Original Investigation
Changes in Intraocular Pressure During Orbital Floor Fracture Repair Preeti J. Thyparampil, M.D.*, Benjamin C. Campbell, B.S.*, Phillip N. Freeman, D.D.S., M.D.†, John D. Ng, M.D.‡, Jeremiah Tao, M.D.§, Michael T. Yen, M.D.*, and Douglas P. Marx, M.D.* *Department of Ophthalmology, Alkek Eye Center, Baylor College of Medicine; †Department of Oral and Maxillofacial Surgery, University of Texas Health Science Center, Houston, Texas; ‡Department of Ophthalmology, Casey Eye Institute, Oregon Health and Sciences University, Portland, Oregon; and §Department of Ophthalmology, Oculofacial Plastic and Orbital Surgery, Gavin Herbert Eye Institute, University of California, Irvine, California, U.S.A.
Purpose: To evaluate changes in intraocular pressure (IOP) during orbital floor fracture repair. Methods: Retrospective chart review of patients undergoing isolated orbital floor fracture repair with implant placement at a level 1 trauma center and tertiary care center. Patients with combined zygomaticomaxillary or medial wall fracture repair, or other significant ocular injuries were excluded. IOP measurements using a handheld applanation tonometer were recorded immediately after induction of anesthesia, immediately after orbital floor implant placement, and on postoperative day 1. Results: Nine patients who underwent isolated orbital floor fracture repair were examined. There was a statistically significant mean decrease of 4.66 mmHg (p < 0.05) in IOP from prior to surgical to immediately after implant placement. There was also a significant mean increase in IOP of 7.44 mmHg (p < 0.05) at postoperative day 1 compared with immediately after implant placement. There was no statistically significant difference in IOP between prior to surgical incision and postoperative day 1. Conclusions: All patients who underwent orbital floor fracture repair in this study had a significant decrease in IOP during orbital floor fracture repair that returned to immediately preoperative levels by postoperative day 1. This initial decrease in IOP may be because of intraoperative manipulation of the globe. (Ophthal Plast Reconstr Surg 2015;31:303–305)
O
rbital floor fractures are common after orbital trauma due to the thinness of the bone and the large maxillary sinus space beneath the floor. The frequency of orbital floor fractures following orbital trauma varies between studies with the most common mechanism of injury usually being motor vehicle accidents. Often these fractures can be managed nonoperatively and prior studies have established accepted indications for surgical repair. Trauma leading to orbital wall fractures can sometimes be accompanied by ocular injuries.1–3 Careful preoperative ocular examination is important to identify any findings that may indicate a more serious injury to the eye before correction of Accepted for publication August 13, 2014. The authors have no financial or conflicts of interest to disclose. Address correspondence and reprint requests to Douglas P. Marx, m.d., 1977 Butler Boulevard, Baylor College of Medicine, Alkek Eye Center, Houston, TX 77584. E-mail: [email protected] DOI: 10.1097/IOP.0000000000000322
Ophthal Plast Reconstr Surg, Vol. 31, No. 4, 2015
the fracture is undertaken. Even with careful inspection, however, some ocular injuries are still missed.1 Consequently, the surgeon must watch for ocular injuries and prevent further injury during fracture repair. It has been the experience of the authors that during or immediately after orbital floor fracture repair the globe can at times feel subjectively soft. Careful inspection, however, reveals an intact globe with no apparent injury. Furthermore, it is generally uncommon for a patient to develop new major ocular injuries following orbital floor fracture repair if there were no preoperative ocular findings.4 This has led to the question of what causes the soft globe during the operation. The purpose of this study is to determine if there is a possible relationship between surgical repair of orbital floor fractures and a decreased intraocular pressure (IOP). This may be of visual significance because large decreases in IOP have been associated with conditions such as hypotony maculopathy and retinal detachment. There have been few studies to date5–8 that have examined the possible relationship between IOP and orbital fracture repair and the results of these studies have been inconclusive. Forrest et al5 showed an increase in IOP, measured by Schiotz tonometer, immediately following graft placement in 35 patients undergoing orbital–zygomatic complex fracture repair. Murray and O’Sullivan,6 however, found a decrease in IOP measured by applanation tonometry in 18 patients immediately after reduction and fixation of zygomatic fractures. Paton et al7 examined 20 patients with orbitozygomatic complex fractures and found no difference in IOP at any time point. Zhou et al.8 found an increase in IOP measured by Schiotz tonometer postoperatively in 40 patients undergoing orbital fracture repair, none of which were orbital floor fractures. They did not check intraoperative IOP. These studies were limited by their small size and the fact that they examined a variety of types of orbital fractures. The literature to date is inconclusive on how orbital fracture repair affects IOP. This study aims to evaluate this relationship. We hypothesize that there is a decrease in IOP after orbital floor fracture repair, possibly due to intraoperative manipulation of the globe.
METHODS This retrospective study was approved by the Baylor College of Medicine Institutional Review Board. The patients were treated according to the tenets of the Declaration of Helsinki and in compliance with The Health Insurance Portability and Accountability Act. A retrospective chart review was conducted on patients who underwent isolated orbital floor fracture repair, with implant placement, from June 2011 to May 2014 at a level 1 trauma center and tertiary care center. Patients who had combined zygomaticomaxillary or
303
Copyright © 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc. Unauthorized reproduction of this article is prohibited.
Ophthal Plast Reconstr Surg, Vol. 31, No. 4, 2015
P. J. Thyparampil et al.
TABLE 1. Patient demographics and IOP measurements Preoperative Intraoperative Postoperative IOP IOP day 1 IOP Patient Gender Age (mmHg) (mmHg) (mmHg) 1 2 3 4 5 6 7 8 9
F M M M F M M F M
22 44 47 30 26 33 48 42 39
12 16 18 13 11 7 13 15 19
4 12 13 11 9 6 6 7 14
13 18 20 21 15 17 18 12 15
1 was 16.6 mmHg. Paired t tests were used to evaluate the differences in the mean IOP measurements at each time period and can be found in Table 2. There was a statistically significant decrease (p < 0.05) in IOP measurements taken intraoperatively immediately after implant placement from presurgical incision values. The increase between postimplant placement IOP and postoperative day 1 measurements was also statistically significant (p < 0.05). There was no statistically significant difference between presurgical incision and postoperative day 1 IOP values.
DISCUSSION
M, male; F, female, IOP, intraocular pressure.
medial wall fracture repair were excluded. Those with other significant ocular injuries were also excluded, including intraocular hemorrhage, iritis, acute retinal detachment, open globe, and retrobulbar hematoma. Patients with active orbital hemorrhage or significant periorbital edema were also excluded from the study. After Institutional Review Board approval, patients were identified who met the criteria outlined above and for whom there were IOP measurements available before, during, and after fracture repair. IOP measurements were recorded from each patient, in the operative eye, immediately after induction of anesthesia, intraoperatively immediately after orbital floor implant placement, and on postoperative day 1. Data collected included patient demographics along with IOP measurements. Statistical analysis was used to compare the IOP measurements at these different time periods. All IOP measurements were done by an ophthalmologist using the Tono-Pen AVIA applanation tonometer (Reichert Technologies, Buffalo, NY, U.S.A.). All patients underwent fracture repair using a lower eyelid transconjunctival incision with an associated canthotomy and inferior cantholysis. A freer elevator was then used to elevate the periosteum to expose the orbital floor fracture and malleable retractors were used to expose the fracture. The herniated tissue was then gently removed from the fracture with the use of a freer elevator. An appropriately sized implant was then placed over the orbital fracture under the periosteum. All subjects involved in the study gave informed consent for the treatment described.
RESULTS Nine patients underwent isolated orbital floor fracture repair with implant during the study period for which there were IOP measurements available. Of these patients, 3 were female and 6 were male. The average age was 36 with a range from 22 to 48 years. The patient demographics, along with the IOP measurements from the 3 different time periods are reported in Table 1. The average length of time between injury and repair was 19 days (range, 3–31 days). All patients had a decrease in IOP immediately following implant placement compared with prior to surgical incision and all patients had an increase in IOP from postimplant placement to postoperative day 1. The mean IOP presurgical incision was 13.8 mmHg, immediately following implant placement was 9.1 mmHg, and on postoperative day
IOP is an important indicator used by ophthalmologists to assess ocular health, especially after orbital trauma. Extreme variations in IOP can aid in the diagnostic workup of orbital trauma, such as low IOP being associated with open globe injuries and high IOP with retrobulbar hematomas. These extremes in IOP also contribute to the pathogenesis of other various conditions. There are several factors that determine the IOP, but for clinical purposes the fluid mechanics of aqueous humor are the most important determinant. The hydraulics of aqueous dynamics can be approximated by the following equation9: IOP = Pe +
Fin − Fu Ctrab
where Pe is the episcleral venous pressure; Fin, the total aqueous humor inflow; Fu, the outflow via uveoscleral pathway; and Ctrab, the facility of outflow via trabecular pathway. The above equation assumes a steady state where the inflow of humor is equal to the outflow. As illustrated in the equation, IOP is directly related to the ease of humor flux through the trabecular meshwork, and the external pressure exerted on the eye by orbital contents, which affects the episcleral venous pressure. Previous studies5–8 examining the relationship between IOP and orbital fracture repair generally hypothesized that there was a possible increase in IOP immediately after orbital fracture repair because of increased external pressure on the eye generated by surrounding ocular muscles, orbital fat, implants, and orbital venous pressure. Forrest et al5 and Zhou et al8 both described an orbital compartment syndrome, where the restoration of intraorbital contents and ensuing edema during orbital fracture repair causes an increase in IOP by raising the episcleral venous pressure and preventing adequate drainage of aqueous humor. Our study evaluated IOP changes during repair of isolated orbital floor fractures. Measurements were performed by trained ophthalmologists using a handheld applanation tonometer which has been proven a reliable and accurate method to determine IOP in previous studies.10,11 We found a statistically significant decrease in pressure intraoperatively immediately following implant placement compared with measurements prior to surgical incision, consistent with our hypothesis. During the measurements taken prior to surgical incision and immediately following implant placement, the patient was in a supine position and under general anesthesia, thus eliminating confounding of the IOP measurements by positional change and anesthetics. Patients with active intraocular or orbital hemorrhage or
TABLE 2. Difference in mean IOP measurements Time period comparison Preoperative versus intraoperative Intraoperative versus postoperative day 1 Preoperative versus postoperative day 1
304
Mean difference in IOP (mmHg)
Lower limit 95% confidence interval
Upper limit 95% confidence interval
Paired t test (p value)
−4.67 7.44 4.33
−6.79 5.41 2.43
−2.55 9.47 6.23
0.0148 0.0002 0.1013
© 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc.
Copyright © 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc. Unauthorized reproduction of this article is prohibited.
Ophthal Plast Reconstr Surg, Vol. 31, No. 4, 2015
significant periorbital edema were not included in the study because these factors can cause an elevation in IOP.12 The decrease in IOP immediately following orbital floor fracture repair may be due to the orbital manipulation that occurs during the operation. External pressure placed on the globe during surgery initially raises the IOP, whereas also forcing aqueous humor into the anterior chamber angle and increasing outflow through the trabecular meshwork. The loss of aqueous that occurs would cause the reduction in IOP that we observed. This phenomenon is the basis for several well-established techniques used to transiently lower the IOP via ocular manipulation. Dynamic or indentation gonioscopy places pressure on the cornea to increase aqueous outflow with a resulting IOP reduction.13 Ocular compression with devices such as a Honan balloon uses the same mechanism to soften the globe prior to cataract surgery or to decrease IOP following peribulbar injections.14–16 Scleral indentation and manual compression of the eye also have been shown to lower IOP.17 We hypothesize that the orbital manipulation that occurs during orbital floor fracture repair causes increased flux through the trabecular meshwork, thus effectively lowering the IOP temporarily. After surgery, the outflow of aqueous humor normalizes and the IOP returns to immediately preoperative levels. There was no significant difference between the preincision and postoperative day 1 IOP measurements. Our results also showed a significant increase in IOP comparing immediately following implant placement to postoperative day 1 measurements. We recognize that these results may not be accurate, however, given the many confounding variables that exist between comparing the preincision and postimplant placement measurements to the postoperative day 1 measurements, such as the time of day the IOP was checked, the position of the patient during measurement, and the effects of anesthesia on IOP. On postoperative day 1, the orbit is also expected to be edematous from surgery, causing an increase in orbital pressure and subsequently the IOP given the correlation between these 2 pressures.12 Although the mean intraoperative IOP in the study was only slightly below the normal range (10–21 mmHg), there may be visual consequences due to the change in IOP observed such as hypotony maculopathy, choroidal detachments, and retinal detachments. Future studies, however, are needed to completely understand if any clinically relevant physiologic changes are common in patients who undergo orbital fracture repair. This study was limited by its small sample size and retrospective nature. There was also a lack of control group as IOP measurements for the nonoperative eye were not available at the same time frames. Hertel measurements were also not available but could have more accurately quantified the extent of orbital edema present pre and postoperatively. Another limitation is that the influence of anesthesia is not accounted for, and it could be possible that certain agents used in general anesthesia or the induction of anesthesia had an effect on IOP. Further studies are needed to compare IOP measurements in the operative eye to the nonoperative eye as a control. Additional IOP measurements shortly following surgery could show how quickly the IOP returns back to preoperative values, and IOP values a few weeks following surgery would demonstrate when IOP returns
Changes in Intraocular Pressure
to its baseline. Furthermore, it would be helpful to measure the intraorbital pressure at these same time points and have a larger, prospective study to accurately assess the relationship between IOP and orbital floor fracture repair. In summary, all patients who underwent orbital floor fracture repair in this study had a significant decrease in IOP, which returned to immediately preoperative levels by postoperative day 1. This initial decrease in IOP may be because of intraoperative manipulation of the globe. Clinicians should be aware of this phenomenon and further studies may be warranted to evaluate the clinical consequences of IOP decrease during orbital surgery.
REFERENCES 1. Cook T. Ocular and periocular injuries from orbital fractures. J Am Coll Surg 2002;195:831–4. 2. al-Qurainy IA, Stassen LF, Dutton GN, et al. The characteristics of midfacial fractures and the association with ocular injury: a prospective study. Br J Oral Maxillofac Surg 1991;29:291–301. 3. Barry C, Coyle M, Idrees Z, et al. Ocular findings in patients with orbitozygomatic complex fractures: a retrospective study. J Oral Maxillofac Surg 2008;66:888–92. 4. Peacock ZS, Boulos T, Miller JB, et al. Orbital fractures and ocular injury: Is a postoperative ophthalmology examination necessary? J Oral Maxillofac Surg 2014;72:1533–40. 5. Forrest CR, Khairallah E, Kuzon WM, Jr. Intraocular and intraorbital compartment pressure changes following orbital bone grafting: a clinical and laboratory study. Plast Reconstr Surg 1999;104:48–54. 6. Murray DJ, O’Sullivan ST. Intraocular pressure variations during zygomatic fracture reduction and fixation: a clinical study. Plast Reconstr Surg 2007;120:746–52. 7. Paton GJ, Aquilina PJ, Lynham A, et al. Intraocular pressure changes secondary to reduction of orbito-zygomatic complex fractures. J Oral Maxillofac Surg 2006;64:100–3. 8. Zhou H, Fan X, Xiao C. Direct orbital manometry in normal and fractured orbits of Chinese patients. J Oral Maxillofac Surg 2007;65:2282–7. 9. Gabelt BT, Kaufman PL. Production and flow of aqueous humor. In: Levin LA, Nilsson SFE, Ver Hoeve J, et al, eds. Adler’s Physiology of the Eye. 11th ed. Elsevier Inc., 2011. 10. Yang HS, Kim JG, Ko HS, et al. In vivo validation of the new Tonopen AVIA tonometer using manometers placed in the anterior chamber and the vitreous cavity under various vitreous conditions. Curr Eye Res 2014;39: 370–7. 11. Bhartiya S, Bali SJ, James M, et al. Test retest variability of TonoPen AVIA. Indian J Ophthalmol 2013;61:129–31. 12. Zoumalan CI, Bullock JD, Warwar RE, et al. Evaluation of intraocular and orbital pressure in the management of orbital hemorrhage: an experimental model. Arch Ophthalmol 2008;126:1257–60. 13. Hoskins HD, Jr. Interpretive gonioscopy in glaucoma. Invest Ophthalmol 1972;11:97–102. 14. Vallance JH, Patton N, Ferguson A, Bennett HG. Effect of the Honan intraocular pressure reducer in sub-Tenon’s anesthesia. J Cataract Refract Surg 2004; 30:433–6. 15. Ling R, Beigi B, Quinn A, et al. Effect of Honan balloon compression on peribulbar anesthesia adequacy in cataract surgery. J Cataract Refract Surg 2002;28:113–7. 16. Bowman R, Liu C, Sarkies N. Intraocular pressure changes after peribulbar injections with and without ocular compression. Br J Ophthalmol 1996;80:394–7. 17. Semes LP, Blash MM, Woolley T. Intraocular pressure response to scleral indentation. Optom Vis Sci 1993;70:729–32.
© 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc.
305
Copyright © 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc. Unauthorized reproduction of this article is prohibited.
Changes in Intraocular Pressure During Orbital Floor Fracture Repair Preeti J. Thyparampil, M.D.*, Benjamin C. Campbell, B.S.*, Phillip N. Freeman, D.D.S., M.D.†, John D. Ng, M.D.‡, Jeremiah Tao, M.D.§, Michael T. Yen, M.D.*, and Douglas P. Marx, M.D.* *Department of Ophthalmology, Alkek Eye Center, Baylor College of Medicine; †Department of Oral and Maxillofacial Surgery, University of Texas Health Science Center, Houston, Texas; ‡Department of Ophthalmology, Casey Eye Institute, Oregon Health and Sciences University, Portland, Oregon; and §Department of Ophthalmology, Oculofacial Plastic and Orbital Surgery, Gavin Herbert Eye Institute, University of California, Irvine, California, U.S.A.
Purpose: To evaluate changes in intraocular pressure (IOP) during orbital floor fracture repair. Methods: Retrospective chart review of patients undergoing isolated orbital floor fracture repair with implant placement at a level 1 trauma center and tertiary care center. Patients with combined zygomaticomaxillary or medial wall fracture repair, or other significant ocular injuries were excluded. IOP measurements using a handheld applanation tonometer were recorded immediately after induction of anesthesia, immediately after orbital floor implant placement, and on postoperative day 1. Results: Nine patients who underwent isolated orbital floor fracture repair were examined. There was a statistically significant mean decrease of 4.66 mmHg (p < 0.05) in IOP from prior to surgical to immediately after implant placement. There was also a significant mean increase in IOP of 7.44 mmHg (p < 0.05) at postoperative day 1 compared with immediately after implant placement. There was no statistically significant difference in IOP between prior to surgical incision and postoperative day 1. Conclusions: All patients who underwent orbital floor fracture repair in this study had a significant decrease in IOP during orbital floor fracture repair that returned to immediately preoperative levels by postoperative day 1. This initial decrease in IOP may be because of intraoperative manipulation of the globe. (Ophthal Plast Reconstr Surg 2015;31:303–305)
O
rbital floor fractures are common after orbital trauma due to the thinness of the bone and the large maxillary sinus space beneath the floor. The frequency of orbital floor fractures following orbital trauma varies between studies with the most common mechanism of injury usually being motor vehicle accidents. Often these fractures can be managed nonoperatively and prior studies have established accepted indications for surgical repair. Trauma leading to orbital wall fractures can sometimes be accompanied by ocular injuries.1–3 Careful preoperative ocular examination is important to identify any findings that may indicate a more serious injury to the eye before correction of Accepted for publication August 13, 2014. The authors have no financial or conflicts of interest to disclose. Address correspondence and reprint requests to Douglas P. Marx, m.d., 1977 Butler Boulevard, Baylor College of Medicine, Alkek Eye Center, Houston, TX 77584. E-mail: [email protected] DOI: 10.1097/IOP.0000000000000322
Ophthal Plast Reconstr Surg, Vol. 31, No. 4, 2015
the fracture is undertaken. Even with careful inspection, however, some ocular injuries are still missed.1 Consequently, the surgeon must watch for ocular injuries and prevent further injury during fracture repair. It has been the experience of the authors that during or immediately after orbital floor fracture repair the globe can at times feel subjectively soft. Careful inspection, however, reveals an intact globe with no apparent injury. Furthermore, it is generally uncommon for a patient to develop new major ocular injuries following orbital floor fracture repair if there were no preoperative ocular findings.4 This has led to the question of what causes the soft globe during the operation. The purpose of this study is to determine if there is a possible relationship between surgical repair of orbital floor fractures and a decreased intraocular pressure (IOP). This may be of visual significance because large decreases in IOP have been associated with conditions such as hypotony maculopathy and retinal detachment. There have been few studies to date5–8 that have examined the possible relationship between IOP and orbital fracture repair and the results of these studies have been inconclusive. Forrest et al5 showed an increase in IOP, measured by Schiotz tonometer, immediately following graft placement in 35 patients undergoing orbital–zygomatic complex fracture repair. Murray and O’Sullivan,6 however, found a decrease in IOP measured by applanation tonometry in 18 patients immediately after reduction and fixation of zygomatic fractures. Paton et al7 examined 20 patients with orbitozygomatic complex fractures and found no difference in IOP at any time point. Zhou et al.8 found an increase in IOP measured by Schiotz tonometer postoperatively in 40 patients undergoing orbital fracture repair, none of which were orbital floor fractures. They did not check intraoperative IOP. These studies were limited by their small size and the fact that they examined a variety of types of orbital fractures. The literature to date is inconclusive on how orbital fracture repair affects IOP. This study aims to evaluate this relationship. We hypothesize that there is a decrease in IOP after orbital floor fracture repair, possibly due to intraoperative manipulation of the globe.
METHODS This retrospective study was approved by the Baylor College of Medicine Institutional Review Board. The patients were treated according to the tenets of the Declaration of Helsinki and in compliance with The Health Insurance Portability and Accountability Act. A retrospective chart review was conducted on patients who underwent isolated orbital floor fracture repair, with implant placement, from June 2011 to May 2014 at a level 1 trauma center and tertiary care center. Patients who had combined zygomaticomaxillary or
303
Copyright © 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc. Unauthorized reproduction of this article is prohibited.
Ophthal Plast Reconstr Surg, Vol. 31, No. 4, 2015
P. J. Thyparampil et al.
TABLE 1. Patient demographics and IOP measurements Preoperative Intraoperative Postoperative IOP IOP day 1 IOP Patient Gender Age (mmHg) (mmHg) (mmHg) 1 2 3 4 5 6 7 8 9
F M M M F M M F M
22 44 47 30 26 33 48 42 39
12 16 18 13 11 7 13 15 19
4 12 13 11 9 6 6 7 14
13 18 20 21 15 17 18 12 15
1 was 16.6 mmHg. Paired t tests were used to evaluate the differences in the mean IOP measurements at each time period and can be found in Table 2. There was a statistically significant decrease (p < 0.05) in IOP measurements taken intraoperatively immediately after implant placement from presurgical incision values. The increase between postimplant placement IOP and postoperative day 1 measurements was also statistically significant (p < 0.05). There was no statistically significant difference between presurgical incision and postoperative day 1 IOP values.
DISCUSSION
M, male; F, female, IOP, intraocular pressure.
medial wall fracture repair were excluded. Those with other significant ocular injuries were also excluded, including intraocular hemorrhage, iritis, acute retinal detachment, open globe, and retrobulbar hematoma. Patients with active orbital hemorrhage or significant periorbital edema were also excluded from the study. After Institutional Review Board approval, patients were identified who met the criteria outlined above and for whom there were IOP measurements available before, during, and after fracture repair. IOP measurements were recorded from each patient, in the operative eye, immediately after induction of anesthesia, intraoperatively immediately after orbital floor implant placement, and on postoperative day 1. Data collected included patient demographics along with IOP measurements. Statistical analysis was used to compare the IOP measurements at these different time periods. All IOP measurements were done by an ophthalmologist using the Tono-Pen AVIA applanation tonometer (Reichert Technologies, Buffalo, NY, U.S.A.). All patients underwent fracture repair using a lower eyelid transconjunctival incision with an associated canthotomy and inferior cantholysis. A freer elevator was then used to elevate the periosteum to expose the orbital floor fracture and malleable retractors were used to expose the fracture. The herniated tissue was then gently removed from the fracture with the use of a freer elevator. An appropriately sized implant was then placed over the orbital fracture under the periosteum. All subjects involved in the study gave informed consent for the treatment described.
RESULTS Nine patients underwent isolated orbital floor fracture repair with implant during the study period for which there were IOP measurements available. Of these patients, 3 were female and 6 were male. The average age was 36 with a range from 22 to 48 years. The patient demographics, along with the IOP measurements from the 3 different time periods are reported in Table 1. The average length of time between injury and repair was 19 days (range, 3–31 days). All patients had a decrease in IOP immediately following implant placement compared with prior to surgical incision and all patients had an increase in IOP from postimplant placement to postoperative day 1. The mean IOP presurgical incision was 13.8 mmHg, immediately following implant placement was 9.1 mmHg, and on postoperative day
IOP is an important indicator used by ophthalmologists to assess ocular health, especially after orbital trauma. Extreme variations in IOP can aid in the diagnostic workup of orbital trauma, such as low IOP being associated with open globe injuries and high IOP with retrobulbar hematomas. These extremes in IOP also contribute to the pathogenesis of other various conditions. There are several factors that determine the IOP, but for clinical purposes the fluid mechanics of aqueous humor are the most important determinant. The hydraulics of aqueous dynamics can be approximated by the following equation9: IOP = Pe +
Fin − Fu Ctrab
where Pe is the episcleral venous pressure; Fin, the total aqueous humor inflow; Fu, the outflow via uveoscleral pathway; and Ctrab, the facility of outflow via trabecular pathway. The above equation assumes a steady state where the inflow of humor is equal to the outflow. As illustrated in the equation, IOP is directly related to the ease of humor flux through the trabecular meshwork, and the external pressure exerted on the eye by orbital contents, which affects the episcleral venous pressure. Previous studies5–8 examining the relationship between IOP and orbital fracture repair generally hypothesized that there was a possible increase in IOP immediately after orbital fracture repair because of increased external pressure on the eye generated by surrounding ocular muscles, orbital fat, implants, and orbital venous pressure. Forrest et al5 and Zhou et al8 both described an orbital compartment syndrome, where the restoration of intraorbital contents and ensuing edema during orbital fracture repair causes an increase in IOP by raising the episcleral venous pressure and preventing adequate drainage of aqueous humor. Our study evaluated IOP changes during repair of isolated orbital floor fractures. Measurements were performed by trained ophthalmologists using a handheld applanation tonometer which has been proven a reliable and accurate method to determine IOP in previous studies.10,11 We found a statistically significant decrease in pressure intraoperatively immediately following implant placement compared with measurements prior to surgical incision, consistent with our hypothesis. During the measurements taken prior to surgical incision and immediately following implant placement, the patient was in a supine position and under general anesthesia, thus eliminating confounding of the IOP measurements by positional change and anesthetics. Patients with active intraocular or orbital hemorrhage or
TABLE 2. Difference in mean IOP measurements Time period comparison Preoperative versus intraoperative Intraoperative versus postoperative day 1 Preoperative versus postoperative day 1
304
Mean difference in IOP (mmHg)
Lower limit 95% confidence interval
Upper limit 95% confidence interval
Paired t test (p value)
−4.67 7.44 4.33
−6.79 5.41 2.43
−2.55 9.47 6.23
0.0148 0.0002 0.1013
© 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc.
Copyright © 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc. Unauthorized reproduction of this article is prohibited.
Ophthal Plast Reconstr Surg, Vol. 31, No. 4, 2015
significant periorbital edema were not included in the study because these factors can cause an elevation in IOP.12 The decrease in IOP immediately following orbital floor fracture repair may be due to the orbital manipulation that occurs during the operation. External pressure placed on the globe during surgery initially raises the IOP, whereas also forcing aqueous humor into the anterior chamber angle and increasing outflow through the trabecular meshwork. The loss of aqueous that occurs would cause the reduction in IOP that we observed. This phenomenon is the basis for several well-established techniques used to transiently lower the IOP via ocular manipulation. Dynamic or indentation gonioscopy places pressure on the cornea to increase aqueous outflow with a resulting IOP reduction.13 Ocular compression with devices such as a Honan balloon uses the same mechanism to soften the globe prior to cataract surgery or to decrease IOP following peribulbar injections.14–16 Scleral indentation and manual compression of the eye also have been shown to lower IOP.17 We hypothesize that the orbital manipulation that occurs during orbital floor fracture repair causes increased flux through the trabecular meshwork, thus effectively lowering the IOP temporarily. After surgery, the outflow of aqueous humor normalizes and the IOP returns to immediately preoperative levels. There was no significant difference between the preincision and postoperative day 1 IOP measurements. Our results also showed a significant increase in IOP comparing immediately following implant placement to postoperative day 1 measurements. We recognize that these results may not be accurate, however, given the many confounding variables that exist between comparing the preincision and postimplant placement measurements to the postoperative day 1 measurements, such as the time of day the IOP was checked, the position of the patient during measurement, and the effects of anesthesia on IOP. On postoperative day 1, the orbit is also expected to be edematous from surgery, causing an increase in orbital pressure and subsequently the IOP given the correlation between these 2 pressures.12 Although the mean intraoperative IOP in the study was only slightly below the normal range (10–21 mmHg), there may be visual consequences due to the change in IOP observed such as hypotony maculopathy, choroidal detachments, and retinal detachments. Future studies, however, are needed to completely understand if any clinically relevant physiologic changes are common in patients who undergo orbital fracture repair. This study was limited by its small sample size and retrospective nature. There was also a lack of control group as IOP measurements for the nonoperative eye were not available at the same time frames. Hertel measurements were also not available but could have more accurately quantified the extent of orbital edema present pre and postoperatively. Another limitation is that the influence of anesthesia is not accounted for, and it could be possible that certain agents used in general anesthesia or the induction of anesthesia had an effect on IOP. Further studies are needed to compare IOP measurements in the operative eye to the nonoperative eye as a control. Additional IOP measurements shortly following surgery could show how quickly the IOP returns back to preoperative values, and IOP values a few weeks following surgery would demonstrate when IOP returns
Changes in Intraocular Pressure
to its baseline. Furthermore, it would be helpful to measure the intraorbital pressure at these same time points and have a larger, prospective study to accurately assess the relationship between IOP and orbital floor fracture repair. In summary, all patients who underwent orbital floor fracture repair in this study had a significant decrease in IOP, which returned to immediately preoperative levels by postoperative day 1. This initial decrease in IOP may be because of intraoperative manipulation of the globe. Clinicians should be aware of this phenomenon and further studies may be warranted to evaluate the clinical consequences of IOP decrease during orbital surgery.
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