Low-Energy Femtosecond Laser–Assisted Cataract Surgery Not a Cause of Myosis

Low-energy femtosecond laser–assisted cataract surgery compares favorably with conventional phacoemulsification, with less pupil variation.

Low-energy femtosecond laser–assisted cataract surgery (FLACS) does not appear to induce significant pupil changes, namely myosis, according to a study published in Clinical Ophthalmology. The research shows less pupil variation in low-energy FLACS compared with conventional phacoemulsification (CP), more so in eyes with comorbidities, particularly in those with shallow anterior chamber, but this is not statistically significant, according to the report. 

“The vast majority of publications approach mainly high-energy femtosecond laser devices, with strong evidence of laser-induced myosis by this type of laser,” the study authors explain. “On the other hand, some recent evidence is being apparent that low-energy femtosecond laser does not induce such narrowing of the pupil.”

Researchers retrospectively reviewed surgical data from 164 eyes from 82 patients (mean age, 73.4±8.5 years; age range, 55-95 years, 55 women, 27 men) who underwent uncomplicated cataract surgery at a single center between February 2015 and September 2020. Patients were randomly assigned low-energy FLACS to 1 eye and CP to the other eye. The research team evaluated recorded pupil images before and after laser treatment (after suction release) and during several surgical time points for both FLACS and CP. They calculated pupil areas and compared the pupil changes in FLACS with CP. 

The researchers found no statistical differences regarding the total surgical procedure time (P =.805) between FLACS and CP. Pupil area comparison between pre and post laser treatment in the FLACS group demonstrated no statistically significant differences (P =.107). 

The vast majority of publications approach mainly high-energy femtosecond laser devices, with strong evidence of laser-induced myosis by this type of laser.

The mean change in pupil area from the start until the end of cataract surgery (total variation) was 6.59±2.08 mm2 in the FLACS group compared with 6.67±2.13 mm2 in the CP group. FLACS was associated with less narrowing of the pupil area, but this was not statistically significant (P =.080). 

Comorbidity group analysis showed less, but not significant pupil narrowing with FLACS (P =.071). Between FLACS and CP, there was a strong but non-statically significant difference in eyes with a shallow anterior chamber (less than 2.5 mm), the report shows. 

No statistically significant differences between FLACS and CP regarding age subgroups were noted.

“No significant pupil changes were observed in the present study with low-energy FLACS, in contrast with the reported common association of laser-induced myosis with high-energy and low-frequency femtosecond pulse machines available in the market,” according to the study authors. “Furthermore, regarding pupil status, low-energy femtosecond laser-assisted energy seems to compare favorably with conventional phacoemulsification in the presence of certain ocular comorbidities. Although not statistically significant, this difference arises an interesting discussion and, also in line with contemporary literature, it recommends revision of some established, global opinions on FLACS.”

Study limitations include the relatively small sample size and the single center design.


Salgado R, Torres PF, Marinho A. Pupil status with low-energy femtosecond laser-assisted cataract surgery versus conventional phacoemulsification: An intraindividual comparative study. Clin Ophthalmol. Published online January 24, 2023. doi.org/10.2147/OPTH.S399788