Accessory structures of the eye
Eyelids, eyelashes, eyebrows, lacrimal apparatus, extrinsic eye muscles
Eyelids
Upper & Lower eyelids/Palpebrae - shade eyes during sleep
Protect eyes- excessive light, foreign objects, and spreading lubricating secretions
The upper eyelid is more movable by the levator palpebrae superioris muscle.
Sometimes a person may have annoying twitching-an involuntary quivering that lasts for only a few seconds due to stress & Fatigue.
Space between upper & lower eyelid- palpebral fissures
Angles are known as lateral commissure- narrower & closer to the temporal bone
Medial commissure - Broader and nearer to
nasal bone
Small reddish elevation - lacrimal caruncle
contains sebaceous glands, sudoriferous glands(Whitish material).
Superficial - deep- Epidermis, dermis, Sub Q,
Fibers of orbicularis oculi muscle
Tarsal plate - Thick fold of connective tissue that gives form and support to eyelids
tarsal gland- Contains elongated modified sebaceous glands (Meibomian glands)- secretes fluids- prevents eyelid adhering to each other - infection of the gland- tumor/cyst-
chalazion.
Conjunctiva
The thin, protective mucous membrane, composed of nonkeratinized stratified columnar epithelium with numerous goblet cells supported by areolar connective tissue.
Palpebral conjunctiva - lines inner aspect of eyelids.
Bulbar conjunctiva - passes from eyelids to surface of an eyeball that covers the sclera but
not cornea.
Over sclera - it is vascular.
Eyelashes and eyebrows
Eyelashes- projects from the border of each eyelid.
Eyebrows-Arch transversely above the upper eyelids protects the eyeball from foreign objects, perspiration, and direct skin rays.
Sebaceous glands at the base of hair follicles are called sebaceous ciliary glands- releases lubricating fluid into follicles, infection of these glands is called a sty.
Lacrimal apparatus
Group of structures that produces and drains lacrimal fluid/tears.
Shapes and size like an almond
Secretes tears- drains through 6-12
excretory lacrimal ducts that empty tears
onto the surface of the conjunctiva of the upper eyelid
Moves medially to enter two small openings called lacrimal puncta
Passes into two ducts, inferior and superior lacrimal canal.
Lacrimal sac
Nasolacrimal duct
Carries lacrimal fluid into nasal cavity just
inferior to inferior nasal conchae
Infection of lacrimal sac - Dacryocystitis
Supplied by parasympathetic fibers of the facial nerve(VII)
Watery solution -salts, mucus, and lysozyme
Protects, cleans, lubricates & Moisturizes the
eyeball
Each gland- 1ml/day.
Extrinsic eye muscles
Extends from walls of bony orbit to the sclera of the eye surrounded by a significant quantity of periorbital fat
Capable of moving eye in almost all direction
Six extrinsic muscles
Superior rectus
Inferior rectus
Lateral rectus
Medial rectus
Superior oblique
Inferior Oblique.
Supplied by cranial nerve-1, IV, VI
Motor units of these muscles are small, which permit smooth, precise & rapid movement of the eye.
Anatomy of Eyeball
Adult eyeball measures 2.5cm in diameter of
total surface area-1/6 is exposed
The remainder is recessed & protected by the
orbit into which it fits
Three layers fibrous tunic
Vascular tunic
Retina.
Fibrous Tunic
The superficial layer of the eyeball consists of the anterior cornea and posterior sclera.
The cornea is a transparent coat that covers the colored iris. Because it is covered, the cornea helps focus light onto the retina.
Outer surface non-keratinized stratified
squamous epithelium
Middle coat collagen fibers & fibroblast
Inner surface - simple squamous epithelium
the central part of the cornea- receives 02 from the outside air.
Sclera
White of the eye - dense connective tissue mostly of collagen fibers and fibroblast
It covers the entire eyeball except for the cornea.
Gives shape to the eyeball, makes it more rigid, protects inner parts
Site for attachment of extrinsic eye muscles
Junction of sclera and cornea sinus(Canal of Schlemm) fluid called aqueous
sclera venous
human drains into this sinus.
Vascular Tunic
The middle layer of the eyeball
Three parts- Choroid, ciliary body, iris
lightly vascularized choroid
The posterior portion of vascular tunic lines most
of the inner surface of the sclera
Numerous blood vessels provide nutrients to the posterior surface of the retina
Contains melanocytes make it appear
dark brown in color.
nice article
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