The Visual System

Question 1

What is the retina?

Answer 1

The retina is actually one of the last places where the light shines –the light passes through other parts of the eye first. The conversion of light into electrochemical signals happens here.

Question 2

What is the cornea?

Answer 2

The cornea is the front, transparent layer of the eye. This part is usually shaved down during LASIK SURGERY.

Question 3

What occurs in the cornea?

Answer 3

Refraction (bending/focusing)

Question 4

What is the iris?

Answer 4

The colored part of the eye

Question 5

What is the pupil?

Answer 5

The little hole where the light enters the eye. It can dilate and let in the right amount of light.

Question 6

What happens in bright lights vs. low and dim lights?

Answer 6

Bright lights : the iris becomes the size of the pupil

Dim lights : the iris relaxes and pupil expands

Question 7

What happens after the light enters the eye?

Answer 7

The light passes through the crystalline lens, a structure with many layers behind the cornea. This works to further refract the light to focus the image on the retina.

Question 8

What is the lens?

Answer 8

The lens is dynamic and flexible because it changes shape to focus on different parts of the visual field. There are special muscles that help it be flexible.

Question 9

What does aging do to the lens?

Answer 9

The lens flexibility reduces with age. This causes a form of farsightedness.

Question 10

How does farsightedness occur?

Answer 10

This is caused because the lens isn’t flexible or the eyeball is shaped so that the distance between the cornea and the retina is too short. The image falls behind the retina.

Question 11

How does myopia (nearsightedness) occur?

Answer 11

This is because the eyeball is shaped so that the distance between the cornea and the retina is too long. The image falls in front of the retina.

Question 12

What can fix myopia and/or farsightedness?

Answer 12

Glasses, corrective lenses, or LASIK surgery which can change the curve of the cornea to bend the light so the image falls exactly on the retina.

Question 13

What is the retina?

Answer 13

This is a many layered sheet of neurons that converts light in the back of the eye.

Question 14

Describe the process for the light to get to the back of the retina.

Answer 14

The light must first go through this sticky, thick liquid and around the first layers of the retina to get to the photoreceptors.

Question 15

What are photoreceptors?

Answer 15

They recieve and convert light.

Question 16

What is the one reason that the retina’s layers are seemingly “inside out”?

Answer 16

The pigmented epithelium needs to be just outside these cells to help support their function.

Question 17

What are the pigmented epithelium cells?

Answer 17

They absorb excess light so it doesn’t scatter and blur the image. They get rid of old light absorbing segments of the photoreceptors.

Question 18

What is just outside the pigmented epithelium layer?

Answer 18

The choroid, which brings oxygen and nutrients to the photoreceptor cells.

Question 19

What is in the very center of the retina?

Answer 19

The fovea - this is where the vision the sharpest and the best.

Question 20

What are the two general types of photoreceptors.

Answer 20

Rods and cones.

Question 21

What do both rods and cones have in common?

Answer 21

Rods and cones both have disks of membranes where a pigment absorbs light and communicates with the molecular machinery needed to convert the light.

They both convert light in a similar way. They use different pigments.

Question 22

What is different about rods?

Answer 22

Rods have more disks which therefore are more sensitive to low light settings.

Question 23

What is different about cones?

Answer 23

Cones are clustered in the center of the retina, in the fovea. The cornea has a good response to bright light which makes them good for a bright light setting and full color vision.

Question 24

What’s another word for pigments?

Answer 24

Opsins, which each absorb a different wavelength or color of light.

Question 25

What opsin do rods have?

Answer 25

Rods have an opsin called rhodopsin. There are usually three types of cones which each absorb a different wavelength.

Question 26

What do primates use?

Answer 26

Primates use a trichromatic (three-cone) which allows them to see in hundreds of thousands of colors.