After undergoing surface ablation or LASIK, some patients report symptoms related to optical aberrations, including glare, ghost images, and halos. These symptoms are most prevalent after treatment with smaller ablation zones (<6.0 mm in diameter), after attempted higher spherical and cylindrical correction, and in patients with symptoms prior to refractive surgery. These vision problems seem to be exacerbated in dim-light conditions when mydriasis occurs. Wavefront mapping can reveal higher-order aberrations associated with these subjective concerns. In general, a larger, more uniform, and well-centered optical zone provides a better quality of vision, especially at night.
Night-vision concerns are often the result of spherical aberration, although other higher-order aberrations also contribute. The cornea and lens have inherent spherical aberration. In addition, excimer laser ablation increases positive spherical aberration in the midperipheral cornea. Wavefront-guided and optimized corneal treatment patterns are designed to reduce existing aberrations and to help prevent the creation of new aberrations, with the goal of achieving a better quality of vision after laser ablation.
Although the excimer laser photoablation causes most of the post-LASIK changes in lower- and higher-order aberrations, several studies have demonstrated that the creation of the flap itself can also result in aberrations (Fig 6-1). Some studies have demonstrated that femtosecond lasers cause little or no change in higher-order aberrations, in contrast to mechanical microkeratomes. Pallikaris showed that LASIK flap creation alone, without lifting, caused no significant change in refractive error or visual acuity but did cause a significant increase in total higher-order wavefront aberrations.
Figure 6-1 Wavefront analysis depicting higher-order aberrations after laser in situ keratomileusis (LASIK), including coma and trefoil.
(Courtesy of Steven I. Rosenfeld, MD.)
Pallikaris IG, Kymionis GD, Panagopoulou SI, Siganos CS, Theodorakis MA, Pellikaris AI. Induced optical aberrations following formation of a laser in situ keratomileusis flap. J Cataract Refract Surg. 2002;28(10):1737–1741.
Tran DB, Sarayba MA, Bor Z, et al. Randomized prospective clinical study comparing induced aberrations with IntraLase and Hansatome flap creation in fellow eyes: potential impact on wavefront-guided laser in situ keratomileusis. J Cataract Refract Surg. 2005; 31(1):97–105.
Waheed S, Chalita MR, Xu M, Krueger RR. Flap-induced and laser-induced ocular aberrations in a two-step LASIK procedure. J Refract Surg. 2005;21(3):346–352.
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.