Line of sight
Line of sight: 'line of sight': line connecting the point with the center of the pupil. It cuts the anterior surface of the cornea to the point called "corneal sighting center." This point is not easily identifiable in clinical practice, unlike the vertex (corneal reflection - image of Purkinje number 1). The vertex is usually located in nasal of "corneal sighting center." The line of sight (line of sight) can be equated to the main Ray ("chief ray") of a beam of incident rays emitted from a point light source.
The eye represented in schematic Cup is a look right, cut horizontally. The upper part of the globe is removed (the eye is seen from above). The cornea, the pupil and the lens are not aligned on a common axis; F is the target set point which the image is formed on the fovea. Point E is located at the center of the entrance pupil (Pe), which is the image formed by the IRIS pupil cornea. The FE segment is the central Ray ("chief ray") of the bunch of rays which contributes to the formation of the Foveal image. The line that connects the attachment point to the center of the IRIS pupil is defined as the line of sight (line of sight). The reflection of F which is formed on the cornea is the vertex, when F is the center of the mires of Placido disc (corneal topography). This axis contains the local center of curvature of the cornea (C). The pupillary axis (in green) corresponds to the normal (perpendicular) to the surface corneal and passing right through the center of the pupil. The pupillary axis angle with the line of sight angle kappa, and with the Visual axis the lambda. In practice, the proximity of the Visual axis to the line of sight allows to consider these angles as equivalent.