Dews definition of dry eye
Reading File
Finding Sources
Searching PubMed
"dry eye" AND definition
Searching the Web
TFOS DEWS II dry eye definition 2017 official
TFOS DEWS II definition of dry eye disease:
“Dry eye is a multifactorial disease of the ocular surface characterized by a loss of homeostasis of the tear film, and accompanied by ocular symptoms, in which tear film instability and hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormalities play etiological roles.”
This is the 2017 DEWS II definition from the TFOS DEWS II report.
What is lacrimal unit
Reading File
Finding Sources
Searching PubMed
"lacrimal functional unit"
Searching the Web
lacrimal functional unit components ocular surface official definition
The lacrimal functional unit (LFU) is the integrated system that produces, distributes, maintains, and drains the tear film to keep the ocular surface healthy.
Core components
- Main and accessory lacrimal glands
- Ocular surface: cornea and conjunctiva
- Interconnecting sensory and autonomic nerves
In the wider practical concept, it also includes meibomian glands, conjunctival goblet cells, eyelids and blinking mechanism, and lacrimal drainage system.
It functions as a reflex loop: ocular-surface stimulation is sensed by sensory nerves, which activate lacrimal secretion and blinking. Dysfunction at any point can cause tear-film instability and dry eye disease. This is consistent with the ocular surface system review.
How does the lacrimal function unit work
Reading File
Finding Sources
Finding Sources
Searching PubMed
"lacrimal functional unit" AND "dry eye"
Searching the Web
lacrimal functional unit reflex arc corneal sensory nerves parasympathetic tear secretion review
The lacrimal functional unit works as a protective sensory-reflex system that maintains a stable tear film and healthy ocular surface.
Sequence
-
Ocular surface senses a stimulus
Dryness, wind, smoke, a foreign body, or inflammation stimulates sensory nerve endings in the cornea and conjunctiva. These afferent fibers travel mainly through the trigeminal nerve (CN V). -
Signal is processed centrally
The sensory input reaches lacrimal centers in the brainstem, especially the superior salivatory/lacrimal nucleus. -
Autonomic nerves stimulate secretion
Efferent fibers, predominantly parasympathetic fibers via the facial nerve (CN VII), stimulate the lacrimal gland. Sympathetic fibers also influence gland blood flow and secretion. -
Tear-film components are produced
- Lacrimal glands produce aqueous fluid, electrolytes, proteins, and antimicrobial factors.
- Meibomian glands provide lipid, limiting evaporation.
- Conjunctival goblet cells provide mucins, helping tears spread and adhere to the ocular surface.
-
Blinking spreads tears
The eyelids spread the tear film evenly across the cornea and conjunctiva, creating a smooth optical surface, keeping the cornea hydrated, and clearing debris. -
Tears drain and feedback continues
Excess tears drain through the puncta and nasolacrimal system. Ongoing sensory feedback adjusts tear secretion and blinking to maintain tear-film homeostasis.
In short:
Ocular surface irritation/dryness → trigeminal sensory input → brainstem processing → facial parasympathetic output → tear secretion and blinking.
Ocular surface irritation/dryness → trigeminal sensory input → brainstem processing → facial parasympathetic output → tear secretion and blinking.
Failure of any part of this loop can result in reduced tear secretion, excessive evaporation, tear-film instability, inflammation, and dry eye disease. The neural regulation review describes this trigeminal-parasympathetic reflex, while the ocular surface review explains how its components act together.
This is a shared conversation. Sign in to Orris to start your own chat.