R B Mandell1. 1. School of Optometry, University of California, Berkeley 94720-2020, USA.
Abstract
BACKGROUND: The corneal sighting center is defined by the intersection of the line of sight with the anterior corneal surface and is usually found by measuring angle lambda, between the pupillary axis and the line of sight. It is to be determined if a measurement of the pupil offset in the corneal map of videokeratography might be used instead of angle lambda to provide a practical clinical method for finding the corneal sighting center. METHOD: Two-dimensional angle lambda measurements were made in a group of 17 young adult Caucasian subjects under natural pupil conditions, using an apparatus designed for this purpose, and were compared to measurements of the corneal sighting center position as located by videokeratography. RESULTS: The correlation between angle lambda as measured directly and the pupil offset as measured by videokeratography was 0.84, which is statistically and clinically significant. CONCLUSIONS: The position of the corneal sighting center may be found relative to the corneal reflex of a fixated light by using the distance and direction of the pupil offset in the corneal map of videokeratography, or indirectly by taking 0.6 times the same value and measuring in the opposite direction from the pupillary axis. The latter method does not require active fixation by the patient.
BACKGROUND: The corneal sighting center is defined by the intersection of the line of sight with the anterior corneal surface and is usually found by measuring angle lambda, between the pupillary axis and the line of sight. It is to be determined if a measurement of the pupil offset in the corneal map of videokeratography might be used instead of angle lambda to provide a practical clinical method for finding the corneal sighting center. METHOD: Two-dimensional angle lambda measurements were made in a group of 17 young adult Caucasian subjects under natural pupil conditions, using an apparatus designed for this purpose, and were compared to measurements of the corneal sighting center position as located by videokeratography. RESULTS: The correlation between angle lambda as measured directly and the pupil offset as measured by videokeratography was 0.84, which is statistically and clinically significant. CONCLUSIONS: The position of the corneal sighting center may be found relative to the corneal reflex of a fixated light by using the distance and direction of the pupil offset in the corneal map of videokeratography, or indirectly by taking 0.6 times the same value and measuring in the opposite direction from the pupillary axis. The latter method does not require active fixation by the patient.