Ocular Injury Associated With Prone Positioning in Adult Critical Care: A Systematic Review and Meta-Analysis


Prone positioning during the COVID-19 pandemic has become increasingly used as an adjunct to increase oxygenation in critical care patients. It is associated with an adverse event profile. This study sought to investigate the occurrence of ocular injuries reported in prone versus supine groups in adult critical care.


Systematic review and meta-analysis.


A systematic review and meta-analysis were carried out in accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. PubMed, SCOPUS, and the Cochrane Library were searched. The search period was January 1, 1990, to July 1, 2020.


Eleven randomized controlled trials were included, with 2,247 patients. Twenty-eight events were recorded in 3 trials (174 patients) and no events in the other 8 trials (2,073 patients). The rates of eye injury were 5 events in 1,158 patients (1.30%) and 13 events in 1,089 patients (1.19%) in the prone and supine groups, respectively, which were reduced to 2 of 1,158 patients (0.17%) and 2 of 1,089 patients (0.18%), respectively, when reports of eye or eyelid edema were removed. Meta-analysis demonstrated no significant differences between groups with (an OR of 1.40 (95% CI: 0.37–5.27) and without (OR: 0.78; 95% CI: 0.11–5.73) reported edema.


This meta-analysis showed no significant difference in the rate of reported ocular injury between prone and supine critical care groups. These rates remain higher than the incidence reported during general anesthesia. There is a need for studies in critical care settings in which ocular injury is an end-point and which include extended patient follow-up.

During the first decade of the 21st century, multiple trials demonstrated an improvement in oxygenation in patients with acute respiratory distress syndrome receiving nurse attendance in the prone position. In combination with lung protective ventilation, this improvement has subsequently been demonstrated to reduce mortality compared to conventional supine ventilation. However, this technique is not without risk. The Faculty of Intensive Care Medicine (FICM) released guidelines for the implementation of this technique in 2019 as there was concern that the increased use of prone positioning was contributing to the rise in critical safety incidents, including pressure injuries to anterior structures.

One such structure was the eye. Vision loss and impairment due to optic nerve, corneal, and scleral injuries, along with extraocular muscle impingement had been reported previously following spinal and plastic surgery procedures performed with the patient in a prone position, with prone positioning having been reported to increase intraocular pressure. FICM prone position guidelines aimed to reduce both exposure and pressure, recommending several measures including taping patients’ eyes shut; ensuring there is no direct pressure on patients’ eyes; placing patients in a 30-degrees foot-down position (reverse Trendelenburg) while being nursed in this position (to limit dependent periocular swelling) and rotating patients’ heads from side-to-side at 2-hour intervals.

Despite the increased use of prone positioning in critical care adults, as highlighted in both popular and scientific press during the recent COVID-19 pandemic, the complication profile of prone positioning is still emerging. A previous review of the complications associated with prone positioning revealed only studies in surgical patients. This is a different cohort from those in critical care, who should be considered separately. Due to longer cumulative time periods in the prone position, the need for increased repositioning and the easier access for nursing staff (no sterile field to avoid) in critical care patients form a distinct patient group and should be regarded as such. It may also be argued that, as a positive fluid balance may be more likely in critical care patients than in surgical patients, the risks of dependent edema and pressure injury are increased.


The purpose of this systematic review was to compare the incidence and types of ocular injury reported in randomized controlled trials of prone positioning versus supine positioning in adult critical care and, if possible, perform a meta-analysis. This investigation has not been conducted previously to the authors’ knowledge.


This systematic review was conducted in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement. A review protocol was registered with the PROSPERO systematic review database (registration number: CRD42020196917).

Study Eligibility Criteria

Studies in adult (18 years of age or older at the time of intervention) hospital inpatients in critical care (defined as patients requiring at least Level 2 care, as defined by the National Health Service Critical Care Service Framework) were eligible, regardless of patients’ sedation level, indication for prone positioning (eg, respiratory- or surgical site-related), or geographical location of care. Studies including any form of prone positioning adjuncts (where the patient is positioned face down on the bed) were included. Only randomized controlled trials (RCTs) that compared prone to supine positioning were included. Any variation of RCT design was eligible, including cluster or cross-over.

Primary outcome was the incidence of ocular injuries, presented as both crude rates and, after meta-analysis, odds ratios (OR). Only papers published in indexed medical journals (conference abstracts were excluded) were included, with English as the language of publication. The date of publication was restricted to the previous 3 decades (January 1, 1990 to July 1, 2020). This range was defined by the authors because prone positioning in critical care patients became increasingly common following a series of RCTs published during the year 2000. Allowing the search to include studies from between 1990 and 2000 would allow capturing any preceding studies within the same era of critical care.

Information Sources and Search

Four databases, PubMed (MeSH and Advanced), SCOPUS, and Cochrane Library were searched. For PubMed, the search was conducted using both MeSH terms and the advanced search option. MeSH terms (“Position,” “Prone’) were used. An advanced search was conducted using the terms “Prone” AND “Randomised.” Ovid, Embase, and SCOPUS were also searched using the same terms with automatic adjustment for Americanized spelling. The Cochrane Library was searched using the term “Prone.”

Study Selection and Data Collection Process

Two independent reviewers each reviewed all titles retrieved from the initial searches. Duplicates were eliminated, and if possible, using the available abstracts, each reviewer decided its inclusion. If the paper could not be included or excluded with certainty on the basis of the abstract, then the full text was read. Any disagreements between reviewers on papers’ eligibility were resolved by discussion or, if necessary, arbitration by a senior author. If an RCT had been reported by more than one publication, the last publication which reported the trial was used as the reference publication in this review.

Data Items

The following variables were recorded: study information (first author, publication year, and country of origin); participant information (total patients, sex, median/mean age); intervention information where available (prone positioning adjuncts, length of time spent in a prone position, head rotation frequency, eye care provided); and follow-up information (mean and median follow-up duration, planned follow-up period, and how many study participants completed follow-up).

The following outcome data were sought: whether ocular injury data were reported as present or absent; number or proportion of participants in each intervention arm with ocular injuries; injury type; laterality and any patient-reported outcomes available. If further information was required, then individual study authors were contacted with a return period of 30 days.

Risk of Bias in Individual Studies and Across Studies

Two authors independently assessed the potential bias using the Cochrane Collaboration bias tool.

Summary Measurements and Synthesis of Results

The rates of ocular injury were shown as crude rates and, if appropriate, mean scores, for example, who diagnosed the ocular injury and how and when may vary in relevant ways between studies.


Meta-analysis was performed for rates of injury overall and for each distinct injury type if there were 2 or more RCTs which examined the same injury type. The outcome groups were divided into supine positioning and prone positioning, with subdivisions into specific prone positioning pressure relief adjuncts if sufficient data were available (2 or more homologous studies).

Review Manager 5 software (Nordic Cochrane Center, Copenhagen, Denmark) was used for results synthesis. If the outcome data were presented in the form of dichotomous categorical variables, ORs would be reported with corresponding 95% confidence intervals (CI). Statistical heterogeneity between studies was checked and reported using the I 2 measure of study heterogeneity. If low heterogeneity (I 2 : <50%) between studies was reported, then a fixed effect model was used. If higher heterogeneity was displayed, then a random effects model was used. If a meta-analysis displayed a heterogeneity of >75%, it was excluded from the results. ,

The primary summary measurement (rate of ocular injuries) of the meta-analysis was given as an OR with 95% CI. If there was a zero-cell count for any given event, then Review Manager 5 software automatically added a 0.5 continuity correction. A sensitivity analysis was also undertaken. Only studies in which the majority of areas (4 or more) of potential bias were low risk would be analyzed and presented in this analysis.


Study Characteristics

Twelve studies met inclusion criteria. Two studies had included the same participants, resulting in 11 studies with unique populations. , The PRISMA flow diagram of search results is presented in Figure 1 .

Figure 1

PRISMA flow diagram of study selection. A total of 11 studies were included in the end quantitative synthesis. PRISMA = Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

There were 2,247 randomly assigned patients included in this analysis (1,089 patients underwent supine positioning only, and 1,158 patients were randomized to receive prone positioning). Length of follow-up reporting heterogeneous. Study details are included in Table 1 .


Study and Patient Characteristics of Included Studies

Study (ref), y Location Patient Group Males/Females Age Mean/Median ± SD, y Number Prone Number Supine Mean Length of Follow-Up, Days Supine/Prone
Gattinoni (1), 2001 Italy ALI or ARDS 214.0/90.0 Prone: 57 ± 16
Supine: 59 ± 17
152.0 152.0 10/10
Watanabe (20), 2002 Japan Post-esophagectomy 14.0/2.0 Prone: 66 ± 5.8
Supine: 63 ± 8.1
8.0 8.0 Not available
Beuret (21), 2002 France Patients requiring intubation because of GCS <9.0 36.0/15.0 Prone: 55 ± 19
Supine: 55 ± 20
25.0 26.0 Not available
Guérin (2), 2004 France Acute respiratory failure 593.0/198.0 Prone: 62 ± 15.7
Supine: 62.5 ± 14.7
413.0 378.0 24.5/26.9
Papazian (22), 2005 France ARDS 23.0/16.0 Prone: 51 ± 10.5
Supine: 55 ± 15
26.0 13.0 Not available
Voggenreiter (23), 2005 Germany Trauma patients with ALI or ARDS 33.0/7.0 Prone: 40 ± 14
Supine: 43 ± 10
21.0 19.0 Not available
Mancebo (3), 2006 Spain ARDS 86.0/50.0 Prone: 54 ± 17
Supine: 54 ± 16
76.0 60.0 Not available
Chan (24), 2007 Taiwan CAP 18.0/4.0 Prone: 54.7 ± 21.8
Supine: 69 ± 15.5
11.0 11.0 3.0/3.0
Fernandez (25), 2008 Spain ARDS 25.0/15.0 Prone: 53.9 ± 17.9
Supine: 55.3 ± 14.6
21.0 19.0 17.5/14.7
Taccone (4), 2009 Italy ARDS 246.0/96.0 Population:
60 ± 16
168.0 174.0 28.0/28.0
Guérin (5), 2013 France ARDS 318.0/148.0 Prone: 58 ± 16
Supine: 60 ± 16
237.0 229.0 26.0 (18.0 non-survivors)/
24.0 (21.0 non-survivors)

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Jul 10, 2021 | Posted by in OPHTHALMOLOGY | Comments Off on Ocular Injury Associated With Prone Positioning in Adult Critical Care: A Systematic Review and Meta-Analysis

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