Kappa Angle Measurement — Complete User Guide

What is Kappa Angle?

Kappa angle is the angle between the visual axis and the pupillary axis. The visual axis connects the fixation point to the fovea; the pupillary axis is perpendicular to the cornea through the pupil center.

Kappa Angle vs Angle Lambda

• Kappa angle: Angle between visual axis and pupillary axis
• Angle lambda: Angle between visual axis and corneal reflex axis (light reflex from cornea center)
• Clinically, the difference is usually small and the terms are often used interchangeably

Clinical Significance

In Refractive Surgery

Large kappa angle patients may experience:

• Decentered ablation if not properly centered on the visual axis
• Postoperative night vision disturbances, halos
• Worse outcomes with small optical zone ablation

In Cataract Surgery

For large kappa angle patients:

• Consider using offset or pupil-centered IOL calculations
• Better to avoid multifocal IOLs
• Preoperative kappa angle measurement helps surgical planning

Measurement Methods

• Purkinje image measurement
• Corneal topography with angle lambda function
• swept-source OCT

References

• Chakrabarti T. Kappa and angle lambda . Indian J Ophthalmol. 2017.
• Packer M. Effect of kappa on visual outcomes. J Cataract Refract Surg. 2018.