Eye Disorders, Fovea, Rods Cones

What is presbyopia?

Hardening of the lens over time leading to a loss of the ability to bend light.

What causes cataracts?

Progressive loss of transparency in the lens.

What is hypermetropia?

Farsightedness caused by the eye being too short, making near objects appear blurry.

What type of lens corrects hypermetropia?

Convex lens, which helps to bend light rays of near objects adequately.

What is myopia?

Nearsightedness caused by the eye being too long, making far objects appear blurry.

What type of lens corrects myopia?

Concave lens, which diverges light rays to reduce excessive bending.

What is the fovea?

A small pit in the retina with the best visual acuity.

What angle represents light rays that hit the fovea?

0 degrees of visual angle.

Why is visual angle important in experiments?

It determines how much a stimulus will appear in a person's vision.

What does visual acuity refer to?

The eye’s ability to resolve fine details.

What happens to visual acuity as the visual angle increases from the fovea?

Visual acuity decreases.

What are three reasons why visual acuity is best at the fovea?

1. Closeness to the optic axis, 2. Less cell bodies in the foveal pit, 3. Mainly cone photoreceptors present.

What types of cells are found at the fovea?

Only cone photoreceptors, no rods.

What are the two types of photoreceptors in the retina?

Cones and rods.

Where are cones primarily located?

In the fovea and everywhere else on the retina.

Where are rods primarily located?

Mostly everywhere else on the retina but not in the fovea.

How do rods and cones differ in relation to their projection to ganglion cells?

Rods have many-to-one projections, while cones have one-to-one projections.

What does neuronal convergence mean?

Many cells projecting to a smaller number of cells.

How does neuronal convergence affect brightness resolution in rods?

It allows ganglion cells wired to many rods to receive more photons, resulting in good brightness resolution.

Why do rods have poor spatial resolution?

Information is averaged out when many rods project to one ganglion cell.

What is the total number of rods in the human retina approximately?

~120 million.

What is the total number of cones in the human retina approximately?

5-8 million.

What type of vision do rods provide?

Scotopic vision, which works well in dim light.

What type of vision do cones provide?

Photopic vision, designed for daylight conditions.

Which photoreceptor is responsible for color vision?

Cones.

How does the structure of the fovea minimize light obstruction?

Ganglion and bipolar cells are pushed to the side.

What type of resolving power do cones possess?

Good spatial resolution.

What type of resolving power do rods possess?

Good brightness resolution.

What visual conditions do rods operate under?

Dim light conditions.

What visual conditions do cones operate under?

Brighter light conditions.

What angle does a thumb at arm's length subtend on the retina?

1 degree.

What does the term 'visual angle' refer to?

The angle that a stimulus subtends on the retina.

Why do we not notice the blur in our peripheral vision?

Because of our rapid eye movements.

What physical aspect of the eye contributes to less distortion at the fovea?

The top of the eye being the least jagged part of the sphere.

What are the functions of cone photoreceptors?

Central vision and color vision.