Questions and Answers
What is the primary function of meibomian secretions?
Which type of epithelium produces the meibomian secretions?
What is a potential consequence of blockage of the meibomian glands?
How many meibomian glands are typically found in the lower lid?
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Which glands are associated with hair follicles in the eyelids?
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What is a unique characteristic of the lower lid compared to the upper lid?
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Which artery primarily supplies blood to the eyelids?
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What role does the capsulopalpebral fascia serve in the lower lid?
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Which artery is an offshoot of the lacrimal artery that supplies the eyelids?
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Which lymphatic vessels drain the upper eyelid?
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What is the role of the sympathetic system in relation to the eyelids?
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Which division of the trigeminal nerve supplies the upper lid?
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Which nerve supplies the levator palpebral muscle?
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What does interruption of the sympathetic system cause regarding eyelid function?
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Which vein receives blood from the conjunctiva and pretarsal drainage?
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What is the primary motor nerve supply to the orbicularis oculi muscle?
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What is the primary difference between reflex blinking and voluntary blinking?
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Which physical response is associated with closing the eyelids during voluntary blinking?
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What triggers reflex blinking?
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What happens to the electrical activity in the levator muscle during eyelid closure?
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Which neural structures are involved in the collaborative reflex of blinking?
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What is the effect of closing the eyelids on the activity of the superior and inferior rectus muscles?
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What is one function of the superficial lipid layer of the tear film?
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Which component is primarily responsible for the thickness of the aqueous layer in the tear film?
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What occurs when the orbicularis tonus is reduced during eye opening?
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Which of the following is NOT a reason for deficiencies in the superficial lipid layer?
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What is a function of the aqueous layer of the tear film?
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Which of the following is included in the composition of the aqueous layer?
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What can be a consequence of keratoconjunctivitis sicca?
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What key role does the superficial lipid layer play in relation to the aqueous layer?
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Which nerve primarily provides sensory innervation to the bulbar conjunctiva?
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What is the primary role of lysozyme found in tears in relation to conjunctival bacteria?
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What anatomical structure accompanies the conjunctival arteries and is involved in venous drainage?
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What characteristic about conjunctival bacteria is noted from the first week of life?
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Which of the following factors contributes to the low propagative capacity of bacteria in the conjunctiva?
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Which division of the ophthalmic nerve serves the upper fornix and palpebral conjunctiva?
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What type of vascular network does the conjunctiva contain?
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Which nerve is responsible for the sensory innervation of the conjunctiva of the lower eyelid?
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Study Notes
Meibomian Glands
- Produce meibomian secretion, functioning as a precorneal tear film to prevent evaporation.
- Help restrain tear overflow at the lid margin and prevent adhesion of the eyelids.
- Approximately 25 glands in the upper lid and 20 in the lower lid.
- Blockage of glands can cause lumps on the lid's inner surface, leading to corneal irritation.
Glands Associated with Eyelashes
- Glands of Zeiss: sebaceous glands associated with cilia, typically paired and opening into hair follicles.
- Glands of Moll: similar to sweat glands, also paired and connected to hair follicles.
Accessory Lacrimal Glands
- Tissue of Krause and Wolfring are present in the eyelids, contributing to tear production.
Anatomy of the Lower Lid
- Reduced version of the upper lid, with no distinct cheek boundary.
- Lower tarsal plate is smaller and rectangular; lacks a separate levator muscle.
- Less mobile than the upper lid; sagging skin common in the lower lid.
- The upper lid overlaps the corneal margin; the lower lid does not.
Blood Supply
- Primarily supplied by ophthalmic artery branches.
- Medially, blood is provided by the medial palpebral artery, which anastomoses with the lateral palpebral artery (an offshoot of the lacrimal artery).
- Venous drainage is extensive with larger veins, including ophthalmic vein divisions draining into the angular and superficial temporal veins.
Lymphatic Supply
- Two lymphatic systems: one draining the lower lid and nose to submandibular nodes, and another draining the upper lid to parotid nodes.
Nerve Supply
- Supplied by the trigeminal nerve (Vth cranial nerve); upper lid via the ophthalmic division, lower lid via the maxillary division.
- Motor innervation of orbicularis oculi from the Facial nerve (7th cranial nerve).
- Sympathetic innervation affects involuntary muscles; interruption leads to ptosis.
Tear Film Composition
- Comprises three layers:
- Superficial lipid layer: produced by meibomian glands, stabilizes tears, reduces evaporation, and lubricates eyelids.
- Aqueous layer: about 7mm thick, produced by main and accessory lacrimal glands, contains salts, proteins, and antibacterial substances, essential for corneal health.
- Mucous layer: provides additional lubrication and stability.
Conjunctival Bacteria
- Conjunctiva hosts bacteria from the first week of life, generally equally distributed between both eyes.
- Low temperature, exposure, and tear composition prevent bacterial overgrowth.
Reflex Blinking
- Involves involuntary reflex from stimuli like light and touch, and voluntary blinking has conscious control.
- Closes eyelids and moves the eye (Bell’s phenomenon), increasing superior rectus activity and decreasing inferior rectus activity.
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Description
This quiz covers the function and structure of meibomian glands. Learn about their role in maintaining the tear film and potential issues that can arise from gland blockage. Test your knowledge on the anatomy of the eyelids and the significance of these glands in eye health.
