Thermal injuries to the eye are potentially blinding eye injuries and constitute true emergencies. Thermal injuries to the eye are less common than chemical injuries, with very different forms of ocular insult, post-injury problems, and treatment approaches.
Thermal injuries are of importance due to increased occurrence during festival and festivities.
Thermal injuries and Festival/ Festivity in India:
Diwali (Deepavali): Diwali is an important Indian festival celebrated by lighting lamps and bursting crackers. Diwali festival also marks end of month Ashwin and beginning of Kartik month of Indian calendar, and it falls in the month of October or November every year.
Firecrackers are extensively used during festivals and festivities in India. Fireworks are used during celebrations because of sound produced, sparkle and sudden burst of colours. Whenever firecrackers are used, there is always a risk of burn and injury. Crackers also cause noise/ air pollution and may aggravate systemic diseases like bronchial asthma.
The chemicals released by the firecrackers are also harmful. Chemicals in fireworks include sulphur dioxide, lead, cadmium, copper, magnesium, nitrate and nitrite.
Firecrackers release chemical pollutants such as carbon dioxide and carbon monoxide.
Magnesium hydroxide is found in sparklers and flares; the combination of thermal injury and chemical injury accounts for more severe injury than that being produced by either type alone.
Facial burns are a frequent component of thermal injury and ocular involvement may be a part of it in some patients. The lids, especially the margins, are selectively protected from burns. This is because protractor spasm causes orbital and preseptal tissue to overlap and cover the tarsal region. The incidence of lid involvement is increased with more extensive burns. This is especially true when patients are unconscious secondary to an explosion or smoke inhalation and the protective reflexes are not intact. Fortunately, thermal injury is not commonly associated with severe ocular sequelae, courtesy of inherent protective mechanism, such as blink reflex, Bell’s phenomenon, and reflex shielding movements of the head and arms. The loss of an eye primarily from thermal trauma is uncommon and the risk of permanent visual impairment can be minimised with effective timely treatment. Involvement of the eyelids and lid margins is the most frequent ophthalmic manifestation. With thermal injury, eyelid damage leads to necrosis of tissues, eschar formation, and, finally, quantitative loss of tissue. Therefore, the eyelid and conjunctival support system of the cornea is compromised, further embarrassing any corneal or anterior segment pathology. Chronic exposure keratitis is one of the greatest threats to corneal integrity and visual rehabilitation. However, ocular trauma may occur in the absence of eyelid injury and all patients who have been exposed to fumes, heat and smoke warrant comprehensive eye examination.
Direct thermal damage to the cornea produces collagen shrinkage, with prominent stress lines radiating away from the area of greatest injury, especially in case of hot metal contact to the surface. This shrinkage might be severe enough to make the cornea distorted and opaque, leading to steepening of the axis of severest injury. Collagen damage may be so severe as to produce a rapidly excavating corneal ulcer originating from liquefactive necrosis. The post-injury phases of thermal injuries have not been studied as comprehensively as chemical injuries.
When both thermal and chemical injuries occur simultaneously, the terms ‘thermal-alkali injury’ or ‘alkali-thermal injury’ might be used, with the most prominent injurious agent stated first. Thermal injuries associated with acid injuries may be referred to in a similar way.
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Jackson DM. The diagnosis of the depth of burning. Br J Surg 1953; 40: 588- 596.
Ballen PH. Mucous membrane grafts in chemical (lye) burns. Am J Ophthalmol 1963; 55: 302- 312.
Roper- Hall MJ. Thermal and Chemical burns. Trans Ophthalmolo Soc UK 1965; 85: 631- 653.
Goldblatt WS, Finger PT, Perry HD, et al. Hyperthermic treatment of rabbit corneas. Invest Ophthalmol Vis Sci 1989; 30: 1778- 1783.
Dua HS, King AJ, Joseph A. A new classification of ocular surface burns. The British Journal of Ophthalmology 2001; 85 (11): 1379- 1383.
Nema HV, Nema Nitin. Textbook of Ophthalmology. Fifth Edition. Jaypee Brothers Medical Publishers (P) Ltd. 2008. P 360.
Yanoff Myron, Sassani Joseph W. Ocular Pathology. Sixth Edition. Mosby Elsevier 2009. P 152.
Symptoms may include:
In massive thermal burns, patient may require systemic resuscitation.
Thermal injuries result from accidents associated with firework explosion, steam, boiling water, or molten metal. Thermal burns include those caused by a flame, which are usually severe with deep tissue injury, and those caused by flash accidents, such as explosions or electrical arcs, which are usually more superficial but may be extensive. The thermal injury is immediate and non-progressive.
The majority of ocular thermal injuries can be divided into:
The severity of burns depends upon the intensity of the burning agent, both the quantity of heat transmitted by the burning agent and amount of the burning agent, the duration of exposure, use of protective device, body response, any first aid or irrigation of the affected eye.
Most of the flash burns are superficial but may be extensive. In burns due to flames, the period of exposure is longer and it results in deep burns.
Liquid thermal burns vary in severity depending on the substance. Injury due to steam and also due to explosion of liquids on removal from microwave may splash into the eye and cause burns. The temperature of non- combustible liquid like water is usually less on body contact, and such liquids dissipate rapidly from the initial contact area, thereby causing superficial burns only. The temperature of combustible liquids (e.g. petrol), is usually high on contact with the body. These liquids are more viscous and may burn the clothes as well. Therefore, the damage is more localised but may be deep.
The skin is made up of two layers:
These layers cover the subcutaneous tissues and a deeper muscular layer.
Jackson (1953) described three zones of burn:
These three zones of burn are three dimensional, and loss of tissue in the zone of stasis will lead to the wound deepening as well as widening.
Healing process of eyelid thermal injuries:
Re-epithelialisation of wounds occurs from epithelium located at wound edges and skin appendages. In large epithelial defects, granulation tissue bridges the wound before epithelialisation. Wound contraction takes place in second- and third-degree burns and aids in restoring epithelial continuity. The property of wound contraction distorts the eyelids and hampers their function. Owing to the thinness of skin and absence of subcutaneous fat and rich blood supply, the slough on the lid separates early. The raw surface needs to be grafted, if contraction of wound is to be avoided.
Adjacent soft tissue injuries (e.g. cheek, forehead): In adjacent soft tissue injuries, skin contraction displaces the eyelids which might pull the canthus. Injuries affecting lower lid tends to be more severe, due to less available loose skin.
Thermal ocular injury:
The severity of thermal ocular injury is a function of the thermal dose and the surface area of contact. A thermal dose can be defined by a time-temperature relationship. Goldblatt et al. explored the limits of thermal tolerance in animal models, by applying well-defined heat doses (time x temperature) and examined the effects on the tissue. They found that a heat dose of 45˚ celsius resulted in no perceptible damage to the cornea when applied for 15 minutes, and produced mild transient stromal oedema only when applied for 45 minutes.
Higher thermal exposure produced damage with total destruction of cellular elements, massive oedema and stromal disorganisation at a temperature of 59˚ celsius for 45 minutes. This degree of thermal exposure resulted in severe degeneration of all structures and total necrosis at one week.
- Initial phase: Initial phase comprises of tissue destruction.
- An interval reactive phase.
- Period of tissue repair.
Minor thermal injuries are typically limited to the conjunctival epithelium. Migration of peripheral epithelial cells then heals the ulceration with no scarring. Deeper injuries involve the stromal connective tissue and may cause coagulation necrosis. The healing process is prolonged and may result in significant scarring.
Aberrant wound healing may result in a vascularised, hypertrophic scar that mimics a pterygium, but it usually lacks the stromal elastosis as seen in pterygium. This scar may encroach on the corneal surface like a pterygium.
Excessive wound healing may also result in a so-called pyogenic granuloma. This rapidly growing and protruding lesion is histologically defined by vascularised, oedematous granulation tissue with abundance of inflammatory cells.
The lining epithelium may be eroded, and pyogenic granuloma may bleed intermittently.
Patients with ocular thermal trauma should undergo early evaluation of the eye to assess the extent of the injury and exclude the possibility of an intraocular or intraorbital foreign body. The frequency of eye examination must balance the risk of ocular sequelae with the risk of contamination.
Examination of eyelids and adjacent tissues:
Burns are categorised into degrees depending on the depth and extent of injury.
Degrees of burns:
Superficial partial-thickness burns affect epidermis and superficial dermis and results in thin-walled, fluid-filled blisters with a moist red base. The exposure of superficial nerves makes these injuries painful. Burn usually heals spontaneously within two weeks without significant scarring or with minimal scarring only.
Deep partial-thickness burns have a pale white or mottled base beneath the blisters. Healing takes three or more weeks, and is accompanied by scarring and contraction. Deeper second-degree burn leads to scar formation and contracture of wound, producing ectropion. These often necessitate early surgery for contraction and eyelid retraction.
Some advocate full-thickness burns with destruction of underlying muscle, bone and vital structures, separately as deep burns (Fourth-degree burns). Such burns require extensive and complex management and often result in severe contracture and prolonged disability.
Based on degrees and the likelihood of surgery, eyelid burns may be classified as:
Exposure keratitis with or without secondary infection leads to conjunctival and corneal damage producing corneal opacities and, in severe cases, there may be destruction of globe.
Ocular surface examination:
Eyes should be examined under slit lamp (bio-microscopy) by an eye specialist.
Examination of eyes should be done as early as possible since eyelid usually swells and shut the eyes. Most ocular thermal injuries result in superficial burns to the cornea or conjunctiva.
Conjunctiva: Conjunctival oedema, if present, may be due to conjunctival surface burn, mild exposure, or due to fluid resuscitation. Look for any loss of conjunctiva due to burns. Involvement of both palpebral and bulbar conjunctiva may lead to formation of symblepharon (adhesion between palpebral and bulbar conjunctiva).
Cornea: Cornea may be examined under slit lamp after instilling fluorescein dye. Corneal injury is usually secondary to exposure, drying, and infection due to deep eyelid burns.
Initial assessment should note corneal sensation in order to appraise the risk of corneal ulceration from corneal exposure. There may be corneal thinning due to lagophthalmos.
Intraocular pressure monitoring and direct ophthalmoscopy is also required.
Extent of tissue damage is a prognostic indicator of recovery following ocular surface injury. Extent of damage to corneal, limbal, conjunctival tissues and intraocular structures influences the visual outcome and may be classified as:
Classification of ocular surface burns:
Dua (2001) provides a classification of ocular surface burns giving prognosis based on corneal appearance, conjunctival involvement and analogue scale recording the amount of limbal involvement in clock hours of affected limbus/ percentage of conjunctival involvement. The conjunctival involvement should be calculated only for the bulbar conjunctiva, up to and including the conjunctival fornices.
Hughes (1946) classification (modified by Ballen in 1963, Roper- Hall in 1965 and Pfister et al in 1982) provides a prognostic guideline based on corneal appearance and extent of limbal ischaemia. The Roper-hall classification system was introduced in the mid-1960s and is the most established and commonly applied system.
Management should be carried out under medical supervision.
Thermal injuries can be devastating from both functional and psychological aspect to the patient. Complications of injuries may be minimised with prompt and adequate treatment. Barring severe and worst injuries, globe and good vision may be saved in most of the cases. Management is directed towards preserving the eye and vision, maintaining function, and restoration of cosmesis.
Any co-existing systemic inhalational burn injury should be treated.
Management of eyelids:
Immediate management of thermal injuries requires:
For mild first degree burns, cold compresses may be required in cases with significant eyelid swelling and drooping. Eyelid burns with no eyelid contraction may be treated conservatively with an antibiotic ointment.
Second- and third-degree burns with significant retraction causing lagophthalmos may require moist chamber or cellophane occlusion. If surrounding skin is severely burnt, surgical suture tarsorrhaphy may be done. Suture tarsorrhaphy is a temporary measure and may not prevent eyelid retraction. Suture tarsorrhaphy is not a substitute for eyelid repair with skin grafting.
Severe third-degree burns of the eyelids may require surgical relaxing incision over the burn eschar to release the cicatrising ectropion.
If both upper and lower eyelid requires grafting, to maximise the stretched graft bed for each eyelid, grafting is performed at separate times. The lower eyelid is operated first followed by upper eyelid.
Management of complications and sequelae of eyelids: The eyelids are evaluated at a later stage for retraction, tear pump function and cosmetic appearance.
- Eyelid defect involving up to 1/3rd of the eyelid may be closed directly.
- Defects involving 1/3rd to 1/2 of the eyelid may be corrected by Tenzel’s semicircular rotation flap.
- Defects involving more than 1/2 of the lower eyelid may be corrected by modified Hughes procedure (tarsal-conjunctival flap).
- Defects involving more than 1/2 of the upper eyelid may be corrected by sliding tarsal-conjunctival flap (variation of modified Hughes procedure).
- Defects involving entire lower eyelid may be reconstructed by Mustardé cheek rotation flap.
- Large central defects of the upper eyelid may require Cutler- Beard procedure involving full thickness segment of the lower eyelid.
Management of ocular surface:
Preparation for vision restoration: Preparation for vision restoration must begin immediately after the injury. Deliberate and timely treatment determines successful outcomes in the rehabilitative process.
In succession, management consists of emergency treatment, pressure control, suppression of inflammation, enhancing stromal repair, and establishing eyelid-globe congruity during the early days, weeks, and months after the injury.
Topical or oral carbonic anhydrase inhibitors and topical beta blockers continue to form the mainstay of intraocular pressure control. Fibroblast inhibiting mitomycin C may improve the success of filtration surgery for glaucoma. Drainage procedures may be done if one or more filtration surgeries fail.
Operative procedures for ocular surface include amniotic membrane transplant, corneal epithelial stem cell transplants, keratoplasty, large-diameter lamellar keratoplasty, and keratoprosthesis.
Acute and reparative phases:
After irrigation, better outcomes may be expected with prompt re-epithelialisation, while delayed or absent re-epithelialisation may require surgical intervention.
Surgical intervention that may help stabilising the ocular surface in severe thermal injury includes:
Monocular injuries allow for procurement of stem cells from the uninjured eye. When the injury is bilateral, Pfister (1993) showed that allografted limbal tissue was capable of restoring the stem cell population from an unrelated donor. Allografted corneal stem cells must be protected from the recipient immune process by systemic immune-suppression e.g. with cyclosporine.
Success in restorative corneal surgery is governed by:
- Lid-globe congruity with normal blinking and the absence of corneal exposure. Preparatory procedures to lyse symblepharon, expand cul-de-sacs, and to eliminate lagophthalmos are often required to re-establish normal lid functioning.
- Quality and quantity of tear film.
- The presence of epithelial stem cells phenotypic for cornea.
- The absence of any current ulceration, inflammation, and/or uncontrolled glaucoma. Secondary glaucoma must also be controlled with medications or filtration surgery.
- Flawless surgical technique.
- Fresh corneal transplant tissue.
The value of preoperative use of LASER for blood vessels at the limbus in high-risk patients is controversial, but at least it reduces bleeding at the time of surgery.
If corneal surgery is delayed 18 months to 2 years after a burn, it increases the chances of success, especially in the absence of pre-existing ulceration, perforation, or glaucoma.
Penetrating keratoplasty: Penetrating keratoplasty refers to the full- thickness replacement of the affected cornea with a healthy donor. Penetrating keratoplasty may be used to provide tectonic support (such as in corneal thinning and perforation), and to improve visual outcome (such as in the replacement of corneal scarring).
Large-diameter penetrating keratoplasty: Replacement of the entire cornea and adjacent stem cells by large-diameter penetrating keratoplasty may be performed. One potential danger might be that such large transplants might interfere with the trabecular outflow channels and hence increase the likelihood of glaucoma. Proximity to the limbal blood vessels makes an immune rejection more likely.
Large-diameter lamellar keratoplasty: A very promising technique in corneal transplantation for injuries includes the use of 12 or 13 mm lamellar corneal transplants, along with the limbal epithelial stem cell population. Smaller lamellar transplants are useful to fill in deep corneal ulcerations, descemetoceles, or frank corneal perforations.
Indications for keratoprosthesis are:
- Corneas exhibiting exuberant vascularity.
- Repeated failures of fresh transplanted corneal tissue.
- Chronic limbal stem cell deficiency.
- Inability to restore normal lid anatomy.
The operation is usually advised in patients with severe bilateral injuries where serviceable vision is not present in either eye. A surprising degree of success may be achieved with keratoprosthesis. Critical to the visual outcome of a keratoprosthesis is the control of intraocular pressure at all times after the injury. Complications of keratoprosthesis include corneal melt, infection, glaucoma and formation of retro-prosthetic membrane.
The prognosis for severe injury is typically poor and may result in widespread damage to the ocular surface epithelium, cornea and anterior segment. However, in recent years, the prognosis of severe ocular burns has improved, with advances in the understanding of the physiology of the cornea and the resultant development of enhanced medical and surgical treatments. The final visual prognosis is influenced by:
Potential complications and sequelae of thermal injuries to the eye are:
Education and training regarding prevention of exposures in the workplace can help in preventing thermal injuries to the eye.
For general prevention, safety glasses may be used to safeguard eyes. Even these measures may not suffice in high-velocity (explosive) injury.