Update on FLACS
The jury is still out on femtosecond laser-assisted cataract surgery. We look at the pros and cons of the procedure
The introduction of the femtosecond laser into the field of refractive surgery brought about a huge transformation. Femtosecond-dissected flaps in LASIK and lenticules in SMILE have almost completely replaced manual microkeratomes. However, despite femtosecond laser-assisted cataract surgery (FLACS) having received FDA approval in 2010, the jury is still out regarding its utility, advantages and disadvantages.
The femtosecond laser is a near-infrared laser of 1053nm wavelength and femtosecond pulse duration (10-15 sec) that uses photodisruption. The laser creates plasma that expands to generate a shock wave. This creates a gas bubble that expands before it collapses, thus creating a cleavage plane. Being of ultra-short pulse, there is minimal collateral damage. The femtosecond laser gives very high precision and predictability together with complex programming abilities. It can also be linked to real-time spectral domain anterior segment optical coherence tomography (ASOCT) or Scheimpflug imaging to accurately create pre-programmed cuts at different levels within the transparent ocular tissues.
Applanating curved contact lens or non-applanating liquid optical immersion docking systems are used for docking. Centration is ascertained and the real-time images are evaluated for quality and tilt. Position of the chosen set of cuts is verified to be within the desired as well as safe zone. The cuts start with the capsulorhexis followed by lens fragmentation and softening, clear corneal incisions (CCI) and astigmatic keratotomy (AK) or corneal toric axis markings. Cuts larger than 6mm should be avoided, and a default clearance of 1,000 microns from the posterior capsule and 250 microns from the pupillary margin should be maintained to avoid complications.
ADVANTAGES OF FLACS
The aim of FLACS is to provide safety and ease of surgery while increasing precision and refractive outcomes. Many of the key steps of the cataract surgery such as capsulorhexis, nuclear fragmentation and softening, CCI and AK incisions are performed in a closed-chamber, no-touch machine-driven technique with high precision with regards to sizing, shape, centration, pattern, architecture etc, thus giving more predictable results and with less dependence on surgeon experience.
Better IOL centration, an accurate 0.5mm overlap of the rhexis edges all around the IOL optic, less tilt and more predictable effective lens position can all enhance premium IOL results. Nuclear fragmentation and softening can decrease intraocular manipulation, effective phaco time and cumulative dissipated energy, thus potentially decreasing endothelial and other complications such as vitreous loss and cystoid macular oedema.
Precise three-dimensional wounds can give better wound closure, greater predictability to the amount of induced astigmatism and lesser risk of endophthalmitis. Accurate depth, arc length and optic zone can improve accuracy of corneal and limbal-relaxing incisions.
Relaxing incisions also have the added advantage of providing the option to be opened in the postoperative period after assessing induced astigmatism. Iris or limbus registration in newer machines improves accuracy further.
USE OF FLACS IN DIFFICULT SCENARIOS
FLACS is helpful to safely create a rhexis in shallow anterior chambers, white cataracts and subluxated cataracts. Both anterior and posterior capsulorhexes can be done in paediatric cataracts. It can also make nucleus removal safer in patients with endothelial dystrophy and hard cataracts. It also makes routine cataract surgery easier for the less experienced surgeon, while increasing precision in the more experienced surgeon.
Significant corneal scarring that interferes with passage of the laser precludes FLACS. A prominent arcus may interfere with recognition of the limbus and cause anteriorly placed incisions that can cause oar locking of instruments and poor visibility. The rhexis in FLACS may not be as strong as a manual rhexis, though different studies have concluded differently regarding this. Scanning electron microscopy shows micro-irregularities in the edges of laser capsulotomies. These can result in radial run-outs of the rhexis. Postage stamp rhexis tags can be avoided by setting the pulses to overlap.
Decentered and partial capsulotomies may still occur because of tilt, corneal folds, poor docking etc. A free-floating capsulotomy should therefore always be verified before removing the central cut capsule to avoid an uncut segment extending outwards. A pupillary size of at least 6mm is desirable for performing rhexis and if less than 5mm can cause iris injury, release of prostaglandins and miosis. Pre-treatment with topical NSAIDs is helpful. A default setting of about 250 microns should be set from the pupil margin to avoid accidental intraoperative iris trauma and miosis. Rhexis in hypermature cataracts may be incomplete because of release of milky fluid interfering with the laser as well as collapse of the capsular bag. In paediatric cataracts, the achieved diameter may be larger than the programmed diameter because of the elastic nature of the capsule.
Intra-lenticular gas released from nuclear fragmentation can cause a capsular block syndrome resulting in nucleus drop. To prevent this, trapped gas should be released manually by rocking the nucleus prior to hydrodissection. Cortex aspiration can be more difficult as the sub-capsular cortex is also cut in line with the rhexis, resulting in absence of wisps of cortex that are routinely caught by the I/A probe in the case of a manual rhexis.
Flat anterior chamber after corneal arcuate keratotomies as well as accidental grid pattern delivery to the cornea and iris have been reported. In traumatic cataracts, overt or occult open globe injury should be ruled out before docking and any anterior capsular tears that may intersect with the FLACS rhexis should be checked for. In addition, intra-lenticular gas may cause a nucleus drop through a pre-existing posterior capsular tear.
A meta-analysis by Popovic et al. of 14,567 eyes reported no statistically significant difference between manual phacoemulsification and FLACS in overall complications or uncorrected and corrected distance visual acuities though there was statistically significant difference for several secondary surgical outcomes.
To conclude, FLACS does have advantages in terms of precision, predictability and usage in difficult situations such as shallow anterior chambers and hard nuclei. However, disadvantages include greater time taken for surgery, potentially weaker rhexis, laser-induced miosis, capsular blow-out etc. Further advancements are needed to give it distinct and definite advantages over manual phaco in routine cataract surgery.
Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India and can be reached at firstname.lastname@example.org