Understanding Eye Axes: A New Method for Optic Axis Determination
Authors: Lopes, B.T., Eliasy, A., Elhalwagy, M., Vinciguerra, R., Bao, F., Vinciguerra, P., Ambrósio, R., Elsheikh, A., and Abass, A.
Journal: Photonics, Vol. 8, No. 2, p. 61
Publication Date: Feb 2021
Three-dimensional positions of the visual, pupillary, and optical axes with the corresponding alpha (α) and kappa (κ) angles in the right eye of an Italian participant. N, T, S, and I stand for the nasal, temporal, superior, and inferior sides of the cornea, respectively.
Summary:
Our eyes are fascinating and complex organs that help us navigate and understand the world around us. However, there is still much to learn about how our eyes function and how they differ among individuals. Our study introduces a new method for identifying the main axes of the eye and explores differences in these axes among Italian, Brazilian, and Chinese populations.
In our research, we focused on three primary axes of the eye: the optical axis, the pupillary axis, and the visual axis. The optical axis is the path light takes when it passes through the eye without being refracted. The pupillary axis is the line that passes through the center of the pupil and is perpendicular to the corneal surface. The visual axis, which is closely approximated by the coaxially sighted corneal light reflex, is the line that connects the fixation point, nodal points, and the fovea of the eye.
Understanding these axes is essential for diagnosing certain eye conditions and improving the outcomes of eye surgeries, such as laser refractive surgery and intraocular lens (IOL) implantation. However, determining these axes can be challenging due to the lack of suitable landmarks.
We developed a method to identify the eye's main axes using topographical elevation data from Scheimpflug-based systems. We validated this method in a large clinical cohort, and we recorded ethnic differences among 1992 normal eyes of 966 healthy participants in Italy, Brazil, and China.
We found that the average values of the kappa angle (the angle between the visual and pupillary axes) and alpha angle (the angle between the visual and optical axes) differed among the three populations. The Chinese population had the lowest values, followed by the Brazilian and Italian populations. These differences might be due to differences in ethnic background or age distribution among the populations.
Our study provides valuable information that can help clinicians improve preoperative screening and better understand the variations in eye axes among different populations. This knowledge can lead to more accurate diagnoses and better surgical outcomes for patients.