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65 Cards in this Set
- Front
- Back
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What is the function of the Lacrimal Apparatus? |
• Tear formation – Multiple constitents and properties
• Channel tears to the ocular surface – Maintain moisture – Flush debris & waste material |
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What is the Lacrimal passage? |
• Lacrimal gland • Conjunctival Sac • Lacrimal Puncta • Lacrimal Canaliculi • Lacrimal Sac • Nasolacrimal duct |
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Lacrimal apparatus overview |
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What is the Lacrimal sac fossa? |
• Depression in inferior-medial orbital rim.
• Bordered by anterior (maxillary bone) and posterior lacrimal crest (lacrimal bone) |
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State the dimensions of the Lacrimal sac fossa. |
≈16 mm high ≈4-9 mm wide ≈2 mm deep |
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What starts as the base of the fossa? |
Naso-lacrimal canal starts at the base of the fossa. |
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What are the Glands of the secretory system? |
Lacrimal and Accessory glands. |
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What do the Lacrimal and Accessory glands do? |
Provide moisture and lubrication to the cornea and conjunctiva. |
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What is reflex secretion? |
Response to pain, external stimuli and foreign bodies |
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What is basal secretion? |
Continuous secretion throughout the day of tears 》 superior fornix |
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State the volume of basal secretion per min. How does it vary? |
2.2μl/min – Varies with humidity & temperature? (debated) |
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What is the lacrimal gland? |
Endocrine gland, soft yellow-ish. |
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Where is the lacrimal gland? |
Above and antero lateral to the globe |
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Where does the lacrimal gland secrete tears into? |
Superior fornix |
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What is the Lacrimal Gland divided into? |
2 connected lobes. Orbital and Palpebral lobes |
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State the dimensions of the lacrimal gland? |
Flat, oval mass ≈20 mm long (largest part) ≈8-9 mm thick |
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What is the orbital lobe of the lacrimal gland? |
Larger orbital lobe
• Shape/size of almond •Lodged in anterolateral part of the orbital roof |
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What is the palpebral part of the lacrimal gland? |
Smaller palpebral lobe
– 1/3rd size – Lodged in lateral part of upper lid – Continuous with aponeurosis of LPS |
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What are Accessory glands? |
• Small, branched, tubular glands • Similar to salivary glands • Contractile myo-epithelial cells (aid secretion) • External portion |
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What do Accessory glands supply? |
Supply aqueous phase of the tear film |
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Name the Accessory glands of the eyelids. |
Glands of Krause Glands of Wolfring |
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What artery supplies the lacrimal gland? |
Lacrimal artery |
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What is the Lacrimal artery? |
One of the largest branches of the ophthalmic artery. |
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Where does the lacrimal artery run? |
• Runs forward in the orbit with lacrimal nerve.
• Passes between the lacrimal gland & the eye. |
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What does the lacrimal artery form? |
Forms dense, branched capillary bed》gland |
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Where does the opthalmic vein run? |
Ophthalmic vein runs superior to the eye》 superior ophthalmic vein |
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How is the lymphatic drained? |
Joins that of conjunctiva • Laterally (2/3rds) – Pre-auricular nodes • Medially – Sub-mandibularnodes |
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What is the parasympathetic input of the Lacrimal Gland? |
Parasympathetic input: from lacrimal nucleus of facial nerve (the majority input) |
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What is the sensory input of the lacrimal gland? |
Sensory: Lacrimal Nerve (branch of Ophthalmic division of Trigeminal nerve) |
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What is the sympathetic input of the lacrimal gland? |
Sympathetic input: from external carotid plexus |
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What is the Puncta? |
Small round oval hole |
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Where is the Puncta? |
• Medial end of the lid margin • Puncta do not overlap |
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Where is the superior and inferior Puncta? |
• Superior punctum 6 mm from medial Canthus. • Inferior punctum 6.5 mm from medial canthus |
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What is the Lacrimal Canaliculi? |
Superior and Inferior canals which exit eye perpendicular to lid margin (2 mm) |
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What does the lacrimal Canaliculi initially form? |
Initially expands to form a sac AMPULLA |
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How long is the Lacrimal Canaliculi? |
8mm horizontally |
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What lines the lacrimal Canaliculi? |
Stratified squamous epithelium and elastic tissue |
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The two canaliculis merge to form what? |
Lacrimal sac |
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How long is the Lacrimal sac? |
10-12 mm |
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What is the Nasolacrimal Duct? |
Continuous of lacrimal sac》 nasal cavity |
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How wide of the Nasolacrimal Duct? |
3-4 mm wide |
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What lines the Nasolacrimal Duct? |
Double layered epithelium |
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What is the Valve of Hanser? |
Several flaps of tissue towards the end of the duct act like a valve.
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What does the Valve of Hanser do? |
Prevents nasal secretions from entering the duct (e.g. sneezing, blowing nose) |
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What is the route of the tear flow ? |
• Eyelid mediation- Tears are pushed medially • Absorbtion • Evaporation- ambient temperature/humidity |
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What is the anatomical drainage routine of tear flow? |
Canaliculi 》 Lacrimal sac 》 Naso-lacrimal duct 》 Nose |
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Explain the route the tear flow takes via eyelid mediation- prior to blink? |
Puncta, cannaliculi & lacrimal sac are fully OPEN |
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Explain the route the tear flow takes via eyelid mediation- with blinking? |
– puncta meet & CLOSE – canaliculi & sac are compressed – fluid moves into duct |
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Explain the route the tear flow takes via eyelid mediation- lids reopen? |
– canaliculi & sac re-expand
– relative nagative pressure develops in sac. |
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Explain the route the tear flow takes via eyelid mediation- as blink ends? |
– puncta RE-OPEN – fluidflows 》 puncta & canaliculi |
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What is the function of the Tear film? |
• Overlays corneal and conjunctival epithelia- prevents/minimise desiccation. • Optical clarity & maintains refractive power. • Defence against infection. • Passage of O2 from air》avascular cornea |
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What is the tear film composition? |
• Salts • Mucus • Proteins(defensive-60+)
Secretory IgA – defensive antibody
Lysozyme – Bacterio-lytic-spectrum is limited
Lactoferrin – bacteriostastic (binds with iron needed for bacterial metabolism)
Tear Specific pre-albumin – unknown function |
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What are the layers of the tear film? |
• Glycocalyx • Mucin • Aqueous • Lipid |
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How thick is the Tear film? |
7.3- 8.3 μm
• Mucin 0.2μm • Aqueous 7-8μm • Lipid 0.1μm |
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What is the Glycocalyx layer of the Tear film? |
Network of polysaccharides that project from the ocular surfaces |
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What does the Glycocalyx layer of the Tear film do? |
Connects corneal layer with mucous (innermost) layer of the tear film |
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What is the Mucin layer? |
• Inner most layer of the Tear film • Contains Mucin • Synthesised and secreted by conjectival globlet cells |
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What is the function of the Mucin layer? |
• Makes the tear film hydrophilic • Stabilises TF • Reduces surface tension • Allow even spread of TF across the ocular surface • Provides protection against micro-organisms |
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How is the Aquesous layer of the Tear film produced? |
By the lacrimal gland |
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What does the Aqueous layer contain? |
• Water (98%) • Proteins (defence) • Salts (2%) • Infection control- lysozyme and lactoferrin • Buffering ions |
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What is the function of the Aqueous layer? |
• Carried nutrients and oxygen to the cornea.
• Aids lubrication of the eye so that the eyelid can open and close smoothly. |
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How is the Lipid layer of the Tear film produced? |
By Meibomian and modified sebaceous glands Zeiss and Moll. |
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What does the Lipid layer contain? |
Mix of lipid and protein |
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What is the function of the Lipid layer? |
• To impart stability to the tear film
• To retard evaporation-hydrophobic barrier-prevents overflow
• To provide a smooth optical surface for the cornea
• To provide a barrier against foreign particles.
• To provide some anti-microbial activity.
• To seal the lid margins during prolonged closure. |
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New model of the Tear film. |
• Layers are not as discrete as previously thought. • Mucins exist as network within the aqueous layer. • Role & structure of glycocalyx (trans-membrane molecules into aqueous). • Identication of new mucins & proteins at ocular surface. |
