Measuring directionality of the retinal reflection with a Shack-Hartmann wavefront sensor

Area of Science:

• Ophthalmic optics
• Retinal physiology
• Wavefront sensing technology

Background:

• The Stiles-Crawford effect (SCE) describes the retina's directional sensitivity, stemming from photoreceptor waveguide properties.
• Traditional SCE studies require specialized optical instruments.
• Shack-Hartmann wavefront sensors (SHWS) are standard clinical tools for measuring ocular aberrations.

Purpose of the Study:

• To explore a novel approach for measuring the optical Stiles-Crawford effect using a Shack-Hartmann wavefront sensor.
• To assess the sensitivity of SHWS for detecting the SCE, particularly at near-infrared wavelengths.
• To investigate the implications of the SCE's sensitivity on SHWS-based ocular aberration measurements.

Main Methods:

• A modified research-grade Shack-Hartmann wavefront sensor was utilized.
• Intensity information was extracted from SHWS measurements in five healthy subjects.
• Measurements were conducted at four retinal eccentricities.

Main Results:

• Intensity distribution from SHWS measurements correlated with the optical Stiles-Crawford effect.
• The technique demonstrated sensitivity to the optical SCE even at faint near-infrared wavelengths.
• The optical SCE signal localized to the SHWS spot cores, with diffuse, non-directional tails, suggesting limited light recapture by cones after scattering.

Conclusions:

• A Shack-Hartmann wavefront sensor can effectively measure the optical Stiles-Crawford effect.
• The high sensitivity of SHWS to the SCE may influence the accuracy of ocular aberration measurements.
• Further research is needed to understand how the intrinsic SCE affects SHWS-based aberration analysis.