Protect the eye from injury Reflex closure of eyelids occurs when some object comes close to the eye or bright light shines into eye (corneal reflex) Regular blinking assists in distribution of tears and prevents drying of the tear film
A transparent mucous membrane that lines the inner surfaces of the eyelids and the front surface of the eyeball.
The Palpebral conjunctiva Starts at the lid margins and is firmly attached to the posterior tarsal plateThe Fornical conjunctiva Is loose and redundant and maybe thrown into foldsThe Bulbar conjunctiva Covers the anterior sclera and is continuous with the corneal epithelium at the limbus
Epithelium is non-keratinizing and about five cell layers thick Basal cuboidal cells evolve from the surface Goblet cells are located within the epithelium Stroma Consists of richly vascularized loose connective tissue Accessory lacrimal glands of Krause and Wolfring are located deep within the stroma
The transparent dome which serves as the window of the eye. The primary (most powerful) structure focusing light entering the eye.
Cornea is composed of 5 layers Epithelium. Bowman’s membrane. Stroma Descemet’s membrane. Endothelium).
No blood vessels. Transparent stroma with low level of fluids. Endothelium cells serves as a pump that supply oxygen and remove fluids. Tear film also supplies oxygen and keep corneal surface smooth and clean.
The white, opaque cover of the eye. Covers 80% of the eye’s outer layer. Contains thick elastic collagen. It provides protection. Serves as an attachment for the extra-ocular muscles which move the eye.
The iris is composed of Endothelium Stroma Epithelium Stroma muscles Dilator - sympathetic innervation Constrictor – parasympathetic innervation
Determined by the amount of pigment present in iris. No pigment - pink iris (albino), some pigment – blue iris, increasing amounts of pigment- green>hazel> brown irides. The pigments: melanin (chromosome 15) and lipochrome (chromosome 19). Heterochromia irides: when one iris has a different color than the other iris.
The pupil is the clear area that is located in the center of the iris of the eye. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye In darkness the iris dilator muscle causes the pupil to “dilate” and allowing more light to reach the retina. In brightness, the iris sphincter muscle (which encircles the pupil) constricts, causing the pupil to “constrict” and allowing less light to reach the retina. Constriction also occurs during accommodation - the “near reflex.”
Pars plana – flat area continuous with the retina Pars plicata – contains the ciliary processes that secretes the aqueous humor Ciliary muscle runs circularly around the eye and controlles accommodation
The posterior segment of the uvea, between the sclera and the retina. Reach in blood supply, supplies oxygen and nutrition to the outer two thirds of the retina.
Produced by the ciliary body. Entering from the posterior chamber, it passes through the pupil into the anterior chamber and filtrates through the angle into the blood stream. Serves to nourish ocular structures.
Iris-corneal junction Contains the trabecular meshwork (TM )which acts like a filter for the aqueous humor. From the TM the humor drains to schlem’s canal and then to blood stream.
Biconvex, avascular, transparent structure. Suspends behind the iris by the zonules which are connected to the ciliary body. Serves to converge light onto the retina.
Ciliary muscle constrict > zonular tension decreases > lens becomes more spherical > more dioptric power that converge light from a near target onto the retina.
This loss of transparency, or opacity formation is called Cataract
The innermost layer of the eye. The retina is a multi-layered sensory tissue that lines the back of the eye. It contains millions of photoreceptors that capture light rays and convert them into electrical impulses. These impulses travel along the optic nerve to the brain where they are turned into images.
Fovea: area with the highest concentration of photoreceptors. Central retina: A circular field of approximately 6 mm around the fovea. Peripheral retina: stretching to the ora serrata.
Phptoreceptors Cones Concentrated in the fovea Most active in daylight Central vision Rods Mostly in the peripheral retina Most active in night vision Peripheral vision
Consists of 1.2 million axons that arise from the retina. Leaves the eye through the optic disc also known as the blind spot.