A majority of the correlation between corneal tilt and corneal densitometry is based on an association with a patient’s age, according to research published in Ophthalmic and Physiological Optics. However, a small correlation between the variables operates directly, according to the report.
Researchers enrolled 86 healthy participants (mean age 42.8±20.0 years, 66% women, 100% White) in the prospective study. The team performed comprehensive eye exams and Scheimpflug tomography, and exported corneal elevation maps to calculate corneal tilt. They considered the axis of the Pentacam Scheimpflug camera as the visual axis. The investigators used a ray tracing algorithm to determine the corneal axis, which involved directing simulated parallel light rays toward the cornea and refracting them through anterior and posterior surfaces. The team applied a simple mediation analysis to study age due to its known role as a confounding factor in the correlation between corneal tilt and densitometry. The primary objective was to determine whether corneal tilt affects Pentacam densitometry readings under natural fixation.
The researchers determined that corneal tilt and corneal densitometry are associated after considering them as independent variables (r=0.45; P <.001). However, the team noted that age is associated with both densitometry (r=0.91; P <.001) and corneal tilt (r=0.50; P <.001) and considering corneal tilt and densitometry as independent variables would not be practical.
A simple mediation analysis of 2 separate cases revealed that a minority of the correlation between tilt and densitometry operates directly (case 1: 3.8%, case 2: 8.6%) while the remaining correlation is age-dependent. According to the report, these findings highlight a strong direct effect between age and corneal densitometry.
“Corneal tilt plays a role in corneal densitometry readings, even though that interaction is strongly influenced by age,” according to the researchers. “Age is a major confounding factor in corneal densitometry readings that should be taken into consideration when considering a corneal analysis in a given patient.”
Study limitations include failure to perform densitometry on eyes fixating at different angles and a disproportionate representation of individuals of White ethnicity.
Consejo A, Jiménez-García M, Rozema JJ, Abass A. Influence of eye tilt on corneal densitometry. Ophthalmic Physiol Opt. Published online June 16, 2022. doi:10.1111/opo.13020