Custom or Multifocal Ablations
An excimer laser may be used to create a multifocal cornea. Prompted by the observation that, following excimer ablation, the uncorrected near vision of many patients improved more than expected (Fig 9-8), ophthalmologists began to investigate the potential for improving near vision without significantly compromising distance vision. To this end, the following ablation patterns have been employed:
a small, central steep zone ablation, in which the central portion of the cornea is used for near vision and the midperiphery is used for distance vision
an inferior near-zone ablation
an inferiorly decentered hyperopic ablation
a central distance ablation with an intermediate/near midperipheral ablation
Some of these patterns generate simultaneous near and distance images, whereas others rely on pupillary constriction (accommodative convergence) to concentrate light rays through the steeper central ablation.
Although the excimer laser offers some potential advantages, the results of multifocal corneal ablations are still under investigation.
Alarcón A, Anera RG, del Barco LJ, Jiménez JR. Designing multifocal corneal models to correct presbyopia by laser ablation. J Biomed Opt. 2012;17(1):018001. doi:10.1117/1. JBO.17.1.018001.
Pallikaris IG, Panagopoulou SI. PresbyLASIK approach for the correction of presbyopia. Curr Opin Ophthalmol. 2015;26(4):265–272.
Figure 9-8 Multifocal ablation. Corneal topographic map showing a multifocal pattern after hyperopic laser in situ keratomileusis in a 62-year-old patient with preoperative hyperopia of +4.00 diopters (D). Postoperatively, the uncorrected distance visual acuity at distance is 20/25−2 and at near is Jaeger score J1. Manifest refraction of –0.25 + 0.75 D × 20 yields visual acuity of 20/20. Corneal topography demonstrates central hyperopic ablation (green) with relative steepening in the lower portion of the pupillary axis (orange), which provides the near add for reading vision.
(Courtesy of Jayne S. Weiss, MD.)
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.