Spinal SurgeryPRONE-ONSDNCT07395115
A Prospective Observational Study on Factors Affecting Optic Nerve Sheath Diameter and Visual Acuity in Prone Spinal Surgery
An observational study of Spinal Surgery and Prone Position, run by Istanbul University - Cerrahpasa at 1 site in Turkey (Türkiye).
Trial summary
The prone position in spinal surgery can alter intracranial pressure and optic nerve sheath diameter (ONSD) and potentially lead to visual complications. This prospective observational study aimed to identify factors influencing ultrasonographic ONSD changes and visual acuity in patients undergoing spinal surgery. Read more about this study
- Who is it for?
- Ages 18 years and older
- Conditions the study is for
- Spinal Surgery, Prone Position
- How many people
- 65 participants
- Where
- 1 siteTurkey (Türkiye)
- Study dates
- 15 Dec 2024to 14 Oct 2025
- Phase
- Observational
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 years and older
- All sexes
- No healthy volunteers
- Adult, Older adult
Study population: Adult patients scheduled for elective spine surgery requiring prone positioning at a university hospital setting.
Who may be able to join
- Age ≥ 18 years
- Scheduled to undergo elective spine surgery in the prone position
- American Society of Anesthesiologists (ASA) physical status I-III
- Preoperative visual acuity measurable using a Snellen chart
Who cannot join
- Preexisting ophthalmologic diseases affecting optic nerve or visual acuity (e.g., glaucoma, optic neuropathy, diabetic retinopathy)
- Previous eye trauma or history of orbital surgery
- Inability to obtain reliable ultrasonographic ONSD measurements (e.g., orbital deformity, ocular infection)
Trial locations and contacts
1 site in 1 country.
Turkey (Türkiye)1 site
Istanbul University - Cerrahpaşa, Cerrahpaşa Faculty of Medicine Hospital
Istanbul
About this study
Official title: Factors Affecting Optic Nerve Sheath Diameter and Visual Acuity Changes in Adult Patients Undergoing Prone Spine Surgery: A Prospective Observational Study
The prone position in spinal surgery can alter intracranial pressure and optic nerve sheath diameter (ONSD) and potentially lead to visual complications. This prospective observational study aimed to identify factors influencing ultrasonographic ONSD changes and visual acuity in patients undergoing spinal surgery.
Read the detailed description
During spine surgery, many patients are positioned face-down (prone position) for several hours. This position may influence blood flow to the head and increase pressure around the brain and eyes. One structure that can reflect these pressure changes is the optic nerve sheath, which surrounds the optic nerve at the back of the eye. When the pressure inside the skull rises, the optic nerve sheath may become wider. This change can be measured non-invasively using ultrasound and is referred to as optic nerve sheath diameter (ONSD).
This prospective observational study will evaluate whether ONSD changes occur in adult patients undergoing prone-position spine surgery and whether these changes are related to temporary alterations in vision. Visual acuity will be evaluated using a standard Snellen chart before surgery and on the first postoperative day to detect any change in vision after the procedure.
Ultrasound ONSD measurements will be performed in three stages: before the patient is placed in the prone position, shortly after the prone position is established, and at the end of the surgery while still in the same position. Clinical variables such as blood pressure, carbon dioxide levels, ventilation parameters, anesthesia technique, the use of a pinned head holder, and patient characteristics will also be recorded. By comparing these variables with ONSD and visual outcomes, the study aims to identify whether specific surgical or physiological factors contribute to increased optic nerve sheath width or temporary vision disturbances.
This research does not involve any experimental drug or device. All measurements are part of routine safe monitoring techniques used to assess patients' condition during surgery. The goal of this study is to help better understand factors that may increase the risk of eye-related complications during prone spine surgery and to contribute to safer surgical practices.
- Conditions
- Spinal Surgery, Prone Position
- Keywords
- logMAR, Snellen, visual acuity, ONSD
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
| Study group | Role | What they receive |
|---|---|---|
| Prone Spine Surgery Cohort | Adults undergoing prone-position spine surgery, evaluated with ultrasound ONSD measurements and visual acuity testing. |
What is being measured
The primary outcome is the main question the study is designed to answer.
Change in ultrasonographic optic nerve sheath diameter (mm)
Optic nerve sheath diameter (ONSD) will be measured bilaterally using standardized transorbital ultrasonography with a high-frequency linear probe (6-13 MHz). Measurements will be obtained 3 mm posterior to the globe, in accordance with established sonographic guidelines. For each eye, three measurements will be recorded, and the mean value will be calculated. The average of both eyes will be used for statistical analysis. The primary outcome will be the absolute change in ONSD (ΔONSD, mm) between baseline and intraoperative prone measurements.
Measured: Baseline (preoperative, supine), after prone positioning (15 minutes after positioning), and at the end of surgery (intraoperative, before repositioning to supine).
Secondary outcomes (8)
Change in visual acuity (logMAR)
Visual acuity will be initially recorded in decimal format using a standard Snellen chart and subsequently converted to logMAR units for statistical analysis. The outcome will be the absolute change in visual acuity (ΔlogMAR) from baseline to postoperative day 1 (postoperative logMAR minus baseline logMAR).
Measured: Baseline (preoperative) and postoperative day 1.
Correlation between change in ONSD and intraoperative end-tidal carbon dioxide (EtCO₂)
Correlation analysis will be performed between changes in ONSD (ΔONSD, mm) and intraoperative end-tidal carbon dioxide levels (EtCO₂, mmHg) recorded simultaneously with ONSD measurements.
Measured: Intraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Difference in ONSD change between pinned head holder and non-pinned positioning
Change in ONSD (mm) will be compared between patients positioned using a pinned head holder and those positioned without pin fixation. The outcome will be the between-group difference in ONSD change (mm).
Measured: ntraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Association between postoperative visual acuity change and intraoperative ONSD change
The association between postoperative change in visual acuity (ΔlogMAR) and intraoperative change in optic nerve sheath diameter (ΔONSD) will be evaluated using regression analysis. Visual acuity will be recorded in decimal format and converted to logMAR for statistical analysis. ONSD will be measured using standardized transorbital ultrasonography and expressed in millimeters.
Measured: Baseline (preoperative) and postoperative day 1.
Correlation between change in ONSD and intraoperative mean arterial pressure (MAP)
Correlation analysis will be performed between changes in ONSD (ΔONSD, mm) and intraoperative mean arterial pressure (MAP, mmHg) recorded simultaneously with ONSD measurements.
Measured: Intraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Correlation between change in ONSD and intraoperative arterial partial pressure of carbon dioxide (PaCO₂)
Correlation analysis will be performed between changes in ONSD (ΔONSD, mm) and arterial partial pressure of carbon dioxide (PaCO₂, mmHg) obtained from arterial blood gas analysis and recorded simultaneously with ONSD measurements.
Measured: Intraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Correlation between change in ONSD and intraoperative arterial partial pressure of oxygen (PaO₂)
Correlation analysis will be performed between changes in ONSD (ΔONSD, mm) and arterial partial pressure of oxygen (PaO₂, mmHg) obtained from arterial blood gas analysis and recorded simultaneously with ONSD measurements.
Measured: Time Frame: Intraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Correlation between change in ONSD and intraoperative positive end-expiratory pressure (PEEP)
Correlation analysis will be performed between changes in ONSD (ΔONSD, mm) and intraoperative positive end-expiratory pressure levels (PEEP, cmH₂O) recorded simultaneously with ONSD measurements.
Measured: Intraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted9 Feb 2026
- Study start15 Dec 2024
- Primary completion4 Jun 2025
- Study completion14 Oct 2025
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Spinal SurgeryStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Observational
- Observational model
- Cohort
- Time perspective
- Prospective
- Enrolment
- 65 participants (actual)
Sponsor and investigators
- Lead sponsor
- Istanbul University - Cerrahpasa
- Sponsor type
- University, hospital or other
- Responsible party
- Principal investigator, Begüm Ramakan, MD, Istanbul University - Cerrahpasa
- Investigators
- Özlem Korkmaz Dilmen, MD, Prof, Principal investigator, Istanbul University-Cerrahpasa, Cerrahpasa Medical FacultyBegüm Ramakan, MD, Anesthesiology Resident, Study director, Istanbul University - Cerrahpasa
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07395115
- Sponsor's protocol ID
- 2024/244
- Acronym
- PRONE-ONSD
- Status last verified
- Feb 2026
- First submitted
- 3 Dec 2025
- Last updated
- 23 Oct 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No: IPD will not be shared because individual-level data are not permitted to be disclosed under the current ethical approval.
Study at a glance
From the registry record, last updated by the sponsor on 23 Oct 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Factors Affecting Optic Nerve Sheath Diameter and Visual Acuity Changes in Adult Patients Undergoing Prone Spine Surgery: A Prospective Observational Study
- ClinicalTrials.gov ID
- NCT07395115
- Acronym / sponsor ID
- PRONE-ONSD / 2024/244
- Conditions
- Spinal Surgery, Prone Position
- Keywords
- logMAR, Snellen, visual acuity, ONSD
- Study type
- Observational
- Recruitment status
- Completed
- Enrolment
- 65 participants (actual)
- Lead sponsor
- Istanbul University - CerrahpasaUniversity, hospital or other
- Study start
- 15 Dec 2024 (actual)
- Primary completion
- 4 Jun 2025 (actual)
- Study completion
- 14 Oct 2025 (actual)
- First posted
- 9 Feb 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
The prone position in spinal surgery can alter intracranial pressure and optic nerve sheath diameter (ONSD) and potentially lead to visual complications. This prospective observational study aimed to identify factors influencing ultrasonographic ONSD changes and visual acuity in patients undergoing spinal surgery.
Detailed description
During spine surgery, many patients are positioned face-down (prone position) for several hours. This position may influence blood flow to the head and increase pressure around the brain and eyes. One structure that can reflect these pressure changes is the optic nerve sheath, which surrounds the optic nerve at the back of the eye. When the pressure inside the skull rises, the optic nerve sheath may become wider. This change can be measured non-invasively using ultrasound and is referred to as optic nerve sheath diameter (ONSD).
This prospective observational study will evaluate whether ONSD changes occur in adult patients undergoing prone-position spine surgery and whether these changes are related to temporary alterations in vision. Visual acuity will be evaluated using a standard Snellen chart before surgery and on the first postoperative day to detect any change in vision after the procedure.
Ultrasound ONSD measurements will be performed in three stages: before the patient is placed in the prone position, shortly after the prone position is established, and at the end of the surgery while still in the same position. Clinical variables such as blood pressure, carbon dioxide levels, ventilation parameters, anesthesia technique, the use of a pinned head holder, and patient characteristics will also be recorded. By comparing these variables with ONSD and visual outcomes, the study aims to identify whether specific surgical or physiological factors contribute to increased optic nerve sheath width or temporary vision disturbances.
This research does not involve any experimental drug or device. All measurements are part of routine safe monitoring techniques used to assess patients' condition during surgery. The goal of this study is to help better understand factors that may increase the risk of eye-related complications during prone spine surgery and to contribute to safer surgical practices.
Study design
- Observational model
- Cohort
- Time perspective
- Prospective
- Number of arms
- 1
| Arm | Type | Receives |
|---|---|---|
| Prone Spine Surgery Cohort | – | –Adults undergoing prone-position spine surgery, evaluated with ultrasound ONSD measurements and visual acuity testing. |
Who may qualify
- Ages
- 18 years and older
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Adult, Older adult
- Study population
- Adult patients scheduled for elective spine surgery requiring prone positioning at a university hospital setting.
Key inclusion criteria (4 listed)
- Age ≥ 18 years
- Scheduled to undergo elective spine surgery in the prone position
- American Society of Anesthesiologists (ASA) physical status I-III
- Preoperative visual acuity measurable using a Snellen chart
Key exclusion criteria (3 listed)
- Preexisting ophthalmologic diseases affecting optic nerve or visual acuity (e.g., glaucoma, optic neuropathy, diabetic retinopathy)
- Previous eye trauma or history of orbital surgery
- Inability to obtain reliable ultrasonographic ONSD measurements (e.g., orbital deformity, ocular infection)
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Primary outcome
Change in ultrasonographic optic nerve sheath diameter (mm)
Time frame: Baseline (preoperative, supine), after prone positioning (15 minutes after positioning), and at the end of surgery (intraoperative, before repositioning to supine).
Optic nerve sheath diameter (ONSD) will be measured bilaterally using standardized transorbital ultrasonography with a high-frequency linear probe (6-13 MHz). Measurements will be obtained 3 mm posterior to the globe, in accordance with established sonographic guidelines. For each eye, three measurements will be recorded, and the mean value will be calculated. The average of both eyes will be used for statistical analysis. The primary outcome will be the absolute change in ONSD (ΔONSD, mm) between baseline and intraoperative prone measurements.
8 secondary outcomes
Change in visual acuity (logMAR)
Time frame: Baseline (preoperative) and postoperative day 1.
Correlation between change in ONSD and intraoperative end-tidal carbon dioxide (EtCO₂)
Time frame: Intraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Difference in ONSD change between pinned head holder and non-pinned positioning
Time frame: ntraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Association between postoperative visual acuity change and intraoperative ONSD change
Time frame: Baseline (preoperative) and postoperative day 1.
Correlation between change in ONSD and intraoperative mean arterial pressure (MAP)
Time frame: Intraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Correlation between change in ONSD and intraoperative arterial partial pressure of carbon dioxide (PaCO₂)
Time frame: Intraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Correlation between change in ONSD and intraoperative arterial partial pressure of oxygen (PaO₂)
Time frame: Time Frame: Intraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Correlation between change in ONSD and intraoperative positive end-expiratory pressure (PEEP)
Time frame: Intraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 23 Oct 2026.
- Individual participant dataSharing planned: No. IPD will not be shared because individual-level data are not permitted to be disclosed under the current ethical approval.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Özlem Korkmaz Dilmen, MD, Prof principal investigator
Istanbul University-Cerrahpasa, Cerrahpasa Medical Faculty
Begüm Ramakan, MD, Anesthesiology Resident study director
Istanbul University - Cerrahpasa
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
An observational study of Spinal Surgery and Prone Position, run by Istanbul University - Cerrahpasa at 1 site in Turkey (Türkiye).
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 4 inclusion and 3 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 23 Oct 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Turkey (Türkiye). Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Change in ultrasonographic optic nerve sheath diameter (mm) (time frame: Baseline (preoperative, supine), after prone positioning (15 minutes after positioning), and at the end of surgery (intraoperative, before repositioning to supine).). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 23 Oct 2026.