Spectral sensitivity of the pupillary system

Area of Science:

• Ophthalmology
• Visual Neuroscience
• Photobiology

Background:

• Pupillary response to blue light is reportedly higher than visual system sensitivity (V(λ)) for a two-degree field.
• This suggests potential rod input to the pupil even at photopic light levels.
• Alternatively, smaller pupil size for blue light may stem from using the CIE V(λ) function, based on a two-degree field, in large-field studies.

Purpose of the Study:

• To investigate the spectral sensitivity of the pupillary mechanism.
• To determine if the enhanced blue light sensitivity of the pupil is an artifact of measurement.
• To clarify the relationship between pupil size, luminance, and wavelength under different adapting field sizes.

Main Methods:

• Static pupil size was measured using an entoptic method.
• The eye was adapted to a large 'Ganzfeld' field across various wavelengths (624-429 nm).
• Luminances ranged from mesopic to photopic levels.

Main Results:

• Pupil size decreased with shorter wavelengths at equal luminance.
• This wavelength-dependent effect vanished at photopic levels when using the V(10 degrees) (λ) function, but persisted at mesopic levels.
• Pupil size was independent of wavelength when plotted against equivalent luminance for a 10-degree field (V(10 degrees)(λ, Leq)).

Conclusions:

• The apparent enhanced pupil sensitivity to blue light at photopic levels is an artifact of using the V(2 degrees)(λ) function with large adapting fields.
• Pupil size is a linear function of log equivalent luminance for large fields across mesopic and photopic ranges.
• Pupil size is independent of wavelength for the entire range of adapting luminances tested.