Study of the Angle Lambda and Ocular Dominance

The angle lambda corresponds to the angle formed by the pupillary axis (line passing through the center of the pupil and perpendicular to the cornea) and the line of sight (broken line between the fixation point and the fovea and passing through the center of the pupil entrance). The angle kappa corresponds to the angle between the visual axis (line between the point of fixation and the fovea: area of the retina allowing precise vision) and the pupillary axis.

The angle lambda and the angle kappa are very close, which is why the lambda angle is often equated with the kappa angle, both in practice and in the literature.

The literature reports a non-null angle kappa ranged between 1.91° ± 0.14° and 5.73° ± 0.10° in the general population. Also, studies have reported a significantly greater angle on the left eye compared to the right eye. Moreover - because of the interpupillary difference - each eye perceives the same image from a different angle, resulting in a fixation disparity, defined as the angle of the residual deviation of the visual axes when the subject fixes and binocularly merges an image. In some cases, too high a value of the disparity can lead to a fixation disorder requiring orthoptic treatment.

Anatomical ophthalmological connections and their dynamics are still debated in the scientific community. However, their considering is essential in many surgeries (strabismus, cataract, refractive...) or in clinical practice.

The correlation between these biometric values would make it possible to refine the knowledge related to these landmarks and thus offer better ophthalmological management by integrating these variables into the clinical examination.

The aim of the study is to analyze the correlation between the angle lambda and the ocular dominance depth and the fixation disparity in a healthy population without ophthalmologic disorder.

Then, seconds goals were defined as the study of the relation between the value of the angle lambda and the fixation disparity quantified with the Rousseau test.

Relation between ocular dominance measured with the Guillon's test and the Hole-in-car test will also studied.

Inclusion criteria

• Informed major subject not opposing to their participation in the study

Exclusion criteria

• Subject with strabismus or organic ophthalmologic pathology
• Or presenting a visual acuity lower than 10/10th
• Or with a history of eye surgery