Effective corneal refractive diameter as a function of the object tangent angle in visual space

Area of Science:

• Ophthalmology
• Optical Engineering
• Vision Science

Background:

• Current laser refractive surgery protocols often select an optical zone diameter equal to or slightly larger than the dark-adapted pupil.
• This practice aims to ensure adequate corneal surface for focusing light, but its efficacy for paracentral and peripheral vision is debated.

Purpose of the Study:

• To evaluate if the standard optical zone diameter in refractive surgery is sufficient for focusing light from paracentral and peripheral visual fields.
• To determine if the accepted method adequately covers the effective corneal refractive diameter (ECRD).

Main Methods:

• An optical model of the anterior segment was developed to calculate the ECRD.
• The model incorporated patient variables: anterior chamber depth (ACD), corneal curvature (K(c)), and apparent entrance pupil (EP) diameter.
• The model was expanded to analyze light rays from objects at various angular displacements from the line of sight (LOS), considering the cornea's prolate nature.

Main Results:

• The ECRD increased significantly with pupil diameter (PP) and object displacement angle (delta(ob)).
• Beyond a critical angle (delta(c)), the ECRD became an annulus, indicating light rays were not refracted through the physical pupil (PP).
• Corneal curvature (K(c)) had minimal influence on ECRD, while ACD affected delta(c).

Conclusions:

• The ECRD expands substantially for objects even slightly off the line of sight.
• Using an optical zone diameter based solely on the dark-adapted pupil may lead to reduced vision quality for paracentral and mid-peripheral objects.
• This suggests a need to reconsider optical zone sizing in laser refractive surgery to optimize visual field coverage.