Fluctuations in angle lambda with the pupil diameter and correlations with biometric values in a healthy population

Area of Science:

• Ophthalmology
• Optometry
• Biomedical Optics

Background:

• Angle lambda (λ) is the angle between the line of sight and pupillary axis at the entrance pupil.
• Previous methods for measuring angle λ were adapted for daily practice.
• Angle λ is known to fluctuate with age and refractive error.

Purpose of the Study:

• To investigate correlations between angle lambda (λ) and biometric values.
• To analyze the effects of pupil dilation and entrance pupil location on angle λ.
• To test the hypothesis that angle λ varies with luminance levels due to changes in pupil diameter.

Main Methods:

• Angle λ was measured under photopic and scotopic luminance conditions in 70 participants.
• Axial length, anterior chamber depth, chord μ, and optic disc to fovea distance (OFD) were measured.
• Pupil centre offset was quantified using digital analysis.

Main Results:

• Mean photopic angle λ was +2.81° and scotopic angle λ was +3.30°.
• Negative correlations were found between angle λ and axial length, anterior chamber depth, and OFD.
• Positive correlations were found between angle λ and spherical equivalent or chord μ. Pupil offset was negatively correlated with angle λ.

Conclusions:

• Angle λ is confirmed to be correlated with biometric values.
• Variations in pupil diameter due to luminance levels induce changes in angle λ.
• A single subject exhibits multiple angle λ values depending on the luminance condition.