SEARCH RESULTS FOR: Corneal-Abrasion

Corneal-Abrasion

Corneal Abrasion: Pathogenesis and clinical findings Mechanical Trauma / Foreign Body (fingernail scratch, dust, sand, debris in eyelid) Trichiasis (Misdirected eyelashes directly abrading the ocular surface) ↓ tear production (See Calgary Guide - Dry eye pathogenesis) ↓ quantity or quality of tear film Any condition causing incomplete or inadequate eyelid closureà↑ exposure of eye surface to atmosphere (Bell’s palsy, proptosis/ exophthalmos) ↑ Tear evaporation ↓ lubrication of eye surface Dryness and desiccative damage to ocular surface structures ↓ protective barriers against mechanical or foreign body damage Infection of epithelial defect by pathogens Damage deepens to inner layers of the cornea Immune response causes white blood cells to accumulate Pathogen and immune cells obstruct blood flow, causing tissue necrosis Infectious corneal ulcer Any condition affecting the trigeminal nerve and/or peripheral corneal nerves (e.g. Herpes zoster/simplex infection, diabetes, medications, surgery) Tight lens ↓ O2 reaching cornea Corneal epithelium hypoxiaà cellular damage Contact Lens use Extended use Lens dehydrates Corneal epithelium adheres to lens and is removed with the lens Neurotrophic keratopathy (corneal damage secondary to loss of innervation) ↓ stimulation of the cornea by neurotransmitters (complex and multifactorial) ↓ Blinking (if bilateral) Area of defect stained bright green under cobalt-blue filtered light Impaired sensory innervation of the corneaàImpaired Reflex Tearing ↓ adhesion between corneal epithelium and Bowman’s layer Trauma from insertion or removal of contact lens Previous traumatic abrasion with damage to Bowman’s layer or inadequate epithelial adherence (e.g. corneal dystrophy) Spontaneous erosion (occurs without antecedent injury or foreign body) ↓ structural integrity of corneal epithelium Fluorescein dyes the exposed Bowman’s layer (inner corneal layer between epithelium and stroma) Corneal Epithelial Damage (the transparent portion of the eye that covers the anterior portion of the eye and covers the pupil iris and anterior chamber) Corneal Abrasion: Focal area of epithelial loss - outermost layer of cornea (damage may extend to the bowman's layer below as well) Abrasions that overlay the pupil Epithelium (outermost portion on cornea) Bowman’s layer Stroma Descemet’s membrane Endothelium Cornea (cross section) Layers of the cornea Concurrent damage to other anterior segment structures in trauma Can induce traumatic uveitis Irritation and spasms of the iris/ciliary body muscle complex Light stimulus induces further movement of irritated/inflamed structures Damaged tissues & ensuing inflammatory responseà Inflammatory mediator release Conjunctival injection (vasodilation of vessels in the conjunctiva) Red eye Damage to corneal nerves stimulates corneal nociceptors Pain/ Foreign body sensation prevent light entry through the pupil Acute vision loss Hyperalgesia (lowered peripheral nerve threshold for firing while damaged tissues are healing, during which normally non- noxious stimuli like light, wind or temperature change - can induce pain) Nociceptors stimulate afferent neurons in trigeminal nerve, which then activates efferent neurons in the facial nerve Stimulation of the lacrimal gland Tearing Anterior chamber of the eye Photophobia (Light sensitivity or light-induced pain/ discomfort) – Pathophysiology is complex and multifactorial Authors: Yejun Hong, Davis Maclean Reviewers: Mehul Gupta, Adam Muzychuk*, Victor Penner*, Yan Yu* *MD at time of publication Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published July 19, 2021 on www.thecalgaryguide.com