THE VISUAL SYSTEM

Question 1

The visual system

Answer 1

detects and interprets information from visible light to build representation of the environment.
The eyes are the organ of vision and sight. They detect light and convert it into electrochemical impulses
of action potential in the neurons. The translation of these signal is processed in the occipital lobe.
The eyes sit inside orbits. Orbits are bony socket in the skull that are padded with fat that contain blood
vessels, nerves and muscles that move the eye and give it its shape.
The eyelid, eye lashes and lacrimal glands (secrete tear) protect the eyes.

Question 2

Structure of the Eye

Answer 2

The structure of the eye is usually divided into two parts:

• The layers of the eye.
• The inner and outer organs of the eye.

Question 3

The Layers of the Eye

Answer 3

Composed of three layers:

• Sclera
• Choroid
• Retina

Question 4

Sclera

Answer 4

The outer most layer that is made of white dense connective tissue. It provides the eye with rigidity and structure. It covers the entire eye and at the front it forms the cornea.
* Cornea – arched, thin and transparent layer located at the front of the eye. It bends and focuses light by refracting in.

Question 5

Choroid

Answer 5

The middle pigmented layer that contain blood vessels that supply oxygen and nutrient
to the eye. It also forms the iris.
* Iris – consist of muscle that regulates the amount of light that enters the pupil.
**Pupil – the hole in the center of the iris, where
light enters.

Question 6

Retina

Answer 6

The inner most layer of the eye that contains nerve tissue and photoreceptors cells that react to light. Photoreceptors in the retina divide into two:

• Rods – responsible for the transmission of black and white images. They respond to low intensity illumination for various types of light waves. They are very useful in night vision.
• Cones – responsible for the transmission of colored images and sharpness. They come in 3 pigmented 𝑅𝐺𝐵 that absorbed differed wavelength of visible light.

The retina also has two special areas:

• • The optical disk – also called the blind spot. It has no photoreceptors at all. The connection site of the optic nerve that leave the eye from there.
• • fovea centralis – high concentration of cones that provide very sharp image.

Question 7

The Organ of the Eye

Answer 7

Composed of:

• Cornea
• Fovea
• Lens
• Ciliary body
• Optic disk
• Optic nerve

Question 8

Cornea

Answer 8

The front of the sclera. It is thin and transparent.

Question 9

Fovea

Answer 9

A region at the center of the retina with high concentration of cones that responsible for
sharp vision.

Question 10

Lens

Answer 10

Transparent disk of protein responsible for converging the light entering the eye on the fovea. Divides the eye into two cavities:

• Aqueous humor – a clear watery substance found in the front of the lens. It includes:
  * Anterior chamber – between the cornea and iris.
  * Posterior chamber – between the iris and lens.
• Vitreous humor – jelly like substance found behind the lens.

Question 11

Ciliary body

Answer 11

Composed of:
* Ciliary muscle – triangular shaped group of muscles that attach to the lens to adjust its
thickness and shape in order to focus the light on the retina.
* Ciliary epithelium – responsible for production of the aqueous humor.

Question 12

Optic disk

Answer 12

The blind spot in the eye. Cause due to the optic nerve that leaves the eye from there.

Question 13

Optic nerve

Answer 13

The nerve that transmit visual information from the retina to the brain.

Question 14

Visual Pathway

Answer 14

The process in done by few steps:
1. Light enters the eyes by passing through the cornea.
2. Light rays then move on through the pupil whose size can be adjusted by the iris determining the
amount of light coming in.
3. Light then passed through the lens, which focuses the images on the retina with the help of the
ciliary muscles.
4. Light stimulates the photoreceptors of the retina with then transforms light into action potential
that leaves the eye through the optic nerve.
5. Electrical signal then moves onto the optic charisma (where two optic nerves meet (to the visual
cortex of the brain that is located in the occipital lobe.
6. The images are finally being proceed there.

Question 15

The light in the cornea

Answer 15

The cornea refract light as it enters the eye, which causes to rays from the top of an image to strike the
bottom of the retina and vice versa. The image on the retina is upside down.
* The retinal image – upside down and real (flat 2𝐷 image).
* Our perception – righted as in reality and virtual (3𝐷 image).

**The images that go into the brain are 2𝐷 and have a blind spots in them (due to the optic nerve), but they
are being proceed in the brain to give us full 3𝐷 image.

Question 16

Left and the right eyes

Answer 16

Both the left and the right eye perceive light from the other field (left can observe a little part of the right
side and vice versa). When the optic nerves of the eyes meet, they diverge into left and right. Meaning:
* Nerves that perceive image from the left field (both on the left and right eyes) will go to the left
side of the occipital lobes.
* Nerves that perceive image from the right field (both on the left and right eyes) will go to the right
side of the occipital lobes.

Question 17

Pathology

Answer 17

the light that hit the retina can be out of focus if the lens accommodation if not perfect.
* Myopia – nearsighted. Inability to see far, due to light being focused in front of the retina.
Usually corrected with diverging lens with a negative value)
* Hyperopia – farsighted. Inability to see near, due to the light being focused behind the retina.
Usually corrected with converging lens with a positive value.