This prospective multicenter diagnostic study aims to externally validate and extend the SUCCESS Score for predicting the need for endothelial keratoplasty after cataract surgery in patients with Fuchs endothelial corneal dystrophy (FECD). The model's performance and clinical utility are assessed using discrimination, calibration, and reclassification metrics.

Fuchs endothelial corneal dystrophy (FECD) is a progressive corneal disorder characterized by endothelial cell loss, corneal edema, and visual impairment. In patients with FECD and cataract, an important clinical challenge is to predict whether cataract surgery alone will suffice or whether endothelial keratoplasty (EK) will be required postoperatively. Accurate preoperative risk stratification is essential for surgical planning and patient counseling.

The SUCCESS Score, derived from Scheimpflug tomography, was proposed as an objective index to estimate the risk of postoperative corneal decompensation in FECD. However, its external multicenter validation and the potential contribution of corneal densitometry have not yet been fully established.

This ongoing prospective, observational, multicenter study aims to externally validate and extend the SUCCESS Score for predicting the need for EK after cataract surgery in patients with FECD. The study is being conducted across five tertiary referral centers in Spain. Eligible participants are adults with FECD grade ≥2 on the modified Krachmer scale and a visually significant cataract requiring phacoemulsification. Patients with epithelial edema, prior ocular surgery, corneal infection, or trauma are excluded.

Preoperative evaluation includes Scheimpflug tomography and corneal densitometry analysis. The primary outcome is the requirement for endothelial keratoplasty after cataract surgery, determined by postoperative visual function and corneal evaluation. Model performance will be assessed through discrimination (Harrell's C statistic), calibration, reclassification (IDI, NRI), and decision curve analysis to estimate clinical utility.

The primary analysis is scheduled for completion in October 2024. Extended follow-up will continue until June 25, 2026, to assess long-term predictive performance and generalizability of the extended SUCCESS model.

An interactive web-based calculator implementing both the original and extended SUCCESS models will be provided as a supplementary tool to facilitate clinical use and standardized patient counseling across participating centers.

Inclusion Criteria:

• Adults aged ≥40 years.
• Clinical diagnosis of Fuchs endothelial corneal dystrophy (FECD) grade ≥2 on the modified Krachmer scale.
• Presence of visually significant cataract requiring phacoemulsification surgery.
• Ability to provide informed consent and comply with study procedures.
• Availability of preoperative Scheimpflug tomography and corneal densitometry measurements.

Exclusion Criteria:

• Epithelial or stromal edema precluding reliable corneal imaging.
• Previous ocular surgery (including corneal or intraocular procedures).
• Corneal trauma, infection, or inflammation affecting endothelial integrity.
• Coexisting ocular pathologies that could confound postoperative assessment (e.g., advanced glaucoma, macular degeneration).

dults with clinically diagnosed Fuchs endothelial corneal dystrophy (FECD) and visually significant cataract who are scheduled to undergo phacoemulsification surgery at participating tertiary referral centers in Spain. Eligible participants present FECD grade ≥2 on the modified Krachmer scale and have available preoperative Scheimpflug tomography and corneal densitometry measurements. The study population represents a real-world clinical cohort of patients routinely evaluated in corneal and cataract units, allowing assessment of the predictive performance and clinical utility of the SUCCESS Score under standard care conditions.

Deidentified individual participant data (IPD) that underlie the results reported in this article will be made available to qualified researchers upon reasonable request. Access will be granted after publication of the primary results and upon approval of a methodologically sound proposal. Data will be shared through a secure institutional platform of the Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS).

Beginning 12 months after publication and ending 36 months after publication.

Qualified researchers affiliated with academic or non-profit institutions may request access to the deidentified individual participant data (IPD), study protocol, statistical analysis plan, and analytic code. Requests must include a methodologically sound proposal describing the intended analyses and objectives.

Data and supporting materials will be shared through a secure institutional data repository managed by the Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS). Access will be granted upon approval by the study's data governance committee and completion of a data use agreement ensuring appropriate data handling and confidentiality.