Abstract
Purpose::
To demonstrate the feasibility of using excimer laser ablations to directly produce higher order aberration (HOA) patterns on the surface of soft contact lenses.
Methods::
A laser ablation algorithm was developed to calculate the laser pulse distribution to create an arbitrary pattern of the HOA. Convolution theory was used to minimize both the residual RMS error and surface roughness in determining laser ablation parameters such as beam size, ablation rate and transition zone. With this algorithm, an ArF2 pulse laser (Xantos S-200 ArF, Coherent) was used to ablate the back surface of soft contact lenses. The laser spot diameter was 500 µm and the fluence was 0.2 mJ which produced an estimated ablation depth per pulse of 0.05 µm on hydrated soft contact lens material. A two axis steering mirror was used to scan laser spots onto designed locations on the surface. The aberrations of the soft contact lenses immersed in saline solution before and after the ablation were measured with a Shack-Hartmann wavefront sensor to evaluate the accuracy of generating the HOA.
Results::
Theoretical calculation with the laser ablation algorithm indicated that a proper transition zone (extrapolated from the ablation profile of the optical zone) of at least half of the laser spot diameter can significantly reduce residual ablation error along the edge of the optical zone. The calculations for different amounts of overlapping spots also showed the tradeoffs between the amplitudes of the residual error and surface roughness. In our experiment of ablating the back surface of soft contact lenses, we created different individual Zernike aberrations, coma, trefoil and spherical aberration with 1 µm RMS. The measured RMS values of the ablated soft contact lenses for coma, trefoil and spherical aberration were 1.02 µm, 0.85 µm and 0.97 µm, respectively. The residual higher order RMS wavefront errors of these samples were 0.26 µm, 0.31µm, and 0.24 µm, respectively.
Conclusions::
We successfully demonstrated the feasibility of using excimer laser to produce the HOA on the surface of soft contact lenses. Back surface customized soft contact lens can have the potential to significantly reduce the ocular HOA and to improve the stability of lens position after blinking which provides stable correction of vision especially in eyes with abnormal corneal conditions.
Keywords: keratoconus • optical properties