Visual Fields and Hemifields Flashcards

Questions and Answers

What is a visual field?

The area visible when both eyes are closed.

The area visible only in darkness.

Only the area visible on the left side.

The area visible when one eye is fixed. (correct)

What is a hemifield?

Half the visual field defined by quadrant created by vertical and horizontal meridian lines.

What is a quarterfield?

One quarter or quadrant of the visual field defined by the quadrant created by vertical and horizontal meridian lines.

What is the anatomy of the eye?

A diagram of the eye cut in half showing different components. Signup and view all the answers

What is the function of the cornea?

It affects light waves. Signup and view all the answers

What does the pupil do?

Controls the amount of light entering the eye. Signup and view all the answers

What is the lens and its purpose?

The lens is situated behind the iris and focuses light on the retina. Signup and view all the answers

What is the blind spot?

Area in the visual field without photoreceptor cells. Signup and view all the answers

What are retinal ganglion cells?

Cells in the retina that transmit visual information to the brain. Signup and view all the answers

What are the types of photoreceptor cells?

Rods and Cones Signup and view all the answers

Rods are primarily responsible for color vision.

False Signup and view all the answers

How do photoreceptor cells distribute across the retina?

Less rods near fovea, more at periphery. Signup and view all the answers

What happens when opsin absorbs light?

It takes time to regenerate back to a functional state. Signup and view all the answers

What are the recovery rates for photopigments?

Rods take longer to recover than cones. Signup and view all the answers

Rods are most active under ________ conditions.

starlight Signup and view all the answers

What is the Troxler effect?

It occurs when staring at a stimulus for too long, causing it to fade from perception. Signup and view all the answers

What are ipRGCs?

Intrinsically photosensitive retinal ganglion cells. Signup and view all the answers

What are the three subtypes of cone photoreceptors?

Short, medium, and long cones. Signup and view all the answers

Study Notes

Visual Field

The visual field is defined as the entire area visible when an eye is fixated on a point in space.
Vertical and horizontal meridians divide the visual field into left/right and top/bottom halves respectively.
Hemifield refers to half of the visual field, while a quarterfield is a quadrant of the visual field.

Anatomy of the Eye

The eye's anatomy includes various structures: iris (color), pupil (black center), and retina (light detection).
The blind spot arises from a lack of light-sensitive photoreceptors in the optic disc, where the optic nerve exits the retina.

Key Structures of the Eye

The cornea is a transparent dome-shaped covering affecting light entry.
The fovea is part of the retina where color vision is most acute, containing only cone photoreceptors.
Retinal ganglion cells serve as the output nodes to the brain.

Cornea's Role

The cornea affects light waves by bending or refracting them, influenced by its thickness.

Pupil and Iris

The pupil is the central hole through which light enters the eye, while the iris is the colored muscular surrounding structure regulating pupil size.

Lens Function

The lens, located behind the iris, focuses incoming light on the retina and is designed to be transparent.

Sclera and Retina

The sclera is the white outer layer providing protection, contrasted by the retina, part of the CNS where visual processing begins.

Blind Spot

The blind spot corresponds to the location of the optic disc, lacking photoreceptors, creating an area of the visual field that goes undetected by the eye.

Optic Nerve

Composed of retinal ganglion cell axons, the optic nerve transmits visual information to the brain and creates a blind spot due to absent photoreceptors.

Light Pathway to Retina

The retina contains a layer of photoreceptors that absorb light, with additional modulatory neurons such as amacrine, horizontal, and bipolar cells aiding in visual information processing.

Photoreceptor Cells

These cells change shape upon absorbing light, allowing for light detection; they come in two main types: rods (low-light) and cones (color).

Function and Process of Photoreceptors

Photoreceptor cells convert light energy into a nervous system communicable form, known as signal transduction.

Types of Photoreceptors

Rods are sensitive to low light, contributing to night vision without color differentiation.
Cones dominate in the fovea, responsible for high visual acuity and color discrimination under bright conditions.

Distribution of Photoreceptors

Rod density decreases towards the fovea, which consists solely of cones.
Conversely, the peripheral retina has more rods than cones.

Cell Size and Information Gathering

Larger cells capture more light but have lower resolution.
Peripheral cells have larger receptive fields, enabling broader information gathering compared to central cells.

Cone Subtypes

Cone photoreceptors are classified into three subtypes: short (blue), medium (green), and long (red).

Photoreceptor Proteins

Photoreceptor proteins undergo a chemical change upon light absorption, facilitating light response.
Rods use rhodopsin, while cones utilize photopsin; melanopsin is found in certain retinal ganglion cells.

Opponent-Processing Color Vision Theory

Color perception operates through opponency channels, contrasting different cones (L vs M, S vs L+M, and dark vs bright).

Opsin Functionality

Absorbing light requires opsins to regenerate, with rods (rhodopsin) taking longer to recover versus faster-recovering cones (photopsin).

Rod Activity Conditions

Rods are most efficient in low-light or starlight conditions, requiring minimal light activation.

Troxler Effect

This phenomenon occurs when prolonged focus on a stimulus leads to visual adaptation, causing the stimulus to fade as the eye becomes accustomed.

Cone Distribution in the Fovea

The fovea contains short, medium, and long cones, with the very center consisting exclusively of medium and long cones.

Retinal Ganglion Cells (RGC)

RGCs receive input from modulatory neurons, transmitting visual signals via the optic nerve.

Types of Retinal Ganglion Cells

Classes include midget (parvocellular), parasol (magnocellular), and small bi-stratified cells (koniocellular), differentiated by size, function, and response characteristics.

Parvocellular and Magnocellular Pathways

Parvocellular pathway: Midget RGCs process color, detail, and texture with a sustained response.
Magnocellular pathway: Parasol RGCs detect motion and have larger cell pools over many receptors.

Koniocellular Pathway

Small bistratified RGCs, which utilize S-cone input, project to visual areas with lower acuity information.

Melanopsin-Containing RGCs

Known as intrinsically photosensitive RGCs, these cells can absorb light directly and manage circadian rhythms due to their unique photopigment.

Optic Chiasm

The optic chiasm is a critical crossover point for optic nerves in the brain, directing visual field information to the opposite hemispheres.

RGC Proximity to the Fovea

RGCs located closer to the fovea are fewer in number and smaller in size.

Size and Spatial Resolution Relations

Midget RGCs located further from the fovea can match the spatial resolution of parasol RGCs positioned closer, indicating broader resolution in parasol cells.

ipRGCs

Intrinsically photosensitive retinal ganglion cells (ipRGCs) function independently of traditional photoreceptors and play roles in signal modulation and circadian regulation.

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Description

Explore key concepts related to visual fields with this quiz. Learn the definitions of visual field, hemifield, and quarterfield, along with their spatial descriptions. Test your understanding of these important terms in vision science.