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)