The study was done to analyze a case of unilateral rainbow glare that required repeated undersurface photoablation using an excimer laser.

A 31-year-old man with bilateral myopia of 6.50 diopters treated with femtosecond laser–assisted in situ keratomileusis immediately experienced a 2-year life-incapacitating rainbow glare exclusively in the right eye. The laser settings were similar for both eyes, but a subtle raster pattern was noticed intraoperatively in the right eye. Postoperative uncorrected distance visual acuity (UDVA) was 20/12.5, but with important subjective visual quality impairment in the right eye.

A 10-µm undersurface photoablation was performed with immediate but incomplete improvement of both subjective symptoms and objective reduction of the grating pattern on confocal microscopy. After 12 months, the patient asked for additional treatment and another 10-µm undersurface photoablation was performed, this time with resolution of the symptoms. At last follow-up, 6 months after the second revision, UDVA was maintained with total absence of rainbow glare and no hypermetropic shift was observed.

The study concluded that the rainbow glare is typically a benign and often spontaneously resolving condition that can rarely cause dramatic life impairment. This case reinforces the hypothesis that it is caused by diffraction created by the raster spot pattern of the femtosecond laser, which can be followed by confocal microscopy. It also further proves that undersur-face photoablation is an efficient, repeatable, and safe treatment for rainbow glare, and should include a thickness of at least 16 to 20 µm.