INTRODUCTION TO THE EYE
The human eye is the organ which gives us the sense of sight, allowing us to
learn more about the surrounding world than any of the other five senses.
We use our eyes in almost everything we do, whether reading, working,
watching television, writing a letter, driving a car, and countless other
activities. Sight is the most precious of the five senses, and many people fear
blindness more than any other disability. The eye allows us to see and
interpret the shapes, colors, and dimensions of objects in the world by
processing the light they reflect or give off. The eye is able to see in dim
light or bright light, but it cannot see objects when light is absent. The eye
changes light rays into electrical signals then sends them to the brain, which
interprets these electrical signals as visual images. The eyeball is set in a
protective cone-shaped cavity in the skull called the orbit or socket and
measures approximately one inch in diameter. The orbit is surrounded by
layers of soft, fatty tissue which protect the eye and enable it to turn easily.
Six muscles regulate the motion of the eye. Among the more important parts
of the human eye are the iris, cornea, lens, retina, conjunctiva, the macula,
and the optic nerve.
THE ORBITA
The orbit is a bony shaped, four sided pyramid lying on its side, with the apex at the back and the base forming the orbital margin on the front of the facial skeleton.
Relations of the orbit
• Above – anterior cranial fossa, meninges, frontal lobe of the cerebral hemisphere
• Medially – nasal cavity,ethmoid sinus,sphenoid sinus
• Below – maxillary sinus
• Posterolaterally-infratemporal fossa,middle cranial fossa
Bony orbit:
Formed by: Frontal bone - superiorly
Zygomatic bone - laterally
Zygomatic and maxilla - inferiorly
Frontal process of maxilla & lacrimal - medially
Walls:
Roof: frontal bone
Lateral wall: zygomatic and sphenoid
Medial wall: sphenoid, ethmoid, lacrimal and maxilla
Floor: maxilla and palatine bone
Features:
- supraorbital notch or foramen for division of frontal nerve
- infraorbital foramen - continuous with the infraorbital
canal and groove (transmits the maxillary branch of trigeminal).
- optic canal optic nerve and the ophthalmic a.
- superior orbital fissure - transmits V1, plus III, IV, VI
and ophthalmic veins.
- ethmoidal foramina for branches of the nasociliary n.
- zygomatic canal for zygomatico-facial and -temporal
branches of maxillary of V.
- nasolacrimal duct for drainage of tears from the anterior
surface of the eye to the inferior meatus of the nasal
cavity.
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