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Valeria Nuzzo, Fatima Alahyane, Karsten Plamann; A laboratory study on the rainbow glare effect after femtosecond laser corneal surgery. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4881.
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© ARVO (1962-2015); The Authors (2016-present)
The rainbow glare effect is reported increasingly often as a side effect of femtosecond (fs) laser corneal surgery. It consists in the appearance of faint coloured images superposed on normal vision. It is likely linked to light diffraction due to regular patterns at the interface of the incision. Our goal was to reproduce the effect in a laboratory setting and identify strategies of its suppression.
Lamellar incisions were performed in pig cornea and glass slides with a fs laser. The transmitted light from three red, bleu and green lasers was viewed on a screen. Corneas were excised from fresh enucleated pig globes, stored in 10% Dextran in Hank’s solution before laser cutting and mounted between two coverslips. Experimental conditions for lamellar incisions were: surface 5mm2, depth 200µm, energy density slightly higher than the threshold (1-2J/cm2), focussing numerical aperture (NA) 0.3 and 0.45; Laser: 1.03µm wavelength, 730fs pulse duration, 10kHz repetition rate; Raster scan: 3µm and 5µm spot separation. Parameters of our experiments were similar to those of clinical practice. After cutting, the sample was irradiated by three collimated superposed continuous lasers of wavelengths 457nm, 532nm, 633nm. Images of the transmitted light viewed on a screen were captured by a camera and post-processed using ImageJ and MATLAB.
When irradiated by the red-green-blue lasers at the positions of the lamellar incisions, corneas (n=3 per set of parameters) showed the formation of a diffraction pattern within the transmitted light. This was observed for raster scans performed at a energy density slightly higher than the threshold and at all combinations of spot separations (3µm or 5µm) and NAs (0.3 or 0.45). The angular separation between the orders of diffraction at the three wavelengths corresponds to the theoretical diffraction values. The diffracted light patterns of corneas and glass slides, incised with the same parameters, were superposed. No diffraction was obtained from non treated regions of the corneas. This phenomenon resembles the clinical rainbow glare effect previously reported.
Our laboratory study shows that the fs laser raster scanning of corneas created a diffraction grating in the tissue, regardless of the combination of spot separations and numerical apertures used. Different cutting strategies should be further investigated to prevent the rainbow glare formation.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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