Chapter 2: Eye Findings

EYELID ANATOMY

(Fig. 2-1)

Eyelids

• Unique and distinct in their anatomy

• Five layers superficial to deep: skin, orbital septum, eyelid retractors, tarsal plates, conjunctiva

• Skin

  • Unique because it is the thinnest in the body, few vellus hair follicles, no subcutaneous fat layer with loose attachments to underlying tissue

• Orbicularis oculi

  • Main protractor, or closing muscle of the eyelid; motor innervation by cranial nerve VII (facial nerve)

  • Three anatomic parts: pretarsal and preseptal (together comprising the palpebral portion of orbicularis) and orbital parts. The pretarsal and preseptal parts involved with involuntary blink; orbital portion involved with voluntary for forced eye closure

  • Concentric muscle fibers shaped like a horse-shoe, covering entire eyelid; insert at medial and lateral canthal tendons and orbital portion interdigitates with frontalis, corrugator, and procerus muscles in the forehead

• Orbital septum

  • Dense fibrous sheath of mesodermal origin forming middle lamella of eyelid

  • Extension of periosteum of orbital bones; extends from arcus marginalis at bony rim toward the tarsus; attaches to levator aponeurosis and capsulopalpebral fascia in upper and lower eyelids, respectively

  • Keeps orbital fat in posterior compartment and acts as a barrier between orbit and eyelid, preventing postseptal spread of infection

• Eyelid retractors

  • Attach to tarsal plates and serve to retract or open eyelids

  • Upper eyelid: levator palpebrae superioris, Müller muscle

  • Lower eyelid: capsulopalpebral fascia, inferior tarsal muscle

• Tarsal plates

  • Dense connective tissue plates in each eyelid, responsible for structural integrity and contour of eyelids; contain meibomian glands

  • Rigid attachments to orbital rim periosteum by lateral and medial canthal tendons

• Conjunctiva

  • Divided into palpebral and bulbar conjunctiva

  • Mucosal membrane with numerous mucin-producing goblet cells, blood vessels, nerve endings, and loose underlying stromal tissue (substania propria)

  • Palpebral conjunctiva is the posterior-most lining of the eyelids and is firmly adherent to tarsal plates

  • Palpebral conjunctiva continues to the cul-de-sac or fornices of the eyelids where it is reflected to form the bulbar conjunctiva that covers the globe

  • Bulbar conjunctiva is delicate and freely movable except where it fuses with the globe at the limbus

• Preaponeurotic fat pads

  • Lie immediately posterior to orbital septum

  • Upper lid: 2 fat pads anterior to levator aponeurosis; nasal smaller and paler than central pad

  • Lower lid: 3 fat pads anterior to capsulopalpebral fascia; lateral pad is small; nasal and middle pads separated by inferior oblique muscle

• Sensory innervation of the eyelids

  • Cranial nerve V (trigeminal nerve) via terminal branches of ophthalmic (V₁) and maxillary (V₂) divisions

• Canthal tendons

  • Medial and lateral tendons attaching to orbital rim periosteum

  • Complex arrangement of fibrous tendon with muscular component from orbicularis muscle, attaching tarsal plates of each eyelid to orbital rim

  • Attachments are important for proper orientation and ...