The halo effect is an optical phenomenon in which the patient perceives rings of light, halos or glows around light sources, particularly in low-light conditions or at night, when the pupil dilates. This phenomenon is associated with the scattering and diffraction of light passing through the eye’s optical system, most commonly at the boundaries between different optical zones or at sites of optical inhomogeneity within the eye’s refractive elements. In a healthy eye, the halo effect may occur physiologically when the pupils are dilated; however, it becomes clinically significant when the intensity or extent of the symptom significantly affects the patient’s visual comfort and quality of life, particularly when driving at night. The most common causes of iatrogenic halo effect include corneal refractive procedures (LASIK, PRK), where the phenomenon results from the difference in refractive power between the ablated optical zone and the untreated corneal periphery, as well as from the presence of higher-order optical aberrations arising after the procedure.
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