Mechanical injuries range from superficial abrasions to complete disruption of the globe depending on the nature of the force striking the eye. Small, sharp, fast-moving objects can penetrate or lacerate the globe, whereas larger objects may exert enough compressive force to cause contusion injury or to rupture the eyeball.
Lid lacerations result from two common mechanisms: (1) contact with sharp, fast-moving objects such as glass or metal parts that cut the skin and subcutaneous tissues (partial-thickness lacerations) or involve the posterior layers, the tarsus, and the conjunctiva (full-thickness lacerations) and (2) avulsion injuries that are caused by blunt trauma (eg, a blow to the malar eminence) and cause abrupt traction of the lid and tear it from its attachment to the medial canthal ligament. The type and extent of injury determine the method of treatment.
Partial-thickness lacerations can be closed by direct suturing with generally good results. Full-thickness lacerations require meticulous repair in two layers by an ophthalmic or oculofacial plastic surgeon to accurately restore the continuity of the lid margin. If notching of the margin occurs with healing, the cornea may not be moistened adequately by tears and protected from abrasions and other trauma. Deep stab wounds above the upper lid may sever the levator muscle of the lid. The cut end of the levator is easier to retrieve and repair if surgery is performed immediately after injury. Inadequate repair can result in chronic ptosis. Severe damage to the upper lid and blinking mechanism also can place the patient at risk for superficial corneal injuries.
In avulsion injuries, lid structures that have pulled away from the globe should be examined carefully and placed as close to their anatomic positions as possible to protect the eye while the patient is awaiting treatment by an ophthalmic surgeon. Retention of avulsed lid structures is important. They frequently can be repaired and usually heal well because of their rich blood supply. It is difficult to substitute skin grafts or skin flaps for the normal lid structures, particularly the tarsal and conjunctival structures that are essential for normal functioning of the lid. Avulsion of the medial canthal ligament sometimes disrupts the lacrimal drainage system, and failure to repair it will result in epiphora (the overflow of tears).
Injuries to the iris can be caused indirectly by contusion and directly by perforating or penetrating injuries of the eye.
Contusion of the globe transmits force to the iris by the rapid displacement of aqueous humor. Because water is incompressible and the eye is essentially inelastic, these forces can be very large and destructive.
Iridoplegia is caused by damage to the pupillary sphincter. The pupil may react to light either directly or consensually and only slightly or not at all. The iris root, where it attaches to the ciliary body, may be torn, producing an iridodialysis. Sometimes the ciliary body with the iris root intact is torn away from its scleral attachment, producing an angle recession that can damage the aqueous outflow, causing a form of glaucoma.
Penetrating injuries, foreign bodies, stab wounds, corneal lacerations, and ruptured globes all may perforate, tear, or disrupt the iris. Iris tissue frequently herniates through corneal or scleral wounds.
Iris injuries usually do not require treatment other than incidental repair of the associated major injuries. Except for an increase in the amount of light entering an eye, it may have quite useful vision without an iris or with an iris with multiple holes. An eye with more than one pupil still sees only one image.
Retinal injuries are caused by both blunt trauma (contusion) and penetrating wounds. When the eye is struck in a contusion injury, the force is transmitted by the fluid contents throughout the interior of the globe. Posteriorly, the retina may become edematous in a discrete area, frequently including the macula—a condition called commotio retinae or Berlin edema. Vision is reduced but may improve to nearly normal when the edema clears. This process may require several weeks to a month to complete. Contusion injuries also cause forceful displacement of the vitreous, resulting in traction at its anterior attachment on the surface of the retina at the posterior edge of the ciliary body. This may disinsert the retina from the ciliary body or tear a hole in the peripheral retina. Hemorrhage may result, clouding the vitreous for a time.
Retinal tears or holes frequently cause retinal detachments, which require prompt surgical repair. Visual prognosis depends on macular involvement. If the macula is intact, vision is usually good; if the macula is detached for even a few days, the prognosis is apt to be poor. Penetrating injuries cause direct perforations and tears in the retina, causing hemorrhage and detachments. Treatment of retinal detachments requires localization and closure of the tears or holes. This is done by creating an adhesion and scar between the retina and the choroid surrounding the hole. A freezing probe placed on the scleral surface over the hole will cause an inflammatory reaction in the choroid that will adhere to the retina. Sometimes it is necessary to bring the scleral, choroidal, and retinal surfaces together. Usually this is done by placing an encircling band of silicone rubber around the entire globe; it also may be done by pushing them together from the inside by injecting a gas bubble into the vitreous space.
Ruptured or Lacerated Globe
If a ruptured or lacerated globe is present or suspected, placing a metal shield or other protective covering (eg, the bottom half of a paper cup) over the injured eye will prevent external pressure from causing further damage during transport to the hospital. Patching the other eye will reduce ocular movements and thus help to prevent further trauma to the injured eye.
Visual acuity should be measured and recorded. Severe injuries almost always are associated with some degree of visual loss, lid swelling, orbital swelling, exophthalmos, and hemorrhage. If lid swelling is extreme, it may be necessary to use a sterile topical anesthetic and lid retractors to lift the lids away from the globe during initial examination.
If the cornea is clear and the pupil is round and reacts to light, the globe probably is intact. Global rupture usually is characterized by the presence of brownish or grayish tissue beneath the conjunctiva (subconjunctival hemorrhage), which is caused by exposure or herniation of uveal tissue, an irregular or disrupted corneal surface, or the presence of blood or gross alteration in the appearance of the iris and pupil. Pupillary light reflexes may be abnormal. The pupil pulled or peaked toward one side of the cornea usually indicates that the iris has herniated through a laceration in that direction.
Ophthalmoscopic examination may be difficult because of corneal irregularities and hemorrhage in the anterior chamber and vitreous. If the fundus can be examined and the disc and vessels appear relatively normal, gross disruption of the globe is unlikely. A bright red reflex usually indicates that the interior of the globe is intact. Intraocular pressure should not be measured if a ruptured or lacerated globe is suspected. A radiograph for detection of any radiopaque material in the region of the globe is an essential part of the initial examination.
Definitive examination and treatment should be performed by an ophthalmic surgeon. Until a surgeon is available, both eyes should be covered again, with a sterile eye pad used on the injured eye to minimize contamination. The patient should be supported with parenteral fluids and be considered a candidate for general anesthesia. The repair of a ruptured globe or corneal laceration usually is done under general anesthesia. A local anesthetic is not considered safe because the distortion from its injection might cause additional damage.
The eye is examined safely under anesthesia, usually with an operating microscope, and the repair is carried out by suturing the torn sclera or lacerated cornea. Exposed intraocular structures such as the iris or ciliary body may be replaced in the eye or excised depending on their condition. When the repair is complete, the eye is filled with saline or an electrolyte solution that simulates aqueous humor. Antibiotics are injected subconjunctivally after the globe is closed and are continued intravenously for 4–5 days to prevent infection that may have been introduced by the injury.
A ruptured globe has a grave prognosis for restoration of vision. Corneal lacerations have a better prognosis because their surgical repair usually is accomplished easily. If scarring occurs, corneal transplant can be performed.
Blunt trauma to the eye causes various contusion injuries ranging in severity from ecchymosis of the eyelids (black eye) to major intraocular damage. Compression injuries of the anterior eye are characterized by corneal edema, anterior chamber hemorrhage, and increased intraocular pressure. These symptoms usually resolve without treatment. In some cases, however, return of normal intraocular pressure is followed several weeks or months later by another increase, which indicates the presence of angle-recession glaucoma. This is caused by a tear in the attachment of the iris and ciliary body from the internal surface of the sclera at the anterior chamber angle, damaging the aqueous outflow pathway. Patients with compression injuries always should receive follow-up care at the hands of an ophthalmologist so that angle-recession glaucoma can be detected and treated to prevent progressive damage to the optic nerve. Treatment usually begins with twice-daily drops of an ophthalmic β-blocker.
Hyphema (hemorrhage into the anterior chamber) frequently clears spontaneously, but secondary hemorrhage occurs after several hours or days in up to one-third of patients as a result of lysis of the thrombus in the injured vessels of the iris or ciliary body. Secondary hemorrhage frequently continues until the anterior chamber is completely filled with blood, during which time the intraocular pressure may rise to 50–60 mm Hg (normal 12–20 mm Hg). Lysis and reabsorption of this blood clot may take many days and cause damage to the aqueous filtration pathways and subsequent glaucoma. Breakdown products of blood also can diffuse into the cornea, stain it, and cause long-term reduction of vision. If reabsorption of the blood clot is prolonged, it sometimes can be aspirated successfully. If not, the anterior chamber is opened, and the clot is removed directly. Secondary hemorrhages may require surgical treatment. The prognosis for good vision in patients with secondary hemorrhage is poor.
The prevention of secondary hemorrhages is difficult. Bed rest with binocular patching has been a standard treatment for many years. More recent experience comparing patients treated with bed rest and others allowed normal activity showed no significant difference in the incidence of secondary hemorrhages.
Aminocaproic acid has been used to retard fibrinolysis in the injured vessels to prevent secondary hemorrhages to the benefit of many patients. This treatment slows the lysis of the primary hyphema but, when given for 5–7 days, does reduce the occurrence of secondary hemorrhages. There are significant side effects, so use of aminocaproic acid must be considered carefully and monitored.
Retinal edema, particularly in the macula, causes acute reduction of vision. Vision usually improves with clearance of edema in a few days to several weeks. Clearance is not always complete, and there may be permanent damage to the macula. In ruptures of the choroid, blood spreads beneath the retina at the time of injury, and reabsorption of blood will reveal a crescent-shaped scar concentric with the optic disk. There is no treatment. Other contusion injuries include dislocation of the lens (partial or complete), traumatic cataracts, and tears in the region of the anterior attachment of the retina to the ciliary body, which lead to vitreous hemorrhages and detachment of the retina.
A damaged lens—either dislocated or cataractous—may reduce vision or may be displaced anteriorly, causing increased intraocular pressure by closing the aqueous filtration angle. In either case, the lens is removed by using one of the cataract surgery techniques. Vitreous hemorrhages are removed with a suction-cutting vitrectomy instrument. Following this procedure, the retinal detachment is repaired by creating an adhesive scar between the choroid and retina, usually by freezing through the scleral surface (cryotherapy) over the area of the retinal tear or hole. The sclera then may be buckled inward to push the adhesion against the retina. This is usually done by compressing the globe with an encircling band of silicone rubber. Sometimes, an intraocular gas bubble is used to push the retina, choroid, and sclera into contact.
Intraocular Foreign Bodies
An intraocular foreign body should be suspected on the basis of the occupational history, particularly if the worker complains of an irritating sensation in the eye and no superficial foreign body is found. For example, when steel tools are used to hammer other steel objects, the hammered steelwork hardens to a glassy surface from which small, sharp chips can fly and penetrate the globe with a minimum of discomfort at the moment of impact. Vision may be nearly normal if the entry wound is small. In cases such as this, in which a radiopaque foreign body is suspected, a radiograph should be taken. Ultrasonography usually will demonstrate nonradiopaque objects (eg, glass and plastic). If a foreign body is found, referral to an ophthalmologist for further evaluation and early treatment is essential.
Failure to remove iron or copper foreign bodies can cause severe impairment or loss of vision owing to their toxic effects on ocular tissue. A retained iron or copper foreign body may dissolve away in several months to a year, but the damage done to the retina by the soluble metallic salts is irreversible, and marked visual loss—even blindness—results. The prognosis for these foreign bodies is good if they are removed before they have time to dissolve. Inert materials such as glass or plastic may cause mechanical damage to the eye, but in the absence of a local toxic reaction, the long-term prognosis is better. It is not necessary to remove every foreign body made of inert material; some of them may be left in place depending on their position in the globe and their effect on visual function. Iron-containing magnetic foreign bodies usually are removed with an ophthalmic magnet—sometimes through the entry wound or through a surgical incision made as close as possible to the foreign body. Nonmagnetic foreign bodies are removed with grasping instruments specially designed for ophthalmic microsurgery. Penetrating wounds caused by potentially contaminated objects such as agricultural implements or by wood fragments thrown from woodworking machinery can introduce severe intraocular infections that lead to complete disruption and loss of the globe; therefore, microbiologic studies and treatment with appropriate systemic and local antibiotics are required.
Injuries to the Orbit & Optic Nerve
Orbital floor (“blowout”) fractures frequently are associated with herniation of intraorbital contents into the fracture line. Usually there is severe edema within the orbit that restricts eye movements for 7–10 days. If restriction continues, surgical repair of the fracture may be indicated to free the entrapped extraocular muscles.
Facial bone and orbital fractures that extend to the posterior orbit may involve the optic canal, with damage to the optic nerve indicated by the presence of an afferent pupillary defect. Initial and later evaluations of the patient should include documentation of visual acuity. If there is progressive loss of vision, surgical decompression of the optic nerve in the canal may preserve or, occasionally, even improve the remaining vision.
Orbital injuries may cause severe hemorrhage, marked exophthalmos of the globe, and a dramatic and abrupt increase in intraocular pressure owing to compression. Although this increased pressure usually is relieved by the normal dissipation of interstitial fluid in a short period of time, it occasionally results in occlusion of the central retinal artery or vein. Pressure sometimes can be reduced by the application of gentle external massage to the globe through the closed lids. Surgical lysis of the lateral canthus of the lids may be required.
Penetrating wounds can damage the optic nerve directly by advancing through the funnel-shaped orbit to reach its apex, where the nerve and its blood supply are trapped by the optic canal. Contusion of the nerve causes severe visual impairment and sometimes is treated with large doses of systemic corticosteroids in a manner similar to treatment of spinal cord injuries.
Injuries of the Corneal Epithelium (Abrasions & Superficial Foreign Bodies)
Abrasions of the corneal epithelium can be caused by superficial mechanical trauma (eg, prolonged wearing of contact lenses); by the presence of a foreign body; or by exposure to ultraviolet radiation, chemicals, aerosols, dust, smoke, and other irritants. The occupational medical history should be taken, as described in Chapter 2.
Photokeratoconjunctivitis (welder's flash) is a specific ocular injury caused by unprotected exposure to ultraviolet radiation with wavelengths shorter than 300 nm (actinic rays). This radiation is generated by the welder's arc and damages the exposed corneal and conjunctival epithelium. Injuries are caused both by direct observation of the arc and in persons nearby who often are not wearing protective filters.
In the first few hours after exposure, there may be only mild discomfort and slight conjunctival redness. After a latent period of several hours—even as long as 6–8 hours—the injured epithelial cells slough, causing an acute onset of severe pain sometimes said to be “as though someone had thrown hot sand in my eyes.” Marked tearing, photophobia, and blepharospasm (tightly closed lids) are usual.
Examination requires a sterile topical anesthetic, which may be introduced through nearly closed eyelids by placing several drops along the lid margins. When the eyes open, more anesthetic may be instilled, along with fluorescein from a sterile paper strip. The fluorescein will diffuse over the cornea where the epithelium has sloughed, staining it bright green—best observed with a blue light. Epithelial loss is confined to the area exposed in the lid opening.
Treatment consists of instillation of an antibiotic ointment and patching the eye or eyes to prevent lid movement or blinking. The epithelium will not heal rapidly and in some cases not at all if it is frequently wiped and disturbed by blinking. It will require 12–24 hours for healing to occur; in some cases, several days may be necessary. The eyes should be examined daily. Anesthetic drops and fluorescein help in following the progress of reepithelialization. Continue to patch with antibiotic ointment until healing has occurred. Corneal epithelium heals without scarring. Antibiotic solutions or ointments containing corticosteroids sometimes are recommended for the treatment of welder's flash burns. The steroids may speed clearing of the associated hyperemia and edema, but they increase the incidence of secondary bacterial, viral, and fungal infections. If steroids are used, frequent examination (every 12–24 hours) is essential to detect early signs of infection until healing occurs. In addition, prolonged use of topical steroids (10–14 days or more), even in low doses, can raise intraocular pressure and, in time, can cause significant glaucomatous field loss. This unpredictable response occurs in approximately 10% of the population. It is therefore probably best to avoid the routine or frequent use of topical corticosteroids in the treatment of corneal and conjunctival injuries and infections.
The patient should not be given anesthetic drops or ointment to use at home. Anesthetics slow and may even prevent epithelial healing, and when used in these circumstances, they have led to severe scarring of the cornea and even the loss of an eye.
These injuries are easily prevented by wearing adequate protective filters in the face masks for the welder and goggles or ultraviolet filter glasses by visitors and workers in nearby areas where the welding flash can be seen.
Symptoms and signs of corneal abrasions include severe ocular pain, tearing, and blurring of vision. Inspection of the anterior eye with a flashlight usually shows irregular light reflections on the corneal surface in the area of the abraded epithelium. Use of sterile topical anesthetic and fluorescein paper strips is helpful for further examination. The fluorescein dye diffuses into the area of disrupted epithelium, stains it bright green, and can be observed easily with a blue light. If further evaluation reveals normal pupillary reactions, a bright red reflex, and no disruption of the anterior segment, the injury usually is confined to the anterior external layer of the cornea.
Small foreign bodies on the surface of the cornea or conjunctiva may be seen directly or detected by evidence of damaged epithelium from the fluorescein stain. Foreign bodies usually can be removed with a cotton-tipped applicator, but a sharp instrument is helpful occasionally. The side bevel of a disposable hypodermic needle can be used to gently detach foreign bodies that are firmly attached to the corneal surface. Rust deposited in the anterior layers of the cornea frequently can be removed by the same gentle scraping maneuver. If all the foreign body or rust is not removed easily, it usually can be left to slough or absorb by itself without causing damage. After foreign bodies are removed, treatment is the same as for abrasions.
Abrasions are treated by applying a sterile ophthalmic antibiotic ointment effective against both gram-positive and gram-negative organisms (eg, gentamicin, tobramycin, or a mixture containing bacitracin, polymyxin, and neomycin) and covering the affected eye with a patch dressing to keep the lids closed. Corneal epithelium usually heals promptly if the surface of the cornea is allowed to rest without blinking the lid. The initial process of healing is one in which the normal epithelial cells slide from the edge of the wound over the smooth surface of the cornea to fill the gap. The eyes should be inspected in 12–24 hours to determine if healing has occurred and to rule out corneal infection, which appears as a white or gray haze in the area of the wound. If the abrasion is not healed completely, a second application of the ointment and patch dressing for an additional 12–24 hours may be required. This process should be continued until the epithelial defect is healed. Scarring usually does not occur, and vision is restored to normal.
Caution: After the initial examination with topical anesthetic, sharp pain may return until the epithelium begins to heal. Under no circumstances should the patient be supplied with anesthetic drops or ointment to use during the healing process because topical anesthetics will delay healing and place the patient at risk for severe corneal infection and scarring. Antibiotic mixtures containing corticosteroids should not be used for treatment because they provide inadequate protection against bacterial infection and enhance the growth of viral and fungal pathogens.
Abrasions caused by fat-soluble petroleum products splashed into the eyes are treated initially by copious irrigation with water or saline solution to remove any remaining material. Staining with fluorescein will demonstrate the amount of epithelial loss, which may vary from a few punctate areas to complete denudation of the cornea. In either case, treatment is the same as outlined above. If the abraded area is large, the corneal stroma may appear slightly gray owing to some degree of edema. This clears rapidly with healing of the epithelium.
Exposure to aerosols (eg, paint sprays), detergents, surfactants, dust, smoke, and vapors can produce both acute and chronic symptoms of abrasion. Acute symptoms almost invariably include marked tearing and blepharospasm, which act to protect the eyes and wash away the offending material. Treatment for acute symptoms is as for other abrasions (see above). Chronic exposure to low-level irritants causes fatigue of the lacrimal reflex and subsequent sensations of dryness and burning of the eyes. Some degree of redness is common. Irrigation with saline solution prevents most of these chronic symptoms. Adequate ventilation and avoidance of irritants in the workplace are obviously the best preventive measures.
Exposure to some chemical substances causes a delayed loss of corneal epithelium. For example, formaldehyde fumes cause diffuse damage to epithelial cells, leading to their accelerated sloughing with normal blinking. Fortunately, the abrasion will heal without scarring when the fumes are avoided subsequently. The long list of other substances that produce this effect includes butylamine, diethylamine, hydrogen sulfide, methyl silicate, mustard gas, osmium tetroxide, podophyllum resin, and sulfur.