September 2015

 

RESIDENTS

 

EyeWorld journal club

Review of Femtosecond laser-assisted compared to standard cataract surgery for removal of advanced cataracts


by Purak Parikh, MD, Aida Bounama, MD, Anne Jensen, MD, Anita Kohli, MD, Neepa Shah, MD, Paul Tapino, MD, Scheie Eye Institute, University of Pennsylvania

 
 

Paul Tapino, MD

Paul Tapino, MD, residency program director, Scheie Eye Institute, University of Pennsylvania

 
Scheie Eye residents

From left to right: Anne Jensen, MD, Purak Parikh, MD, Aida Bounama, MD, Anita Kohli, MD, and Neepa Shah, MD Source: Scheie Eye Institute

Any advantages of femtosecond laser nuclear fragmentation should be most apparent with dense cataracts. I asked the Scheie Eye residents to review this study, which appears in this months issue of JCRS.

David F. Chang, MD, EyeWorld journal club editor

The advent of phacoemulsification has revolutionized cataract surgery, leading to improved patient safety, better visual outcomes, and shorter surgical time. However, the power from ultrasound energy generates heat, free radicals, and oxidative tissue damage leading to corneal endothelial cell loss, iris damage, and cystoid macular edema.1,2,3 Studies have shown that increased ultrasound energy, typically reserved for more advanced cataracts, leads to a higher incidence of these complications.4

In the past 6 years, the femtosecond laser has offered an alternative approach to several critical steps of cataract surgery, including corneal incisions, capsulotomy, lens softening, and lens fragmentation. In contrast to phacoemulsification, the femtosecond laser does not pose the same risk of damage to the cornea when softening or fragmenting a lens because of the 12-fold smaller cavitation bubbles it forms and the decreased thermal energy it produces.5 In addition, recent literature has suggested that femtosecond laser use with cataracts of moderate density, graded by the standardized LOCS III scale,6 can result in decreased additional phacoemulsification energy needed to further soften the lens prior to aspiration. In fact, these reports suggest that in moderate density lenses, zero effective phacoemulsification time (EPT) is required.5,7 EPT is a common metric used to measure the amount of ultrasound energy transmitted to the eye during cataract surgery. It is determined by multiplying the total phacoemulsification time in seconds by the mean power used.8

Previous studies have established that pretreatment of lenses with the femtosecond laser reduces EPT, but there has been no study comparing the EPT needed when treating dense, brunescent cataracts compared to lenses of moderate density. In the September issue of the Journal of Cataract & Refractive Surgery, Hatch and colleagues examined this relationship. In this consecutive, prospective, comparative study, the authors divided 240 patients into 4 equal groups of 60 patients each. Group 1 underwent conventional phacoemulsification of cataracts of nuclear opalescence (NO) grade 3 (moderate opalescence). Group 2 included patients with cataracts of the same NO grade 3, but these eyes underwent pretreatment with the femtosecond laser. Group 3 included conventional phacoemulsification of more dense, brunescent NO grade 5 cataracts. Group 4 also included patients with NO grade 5 cataracts, but removal included femtosecond pretreatment. As expected, patients with dense brunescent lenses (groups 3 and 4) were significantly older than the patients in groups 1 and 2 who had less advanced cataracts. However, the age difference between patients treated with conventional phacoemulsification versus femtosecond pretreatment was not statistically significant. General exclusion criteria included pupillary dilation less than 5.5 mm, decreased endothelial cell count, axial lengths less than 21 mm or greater than 28 mm, and previous significant ocular disease. The measured endpoints included the EPT and total surgical time. For the conventional phacoemulsification group, the surgical time was measured from the initial corneal wound creation until wound closure. For the femtosecond pretreatment group, the total surgical time was measured from the time of vacuum creation during docking of the laser until wound closure. In this study, the femtosecond laser and operating microscope were in the same operating room and their sequential use required only a rotation of the operating bed.

In this study, within the same grade of cataract opalescence, the EPT was found to be significantly less in the femtosecond pretreatment groups (group 2 had significantly less EPT compared to group 1 and group 4 had significantly less EPT then group 3). In fact, the EPT for all eyes in group 2, patients with moderate opalescence and pretreatment with femtosecond laser, was zero (i.e., requiring aspiration only and no phacoemulsification energy). In addition, the EPT required for femtosecond pretreated brunescent cataracts (group 4) was also statistically significantly lower than that of moderate density lenses without pretreatment (group 1). Surgical times for NO grade 5 brunescent cataracts were significantly higher compared to NO grade 3 moderate density lenses, but there was no difference in surgical time when comparing femtosecond pretreatment to conventional phacoemulsification in either the moderate or brunescent lens groups. This study supports previous literature suggesting that with moderate grade cataracts, femtosecond pretreatment can lead to zero phacoemulsification energy entering the eye. However, it is the first known study to demonstrate that pretreating a brunescent cataract with the femtosecond laser results in less EPT compared to conventional phacoemulsification of a softer, moderately dense lens. This finding may support a lower threshold to operate on brunescent lenses if a femtosecond laser is available. Although extracapsular cataract extraction (ECCE) is a viable technique to remove dense lenses, it has disadvantages including decreased surgeon experience with the procedure, induced astigmatism, wound leaks, and prolonged visual recovery. In this regard, with femtosecond pretreatment, the phacoemulsification technique may still be applied to dense lenses instead of considering ECCE. The second metric measured in this study, surgical time, found that dense, brunescent cataracts took significantly longer to remove compared to lenses of moderate density. However, when comparing femtosecond pretreated eyes to conventional phacoemulsification, there was no significant difference in the surgical time. However, the authors of this study were fortunate to have an operating room large enough to accommodate the femtosecond laser in the same room as the operating microscope, requiring only a rotation of the operative bed. In many surgical settings, the laser treatment would need to be performed in one room and then the patient would be transferred to another room housing the operating microscope. In these situations, a significant amount of surgical time would likely be added to the femtosecond-assisted cases.

This study supports previous research demonstrating that the amount of phacoemulsification energy needed in cataract surgery can be significantly reduced with femtosecond laser pretreatment. In addition, it shows that pretreating a brunescent lens with the femtosecond laser can lead to even less EPT compared to conventional phacoemulsification of a moderately dense lens. The authors acknowledge the limitations of their study such as the non-randomized nature of the study and the same surgeon performing all of the operations (which leads to no interoperator variability but individual bias). However, they do not explain the method by which patients were assigned to either the femtosecond laser or conventional group. Finally, no endpoints measuring true clinical metrics were used, such as postoperative endothelial cell count, central corneal thickness, or visual acuity, which are the main concerns with increased phacoemulsification energy. Although there are statistically significant differences in EPT when comparing the groups, it is not clear if this leads to any clinical difference to the patient. Given the high cost of acquiring a femtosecond laser, clinical endpoints would be helpful in determining whether the cost-benefit ratio makes it worthwhile to pretreat dense lenses with the femtosecond laser. Despite these limitations, this study further supports the role of femtosecond laser pretreatment for dense cataracts, and we look forward to future studies investigating long-term clinical outcomes in these patients.

References

1. Shimmura S, Tsubota K, Oguchi Y, et al. Oxiradical-dependent photoemission induced by a phacoemulsification probe. Invest Ophthalmol Vis Sci 1992;33(10):29042907.

2. Murano N, Ishizaki M, Sato S, et al. Corneal endothelial cell damage by free radicals associated with ultrasound oscillation. Arch Ophthalmol 2008;126(6):816821.

3. Augustin AJ, Dick HB. Oxidative tissue damage after phacoemulsification: influence of ophthalmic viscosurgical devices. J Cataract Refract Surg 2004;30(2):424427.

4. Miyata K, Nagamoto T, Maruoka S, et al. Efficacy and safety of the soft-shell technique in cases with a hard lens nucleus. J Cataract Refract Surg 2002;28(9):15461550.

5. Abell RG, Kerr NM, Vote BJ. Toward zero effective phacoemulsification time using femtosecond laser pretreatment. Ophthalmology 2013;120(5):942948. 6. Chylack LT, Wolfe JK, Singer DM. The Lens Opacification Classification System III. Arch Ophthalmol 1993;111(6):831836.

7. Dick HB, Schultz T. On the way to zero phaco. J Cataract Refract Surg 2013;39(9):14421444. 8. Conrad-Hengerer I, Hengerer FH, Schultz T, Dick HB. Effect of femtosecond laser fragmentation of the nucleus with different softening grid sizes on effective phaco time in cataract surgery. J Cataract Refract Surg 2012;38(11):18881894.

Contact information

Tapino: Paul.Tapino@uphs.upenn.edu

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The femtosecond choice by Enette Ngoei EyeWorld Contributing Editor

The future of laser-assisted cataract surgery: Clinical results and patient flow

Review of Femtosecond laser compared to standard cataract surgery Review of Femtosecond laser compared to standard cataract surgery
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