Postoperative CCT in FECD vs. Non-FECD

This is a single-centre, prospective, controlled, non-interventional observational clinical study conducted at the Augenabteilung, Klinik Hietzing, Wiener Gesundheitsverbund, Vienna, Austria.

Fuchs endothelial corneal dystrophy (FECD) is a progressive disorder of the corneal endothelium characterized clinically by central guttae and a gradual loss of endothelial barrier and pump function, ultimately leading to corneal edema, increased corneal thickness, and visual impairment. In FECD, thickening is primarily a consequence of stromal hydration (deturgescence failure), and corneal edema can be present even when it is not yet obvious on slit-lamp examination ("subclinical edema"), which complicates clinical staging and risk estimation in routine practice.

Because cataract prevalence increases with age, cataract and FECD frequently coexist, and cataract surgery planning in FECD must account for the reduced endothelial reserve. Phacoemulsification - although highly standardized and effective - exerts mechanical, ultrasonic, and fluidic stress on the endothelium and can cause postoperative endothelial cell loss even in otherwise healthy eyes. Large, randomized data have shown that modern cataract surgery can measurably affect the corneal endothelium and that the magnitude of endothelial impact depends on patient- and surgery-related factors. Clinically, inadequate endothelial pump function is a key mechanism underlying postoperative corneal edema after cataract surgery, making endothelial vulnerability a central safety consideration in FECD eyes.

Central corneal thickness (CCT) is a routinely available, quantitative parameter that reflects corneal hydration status and is commonly used in clinical decision making in FECD, because the central cornea thickens as edema develops. In FECD specifically, clinicians frequently incorporate CCT into perioperative assessment; however, isolated CCT values have limitations because normal corneas can occasionally be thick and because "pre-edematous" baseline thickness varies across individuals. As a result, thresholds (e.g., around 640 µm) have been proposed as practical indicators of clinically relevant edema in FECD, but the overlap between normal variation and early/subclinical disease underscores the need to interpret CCT in context and - when possible - relative to baseline.

In the postoperative setting, transient corneal swelling (reflected by increased CCT) is a well-recognized phenomenon after phacoemulsification, and it is mechanistically linked to surgical endothelial stress. Studies evaluating postoperative corneal swelling after phacoemulsification show that CCT can increase early after surgery and then trend back toward baseline in uncomplicated cases, whereas persistent edema is more likely when endothelial reserve is compromised. Moreover, postoperative corneal swelling has been shown to correlate with endothelial cell loss after phacoemulsification, supporting the use of CCT as a clinically meaningful, non-invasive outcome reflecting endothelial "load" in the early postoperative period.

From a methodological perspective, comparing postoperative CCT between FECD and non-FECD eyes requires careful handling of baseline variability, because corneal thickness differs substantially between individuals and baseline imbalance can bias or obscure group differences if not appropriately addressed. In controlled clinical studies with baseline and follow-up measurements, inclusion of the baseline value as a covariate in an analysis of covariance (ANCOVA) framework is widely recommended because it conditions the comparison on baseline, improves precision, and avoids the bias that can arise with alternative approaches (e.g., analysing change scores without proper adjustment), particularly when baseline and follow-up are correlated. This is directly aligned with the statistical objective of estimating the group effect on postoperative CCT while accounting for preoperative thickness heterogeneity.

Against this background, the present study is designed as a prospective, controlled, non-interventional observational clinical investigation to quantify early postoperative CCT outcomes after routine phacoemulsification in FECD compared with non-FECD controls. The primary objective is to compare CCT at 6 weeks postoperatively between groups while adjusting for baseline preoperative CCT using ANCOVA, thereby providing an interpretable, baseline-conditioned estimate of the association between FECD status and postoperative corneal thickness under real-world clinical conditions. Secondary objectives include characterizing the magnitude of postoperative CCT change relative to baseline and exploring whether baseline corneal/lens characteristics (including FECD severity graded by commonly used clinical grading frameworks) are associated with postoperative CCT trajectories. By relying exclusively on standard-of-care perioperative assessments, the study aims to generate clinically applicable evidence to support perioperative risk stratification and patient counselling in FECD patients undergoing cataract surgery.