Conjunctiva and sclera

• Conjunctiva


  Thin, translucent mucous membrane that runs from the limbus over the anterior sclera, forms a cul-de-sac at the superior and inferior fornices, and turns anteriorly to line the eyelids
• Conjunctiva


  • Ensures smooth movement of the eyelids over the globe
  • The limbus is the location of stem cells for bulbar conjunctiva and the mucocutaneous junction is the site of stem cells for palpebral conjunctiva
• Parts of conjunctiva


  • Palpebral (marginal, tarsal & orbital)
  • Bulbar conjunctiva
  • Fornix conjunctiva (superior & inferior)
• Bulbar conjunctiva


  Translucent, allowing the sclera to show through, colorless except when its blood vessels are engorged, loosely adherent to the underlying tissue up to within 3 mm of the cornea, where it becomes tightly adherent and merges with the underlying Tenon's capsule and sclera
• Conjunctival epithelium


  • Marginal (5 layer)
  • Tarsal conjunctiva (2 layer)
  • Fornix & bulbar (3 layer)
  • Limbal (8 to 10 layer)
• Conjunctival cells


  • Goblets cells
  • Melanocytes
  • Langerhan cells
• Adenoid layer


  Lymphoid layer consist of CT lymphocytes
• Conjunctival glands


  • Main mucin secretory glands: goblet cells, crypts of henle, glands of manz)
  • Accessory glands (krause & wolfring)
• Plica semilunaris


  Crescentric folds in the medial canthus
• Caruncle


  5mm x 3mm mound of tissue that overlies the medial edge of the plica semilunaris
• The surface of the superficial conjunctival cells and their microvilli and microplicae are covered with a glycocalyx similar to that of the corneal surface
• Melanin granules often are found in the cytoplasm of conjunctival epithelial cells, especially near the limbus; these are particularly prevalent in individuals with heavily pigmented skin
• Goblet cells, which produce the mucous component of the tear film, are located in the epithelium
• Subsurface vesicles, found below the outer membrane of the superficial conjunctival cell, may be an additional source of mucous material
• As these vesicles fuse with the epithelial cell membrane, chains extend outward and may form a chemical bond with the mucous layer secreted by the goblet cells, increasing the adherence of the tear film to the globe
• These vesicle membranes may contribute to the microvilli present on the surface epithelial cells
• Conjunctival Submucosa


  Stromal (substantia propria) layer composed of vascularized, loose connective tissue containing the same components as in palpebral conjunctival stroma
• Plica semilunaris


  Crescent-shaped fold of conjunctiva located at the medial canthus, containing numerous goblet cells, highly vascularized, and containing smooth muscle and adipose tissue
• Caruncle


  Mound of tissue that overlies the medial edge of the plica semilunaris, containing non-keratinized epithelium, accessory lacrimal glands, hair follicles, and sebaceous and sweat glands
• Conjunctival blood vessels


  • Palpebral conjunctiva receives blood supply from palpebral arcades
  • Fornices supplied by branches from peripheral arcades, which then branch again and enter the bulbar conjunctiva, forming a plexus of vessels, the posterior conjunctival arteries
  • Anterior conjunctival arteries formed by branches from the anterior ciliary arteries
  • Conjunctival veins parallel the arteries but are more numerous, draining into the palpebral and ophthalmic veins
• Conjunctival lymphatics


  • Superficial and deep networks within the submucosa
  • Drain into the lymphatics of the eyelids, those from the lateral aspect empty into the parotid lymph node, and those from the medial aspect empty into the submandibular lymph node
• Conjunctival innervation


  • Sensory innervation of the bulbar conjunctiva is through the long ciliary nerves
  • Sensory innervation of the superior palpebral conjunctiva is provided by the frontal and lacrimal branches of the ophthalmic nerve
  • Innervation of the inferior palpebral conjunctiva is provided by the lacrimal nerve and the infraorbital branch of the maxillary nerve
  • All sensory information is carried in the trigeminal nerve
• Sclera


  Forms the posterior five sixths of the connective tissue coat of the globe, maintains the shape of the globe, and provides an attachment for the extraocular muscle insertions
• The thickness of the sclera varies from 1 mm at the posterior pole to 0.3 mm just behind the rectus muscle insertions
• Sclera


  Its whole outer surface is covered by Tenon's capsule, and in the anterior part it is also covered by bulbar conjunctiva, its inner surface lies in contact with choroid with a potential suprachoroidal space in between
• The thickness of the sclera varies considerably in different individuals and with the age of the person, it is generally thinner in children than the adults and in females than the males
• Scleral apertures


  • Posterior apertures around the optic nerve transmit long and short ciliary nerves and vessels
  • Middle apertures (four in number) slightly posterior to the equator transmit the four vortex veins
  • Anterior apertures 3 to 4 mm away from the limbus transmit the anterior ciliary vessels
• Scleral layers


  • Episcleral tissue
  • Sclera proper
  • Lamina fusca
• Episclera


  Loose, vascularized, connective tissue layer that lies just outer to the sclera
• Sclera proper


  Thick, dense connective tissue layer that is continuous with the corneal stroma at the limbus, containing collagen fibrils arranged in irregular bundles that branch and interlace
• Lamina fusca


  Innermost part of sclera which blends with suprachoroidal and supraciliary laminae of the uveal tract, brownish in color due to the presence of pigmented cells
• Scleral spur


  Region of circularly oriented collagen bundles that extends from the inner aspect of the sclera, the posterior scleral spur is the origin of the longitudinal ciliary muscle fibers, and most of the trabecular meshwork sheets attach to its anterior aspect
• Scleral opacity


  Depends on the number of GAGs, the amount of water, and the size and distribution of the collagen fibrils, the sclera contains 1/4 the number of GAGs that are present in the cornea and is relatively dehydrated (68%) compared with the cornea
• The anterior sclera is visible through the conjunctiva
• Sclera


  The outermost layer of the eye that protects the internal structures and maintains the shape of the eye
• Lamina fusca


  The innermost part of the sclera which blends with the suprachoroidal and supraciliary laminae of the uveal tract, brownish in color due to the presence of pigmented cells
• Scleral spur


  • A region of circularly oriented collagen bundles that extends from the inner aspect of the sclera, the posterior scleral spur is the origin of the longitudinal ciliary muscle fibers, and most of the trabecular meshwork sheets attach to its anterior aspect
• Scleral opacity


  Depends on the number of GAGs, amount of water, and size and distribution of collagen fibrils, the sclera contains 1/4 the number of GAGs as the cornea and is relatively dehydrated
• Scleral color


  The anterior sclera is visible through the conjunctiva and may appear colored due to age or disease, newborns have a bluish tint, can appear yellow due to fatty deposits or liver disease
• Scleral foramina and canals


  • The sclera contains foramina and canals that carry nerves and vessels, the anterior scleral foramen is the area occupied by the cornea, the optic nerve passes through the posterior scleral foramen which is bridged by the lamina cribrosa, the lamina cribrosa is the weakest area of the outer connective tissue tunic