The effect of prone positioning on intraocular pressure in anesthetized patients

The prone position in COVID-19 impacts the thickness of peripapillary retinal nerve fiber layers and macular ganglion cell layers

The prone position reduces mortality in severe cases of COVID-19 with acute respiratory distress syndrome. However, visual loss and changes to the peripapillary retinal nerve fiber layer (p-RNFL) and the macular ganglion cell layer and inner plexiform layer (m-GCIPL) have occurred in patients undergoing surgery in the prone position. Moreover, COVID-19-related eye problems have been reported. This study compared the p-RNFL and m-GCIPL thicknesses of COVID-19 patients who were placed in the prone position with patients who were not. This prospective longitudinal and case-control study investigated 15 COVID-19 patients placed in the prone position (the "Prone Group"), 23 COVID-19 patients not in the prone position (the "Non-Prone Group"), and 23 healthy, non-COVID individuals without ocular disease or systemic conditions (the "Control Group"). The p-RNFL and m-GCIPL thicknesses of the COVID-19 patients were measured at 1, 3, and 6 months and compared within and between groups. The result showed that the Prone and Non-Prone Groups had no significant differences in their p-RNFL thicknesses at the 3 follow-ups. However, the m-GCIPL analysis revealed significant differences in the inferior sector of the Non-Prone Group between months 1 and 3 (mean difference, 0.74 μm; P = 0.009). The p-RNFL analysis showed a significantly greater thickness at 6 months for the superior sector of the Non-Prone Group (131.61 ± 12.08 μm) than for the Prone Group (118.87 ± 18.21 μm; P = 0.039). The m-GCIPL analysis revealed that the inferior sector was significantly thinner in the Non-Prone Group than in the Control Group (at 1 month 80.57 ± 4.60 versus 83.87 ± 5.43 μm; P = 0.031 and at 6 months 80.48 ± 3.96 versus 83.87 ± 5.43 μm; P = 0.044). In conclusion, the prone position in COVID-19 patients can lead to early loss of p-RNFL thickness due to rising intraocular pressure, which is independent of the timing of prone positioning. Consequently, there is no increase in COVID-19 patients' morbidity burden.

Validation of intraocular pressure measurement using tonometer AVIA across different postures: A Bland Altman analysis

AIMS/OBJECTIVES

Tonometry is a fundamental procedure in the diagnosis and management of glaucoma. Different tonometers have been proposed but none are as accurate as the Goldman applanation tonometry (GAT). Nonetheless, due to the limitations of GAT, mobile tonometry methods became prevalent. This study aims to examine the reliability of the Tono-Pen AVIA® (TPA) in measuring intraocular pressure (IOP) across different postures.

METHODS

A total of 196 eyes were prospectively examined for IOP changes using GAT and TPA. IOP measurements were taken across different postures using the TPA. Reliability of measurements was compared using interclass correlation coefficients (ICC), while agreement was represented using Bland-Altman analysis. Pearson r coefficient was used to measure correlations.

RESULTS

When compared to GAT (14.5 ± 4.4 mmHg), IOP readings were significantly higher for TPA at both seated (16.5 ± 4.5 mmHg; p < 0.001) and supine (16.9 ± 5.7; p < 0.001) positions. The ICC values for GAT and TPA among seated and supine patients were 0.79 (0.54-0.90) and 0.76 (0.48-0.87) indicating good reliability between the readings. There were significantly positive correlations between GAT and TPA at both seated (r = 0.626, p < 0.001) and supine (r = 0.727, p < 0.001) positions. Per Bland-Altman analysis, limits of agreement were -8.57 to 4.37 for GAT and seated TPA and -10.34 and 5.34 for GAT and supine TPA.

CONCLUSION

Good reliability exists between IOP measurements using GAT and TPA. However, the devices are not interchangeable and therefore cannot be used reciprocally in the same patient.

Perioperative Blindness in Spine Surgery: A Scoping Literature Review

Perioperative vision loss (POVL) is a devastating surgical complication that impacts both the recovery from surgery and quality of life, most commonly occurring after spine surgery. With rates of spine surgery dramatically increasing, the prevalence of POVL will increase proportionately. This scoping review aims to aggregate the literature pertinent to POVL in spine surgery and consolidate recommendations and preventative measures to reduce the risk of POVL. There are several causes of POVL, and the main contribution following spine surgery is ischemic optic neuropathy (ION). Vision loss often manifests immediately following surgery and is irreversible and severe. Diffusion weighted imaging has recently surfaced as a diagnostic tool to identify ION. There are no effective treatments; therefore, risk stratification for counseling and prevention are vital. Patients undergoing prone surgery of long duration and/or with significant expected blood loss are at greatest risk. Future research is necessary to develop effective treatments.

Effect of neck extension on intraocular pressure in paediatric patients undergoing palatoplasty

BACKGROUND

Intraocular pressure (IOP) can increase with postural changes, which can cause ocular complications. Neck extension is commonly used during palatoplasty to improve surgical angulation. This study evaluates whether neck extension affects IOP during palatoplasty.

METHODS

In this prospective observational study, IOP was measured using a rebound tonometer at four specific time points: T1, 10 min after anaesthesia while in the supine position; T2, 5 min after neck extension; T3, at completion of palatoplasty with neck extended; and T4, 5 min after returning to the supine position. The primary outcome was the IOP at T2, and the secondary outcomes were the IOPs at T3 and T4. Haemodynamic and respiratory variables were also measured at each time point.

RESULTS

Thirty-seven patients were included. IOP at T2 was significantly higher than at T1 (15.8 ± 3.4 mmHg vs 10.5 ± 2.8 mmHg, P < 0.001), and IOPs at T3 and T4 were also significantly higher than at T1 (T3 vs T1: 18.9 ± 3.6 mmHg vs 10.5 ± 2.8 mmHg, P < 0.001; T4 vs T1: 13.3 ± 3.7 mmHg vs 10.5 ± 2.8 mmHg, P < 0.001). However, no significant differences were observed for the haemodynamic and respiratory variables at any time point.

CONCLUSION

Our findings indicate that the intraoperative neck extension position during palatoplasty significantly increases IOP in paediatric cleft palate patients undergoing a palatoplasty.

Neck Extension and Intraocular Pressure Elevation During Palatoplasty in a Patient with Patau Syndrome and Congenital Glaucoma: A Case Report

Patau syndrome (trisomy 13) is a severe disorder associated with multiple systemic defects. Patau syndrome is commonly associated with ocular abnormalities but rarely associated with congenital glaucoma. To obtain a better surgical view, palatoplasty requires neck extension during surgery. The intraocular pressure (IOP) of patients with Patau syndrome can increase owing to the neck extension position while undergoing palatoplasty, particularly in those with congenital glaucoma. Here, we describe a case with increased IOP measured using a rebound tonometer during palatoplasty in a pediatric patient with Patau syndrome and congenital glaucoma. This case shows that it may be important to reduce the degree of neck extension and shorten the operation time to minimize any increase in the IOP during palatoplasty in pediatric patients with Patau syndrome accompanied by congenital glaucoma.

The effect of restrictive vs. liberal fluid protocols on ocular parameters in patients undergoing prone spine surgery: a randomized controlled trial

BACKGROUND

Elevated intraocular pressure (IOP) and optic nerve edema occurring during prone surgeries may cause ocular and optic nerve ischaemia injury. We hypothesized that a liberal fluid protocol might further increase IOP and optic nerve sheath diameter (ONSD) than a restrictive fluid protocol for patients in the prone position.

METHODS

A single-centre, prospective and randomized trial was conducted. Patients were randomly allocated into 2 groups: the liberal fluid infusion group, in which repeated bolus doses of Ringer's lactate solution were given to maintain pulse pressure variation (PPV) within 6~9%, and the restrictive fluid infusion group, where PPV was maintained within 13-16%. IOP and ONSD were measured in both eyes at 10min after the anaesthesia induction in the supine position, 10min after the prone position placement, and 1h and 2h since the prone position was placed, at the conclusion of surgery, and returned to the supine position.

RESULTS

A total of 97 patients were recruited and completed the study. IOP increased significantly from 12±3mmHg in the supine position to 31±5 mmHg (p<0.001) at the end of surgery in the liberal fluid infusion group and from 12±2 to 28±4 mmHg (p<0.001) in the restrictive fluid infusion group. There was a statistically significant difference in the change of IOP over time between the two groups (p=0.019). ONSD increased significantly from 5.3±0.3mm in the supine position to 5.5±0.3mm (p<0.001) at the end of surgery in both groups (both p<0.001). There was no statistically significant difference in the change of ONSD over time between the two groups (p>0.05).

CONCLUSIONS

Compared to the restrictive fluid protocol, the liberal fluid protocol increased IOP but not ONSD in patients undergoing prone spine surgery.

TRIAL REGISTRATION

The study was registered in ClinicalTrials.gov ( https://clinicaltrials.gov ) prior to patient enrollment, ID: NCT03890510, on March 26, 2019. The principal investigator was Xiao-Yu Yang.

An Observational Pilot Study on Supine Percutaneous Nephrolithotomy: Initial Experience at a Single-Centre

Objective To assess the surgical outcome of supine percutaneous nephrolithotomy (PCNL) in patients with co-morbidities. Materials and methods We retrospectively reviewed the data of 15 patients who underwent supine PCNL at our centre from September 2019 to May 2021. Preoperatively, a complete examination of the patients, along with biochemical and radiological investigations, was done. The data, which included patient demographics, comorbidities, complexity of renal calculi, complications, and stone clearance rate, were collected from the patients' medical records. Results Patients aged between 31 and 70 years were included in the study. The mean (SD) BMI was 26.01 (2.31). Twelve patients (80%) were overweight with a BMI of 25.3 to 29.3 kg/m². The most common comorbidities were diabetes (33.3%) and hypertension (26.7%). In our study, six patients were American Society of Anesthesiologists (ASA) grade 3 (40%), followed by grade 2 in five patients (33.3%), grade 4, and grade 1 in two patients (13.3%) each. The Guy's Stone score was one in nine patients (60%) and two in six patients (40%). Complete clearance was achieved in 13 (86.7%) patients. Two patients (13.3%) had a stone clearance of more than 80%. Data analysis showed that 14 patients (93.3%) had no perioperative complications. Postoperative abdominal distension was noted in one patient (6.7%), which was managed conservatively (Clavien-Dindo grade 1). We did not encounter any cases of organ injury following supine PCNL. Postoperatively, none of our patients received blood transfusions. Conclusion Our study shows that supine PCNL is a good surgical option, especially for high-risk patients with good stone clearance and low complication rates.

Perioperative corneal abrasions: A report of 42 cases from the webAIRS database

Corneal abrasions are an uncommon complication of anaesthesia. The aim of this study was to identify potential risk factors, treatment and outcomes associated with corneal abrasions reported to the web-based anaesthesia incident reporting system (webAIRS), a voluntary de-identified anaesthesia incident reporting system in Australia and New Zealand, from 2009 to 2021. There were 43 such cases of corneal abrasions reported to webAIRS over this period. The most common postoperative finding was a painful eye. Common features included older patients, individuals with pre-existing eye conditions, general anaesthesia and procedures longer than 60 minutes. Most cases were treated with a combination of lubricating eye drops or aqueous antibiotic eye drops. The findings indicate that patients who sustain a perioperative corneal abrasion can be reassured that in many cases it will heal within 48 hours, but they should seek earlier review if symptoms persist or deteriorate. None of the cases in this series resulted in permanent harm. Well established eye protective measures are important to utilise throughout the perioperative period, including the time until the patient has recovered in the post-anaesthesia care unit.

Gravitational effects on intraocular pressure and ocular perfusion pressure

Changes in the gravitational vector by postural changes or weightlessness induce fluid shifts, impacting ocular hemodynamics and regional pressures. This investigation explores the impact of changes in the direction of the gravitational vector on intraocular pressure (IOP), mean arterial pressure at eye level (MAP_eye), and ocular perfusion pressure (OPP), which is critical for ocular health. Thirteen subjects underwent 360° of tilt (including both prone and supine positions) at 15° increments. At each angle, steady-state IOP and MAP_eye were measured, and OPP calculated as MAP_eye - IOP. Experimental data were also compared to a six-compartment lumped-parameter model of the eye. Mean IOP, MAP_eye, and OPP significantly increased from 0° supine to 90° head-down tilt (HDT) by 20.7 ± 1.7 mmHg (P < 0.001), 38.5 ± 4.1 mmHg (P < 0.001), and 17.4 ± 3.2 mmHg (P < 0.001), respectively. Head-up tilt (HUT) significantly decreased OPP by 16.5 ± 2.5 mmHg (P < 0.001). IOP was significantly higher in prone versus supine position for much of the tilt range. Our study indicates that OPP is highly gravitationally dependent. Specifically, data show that MAP_eye is more gravitationally dependent than IOP, thus causing OPP to increase during HDT and to decrease during HUT. In addition, IOP was elevated in prone position compared with supine position due to the additional hydrostatic column between the base of the rostral globe to the mid-coronal plane, supporting the notion that hydrostatic forces play an important role in ocular hemodynamics. Changes in OPP as a function of changes in gravitational stress and/or weightlessness may play a role in the pathogenesis of spaceflight-associated neuro-ocular syndrome.NEW & NOTEWORTHY Maintaining appropriate ocular perfusion pressure (OPP) is critical for ocular health. We measured the relative changes in intraocular and mean arterial pressures during 360° tilt and calculated OPP, which was elevated during head-down tilt and decreased during head-up tilt. Experimental data are also explained by our computational model. We demonstrate that OPP is more gravitationally dependent than previously recognized and may be a factor in the overall patho-etiology behind the weightlessness-induced spaceflight-associated neuro-ocular syndrome.

[Potential complications of patient positioning in spine surgery]

Patient position on the operating table during spine surgery is important for optimal intraoperative manipulations. However, this position is far from physiological one. An unnatural position, surgery time and sometimes necessary intraoperative change in body position can lead to certain neurological and somatic complications. Most of these events can significantly reduce the patient's working capacity and quality of life and even result disability. Medical staff placing the patient on operating table, neurosurgeons and anesthesiologists should be aware of risk factors of similar complications and their prevention. The authors describe the most serious and difficult for correction conditions, such as peripheral neuropathy, damage to visual analyzer, as well as optimal method of patient positioning.

COVID-19 and the Eye: Ocular Manifestations, Treatment and Protection Measures

The novel pandemic coronavirus disease 2019 (COVID-19) leading to health and economic problems worldwide is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although COVID-19 mainly occurs as a lower respiratory tract infection, there is multiorgan involvement in infected patients. The disease is transmitted from person to person through air droplets or contact with contaminated surfaces. SARS-CoV-2 leads to this systemic involvement by attaching to angiotensin-converting enzyme 2 (ACE2) receptors located on several human cells. Since SARS-CoV-2 RNA has been found in tears of infected patients, ocular surface may allow the virus to transmit to nasopharynx via the nasolacrimal duct. This narrative review aims to sum up all segmental ocular complications, ocular adverse effects of COVID-19 treatment, and preventive measures suggested to minimize the SARS-CoV-2 transmission between patients and ophthalmologists by reviewing currently available literature.

Posterior ischemic optic neuropathy following a major burn injury and review of the literature

Posterior ischemic optic neuropathy following burns is a rare but devastating condition that can result in total bilateral visual loss. Numerous treatment modalities have been trialed, yet there is no effective therapy to delay or reverse the disease. Hence, it is imperative for burns surgeons to be aware of the potential risk factors and have a high index of suspicion right from the outset to prevent this outcome. Here, we discuss the case of a patient that developed posterior ischemic optic neuropathy subsequent to a major burn injury. We also present a literature review on optic neuropathies following burns to describe the etiology, clinical signs, and potential management.

A case of esophageal cancer with an aberrant right subclavian artery treated with mediastinoscopic esophagectomy

An aberrant right subclavian artery (ARSA) is one of the famous anatomical abnormalities with a prevalence of 0.16-4.4%. In esophagectomy, anatomical abnormalities of the ARSA could cause complications with some surgical procedures. An 85-year old man was referred to our department for esophageal adenocarcinoma that was at a slightly high position for esophagectomy with the abdominal approach. However, he had a significant past medical history. This risk factor made it difficult to perform thoracoscopic esophagectomy. He underwent mediastinoscopic esophagectomy (ME) with the left cervical and laparoscopic approach. The ARSA presented no difficulties with the ME surgical technique including the dissection of the left recurrent laryngeal nerve lymph node. Although this patient had a respiratory dysfunction and some difficulties in a prone position, ME enabled a safe esophagectomy with lymph node dissection.

Changes in intraocular pressure during coronary artery bypass graft surgery: an observational study

Background

In this study, the effects of pulsatile and non-pulsatile on-pump Coronary Artery Bypass Graft surgery (CABG) and off-pump CABG techniques on the intraocular pressure were investigated.

Methods

Forty-five patients who planned to elective coronary artery bypass surgery with on-pump pulsatile (n = 15), non-pulsatile (n = 15), or off-pump (n = 15) were included. Intraocular Pressure (IOP) measurements were performed on both eyes at nine time-points: 1) Before the operation, 2) After anesthesia induction, 3) 3 minutes after heparin administration Left Internal Mammary Artery (LIMA) harvesting, 4) End of the first anastomosis, 5) End of LIMA anastomosis, 6) 3 minutes after protamine administration, 7) End of the operation, and 8) Second hour in Intensive Care Unit (ICU), 9) Fifth hour in ICU. Mean Arterial Pressure (MAP) and Central Venous Pressure (CVP) were also recorded at the same time points as IOP.

Results

In Cardiopulmonary Bypass (CPB) groups (pulsatile or non-pulsatile CPB) with the beginning of CPB, there were significant decreases in IOP values when compared to baseline (p = 0.012). This decrease was more prominent in the non-pulsatile group when compared to the pulsatile group (T₄ IOP values: pulsatile, 9.7 ± 2.6; non-pulsatile, 6.8 ± 1.9; p = 0.002; T₅ IOP values: pulsatile, 9.5 ± 1.9; non-pulsatile, 6.7 ± 2.1; p = 0.004). At the end of the surgery (T₇), IOP values returned to the baseline and stayed stable at the remaining time-points. In-off pump group, IOP values significantly increased with a head-down position (T₄ IOP values: off-pump surgery, 19.7 ± 5.2; p = 0.015). IOP values remained high until the normalization of head-down position (T₆) and stayed stable through the rest of all remaining time-points.

Conclusion

During cardiac surgery regardless of the technique (on-pump CABG, off-pump CABG), intraocular pressures remain in the normal ranges. It should be kept in mind that patients should be avoided from long and extreme Trendelenburg position, low CVP, and MAP levels during cardiac surgery to prevent eye-related complications.

A study to evaluate ocular changes in patients undergoing spine surgery in the prone position

Background and Aims:

AA present prospective study was conducted to evaluate ocular changes occurring in patients undergoing spine surgery in the prone position.

Material and Methods:

A total of 44 patients of either sex, belonging to American society of Anaesthesiology I and II (aged 18-60 years) scheduled for elective spine surgery in prone position were enrolled in the study. Baseline IOP and MAP measurement were taken prior to induction. After induction of anaesthesia patients were intubated using flexo-metallic tube of appropriate size. IOP and MAP were recorded after induction of anaesthesia, following completion of surgery and immediately after turning the patient supine and 30 min following extubation. Blood loss and duration of surgery was also noted. The OPP was derived using the formula (OPP = MAP-IOP). Ophthalmic examination was also performed using direct and indirect ophthalmoscopy on the day prior to surgery and on first post-operative day to rule out anterior ischemic optic neuropathy (AION), posterior ischemic optic neuropathy (PION), and retinal ischemia.

Results:

Mean IOP significantly increased (18.91 ± 3.56 mm Hg) (P < 0.001) at the end of surgery as compared to baseline value 12.85 ± 3.07 mm Hg. As a result mean OPP significantly reduced (75.12 ± 16.45) (P = 0.0018) at the end of the procedure.

Conclusion:

In patient’s undergoing spine surgery in the prone position, careful patient positioning with no extrinsic pressure on the eyes, minimal surgical time and blood loss, and prevention of intraoperative hypotension, should be ensured to prevent the IOP rise and a reduction in OPP which can further prevent post-operative visual disturbance.

Ocular Complications in the Prone Position in the Critical Care Setting: The COVID-19 Pandemic

PURPOSE

Ocular complications are common in the critical care setting but are frequently missed due to the focus on life-saving organ support. The SARS-CoV-2 (COVID-19) pandemic has led to a surge in critical care capacity and prone positioning practices which may increase the risk of ocular complications. This article aims to review all ocular complications associated with prone positioning, with a focus on challenges posed by COVID-19.

MATERIALS AND METHODS

A literature review using keywords of "intensive care", "critical care", "eye care", "ocular disorders", "ophthalmic complications," "coronavirus", "COVID-19," "prone" and "proning" was performed using the electronic databases of PUBMED, EMBASE and CINAHL.

RESULTS

The effects of prone positioning on improving respiratory outcomes in critically unwell patients are well established; however, there is a lack of literature regarding the effects of prone positioning on ocular complications in the critical care setting. Sight-threatening ophthalmic disorders potentiated by proning include ocular surface disease, acute angle closure, ischemic optic neuropathy, orbital compartment syndrome and vascular occlusions.

CONCLUSIONS

COVID-19 patients may be more susceptible to ocular complications with increased proning practices and increasing demand on critical care staff. This review outlines these ocular complications with a focus on preventative and treatment measures to avoid devastating visual outcomes for the patient.

Ocular Findings in COVID-19 Patients: A Review of Direct Manifestations and Indirect Effects on the Eye

The novel pandemic coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has challenged the medical community. While diagnostic and therapeutic efforts have been focused on respiratory complications of the disease, several ocular implications have also emerged. SARS-CoV-2 RNA has been found in tears of the infected patients, and reports suggest that the ocular surface could serve as a portal of entry and a reservoir for viral transmission. Clinically, COVID-19 has been associated with mild conjunctivitis, which can be the first and only symptom of the disease. Subtle retinal changes like hyperreflective lesions in the inner layers on optical coherence tomography (OCT), cotton-wool spots, and microhemorrhages have also been reported. In addition, COVID-19 has been associated with an increased incidence of systemic diseases like diabetes mellitus and Kawasaki disease, which are particularly relevant for ophthalmologists due to their potentially severe ocular manifestations. Several treatment strategies are currently under investigation for COVID-19, but none of them have been proved to be safe and effective to date. Intensive care unit patients, due to risk factors like invasive mechanical ventilation, prone position, and multiresistant bacterial exposure, may develop ocular complications like ocular surface disorders, secondary infections, and less frequently acute ischemic optic neuropathy and intraocular pressure elevation. Among the array of drugs that have shown positive results, the use of hydroxychloroquine and chloroquine has raised a concern due to their well-known retinal toxic effects. However, the risk of retinal toxicity with short-term high-dose use of antimalarials is still unknown. Ocular side effects have also been reported with other investigational drugs like lopinavir-ritonavir, interferons, and interleukin-1 and interleukin-6 inhibitors. The aim of this review was to summarize ophthalmological implications of SARS-CoV-2 infection to serve as a reference for eye care and other physicians for prompt diagnosis and management.

Orbital infarction syndrome after cerebral aneurysm surgery: A case series and literature review

To report the clinical characteristics and retinal abnormalities associated with orbital infarction syndrome after cerebral aneurysm clipping surgery.In this retrospective case series, we evaluated 4 cases of orbital infarction syndrome using fluorescein angiography, optical coherence tomography, and computed tomography images from January 2011 to May 2014. The medical records of these patients including age, sex, laterality of the eyes, visual acuity, intraocular pressure, duration of the operation, location of the aneurysms, and surgical method with the type of approach used to reach the aneurysmal lesions were evaluated.Aneurysms were located in either the anterior or the posterior communicating artery. Two patients had subarachnoid hemorrhage arising from a ruptured aneurysm, whereas 2 other patients had unruptured aneurysms. Clipping was performed by 3 different surgeons using the pterional craniotomy. The mean time interval from aneurysmal clipping to awareness of vision loss was 10.75 ± 13.8 days. In all patients, optic atrophy and irreversible deterioration of visual acuity ensued. Retinal edema, retinal vascular abnormality, or choroidal hypoperfusion was identified in these patients.Orbital infarction syndrome is a rare but devastating complication of brain aneurysm clipping surgery. The associated retinal ischemia is not only due to the involvement of the retinal vessels, but also the choroidal circulation.

Posterior ischemic optic neuropathy: Perioperative risk factors

Perioperative posterior ischemic optic neuropathy (PION) is a rare but devastating condition. Visual impairment is commonly bilateral, profound, and irreversible. The most frequently associated triggering events are spine surgeries, other orthopedic surgeries, cardiac bypass surgeries, and radical neck dissection. The etiology is multifactorial. The most commonly reported risk factors are severe and prolonged hypotension, anemia, hemodilution, orbital and periorbital edema, direct orbital compression by prone position, and abnormal autoregulation. This review discusses the current literature on perioperative PION and includes a study conducted by our group to investigate the perioperative risk factors of PION in order to better understand the pathogenesis and help identify high-risk patients. Our results provide further corroborating evidence that PION is associated with spinal, cardiovascular, and abdominal surgeries, longer duration of procedure, and facial edema. Anemia and chronic hypertension are frequent risk factors. Treatment for perioperative PION is uncertain and depends largely on the immediate reversal of hemodynamic alterations. Hence, it is important to identify patients at risk and accordingly take prophylactic measures to prevent its occurrence. Optimizing hemoglobin levels, hemodynamic status, and tissue oxygenation is crucial.

Eye care in the intensive care unit during the COVID-19 pandemic

Ocular complications in critical care patients are common. There has been a surge in intensive care admissions following the COVID-19 outbreak. The management of COVID-19 exposes patients to a number of specific risk factors for developing ocular complications, which include non-invasive ventilation, mechanical ventilation and prone positioning. Consequently, it is likely that there will be an increase in the number of ocular complications secondary to the management of COVID-19 patients in the intensive care unit setting, and these complications could lead to permanent visual loss and blindness. Increased awareness of eye care in the intensive care unit setting is therefore vital to help prevent visual loss and maintain quality of life for patients recovering from COVID-19.

A case report of optic neuropathy following dacryocystorhinostomy in a 57-year-old female patient with May-Hegglin anomaly

Background

We report a rare case of optic neuropathy following dacryocystorhinostomy (DCR) in a 57-year-old female patient with May-Hegglin anomaly.

Case presentation

The patient was presented with sudden onset of vision loss for the left eye after DCR under general anesthesia. Her best corrected visual acuity was light perception in the left eye. Relative afferent pupillary defect was detected in her left eye. Magnetic resonance imaging of the orbit revealed an hyperintensity at the intra-orbital segment of the left optic nerve on T2-weighted image and Flair image. The patient was diagnosed with acute postoperative optic neuropathy and treated with methylprednisolone. Although her vision partially improved, she was left with a visual field defect in the left eye.

Conclusions

In patients with hematologic diseases, postoperative vision loss can occur following even minor surgery under general anesthesia, such as DCR. Therefore, preoperative counseling regarding the risk of visual loss should be given to high-risk patients.

Systematic Review and Meta-Analysis of Prone Position on Intraocular Pressure in Adults Undergoing Surgery

BACKGROUND

Patients undergoing surgery in the prone position may be at risk for postoperative vision loss associated with increased intraocular pressure. The purpose of this systematic review and meta-analysis is to estimate the magnitude of the increase in intraocular pressure at specific perioperative time points in adult patients. The research question to be addressed is "What is the magnitude of the increase in intraocular pressure at specific perioperative time points in adults undergoing surgery in the prone position?"

METHODS

Comprehensive search strategies were used to identify nine eligible studies (N = 229). Standardized mean difference effect sizes were calculated for two intraoperative time points.Time points for meta-analysis were selected to achieve the greatest number of comparisons for analysis at each time point. Prediction intervals for each time point were also calculated to show the dispersion of true effect sizes around the mean.

RESULTS

Meta-analysis showed that intraocular pressure increased significantly between induction of anesthesia and up to 10 minutes of prone position (T1: standardized mean difference [d] = 2.55; P < .001) and continued to increase significantly until the end of the prone position (T2: d = 3.44; P = .002).

CONCLUSIONS

Intraocular pressure increases of this magnitude demonstrate the need for implementing interventions to reduce the risk for postoperative vision loss in patients undergoing surgery in the prone position.

CLINICAL RELEVANCE

Implementing preoperative ophthalmologic examinations for patients undergoing surgery in the prone position may help to reduce the risk for ocular injury. Intraoperative interventions that can be implemented to reduce or mitigate the increase in intraocular pressure include implementing a 5- to 10-degree reverse Trendelenburg prone position, reducing the amount of time the patient is in the prone position, considering staged procedures, monitoring intraocular pressure, providing periodic position changes or rest periods, preventing pressure on the eye, and administering specific medications or anesthetics.

Hypercapnia augments resistive exercise-induced elevations in intraocular pressure in older individuals

NEW FINDINGS

What is the central question of this study? Astronauts on-board the International Space Station (ISS) perform daily exercises designed to prevent muscle atrophy and bone demineralization: what is the effect of resistive exercise performed by subjects while exposed to the same level of hypercapnia as on the ISS on intraocular pressure (IOP)? What is the main finding and its importance? The static exercise-induced elevation in IOP during 6° prone head-down tilt (simulating the headward shift of body fluids in microgravity) is augmented by hypercapnia and exceeds the ocular hypertension threshold.

ABSTRACT

The present study assessed the effect of 6° head-down (establishing the cephalad fluid displacement noted in astronauts in microgravity) prone (simulating the effect on the eye) tilt during rest and exercise (simulating exercise performed by astronauts to mitigate the sarcopenia induced by unloading of weight-bearing limbs), in normocapnic and hypercapnic conditions (the latter simulating conditions on the International Space Station) on intraocular pressure (IOP). Volunteers (mean age = 57.8 ± 6 years, n = 10) participated in two experimental sessions, each comprising: (i) 10 min rest, (ii) 3 min static handgrip exercise (30% max), and (iii) 2 min recovery, inspiring either room air (NCAP) or a hypercapnic mixture (1% CO₂ , HCAP). We measured IOP in the right eye, cardiac output (CO), stroke volume (SV), heart rate (HR) and mean arterial pressure (MAP) at regular intervals. Baseline IOP in the upright seated position while breathing room air was 14.1 ± 2.9 mmHg. Prone 6° head-down tilt significantly (P < 0.01) elevated IOP in all three phases of the NCAP (rest: 27.0 ± 3.7 mmHg; exercise: 32.2 ± 4.8 mmHg; recovery: 27.4 ± 4.0 mmHg) and HCAP (rest: 27.3 ± 4.3 mmHg; exercise: 34.2 ± 6.0 mmHg; recovery: 29.1 ± 5.8 mmHg) trials, with hypercapnia augmenting the exercise-induced elevation in IOP (P < 0.01). CO, SV, HR and MAP were significantly increased during handgrip dynamometry, but there was no effect of hypercapnia. The observed IOP measured during prone 6° HDT in all phases of the NCAP and HCAP trials exceeded the threshold pressure defining ocular hypertension. The exercise-induced increase in IOP is exacerbated by hypercapnia.

Iatrogenic ophthalmic artery occlusion and retinal artery occlusion

Iatrogenic ophthalmic artery occlusion (IOAO) is a rare but devastating ophthalmic disease that may cause sudden and permanent visual loss. Understanding the possible etiologic modalities and pathogenic mechanisms of IOAO may prevent its occurrence. There are numerous medical etiologies of IOAO, including cosmetic facial filler injection, intravascular procedures, intravitreal gas or drug injection, retrobulbar anesthesia, intraarterial chemotherapy in retinoblastoma. Non-ocular surgeries and vascular events in arteries that are not directly associated with the ophthalmic artery, can also cause IOAO. Since IOAO has a limited number of treatment modalities, which lead to poor final visual prognosis, it is imperative to acknowledge the information regarding medical procedures that are etiologically associated with IOAO. We accumulated all searchable and available IOAO case reports (our cases and previous reported cases from the literature), classified them according to their mechanisms of pathogenesis, and summarized treatment options and responses of each of the causes. Various sporadic cases of IOAO can be categorized into three mechanisms as follows: intravascular event, orbital compartment syndrome, and increased intraocular pressure. Embolic IOAO, which is considered the primary cause of the condition, was classified into three subgroups according to the pathway of embolic movement (retrograde pathway, anterograde pathway, pathway through collateral channels). Despite the practical limitations of treating spontaneous (non-iatrogenic) retinal artery occlusion, this article will contribute in predicting and improving the prognosis of IOAO by recognizing the treatable factors. Furthermore, it is expected to provide clues to future research associated with the treatment of retinal artery occlusion.

Intraocular pressure during neurosurgical procedures in context of head position and loss of cerebrospinal fluid

OBJECTIVE

Perioperative visual loss (POVL) is a rare but serious complication in surgical disciplines, especially in spine surgery. The exact pathophysiology of POVL remains unclear, but elevated intraocular pressure (IOP) is known to be part of it. As POVL is rarely described in patients undergoing intracranial or intradural surgery, the aim of this study was to investigate the course of IOP during neurosurgical procedures with opening of the dura mater and loss of CSF.

METHODS

In this prospective, controlled trial, 64 patients fell into one of 4 groups of 16 patients each. Group A included patients undergoing spine surgery in the prone position, group B patients had intracranial procedures in the prone position, and group C patients were treated for intracranial pathologies in a modified lateral position with the head rotated. In groups A-C, the dura was opened during surgery. Group D patients underwent spine surgeries in the prone position with an intact dura. IOP was measured continuously pre-, peri-, and postoperatively.

RESULTS

In all groups, IOP decreased after induction of anesthesia and increased time dependently after final positioning for the operation. The maximum IOP in group A prior to opening of the dura was 28.6 ± 6.2 mm Hg and decreased to 23.44 ± 4.9 mm Hg directly after dura opening (p < 0.0007). This effect lasted for 30 minutes (23.5 ± 5.6 mm Hg, p = 0.0028); after 60 minutes IOP slowly increased again (24.5 ± 6.3 mm Hg, p = 0.15). In group B, the last measured IOP before CSF loss was 28.1 ± 5.0 mm Hg and decreased to 23.5 ± 6.1 mm Hg (p = 0.0039) after dura opening. A significant IOP decrease in group B lasted at 30 minutes (23.6 ± 6.0 mm Hg, p = 0.0039) and 60 minutes (23.7 ± 6.0 mm Hg, p = 0.0189). In group C, only the lower eye showed a decrease in IOP up to 60 minutes after loss of CSF (opening of dura, p = 0.0007; 30 minutes, p = 0.0477; 60 minutes, p = 0.0243). In group D (control group), IOP remained stable throughout the operation after the patient was prone.

CONCLUSIONS

This study is the first to demonstrate that opening of the dura with loss of CSF during neurosurgical procedures results in a decrease in IOP. This might explain why POVL predominantly occurs in spinal but rarely in intracranial procedures, offers new insight to the pathophysiology of POVL, and provides the basis for further research and treatment of POVL.German Clinical Trials Register (DRKS) no.: DRKS00007590 (drks.de).

Observational prospective study for surgical outcome and anesthetic feasibility of tubeless and totally tubeless supine PCNL: A single centre initial experience

OBJECTIVE

To evaluate surgical outcome and spinal anesthetic feasibility of supine percutaneous nephrolithotomy (PCNL) by tubeless and totally tubeless method.

MATERIAL AND METHODS

This observational study included a totally 53 patients. Initial diagnosis of renal stone was based on urinary ultrasonography, kidney, ureter and bladder X-ray, and later confirmed by computed tomography urography. PCNL was done with the patient in Galdakao-modified supine Valdivia position. Nephrostomy was not done using tubeless method, while in totally tubeless method instead of insertion of double j stent, ureteral catheterization was done and the ureter catheter was kept for <24 hours. During postprocedural period, patients were observed for development of fever, perinephric collection, need for blood transfusion and duration of hospital stay.

RESULTS

Patients aged between 14 and 75 years were included in the study. Out of totally 53 patients, supine tubeless PCNL was done in 23 patients while 30 were operated using totally tubeless method. Twenty-nine patients were induced by spinal anesthesia and 24 by general anesthesia. Stone sizes were found to be in the range of 1.4cm to 5.1 cm. Forty-six (86.7%) patients were managed by inferior calyceal puncture. Three patients required double puncture in whom 2 had developed perinephric collection. Complete stone clearance achieved in 49 (92.4%) patients. Four patients developed fever and 2 cases required one unit blood transfusion postoperatively.

CONCLUSION

Tubeless and totally tubeless supine PCNL is technically feasible with good surgical outcomes and can be done under spinal and general anesthesia in properly selected patients.

Alert for Perioperative Visual Loss: An Unusual Presentation of an Orbital Haemangioma during Spinal Surgery

A 62-year-old man with a history of non-insulin-dependent diabetes mellitus, hypertension and obesity, presented for elective lumbar laminectomy for spinal canal stenosis. Twenty minutes after placement in the prone position, he developed left orbital proptosis. The surgery was deferred and a subsequent CT scan showed an orbital haemangioma. This case highlights the importance of meticulous attention to eye-care for patients in the prone position.

LumbarIschemic Optic NeuropathyComplicating Spine Surgery-A Case Report

Introduction

Post-operative vision loss (POVL),i.e., blindness is an uncommon complication of any major surgery. In orthopedics, it is encountered mostly in spine surgery. POVL may be due to various pathologies such asischemic optic neuropathy (ION) and central retinal artery occlusion. A rise in intraocular pressure is one of the contributing factors. ION associated with lumbar spine surgery has been designated as lumbar ION. Even though its incidence is as low as 0.02%, once occurs, the consequence is disastrous. Our case of POVL due to posterior ION has certain distinct features which differentiate it from the routine cases reported in literature.

Case Report

Our case is a 33-year-old gentleman who underwent revision lumbar spine surgery, for L3-L4 disc protrusion (recurrence) and L4-L5 disc protrusion with bilateral foot drop, in the form of posterior decompression, pedicle screw fixation from L3 to L5, and two-level transforaminal lumbar interbody fusion using cages. The patient developed POVL involving one eye which was diagnosed on operating table itself (immediately after extubation). Immediate appropriate treatment was initiated with the cooperation of ophthalmologist. The patient subsequently recovered, from no perception of light, to a visual acuity of 6/24, and is doing well regarding vision as well as neurology.

Conclusion

Since POVL is an avoidable complication, knowledge regarding POVL and its contributing factors can lead to the prevention of the development of this complication. Moreover, since POVL has poor prognosis for recovery, prevention is the key. Since POVL can occur after any major surgery (apart from orthopedics), its knowledge can help surgeons in other specialties also.

Safety in Body Contouring to Avoid Complications

Body contouring after weight loss is becoming more prevalent. An appropriate systematic approach that starts from the first consultation needs to focus on residual comorbidities and weight of the patient. A thorough discussion about potential outcomes manages expectations. Preoperative optimization with smoking, herbal cessation, and nutritional assessment is mandatory. Planned staged approach minimizes lengthy procedures associated with increased postoperative morbidity. In the operating room, appropriate ambient temperature, positioning of the patient, and continuous discussion between surgeon and anesthesiologist prevent further complications. Careful transition to postoperative care with early ambulation and use of compressive garments add to an approach to minimize postoperative complications.

Acute Glaucoma Attack Following Microvascular Decompression Surgery for Trigeminal Neuralgia

Microvascular decompression (MVD) is widely accepted as an effective surgical method to treat trigeminal neuralgia (TN), but the risks of morbidity and mortality must be considered. We experienced a case of acute angle-closure glaucoma attack following MVD for TN in an elderly patient, considered to be caused by lateral positioning during and after the surgery. A 79-year-old female underwent MVD for right TN in the left lateral decubitus position, and TN disappeared after the surgery. Postoperatively, the patient tended to maintain the left lateral decubitus position to prevent wound contact with the pillow, even after ambulation. Two days after the surgery, she complained of persistent left ocular pain with visual disturbance. The left pupil was dilated with only light perception, and the intraocular pressure (IOP) was 44 mmHg. Acute angle-closure glaucoma attack was diagnosed. After drip infusion of mannitol, emergent laser iridotomy was performed. The corrected visual acuity recovered with normalization of IOP (14 mmHg). The subsequent clinical course was uneventful and she was discharged from our hospital. The left lateral positioning during and after the surgery was considered to have contributed to increase IOP of the eye on the dependent side, which resulted in acute angle-closure glaucoma attack. The potential pathology is difficult to assess preoperatively, but patient management should always consider the increased possibility of this condition with age.

The effect of spinal versus general anesthesia on intraocular pressure in lumbar disc surgery in the prone position: A randomized, controlled clinical trial

OBJECTIVE

To compare IOP changes between spinal anesthesia (SA) and general anesthesia (GA) in patients who underwent lumbar disc surgery in the prone position.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Operating room.

PATIENTS

Forty ASA I-II patients scheduled for lumbar disc surgery in prone position.

INTERVENTION

Patients were randomly allocated to the SA or GA groups.

MEASUREMENTS

IOP was measured before anesthesia (IOP1), 10 min after spinal or general anesthesia in supine position (IOP2), 10 min after being placed in the prone position (IOP3), and at the end of the operation in the prone position (IOP4).

MAIN RESULTS

There was no significant difference between baseline IOP1 (group GA = 19.4 ± 3.2 mmHg; group SA = 18.6 ± 2.4 mmHg) and IOP2 values (group GA = 19.7 ± 4.1 mmHg; group SA = 18.4 ± 1.9 mmHg) between and within the groups. IOP values after prone positioning and group GA measurements (IOP3 = 21.6 ± 3.1 mmHg; IOP4 = 33.9 ± 3.1 mmHg) were significantly higher when compared with the SA group (IOP3 = 19.3 ± 2.7 mmHg, IOP4 = 26.9 ± 2.4 mmHg) (p = 0.018 and p < 0.001, respectively). Furthermore, IOP3 was significantly increased when compared with IOP2 in the GA group but not in the SA group (p = 0.019 and p = 0.525, respectively). In both groups, IOP4 values were significantly higher than the other three measurements (p < 0.001).

CONCLUSION

The results indicated that IOP increase is significantly less in patients who undergo lumbar disc surgery in the prone position under SA compared with GA.

Ocular parameters before and after steep Trendelenburg positioning for robotic-assisted laparoscopic radical prostatectomy

Purpose

Intraocular pressure (IOP) increases in patients in a steep Trendelenburg position during robotic-assisted laparoscopic radical prostatectomy (RALP). We hypothesized that a steep Trendelenburg position during RALP, an unusual systemic condition involving a transiently increased IOP, may induce ocular pathology that can be detected by detailed evaluations long after the surgery. This study aims to explore ocular structural and functional parameters in patients before and in the long term after the surgery.

Patients and methods

A comparative observational study was performed. A total of 44 eyes of 22 male patients scheduled for RALP at Aichi Medical University from August 2012 to July 2013 were included. Clinical parameters before and after RALP were compared. Perioperative IOP was measured immediately post-induction of anesthesia in the flat supine position (T1), immediately post-steep Trendelenburg position (T2), and prior to returning to a flat supine position while in a steep Trendelenburg position (T3). The thicknesses of the peripapillary retinal nerve fiber layer, ganglion cell complex (GCC), and central fovea were measured with spectral domain optical coherence tomography. Humphrey perimetry was performed before and at 3 and 6 months after surgery.

Results

The average IOPs (mmHg) at each stage were T1=10.4, T2=21.7, and T3=29.6, and differed significantly. The mean visual acuity (logarithm of the minimal angle of resolution), IOP, mean deviation, and pattern standard deviation measured by the Humphrey field analyzer showed no statistically significant difference before and after surgery. The ganglion cell complex and retinal nerve fiber layer thicknesses measured at each location and the central fovea thicknesses measured before and after surgery did not differ significantly.

Conclusion

No significant disorders in ocular structural and functional parameters were found until long after RALP.

Perioperative Vision Loss after Non-Ocular Surgery

Perioperative vision loss (POVL) may cause devastating visual morbidity. A prompt anatomical and etiologic diagnosis is paramount to guide management and assess prognosis. Where possible, steps should be undertaken to minimize risk of POVL for vulnerable patients undergoing high-risk procedures. We review the specific risk factors, pathophysiology, and management and prevention strategies for various etiologies of POVL.

Optic disc pit maculopathy after prone positioning spine surgery

PURPOSE

To report a case of optic disc pit maculopathy after spine surgery performed in the prone position.

METHODS

Case report.

RESULTS

A 32-year-old man underwent spine surgery for disc herniation repair. He complained of visual acuity loss immediately after the procedure. Optic disc maculopathy with internal limiting membrane detachment was found to be the cause. Vitrectomy was scheduled after a 12-month follow-up without resolution of the maculopathy.

CONCLUSIONS

Optic disc maculopathy has not previously been associated with nonocular surgery or patient positioning. Physiologic changes induced by the prone position likely altered the pressure gradient in the eye and led to the development of the maculopathy.

Ocular changes over 60 min in supine and prone postures

Some astronauts are returning from long-duration spaceflight with structural ocular and visual changes. We investigated both the transient and sustained effects of changes in the direction of the gravity vector acting on the eye using changes in body posture. Intraocular pressure (IOP; measured by Perkins tonometer), ocular geometry (axial length, corneal thickness, and aqueous depth-noncontact biometer), and the choroid (volume and subfoveal thickness optical coherence tomography) were measured in 10 subjects (5 males and 5 females). Measures were taken over the course of 60 min and analyzed with repeated-measures analysis of covariance to assess the effects of posture and time. In the supine position, choroidal volume increased significantly with time (average value at <5 min = 8.8 ± 2.3 mm³, 60 min = 9.0 ± 2.4 mm³, P = 0.03). In the prone position, IOP and axial length increased with time (IOP at <5 min 15 ± 2.7 mmHg, 60 min = 19.8 ± 4.1 mmHg, P < 0.0001; axial length at <5 min = 24.29 ± 0.77 mm, 60 min = 24.31 ± 0.76 mm, P = 0.002). Each increased exponentially, with time constants of 5.3 and 14 min, respectively. Prone corneal thickness also increased with time (<5 min = 528 ± 35 μm, 60 min = 537 ± 35 μm³, P < 0.001). Aqueous depth was shortened in the prone position (baseline = 3.22 ± 0.31 mm, 60 min = 3.18 ± 0.32 mm, P < 0.0001) but did not change with time. The data show that changes in the gravity vector have pronounced transient and sustained effects on the geometry and physiology of the eye.NEW & NOTEWORTHY We show that gravity has pronounced transient and sustained effects on the eye by making detailed ocular measurements over 60 min in the supine and prone postures. These data inform our understanding of how gravitational forces can affect ocular structures, which is essential for hypothesizing how ocular changes could occur with microgravity exposure.

Effect of anesthesia on intraocular pressure measurement in children

Measurement of the intraocular pressure (IOP) is central to the diagnosis and management of pediatric glaucoma. An examination under anesthesia is often necessary in pediatric patients. Different agents used for sedation or general anesthesia have varied effects on IOP. Hemodynamic factors, methods of airway management, tonometry technique, and body positioning can all affect IOP measurements. The most accurate technique is one that reflects the awake IOP. We review factors affecting IOP measurements in the pediatric population and provide recommendations on the most accurate means to measure IOP under anesthesia based on the present literature.

Long-Term Changes in Intraocular Pressure after Vitrectomy for Rhegmatogenous Retinal Detachment, Epi-Retinal Membrane, or Macular Hole

Purpose

To determine the long-term changes in the intraocular pressure (IOP) following vitrectomy for rhegmatogenous retinal detachment (RRD), epiretinal membrane (ERM), and macular hole (MH), and to investigate the relationship between the retinal disease and the incidence of late-onset IOP elevation.

Methods

This was a retrospective, observational, comparative study. We reviewed the medical records of 54 eyes of 54 RRD patients, 117 eyes of 117 ERM patients, and 75 eyes of 75 MH patients who underwent 20-, 23- or 25-gauge vitrectomy. The IOPs before surgery and 1, 3, 6, and 12 months following vitrectomy, and also at the final visit (average, 23.95 months) were evaluated. We defined a significant increase in the IOP as an increase of ≥4 mmHg from the preoperative IOP, and this increase was taken to be a ‘death’ event for the Kaplan-Meier survival analyses.

Results

The mean follow-up period was not significantly different among the groups. The mean IOP at 3 (P = 0.001) and 12 (P = 0.011) months following the vitrectomy and at the final visit (P = 0.002) were significantly higher than that before the vitrectomy in the RRD group. The mean IOP in the RRD group was significant higher than that in the ERM group at 1 (P = 0.005), 3 (P = 0.009), and 12 (P = 0.013) months following vitrectomy, and at the final visit (P = 0.032). Kaplan-Meier survival analyses showed that the RRD group had a significantly higher risk of an IOP increase following vitrectomy than the other groups (P<0.001 by log-rank test). Multivariate logistic regression analyses showed that a preoperative diagnosis of RRD was the only risk factor that was significantly associated with a postoperative IOP elevation after excluding eyes with a low preoperative IOP (odds ratio, 3.208; P = 0.003).

Conclusions

A late-onset IOP elevation following vitrectomy was observed only in eyes that underwent RRD surgery. The elevation was probably caused by the specific characteristics and surgical procedures of RRD. Clinicians should pay more attention to the IOP elevation for long times after vitrectomy especially in eyes with RRD.