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
