Relationship between Choroidal Thickness and Anterior Scleral Thickness in Patients with Keratoconus

Purpose: To evaluate the relationship between choroidal thickness (CT) and anterior scleralthickness (AST) in patients with subclinical keratoconus (SKC) and established keratoconus (KC). Methods: This single-center prospective case-control study included 97 eyes of 97 patients: 44 KCeyes, 14 SKC eyes, and 39 age- and axial length (AL)-matched healthy eyes. Using swept-sourceoptical coherence tomography, the AST was manually measured in four directions and the CT wasobtained automatically from the Early Treatment Diabetic Retinopathy Study (ETDRS) grid. Principal component analysis (PCA) was used to linearly reduce the dimensionality of nine CT inputs to onesignificant component, CT1. A multivariate model was created to evaluate the association betweenCT1, AST, and several ocular parameters in SKC and KC patients. Partial correlation was thenperformed to adjust the confounding factors and to examine the effect of AST on CT1. Results:The PCA showed that CT1 accounts for 86.54% of the total variance in the nine original CTs of theETDRS grid. The CT1 model was associated with age, AL, and AST in the superior meridian in SKCeyes, whereas in KC eyes, it was correlated with gender, age, AL, and AST in the inferior meridian(p < 0.001). The partial correlation between CT1 and AST in the superior zone was found to besignificant, positive, and strong in SKC eyes (r = 0.79, p = 0.019), whereas a significant, positive, andmoderate correlation between CT1 and AST at the inferior zone (r = 0.41, p = 0.017) was observed inKC eyes. Conclusions: Choroidal tissue was significantly correlated with the anterior sclera acrossthe vertical meridian. This relationship was observed over the superior sclera in SKC eyes, whereasin established KC, it was over the inferior sclera. These results reveal new insights regarding theinteractions between the anterior and posterior structures of the KC eyes and confirm the enigma ofthe pathophysiology of KC.