Silicone Effect on Corneal Endothelium and Corneal Biomechanics Using Corvis ST

This prospective observational study evaluates the impact of silicone oil tamponade on corneal endothelial integrity and biomechanical properties in patients undergoing vitrectomy for retinal detachment. Below is an expanded description of the study protocol, emphasizing methodological rigor and technical specifics.

Study Design Type: Single-center, prospective, longitudinal observational study. Primary Objective: To quantify postoperative changes in corneal endothelial cell density (ECD), morphology, and biomechanical stability over a 6-month period following silicone oil tamponade.

Secondary Objectives:

Correlate corneal changes with clinical outcomes (BCVA, IOP).

Identify risk factors for endothelial cell loss or biomechanical weakening.

Rationale for Time Points: Assessments at 1, 3, and 6 months were selected to capture early postoperative stress responses (1 month), intermediate healing (3 months), and longer-term stabilization (6 months), aligning with standard vitrectomy follow-up protocols.

Participant Enrollment Recruitment: Consecutive patients scheduled for vitrectomy with silicone oil tamponade at a tertiary eye care center.

Informed Consent Process: Participants received detailed verbal and written explanations of study procedures, risks, and benefits prior to enrollment.

Data Collection Procedures Clinical and Imaging Assessments

Best-Corrected Visual Acuity (BCVA):

Measured using Snellen charts under standardized lighting conditions.

Converted to logMAR for statistical analysis.

Intraocular Pressure (IOP):

Assessed via Goldmann applanation tonometry (calibrated weekly), with three consecutive readings averaged.

Corneal Endothelial Analysis:

Specular Microscopy (Konan Noncon Robo NSP-9900):

Parameters:

Endothelial Cell Density (ECD): Cells/mm².

Coefficient of Variation (CV): Reflects cell size variability (polymegathism).

Hexagonality: Percentage of hexagonal cells (pleomorphism).

Protocol: Central corneal measurements taken in triplicate, with the median value recorded.

Corneal Biomechanical Evaluation:

Corvis ST (Oculus Optikgeräte GmbH):

Parameters:

Stress-Strain Index (SSI): Quantifies corneal stiffness.

Deformation Amplitude (DA): Maximum corneal displacement during air-puff applanation.

Protocol: Three valid scans per eye, performed under mesopic conditions.

Follow-Up Protocol Baseline: Preoperative assessment within 1 week of surgery.

Postoperative: Follow-up visits at 1, 3, and 6 months (±7 days), including:

BCVA and IOP measurement.

Specular microscopy and Corvis ST imaging.

Documentation of complications (e.g., corneal edema, elevated IOP).

Quality Assurance Measures

Equipment Calibration:

Specular microscopy and Corvis ST devices underwent daily calibration checks and quarterly manufacturer servicing.

Standardized Protocols:

All measurements performed by a single trained ophthalmologist to minimize inter-observer variability.

Consistent time-of-day scheduling for IOP assessments (9 AM-11 AM) to control diurnal fluctuations.

Blinded Analysis:

Endothelial and biomechanical data were analyzed by masked investigators unaware of clinical outcomes or time points.

Data Management and Statistical Analysis

Data Storage:

Clinical and imaging data stored in a HIPAA-compliant REDCap database with role-based access.

Regular backups to encrypted cloud storage.

Statistical Methods:

Primary Analysis: Linear mixed-effects models to evaluate longitudinal changes in ECD, SSI, and DA.

Secondary Analysis: Pearson/Spearman correlations between endothelial parameters, biomechanics, and BCVA/IOP.

Missing Data: Multiple imputation used for sporadic missing follow-up data (<10% attrition anticipated).

Software: Analyses performed using R (v4.3.1) and SPSS (v28.0).

Ethical and Safety Considerations

Adverse Event Management:

Complications (e.g., corneal decompensation, IOP spikes) were managed per institutional guidelines and reported to the IRB.

Protocol Compliance:

Internal audits conducted quarterly to ensure adherence to GCP and study protocols.

Technical Rationale Silicone Oil Tamponade: While effective for retinal reattachment, silicone oil may mechanically stress the corneal endothelium or alter aqueous humor dynamics, potentially accelerating cell loss.

Biomechanical Relevance: Corneal stiffness (SSI) and deformability (DA) are critical for refractive stability and surgical planning (e.g., cataract surgery post-vitrectomy).

Clinical Implications

This study aims to provide evidence-based recommendations for:

Timing of silicone oil removal to mitigate corneal damage.

Enhanced monitoring strategies for high-risk patients.

Personalized interventions to preserve endothelial health.