Femtosecond Laser–Assisted Cataract Surgery

17   Femtosecond Laser–Assisted Cataract Surgery


Ronald Yeoh


Femtosecond laser–assisted cataract surgery (FLACS) is rapidly gaining momentum, and I estimate that one thousand of these lasers have been installed worldwide. If cost was not an issue, I believe that most cataract surgeons would adopt this new technology, as it makes the surgery simpler and arguably safer. Proof of improved refractive precision is awaited.


The procedure itself is similar, whichever FLACS platform a surgeon selects. It involves the “femto” step followed by the “phaco” step. This chapter describes both steps, in particular the modifications in technique needed when changing from phaco to femtophaco, and discusses the potential complications and their management and prevention.


Preoperative Preparations


One hour before surgery, I administer my standard pre-phaco dilatation regime: Guttae tropicamide 1% ×4 and Guttae phenylephrine ×2, both an hour prior to surgery. For FLACS, I add a topical nonsteroidal anti-inflammatory drug (NSAID), typically G nepafenac × 2.


The Femto Step


All FLACS machines do the same three steps: continuous curvilinear capsulorrhexis (CCC), nuclear fragmentation, and corneal incisions. They all require that the eye be docked into a patient interface (PI) to stabilize the eye, and this enables precise delivery of laser energy as needed to the anterior capsule, lens nucleus, and cornea. There are variations in the type of docking between the major platforms, the most obvious being the single-piece docking device of the Lensx system (Alcon, Fort Worth, TX) (versus the two-piece docking devices of Catalys, Victus, Lensar, and the Ziemer Z8.


The Lensx PI has a proprietary contact lens inserted into the suction cup and this is lowered directly onto the eye, and suction is then applied. The other two-piece designs require that a suction ring or cup is first applied to the patient’s eye and suction applied prior to the docking of the laser PI into this ring or cup.


Good, secure docking without tilt generally yields good femtolaser outcomes. But if there is significant tilt or inadequate suction, poor capsulorrhexis, nuclear fragmentation, or incision may result. One of the most important determinants of how easy or difficult a dock may be is the size of the palpebral aperture.



Femto Tip 1



  • Avoid patients with narrow palpebral apertures and poorly dilating pupils, which may challenge the beginning FLACS surgeon.

Docking


The docking process is a critical step, as it stabilizes the eye and enables delivery of the femtolaser pulses in a controlled and precise manner. All the major FLACS platforms require docking, and there are two fundamentally different ways of docking: the single-piece patient interface, and the two-piece interface.


The Lensx utilizes a single-piece docking system in which no suction ring or cup is used; a speculum is used to open the palpebral aperture widely and the PI is lowered directly onto the patient’s eye under direct visualization (Fig. 17.1).


The single-piece docking is very simple and intuitive to use, and even the surgeon who has no prior experience with laser-assisted in situ keratomileusis (LASIK) docking should find it straightforward. Viewing, centration, and applying suction on single-piece PIs is easy, as there is an unblocked view of the limbus (Fig. 17.2).


The patient who exhibits a strong Bell’s reflex at the time of suction may end up with a decentered or tilted dock, and the surgeon needs to recognize this so that a re-dock can be performed.


The other FLACS platforms all utilize a two-piece patient interface in which a suction ring or cup is first applied to the patient’s eye, usually without a speculum, and then approximated to the laser head (Figs. 17.3 and 17.4).



Experienced LASIK surgeons who are familiar with placing a suction ring on the eye and then docking the PI will find the transition to two–piece docking extremely easy. Centration in two–piece docking systems is based on aligning the superior portion of the PI with the already applied suction ring or cup, and not the limbus (Figs. 17.5 and 17.6).


Certain femtolaser parameters are preset before docking, such as CCC size, nucleus fragmentation pattern and size, and incision size. Laser power and spot and layer separations are all designated at this stage. The placement of the CCC outline, the fragmentation depth, and the incision location for a particular eye are then determined after docking. Some systems feature automated planning of these parameters, and some require manual input. Preferred CCC sizes average 5 mm. Nuclear fragmentation diameters are often 1 to 2 mm larger than the CCC size, and the posterior offset from the posterior capsule ranges from 500 to 700 µm. Incision widths are ~ 2.3 mm for main incisions and vary from 0.8 to 1.2 mm for the side port. Checking and confirming that all the above parameters are correct is vital, similar to the preflight checks that pilots perform prior to takeoff. Because even automated planning systems can have problems (e.g., a small pupil), it is good practice for the surgeon to know how to input and control these variables rather than relying on a technician.



The final stage of the femto step is the actual firing of the femtosecond laser itself, usually controlled by a foot pedal. Treatment starts with the CCC, continues with the nuclear fragmentation, and ends with corneal incisions and astigmatic keratotomies. Suction or vacuum is then turned off and the eye undocked.



Femto Tip 2



  • Once the femtolaser pedal is depressed, do not lift your foot or let it slip off the pedal, as some systems may not allow the treatment to continue. The eye then needs to be undocked and re-docked and the procedure started again.

Outcomes with the Femto Step


The FLACS procedure has been in clinical usage since 2011; in the first 3 years, the few systems available issued numerous software and hardware upgrades, all for the betterment of our patient outcomes. Patient interfaces have become smaller, treatment planning and delivery protocols have become quicker, and nuclear fragmentation patterns have become more sophisticated.


One concern when the eye is docked is the elevation in intraocular pressure (IOP), but the new-generation machines only raise the IOP between 10 and 17 mm Hg.1 Another consideration is the amount of time that the patient’s eye is subjected to this elevated pressure; this varies widely between the different platforms (1.5 to 3.5 minutes) and some platforms can take twice as long.2 Although there is little danger to the optic nerve with such small elevations of IOP, prolonged suction-on times lead to greater patient discomfort and bruising, and may increase the risk of suction loss.



The Phaco Step


Although the femto step includes three main steps of CCC, nuclear fragmentation, and incisions, it would be naive to expect that the phaco step of the procedure would be simple. With any change in instrumentation, surgeons also needs to adapt their surgical technique, and so it is with FLACS.


First, the eye after the femto step is different in several ways (Fig. 17.7):



  1. The pupil may be constricted.
  2. Incisions are present.
  3. There is a perfectly round but white-edged CCC.
  4. The fragmentation pattern is visible.
  5. Gas is present anteriorly and deep within the lens.

The Pupil with Miosis


About 20 to 25% of all eyes show a constricted pupil (likely prostaglandin mediated) to some extent after the femto step.3 This is obviously disconcerting, especially if a 2- to 3-mm pupil results, making it difficult to assess the completeness of the CCC and to fragment the nucleus (Fig. 17.8). If this happens, use an ophthalmic viscosurgical device (OVD) to enlarge the pupil or a Kuglen hook to push aside the iris so that the quality of the CCC can be ascertained before proceeding. It is much better to prevent this situation, and the use of a preoperative drop of NSAID with the dilating drops is most useful in eradicating this problem.4





Femto Tip 3



  • Apply your preferred NSAID with the dilating drops in your preoperative medication.

Femtolaser Incisions


One of the three fundamental capabilities of FLACS is the creation of the main and side-port incisions as well as astigmatic keratotomies (AK). Femtolaser-created incisions are similar to femtolaser-created LASIK flaps; they can be adherent and require some effort to open. Two problems that may be encountered by the beginning FLACS surgeon are (1) imprecise placement of incisions, and (2) difficulty in opening FLACS incisions. With better sizing of suction cups and rings and software improvements in incision placement, FLACS incision creation is now a routine part of the procedure.


Undoubtedly, the most important point about opening a FLACS incision is to have the right spatula with the right profile and bevel for that particular incision. It is worth noting that most side-port incisions angle slightly downward at about 10 degrees, whereas many main-port configurations angle downward at about 40 degrees for the first plane before flattening out to about 10 degrees. I therefore designed a double-ended spatula taking into consideration these angles (AE2332, Asico, Westmont, IL; I have no financial interest in this product). I usually perform 0.9-mm-wide side-port incision and a 2.3-mm-wide main-port incision. Some surgeons favor bimanual irrigation and aspiration (I/A), and they require a much larger side port of 1.2 mm. The more difficult incision to open is always the smaller side-port incision, so I invariably start with this. Place the spatula just proximal to the external opening of the incision, press downward and forward while moving the spatula tip left and right, and entry is usually easily effected (Figs. 17.9 and 17.10).


May 13, 2018 | Posted by in OPHTHALMOLOGY | Comments Off on Femtosecond Laser–Assisted Cataract Surgery
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