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THE EYE (OCULAR ANATOMY).
THE ORBIT:
The orbits are pyramidal, bony cavities in the facial skeleton with their bases (orbital opening)
directed anterolaterally and their apices directed posteromedially. The orbit contain the eyeballs
and their muscles, nerves and vessels together with most of the lacrimal apparatus. The space not
occupied by structures contain orbital fat. Conditions resulting in increased overall volume of the
orbital fat e.g. hyperthyroidism may lead to exophthalmos. The bones forming the orbit are lined
with periorbita(periosteum).
Shape:
The orbit has a base, four walls and an apex.
Walls of the orbit:
1. Superior wall ( roof ): This is approximately horizontal and is formed
a. Mainly by the orbital part of the frontal bone, which separates the orbital cavity from
the anterior cranial fossa.
b. Near the apex of the orbit, the superior wall is formed by the lesser wing of the lesser
wing of the sphenoid bone.
Note: anterolaterally, the lacrimal gland occupies the fossa for the lacrimal gland
(lacrimal fossa) in the orbital part of the frontal bone.
2. Medial wall: This is formed by the ethmoid bone along with contributions from the frontal,
lacrimal and sphenoid bones.
NOTE: - Anteriorly, the medial wall is indented by the lacrimal groove and fossa for the
lacrimal sac.
- The bone forming the medial wall is paper-thin.
3. Lateral wall: This is formed by the frontal process of the zygomatic bone and the greater
wing of the sphenoid.
NOTE: this is the strongest and thickest wall which is important because it is exposed and
vulnerable to direct trauma.
4. Inferior wall (floor): This is formed mainly by the maxilla and partly by the zygomatic and
palatine bones.
NOTE: - The thin inferior wall is shared by the orbit superiorly and the maxillary sinus
inferiorly.
- The inferior wall is demarcated from the lateral wall by the inferior orbital fissure.
APEX OF THE ORBIT:
The apex of the orbit is at the optic canal in the lesser wing of the sphenoid just medial to the
superior orbital fissure.