Fundamentals and Principles of Ophthalmology Flashcards
What is the volume of the adult orbit?
Slightly less than 30cc
What is the average orbital height and width at the entrance, respectively?
35mm and 45mm
What is the depth of the orbit from the orbital entrance to the orbital apex?
40-45mm
What seven bones make up the bony orbit?
Frontal, zygomatic, maxillary, ethmoidal, sphenoid, lacrimal, palatine
These four bones make up the medial wall of the orbit.
Frontal process of maxillary bone, lacrimal bone, orbital plate of ethmoid bone, and lesser wing of sphenoid bone
These three bones make up the orbital floor.
Maxillary, palatine, and orbital plate of the zygomatic bone
This is a small elevation of the orbital margin of the zygomatic bone that lies ~11mm below the frontozygomatic suture. It is the site of attachment for: ligament of lateral rectus, suspensory ligament of the eyeball (Lockwood suspensory ligament), aponeurosis of levator palpebrae superioris, and the Whitnall ligament.
Whitnall tubercle (lateral orbital tubercle)
The superior orbital fissure transmits these four structures.
Lacrimal nerve (CN V1), frontal nerve (V1), CN IV (trochlear), superior ophthalmic vein
These are the three roots that are received by the ciliary ganglion (located about 1cm in front of the annulus of Zinn).
Nasociliary branch of V1 (sensory from cornea, iris, ciliary body), inferior division of CN III (inferior oblique, parasympathetic to iris), sympathetics (do not synapse; innervates blood vessels and dilator muscle of pupil)
These are the lengths of insertions of the medial, inferior, lateral, and superior recti, respectively, that form the spiral of Tillaux.
5.5, 6.5, 6.9, and 7.7mm
This consists of superior and inferior orbital tendons and is the origin of the four rectus muscles.
Annulus of Zinn
This muscle arises from the lesser wing of the sphenoid bone, at the apex of the orbit, just superior to the annulus of Zinn.
Levator palpebrae superioris
This muscle originates from the periosteum of the body of the sphenoid bone, above and medial to the optic foramen.
Superior oblique
This muscle originates anteriorly, from a shallow depression in the orbital plate of the maxillary bone, at the anteromedial corner of the orbital floor near the lacrimal fossa.
Inferior oblique
Innervation of the lateral rectus.
CN VI (abducens nerve)
The upper division of CN3 (oculomotor) innervates these muscles.
Levator palpebrae superioris and superior rectus
The lower division of CN3 (oculomotor) innervates these muscles.
Medial rectus, inferior rectus, and inferior oblique
This type of muscle fiber is unique to extraocular muscles. They are smaller than twitch-type fibers and contract slowly and smoothly. They tend to be more superficial (near the orbital wall) and are innervated by multiple grapelike nerve endings (en grappe). Theya re useful for smooth pursuit.
Tonic-type muscle fibers
These muscle fibers are similar to skeletal muscle fibers. The are larger and located deeper in the muscle. They contract rapidly and have platelike nerve endings (en plaque). They aid in rapid saccadic movements of the eye.
Twitch-type muscle fibers
How much can the upper eyelid be raised by the action of the levator palpebrae superioris muscle alone?
15mm
How much can the upper eyelid be raised by the frontalis muscle?
2mm
The superior eyelid fold is present near the upper border of the tarsus, where this establishes its first insertional attachments. Since few attachments are present in many Asian individuals, the superior eyelid fold is minimal or absent.
Levator aponeurosis
The delicate gray line (or intermarginal sulcus) corresponds histologically to the most superficial portion of this muscle, as well as to the avascular plane of the eyelid. Anterior to this line, the eyelashes (cilia) arise, and posterior to this line are the openings of the tarsal (or meibomian) glands.
Orbicularis oculi (muscle of Riolan)
These are modified sebaceous glands associated with the cilia (eyelashes).
Glands of Zeis