Friday, January 18, 2008

Eye Exam in Facial Trauma

I perhaps should have done this sooner in the facial fracture series, but am doing it here before doing the orbital fracture post.

In major facial trauma, 15-20% of patients suffer vision-threatening injuries. Early identification and management of such ophthalmic insults often improve the visual prognosis. Manipulations during facial fracture repair can exacerbate unrecognized eye trauma. In addition, ophthalmic problems not documented before facial reconstruction may be interpreted as direct complications of surgery. For these reasons, all physicians who treat patients with trauma above the mandible should appreciate the fundamentals of ophthalmic evaluation and emergency management. This post is to educate myself and others, but it should not be viewed as a substitute for consultation by a qualified eye care provider when an ocular injury is strongly suspected. Eye exams are often not easy in trauma patients, so be sure to document what you are able to do and see, as well as what you are unable to do. A good example is the unconscious patient who will not be able to participate in the visual acuity portion of the exam.

THE EYE EXAMINATION

VISUAL ACUITY

In the United States, normal visual acuity is designated as 20/20. This indicates that a person being tested can see at 20 feet away what the average person can see at this same distance. In Europe, where the testing distance is 6 m, normal vision is depicted as 6/6.

Decreased visual acuity of 20/50 indicates that an individual being tested can see at 20 feet what an average person can see at 50 feet, whereas someone with spectacular 20/10 vision can see at 20 feet what the average person must be 10 feet away to see.

In youth, the intraocular lens is able to change shape and thicken, increasing refractive power and allowing the eye to focus on close objects in a complex process called accommodation.

The ability to accommodate starts to diminish (presbyopia) in most people older than 40 years; thus, there is the need for extra convergence lens power, or reading glasses. As a direct result, the majority of people older than 40 years who are screened in emergency departments using a near-vision card without corrective reading lenses will test as having diminished vision, even though their distance vision and eyes may be perfectly normal.

In addition, consider the relative apparent size of a thread held at 6 inches from the eye versus 3 feet away. Realize that a near-vision card is standardized for use for a standard distance (ie 33 cm or 40 cm) from a subject's eyes. If the card is held closer, the numbers will appear larger than they should be. Likewise, if a presbyopic individual holds the card farther than precisely 33 cm to bring the numbers into better focus, the characters will be effectively smaller and decreased vision may be recorded.

Visual acuity is perhaps the best single test of overall ocular integrity and function, accurate testing is very difficult (if not impossible) in the emergency room setting. Eyelid or orbital swelling may minutely deform the shape of the eye, temporarily altering a patient's refractive need and leading to spuriously low vision testing, even in the presence of usual corrective lenses. Serious ocular injuries, such as a penetrating scleral laceration or a peripheral retinal tear, may have no immediate effect on central visual acuity. Bad vision in the emergency room often results from simple things such as lack of appropriate spectacle correction, blood or mucus in the tear film, and poor effort resulting from anxiety, pain, or intoxication. An eye that can see no light at all, however, is a clear indication of severe ophthalmic injury, unless, of course, the patient is malingering (a complicated topic left to others).

EXTERNAL EXAMINATION

Gross inspection of the eye and ocular adnexa should be part of every examination. Lacerations and contusions over the lateral eyebrow or in the mid glabella are worrisome for the association with posttraumatic optic neuropathy (discussed below). Eyelid lacerations may be full-thickness with underlying globe injury. Remember that forced closure of the eye, such as might occur in anticipation of a blow, creates upward rotation of the globe behind the closed eyelids, known as Bell's phenomenon, in about 75% of the normal population. So when exploring a through-and-through upper eyelid injury, one must not forget to examine the inferior corneal limbus, often hidden beneath the margin of the lower eyelid. Fat prolapsing through an eyelid laceration is strongly suggestive of orbital penetration. Foreign bodies may be difficult to identify in the fat tissue.

Blunt trauma to the eyelids may result in a medial, full-thickness eyelid tear. The medial canthal tendon is a relative, focal weak are and often such an injury will lacerate the canaliculus. Posttraumatic telecanthus usually indicates a nasal side wall fracture with the bone fragment and the still attached medial canthal tendon insertion moving laterally together.

OPTIC NERVE FUNCTION

In the verbal, cooperative patient, one of the best tests of overall optic nerve function is subjective red color saturation. A bright red object is presented to one eye at a time. The patient is asked whether the object's color is of equal hue and intensity in each eye. If an optic nerve has suffered significant injury, ipsilateral color perception will be altered. The red object may appear more dull, orange, or brown than it does with the contralateral eye. Even patients with mild color appreciation deficiencies (8 percent of male subjects in the United States) will be able to tell a difference.

A similar white light intensity test is performed by shining a bright white light in one eye and then the other. Although this is less sensitive than the red color test, it is more useful if there has been trauma within the eye. An eye filled with blood will see approximately the same light intensity as an eye that is not. Also, eyes with unequal-sized pupils may appreciate differences in the low ambient illumination of a red color test, whereas the brighter stimulus of a white light may be seen erroneously as even brighter in an eye where the pupil cannot constrict, casting doubt on the ocular function in the contralateral eye. Importantly, both red and white light saturation tests may yield false-normal results if there is equal compromise of both optic nerves.

PUPIL EVALUATION

In the nonverbal or uncooperative patient the pupil examination may be the only available measure of total ocular function. There are three parts to a pupil examination.

  • First, the size and shape of each pupil should be recorded. An irregularly shaped pupil (corectopia), especially a teardrop- shaped pupil, should raise concern about an anterior penetrating injury to the eye. The point of the teardrop may point toward a laceration hidden beneath conjunctival swelling (chemosis), where the iris has become incarcerated and sealed the wound.
  • The second part of the pupil examination is an assessment of the reactivity to bright light. Each pupil should be viewed independently. A grading system understood by all non- ophthalmologists is trace, sluggish, and brisk. Then, one should swing the light from one eye to the other and back to determine whether there is a relative afferent pupillary defect. An easy way to test this is to watch just one pupil, for example, the left. One should shine the light in the left eye and watch the degree of constriction. While still watching the left pupil, one should move the light into the right eye. The left pupil should minimally dilate in the time it takes to move the light from the left eye to the right, but should then constrict to the same degree as when the light was shined directly into the left eye. If the left pupil does not constrict as well when the light is shined in the right, then there is a problem somewhere along the right visual pathway (retina, optic nerve, optic chiasm, or optic tract). Very nice explanation of anisocoria and abnormal light reflexes by Dr Jeff Mann here.

  • The third part of the pupil examination is assessment of miosis during near synkinesis, often erroneously referred to as pupillary accommodation. This test, in fact, is of little value when evaluating eye trauma, especially if the remainder of the pupil examination is normal, and more properly belongs as part of a complex neurologic evaluation.

Pupil size has no relationship to optic nerve function or visual potential. Instead, pupil size is determined by sympathetic fibers traveling along cranial nerve V and parasympathetic fibers traveling along the inferior division of cranial nerve III, whereas vision is dependent on cranial nerve II, the optic nerve. A totally blind eye is likely to have a normal sized pupil, and an eye with a blown, dilated pupil may have totally normal vision. Also remember that many medications seen in the emergency room setting, such as narcotics and recreational drugs, affect pupil size.

In the setting of trauma, carefully performing and recording a pupil examination is always critical. Too often, PERRLA (pupils equal, round, react to light, and accommodation) is jotted on the chart. A better description might be pupils: 4 mm, round, briskly, and equally reactive to light.

VISUAL FIELD DETERMINATION

In the emergency room, visual field testing in an awake and fully cooperative patient can be more revealing than measuring visual acuity. There are three parts to the visual field assessment.

  • The first, central visual field, evaluates overall central retinal (or macular) function. There are several formal testing mechanisms, such as the Amsler grid. A simplified test is to stand roughly 2 feet from the patient, cover one of the patient's eyes, ask the patient to focus on your nose, and while doing so, the patient should be able to see all the features of your face, including your ears, without any dark or blurry spots. Repeat this test for the patient's second eye.
  • Secondly, to assess peripheral visual field, position yourself 2 to 3 feet in front of the patient with both of you covering mirror eyes (if the patient covers the left eye, you should cover your right eye). Then, with your contralateral hand equidistant between your two heads, bring a wiggling finger in from the far periphery. Have the patient say when the moving finger is first visible. You and the patient should see the finger at approximately the same time. This assumes that you don't have any peripheral vision problems.
  • The third part of visual field analysis, double simultaneous confrontation, more properly belongs as part of a complex neurologic evaluation.
PENLIGHT EXAMINATION

With a penlight, an assessment should be made of the conjunctiva, the cornea, the anterior chamber, and the lens. The conjunctiva, the thin mucous membrane covering the eye, runs from the edge of the cornea, across the surface of the eye, and up the insides of the upper and lower eyelids almost to the eyelashes. Vascular engorgement in the conjunctiva gives a red eye or pink eye appearance that is nonspecific for ocular surface irritation. The conjunctival examination should focus on identifying any foreign bodies, tears in the conjunctiva, and chemosis (conjunctival swelling, either pale or hemorrhagic). Although most subconjunctival blood results from a simple bruise on the surface of the eye, focal globe penetration below the blood must be ruled out. Pale (nonhemorrhagic) chemosis may also represent an occult globe rupture with subconjunctival accumulation of ocular aqueous from the anterior chamber.

The cornea and lens should appear clear, with intact red reflex through both. Clouding of the cornea most likely suggests either old scar or acute infection, and clouding of the lens is generally a cataract. Some types of posttraumatic cataracts can develop acutely.

The anterior chamber, the area between the cornea and the iris or lens, should likewise be totally clear, and there should be an appreciable depth to the front part of the eye. If the anterior chamber is flat, with no space between the cornea and the iris, an occult globe rupture must be suspected. Red or white blood cells filling the anterior chamber are called a hyphema or hypopyon,  respectively.

INTEROCULAR PRESSURE MEASUREMENT

Most techniques for evaluating intraocular pressure are not amenable to being performed by an infrequent examiner. Very high intraocular pressure induced by orbital hemorrhage should not be managed by passing a needle into the anterior chamber. This maneuver lowers intraocular pressure only temporarily and then results in a flat anterior chamber, which may occlude the trabecular meshwork, block aqueous outflow, and create even higher intraocular pressure. If an ocular laceration is suspected, call the ophthalmic specialist.

MOTILITY

The first part of a motility examination determines whether both eyes work together while the patient is looking straight ahead in primary gaze position.

  • If there is sufficient vision to see a finger or pencil held at 3 feet, and the vision is roughly equal in both eyes. It is enough to simply ask a cooperative patient whether or not he or she sees one image. The finger should be held first vertically and then horizontally to check for diplopia in both primary meridians. If diplopia is present, then record the approximate test distance and type of diplopia (e.g., vertical, horizontal, torsional, or a combined).

The second part of the motility examination tests eye movement in each of six major gaze positions: left, right, up and in, up and out, down and out, and down and in.

  • Most significant movement disorders are identified by simply testing up, down, left, and right gaze. Clearly record which movement are normal or abnormal in the medical record. For example, if only four positions of movement are tested, a plus sign should be noted, as opposed to an H, if six positions are examined. For the uninitiated, simply writing the left eye has trouble in up-gaze is probably adequate.
  • When evaluating orbital trauma, a carefully performed and documented ocular motility assessment is critical. Whereas globally restricted movement may indicate diffuse orbital swelling needing delay before surgery, movement more limited in one meridian (e.g., up-gaze and down-gaze) is worrisome for an inferior rectus entrapment that may require urgent orbital exploration and fracture repair to avoid muscle ischemia and permanent dysfunction.
  • Children younger than 12 years, and certainly those younger than 6 years, are at risk for developing amblyopia if they have prolonged dysmotility and do not use their eyes together.
FUNDUS EXAMINATION

Examination of the retina, optic nerve, and retinal vessels is the most technically difficult part of an eye evaluation, especially through an undilated pupil with a direct ophthalmoscope. Dilating the pupil with 1% Mydriacyl (Alcon, H√ľnenberg, Switzerland) and 2.5% phenylephrine can greatly facilitate the examination.

NOTE: If there is any question about vision, optic nerve injury, visual field, or general neurologic status, dilating drops should not be placed in both eyes, so that pupil function can be assessed independently by other physicians. However, the presumed pathologic eye can usually be dilated without problems, but one should be certain to note in the chart and advise nursing personnel that one pupil has been dilated.

If an accomplished observer finds that there is a good red reflex but no view of the retina, perhaps the posterior chamber is filled with blood. A large white or pale area in an otherwise red retina may indicate retinal ischemia or ocular contusion. A retinal detachment may appear as large undulating, pale folds. Likewise, finding that different parts of the retina are out of focus as compared with others while the power correction in the direct ophthalmoscope is held constant suggests the retina is sitting at different levels. Optic nerve avulsion (picture below) is a rare clinical entity that occurs when there is partial or complete tearing of the optic nerve from the globe at the level of the lamina cribrosa.

IMAGING

The single most useful imaging study in the setting of trauma is probably computed tomography. Relative to computed tomography, plain films are often not as sensitive. Magnetic resonance imaging is contraindicated in the presence of possible metal foreign bodies, more expensive, often more difficult to obtain quickly, and does not show bone as well.

For the orbit, 3-mm computed tomographic sections are usually sufficient, unless a small foreign body is sought. Coronal images are preferred over axial images, although the combination is most helpful.

TRUE OPHTHALMIC EMERGENCIES

Although there are many ocular insults that require rapid attention, the two ophthalmic emergencies where every minute may count are chemical exposure (particularly alkali burns) and ophthalmic infarct.

Industrial chemicals are more likely to be acids, whereas household solutions are more likely alkaline, and the latter are generally more dangerous for the eye. The treatment in either case is

  • copious irrigation with any pH-neutral solution such as water, half-normal saline, or even lactated Ringer's solution. In the presence of severe chemical burns, 10 to 20 liters of irrigant may be appropriate. One way to determine when enough irrigation has been performed is to check for a pH of 7 in the inferior ocular fornix, wait 10 minutes, and check again. In the absence of narrow-range pH paper, a urine dipstick (trimmed if necessary) may offer some indication.
  • Placing a topical anesthetic in the eye first will greatly facilitate the process.
  • Irrigating contact lenses should be used with caution, as they can trap injurious chemical particles.
  • Remember, a bone-white appearance to the conjunctiva may be a bad prognostic sign, indicating severe ocular surface ischemia.

Based on studies in monkeys, the best hope for vision return after a stroke to the eye comes with intervention implemented within 1.5 hours of the insult. In an ophthalmic infarct, the patient reports sudden vision loss, and the only objective finding is an afferent pupillary defect. Other insults, such as posttraumatic optic neuropathy, may present in this fashion, but a vascular accident must always be considered. Intervention should be individualized and directed by someone trained in managing this acute emergency (call the ophthalmologist).

ORBITAL COMPARTMENT SYNDROME

Any sudden increase in orbital pressure can create a compartment syndrome leading to arterial compression or spasm and ophthalmic stroke. In the presence of an orbital fracture with sinus communication, air from nose blowing or sneezing may be forced into the orbit. When the pressure drops after the sneeze, orbital fat falls back into the bone defect, acting as a ball valve and trapping air. A sudden increase in air volume in the enclosed orbit results in sudden increased orbital pressure. Treatment in vision-compromised patients consists of expeditious air evacuation, either through open surgical technique or computed tomography-guided needle aspiration. Alternatively, lysis of the lateral canthal tendon (cantholysis) can rapidly decrease orbital pressure. This requires very little skin incision and fully releases the eyelid when performed correctly.

Retrobulbar hemorrhage (picture below) occurs when an orbital vessel ruptures and leaks blood products into the orbit. This is another form of a compartment syndrome as the orbital space is a closed environment. Any added contents will inevitable increase the pressure inside the orbit and have the potential to negatively impact the ocular structures.

In the setting of an active orbital hemorrhage, however, cantholysis must be performed with caution, as continued bleeding with growing posterior pressure may lead to progressive proptosis and stretch optic neuropathy (or even very rarely partial optic nerve avulsion). The most likely culprit of such heavy bleeding is the infraorbital artery, although the anterior and/or posterior ethmoidal arteries may also be culpable. In suspected, heavy orbital bleeding, the treatment is emergent orbital exploration to obtain artery control.

POSTTRAUMATIC OPTIC NEUROPATHY

Posttraumatic optic neuropathy is vision loss of any degree from optic nerve injury following head trauma. Causes of posttraumatic optic neuropathy include direct optic nerve injury from penetrating objects, fractured bone fragments impinging on the nerve, nerve ischemia, and nerve compression from intrinsic or extrinsic hematoma or edema. Often, more than one mechanism is involved. Posttraumatic optic neuropathy may affect any or all of the following: visual acuity, visual field, pupillary response, and color perception. Dr.Soparkar feels that red color desaturation is perhaps the most sensitive indicator of posttraumatic optic neuropathy in the emergency room. The management of posttraumatic optic neuropathy remains highly controversial and is beyond the scope of this post. Call the ophthalmologist.

CORNEAL EXPOSURE

Many head trauma patients suffer from multiple medical problems and are unable to protect their eyes because of cranial nerve VII injuries, gross exophthalmos, periocular lacerations, or tissue loss. A suture tarsorrhaphy can be temporarily curative, but the eye becomes hidden, and any complications will go unnoticed. Instead, the frequent use of thick, lubricating ointment is preferred. Pure petroleum jelly (Vaseline) is an inexpensive option. Alternatively, a clear adhesive dressing, as is used to dress intravenous line sites, can be applied directly over the eye. It will not stick to the wet eye but adheres strongly to the surrounding skin and forms an effective moisture chamber.

REFERENCES

The Eye Examination in Facial Trauma for the Plastic Surgeon; Plastic & Reconstructive Surgery. Craniofacial Trauma. 120(7) Supplement 2:49S-56S, December 2007; Soparkar, Charles N. S. M.D., Ph.D.; Patrinely, James R. M.D.

Head, Face, and Neck Trauma: Comprehensive Management By Michael G. Stewart; Google Book

Assessment and Management of Ocular Trauma by Sudeep Pramanik, M.B.A., M.D.; University of Iowa Health Care

Ocular Trauma Management for the Primary Care Provider by Joseph M. Rappon, O.D., M.S., F.A.A.O.

2 comments:

Kim said...

My eyes are burning and I swear that red square looks like a deeper red with my left eye, but this was a fantastic post. : )

This was a case of not knowing what I didn't know.

We don't often see major facial trauma, but we do see it and now I'll have a better idea behind the exams. At the very least I have much more respect for the basic visual acuity and its place in the assessment!

School Kids Healthcare said...

You’ve got a lot of great info here. I really liked the normal/abnormal pupil dilation chart. Happy autumn!