Original article
Laser In Situ Keratomileusis Disrupts the Aberration Compensation Mechanism of the Human Eye

https://doi.org/10.1016/j.ajo.2008.09.027Get rights and content

Purpose

To study how changes induced on corneal optics by myopic and hyperopic laser in situ keratomileusis (LASIK) refractive surgery affect the aberration compensation mechanism.

Design

Interventional case series and modeling theory.

Methods

We measured ocular, corneal, and internal aberrations for a 6-mm pupil in 15 myopic and 6 hyperopic eyes with similar age range before and 6 months after standard LASIK. Ocular aberrations were measured using our own developed Hartmann-Shack wavefront sensor, whereas corneal aberrations were calculated by using the elevation data obtained by corneal topography. Ocular, corneal, and internal root mean square (RMS), spherical aberration (SA), coma, and compensation factor were compared for each patient.

Results

After myopic LASIK, we obtained an average 1.6-fold increase in ocular RMS, mainly positive SA, and coma, associated with a similar increase in corneal aberrations. In the hyperopes, we found a higher (2.3-fold) induction of ocular aberrations after surgery, mainly negative SA and coma, but without net increases of corneal aberrations. Aberration compensation clearly decreased or even inverted after hyperopic LASIK, decreasing the ocular optical quality in a higher level than myopic LASIK.

Conclusions

Although ocular aberrations after myopic LASIK usually were smaller than corneal aberrations because of partial compensation of SA, after hyperopic LASIK, because of induction of negative SA and change in coma, disruption of the compensation mechanism lead to a larger increase of ocular aberrations. Customized procedures should maintain the natural compensation to achieve improved visual outcomes.

Section snippets

Subjects

Ocular, corneal, and internal aberrations were measured before and 6 months after standard LASIK. Surgical procedures were performed using a VISX S2 (AMO, Santa Ana, California, USA) excimer laser platform at “Clinica Ircovisión” (Cartagena, Murcia, Spain). The measured population included 21 eyes (n = 11 subjects) classified according to their preoperative refractive error: 1 group including myopic eyes (n = 15 eyes; mean age ± standard deviation [SD], 28.0 ± 3.6 years; mean sphere, −4.08 ±

Results

Figure 2 shows average ocular, corneal, and internal aberrations for a 6-mm pupil for the groups of myopic and hyperopic eyes. Before surgery, hyperopic eyes had more corneal and internal aberrations than myopes, mainly because of a higher coma for each component (cornea and lens). However, the overall ocular aberrations were similar to myopes because of the previously described coupling of corneal and internal SA and coma in young hyperopes. This scenario clearly was modified by the surgery:

Discussion

We estimated the corneal aberrations by considering a simplified cornea with one single surface, the measured corneal anterior surface, and by using an effective refractive index for corneal aberration calculations. By doing so, we did not completely consider the effect of the corneal posterior surface. This is probably a minor issue in normal eyes, but this may not be the case after LASIK. The behavior of the corneal posterior surface after LASIK and it role in the increment of aberrations has

Antonio Benito, after finishing his degree in Optics and Optometry, joined the Pablo Artal's “Laboratorio de Óptica de la Universidad de Murcia”, Murcia, Spain in 1998. He has recently completed an MSc course at the Department of Physics at the Universidad de Murcia, Spain. His research interests have been focused on aberrations of the human eye, especially on ocular aberration compensation mechanism and optical effects of laser in situ keratomileusis on the aberrations of the eye and it

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