Paris—Undersurface ablation of the LASIK flap appears to be an effective method for resolving rainbow glare after femto-LASIK surgery, according to Damien Gatinel, MD.
In 2015, Dr. Gatinel and colleagues published their first experience using this technique to correct rainbow glare [J Refract Surg. 2015;31(6):406-410]. The patient was a 33-year-old woman who complained of rainbow glare in her right eye and also had about -0.75 D of residual myopic astigmatism. A single refractive ablation of the flap undersurface successfully corrected both the residual astigmatism and the rainbow glare.
More refractive: What a novel scleral implant may mean for presbyopia
Subsequently, Dr. Gatinel has performed the procedure in several other patients and found it to be consistently safe and effective, resulting in immediate resolution of the symptoms without any adverse events, including no changes in uncorrected vision in patients who already had a good refractive and functional outcome after LASIK.
“Rainbow glare is a rare optical side effect of femto-LASIK that usually occurs unilaterally, or at least is much more prominent in one eye, and is usually transient, disappearing within a few weeks or months,” said Dr. Gatinel, assistant professor of ophthalmology, and head, anterior segment and refractive surgery department, Rothschild Ophthalmology Foundation, Paris. “Occasionally, however, the visual symptoms are persistent and very disturbing to patients.
“Rainbow glare is thought to occur secondary to light diffracted from the grating pattern created on the backside of the LASIK flap by the femtosecond laser,” he said. “The therapeutic strategy of ablating the undersurface of the LASIK flap is successful because it targets and eliminates the source of the unwanted diffraction.”
Rainbow glare, so-called because patients describe seeing a spectrum of colored bands in a rainbow pattern, usually occurs in dark environments when the individual is looking at pinpoint sources of light. Consequently, patients may avoid nighttime driving or even going out in the dark. In addition to seeing the rainbow pattern of light, patients may experience some blurring of vision.
Documentation of a visible raster pattern at the flap-stromal interface supports the hypothesis that rainbow glare arises from diffraction of light by these spots.
“Confocal microscopy imaging in patients with rainbow glare reveals multiple rows of hyper-reflective spots located at about 125 μm below the anterior corneal surface and spaced at horizontal and vertical distances matching the spot and line distances programmed into the laser,” Dr. Gatinel said.
“It is reasonable to assume that these hyper-reflective spots are located at the back surface of the LASIK flap, where no ablation was delivered, rather than on the stromal bed where any raster pattern would have been erased by the excimer laser ablation for refractive correction. Thus, it seems logical that ablating the undersurface of the LASIK flap to erase the evenly spaced singularities created by the laser spots could be an effective solution for patients bothered by disabling rainbow glare.”
Simulations recorded through a calibration plate provide further support for the hypothesis about the cause of rainbow glare and also help clinicians to understand the exact nature of the complaints of affected patients, Dr. Gatinel said.
To perform the ablation, the center of the pupil is marked with an ink dot, and then the flap is lifted and everted on a special spatula. With the eye tracker deactivated, a phototherapeutic keratectomy correction with a 6-mm optical zone is delivered on the back side of the flap and centered on the ink mark.
“Based on my experience in the limited number of eyes treated so far, I believe the depth of the ablation must exceed 15 μm in order to successfully erase the raster pattern,” Dr. Gatinel said.