Optical modulation transfer and contrast sensitivity with decentered small pupils in the human eye

Area of Science:

• Ophthalmology
• Visual Neuroscience
• Optical Physics

Background:

• The Campbell effect describes reduced visual acuity when a small artificial pupil is decentered.
• Previous research attributed this effect to retinal or optical factors, with uncertainty regarding their relative contributions.

Purpose of the Study:

• To objectively measure retinal image quality and psychophysically assess visual performance with decentered pupils.
• To differentiate the roles of monochromatic aberrations and transverse chromatic aberration in the Campbell effect.

Main Methods:

• Objective measurements of optical transfer function (MTF) modulus using double-pass technique.
• Psychophysical contrast sensitivity function (CSF) measurements using green gratings on a monitor.
• Comparison of MTF and CSF under identical conditions with decentered pupils.

Main Results:

• Decentering the pupil caused a significant decrease in the optical transfer function (MTF), indicating a notable contribution from monochromatic aberrations.
• The decline in contrast sensitivity function (CSF) was substantially greater than the MTF decline, especially at higher spatial frequencies.
• This discrepancy was largely explained by transverse chromatic aberration, influenced by the stimulus bandwidth.

Conclusions:

• Both monochromatic aberrations and transverse chromatic aberration significantly contribute to the loss of visual sensitivity with a decentered pupil.
• Transverse chromatic aberration plays a crucial role, particularly at low and intermediate spatial frequencies.
• Understanding these optical aberrations is key to explaining the Campbell effect.