells: the photoreceptor, bipolar and ganglion cells

Question 14

Describe the retina visual pathway

Answer 14

The retinal visual pathway extends from the photoreceptor cells to the bipolar cells, and then to the
ganglion cells. Note that the direction of light is opposite the direction of retinal visual processing

Question 15

What is the function of rods and cones in the ganglia

Answer 15

These are photoreceptor cells.

The outermost layer of the retina contains rods and cones. Cones are those cells sensitive to colour, and rods are responsible for vision in low lighting.

Question 16

What are bipolar cells in the retina?

Answer 16

The middle layer of the retina of bipolar cells are involved in the transmission of signals from the rods and cones to the ganglion cells.

Question 17

What are ganglion cells in the retina?

Answer 17

The neurons located at the inner surface of the retina. Axons of the ganglion cells make up the optic
nerve

Question 18

Why is there a blind spot in the eye?

Answer 18

The retina is continuous throughout the entire inner surface of the eye with the exception of the optic
disc, where the ganglion cell axons bundle together to form the optic nerves (1 per retina) and leave the eye. Because this region has no rods and cones, it creates a blind spot in the eye. Interestingly,
higher visual processing fills in this blind spot so it is generally not noticed.

Question 19

Describe the central processing of vision

Answer 19

Information from the optic nerves is transmitted to the visual pathway in the thalamus. The thalamus does initial processing by separating different visual stimuli (colour, form, depth, movement, etc.) and relaying each to different zones in the cortex. Recall from Module 02 that the thalamus is an integrating centre for all sensory input on its way to the cortex.

Like other areas of the cortex, the visual cortex is organized into functional columns with alternating columns devoted to the left and right eyes. The brain can compare these neighbouring columns to allow depth perception and allow you to estimate distance.

Vision takes up a tremendous amount of cortex processing, estimated to be about 30% of total cortex capacity.

Question 20

Having two eyes improves ________ perception, which is lost if a person loses their sight in one eye.

Answer 20

depth

Question 21

How is vision processed from the right and left side?

Answer 21

We have two eyes that
are set apart, and because they are set apart, they receive different visual input and send different information to the brain.

vision to the right visual field is processed in the left side of the brain, and vision to the left visual field is processed in the right side of the brain

Question 22

What happens to visual information after it leaves the retina?

Answer 22

Visual information travels through the optic nerve to reach the brain’s visual cortex, primarily in the occipital lobe. In the visual cortex, the brain processes the signals to construct a coherent visual image, interpreting aspects like color, shape, motion, and depth. This central processing enables meaningful visual perception.

Question 23

Describe the structure and function of the retina.

Answer 23

The retina is a multilayered structure in the eye’s interior. It converts incoming light into electrical signals through photoreceptor cells (rods and cones). These signals are transmitted to the brain via bipolar and ganglion cells, forming the optic nerve. The retina plays a crucial role in visual perception.

Question 24

What is the purpose of the lens in the eye, and how does it function?

Answer 24

The lens’s purpose is to focus incoming light onto the retina for clear vision. It achieves this through accommodation, where ciliary muscles alter the lens’s shape. Contracting muscles make the lens thicker for near vision, while relaxed muscles flatten it for distant vision.