An experimental evaluation of traumatic globe rupture

J Oral Maxillofac 56: 1275-l 280,

Surg

1998

An Experimental Richard

Evaluation Globe Rupture H. Haug, DDS, * Doughs B. Haghighi, and J. Edward Barber, BSf

of Traumatic DMD, f

The purpose of this investigation was to evaluate the surgeon’s ability to assessvarious types of globe injury, to determine the force necessary to rupture the globe with these types of injuries, and to determine typical orbital retraction forces used in the clinical setting. Forty-four enucleated globes from recently killed cows were divided into four Materials and Methods: equal groups-one uninjured control group, one group with a through-and-through scleral laceration, another group with a subtotal scleral laceration, and the last group with an l&gauge needle perforation. Twenty-seven boarded or board eligible oral and maxillofacial surgeons were asked to assessone sample from each of the four groups. They were then asked to retract a simulated globe on a custom-fabricated jig to determine clinical retraction forces. Ten globes from each of the four groups were then subjected to forces until rupture on an Instron 8501M mechanical testing unit. Accuracy of the clinical assessmentwas determined, and means and standard deviations of the retraction forces and globe rupture forces were derived. Through-and-through lacerations were assessedby surgeons with 100% accuracy, subtotal Results: lacerations with 96% accuracy, uninjured globes with 74% accuracy, and perforated globes with 15% accuracy. Globe rupture occurred at 16.72 2 7.87 kg in the control group, 20.36 + 7.87 kg in the perforated group, 15.38 + 6.06 kg in the subtotal laceration group, and 4.94 & 2.56 kg in the through-and-through laceration group. Statistically significant differences (P < .OOl) were noted between the total laceration group and all other groups. The mean retraction force was 0.35 t 0.47 kg, which was statistically lessthan the force used in all of the rupture groups (P < ,001). Conclusions: Severe injuries (through-and-through lacerations) were assessedwith 100% accuracy by the clinicians, and lesssevere injuries with lessaccuracy. Rupture forces for globes with perforations and subtotal lacerations were no different than for the control group, but substantially lessthan for the total laceration group. The simulated clinical retraction forces were substantially more than the rupture forces in all of the groups, including the through-and-through laceration group. Purpose:

Traumatic globe rupture is a devastating injury that is often difficult to diagnoseand is frequently considered a comorbid event.‘-* It has been suggested that its intraoperative occurrence is the result of the manipulation of an undiagnosed, yet injured, globe.5 This

premise seems to be substantiated by the focus of recent case reports and investigations that implicate radial keratotomy incisions and peribulbar anesthetic injections as compromising the integrity of the globeG10Yet, questions remain. Does the traumatized globe possessany less structural integrity than the uninjured globe? Does routine intraoperative retraction of the orbital contents induce enough force to compromise either the injured or uninjured globe? Moreover, can these types of injuries be diagnosed by visual examination alone?The purposes of this in vitro investigation were to establish the forces resisted by bovine globes with perforations, subtotal lacerations, or through-and-through lacerations until rupture; to determine routine orbital retraction forces used by the surgeon in clinical practice; and to evaluate whether the aforementioned injuries could be identified by the surgeon with a visual examination alone.

*Director, Division of Oral and Maxillofacial Surgery, MetroHealth Medical Center and Associate Professor of Surgery, Case Western Reserve University School of Medicine, Cleveland, tRcsident, Division of Oral and Maxillofacial Health Medical Center, *Research Assistant,

Cleveland, Department

OH. of Orthopaedics,

Medical Center, Cleveland, OH. Address correspondence and reprint tor, Division of Oral and Maxillofacial Dr, Cleveland, 0 1998 0278.234‘1

OH. Surgery,

requests Surgery,

Metro-

MetroHealth

to Dr Haug: Direc2500 MetroHealth

OH 44109.

American /Y8/561

Assoclotion l-0009$3

oi Oral and Max&foclal

Surgeons

00/o

1275

1276

EXPERIMENTAL

FIGURE 1.

A simulated subtotal laceration “A” by making an incision through the through the sclera.

was created confunctiva

GLOBE RUPTURE!

in specimen and partially

FIGURE 2.

Materials

specimen tiva and

and Methods

This investigation was performed in two phases. The clinical assessmentand determination of retraction forces were accomplished with the aid of 27 volunteer boarded or board-eligible oral and maxillofacial surgeons. The force to rupture phase was performed with recently enucleated bovine globes on an Instron 8501M mechanical testing unit (Instron Corp, Canton, MA). This investigation was approved by the Institutional Animal Care and Use Committee. CLINICAL OF

ASSESSMENT

RETRACTION

AND

DETERMINATION

FORCES

Four enucleated eyes from recently killed cows were prepared for evaluation. The cornea, orbital fat, and extraocular muscles were retracted and secured with 3-O silk suture. A Bard Parker #15 scalpel (Becton Dickinson, Franklin Lakes, NJ) was used to create a subtotal laceration 5.0 mm long through conjunctiva and partially through sclera in one eye (specimen A) (Fig 1). A second noninjured eye was used as a control (specimen B). The samescalpel was then used to create a 5.0-mm-long incision through the conjunctiva and completely through the sclera in a third eye (specimen C) (Fig 2). A fourth eye was prepared by puncturing the conjunctiva and sclera with an l&gauge angiocatheter (Becton Dickinson Vascular Access, Sandy, UT) (specimen D) (Fig 3). The eyes were placed in specimen cups with the simulated injury superior, and labeled “A,” “B,” “C,” “D.” Twenty-seven boarded or board-eligible volunteers from among the 269 in the general membership who attended the Ohio Society of Oral and Maxillofacial Surgeons 1997 scientific session participated in this phase of the investigation. A single-blinded moderator asked each surgeon after registration whether they would be willing to volunteer. When the response was affirmative, the surgeon was asked, “Is there a

A simulated through-and-through laceration was created in “C” by making an incision completely through the conjuncsclera.

laceration or perforation of the sclera in specimen A? B? C? or D?” Only yes or no answers were accepted. These were recorded. Next, each surgeon was asked to provide simulated orbital retraction with a Rowe Orbital Floor Retractor (Walter Lorenz Surgical Inc, Jacksonville, FL) using a custom-fabricated jig designed to mimic the clinical setting (Fig 4). A 5.0-mm-thick foam pad was placed over the top of a self-recording spring balance to simulate the sensation of retracting the soft tissuesof the orbit. The resistance arm of the spring balance was placed through the orbital roof of a synthetic skull (Saw Bones, Pacific Research Lab, Vashon Island,

FIGURE perforation

3. An 18.gauge in specimen “D.”

angiocatheter

was

used

to create

a

HAUG, HAGHIGHI,

1277

AND BARBER

retracFIG URE 4. The simulated using an ortion was pel ,formed skull, bital floor ret ractor, synthetic and self-rt ?COI ,ding spring balance.

WA). The skull was secured to the jig in such a manner that right and left rotation as well as superior and inferior (extension or flexion) motion was permitted, as would occur with a patient’s head in the surgical setting. The jig was secured to a stationary benchtop that was immobile, representing an operating room table. The surgeons were asked to insert the orbital retractor along the orbital floor and retract superiorly with as much force as they would in the operating room. The foam pad and arm of the spring balance were engaged, and the retraction forces were recorded.

Results Twenty-six of 27 surgeons (96%) were able to accurately identify the subtotal laceration (Table 1). Seven falsely suspected an injury of the noninjured control eye. This was a 74% accuracy. All (100%) of the surgeons identified the total scleral laceration, but only four surgeons (15%) accurately assessedthe l&gauge needle perforation of the sclera. The control globes ruptured at 16.72 + 7.87 kg (range, 7.23 to 31.96 kg), the subtotally lacerated globes ruptured at 15.38 +- 6.06 kg (range, 8.02 to

Rupture Forces Forty enucleated globes from recently killed cows were used for the second portion of this study. Ten each were placed into the subtotal laceration group, total laceration group, and perforation group, and 10 uninjured globes were used ascontrols. The simulated injuries were created in each of these globes in a manner similar to the first phase of the experiment (Figs l-3). Each globe was placed in a custom-fabricated jig that resembled an orbital floor retractor (Fig 5) and mounted on the Instron 8501M mechanical testing unit. The load cell/actuator was advanced at a rate of 20 mm/min until globe rupture (height of the load displacement curve). Data were recorded at 100 Hz using a custom-designed program written in Labview Software (National Instruments Corp, Austin, TX). The load at rupture was recorded. After testing, the means and standard deviations of the data were derived and compared for statistical significance using a Scheffe multiple comparison test at the .05 significance level. The rupture force of each experimental group was then compared with the mean clinical retraction force for statistical signiticance using an independent samplest-test.

FIGURE 5. A custom-fabricated retractor attached to the lnstron the globes.

jig 850

consistin

1 M load

of an orbital floor ce 4I was used to rupture

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EXPERIMENTAL

Specimen

Yes No

A (Subtotalsclerallaceration)

26

B (No injury)

C (Through-and-throughlaceration) D (l&Gauge needlepuncture)

1

7

20

27

0

4

23

Accuracy Co/o) 96 74

100 15

25.22 kg), the perforated globes ruptured at 20.6 + 7.87 kg (range, 11.8 to 34.49 kg), and the through-andthrough lacerated globes ruptured at 4.94 ? 2.50 kg (range, 0.58 to 9.89 kg) (Table 2). The through-andthrough laceration group was statistically different (FoS5) = 8.963, P < .OOl) from all other groups. No significant differences were noted between any of the other groups. The pattern of behavior before and during rupture of the globe differed for each group. Rupture for the control group occurred with a dramatic sudden explosion of the internal contents. Before the explosion, the globe appeared to tense, but no visual defects or faults were noted. Rupture for the subtotal laceration group occurred with a lengthening and widening of the defect and then an explosion of the contents through this extended laceration. Rupture of the through-andthrough laceration group occurred after leakage of the orbital contents through the defect, lengthening or tearing of the defect, and then eventual collapse. The behavior of the perforated group was much different. As the pressure increased, the internal contents extruded out of the scleral perforation into a space between the sclera and cornea, then through the cornea1 perforation into a space between the cornea and conjunctiva, and then finally the orbit collapsed. The increased (but not statistically signiticant) force required to rupture the perforated globes reflected the accumulated force necessary for the

Range Rupture point of uninjured globe (n = 10) Rupture point of partially laceratedglobe (n = 10) Rupture point of perforated globe (n = 10) Rupture point of through-andthrough lacerated globe (n = 10) Clinical retraction force (n = 27)

Mean 2 SD

7.23-31.96 16.72 + 7.87 8.02-25.22

15.38 + 6.06

11.18-34.49 20.36 ? 7.87 0.58-9.89

4.94 t 2.56

0.05-2.05

0.35 + 0.47

GLOBE RUF’TLJRE

internal orbit contents to extrude through layer by layer, rather than the all-or-nothing response of the other groups. The force for retraction among the 27 surgeons ranged between 0.05 and 2.05 kg. The mean force of retraction was 0.35 + 0.47 kg (Table 2). The simulated clinical retraction force was statistically different from the rupture forces for the control (tcs, = 6.58, P < .OOl), perforated (tcs, = 8.04, P < .OOl>, subtotally lacerated (t (9) = 7.83, P < ,001) and totally lacerated (tc8, = 6.94, P < .OOl>groups.

Discussion Orbital rupture is a devastating injury that could result in diminished visual acuity, blindness, or the need to perform an orbital exenteration.11-15When associatedwith orbital fractures, it is generally considered to be a comorbid event. It has been suggested that the intraoperative occurrence of globe rupture during the treatment of orbital fractures is the result of the manipulation of an undiagnosed, yet previously injured globe.5 This premise seemsto be substantiated by numerous reports of patients whose globe integrity had been compromised by radial keratotomy or local anesthetic injection and then ruptured after incidental trauma or digital manipulation.~9 However, a distinct relationship between the amount of force needed to rupture an already traumatized globe has yet to be determined. Does injury compromise the integrity of the globe? Can these injuries be identified before initiating surgical therapy? Does retraction exert enough force to rupture an injured globe? This investigation provides answers to the aforementioned ques tions. Casereports of globe rupture in patients who were victims of incidental trauma or mere digital manipulation after radial keratotomy or local anesthetic injection have led to initiation of a series of benchtop investigations that focus on this matter. These investigations approached the rupture of globes from two different perspectives. The first experimental design incorporated increasing hydrostatic pressure by globe inflation until the tension was great enough to cause rupture. The second method used increasing external compression until the force was great enough to rupture the globe. Common to each method of experimentation were uncompromised globes (control) and those that had their integrity compromised or various degrees of subtotal orbital injury (puncture wound, keratotomy, or keratectomy).10JG18 Each of these conditions are germane to the results of our investigation. Magnante et al9 used 2 1 human eye bank eyes in an experiment designed to investigate globe rupture and hydrostatic pressure.9 In their investigation, normal

HAUG,

HAGHIGHI,

AND

BARBER

saline was introduced into the eyes, which led to an increased hydrostatic pressure and finally rupture of the sclera. They observed that rupture in the perilimbal region did not occur at the site of needle penetration. Rather, it occurred at sites remote from the perforation. Although different in purpose and design, our investigation provided a similar observation, showing that no statistical differences (P > ,001) existed in load to rupture between the uninjured control group and the 18 gauge needle-perforated group. Thus, it can be concluded that small-needle penetration does not compromise globe integrity and predispose it to rupture. Numerous investigations appear in the ophthalmologic literature that attempt to identify whether globe integrity is compromised by incisions, radial keratotomy, and laser photorefractive keratectomy. Burnstein et ali6 used 16 human eyes and 14 porcine eyes to determine whether corneal weakening occurred after photorefractive keratectomy.16 In their investigation, nitrogen gas was introduced into the globe until rupture. They concluded that keratectomy does not weaken the cornea after the degree of ablation commonly used in the clinical setting. Campos et all7 sought to evaluate occular integrity after refractive surgery using 46 porcine eyes. They divided the eyes into a control group, radial keratotomy group, photorefractive keratectomy group, and phototherapeutic keratectomy group. The eyes in these groups were then subjected to vertical compression forces. Statistically significant differences were not found between the control group, the photorefractive keratectomy group, and phototherapeutic keratectomy group. Although different in design and purpose, our investigation showed similar observations to these two studies. Our subtotal laceration group could be considered similar to the keratectomy groups of both Burnstein et all6 and Campos et al. I7 No statistically significant differences (P > ,001) were found between our uninjured control eyes and the subtotal laceration eyes in load to rupture. However, different findings appear to have been observed by other investigators. Rylander et all8 performed a benchtop investigation using 160 porcine eyes and an Instron unit with an experimental design similar to ours. l8 Radial keratectomy was performed to a constant 0.6-mm depth. Statistically different (P > .05) forces were noted between the control and radial keratectomy groups at rupture load. It seems that the depth of the incision may have been the critical factor. Kung et allo substantiated this observation. Their experiment compared incision depth versus number in compromising the integrity of the globe. That group used 70 porcine eyes and performed incisions at lOO%, 75%, and 50% cornea1 thickness, as well as, 4, 8, and 16 incisions. The eyes

1279 were then subjected to vertically deforming forces. Kung et allo concluded that incision depth was the most significant factor in compromising globe integrity. This observation was also noted in our investigation, although more exaggerated incision depths were used (subtotal vs total). No statistically significant differences (P > ,001) were noted between the uninjured control group and subtotal laceration group. However, the total laceration group differed from all other groups in load to rupture. The study with the 27 surgeons who performed a simulated globe retraction on the experimental device provided some very surprising information (Table 2). The mean retraction force was 0.35 t 0.47 kg. The nearest group in load to rupture was the total laceration group at a mean of 4.94 +- 2.56 kg. This was almost 15 times greater than the mean clinical retraction force. The rupture forces in the control and other injury groups were 40 to 60 times greater than the mean clinical retraction force. Although retraction causing rupture appears impossible, a comparison of the ranges for the retraction group and total laceration group (Table 2) indicate that, although not statistically probable (P < .OOl>, rupture is possible. It also must be taken into consideration that our experimental design incorporated retraction instrumentation that could only mimic the clinical setting and that bovine globes possessing a thicker sclera and cornea than humans were used. Our choice of animal rather than human globes was based on ethics, economy, and precision in experimentation. The use of 44 human eyes would have significantly limited the donor pool for patients requiring transplants. Also, the preservation modalities (chemical or thermal) used to maintain the cadavers would have compromised the structural integrity of the globe. Additionally, the use of fresh cadavers would have limited precision by the need to calibrate and recalibrate the Instron mechanical testing unit each time a new source became available. Finally, 44 human eyes range in cost from $6,500.00 to $15,000.00, as opposed to $2.00 from animal sources. Animal sources have been used numerous times for similar research projects, but the eye differs in dimension from that of humans. Human eyes possess a scleral thickness ranging from 0.4 to 1.0 mm and a cornea1 thickness ranging from 0.5 to 1.2 mm.” The bovine eyes in our investigation had a combined scleral/corneal thickness of 1.5 to 2.2 mm. Thus, we would expect that slightly greater forces would be required to rupture globes in cows than in humans. Although significant thought was given to the design of the instrumentation used for the measurement of retraction (see Materials and Methods), no benchtop mechanical instrumentation can entirely replicate the clinical setting.

1280 It was comforting to note that the injury that would be most likely to result in rupture in the intraoperative setting (through-and-through laceration) was the one that was diagnosed with 100% accuracy by the surgeons. However, the broad range of inaccuracy (4% to 85%) in diagnosing lesser forms of injury was disappointing. This emphasizes the need for a complete occular examination that includes not just a gross external examination, but also an examination of visual acuity, occular motility, visual fields, the fundus, and intraocular pressure using the proper instrumentation and techniques. If this cannot be performed, or if the surgeon is unfamiliar with these techniques, then ophthalmologic consultation and management are in order.‘JO Al-Qurainy et al *,*O have substantiated this philosophy in their prospective assessment of occular injury and determination of which patients are at risk. Their premise was that although occular injuries may be diEcult to detect without the requisite expertise and equipment, it is also impractical to refer all patients for ophthalmologic assessment. They developed a system based on their experience with 363 patients, using 54 parameters and outcomes, to determine which patients to refer. This Information was coupled with statistical methods of regression, the analysis of contingency tables, and identification of predictors Indicative of underlying ophthalmic injury. The predictors of blowout fracture, diminished visual acuity, diplopia, amnesia, and cornminuted trauma were most often associated with the need for ophthalmologic consultation and management. This is best remembered by the pneumonic BAD ACT (the first letter of each of the predictors). These predictors include those traditionally associated with scleral rupture-diminished visual acuity, decreased intraocular pressure, afferent pupillary defects, hyphema, and chemosis.2-4 Our investigation used synthetic materials and human anatomic substitutes and was performed as a benchtop experiment. Therefore, no direct applications to the clinical setting can be made. Despite this, certain trends were obvious and should influence the clinical decision-making process. First, although severe forms of injury were diagnosed with 100% accuracy by visual examination alone, lesser forms of injury were not. Hence, a thorough clinical examination with the proper instrumentation should be performed on all patients with suspected occular injuries. If the proper instrumentation is not available, or the proper training in examination has not been acquired, ophthalmologic consultation is required. Next, eyes with lesser forms of injury (small-gauge needle perforation or subtotal laceration) appear to react no differently than the uninjured eye when compressed. Also, the mean clinical retraction force did not approach the mean rupture force in eyes with lesser forms of

EXPERIMENTAL

GLOBE

RUPTURE

injury, and thus it would appear that concern for inducing intraoperative globe rupture is unfounded with these injuries. Yet, a comparison of the range of rupture forces in globes with total lacerations to the range of retraction forces suggests that rupture is possible. Certainly, care must be taken when the globe is manipulated in any fashion.

Acknowledgment The authors thank the members of the Ohio Society of Oral and Maxillofacial Surgeons who participated in this investigation.

References 1. Al-Qurainy AI, Titterington DM, Dutton GN, et al: Midfacial fractures and the eye: The development of a system for detecting patients at risk of eye injury. Br J Oral Maxillofac Surg 29:363, 1991 2. Kylstra JA, Lamkin JC, Runyan DK: Clinical predictors of scleral rupture after blunt trauma. Am J Ophthahnol 115530, 1993 MS, Dana MR, Viana MAG, et al: Predictors of occult 3. Werner scleral rupture. Ophthalmology 101:1941, 1994 4. Russell SR, Olsen KR, Folk JC: Predictors of scleral rupture and the role of vitrectomy in severe blunt ocular trauma. Am J Ophthahnol105:253, 1988 5. Haug RH, Bradrick JP, Morgan JP: Complications in the treatment of midface fractures. Chap 10, in Kaban LB, Pogrel MA, Perrott DH (eds): Complications in Oral and Maxillofacial Surgery. Philadelphia, PA, Saunders, 1997, pp 147-164 6. Pearlstein EX, Agapitos PJ, CantriLl HC, et al: Ruptured globe after radial keratotomy. Am J Ophthahnol1061755, 1988 7. McDonnell PJ, Lean JS, Schanzlin DJ: Globe rupture from blunt trauma after hexagonal keratotomy. Am J Ophthalmol 103:241, 1987 8. Rathi V, Basti S, Gupta S: Globe rupture during digital massage after peribulbar anesthesia. J Cataract Refract Surg 23:297, 1997 DO, Bullock JD, Green WR: Ocular explosion after 9. Magnante peribulbar anesthesia: Case report and experimental study. Ophthalmology 104608, 1997 10. Kung JS, Lucca JA, Santamaria J: Incision depth vs. incision number in the rupture strength of pig eyes following radical keratotomy. J Refract Surg 12:5294, 1996 11. Cherry PMH: Factors influencing prognosis in indirect traumatic rupture of the globe. Ann Ophthalmol95:275, 1979 12. Esmaeli B, Elner SG, Schork M, et al: Visual outcome and occular survival after penetrating trauma: A clinicopathologic study. Ophthalmology 102:393, 1995 of traumatic 13. L&get PE, Mani N, Green RE, et al: Management rupture of the globe in aphakic patients. Retina 10:59S, 1990 14. Freitag SK, Eagle RC, Jaeger EA, et al: An epidemiologic and pathologic study of globes enucleated following trauma. Ophthalmic Surg 23:409, 1992 PMH: Indirect traumatic rupture of the globe. Arch 15. Cherry Ophthalmol96:252,1978 Y, Klapper D, Hersh PS: Experimental globe rupture 16. Burnstem after excimer laser photorefractive keratectomy. Arch Ophthalmol 113:1056, 1995 M, Lee M, McDonnell PJ: Occular integrity after 17. Campos refractive surgery: Effects of photorefractive keratectomy, phototherapeutic keratectomy and radical keratotomy. Ophthalmic Surg 23:598, 1992 HG, Walsh AJ, Freinming B: The effect of radial 18. Rylander keratotomy in rupture strength of pig eyes. Ophthalmic Surg 14:744, 1983 19. William PL, Warwick R: Gray’s Anatomy (ed 36). Philadelphia, PA, Saunders, 1980, p 1152 AI, Stassen LFA, Dutton GN, et al: The characteris20. Al-Qurainy tics of midfacial fractures and the association with occular injury: A prospective study. Br J Oral Maxillofac Surg 29:291, 1991