Laser, Manual Cataract Surgery Equivalent

Laird Harrison

August 31, 2016

Compared with manual surgery, the advantages and disadvantages of femtosecond laser-assisted cataract surgery may cancel each other out, a meta-analysis suggests.

"From an efficacy standpoint, we were unable to detect a difference" between the two approaches, write Marko Popovic, MD candidate, from the Faculty of Medicine, University of Toronto, Ontario, Canada, and colleagues.

The laser approach resulted in better horizontal centration of intraocular lenses, shorter phacoemulsification time, and less corneal endothelial cell loss. However, it was also associated with greater concentration of intraocular prostaglandins and more posterior capsular tears.

Popovic and colleagues published their findings in Ophthalmology.

The development of phacoemulsification, foldable intraocular lenses, and better measurement technology have made cataract surgery more effective, safer, and more predictable, they write.

Yet complication rates still vary considerably from one surgeon to another, suggesting that there is room for improvement.

The manual procedure requires cutting the cornea with a keratome blade, a continuous curvilinear capsulorrhexis using forceps or a cystotome, splitting or cracking of the nucleus, phacoemulsification, and cortical aspiration.

Femtosecond laser generates free electrons and ionized molecules to photodisrupt and photoionize optically transparent tissue via an acoustic shock wave.

In theory, this more automated approach should at least produce more consistent results.

The US Food and Drug Administration approved the femtosecond laser for cataract surgery in 2010. By 2014, 30% of patients with cataracts were choosing this technology over the manual approach, the researchers report, citing previous studies.

However, previous reviews and meta-analyses of studies comparing the two approaches have produced equivocal results. Therefore, Popovic and his colleagues conducted a broad search for pertinent studies and combined the results in a new meta-analysis.

They looked at 2802 abstracts and 86 full texts, finally narrowing these down to 37 articles with data they considered useful. Of these, 22 were observational studies and 15 were randomized controlled trials.

Authors of 23 of the studies had conflicts of interest, including 3 with direct funding from industry. In addition, various methodologic flaws could have introduced bias. For example, only 5 of the observational studies attempted to demonstrate comparability of cohorts at baseline and adjusted for confounding variables.

Overall, the studies included 7127 eyes undergoing laser treatment and 7440 undergoing manual treatment. The mean baseline age ranged from 58.5 to 75.0 years in the laser patients and 56.5 to 74.3 years in the manual patients.

In the 14 studies that reported on baseline cohort axial length, this parameter ranged from 23.33 to 25.09 mm in the laser cohort and from 23.08 to 26.94 mm in the manual cohort.

By the key measure of visual acuity, the procedures produced similar results. Postoperative uncorrected and corrected visual acuity did not significantly differ between groups (P = 0.19 and 0.26, respectively).

Phacoemulsification lasted 3 seconds longer on average for the manual procedure than for the laser procedure, a statistically significant difference (P < .001). But the difference in total surgery time fell just short of statistical significance (P = .07). Also, the authors note there was considerable heterogeneity in this measure.

Comparisons of the circularity of the removed capsule varied depending on the measurement, with some studies showing that capsules extracted by laser were more circular and others showing no difference.

The studies showed great heterogeneity in capsule opening diameter but no statistically significant differences between the two surgical approaches.

The laser procedure resulted in more horizontally centered intraocular lenses by an average of 128.84 μm (P < .001). However, vertical decentration was not significantly different (P = .90).

The central corneal thickness after surgery was thinner by a significant average of 6.37 μm (P = .02) in those treated by laser. But there was no significant difference in the number of postoperative endothelial cells per square millimeter for the two procedures (P = .07).

Two studies by the same research team looked at prostaglandin concentration, and both of these showed a greater concentration in eyes treated by laser than those treated manually (P < .001).

Laser surgery resulted in a significantly higher incidence of posterior capsular tears (P = .005). Otherwise, there was no statistically significant difference between the laser and the manual cohorts in overall adverse events (P < .001) or in other particular categories of events, such as other capsular complications, corneal complications, and pupillary complications.

The authors point out that the higher rate of posterior capsular tears might disappear as surgeons gain more experience with femtosecond lasers.

They also speculate that the lasers might have advantages for specific clinical scenarios, such as a subluxated lens.

However, some differences have been noted by other research groups. For example, as reported by Medscape Medical News, one group of researchers in May reported that the lasers work better in shallow anterior chambers.

The researchers did not obtain any funding for the study. One of the authors reported financial support from Alcon, Abbott Medical Optics, Bausch & Lomb, and Carl Zeiss.

Ophthalmology. Published online August 16, 2016. Abstract

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