2-29 Lacrimal + Dry Eye Flashcards
List the parts of the Lacrimal Functional Unit (6 total)
- Lacrimal gland
- Accessory glands
- Conj.
- Cornea
- Neural reflexes
- Eyelids
1) Tear film thickness and volume?
2) Tear film turn over rate?
3) Ways that tear film is lost?
1) 4μm thick, 7μl volume (drops are significantly more so lots of drops lost)
2) 1.2μl/min unstimulated -> 100μl/min stimulated
3)
- Nasolacrimal drain
- Evaporation
- Conj. absorption
Distribution of tears across eye surface? How to observe this?
Fluorescein staining shows light band around top and bottom edges of conj. to eyelid margins and around the caruncle. This is where 90% of tear volume is. Also has dark band next to light band resulting from gravity next to light band. Rest of eye is covered w/ 10% of tear volume.
Non-invasive method of measuring tear film stability?
Keratograph shines mires. Rings will distort when tears break up. Non-invasive avoids fluorescein which could disrupt natural tear film.
Describe tear drainage
- Tears move temporally at start
- Tears fill up meniscus which covers nasal area
- Drain from both sup. and inf. puncta
- Lacrimal canaliculi
- Lacrimal sac (blinking = suction)
- Nasolacrimal duct
- Valve of Hasner
The aqeuous component of tears is created by…
Mainly lacrimal gland, w/ some help from accessory glands of Krause and Wolfring
Describe lacrimal gland cellular structure
- Tubulo-acinar structures in lobules.
- Columnar cells secrete into lumen via secretory granules
- Innervation from both PNS and SNS
Describe what makes up the aqeuous component of the tear film. What happens when reflex tearing?
- Electrolytes (pH = 7.4)
- Proteins + enzymes
– From lacrimal gland: Lysozome, lactoferrin, sIgA, lipocalin
– Leaked from conj.: albumin, IgG, IgM (therefore reflex tearing will increase protein concentration for those coming from lacrimal gland) - Metabolites (glucose + urea)
- Misc
Describe the lipid layer
- Properties
- Contains?
- Purpose?
- Low melting point (eye temperature should melt it into clear form)
- Mixture of wax, sterol esters, phospholipids, glycerides, hydrocarbons.
- Important for tear stability, spreading, and prevent evoparation.
Describe the mucin layer
- Made from?
- Purpose?
- How?
- Conj. goblet cells (and some from crypts of Henle at fornix and epithelial cells)
- Lubrication (allows aqueous to stick to eye) + protection (wrap around foreign bodies and safely move to corner for wiping out) + wetability
- Mucoproteins. Binds strongly to corneal epithelium via glycocalyx (protein strands w/ sugar attached)
Dry eyes is defined as
1) uni/multifactoral?
2) characterised by?
3) Symptoms resulting from what features?
1) Multi
2) Loss of tear film homeostasis
3) Tear film instability, hyperosmolarity, ocular surface inflammation
Dry eye signs?
- Conj. injection
- Tear meniscus minimal/absent
- Tear film instability/hyperosmolarity
- Characteristic staining at cornea or conj. (SPK) using lissamine green (definitive as it stains dead cells) or fluorescein which highlights epithelial loss
- Corneal luster loss, corneal filaments, mucus debri/strands if severe
Describe Sjogren’s disease in relation to dry eyes
Autoimmune attacks lacrimal + salivary glands
- Aqueous deficient
- Dry eyes, mouth
- Often associated w/ CT issue like RA
Describe non-Sjogren related ways of getting aqeuous deficient dry eyes
Menopause
- Testosterone can bind to tear glands to stimulate it
- Women aging reduces testosterone (along w/ other androgens)
Latrogenic hyposecretion (drug induced)
Describe filamentary keratitis
- What is it?
- Effects?
Mucus/epithelial cell strands adherent to cornea
- Very painful, especially when blinking
- Viscous mucus sticks to deep cells of cornea via epithelial defects or dry epithelial surface
- Sloughing epithelial cells incorporated w/ mucus
- Occurs in severe cases
Describe evaporative dry eye and what it’s mostly caused by.
“Blepharitis” = eyelid inflammation
- Either ant. or post. blepharitis
- Most commonly called MGD
- Associated w/ skin disorders
- Lipids released by meibomian gland more thick toothpaste texture and less clear due to high melting point so not melted.
Describe Seborrhoeic blepharitis
“Dandruff of the eyelashes”
- Associated w/ S. aureus
- Lid margin inflammation
- Dry flakes or oily secretions
- Photophobia + “Heavy eyelids” feeling
- Common, mild cases are asymptomatic
Describe Staphylococcal belpharitis
- Caused by S. aureus or epidermis (commensale when lower count)
- Eyelash follicle sterile ulceration/collaretes (white lashes)
- Localised poliosis (pigment change)/madarosis (lash loss)/trichasis (wrong way)
- SPK + marginal keratitis
- Speads, hard to eradicated, can be chronic
Describe Demodex blepharitis
- Saprophytic (lives off dead matter) parasite (D. Folliculorum in lash follicles whilst D. brevis in meibomian glands) (commensal when lower count)
- Dermatitis, folliculitis, blepharitis
Irritation due to: - Blocking follicles
- Transmits bacteria
- Inflamm response to chitin
- Immune response to dead mites/waste products
MGD
- Most common cause?
- Effects on eye?
- Associations?
- Grading?
Acne rosacea
- Inflammed lid margins
- Telangiectasia around meibomian gland orifices
Orifices may be: - Pouting
- Obstructed
- Displaced
- Number reduced
Associated w/:
- Foam (Lipase exotoxin from bacteria breaks down tears via soponification to give soapy look)
- Tear film debri
- Lid notching (gland dropout)
- Scaring and entropion (from scarring)
0 = Clear fluid
1 = Greasy, slightly turbid
2 = Opaque
3 = Semi-solid
4 = Waxy (if anything is expressed)
Describe exposure keratopathy
Infrequeny or incomplete blinking, or laghophalmos exposes corneal surface. Evaporates tear film.
List what can cause mucin deficiency
- Steven-Johnson syndrome (poor med response)
- Ocular cicatricial pemphigoid (tissues join together)
- Trachoma
- Chemical burns
- Hypovitamin A
Describe hypovitamin A in causing dry eyes
- Necessary for mucus membrane + epithelium
- Inadequate amounts causes Xeropthalmia (no tears)
- Cornea + conj. dry + thick + wrinkled.
Signs common in both canaliculitis and dacryocystitis
- Typically what happens?
- Acute or chronic
- Partial or complete blockage of drainage. Multiple reasons possible.
Signs: - Purulent/mucopurulent discharge (can express w/ pressure)
- Epiphora
Describe Canaliculitis
- Commonly due to what species?
- Signs?
Canaliculus infected
- Commonly from Actinomyces israelii
- Inferior often more infected than superior.
Signs:
- Dilation + pouting of puncta
- Medial eyelid oedema
- Medial conj. Injection
Describe Dacryocystitis
- commonly due to what species?
- Signs?
- If acute…
Lacrimal sac infection
- Caused by Haemophilus influenze, or staph aureus, pyogenes, pneumoniae
Signs:
- Oedema + erthema of area around sac
If acute,
- Probably due to nasolacrimal duct obstrcution
- Tender inner canthal swelling
- Mild preseptal cellulitist
Describe dacryoadenitis
- Signs/symptoms?
- Causes?
Lacrimal gland infected
- Unilateral pain, redness, and swelling of outer 3rd upper eyelid
- Tearing, discharge, chemosis associated
- “S-shaped” upper lid
- If upper lid infected, propotosis or EOM restriction possible.
- If bilateral, probably due to systemic diseass/infection
- If unilateral, probably penetaring injury or bacterial conjuncitivitis spread
