Ocular Anatomy & Physiology

• Anatomy is the identification and description of the structures of living things, a branch of biology and medicine that goes back over 2,000 years to the Ancient Greeks.
• The word "anatomy" comes from the Greek words "ana," meaning "up," and "tome," meaning "a cutting."
• Studies of anatomy have traditionally depended on cutting up, or dissection, but now, with imaging technology, it is increasingly possible to see how a body is made up without dissection.
• Sagittal or antero-posterior (A-P) diameter measures the length along the geometric axis, ranging from 22-27mm, with an average of 24mm.
• Transverse or horizontal diameter measures the width of the eyeball, which is 24.5mm.
• Vertical diameter measures the height of the eyeball at the equator, which is 23.5mm.
• Vitreous Humor is a clear, jelly-like substance that fills the middle of the eye.
• Anatomy is divided into three broad areas: Human anatomy, which is the study of the structures of the human body, Zootomy, which is animal anatomy, and Phytotomy, which is plant anatomy.
• Physiology is the branch of biology that deals with the normal functions of living organisms and their parts.
• The anterior chamber is a fluid-filled space inside the eye between the iris and cornea, filled with a watery substance called the aqueous humor that maintains the pressure within the eye.
• The aqueous humor is the clear, watery fluid between your lens and cornea.
• The drainage area of the eye formed between the cornea and the iris, named for its angular shape, is called the angle, which is why you see the word "angle" in the different glaucoma names.
• The anterior pole is the center of curvature of the cornea.
• The blind spot is a small area in the visual field corresponding to the retina's optic disc or optic nerve head, where no photoreceptors are present and where there is no sensitivity to light, not noticed with both eyes open because the part of the visual field containing the blind spot of one eye is overlapped by a light-sensitive area in the other eye.
• The conjunctiva is the thin, moist tissue that lines the inner surfaces of the eyelids and the outer surface of the sclera.
• The cornea is the transparent, anterior, dome-shaped portion of the eyeball that covers the iris and pupil, acting like a window which admits light into the eye.
• The crystalline lens is the highly transparent biconvex, lens-shaped or nearly spherical body in the eye, situated immediately behind the pupil, which focuses light rays entering the eye typically onto the retina.
• Eyelid: Either of the movable lids of skin and muscle that can be closed over the eyeball, providing eye protection and distribution of tears over the cornea while blinking.
• Equator: Line encircling the eyeball equdistant from the two poles dividing the eyeball into anterir and posterior hemisphere.
• Fovea: In the human eye the term fovea (or fovea centralis) is the "pit" in the retina that allows for maximum acuity of vision.
• The human fovea has a diameter of about 1.0 mm with a high concentration of cone photoreceptors.
• Foveola: The center of the fovea, about 0.2 mm in diameter, where only cone photoreceptors are present.
• The central fovea consists of very compact cones, thinner and more rod-like in appearance than cones elsewhere.
• Gland, Lacrimal: Tear gland; a gland, about the size and shape of an almond, that is the major producer of a watery secretion which forms the middle (lacrimal), thickest layer of the tear Film.
• Glands, Tear: Glands located near the eye and in the eyelids which produce the lipid, lacrimal, and mucoid layers of the tear film coating the surface of the cornea.
• Human Eye: specialized sense organ capable of receiving visual images, which are then carried to the brain.
• Iris: Contains pigment that determines the color of the eye and helps regulate the amount of light that enters the eye.
• Limbus: Junction between the cornea and the sclera.
• Lens: curved surface of the eye that brings rays of light to a focus in the retina.
• The lens accounts for approximately one-third of the eye's total focusing power.
• Macula: The central portion of your retina, which is required for high resolution vision.
• Macular edema: A swelling of the macula that makes it hard to see.
• Meridian: Any line encircling the surface of the eyeball that passes thru both poles and crosses equator at right angle from the limbus to the posterior pole passing the meridian (32mm).
• Night blindness: When you have trouble seeing in dim or darkened conditions.
• Nyctalopia: night blindness.
• Optic nerve: It carries light signals from your retina to your brain, which turns them into images.
• Cupping is an enlargement of the cup or central depression in the optic nerve head, visible when viewing the back of the eye with an ophthalmoscope, and is a clinical sign that indicates that a large number of nerve fibers in the optic nerve have been lost.
• Optic disc (or disk) is the optic nerve head in the eye, in which no photoreceptors are present, resulting in a blind spot in the visual field.
• Optic nerve is the sensory nerve which carries electrical impulses from visual stimuli in the retina out of the eye to the visual cortex of the brain for interpretation.
• Optic neuritis is an inflammation of the optic nerve within the eyeball or behind the eyeball.