Eye

Vocabulary terms and definitions from Module 14, covering the anatomy and physiology of the eye, accessory structures, tunics, and the process of phototransduction.

Photoreceptors

The receptors for light located in the eye that include rods and cones.

Accessory structures

Structures found outside or attached to the eyeball that assist the eye in its functioning, including eyebrows, eyelids, and extrinsic eye muscles.

Eyebrows

Coarse hairs on the arches above the eye that help to keep debris out of the eye.

Palpebrae

Another name for the upper and lower eyelids, which are separated by the palpebral fissure.

Canthi

The medial and lateral angles where the upper and lower eyelids meet.

Conjunctiva

Thin transparent mucous membranes that line the white of the eye and the inner surface of the eyelid.

Bulbar conjunctiva

The portion of the conjunctiva found on the white of the eye.

Palpebral conjunctiva

The portion of the conjunctiva found on the inner surface of the eyelid.

Conjunctival sac

The space between the bulbar and palpebral conjunctiva.

Lacrimal gland

Structure that produces lacrimal fluid (tears) to moisten the eye and remove debris.

Lacrimal sac

Receives tears from the surface of the eye and conveys them to the nasolacrimal duct.

Nasolacrimal duct

Conveys lacrimal fluid from the lacrimal sac to the nasal cavity.

Extrinsic eye muscles

Six skeletal muscles (lateral rectus, medial rectus, superior rectus, inferior rectus, superior oblique, and inferior oblique) that control eyeball movement.

Tunics

The layers that compose the wall of the hollow sphere of the eyeball.

Anterior cavity

The segment of the eye between the lens and the cornea that is filled with aqueous humor.

Posterior cavity

The segment of the eye between the lens and the back of the eye that is filled with vitreous humor.

Aqueous humor

A fluid formed as a blood filtrate by the ciliary body that supplies nutrients to the lens and cornea.

Scleral venous sinus

The structure through which aqueous humor is drained to move back into general circulation.

Posterior chamber

The space within the anterior segment located between the lens and the iris.

Anterior chamber

The space within the anterior segment located between the iris and the cornea.

Vitreous humor

A clear, jelly-like substance in the posterior cavity that supports the lens and helps maintain intraocular pressure.

Fibrous tunic

The outermost layer of the eyeball composed of the sclera and the cornea.

Sclera

The opaque ‘white’ of the eye composed of dense white connective tissue that helps provide the eye its shape.

Cornea

The anterior portion of the fibrous tunic that allows light to enter and is highly innervated but lacks vascularization.

Vascular tunic

The middle layer of the eyeball composed of the choroid, ciliary body, and iris.

Choroid

A vascular, darkly pigmented membrane that absorbs excess light and prevents light rays from scattering inside the eye.

Ciliary body

A thickened ring of tissue encircling the lens composed of the ciliary muscle and ciliary processes.

Ciliary muscle

Muscle that attaches to suspensory ligaments and changes the shape of the lens by increasing or decreasing tension.

Iris

The visible, colored portion of the eye composed of smooth muscle that controls the diameter of the pupil.

Pupil

The round central opening of the iris that controls the amount of light entering the posterior segment.

Neural tunic

The deepest tunic of the eyeball, also known as the retina.

Pigmented layer

A single layer of melanocytes in the retina that helps to absorb excess light.

Rod cells

Photoreceptors more sensitive to light that allow vision in dim light and are located more towards the periphery of the retina.

Cone cells

Photoreceptors that operate best in bright light, enable high-acuity color vision, and are located near the center of the retina.

Ora serrata

The posterior margin of the ciliary body where the retina ends.

Macula lutea

A yellow-colored portion at the back of the retina with many cones that is responsible for much of our vision.

Fovea centralis

A tiny pitted area at the center of the macula lutea containing only cones; it is the region of highest visual acuity.

Optic disc

The blind spot where ganglion cell axons converge and exit the eye; it lacks photoreceptors.

Refraction

The bending of light rays as they enter the eye, primarily performed by the cornea and the lens.

Accommodation

The process of adjusting the lens shape for near vision where the ciliary muscle contracts and the lens becomes rounder and thicker.

Lens fibers

Tightly-packed proteins that make up the thick, transparent biconcave disc of the lens.

Rhodopsin

The photopigment in rods consisting of opsin and retinal.

Transducin

The intracellular G protein stimulated by activated rhodopsin during phototransduction.

cGMP

An intracellular molecule that, in the dark, keeps ligand-gated $Na^+$ channels open in the photoreceptors.