MHS 227b Eye

Fibrous Tunic

Eyes are the sensory organs responsible for vision. Light is focused by the lens on the retina.

Although this eye is missing a retina, the fibrous and uveal tunics well preserved. These will be examined before examining the eyelid.

(Note the lens is missing from this specimen.)

Fibrous Tunic is the outer layer of the optic wall composed of the opaque sclera and the transparent cornea.

• Sclera - opaque, heavily vascularized connective that covers the posterior 5/6th of the eye.
• Cornea - transparent, avascular connective tissue that covers the anterior 1/6th of the eye. It is composed of five layers:
  • Corneal Epithelium - non-keratinized stratified squamous epithelium that covers its anterior surface exposed to air.
  • Bowman Membrane - a distinctive layer of collagen fibers (7 to 12 µm thick).
  • Stroma - avascular layer of collagen fibers and fibroblasts. The thickest layer of the cornea.
  • Descemet's Membrane - a thick (5 to 10 µm) basement membrane underneath the corneal endothelium.
  • Corneal Endothelium - simple squamous epithelium that covers the posterior surface exposed to the aqueous humor.

Uveal Tunic

The uveal tunic is the pigmented middle layer of the optic wall composed of the choroid, ciliary body and iris.

• Choroid - highly vascular, pigmented layer in the posterior 2/3rd of the eye composed of two layers:
• Ciliary Body - thickening of the choroid at the junction between the posterior 2/3rd and anterior 1/3rd of the eye.
  • Ciliary Muscle - attached to sclera and ciliary body and control the shape of the lens.
  • Ciliary Processes -ridge-like projections of the choroid into the posterior chamber towards the lens.
    • Surface covered by an outer pigmented and an inner nonpigmented simple columnar epitheliums.
• Iris - most anterior extension of the choroid and separates the anterior and the posterior chambers. (The upper and lower leafs are fused together in this specimen.)

Conjunctiva and Lacrimal Gland

The conjunctiva is an epithelial membrane that lines the inner surface of the eyelid, reflects onto the eyeball, and extends as fas as the limbus where it becomes continuous with the anterior corneal epithelium. The conjunctiva is supplied by a rich capillary plexus.

• Palpebral (or Tarsal) Conjunctiva - stratified columnar epithelium with many mucus-producing goblet cells on the inner surface of the eyelid.
• Bulbar Conjunctiva - the conjunctiva reflects onto the sclera and transitions into a stratified squamous epithelium with very few goblet cells.

Limbus - the junction of the opaque sclera and transparent cornea.

• The conjunctiva is continuous with the anterior corneal epithelium.
• Blood vessels abruptly stop at the limbus.

Lacrimal Gland - almond-shaped gland in the core of connective tissue within the eyelid that secretes the aqueous layer of the tear film.

• Simple columnar (serous) cells form the aqueous tears that moisten and lubricated the conjunctiva and anterior corneal epithelium.
• Ducts are lined with simple cuboidal epithelium.