Ocular Anatomy and Physiology Laboratory: Eyelids, Orbit, Extraocular Muscles, and Lacrimal System

Vocabulary flashcards covering eyelids, orbit anatomy, extraocular muscle dynamics, and the lacrimal system based on Ocular Anatomy and Physiology Laboratory activities.

Palpebral Aperture

The elliptical opening formed between the upper and lower eyelids through which the eye is exposed.

Anterior Lamella

The most superficial structural layer of the upper eyelid, composed of skin and the orbicularis oculi muscle.

Glands of Zeis

Modified sebaceous glands associated with the eyelashes whose oily secretions lubricate the hair follicles and eyelid margin.

Glands of Moll

Modified apocrine sweat glands situated along the eyelid margin near the base of the eyelashes.

Dermatochalasis

An excess accumulation of skin in the upper eyelid that can produce pseudoptosis and impair the superior visual field.

Orbicularis Oculi Muscle

A circular skeletal muscle innervated by the facial nerve (CN VII) that controls eyelid closure, divided into orbital, palpebral, and lacrimal portions.

Middle Lamella

The structural layer of the eyelid consisting of retro-orbicularis oculi fat (ROOF), the orbital septum, and preaponeurotic fat pads.

Orbital Septum

A thin fibrous sheet originating from the orbital periosteum that separates preseptal from postseptal compartments and contains orbital fat.

Gray Line

An anatomical and surgical landmark located along the eyelid margin that demarks the boundary between the anterior and posterior lamellae.

Posterior Lamella

The deep layer of the eyelid composed of the levator palpebrae superioris muscle, Müller's muscle, superior tarsal plate, and palpebral conjunctiva.

Levator Palpebrae Superioris (LPS) Muscle

The principal muscle responsible for voluntary upper eyelid elevation, innervated by the superior division of the oculomotor nerve (CN III).

Whitnall's Ligament

A transverse fibrous band that acts as a fulcrum to redirect the pull of the levator palpebrae superioris muscle from a horizontal to a vertical direction.

Müller's Muscle

A smooth muscle innervated by sympathetic fibers from the superior cervical ganglion that provides approximately $2\, \text{mm}$ of resting upper eyelid elevation.

Superior Tarsal Plate

A dense connective tissue plate measuring approximately $25\text{--}30\, \text{mm}$ wide and $10\text{--}12\, \text{mm}$ high that provides structural rigidity and contour to the upper eyelid.

Meibomian Glands

Specialized sebaceous glands embedded in the tarsal plates that secrete meibum, forming the outer lipid layer of the tear film.

Capsulopalpebral Fascia (CPF)

The primary retractor muscle structure of the lower eyelid originating from the fascial sheath of the inferior rectus muscle and Tenon's capsule.

Lockwood's Ligament

A hammock-like suspensory connective tissue sling beneath the globe formed by the fusion of sheaths from the inferior rectus and inferior oblique muscles with Tenon's capsule.

Palpebral Conjunctiva

The innermost lining of the eyelids, composed of non-keratinized stratified columnar epithelium containing mucin-secreting goblet cells.

Marginal Reflex Distance 1 (MRD-1)

The clinical distance measured from the central corneal light reflex to the upper eyelid margin in primary gaze, normally $4\text{--}5\, \text{mm}$ in healthy adults.

Marginal Reflex Distance 2 (MRD-2)

The clinical distance measured from the central corneal light reflex to the lower eyelid margin in primary gaze, normally $5\text{--}6\, \text{mm}$ in healthy adults.

Palpebral Fissure Height (PFH)

The total vertical height of the eye opening calculated as $\text{MRD-1} + \text{MRD-2}$, typically measuring around $10\, \text{mm}$ in healthy adults.

Levator Function Test

A diagnostic procedure measuring upper eyelid excursion from maximum downgaze to maximum upgaze while immobilizing the frontalis muscle with a thumb.

Meibography

A non-invasive imaging method using infrared illumination and a digital camera to evaluate the anatomical structure and dropout of meibomian glands.

Meiboscore

A grading scale from Grade 0 to Grade 3 per eyelid evaluating the percentage extent of meibomian gland loss, yielding a total score up to 6 per eye.

Figure 1.0 Anatomy of the Eyelid

A comprehensive diagram displaying external eyelid structures, internal soft-tissue anatomy, and a detailed cross-sectional view of the eyelid layers.

Bony Orbit

A paired quadrangular pyramidal skeletal cavity in the skull with an average adult volume of approximately $30\, \text{mL}$ that houses and protects the eyeball and associated structures.

Whitnall's Tubercle

A bony prominence on the zygomatic bone $11\, \text{mm}$ inferior to the frontozygomatic suture and $4\text{--}5\, \text{mm}$ posterior to the lateral orbital rim that serves as an attachment site for multiple supportive orbital structures.

Lamina Papyracea

The paper-thin orbital plate of the ethmoid bone forming the majority of the fragile medial orbital wall.

Blowout Fracture

A fracture mechanism involving the thin orbital floor overlying the maxillary sinus, commonly caused by a sudden increase in intraorbital pressure during blunt trauma.

Optic Canal

An opening located within the lesser wing of the sphenoid bone at the orbital apex that transmits the optic nerve (CN II) and the ophthalmic artery.

Superior Orbital Fissure

A major anatomical aperture between the greater and lesser wings of the sphenoid bone transmitting CN III, CN IV, CN V1, CN VI, and the superior ophthalmic vein.

Annulus of Zinn

A common tendinous ring surrounding the optic canal and medial superior orbital fissure at the apex, serving as the origin for the four rectus muscles.

Inferior Orbital Fissure

A fissure between the orbital floor and lateral wall transmitting the infraorbital nerve, zygomatic nerve, infraorbital vessels, and inferior ophthalmic vein.

Ophthalmic Artery

The primary arterial trunk supplying the orbit and globe, entering via the optic canal as the first major branch of the internal carotid artery.

Periorbita

The periosteal lining membrane covering the internal surfaces of the bony orbital walls.

Tenon's Capsule

A smooth connective tissue membrane enveloping the eyeball from the optic nerve to the limbus, separating it from the surrounding orbital fat.

Figure 2.0 Anatomy of the Bony Orbit

An anterior view diagram illustrating the seven bones, landmarks, foramina, canals, and fissures forming the right bony orbit.

Muscle Cone

A retrobulbar cone-shaped region formed by the four rectus muscles originating at the annulus of Zinn and inserting onto the anterior sclera.

Spiral of Tillaux

The imaginary spiral line formed by the scleral insertion distances of the four rectus muscles relative to the limbus: MR ($5.5\, \text{mm}$), IR ($6.5\, \text{mm}$), LR ($6.9\, \text{mm}$), and SR ($7.7\, \text{mm}$).

Listing's Plane

An imaginary equatorial reference plane passing through the globe's center of rotation, perpendicular to the line of sight in primary gaze.

Fick's Axes

Three mutually perpendicular axes (X, Y, Z) intersecting at the center of rotation of the globe used to define vertical, torsional, and horizontal eye movements.

Arc of Contact

The tangential portion of an extraocular muscle that remains in direct contact with the scleral surface before pulling away toward its origin.

Ductions

Monocular rotations of a single eye around one of Fick's axes.

Versions

Conjugate binocular eye movements where both eyes rotate simultaneously in the same direction.

Vergence

Disjunctive binocular eye movements where both eyes rotate simultaneously in opposite directions (e.g., convergence or divergence).

Agonist Muscle

The primary muscle directly responsible for producing a given eye movement.

Antagonist Muscle

The muscle in the same eye that acts in direct opposition to the movement produced by the agonist muscle.

Yoke Muscles

A pair of muscles—one in each eye—that receive equal innervation to execute conjugate movement in a specific direction of gaze.

Hering's Law of Equal Innervation

The principle stating that equal and simultaneous neural impulses are distributed to a pair of yoke muscles during binocular version movements.

Sherrington's Law of Reciprocal Innervation

The principle stating that contraction of an agonist extraocular muscle is accompanied by a proportional relaxation of its antagonist muscle in the same eye.

Donders' Law

The rule stating that the torsional orientation of the eye for any specific gaze direction is constant and independent of the pathway taken to reach it.

Listing's Law

The principle stating that rotations from primary position to any gaze position can be defined as a single rotation around an axis lying in Listing's plane.

Figure 3.0 Anatomy of the Muscles for Eye Movement

Diagram showing the anterior view of the right eye and superior view of the orbit, illustrating EOM origins, insertions, tendons, and trochlea.

Epiphora

Excessive tear overflow onto the cheek caused by overproduction of tears or anatomical/functional impairment of lacrimal drainage.

Main Lacrimal Gland

A bilobed exocrine gland located in the superotemporal frontal lacrimal fossa divided by the levator aponeurosis into orbital and palpebral lobes.

Accessory Lacrimal Glands of Krause and Wolfring

Small serous glands located in the conjunctival fornices (Krause) and tarsal regions (Wolfring) providing continuous baseline aqueous tear production.

Conjunctival Goblet Cells

Unicellular epithelial cells scattered throughout the conjunctiva that synthesize and secrete the mucin component of the tear film.

Glycocalyx

A carbohydrate-rich cell surface coating on apical corneal and conjunctival epithelial cells composed of membrane-associated mucins (MUC1, MUC4, MUC16) that facilitates tear adhesion.

Valve of Rosenmüller

A mucosal fold situated at the junction between the common canaliculus and the lacrimal sac that prevents retrograde tear flow.

Valve of Hasner

A mucosal flap located at the opening of the nasolacrimal duct inside the inferior nasal meatus that regulates drainage and limits nasal reflux.

Lacrimal Pump Mechanism

The active drainage process where orbicularis oculi contraction during a blink compresses canaliculi and creates negative pressure in the lacrimal sac to pull tears, while opening creates positive pressure to drive tears down.

Tear Break-Up Time (TBUT)

A diagnostic parameter measuring tear-film stability by recording seconds elapsed between a blink and the first appearance of a dry spot.

Schirmer Test

A clinical procedure using standardized filter paper strips placed in the lower fornix for $5\, \text{minutes}$ to measure aqueous tear production.

Jones I Test

The primary dye test evaluating physiological tear drainage patency by checking for fluorescein in the inferior nasal meatus after topical instillation.

Jones II Test

The secondary dye test performed after a negative Jones I test by irrigating saline into the puncta to evaluate anatomical patency of the lacrimal pathway.

Figure 4.0 Anatomy of the Lacrimal System and Flow of Tears

A schematic diagram detailing the secretory and excretory components of the lacrimal system and mapping the directional pathway of tear flow.