PerLecture 2 - Physiology of the Eye Flashcards

A comprehensive set of vocabulary flashcards covering the history, anatomy, optics, and physiological processes of the human eye and comparative vision in nature.

Alhazen

A historical figure who suggested vision occurs when light from external sources is reflected from surfaces and enters the eye, acting like a pinhole camera.

Kepler

A researcher who used dissection to describe refraction as light enters the eye and observed the inversion of retinal imagery.

Visual Pathway Step 1

Optical information is received in the eye via ganglion cells after being combined by bipolar cells.

Primary Visual Cortex

The visual center located in the occipital lobe at the back of the head where information is passed from the eyes.

Cornea

The transparent window into the eyeball that provides approximately $\frac{2}{3}$rds of the eye's refractive power.

Aqueous Humor

The watery fluid found in the anterior chamber of the eye that assists with refraction.

Crystalline Lens

The lens inside the eye that refracts light hitting the retina to enable changes in focus.

Pupil

The dark circular opening at the center of the iris where light enters; it enlarges in low light and shrinks in abundant light.

Vitreous Humor

The transparent fluid filling the vitreous chamber in the posterior (back) part of the eye.

Retina

A light-sensitive membrane in the back of the eye containing rods and cones that sends images to the brain through the optic nerve.

Pupil Size and Emotion

Pupil size serves as a cue for emotions: angry corresponds to smaller pupils, while fearful or happy states correspond to larger pupils.

Premotor Cortex

Area containing mirror neurons that respond during performance and observation of an action, particularly useful for expressing a sad response.

Harrison et al. (2006) Finding

Discovered that a larger pupil size in a sad model caused the observer's own pupils to mirror the size, associated with brain regions for social cognition.

The Blindspot

The point in the retina where the optic nerve sits; it contains no cones or receptors because information converges here to be sent to the brain.

Floaters

Collagen strands floating in the vitreous humour with a fixed location, caused by photoreceptors shedding old material.

Pressure Phosphenes

The sensation of 'seeing stars' resulting from mechanical stimulation of rods and cones, or from radiation, hits to the head, or sneezes.

Camera Obscura

A simple optical device where light from a pinhole projects an inverted image (top-bottom and left-right) from the outside.

Convex Lenses

Lenses that bend parallel rays from a distant source toward a single focal point; the more convex the lens, the closer the focal point.

Emmetropia

A state of refraction where parallel lines are imaged onto a single point on the retina.

Myopia

A refractive error where the eyeball is too long, causing light to converge in front of the retina and resulting in a blur.

Hyperopia

A refractive error where the eyeball is too short.

Accommodation

The process where the crystalline lens becomes more spherical to increase refractive power, allowing for focus on near points.

Ciliary Muscle

The muscle behind the lens that weakens with age ($40-50$ years old), causing the lens to be stiff and making near-sight difficult.

The Near Triad

The three actions required to shift from far to near distance: accommodation, vergence (eye rotation), and pupil size optimization.

Rods

$120$ million receptors sensitive to low light conditions with limited or no color sensitivity.

Cones

$6-7$ million receptors that function in normal light levels and provide the beginning of color sensitivity.

Central Fovea

A region spanning a $2^{\circ}$ angle that contains only cones and no rods, featuring a much higher cone distribution than the rest of the eye.

Human Spectral Sensitivity

The total range of human light sensitivity, which is approximately $400-700\,nm$.

Cone Pigment Peaks

The peak sensitivities for cones are S-Cone at $430\,nm$, M-Cone at $530\,nm$, and L-Cone at $570\,nm$.

Purkinje Shift

The shift where longer wavelengths (red) are harder to see in low light (scotopic), while yellow-green is brightest in bright light (photopic).

Visual Transduction

The process in the retina where visual pigment molecules absorb photons and isomerise (change shape), creating an electrical response.

Optic Nerve Composition

Made of the same material as the sclera, it contains approximately $1.2$ million axons.

Fish Eye Adaptation

Fish possess a spherical, powerful lens and no power in the cornea because underwater the refractive index of water matches the eye's humor.

Semi-aquatic Eye Adaptation

Animals that spend time on land and water have a less powerful cornea and nearly spherical lens, causing myopia on land and hyperopia in water.

Compound Eyes

Eyes with multiple small units, each with its own lens and photoreceptor; they provide a high field of view but poor image resolution.