Laser-Assisted Cataract Surgery

Benefits and Barriers

Kathryn M. Hatch; Jonathan H. Talamo

Disclosures

Curr Opin Ophthalmol. 2014;25(1):54-61. 

In This Article

Benefits of the Femtosecond Laser

Current functions of FSLs produced for cataract surgery include precise circular capsulotomy formation, lens fragmentation, lens softening, anterior penetrating and intrastromal arcuate corneal incisions [limbal relaxing incisions (LRIs)] (Fig. 2), and multiplanar clear corneal incisions (CCIs) used to access the anterior chamber (Figs. 2 and 3). Some studies have found that CCIs created with FSLs (Fig. 3) are square and significantly more resistant to deformation and leakage with increased stability compared with manually created incisions.[9,10] Consequently, FSL CCIs have lower risk of hypotony, iris prolapse, and endophthalmitis, and may also reduce the risk of would slippage and induced astigmatism. Manual incisions may also offer more risk for descemet's tears and gaping of internal aspects of the wound at the point of anterior chamber entry. With image-guided FSL, the surgeon is able to specify the angles of incision into the cornea as well as its precise location in degrees. Being able to indicate precise location of the incision may be of benefit when treating astigmatism either in conjunction with LRIs or when used in isolation. LRI placement can be programmed reliably and precisely, and can be performed with either anterior penetrating or intrastromal incisions, based on the surgeon's preference. With a FSL, the angular orientation, arc length, and a uniform incision depth (as % of total corneal thickness-not possible with a blade) can be executed more reproducibly and with less dependence on the surgeon's skill. Given the potential that even small amounts of astigmatism could be treated reliably and predictably with the FSL, the FSL could become the standard of care for the treatment of low astigmatism, rendering manual LRIs obsolete. For higher degrees of astigmatism, toric IOLs will likely continue to represent the most reliable treatment modality [1].

Figure 2.

OR view of LRI and clear corneal incisions. LRI, limbal relaxing incision. Reproduced by courtesy of OptiMedica (Sunnyvale, California, USA).

Figure 3.

OCT image of CCI. CCI, clear corneal incision. Reproduced by courtesy of OptiMedica (Sunnyvale, California, USA).

The capsulotomy is known to be one of the most important, yet challenging, steps of the cataract operation. Size, shape, and centration are key determinants of the positioning and refractive outcomes. Small capsulotomies can result in fibrosis and hyperopic shift,[11] whereas large asymmetric capsulotomies can cause myopic shift as well as IOL tilt, rotation, decentration, and posterior capsular opacification. In order to ideally achieve the planned power calculation and avoid these issues, the capsulotomy should ideally be covering the optic by 0.5 mm for 360°[12–14] (Fig. 4). The effects of asymmetric, eccentric, too small or too large a capsulotomy can be even more profound in patients undergoing surgery with toric, multifocal, or accommodating IOLs.[15] The properties of the capsulotomy influence the effective lens position (ELP) and thus may be the greatest cause for a 'refractive surprise' after otherwise accurate IOL power calculations.[16,17] Manual capsulotomies are usually centered on the pupil, which can often dilate asymmetrically. With an FSL, the surgeon has now has the option to center the capsulotomy on the scanned capsule or on the pupil (with manual fine-adjustment capabilities as desired using an interactive graphic user interface) with the FSL. Figure 5 illustrates the scanned center in purple compared to the pupillary center based on the iris anatomy in yellow. In addition, FSL created capsulotomies are significantly more accurate and precise in size and shape (and are stronger) compared with those created manually[12,18,19] (Fig. 6). Not only could these attributes be of benefit to the resultant ELP and effective IOL power, but also could benefit patients with weak zonule conditions including pseudoexfoliation or posttrauma because of more even forces on the capsule during phacoemulsification. The capsule may be able to withstand more manipulation when its size, shape, and location are precisely created and placed.

Figure 4.

Image of capsulotomy covering optic evenly for 3608. Reproduced by courtesy of OptiMedica (Sunnyvale, California, USA).

Figure 5.

Catalys screen shot of scanned capsule centration (purple) versus pupil centration capsulotomy (yellow) Reproduced by courtesy of OptiMedica (Sunnyvale, California, USA).

Figure 6.

Capsulotomies; manual versus FSL. FSL, femtosecond laser. Reproduced by courtesy of OptiMedica (Sunnyvale, California, USA).

The other important functions of the FSL are lens fragmentation and softening. Lens pretreatment with these functions offers significant advantage compared with manual surgery. Fragmentation is performed by dividing the lens into quadrants (Fig. 7), sextants (Fig. 8), or octants, followed by softening the lens into cubes with preprogrammed grid patterns (Figs. 7 and 8). These grid patterns may or may not be customized, depending on the laser system, to match the density of the cataract. In general, phacoemulsification for dense cataracts can be difficult because of high energy settings required and the resulting effects of thermal and acoustic trauma to surrounding ocular tissues. Removing dense cataracts can often require longer than average surgical times, and because of the presence of scant epinuclear and cortical material, there is a potential increased risk of posterior capsular tears, vitreous loss, and retained lens material. Hydrodissection is often difficult in these cases and the laser can assist by creating a tissue plane with 'pseumodissection'. This avoids the need for aggressive hydrodissection for dense cataracts which carries high risk for capsular problems. Additionally, the use of high vacuum and flow settings is common, resulting in chamber instability potentially leading to complications during surgery. Significant postoperative inflammation, endothelial cell loss, and longer recovery times are all more common as a result. Additionally, laboratory and animal studies have shown that ultrasound power within the anterior chamber causes oxidative stress and cellular injury and production of free radicals, which can damage the corneal endothelium.[20,21]

Figure 7.

Grid and quadrant fragmentation pattern. Reproduced by courtesy of James Jones, MD, and the Oftalvis Group Alicante of Alicante, Spain.

Figure 8.

Sextant and grid pattern illustration. Reproduced by courtesy of James Jones, MD, and the Oftalvis Group Alicante of Alicante, Spain.

Fragmentation and softening by the FSL offer many advantages over manual surgery, as pretreatment may allow for reduced instrumentation, movement, and effective phacoemulsification time (EPT) during cataract removal, resulting in increased safety. Lower EPT also often means that less vacuum, fluid, and intraocular manipulation are needed during surgery, leading to improved clinical outcomes secondary to lower risk of injury to the capsule, iris, and corneal endothelium, reduced endothelial cell loss, postoperative inflammation, and corneal edema. Abell et al.[22] showed that FSL pretreatment resulted in significant reduction in EPT, including the possibility of 0 EPT. Additionally, a prospective case series comparing the cataracts with LOCS III grade 3.4 ± 0.9 undergoing LARCS to cataracts LOCS III grade 3.1 ± 0.9 by Conrad-Hengerer et al.[23] showed that lower EPT was observed in the FSL-assisted system eyes compared with standard surgery eye group. Adjusting the FSL grid patterns during nucleus softening may also have an effect on EPT. Conrad-Hengerer et al.[24] showed that use of the 350 μm grid softening with the FSL led to lower EPT compared with the 500 μm grid. These data suggest there could be significantly increased safety and efficiency of the cataract removal with the use of FSL.

Another benefit is the user-friendly nature of the FSL for the surgeon. Feedback from patients thus far in our practice suggests that being docked under the FSL using a liquid immersion interface[8] is extremely comfortable. As a result, we are able to use lesser amounts of sedation with the laser patients. All patients are treated with topical anesthesia and many receive only a small dose of oral benzodiazepine for the entire procedure. This could be a significant advantage and may reduce the perioperative risks associated with anesthesia.

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