Corneal Injury is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye’s total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. The cornea can be reshaped by surgical procedures such as LASIK.[rx]
Classification of Mechanical Ocular Injuries
Based on the injury to the eyewall(outer fibrous coat of the eye consisting of cornea and sclera)
- Closed globe injury- The eye globe is intact, but the seven rings of the eye have been classically described as affected by blunt trauma.Types include:1) Contusion 2)Lamellar Laceration
- Open globe injury – There is a full thickness injury of the eye wall(cornea and sclera)
A) Globe rupture:caused by blunt trauma and is an inside-out injury.
B) Globe laceration:It is full-thickness wound caused by sharp objects. It includes
1)Penetrating trauma:The globe integrity is disrupted by a full-thickness entry wound and may be associated with prolapse of the internal contents of the eye. Such injuries are often referred to as a Globe fracture or a Globe rupture, although these can be incurred by blunt trauma as well.
2) Perforating trauma: The globe integrity is disrupted in two places due to an entrance and exit wound (through and through injury). This is a quite severe type of eye injury.
Other types include
- Blowout fracture of the orbit is caused by blunt trauma, classically described for fist or ball injury, leading to fracture of the floor or medial wall of the orbit due to sudden increased pressure on the orbital contents.
- Muscular Entrapment Fracture of the orbital bones can lead to muscular entrapment limiting gaze in one direction.
Approximately 3% of all visits to the emergency department are due to eye trauma, with the vast majority of these presentations involving corneal injury. The morbidity from corneal injuries can vary greatly, from minor and insignificant to potentially vision-threatening. Injuries to the cornea can broadly be categorized into traumatic and exposure related. Traumatic injuries most commonly include corneal abrasions and foreign bodies. Exposure-related injuries to the cornea include burns from chemical, thermal, and radiation sources.
Abrasion and Foreign Body
Corneal abrasions may be caused by any number of objects including fingernails, contact lens wear, branches, foreign objects blown into the eyes, or objects that drop into the eye while working overhead.
Cases of corneal laceration and perforation typically involve activities that cause high-speed projectiles such as saws, grinders, and pounding metal objects.
Exposure-related burns of the eye can be categorized into chemical (acid and alkali burns), radiation burns from ultraviolet (UV) sources, and thermal burns. Alkali corneal injuries are more common than acid due to the prevalence of household cleaning agents containing ammonia and lye. Acidic burns are typically work-related injuries involving industrial processes. Radiation burns result in ultraviolet keratitis from tanning beds, high-altitude environments, welding arcs, and the occasional solar eclipse. Thermal burns are distinctly uncommon but can occur with objects such as curling irons and with fire-related injuries.
Eye trauma accounts for about 3% of all emergency department visits, with approximately 80% of these visits for corneal abrasions or foreign bodies. The incidence of corneal abrasion is higher among people of working age, with automotive workers between the ages of 20 and 29 years having the highest incidence of eye injuries.
Ocular burns represent 7% to 18% of the eye injuries seen in the emergency department, with 84% of burns due to chemicals. Alkali burns are up to four times as prevalent as acid burns according to some studies.
Fragile and easily damaged, the corneal epithelium is richly innervated, and therefore, very painful when an injury occurs. The epithelium does regenerate quickly, with most abrasions healing within 1 to 2 days. Ocular burns can result in significant corneal injury and permanent scarring. The duration of exposure and the causative agent are directly correlated with the severity of an ocular burn. Exposure to strong alkaline chemicals produces liquefactive necrosis that penetrates and dissolves tissues until the alkaline agent is removed. Acid burns cause a coagulation necrosis that tends to be less severe than alkali burns due to the precipitation of tissue proteins that act as a barrier to further tissue penetration. UV light exposure causes direct corneal epithelial damage but is typically self-limiting.
History and Physical
Pain from injury to the cornea may be delayed for several hours after the inciting event, and often, the patient does not know the mechanism of injury. Practitioners should ask about the work environment and specifically, the use of high-speed machinery and metalworking, as these injuries are frequently associated with corneal laceration and perforation of the globe. A history of eye pain that occurs after hammering metal on metal suggests a metal projectile as the cause of the ocular injury, and the possibility of globe rupture should be thoroughly investigated in this setting. For ocular burns, it is important to identify the chemical(s) the eye was exposed to, as this can impact treatment and prognosis.
Corneal Abrasion and Laceration/Perforation
Conjunctival erythema, lid swelling, tearing, and blepharospasm can be seen upon eye inspection. The corneal defect can often be seen under the magnification even without the use of fluorescein. With severe pain, treatment with a topical anesthetic may be needed to obtain a complete physical exam. Relief of pain with the application of a topical anesthetic such as proparacaine strongly suggests a superficial (corneal) etiology of ocular pain. Visual acuity should be considered the vital sign of the eye and be determined in every patient with an ocular complaint. Acuity should be assessed while the patient is wearing any corrective lenses should they have them and is typically normal in the setting of corneal abrasions unless there is an associated iritis or corneal defect in the central visual axis. Instillation of fluorescein and examination with a cobalt blue light will demonstrate the corneal abrasion as a bright green, superficial defect of the cornea.[rx]
Signs that suggest a full-thickness corneal laceration or perforation include a misshapen iris, hyphema, microhyphema, decreased visual acuity, and a shallow anterior chamber. Aqueous humor leaking from the anterior chamber during fluorescein examination suggests a corneal perforation (Seidel’s test). Although, for small lacerations, it is possible for the Seidel test to be negative with grossly normal appearing eye anatomy. The entire thickness of the cornea should be evaluated with a slit lamp. A high index of suspicion for globe penetration should be maintained and a CT of the orbit should be obtained when the history or physical examination suggests the possibility of such an injury. While fairly accurate, CT is an imperfect diagnostic test; ophthalmology consultation is recommended for situations where there is a very high index of suspicion even when the orbital CT is unremarkable.
Corneal Foreign Bodies
Similar to corneal abrasions, patients usually complain of pain with foreign body sensation, tearing, and blepharospasm. Application of a topical anesthetic improves physical examination and diagnosis may be aided by the use of a slit lamp. Ocular foreign bodies may lodge under the upper eyelid and cause repeated abrasions to the cornea whenever the patient blinks. The resulting corneal injury can have the appearance of numerous linear or curvilinear abrasions of the cornea which has been described as the “ice-rink sign”. The upper eyelid should, therefore, be everted and examined for foreign bodies when a corneal or conjunctival foreign body is suspected or in the presence of the ice rink sign. In the setting of a metallic foreign body, a rust ring will generally form in the surrounding cornea within several hours.
Chemical burns to the eye are a real ocular emergency with scarring and permanent loss of vision and the eye being a possibility. Irrigation of the eyes must be done immediately, before any evaluation or examination, including testing of vision. Once completed, the visual acuity should be documented and intraocular pressure measured. Patients with radiation burns and photokeratitis are typically in severe pain and discomfort. In addition to decreased visual acuity, tearing, and chemosis of the conjunctiva, instillation of fluorescein reveals a characteristic superficial punctate staining of the cornea.
Treatment / Management
The majority of corneal abrasions heal spontaneously, so treatment consists primarily of pain control and preventing infection. For abrasions greater than 2 mm, or for those that are very painful, a cycloplegic agent such as cyclopentolate 1% or homatropine 5% can help control discomfort by relaxing the ciliary body and relieving pain from spasm. The cycloplegia of both these agents lasts approximately 24 hours.
The majority of corneal abrasions heal spontaneously, so treatment consists primarily of pain control and preventing infection. For abrasions greater than 2 mm, or for those that are very painful, a cycloplegic agent such as cyclopentolate 1% or homatropine 5% can help control discomfort by relaxing the ciliary body and relieving pain from spasm. The cycloplegia of both these agents lasts approximately 24 hours, so a single administration at the time of care should be adequate given the rapidity of corneal healing. Homatropine may cause cycloplegia for up to 72 hours and is therefore recommended for large abrasions that may take more than 24 hours to heal. A topical nonsteroidal anti-inflammatory agent such as ketorolac 0.5% has been shown to reduce pain as well. Topical anesthetics should never be prescribed for home use as they can inhibit corneal healing, impair the protective blinking reflex, and prolong identification of the progression of the ocular pathology or development of complications.
In cases not related to contact lens wear, erythromycin ophthalmic ointment is a suitable antibiotic, but for contact lens wearers antipseudomonal coverage is needed. A fluoroquinolone such as ciprofloxacin or ofloxacin will provide adequate antibiotic prophylaxis. Tetanus prophylaxis should be administered if necessary. Patients should be counseled to not wear contacts until the abrasion has healed completely. Patients with corneal abrasions should be reevaluated within 24 to 48 hours to assure complete resolution of the injury.
Unrecognized corneal perforations can quickly result in endophthalmitis or traumatic cataract. These should be treated similarly to scleral (globe) rupture with the placement of a protective eye shield to prevent accidental pressure on the globe and broad-spectrum intravenous antibiotics to cover common organisms that cause post-traumatic endophthalmitis. A third-generation cephalosporin, gentamycin, and vancomycin would be appropriate.
Corneal Foreign Bodies
Corneal foreign bodies should be removed at the time of diagnosis, preferably under slit lamp magnification, after anesthesia has been achieved with a topical agent such as proparacaine 0.5%. A cotton applicator may occasionally be effective in removing a foreign body but a sterile needle or eye spud may be necessary. Residual rust ring removal can be performed similarly or be deferred for removal by an ophthalmologist the following day. Scarring can occur with rust removal so care should be exercised with rust in the central visual axis and consideration given to referral to an ophthalmologist for removal. If there is any possibility that the foreign body penetrated the entire length of the cornea, the injury should be treated as a globe perforation as described above.
Following removal of the foreign body, the treatment of the remaining corneal defect should be as described above in the discussion of corneal abrasion management.
Treatment of chemical corneal burns should begin at the scene of the injury with copious irrigation with water for at least thirty minutes and continue upon arrival to the hospital. Use of irrigation devices, such as a Morgan Lens, is helpful in delivering continuous irrigation to the affected eye. If available, buffered eyewash solutions may be better for irrigation of caustic exposures than standard normal saline. After irrigation of one to two liters, the pH should be tested with litmus paper. Irrigation should be continued until the pH remains neutral for at least 30 minutes after the last irrigation. Ophthalmology consultation should be obtained for all but minor burns. Any patient with corneal clouding or an epithelial defect should be promptly referred to an ophthalmologist.
Treatment of radiation burns (ultraviolet keratitis) is supportive with pain control and topical antibiotics, although there is minimal evidence for the latter. Oral opioids are typically needed. Generally a self-limiting condition, ophthalmology follow up in 24 hours is needed if symptoms have not resolved. Patients should be counseled on the adverse effects of ultraviolet radiation including cataract formation, pterygium, and skin cancer.
[bg_collapse view=”button-orange” color=”#4a4949″ expand_text=”Show More” collapse_text=”Show Less” ]