Post on 23-Aug-2014
description
CHEMICAL BURNS
PRESENTER -DR RAHULMODERATOR -DR SANGIT
OCULAR BURNSOcular burns constitute true ocular
emergencies
Both thermal and chemical burns represent potentially blinding ocular injuries
Thermal burns result from accidents associated with
-firework explosions- steam- boiling water -molten metal (commonly aluminium)
Chemical burnsChemical burns may be caused by either
alkaline or acidic agents
Alkali more frequently used in household cleaning agents and many building materials
So Alkali injuries occurs more frequently than acid injuries
Causes
Common sources of alkali are as follows:Cleaning products (eg .ammonia) most
serious injuryFertilizers (eg, ammonia)
Cement, plaster, (eg, lime)most common injury
Fireworks (eg, magnesium hydroxide)
PathophysiologyAlkaline agents have both hydrophilic and
lipophilic properties
which allow them to rapidly penetrate cell membranes and enter the anterior chamber
Alkali damage results from interaction of the hydroxyl ions
Pathophysiology
It causes saponification of cell membranes and cell death along with disruption of the extracellular matrix
Cations react with carboxyl group of stromal collagen
And Glycosaminoglycans (GAGS)
Hydration of Gagas result in loss of clarity of stroma
Increased IOP:
collagen deformation and shortening
distorts trabecular meshwork
An immediate rise in IOP
Pathophysiology
Penetration into AC may be almost immediately after ammonia
Within 3-5 min after sodium hydroxide injury
Penetration into ACDamage to ciliary body
epithelium
Decreased secretion of ascorbate
Concentration in AC decreases
stromal repair and collagen synthesis
decreases
Acid injury
Common sources of acids are as follows:
Battery acid (eg, sulfuric acid)
Bleach (eg, sulfurous acid)
Glass polish (eg, hydrofluoric; )
PathophysiologyAcids tend to cause less damage than alkalis
corneal proteins bind acid and act as a chemical buffer.
coagulated tissue acts as a barrier to further penetration of acid.
Acid binds to collagen and causes fibril shrinkage which can cause symblepharon formation
ClassificationThere is no ideal classification or grading
system for ocular alkali burns
The principal weakness of grading system is that injuries to the cornea are not uniformly associated with injuries to the surrounding tissues
Classification of severity of ocular surface burns by Roper-Hall
Grade prognosis cornea limbus
1 good Corneal epithelial damage
No limbal ischaemia
2 good Corneal haze, iris details seen
<1/3 limbal ischaemia
3 guarded Total epithelial loss,stromal haze,iris details obscured
1/3-1/2 limbal ischaemia
4 poor Cornea opaque,iris and pupil obscured
>1/2 limbal ischaemia
Grade Prognosis Clinical findings
Conjunctival involvement
Analogue scale
1 Very good 0 clock hours of limbal involvement
0% 0/0%
2 good <3 clock hours of limbal involvement
<30% 0.1-3/1-29.9%
3 good >3-6 clock hours of limbal involvement
>30-50% 3.1-6/31-50%
4 Good to guarded
>6-9 clock hours of limbal involvement
>50-75% 6.1-9/51-75%
5 Guarded to poor
> 9-<12 clock hours of limbal involvement
>75-<100% 9.1-11.9/75.1-99.9%
6 Very poor Total limbus (12 clock )involved
Total conjunctiva
12/100%
Clinical stagesThe clinical course can be divided into three
distinct stagesI )Acute stage (immediate to 1 week)
II) Early repair stage (1-3week)
III) Late repair stage and sequel ( 3 weeks andlonger )
I )Acute stage (immediate to 1 week)
In mild burns the corneal and conjunctival epithelium
have defects with sparing of limbal blood vessels
in severe burns the epithelium is destroyed and there is immediate limbal ischaemia due to damage to blood vessels.
intraocular pressure
Rise in intraocular pressure in a bimodal manner
An initial peak is due to compression of the globe as a result of hydration and longitudinal shortening of collagen fibrils.
The second peak due to impedence of aqueous humor outflow
II Early repair stage (1-3week):
This stage is characterized by replacement of destroyed cells and extracellular matrix.
In grade I and II chemical burns - regeneration of epithelium -neovascularization of cornea-clearing of stroma -beginning of synthesis of collagen
glycosaminoglycans
In grade III and IV - regeneration of epithelium may not start and
progress
- stroma remains hazy
- endothelium replaced by a retrocorneal membrane.
Cont..In this stage, corneal ulceration tends to
occur.
Stromal ulceration is due to action of digestive enzymes such as collagenase,metalloprotinase
released from regenerating corneal epithelium and polymorphonuclear leukocytes.
III Late repair stage and sequele ( 3 weeks and longer )This stage is characterized by completion of
healing
with a good prognosis (grade I and II )
complication in those with a guarded visual prognosis
(grade III and IV)
Complications are primary and secondary
Complications
Primary complications Conjunctival inflammationCorneal abrasionsCorneal haze and edemaAcute rise in IOPCorneal melting and perforations
Secondary complicationsSecondary glaucomaSecondary cataractConjunctival scarringCorneal thinning and perforationComplete ocular surface disruption with
corneal scarring and vascularizationCorneal ulceration (sterile or infectious)Complete globe atrophy (phthisis bulbi):
Clinical case4 yr boy presented to LEI with h/o plaster
falling into eyes while playing at construction site
Eye wash given
History
Most often, the patient gives a history of a liquid or a gas being splashed or sprayed into the eyes or of particles falling into the eyes.
we have to ask the patient regarding the specific nature of the chemical and the mechanism of injury (eg, simple splash vs high-velocity blast).
Physical examination
A thorough physical examination should be deferred until the affected eye is irrigated copiously
The pH of the ocular surface is neutralized.
Topical anesthetic drops may be used to aid in patient comfort and cooperation.
Cont..After irrigation, a thorough eye examination
is performed
special attention given to- clarity and integrity of the cornea-degree of limbal ischemia- IOP.
Physical manifestations
Decreased visual acuity: It can be decreased because of -corneal epithelial defects,-haze, -increased lacrimation or discomfort.
Particles in the conjunctival fornices
- This finding is more common with particulate injuries, such as plaster.
- If not removed the residual particles can serve as a reservoir for continued chemical release and injury.
-These particles must be removed before ocular surface healing can begin
Perilimbal ischemia:
-The degree of limbal ischemia (blanching)is the most significant prognostic indicator for future corneal healing
-The limbal stem cells are responsible for repopulating the corneal epithelium.
-The greater the extent of blanching, the worse the prognosis.
Cont..But, the presence of intact perilimbal stem
cells does not guarantee normal epithelial healing.
The extent of blanching should be documented in terms of clock hours involved
Corneal epithelial defect
It can range from mild diffuse punctate
epithelial keratitis (PEK) to a complete epithelial defect.
A complete epithelial defect may not take up fluorescein dye rapidly , so, it may be missed.
Cont..If an epithelial defect is suspected but not
found on the initial evaluation, the eye should be reexamined after several minutes.
The size of the defect should be recorded so as to document response to treatment on subsequent visits
Stromal haze:
Haze can range from a clear cornea (grade 0) to a complete opacification (grade 5) with no view into the anterior chamber.
Corneal perforation: A very rare finding at presentationit is more likely to occur after the initial
presentation (from days to weeks) in severely injured eyes that have poor healing capacity.
A. c inflammatory reaction
This can vary from trace cell and flare to a vigorous fibrinoid anterior chamber reaction.
Generally, this finding is more common with alkaline injuries because of the greater depth of penetration
Adnexal damage/scarring:
Similar to chemical injuries on other skin areas, it can lead to severe exposure problems
eyelid scarring prevents proper closure, exposing an already damaged ocular surface
Medical Care
Regardless of the underlying chemical involved, common goals of management include
(1)removing the offending agent, (2) promoting ocular surface healing(3) controlling inflammation, (4) preventing infection, (5) controlling IOP.
Immediate therapy
Immediate copious irrigation remains the single most important therapy for treating chemical injuries.
Ideally, the eye should be irrigated with a sterile balanced buffered solution, such as normal saline solution or Ringer's lactate solution.
However, immediate irrigation with even plain tap water is preferred without waiting for the ideal fluid.
The irrigation solution must contact the ocular surface.
This is best achieved with a special irrigating tubing (eg, Morgan lens) or a lid speculum.
Irrigation should be continued until the pH of the ocular surface is neutralized, usually requiring 1-2 liters of fluid.
artificial tear supplements play an important role in healing.
Ascorbate plays a fundamental role in collagen remodeling, leading to an improvement in corneal healing.
Placement of a therapeutic bandage contact lens helpful in some patients.
Control inflammation
Inflammatory mediators released from the ocular surface at the time of injury cause tissue necrosis
This inflammatory response not only inhibits reepithelialization but also increases the risk of corneal ulceration and perforation.
Controlling inflammation with topical steroids can help break this inflammatory cycle.
.
Citrate both promotes corneal wound healing and inhibits PMNs via calcium chelation.
Acetylcysteine (10% or 20%) can inhibit collagenase to reduce corneal ulceration
Prevent infection
When the corneal epithelium is absent, the eye is susceptible to infection.
Prophylactic topical antibiotics are warranted during the initial treatment stages.
Control IOPThe use of aqueous suppressants is
advocated to reduce IOP secondary to chemical injuries
both as an initial therapy and during the later recovery phase, if IOP is high (>30 mm Hg)
Carbonic anhydrase inhibitorsTopical beta-blockers
Control painSevere chemical burns can be extremely
painful.
Ciliary spasm can be managed with the use of cycloplegic agents
however, oral pain medication may be necessary initially to control pain
Cycloplegic mydriatics
Surgical therapy
A)Promote Reepithelialization
B)Support repair and minimize ulceration
C)Late rehabilitation
A)Promote Reepithelialization
1)Conjunctival /tenons advancement (tenoplasty)
2)Limbal stem cell transplantation
3)Conjunctival transplantaion
4)keratoepithelioplasty
B)Support repair and minimize ulceration
1)Tenoplasty
2)Limbal stem cell transplantation
3)Large diameter therapeutic pk
4)Tissue adhesive
C)Late rehabilitation
1)Late stem cell transplantation
2)Conjunctival transplantation
3)Mucosal membrane grafts
4)PK
Prevention
Education and training regarding the prevention of chemical exposures in the workplace can help prevent chemical injuries to the eye.
Persons who may be exposed to chemicals in the workplace are advised to wear safety goggles.
Patient Education
If the injury resulted from a preventable accident, proper safety instruction should be provided.
If a patient is left functionally monocular from an injury, the patient should be instructed in the use of safety eyewear (eg, polycarbonate lens)