Corneal Relaxing Incisions
Modern corneal relaxing incisions include the use of both astigmatic (or arcuate) keratotomies and limbal relaxing incisions (Fig 9-8). Both of these techniques employ partial-thickness arcuate incisions to reduce regular corneal astigmatism without altering the spherical equivalent power of the cornea. These incisions decrease the curvature of the incised steep meridian and increase the curvature of the meridian 90° away (a phenomenon known as coupling).
Although they were previously studied as a technique for correcting several diopters of astigmatism, corneal relaxing incisions are now most commonly used for treating lower amounts of astigmatism, and toric IOLs are used instead for treating higher amounts of astigmatism.
Figure 9-8 Corneal relaxing incisions. A, Limbal relaxing incision. B, Anterior penetrating astigmatic keratotomy. C, Intrastromal astigmatic keratotomy.
(Illustration courtesy of Mark Miller.)
Astigmatic (arcuate) keratotomy
Astigmatic (or arcuate) keratotomies (AKs) can be single or paired. They are placed centered on the steep meridian of the cornea, typically in the 7–10 mm optical zone. If they are placed too close to the visual axis, glare and irregular astigmatism can be problematic.
AKs can be performed with a diamond blade or with a femtosecond laser platform. Femtosecond lasers can create AKs of a specified arc length, optical zone, and depth. Laser-created AKs that are placed to penetrate anteriorly can be manually opened later, if necessary, to “titrate” the astigmatic effect. Alternatively, the laser can also create intrastromal AKs (ie, AKs that do not penetrate the epithelial surface). Nomograms for both intrastromal and anterior-penetrating AKs have been created; existing nomograms have also been modified for use with the femtosecond laser.
Day AC, Lau NM, Stevens JD. Nonpenetrating femtosecond laser intrastromal astigmatic keratotomy in eyes having cataract surgery. J Cataract Refract Surg. 2016;42(1):102–109.
Roberts HW, Wagh VK, Sullivan DL, Archer TJ, O’Brart DPS. Refractive outcomes after limbal relaxing incisions or femtosecond laser arcuate keratotomy to manage corneal astigmatism at the time of cataract surgery. J Cataract Refract Surg. 2018;44(8):955–963.
Limbal relaxing incisions
Limbal relaxing incisions (LRIs) can be single or paired and are placed in the peripheral cornea near the limbus. LRIs are more peripheral than AKs, reducing the risk of glare or irregular astigmatism. However, their peripheral location also means that LRIs need to be longer than AKs for the same astigmatic effect.
These incisions are often performed with a diamond blade. Some surgeons place the cataract incision within 1 of the paired LRIs; others prefer to use a separate location. LRIs may also be done postoperatively in an office setting. Various LRI nomograms have been published (Tables 9-3 and 9-4 offer 2 examples), and some are available online (eg, www.lricalculator.com/).
Table 9-3 Donnenfeld LRI Nomogram
Table 9-4 Nichamin Age- and Pachymetry-Adjusted LRI Nomogram
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.