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[EMERGENCIES]


Assessment of Ocular Foreign Bodies

Michael Easterbrook, MD; Richard H. Johnston, MD; Michael J. Howcroft, MD

Emergencies Series
Editor: Warren B. Howe, MD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 25 - NO. 2 - FEBRUARY 97


In Brief: Ocular trauma in sports is unexpected and can result in dramatic vision loss. Some of the most insidious yet serious ocular injuries result from retained intraocular foreign bodies, and therefore sports physicians, trainers, and emergency physicians should have a high degree of suspicion when evaluating sports- and work-related eye injuries. This article presents a stepwise approach to history, physical exam, management, and referral when intraocular foreign bodies are a possibility. The authors also present pitfalls in diagnosis, give specific treatment options, and stress the importance of primary prevention and safety protection.

Ocular foreign bodies are rare but do occur in recreational and professional sports. Most cases of ocular trauma in recreational activities are related to injury from blunt objects, but a small percentage of injuries are penetrating and may involve corneal or both corneal and intraocular foreign bodies. A healthy suspicion of an intraocular foreign body is important for early diagnosis and timely surgical removal. Early diagnosis and intervention can make the difference between a good visual result and eventual enucleation (removal of the eye) (1).

The eye is well protected within the confines of the bony orbit. The large opening between the eyelids, however, is totally unprotected against oncoming projectiles. The usual intraocular foreign body is a very small (less than 2 mm), sharp-edged object that enters the eye at high speed. It certainly moves too fast for the person to respond by closing the eyelids, which in turn are too thin to offer significant protection from such projectiles.

Approximately 1,300 eye injuries occur each year from BB guns and air guns. On occasion, the emergency physician might see a patient who has been struck in the eye with a shotgun pellet. Despite major advances in surgical techniques, most patients who have an eye perforated by a BB or pellet suffer permanent visual loss. Forty percent of injured eyes become legally blind and up to 18% are enucleated as a result of the injury.

Because most intraocular foreign bodies enter through the palpebral fissure, the entrance into the eye is often through the cornea or the immediately visible surrounding sclera. If the object has sufficient force to penetrate the thick fibrous sclera, it usually passes easily through the iris or both the lens and iris and ends up in the posterior segment of the eye. Most intraocular foreign bodies will be lodged in the vitreous humour or retina.

Presenting Symptoms

A patient who complains of irritation when blinking might have a foreign body under the upper lid, which might produce a corneal abrasion. In cases of blunt perforating injury to the eye or penetration by large objects, the diagnosis is obvious. The patient might complain of dramatically decreased vision and usually will be in significant pain. The lids are often too swollen to open, and referral to a specialist is not in doubt. This presentation, however, is in stark contrast to the presentation of an intraocular foreign body, which is usually quite small and does not result in major lid edema.

If penetration has occurred, the patient will usually complain of moderate ocular pain, redness, and watering. Impaired vision is not a reliable indicator of an intraocular foreign body, since visual acuity might remain excellent as long as the visual axis is not involved. If, however, the injury results in corneal distortion, a cataract, vitreous hemorrhage, or macular damage, the vision can be dramatically reduced.

[FIGURE 1]Physicians should refer any patient to an ophthalmologist if, on the basis of history, signs, or symptoms, an intraocular foreign body is suspected. The ophthalmologist then completes the examination of the peripheral retina using the indirect ophthalmoscope, the three-mirror lens, or both instruments. He or she may also request plain or special x-rays to detect or confirm the presence of an intraocular foreign body.

Physical Examination

Physical examination is critical in making the diagnosis of an ocular foreign body, and in determining which injuries might be vision-threatening. At track meets, a cinder might be found under the upper lid or on the cornea (figure 1). A flashlight may be used to detect a corneal foreign body; and careful eversion of the eyelid will often demonstrate conjunctival foreign bodies. A procedure for everting an upper lid is shown in figure 2.

Examination with fluorescein and the ophthalmoscope will demonstrate most corneal abrasions. The cornea can be examined using fluorescein strips. The sterile strips should always be moistened with tap water or with a drop of topical anesthetic before being placed in the lower conjunctiva. A dry strip is very irritating.

[FIGURE 2]

[FIGURE 3]Examination of the cornea with the blue filter on the ophthalmoscope or on a penlight will often reveal a corneal abrasion in patients complaining of photophobia (figure 3). Careful examination of the cornea might also reveal foreign bodies (figure 4), the removal of which is discussed later.

Thorough assessment of the pupils can often be very helpful in recognizing major ocular trauma. Inspect the shape of the iris for any pupillary irregularities. A peaked pupil is sometimes seen if the iris is punctured or trapped in a corneal perforation. The iris moves up to seal the perforation site, and thereby creates an irregular pupil. Carefully assess the pupillary direct reflex. The pupils should respond briskly and symmetrically to direct illumination with a flashlight. If the pupil moves irregularly, one should suspect an iris abnormality that could be caused by damage from a projectile.

[FIGURE 4]When examining the pupils, it is always useful to look for a relative afferent pupillary defect by performing the swinging flashlight test. When a flashlight is moved from one pupil to the other, symmetrical brisk contraction of the pupils should take place. Suspect serious ocular injury if the pupil in the eye suspected of injury paradoxically dilates when the flashlight illuminates it. A relative afferent pupillary defect is usually related to damage to the optic nerve or retinal injury.

Many of the signs of penetrating ocular injuries are quite subtle and require the use of a slit lamp biomicroscope to be seen. Look first for any site of ocular penetration (figure 5). Always remember to look at the eyelids for signs of skin penetration as well. A fast-moving object such as a shotgun pellet or BB could easily go right through the eyelid and lodge inside the eye after passing through the sclera. Most intraocular foreign bodies, however, enter through the cornea or very near the cornea. An entry site through the surrounding sclera will result in marked chemosis of the conjunctiva and often a small-to-moderate amount of conjunctival hemorrhage.

[FIGURE 5]The anterior chamber can be either of normal depth or shallow after ocular penetration. If the entrance site is still leaking, all the aqueous humour might flow out via this point, producing a collapsed anterior chamber. The intraocular pressure in this case would be very low. If, however, the entrance site has self-sealed or been sealed by the iris, the anterior chamber might remain formed. There might be an anterior-chamber reaction; expect to see floating cells and flare within the anterior chamber under the slit lamp's high magnification.

A magnified close inspection of the iris is also very helpful. If the light is directed through the pupil, transillumination defects of the iris can often be seen, signifying an area of iris perforation by the foreign body. This is often a very good clue that the intraocular foreign body has passed through the anterior chamber and entered the posterior segment. On direct inspection, look for any areas of iris hemorrhage or obvious holes that would signify disruption by the foreign body (figure 6).

After pupillary dilatation, the lens can be inspected for any signs of a cataract. A localized area of whitening in an otherwise normal lens is often indicative of a traumatic event. A careful and thorough inspection of the central and peripheral retina and optic nerve then concludes the clinical exam (figure 7). If the intraocular foreign body has resulted in vitreous hemorrhage, the posterior segment might be obscured.

[FIGURE 6]

Imaging Studies

Imaging is required whenever a patient is believed to have a retained intraocular foreign body. Plain films are often very useful in determining if an intraocular foreign body is present. Most projectiles are metallic and will be seen by this method. Depending on its lead content, glass may or may not be visible by radiologic examination.

Exact localization of foreign bodies by the ophthalmologist is of primary importance before surgical removal. The patient should have a CT scan with 1- to 2-mm cuts in both the axial and coronal planes for the most precise localization. Ocular ultrasound is also superb for identifying and localizing ocular foreign bodies, but it should be performed with caution to avoid placing too much pressure on the globe.

[FIGURE 7]

Wood is one type of foreign body that would not be detected by normal radiologic techniques. It can, however, be seen by MRI examination, and this could be considered if a wooden intraocular foreign body is suspected.

Management

[FIGURE 8]Corneal foreign bodies can usually be readily removed. If the corneal foreign body is metallic, removal should be approached with caution. It can be easily removed with a sharp needle under local anesthetic, but experience with the procedure and access to a slit lamp are essential. A metallic corneal foreign body might leave a rust ring (figure 8). If the rust ring persists, apply antibiotic ointment, patch the eye, and refer the patient to an ophthalmologist for removal of the ring. A rust ring is easier to remove 24 hours after the foreign body is removed, when the cells around the ring have loosened; it can then be readily lifted off or removed with a small burr.

If an intraocular foreign body is suspected, a hard shield should be placed over the eye to protect it against rubbing prior to further examination by an ophthalmologist. The patient should be told not to squeeze the affected eye. The patient's tetanus immunization status should be reviewed and broad-spectrum antibiotics should be started by the ophthalmologist to prevent intraocular infection or endophthalmitis.

The prognosis for recovery of vision is much better if an intraocular foreign body is removed within the first 24 hours (1). Glass, plastics, and gold, however, are moderately inert and can be left in the eye for long periods of time. Foreign bodies containing iron cannot be left in the eye because of long-term toxicity (siderosis). Copper foreign bodies are by far the most irritating and cause a marked inflammatory response.

If the foreign body is magnetized, and if the object is near the surface of the eye, it can be removed by an eye surgeon using a high-powered magnet (2). Usually, however, a vitrectomy is performed in which incisions are made through the pars plana so that the foreign body can be visualized and removed.

Prognosis

Patients who have corneal foreign bodies rarely develop infection if the objects are removed immediately. Removal of a rust ring might leave a small scar, but vision is usually not affected. If a scar from a foreign body or from a rust ring is in the central axis of the cornea, visual acuity might be compromised; however, a foreign body scar in the peripheral cornea does not compromise vision.

Vision prognosis for patients who have had intraocular foreign bodies depends upon the size of the object, the amount of associated damage to vision, and whether infection developed.

Prevention Education

Most corneal and intraocular foreign bodies are preventable, and physicians should take advantage of any opportunity to educate patients about prevention. BB guns and air rifles pose particular hazards, since they are used by children and they shoot projectiles that can easily penetrate the eye. High-powered general-purpose air rifles, for example, might have muzzle velocities as high as 620 feet per second—well above the 408 feet per second velocity required for penetration of skin, bone, and the human eye (3).

Polycarbonate lenses provide the best eye protection. BBs can readily penetrate hardened safety glass and CR-39 plastic, the type of plastic used in most prescription lenses, but cannot penetrate polycarbonate lenses. Polycarbonate has tremendous impact resistance; it is used in jet canopies and police riot shields and will withstand a .22-caliber bullet. Polycarbonate is available in most prescriptions and is also available for athletes and recreational players who do not require corrective lenses. The usefulness of polycarbonate lens protection for prevention of eye injury should be stressed to all patients who are recreational or professional athletes.

References

  1. Thompson JT, Parver LM, Enger CL, et al: Infectious endophthalmitis after penetrating injuries with retained intraocular foreign bodies. National Eye Trauma System. Ophthalmology 1993;100(10):1468-1474
  2. Howcroft MJ, Shea M: Management of posterior-segment foreign bodies. Can J Ophthalmol 120212;17(6):255-261
  3. Vinger, P: The eye and sports medicine, in Tasman W, Jaeger E, Parks MM, et al (eds): Duane's Clinical Ophthalmology, Philadelphia, JB Lippincott Co, 1994 Update, pp 1-94

Dr Easterbrook is an associate professor of ophthalmology at the University of Toronto, chief of the department of ophthalmology at Wellesley-Central Hospital in Toronto, a senior staff member at Toronto General and Toronto Western Hospitals, a consultant at the Orthopaedic and Arthritic Hospital in Toronto and Princess Margaret Hospital in Toronto, and eye surgeon for the Toronto Maple Leafs hockey team. He is also a consultant ophthalmologist for the Toronto Raptors basketball team and to several North American racket sports associations, and is an editorial board member of the The Physician and Sportsmedicine. Dr Johnston is chief resident in the department of ophthalmology at the University of Toronto. Dr Howcroft is a vitreoretinal surgeon, a diplomate of the American Board of Ophthalmology, assistant professor of ophthalmology at the University of Toronto, and chief of the department of ophthalmology at St Michael's Hospital in Toronto. Dr Howe is a team physician at Western Washington University in Bellingham, Washington, and an editorial board member of The Physician and Sportsmedicine. Address correspondence to Michael Easterbrook, MD, Suite 826, 170 St George St, Toronto, Ontario, Canada M5R 2M8.


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