Femtosecond Laser-Assisted Cataract Surgery (FLACS) is a technology that automates key steps of cataract surgery using a near-infrared femtosecond laser (wavelength 1,053 nm, pulse width 200–800 fs)1). Guided by real-time optical coherence tomography (OCT) or Scheimpflug imaging, it performs corneal incisions, capsulotomy (anterior capsule opening), lens fragmentation, and arcuate keratotomy5).
Cataract surgery is one of the most frequently performed surgeries worldwide, with approximately 7 million procedures annually in Europe, 3.7 million in the United States, and 20 million globally1). FLACS was first applied to humans by Nagy et al. in 20091) and received FDA approval in 20104). It was developed to achieve higher precision and reproducibility compared to conventional phacoemulsification (PCS).
The main platforms currently used in clinical practice are as follows:
The laser is only responsible for the initial steps: corneal incision, capsulotomy, nuclear fragmentation, and arcuate incision. For aspiration of lens fragments and intraocular lens insertion, conventional phacoemulsification is still required 1).
Cataract patients eligible for FLACS present with the following symptoms.
Clinical findings of cataract are evaluated based on the LOCS III classification. Nuclear sclerosis grade (2–4) is directly related to the amount of ultrasound energy used during surgery 3).
Findings that may be observed after FLACS are as follows.
The indications for FLACS are the same as for conventional PCS, targeting cataracts that impair visual function. The following patient groups may particularly benefit from this procedure:
On the other hand, the following are contraindications or require caution:
The diagnosis of cataract and determination of surgical indications are the same as for conventional methods, but FLACS requires the following additional evaluations.
FLACS devices are equipped with integrated imaging systems 5).
These allow precise planning of capsulotomy position, nuclear fragmentation safety margins, and corneal incision depth.
FLACS surgery consists of the following steps.
This is the process of connecting the patient interface (PI) to the laser device and the eyeball 1)5). There are two types of PI.
| Type | Features | Advantages |
|---|---|---|
| Applanating type | Flattens the cornea with a curved lens | High stability |
| Liquid immersion type | Scleral suction ring + liquid immersion chamber | Less IOP elevation. Reduces corneal folds. |
Poor docking or suction loss rarely occurs, but has improved from an initial 2.5% to currently about 0.1% 1).
This is considered the greatest advantage of FLACS 1)5).
Manual continuous curvilinear capsulorhexis makes it difficult to create a perfect circle and is prone to decentration or deformation, whereas FLACS can create an accurate anterior capsulotomy with the set diameter and position.
The laser pre-fragments the lens nucleus, reducing the consumption of ultrasonic energy5).
It is effective for correcting low to moderate astigmatism (≤1.5 D) during cataract surgery1)10). It offers higher precision than manual LRI (limbal relaxing incisions). However, for moderate or higher astigmatism, toric IOLs are superior10). Compared to manual methods, incision accuracy is higher and the predictability of astigmatic correction is better.
FLACS
Anterior capsulotomy: High precision and reproducibility. Enables creation of perfectly round and uniform diameter.
Nucleus fragmentation: Reduces CDE through laser pretreatment.
Posterior capsule rupture rate: Multiple RCTs report 0% 8).
Cost: High equipment and consumable costs.
Conventional method (PCS)
Anterior capsulotomy: Depends on surgeon skill. Variability in circularity.
Nucleus fragmentation: All performed with ultrasound energy. High CDE.
Posterior capsule rupture rate: RCTs report 0.5–3% 8).
Cost: Cheaper than FLACS. Higher cost-effectiveness.
The ESCRS guidelines recommend that both PCS and FLACS are safe and effective, with equivalent visual and refractive outcomes (GRADE +/++) 10). However, in cases of hard cataracts or low corneal endothelial cell count, FLACS has shown reduced endothelial cell loss and less increase in postoperative central corneal thickness 10).
In the French FEMCAT trial (multicenter RCT, 909 patients), the success rate was 41.1% in the FLACS group and 43.6% in the PCS group, with no significant difference (OR 0.85, 95% CI 0.64–1.12) 11). The incremental cost-effectiveness ratio was “€10,703 saved per additional patient successfully treated with PCS,” concluding that FLACS is not cost-effective 10).
In the UK FACT trial, the incremental cost-effectiveness ratio for FLACS was £167,120 per QALY, indicating no cost-effectiveness 10).
In FLACS, compression by the patient interface may damage conjunctival goblet cells, potentially increasing the risk of postoperative dry eye 6). However, it has been reported that many indicators return to preoperative levels after 3 months. For details, see the “Pathophysiology” section.
The femtosecond laser (pulse width 10⁻¹⁵ seconds) uses ultrashort pulses of near-infrared light (1,053 nm) to cause photodisruption within tissue 1)5). The near-infrared laser passes through corneal tissue outside the focal point and causes photodisruption only at the focused tissue, breaking molecular bonds. It is characterized by the ability to form voids of several micrometers without thermal diffusion to surrounding tissue.
Photodisruption proceeds in the following three stages:
When the energy threshold is exceeded, tissue separation is achieved through two mechanisms 5).
Laser anterior capsulotomy is created by continuous irradiation similar to a “postage stamp perforation.” Electron microscopy shows notches on the incision edge compared to manual continuous curvilinear capsulorhexis, and it has been reported that tensile strength is lower1).
However, optimization of laser settings (especially increasing vertical spot spacing to 20 μm) has significantly reduced the incidence of anterior capsule tears8).
Scott et al. (2021) reported that the anterior capsule tear rates with vertical spot spacings of 10, 15, and 20 μm were 0.79%, 0.35%, and 0.09%, respectively8).
Dry eye after FLACS shares common mechanisms with conventional methods, but also has the following unique factors6).
In FLACS, intraoperative miosis (small pupil) occurs significantly more frequently (OR 3.05, 95% CI 1.83–5.07)4). The main cause is an increase in prostaglandin E₂ concentration in the aqueous humor during anterior capsulotomy1). Low-energy pulse devices are reported to have less miosis5).
With multifocal IOLs, EDOF (extended depth of focus) IOLs, and toric IOLs, accurate centration of the IOL and overlap of the anterior capsule are directly linked to optical performance. The precise anterior capsulotomy of FLACS may maximize the effectiveness of these premium IOLs5)8).
Levitz et al. (2021) pointed out that the accuracy of laser capsulotomy may reduce decentration of EDOF and toric lenses, preventing image quality degradation8).
The concept of using femtosecond laser to modify the refractive index of an implanted IOL to adjust power, astigmatism, and multifocality, or to create a pinhole aperture, has been investigated in vitro1). This could potentially reduce the rate of IOL exchange.
In pediatric cataract, the anterior capsule is highly elastic and the lens nucleus is soft. FLACS can be used for both anterior and posterior capsulotomy, but its use in children is off-label, and correction factors accounting for elastic enlargement are necessary1).
There is a concept of a fully automated cataract surgery platform combining femtosecond laser technology with robotic lens aspiration1). This is expected to standardize surgery and improve cost-effectiveness.
