A Prospective Observational Study on Factors Affecting Optic Nerve Sheath Diameter and Visual Acuity in Prone Spinal Surgery

NCT07395115 | Completed

• 1 other identifier: 2024/244
• Study Type: observational
• Target: 65
• Locations: 1 country
• Sites: 1

Brief 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.

Conditions

Spinal Surgery; Prone Position

Keywords

logMAR; Snellen; visual acuity; ONSD

Outcome Measures

Primary Outcomes (1)

• 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.

  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)

  Baseline (preoperative) and postoperative day 1.

• Correlation between change in ONSD and intraoperative end-tidal carbon dioxide (EtCO₂)

  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

  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

  Baseline (preoperative) and postoperative day 1.

• Correlation between change in ONSD and intraoperative mean arterial pressure (MAP)

  Intraoperative period: baseline (supine), after prone positioning (15 minutes), and at the end of surgery.

Study Arms (1)

Prone Spine Surgery Cohort

Adults undergoing prone-position spine surgery, evaluated with ultrasound ONSD measurements and visual acuity testing.

Eligibility Criteria

• Age: 18 Years+
• Sex: all
• Healthy Volunteers: No
• Age Groups: Adult (18-64), Older Adult (65+)
• Sampling Method: Non-Probability Sample

Study Population

Adult patients scheduled for elective spine surgery requiring prone positioning at a university hospital setting.

You may qualify if:

• 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

You may not qualify if:

• 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)

Sponsors & Collaborators

• Istanbul University - Cerrahpasa: lead

Study Sites (1)

Istanbul University - Cerrahpaşa, Cerrahpaşa Faculty of Medicine Hospital

Istanbul, Turkey (Türkiye)

Location

Study Officials

• Özlem Korkmaz Dilmen, MD, Prof

  Istanbul University-Cerrahpasa, Cerrahpasa Medical Faculty

  PRINCIPAL INVESTIGATOR

• Begüm Ramakan, MD, Anesthesiology Resident

  Istanbul University - Cerrahpasa

  STUDY DIRECTOR

Study Design

• Study Type: observational
• Observational Model: COHORT
• Time Perspective: PROSPECTIVE
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Resident Physician in Anesthesiology and Reanimation

Study Record Dates

• First Submitted: December 3, 2025
• First Posted: February 9, 2026
• Study Start: December 3, 2024
• Primary Completion: June 4, 2025
• Study Completion: June 5, 2025
• Last Updated: February 9, 2026

Record last verified: 2026-02

Data Sharing

• IPD Sharing: Will not share

Locations

TU (1)