Article Date: 7/1/2007

Blunt-force Injuries Involving the Posterior Segment
PEER REVIEWED

Blunt-force Injuries Involving the Posterior Segment

FERENC KUHN, MD, PhD. ROBERT MORRIS, MD. C. D. WITHERSPOON, MD. LORETTA MANN, COT

There are 2 basic types of objects causing mechanical damage to the posterior segment: sharp (blade, glass splinter) and blunt (fist, BB pellet). A sharp object's impact results in a lacerating injury; after penetrating the eye wall (ie, the cornea or the sclera), the object either remains inside the globe (intraocular foreign-body injury)1 or it leaves the eye. In the latter case, the object exits either via the same wound (penetrating trauma)2 or through a different wound (perforating trauma).3-5

If the object is blunt, however, an entirely different scenario presents. The object may not have sufficient momentum to overcome the resistance of the eye wall; in this case a contusion results. Conversely, if the momentum of the object exceeds the eye wall's resistance, the globe ruptures.6 A rupture, in contrast to a lacerating type of trauma, occurs via an inside-out mechanism: as the object makes contact with the eye, the intraocular pressure (IOP) rises and the eye wall gives way at its weakest point. The valve for the elevated IOP is the wound, and pressure relief (ie, equalization of the atmospheric pressure and IOP) is achieved by the loss of intraocular fluid and/or tissue. The amount of tissue/fluid expressed is proportional to the momentum (ie, consequent pressure build-up) exerted by the object.

A rupture thus may or may not be found at the point of impact. Its predilective sites are the limbus, where the scleral and corneal collagen fibers intersect; the area at the insertions of the extraocular muscles, where the sclera is the thinnest; at the insertion of the optic nerve, where the scleral and perineuronal collagen fibers intertwine; or at any scleral or corneal area with weakened resistance.7 Such weak areas may be along old wounds, whether surgical or traumatic, or at sites of previous inflammation, where the eye wall has become thinner.8 It is important to remember that even a completely healed surgical wound, such as that created for extracapsular cataract extraction, does not possess the same structural strength as the intact sclera. The eye's vulnerability remains a fact with which to reckon even decades after the surgery. In cases of corneal transplantation, the eye is more susceptible to rupture for the life of the patient. The gravity of this risk is supported by data from the United States Eye Injury Registry (USEIR), the largest database in the world on severe eye injuries: In 6% of all eyes with open-globe injury, the pathomechanism is dehiscence of a well-healed surgical wound, and among eyes with rupture, the prevalence of wound dehiscence reaches 16%.

Ferenc Kuhn, MD, PhD, is executive vice president of the International Society of Ocular Trauma and president of the American Society of Ocular Trauma. Robert Morris, MD, and C. D. Witherspoon, MD, are ophthalmologists with the Helen Keller Foundation, in Birmingham, AL. LoRetta Mann, COT, is technical director of the United States Eye Injury Registry. None of the authors have any financial interest in any product mentioned in this article. Dr. Kuhn may be reached via e-mail at fkuhn@mindspring.com.

According to USEIR data, 28% of all scleral traumas are ruptures, and 54% of all ruptures involve the sclera.9-11 Regarding the etiology, certain scenarios deserve special attention; most importantly, elderly patients often sustain a rupture due to fall. A recent USEIR study, funded by a grant from the EyeSight Foundation in Birmingham, AL, and distributed to foundation members, found elderly patients have a poorer outcome than younger people after a similar injury. This is true even if the older person's eye was healthy at the time of injury. However, because preexisting conditions (such as a previous surgery or age-related macular degeneration) are common in elderly patients and such conditions increase risk for poor outcomes, the results in older patients are statistically significantly worse than in younger patients. Additionally, the number of surgical attempts to reconstruct the injured eye is higher per injury among older than among younger patients.

AIRBAGS AND PAINTBALLS

The list of blunt objects causing contusion or rupture is long. Two objects are discussed here in more detail: airbags and paintballs. In the USEIR database, 9% of all eye injuries are sustained during a motor-vehicle crash; among these, 10% are caused by airbags. Of the airbag-related injuries, 10% are open globe (the majority are ruptures, although some are caused by sharp objects such as a shattered prescription glass) and 90% are contusions. Of those injured, 73% are younger than 40 years old, and 61% are female. The injury is bilateral in 15% of the cases — an exceptionally high figure. The posterior segment is involved in 71% of the open-globe and in 48% of the closed-globe injuries. The severity of the trauma is shown by the finding that 4% of the eyes lose light perception and only 62% of eyes have 20/40 or better final vision. This, however, is a somewhat misleading number: many of the patients may not have survived the crashes, and so the potential for sustaining a severe eye injury during a motor-vehicle crash should not be used as an argument against having the airbag operational in the car. Airbags save lives and prevent injuries, even if they occasionally cause (ocular) trauma.

Paintballs are a relatively new, but also rather dangerous, source of ocular injuries; they represent 1% of all entries in the USEIR database. The average person is young: only 4% of the patients are 40 years or older, and only 8% are females. Of the injuries, 9% are open and 91% closed globe; the rate of posterior-segment involvement is 33% and 55%, respectively. Of those injured, 83% wore no eye protection, and 5% claimed to have worn safety eyewear. The typical injury is rather severe: 11% of eyes had worse than 5/200 final visual acuity (VA), and only 61% had better than 20/40.

RUPTURES AND CONTUSIONS

Ruptures represent the most severe form of ocular trauma; the prognosis is much worse than in other cases of open-globe trauma or in contusion. Based on information provided by the USEIR, only 11% of ruptured eyes reach 20/40 or better final VA, and 80% of eyes remain worse than 20/200. One reason explaining the poor prognosis is that tissue prolapse is very common in ruptures, and any intraocular tissue may be extruded: vitreous, iris, ciliary body, choroid, lens, and retina. The list of potential tissue pathologies includes virtually all those that can be associated with injury, ranging from corneal edema to subretinal hemorrhage. In addition to retinal damage, another important factor in the poor outcome is the body's reaction to the injury (eg, scar formation).

The pathomechanism of tissue damage is very different in a contusion. Since the eye wall is not violated, there is no risk of tissue extrusion or endophthalmitis, nor of expulsive choroidal hemorrhage (as in Figure 1). The damage is mostly instantaneous, either by direct impact, by the pressure waves created as the energy from the object is transferred onto the globe, or by changes in the eye wall and structures attached to the eye wall. The damage can present at or near to site of impact (subconjunctival hemorrhage, corneal edema, contusion retinopathy), in adjacent areas (hyphema, iridodialysis, zonular rupture, peripheral retinal breaks), or at the opposite pole of the eye (contracoup mechanism, macular hole, contusion retinopathy, choroidal rupture). What makes treatment of the contused eye easier than that of an open-globe trauma is the fact that immediate intervention is rarely required: there is almost always time to carefully consider all factors before instigating intervention.

The diagnosis of rupture is usually fairly straightforward: The patient describes his eye having been hit by a large blunt object, which caused immediate and substantial loss of vision. A corneal wound is obvious to see, even with the naked eye. There usually is a conjunctival wound and subconjunctival as well as intravitreal bleedings. The lack of a conjunctival wound, however, should not exclude the possibility of a scleral wound.12 An occult rupture can also be present,13 and if this is not identified, the consequences — both medical and legal — can be extremely severe. In addition to those listed above, the following signs should raise the possibility of an occult rupture: thick subconjunctival hemorrhage, especially if a "step sign" is present (incongruence in the shape of the eye); bulge under the conjunctiva (extruded lens); shallow anterior chamber in a phakic or pseudophakic eye, usually accompanied by hyphema; deep anterior chamber in a previously phakic or pseudophakic eye; peaked pupil; and/or loss of the iris. The IOP is somewhat dubious: it may be normal or even elevated. Conversely, low IOP can be present in contused eyes, often as a result of cyclodialysis. The presence of a hemorrhagic choroidal detachment almost always suggests the presence of ocular rupture following blunt impact. Finally, computed tomography or magnetic resonance imaging scans, or carefully employed ultrasonography, may yield useful information about the contour of the globe or show extensive choroidal swelling.

A contusion can produce many of the symptoms of a rupture, but there is no wound, and the visual deterioration is usually less severe. Conversely, certain, rather common (~10%) consequences of a contusion, such as a choroidal rupture, may be impossible to treat. Chorioretinitis sclopeteria is a condition similar to contusion retinopathy; retinal hemorrhages, breaks, or even necrosis can occur. The latter 2 complications should be treated, preferably by lasering around the lesion to wall it off, but no specific treatment exists to improve the intraretinal damage.

Figure 1. Complete loss of intraocular contents after a rupture; irreversible anatomical and functional loss.

SURGERY AND COMPLICATIONS

If the diagnosis of a scleral rupture has been made or its presence is highly likely, all further diagnostic manipulations should be kept to the absolute minimum and the patient should be prepared for urgent surgery.14 These precautions are important to prevent the most feared complication, an expulsive choroidal hemorrhage (Figure 1). It is particularly important that the repair of associated orbital fractures is delayed until the condition of the globe is evaluated (open wound). If the presence of an occult scleral rupture cannot be excluded, exploratory (diagnostic) surgery is preferred to observation.

Before the patient is taken to the operating room, the surgeon should consider whether a staged approach is more ideal (eg, wound closure as the primary goal of the first surgery, followed by major reconstruction a week or so later) or a primary comprehensive surgery is indicated (during which wound closure is the initial goal, but this is followed in the same surgical session by a complex intraocular procedure, typically vitrectomy).15 The latter has more advantages (early treatment, even prophylaxis, of retinal pathologies; removal of a crystalline or intraocular lens dislocated into the vitreous cavity; early visual rehabilitation) but also more risks, especially that of a major intraoperative hemorrhage. Not only must the surgeon who undertakes such a comprehensive primary surgery be experienced in the management of injuries to any anterior or posterior segment structure, but the facility's infrastructure must also be fully at the ready: trained operating room personnel, availability of all equipment and materials, etc.

Furthermore, the wound must either be closed before vitrectomy is performed or the unsutured posterior wound must be small. Finally, the IOP must be closely monitored during vitrectomy, avoiding high values to prevent secondary tissue extrusion. If any of these criteria are lacking, it is best to select a staged approach.

Surgery is best performed under general anesthesia, but if this cannot be safely executed or surgery would have to be substantially delayed, careful wound closure under some form of local anesthesia must be considered.

During surgery, the initial step is to carefully dissect the conjunctiva. If the wound is entirely anterior (ie, along the limbus or anterior to the insertion of the extraocular muscles — zones 1 and 2 in the classification system), the wound is usually exposed in its entirety. Any tissue prolapse is addressed: Vitreous must be removed, preferably using the vitrectomy probe, rather than the typical scissors-sponge combination (Figure 2). This avoids exerting traction on the peripheral retina with consequent tearing of the retina. If iris is extruded, this is usually reposited, unless it is contaminated beyond the surgeon's capability of cleaning/disinfecting it. Excision of the iris must be kept to the minimum, and reconstruction of the iris diaphragm must eventually be attempted. All lens material should be removed, but the posterior uvea and the retina are to be reposited.

Figure 2. The vitrectomy probe is used to remove the prolapsed vitreous from the rupture wound. A preplaced vicryl suture is visible, allowing for instant globe closure should an expulsive hemorrhage occur.

The wound is then closed; nonabsorbable suture (eg, nylon, 10-0) is used at the limbus, while absorbable materials (eg, vicryl, 6-0 to 8-0) represent a viable alternative for more posterior wounds. The suture is introduced with the "halving" technique if the wound provides easy access; otherwise, a from-one-end-to-the-other sequence is recommended. Unless the wound is in the limbus, where a running suture is ideal, interrupted sutures should be used.

POSTERIOR WOUND TREATMENT

A completely different treatment philosophy is in order if the wound is posterior. Since the risk of additional tissue extrusion is high during manipulations over the posterior sclera, the conjunctiva should be opened only partially in the initial phase. The scleral wound is closed here, starting from its anterior endpoint, and then the conjunctiva is opened a little more posteriorly. This is again followed by scleral closure. This sequential ("close-as-you-go") closure of the wound is continued until it becomes difficult to gain access to the scleral wound. At this point the surgeon should stop the process and close the conjunctiva only. This eliminates the risk of endophthalmitis. The scleral wound rapidly closes spontaneously, and any incarcerated issue will have to be addressed via an internal approach. The eye must be shielded for a few days, especially during the night.

An assistant's help is very important during closure of a posterior scleral wound. The assistant can carefully turn the globe, keep orbital tissues from blocking view and access, and hold back prolapsing intraocular tissues with a spatula. If the wound is under the insertion of the extraocular muscle, the muscle may have to be temporarily disinserted. The surgeon should be careful not to lose the muscle.

Once the wound is closed, the surgeon should consider the use of prophylactic scleral buckling. If he decides to place such a buckle, it should be circumferential, and it is best placed over the vitreous base. Prophylactic cryopexy is contraindicated. If the peripheral retina is visible and a break is found, laser retinopexy should be performed.

The surgeon should also contemplate whether additional manipulations during the initial repair are indicated. Primarily, removal of significant hyphema or the injured lens is considered. These maneuvers may be important to prevent secondary complications (IOP elevation, inflammation, corneal blood staining) as well as to allow visualization of the retina in eyes with only modest vitreous hemorrhage.

NONPRIMARY COMPREHENSIVE SURGICAL INTERVENTION

If the surgeon has decided against primary comprehensive surgery, intensive topical corticosteroid therapy must be instigated postoperatively (such treatment is also necessary after a comprehensive primary surgery), and the secondary reconstruction's timing should be carefully weighed. If the wound is anterior, the intervention can wait for a week or so. If, however, the scleral wound is posterior, the risk is very high for the retina to be incarcerated either primarily (ie, at the time of injury or during wound closure) or secondarily (into the developing scleral scar during the natural healing process; see Figure 3). Well over half of eyes with a posterior scleral wound develop proliferative vitreoretinopathy (PVR) subsequently, and even in those eyes without this devastating secondary complication, retinal fold formation is very common. These folds can reach into the macula and cause serious visual disturbance even if the scar is rather far from the macula.

In eyes with posterior scleral wound, it is therefore recommended to perform very early secondary reconstruction (within 4 days or so). This is useful also because retinal tears, including giant tears, are often present and can lead to retinal detachment in the presence of vitreous hemorrhage at a very early stage.

Figure 3. The retina becomes incarcerated into the posterior scleral wound; radiating folds in the detached retina point toward the scleraL scar.

Vitrectomy is not an easy procedure in a traumatized eye with severe hemorrhage. The difficulty is exacerbated by the possibility that a retinal detachment may already have occurred or it has developed intraoperatively, and by the fact that recognition of the detached retina, covered by layers of vitreous with locked-in pockets of blood, is not easy. The surgical technique therefore involves a radically different one from what instinct would first suggest. The surgeon should not peel vitreous layers in broad horizontal movements with the vitrectomy probe but do the opposite: Dig a vertical "well" on the nasal side to try to identify the retina before too much of it is inadvertently removed. This well is of such a small diameter that even if an unintended retinectomy has been created, it is limited both in size and significance (ie, nasally located).

Once the retina is identified, the surgeon can proceed with completion of the posterior vitreous detachment, which can be aided by the use of liquid perfluorocarbon. The vitrectomy is then completed and the internal aspect of the scleral wound inspected. If the wound is over the retina, incarceration of the retina into the scar must be prevented via performing prophylactic chorioretinectomy (Figures 4 and 5). Endodiathermy at the highest setting is used to necrotize the retina and the choroid around the wound, creating a roughly 1-mm–wide zone of bare sclera as a barrier between the scleral scar and the remaining retinal edge. Experience shows that this barrier has a good chance of preventing the development of both PVR and retinal fold formation. In a prospective, international, multicenter study being conducted by the USEIR, early results show the risk as having been reduced from over 60% to below 10%. All other periretinal pathologies (tears, detachment, subretinal blood) are treated in the usual manner.

Endolaser treatment is then performed, followed by additional procedures as needed (pupilloplasty, removal of submacular/subretinal hemorrhage), and the eye is filled with silicone oil or a long-acting gas. All subsequent interventions are determined by the eye's reaction to the injury and to the prior treatments; the silicone oil should not be removed early (it should be kept for at least 6 months), and intraocular lens placement should be deferred until the retina's condition is deemed final.

If the intervention is late, the retina is likely to have totally detached and it is typically incarcerated into the wound, making retinectomy unavoidable. All subretinal membranes must be removed, the closed funnel opened using a cohesive viscoelastic, and all preretinal membranes removed. Then the viscoelastic should be exchanged for silicone oil (usually using perfluorocarbon liquid first). This procedure usually achieves anatomical success initially, but the risk of secondary reproliferation is very high, and the visual outcome is very poor. This is why the prophylactic chorioretinectomy appears to be a much more promising intervention than the traditional wait-and-see approach.

Figure 4. Subretinal bleeding surrounds the unsutured posterior scleral wound. The only reasonable option to save the retina from becoming incarcerated into the developing scar (see Figure 3) is a prophylactic chorioretinectomy.

THE IMPORTANCE OF COUNSELING

Last but not least, we must emphasize the importance of counseling. The ophthalmologist should inform the patient about the various management options prior to any intervention and preferably choose the type of treatment with the patient's consent. This may be a rather time-consuming process, but it makes the patient a partner in, rather than a simply a target of, the process. It also helps reduce the risk of a malpractice suit. Similarly, counseling regarding the importance and types of protective eyewear is mandatory. With carefully planned and executed management, the prognosis of a ruptured eye is dramatically better today than only a few years ago. RP

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Figure 5. Following prophylactic chorioretinectomy, bare sclera is visible with some reactive pigmentary changes at the border, but the retina remains attached and fold-free (see the text for more details).

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Retinal Physician, Issue: July 2007