Anatomy and Physiology of the Eye and Retina

Flashcards covering the anatomy of the eye, clinical disorders, the mechanism of phototransduction, and the circuitry of the retina based on class notes.

Retina

The innermost layer of the eye that contains light-sensitive neurons and transmits visual signals to central targets.

Uveal tract

The middle layer of the eye tissue that includes three continuous structures: the choroid, the ciliary body, and the iris.

Choroid

The largest component of the uveal tract, consisting of a capillary bed that nourishes photoreceptors and contains light-absorbing melanin.

Ciliary body

A ring of tissue encircling the lens; its muscular component adjusts refractive power, and its vascular component produces aqueous humor.

Refractive power

The degree to which an optical system, such as the lens or cornea, converges or diverges light.

Iris

The colored, most anterior component of the uveal tract that adjusts the size of the pupil under neural control.

Sclera

The outermost layer of the eye, composed of tough, white, opaque fibrous tissue.

Cornea

The transparent tissue at the front of the eye that allows light rays to enter and provides the majority of the eye's refractive power.

Aqueous humor

A clear, watery liquid that supplies nutrients to the cornea and lens, filling the anterior and posterior chambers.

Glaucoma

An eye disorder caused by the failure of aqueous humor drainage, leading to high intraocular pressure and damage to retinal neurons.

Vitreous humor

A thick, gelatinous substance between the lens and the retina that contains phagocytic cells to remove blood and debris.

Cataracts

Opacities in the lens that reduce transparency and lower the quality of vision.

Accommodation

The process by which the lens changes its shape (thickening or flattening) to focus on objects at different distances.

Zonule fibers

Fibers that exert an opposing force on the lens to flatten it for distant vision.

Myopia

Nearsightedness; a refractive error where distant objects are focused in front of the retina, often due to an elongated eyeball or highly curved cornea.

Hyperopia

Farsightedness; a refractive error where near objects are focused behind the retina.

Presbyopia

A condition in which the accommodative ability of the eye is severely reduced, making near-vision tasks difficult as one ages.

Optic disk

The region where retinal axons leave the eye and blood vessels enter; it contains no photoreceptors and creates a scotoma (blind spot).

Macula lutea

A circular region near the center of the retina containing yellow pigment that supports high visual acuity.

Fovea

A small pit at the center of the macula where cone density is highest and visual acuity is at its peak.

Age-related macular degeneration (AMD)

A progressive loss of central vision caused by the degeneration of photoreceptors, categorized into 'wet' (neovascular) and 'dry' forms.

Transduction

The process by which a cell converts one kind of signal, such as light, into another, such as electrochemical signals.

Pigment epithelium

A layer of cells that removes old photoreceptor disks, regenerates photopigment molecules, and provides nourishment from underlying capillaries.

Retinitis Pigmentosa

A hereditary eye disorder causing progressive vision loss due to the gradual degeneration of photoreceptors by apoptosis.

Dark current

The depolarized state of a photoreceptor in the dark ($-40\,mV$) caused by high levels of intracellular cGMP keeping Na⁺ and Ca²⁺ channels open.

Rhodopsin

The photopigment found in the disks of rod outer segments, consisting of an opsin protein and the light-sensitive molecule retinal.

Transducin

A G protein activated by rhodopsin that in turn activates phosphodiesterase (PDE) during the phototransduction cascade.

Retinoid cycle

The process of restoring all-trans retinal to the 11-cis retinal form to maintain the light sensitivity of photoreceptors.

Interphotoreceptor retinoid binding protein (IRBP)

A protein that transports retinoids between the photoreceptor outer segment and the pigment epithelium.

Scotopic vision

Vision under low light levels mediated by rods, characterized by high sensitivity but low spatial resolution and no color perception.

Photopic vision

Vision under bright light conditions mediated by cones, providing high spatial resolution and color perception.

Mesopic vision

Vision at intermediate light levels (like twilight) where both rods and cones contribute.

Tapetum lucidem

A reflective layer in the back of the eye of some animals (like cats) that reflects light back through the retina to increase sensitivity.

Trichromatic vision

Color vision based on the comparison of activity in three types of cones: S- (short), M- (medium), and L- (long) wavelength cones.

ON-center bipolar cells

Cells that depolarize in response to light and hyperpolarize in response to dark, utilizing metabotropic glutamate receptors.

OFF-center bipolar cells

Cells that hyperpolarize in response to light and depolarize in response to dark, utilizing ionotropic glutamate receptors.

Horizontal cells

Retinal neurons that enable lateral interactions between photoreceptors and bipolar cells to maintain contrast sensitivity.

Amacrine cells

Specialized retinal cells that allow bipolar cells to send information to ganglion cells and facilitate horizontal connectivity.