Dry Eyes Flashcards
What is the definition of dry eye disease?
a multifactorial disease of the ocular surface and tear film accompanied by increased osmolarity of the tear
film and inflammation of the ocular surface.
What is the definition of keratoconjunctivitis sicca?
refers to any eye with some degree of dryness.
What is the definition of Xerophthalmia?
describes a dry eye associated with vitamin A deficiency.
What is the definition of Xerosis?
refers to the extreme ocular dryness and keratinization that occurs in eyes with severe conjunctival cicatrization.
What is Sjogren syndrome?
an autoimmune inflammatory disease of which dry eyes is a feature.
What are the layers of the tear film?
- Lipid layer secreted by the meibomian glands.
- Aqueous layer secreted by the lacrimal glands.
- Mucous layer secreted principally by conjunctival goblet cells.
What is the composition of the outer lipid layer of tear film?
a polar phase containing phospholipids adjacent to the aqueous-mucin phase and a non-polar phase containing waxes, cholesterol esters and triglycerides.
What is the function of the lipid layer of the tear film?
○ To prevent evaporation of the aqueous layer and maintain tear film thickness.
○ To act as a surfactant allowing spread of the tear film.
○ Deficiency results in evaporative dry eye.
What % of aqueous do the lacrimal glands produce?
95%
Where is the remaining 5% of aqueous produced?
Glands of Wolfring and Krause
How is the reflex tearing mechanism mediated?
in response to corneal and conjunctival sensory stimulation, tear break-up an ocular inflammation and is mediated via the fifth cranial
nerve. It is reduced by topical anaesthesia and falls during sleep. Secretion can increase 500% in response to injury.
What is the function of the aqueous layer?
○To provide atmospheric oxygen to the corneal epithelium.
○Antibacterial activity due to proteins such as IgA, lysozyme and lactoferrin.
○To wash away debris and noxious stimuli and facilitate the transport of leukocytes after injury.
○To optically enhance the corneal surface by abolishing minute irregularities.
What is the composition of the mucous layer of tears?
○ Mucins are high molecular weight glycoproteins that may be transmembrane or secretory in type.
○ Secretory mucins are further classified as gel-forming or soluble. They are produced mainly by conjunctival goblet cells but also by the lacrimal glands.
What is the function of the mucous layer of tear film?
○ To permit wetting by converting the corneal epithelium from a hydrophobic to a hydrophilic surface.
○Lubrication.
○Deficiency of the mucous layer may be a feature of both aqueous deficiency and evaporative states. Goblet cell loss occurs with cicatrizing conjunctivitis, vitamin A deficiency, chemical burns and toxicity from medications.
What are the 4 core inter-related mechanisms postulated to be causing dry eye?
tear instability,
tear hyperosmolarity,
inflammation
ocular surface damage.
What are the 2 types of Aqueous deficient dry eye?
*Sjögren syndrome dry eye (primary or secondary).
*Non-Sjögren syndrome dry eye.
○Lacrimal deficiency
○Lacrimal gland duct obstruction
○Reflex hyposecretion: sensory
What are the 2 types of Evaporative dry eye?
Intrinsic
Extrinsic
What are the causes for Non-Sjogren syndrome dry eyes?
○Lacrimal deficiency: primary (e.g. age-related dry eye, congenital alacrima, familial dysautonomia) or secondary (e.g. inflammatory and neoplastic lacrimal gland infiltration, acquired immunodeficiency syndrome (AIDS), graft-versus-host disease, lacrimal gland or nerve ablation).
○Lacrimal gland duct obstruction, e.g. trachoma, cicatricial pemphigoid, chemical injury, Stevens–Johnson syndrome.
○Reflex hyposecretion: sensory (e.g. contact lens wear, diabetes, refractive surgery, neurotrophic keratitis) or motor block (e.g. seventh cranial nerve damage, systemic drugs).
What are the causes of Evaporative Intrinsic dry eyes?
○Meibomian gland deficiency, e.g. posterior blepharitis, rosacea.
○Disorders of lid aperture, e.g. excessive scleral show, lid retraction, proptosis, facial nerve palsy.
○Low blink rate, e.g. Parkinson disease, prolonged computer monitor use, reading, watching television.
○Drug action, e.g. antihistamines, beta-blockers, antispasmodics, diuretics.
What are the causes of Evaporative extrinsic dry eyes?
○Vitamin A deficiency.
○Topical drugs including the effect of preservatives.
○Contact lens wear.
○Ocular surface disease such as allergic conjunctivitis.
What is the pathophysiology of Sjogren Syndrome?
an autoimmune disorder characterized by lymphocytic inflammation and destruction of lacrimal and salivary glands and other exocrine organs. The classic clinical triad consists of dry eyes, dry mouth and parotid gland enlargement, but other features are common and
can affect all organ systems.
What is the ACR criteria for Sjogren syndrome?
*Positivity for anti-SSA or anti-SSB antibodies, or positive rheumatoid factor together with significantly positive antinuclear antibody.
*Ocular surface staining above a certain grade.
*Focal lymphocytic sialadenitis to a specified extent on salivary gland biopsy
What is keratoconjunctivitis sicca exacerbated by?
by exposure to wind, air-conditioning and central heating.
What are some signs seen in patients with Sjogren syndrome?
*Posterior (seborrhoeic) blepharitis with meibomian gland dysfunction is often present
*Conjunctiva redness, stain with Rose Bengal and Lissamine green and conjunctivochalasis
*Reduced tear film meniscus <0.25mm
*Cornea shows PEE’s, filaments of mucus and debris staining well with Rose Bengal
*Epithelial breakdown, melting and perforation