Dry eye

• Dry eye disease


  Inadequate tear volume or function causing unstable tear film and ocular surface disease
• Keratoconjunctivitis sicca


  Eye with some degree of dryness
• Xerophthalmia


  Extremely dry ocular surface with Vitamin A deficiency (retinoic acid)
• Vitamin A


  • Improves the smoothness of the tear film
  • Supports formation of tears
  • Daily dose up to 5000 IU for dry eye relief
• Vitamin A helps mucus membranes to be effective barriers against bacteria and viruses
• Vitamin A is shown to help specifically for Keratoconjunctivitis sicca
• Vitamin A decreases the risk of vision loss due to AMD, but that's for next year
• Xerosis


  Extreme ocular dryness and keratinization that occurs in eyes with severe conjunctival cicatrisation
• Sjögren syndrome


  Autoimmune inflammatory disease of which dry eyes is a feature
• Tear film constituents


  • Lipid layer
  • Aqueous layer
  • Mucous layer
• Spread of tear film

  1. Mechanically distributed over the ocular surface

  2. Neuronally controlled blinking mechanism

  3. 3 factors required for effective resurfacing: normal blinking reflex, contact between external ocular surface and eyelids, normal corneal epithelium
• Lipid layer


  • Composition: 2 thin inner layers - polar phase (charged or uncharged) that contains phospholipids adjacent to aqueous-mucin phase, Outer layer - non polar phase containing waxes, cholesterol esters and triglycerides with low aqueous solubility
  • Function: Prevent evaporation of aqueous layer and maintain tear film thickness, Act as surfactant allowing spread of the tear film
  • Deficiency results in evaporative dry eye
• Aqueous layer


  • Secretion: Lacrimal glands produce 95% of aqueous component of tears, Accessory lacrimal glands of Krause and Wolfring produce remainder
  • Function: Provide oxygen from atmosphere to corneal epithelium, Antibacterial activity due to proteins, Washes away debris and facilitates transport of leukocytes after injury, Optically enhances the corneal surface by taking away small irregularities
• Reflex tears


  • Due to corneal and conjunctival sensory simulation, tear break-up, ocular inflammation, mediated by 5th cranial nerve
  • Decreases during sleep, Reduced by topical anaesthesia, Increases up to 500% in response to injury
• Aqueous layer composition


  Water, electrolytes, dissolved mucins and proteins, Growth factor derived from lacrimal gland, Production of growth factor increases in response to injury
• Mucous layer composition


  High molecular weight glycoproteins (defence and immunity), Transmembrane, secratory, Gel forming or soluble, Produced mainly by goblet cells but also lacrimal gland
• Mucus layer


  • Corneal and conjunctival superficial epithelial cells produce transmembrane mucins that form extracellular coating
  • Function: Permit wetting by changing cells of cornea from hydrophobic to hydrophilic, Lubrication
  • Deficiency may be indicative of both aqueous deficiency and evaporative states
• Goblet cell loss occurs in 4 conditions: Cicatrizing conjunctivitis, Vitamin A deficiency, Chemical burns, Toxicity from medication
• Regulation of tear film components

  • Hormonal: Androgens responsible for regulation of lipid production, Oestrogen and progesterone for normal functioning of conjunctival and lacrimal gland tissues
  • Neural: Fibres adjacent to the lacrimal gland, Goblet cells that stimulate aqueous and mucus secretions
• Mechanism of dry eye disease

  • 4 core inter-related mechanisms: Tear instability, Tear hyperosmolarity, Inflammation, Ocular surface damage
  • Inflammation in conjunctiva and accessory glands as well as ocular surface is present in 80% of patients with KCS (keratoconjunctivitis sicca)
• Classification of dry eye

  • Aqueous-deficient: Sjögren syndrome, Non-Sjögren syndrome
  • Evaporative: Intrinsic, Extrinsic
• Sjögren syndrome


  Autoimmune disorder, Lymphocytic inflammation and destruction of lacrimal and salivary glands and other exocrine organs, Classic clinical triad: Dry eyes, Dry mouth, Parotid gland enlargement
• Sjögren syndrome classification


  • Primary: Exists in isolation, Affects females more
  • Secondary: Associated with another disease such as rheumatoid arthritis or SLE
• Sjögren syndrome clinical features

  • Symptoms: Feeling of dryness, grittiness or burning that worsens during day, Stringy discharge, Transient blurring of vision, Redness, Crusting of lids, Exacerbated by conditions that increase tear evaporation
  • Signs: Posterior (seborrhoeic) blepharitis with Mybomian Gland Dysfunction, Conjunctiva: Redness, Staining with Rose Bengal, Keratinization, Conjunctivochalasis response to and exacerbating factor for chronic irritation of dry eye, Tear film: Lipid-contaminated mucin accumulates, Marginal tear meniscus less than 0.25 mm or absent, Cornea: PEE that stain with NaFL, Filamentary strands of mucus and debris, Mucous plaques
• Sjögren syndrome complications


  Vision threatening: Epithelial breakdown, Melting, Perforation, Bacterial keratitis