Structural Iris Changes Across Various Stages Of Keratoconus In Comparison To Healthy Eyes Using Scheimpflug Photography

This retrospective study was conducted in a tertiary care University Hospital in Eskisehir. The study started in January 2025 and was completed in February 2025.

This retrospective cross-sectional study included keratoconic eyes (TKC 0–4) and healthy emmetropic controls (SE ±1 D). Patients with prior cross-linking, keratoplasty, or intraocular surgeries were excluded. Pentacam Scheimpflug imaging assessed iris curvature and flaccidity. The iris was divided into three regions: base, mid-iris, and pupil margin. Geometric properties, including curvature, arc length, and angle variations, were computed using custom Python scripts. Flaccidity was measured as the standard deviation of angular differences between successive tangent vectors. ANOVA was used for statistical analysis (p < 0.05).

Fifty healthy control eyes, 102 eyes with subclinical keratoconus (SKC), and keratoconic eyes categorized as TKC Grade 1 (n=46), Grade 2 (n=175), Grade 3 (n=144), and Grade 4 (n=34) were assessed. In the mid-iris region, curvature was highest in controls and progressively decreased with increasing keratoconus severity (p < 0.05 for comparisons between controls, SKC, and TKC Grade 1 versus advanced grades). Conversely, at the pupil margin, curvature was lowest in controls and increased with KC severity (p < 0.05 comparing TKC 4 to controls and SKC). Flaccidity was most pronounced at the pupil margin and increased with KC severity, while angular variations in the mid-iris decreased as severity advanced.

The increased curvature at the pupil margin may alter anterior chamber fluid dynamics in keratoconus creating a predisposition to pupil block, particularly after intraocular surgeries. In contrast, the straightening of the mid-iris likely reflects intrinsic changes in iris tissue properties. We speculate that altered corneal geometry may lead to subtle changes in aqueous humor dynamics and force redistribution in the anterior chamber, which in turn could affect the iris tissue by remodeling stromal collagen fibers and resulting in mechanical changes.