DIS - Eye Trauma III: Chemical - Week 8 Flashcards
Where do majority of chemical eye injuries occur?
At work
Do chemical injuries tend to be urgentocular emergencies or are they self-limiting?
Are urgent
What improves visual prognosis with chemical injuries?
Immediate irrigation
List 6 factors that affect the severity of a chemical ocular injury.
Nature of the chemical Concentration pH Volume Duration of exposure How quickly treatment is initiated
What is the main group of chemicals that causes damage? List three others.
Alkali (80%)
Acids
Surfactants
Aerosols
List two common acids that can cause injury.
Sulphuric acid
Hydrochloric acid
List 4 common alkalis that can cause injury. List some common items these chemicals are found in.
Ammonia -household leaning agents -fertilisers -refrigerants Lye -drain/oven cleaners -airbags Magnesium hydroxide -firework sparklers -flares Lime -plaster -mortar -cement -whitewash
What are three common sources of chemicals that cause injury?
Household cleaning products -especially bleach Personal care products -especially hair products Car products -especially battery acid
List four things that affect the severity of a burn with acids.
Concentration
Duration of exposure
pH
Protein affinity of acid anion
What happens when an acid reacts with the anterior cornea? Does it commonly reach the anterior chamber?
Binds with tissue protein and coagulates the corneal epithelium
Proteins precipitate in the anterior cornea
Forms a barrier to further penetration
Rarely reaches the anterior chamber
Do organic acids have strong or minimal penetration of the cornea? Do they often cause severe or mild symptoms?
Minimal
-mild symptoms
Which penetrates tissue quicker, alkali or acids?
Alkali
Above what pH are alkalis exceedingly dangerous?
> 11
What does the amount of damage from an alkali burn depend on?
Fat solubility
What common household product has a strong ability to dissolve fat?
Ammonium hydroxide
What effect do alkalis have on collagen?
Destroys them
What is often seen with alkali burns of the eye?
Initial appearance can be decieving
May be worse with time
Can alkalis penetrate into the anterior chamber?
Yes
What is the major ingredient in cement and lime that can result in alkali burns? Does this account for many or few causes of chemical injury? Are they serious?
Calcium oxide in the major ingredient
Lime burns are very serious and one of the most common causes
List the three main groups of detergents. Note the charge for each.
Cationic - positive
Anionic - negative
Non-ionic - neutral
What effect do cationic detergents generally have on the eye? What about when severe?
Precipitates proteins of the cornea and conjunctiva
If severe, corneal opacification and vascularisation
What effect do anionic detergents generally have on the eye?
Heals quickly with no permanent damage
What effect do non-ionic detergents generally have on the eye?
Can produce corneal erosion, but heals without scarring
What effect do surfactants and solvents generally have on the eye (4)?
Persistent corneal epithelial defects
Stromal oedema
Endothelial cell loss
Subepithelial plaques
List 8 signs and symptoms of chemical injury due to aerosols.
Hyperaemia Swelling Blepharospasm Lacrimation Pain SPK Cornea/conj sloughing off Corneal oedema
What is the principle ingredient of capsicum sprays? What are the signs/symptoms (5)?
Oleoresin capsicum Signs and symptoms as in aerosols with the addition of: Total epithelial defect Conjunctival chemosis and necrosis Stromal oedema Symblepharon
List 8 general signs and symptoms of chemical ocular injury.
Hyperaemia Haemorrhage -conjunctival -periorbital Lacrimation Photophobia Pain -can cause damage to the extent of no pain FB sensation Reduced vision Concurrent trauma
What is the immediate management of a chemical injury?
Immediate and prolonged irrigation of the eye with sterile saline/water for 30 minutes or until neutral with litmus paper
How long can alkali injuries take to turn neutral?
Up to 2 hours
What part of the eye should be used to assess pH?
Tears
Should eyes with chemical injury be padded?
no
Once immediate care is given, how should severe chemical injury be managed?
Refer grades 3 and 4 for ophthalmological care
Consider less severe grades of chemical injury. How should they be worked up and managed once immediate care has been given (5)?
After 30 mins of irrigation, use topical anaesthesia
Measure VA
Slit lamp exam
Evert upper lids
Remove particles/crystalline matter and necrotic tissue
-cotton bud soaked in anaesthetic
NaFl stain
What two things should you look for when working up a chemical injury?
Limbal ischaemia
AC reaction
Describe grade 1 chemical injury (2). Note the prognosis.
Clear cornea
No limbal ischaemia
Excellent prognosis
Describe grade 2 chemical injury (2). Note the prognosis.
Cornea hazy, but iris details visible
Limbal ischaemia >1/3
Good prognosis
Describe grade 3 chemical injury (2). Note the prognosis.
No iris details
Limbal ischaemia 1/3 to 1/2
Guarded prognosis
Describe grade 4 chemical injury (2). Note the prognosis.
Opaque cornea
Limbal ischaemia >1/2
Very poor prognosis
What are injuries of grade 1 chemical injury confined to?
Corneal epithelium
What may occur when grade 2 chemical injury resolves (3)?
Cornea may develop focal haze and neovascularisaion at the site of limbal stem cell loss
What is the focus of management of chemical injury (2)?
Reepithelialisation
Reduction of inflammation
Why is limbal ischaemia important in chemical injury? What clinical presentation regarding this should you be wary of?
Stem cells that renew the corneal epithelium are located exclusively in the limbal region
Loss or malfunction disrupts epithelial maintenance
Beware the very white eye
List 10 treatment options for grade 1 and 2 chemical injury. Note dosages where appropriate.
Prophylaxis -chlorsig/tetracycline qid Cycloplegia -for pain, qid Analgaesia as appropriate -ibuprofen Artifical tears q1h -to aid reepithelialisation Topical steroids for more severe damage -use for AC reaction q2h Manage IOP -timolol bid when needed Adjunct therapy -mostly for grade 3 to 4 Sodium citrate 4g po Sodium ascorbate 500mg po Tetracycline/acetylcysteine
What is an acceptable IOP for chemical injury and what should be used when needed?
Accept ~30mmHg for 24h
-else use timolol 0.5% bid
What grades are adjunct therapy typically used for?
Grade 3 or 4
How does sodium citrate aid in chemical injury treatment (2)?
Inhibits infiltration and activation of PMNs reducing inflammation and degradation
Also inhibits corneal collagenases
How does sodium ascorbate aid in chemical injury treatment (2)?
Promotes collagen synthesis
-reduces loss of stroma
How does tetracycline/acetylcysteine aid in chemical injury treatment (2)?
Inhibits MMP by binding to Zn2+ in collagenase
Prevents stromal degradation
What should the follow-up of chemical injury be?
Daily until epithelium is healed
What are five later referrals that could be made for chemical injury?
Division of scarring adhesions of the conjunctiva
Conjunctival graft
Amniotic membrane graft to aid conjunctival and corneal reepithelialisation
Limbal stem cell graft to provide new corneal epithelium
Penetrating keratoplasty
Does an amniotic membrane graft replace stem cells?
No
