This prospective, single-center observational study aims to evaluate the acute effects of transitioning from mechanical ventilation to spontaneous breathing on intraocular pressure (IOP) in intensive care unit patients. Forty adult patients receiving invasive mechanical ventilation and undergoing weaning will be enrolled. IOP will be measured non-invasively before and after the transition, without any intervention beyond routine clinical care. The primary objective is to determine whether spontaneous breathing after mechanical ventilation causes significant changes in IOP. Findings may provide insights into ocular physiology during weaning and contribute to the safe management of critically ill patients, particularly those with ocular risk factors.

Mechanical ventilation is an essential life-supporting therapy for critically ill patients with respiratory failure. However, prolonged mechanical ventilation is associated with increased risks of complications, making the weaning process a critical step in intensive care management. During weaning, patients are transitioned from supported modes (such as SIMV or PSV) to spontaneous breathing modes (such as CPAP or T-tube). This transition leads to changes in thoracic pressure and venous return, which may in turn affect intracranial and intraocular pressures.

Intraocular pressure (IOP) is a key parameter for maintaining ocular perfusion and is influenced by systemic hemodynamics, respiratory patterns, and intrathoracic pressure changes. Previous studies have shown that posture, Valsalva maneuvers, and mechanical ventilation can alter IOP. However, evidence on the acute effects of transitioning from invasive mechanical ventilation to spontaneous breathing on IOP remains limited.

This prospective, observational, single-center study will be conducted in the intensive care unit of Elazığ Fethi Sekin City Hospital, Department of Anesthesiology and Reanimation. Forty adult patients receiving invasive mechanical ventilation and undergoing clinically indicated weaning will be enrolled. IOP will be measured non-invasively before and after the transition to spontaneous breathing, using portable tonometry, without the use of topical anesthesia. Measurements will be taken in both eyes, and average values will be recorded.

Demographic and clinical data, including age, sex, diagnosis, duration of ventilation, sedation status (RASS), and timing of mode transition, will also be collected. The primary endpoint is the difference in IOP before and after the transition. Statistical analysis will include paired t-test or Wilcoxon signed-rank test, depending on data distribution. Repeated measures ANOVA or Friedman test will be used when applicable, with significance set at p < 0.05.

This study does not involve any intervention or deviation from standard clinical care. All weaning procedures will be conducted according to routine ICU protocols. The findings of this study are expected to contribute to the understanding of ocular physiology during critical illness and may be particularly relevant for the safe management of patients with ocular comorbidities such as glaucoma.

Inclusion Criteria:

• Age between 18 and 85 years
• Admitted to intensive care unit (ICU) and receiving invasive mechanical ventilation
• Clinically scheduled for weaning and transition to spontaneous breathing
• Able to undergo intraocular pressure (IOP) measurement before and after transition
• Written informed consent obtained from the patient or legal representative

Exclusion Criteria:

• History of glaucoma, ocular hypertension, or previous eye surgery
• Active ocular infection or trauma
• Hemodynamic instability that prevents safe measurement
• Inability to obtain reliable IOP measurements
• Refusal of consent by patient or legal representative

Adult patients admitted to the intensive care unit of Elazığ Fethi Sekin City Hospital, Department of Anesthesiology and Reanimation, who are receiving invasive mechanical ventilation and undergoing clinically indicated weaning.

Individual participant data (IPD) will not be shared because this is a single-center observational study with a limited sample size. Only aggregate data will be analyzed and reported in publications. Sharing IPD is not planned in order to protect patient confidentiality and comply with local ethical regulations.