A patient presents with irregular astigmatism post-LASIK with complaint of 'starbursts' and halos at night. Topography shows central island pattern. The refractive mechanism causing the symptoms is:

• A Elevated corneal haze reducing contrast sensitivity
• B Multifocal cornea with simultaneously two different powers in the visual axis causing diplopia
• C Epithelial ingrowth under the flap distorting anterior corneal surface
• D Diffraction pattern from the ablation zone edge when pupil dilates beyond ablation zone diameter ✓

Explanation

Halos and starbursts after LASIK are typically caused by the pupil dilating beyond the optical ablation zone diameter in dim light. The peripheral untreated cornea has higher curvature (myopic) than the central ablated zone, creating a step-change in refraction at the ablation zone edge. When the pupil is large (mesopic/scotopic conditions), light passing through this peripheral zone is refracted differently, creating diffraction and interference patterns perceived as halos/starbursts. Modern LASIK protocols use larger ablation zones and transition zones to minimize this. Central islands cause additional irregular astigmatism.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.