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Inadvertent corneal laser application in femtosecond laser-assisted cataract surgery

by Elsev An 81-year-old man had femtosecond laser–assisted cataract surgery in his right eye. During the final few seconds of treatment, there was an abrupt loss of suction that resulted in inadvertent corneal application. Under the operating microscope, a central waffle pattern without corneal opacification was seen over the cornea. Conventional phacoemulsification was carried out uneventfully. The corneal laser marks did not significantly obscure the surgical view. Postoperatively, the corrected distance visual acuity (CDVA) was 6/6 at 1 day and 6/9 at 1 year. The corneal stromal scars were still present, but the patient maintained good CDVA and had no visual complaints. There was a significant endothelial cell loss of 47.9% at 2 weeks and 64.6% at 1 year. This case illustrates an uncommon complication of femtosecond laser–assisted cataract surgery and its possible effect on endothelial cell loss, although good visual acuity can be achieved.

The attempt to reduce morbidity and increase the precision and outcomes of cataract surgery has led to increasing use of the femtosecond laser as an adjunct to conventional phacoemulsification. It has improved surgical predictability by enabling consistent capsulorhexis creation, 1 thereby improving intraocular lens (IOL) centration and position. 2,3 This is especially useful when implanting premium IOLs such as toric or multifocal IOLs or performing lamellar or fullthickness astigmatic keratotomy at the time of phacoemulsification. The ability to fragment and liquefy lens material has decreased the amount of phacoemulsification energy required to complete cataract surgery, particularly in dense hard nuclei, leading to a decrease in endothelial cell damage. 4 The laser also enables corneal wound creation and corneal arcuate incisions for astigmatic correction. Thus, femtosecond laser-assisted cataract surgery appears to have a distinctive role in dense hard cataracts, 4 patients with preexisting endothelial cell count (ECC) deficiency, 5 and patients with mild to moderate corneal astigmatism. 6 However, the addition of femtosecond assistance incurs additional cost to the patient and investment to the physician. 7 This additional cost may not translate to significant differences in visual outcomes in most standard cataract cases. Femtosecond laser-assisted cataract surgery is also not reimbursed by insurance in most countries. Furthermore, transferring the patient from the laser machine to the operating bed lengthens the total surgical time, decreasing efficiency and productivity. 8 Femtosecond laser-assisted cataract surgery has been found to be safe and not inferior to traditional cataract surgery. 9 Reported intraoperative complications include anterior capsule tags, tears, and incomplete capsulotomy. These anterior capsule complications were more common in femtosecond laser-assisted cataract surgery than in traditional cataract surgery. 9 However, these complications have minimal effect on the refractive outcome. Posterior capsule ruptures have also been reported, probably secondary to intracapsular gas accumulation. 10 These complications may be related to the learning curve.
Various types of femtosecond laser-assisted cataract surgery systems are available. They vary in their docking interface, type of imaging guidance, treatment algorithms, and type of laser used. Depending on the practice, the laser machine may be located in a different room or in the same operating room. The process of docking requires firmly attaching a suction ring to the patient's eye. This can be challenging in patients with features such as a narrow palpebral aperture, a high nose bridge, or deep-set eyes. Suction loss can occur before the laser is activated or any time during the laser treatment; eg, when a patient squeezes the eye or makes abrupt head or eye movements or because of inadequate contact from eyelashes or eye debris. We report an uncommon complication of femtosecond laser-assisted cataract surgery due to a sudden loss of suction during the laser procedure.

CASE REPORT
An 81-year-old Chinese man had femtosecond laser-assisted cataract surgery for a cataract of grade 4 nuclear opalescence and color (scored according to the Lens Opacities Classification System III scale) in the right eye. Preoperatively, the corrected distance visual acuity (CDVA) in the eye was 6/15 and the patient complained of the poor vision. The CDVA in the fellow eye was 6/6 after previous complicated cataract surgery with toric monofocal IOL implantation, which had been performed elsewhere. Bilateral retinal pigment epithelium atrophy was noted over the macula on dilated fundus examination. The pupillary dilation with mydriatic drops was good, and the preoperative ECC was 2231 cells/mm 2 in the right eye and 827 cells/mm 2 in the pseudophakic left eye.
The Catalys Precision Laser System (Abbot Medical Optics, Inc.) with a liquid-optic patient interface was used for the surgery. After successful docking was confirmed, the laser was activated. A pupil-centered capsulotomy (0.8 J energy, 5.0 mm, 600 mm incision depth) followed by lens fragmentation (13.1 J energy, grid spacing 350 mm, horizontal spot spacing 10 mm, vertical spot spacing 40 mm, anterior capsule safety margin 500 mm, posterior capsule safety margin 700 mm) was performed. The total treatment time was 30.8 seconds (anterior capsulotomy 1.6 seconds and lens fragmentation 29.2 seconds). During the final seconds of the procedure, there was an abrupt loss of suction with a time lag in the release of the footpedal, resulting in inadvertent corneal application.
The patient was transferred to the operating table, and the cornea was examined using the operating microscope. A central waffle pattern was seen over the cornea with no corneal edema or opacification. The patient was informed of the findings, and a decision was made to proceed with the planned phacoemulsification. The patient was seated upright to make corneal markings to assist toric IOL implantation. The femtosecond laser-created capsulotomy appeared complete with adequate lens treatment.
Conventional phacoemulsification was carried out using the Whitestar Signature phacoemulsification system (Abbot Medical Optics, Inc.). Corneal wounds were created, and a cohesive ophthalmic viscosurgical device (OVD) was injected. The anterior capsule flap of the completed capsulotomy was removed. Phacoemulsification was performed using the stop-and-chop technique. Sculpting was performed at a power of 45% and vacuum of 50 mm Hg. Segment removal was performed at a power of 40% and vacuum of 230 mm Hg. After the cortex was removed and the capsular bag filled with OVD, a toric monofocal IOL was placed and the procedure was completed uneventfully. The entire surgical time including phacoemulsification was 21 minutes. The cornea remained clear throughout the surgery, and the corneal laser marks did not significantly obscure the surgeon's view. The patient was discharged with topical prednisolone acetate 1.0% and tobramycin and dexamethasone (Tobradex) 4 times a day.
One day postoperatively, the acuity CDVA was 6/6. Subjectively, the patient was happy with the visual outcome. On examination, a waffle laser pattern was seen in the deep posterior stromal to the predescemetic layer of the central cornea ( Figure 1). Minimal inflammation was seen in the anterior chamber. The CDVA remained good despite the stroma scars. At 2 weeks (Figure 2), the ECC was 1162 cells/mm 2 . At 1 year (Figure 3), the patient was asymptomatic with "good vision." Examination revealed corneal stromal scars with a CDVA of 6/9. Central corneal thickness was 567 mm in the right eye and 582 mm in the left eye. Endothelial cells counts were 789 cells/mm 2 and 798 cells/mm 2 , respectively.

DISCUSSION
The femtosecond system provides image guidance, which has improved the precision and consistency of cataract surgery. Femtosecond-assisted surgery enables  minimal use of phacoemulsification energy and preservation of endothelial cells. 4 With increasing surgical experience, the adjunctive use of the laser in cataract surgeries is being explored in more complex cases. 11 The Catalys laser system allows the creation of a lens fragmentation pattern of a central cross and multiple small cubes to soften the lens. The laser begins the lens fragmentation treatment from the posterior aspect of the lens and then moves anteriorly. Hence, in our case, when suction was broken toward the end of surgery, the misfiring of the laser created a waffle pattern that was seen on the patient's cornea. The laser-created capsulotomy and lens fragmentation were otherwise fairly complete. The machine has an inbuilt safety mechanism with motion sensors to detect excessive head movements. It is likely that before the machine was able to detect the suction break, air entered the liquid-optic interface, changing the point of focus of the laser beam.
To our knowledge, there are 2 other case reports of laser energy delivered to the corneal stroma during femtosecond laser-assisted cataract surgery. 12,13 In all 3 cases, there was an abrupt suction loss during lens fragmentation treatment. Fortunately, good visual acuity was achieved in all cases and patients were satisfied with their visual outcomes. There could have been endothelial injury if the laser had been fired at the level of the endothelium or superficial to that layer. Suction breaks during the laser procedure are a known intraoperative occurrence. 14,15 However, in most cases, treatment is discontinued when the foot switch is released, with no adverse events. 10,16 The fraction of a second time lag between suction break and release of the foot switch was probably what led to the laser being applied to the cornea in these cases.
Conrad-Hengerer et al. 5 compared femtosecond laser-assisted cataract surgery and conventional cataract surgery and found a mean endothelial cell loss of 7.9% at 1 week postoperatively and 8.1% at 3 months in the femtosecond laser-assisted cataract surgery group compared with 12.1% and 13.7%, respectively, in the conventional cataract surgery group. Our case shows a dramatic postoperative endothelial cell loss of 47.9% at 2 weeks after femtosecond laser-assisted cataract surgery and 64.6% at 1 year. As the phacoemulsification was otherwise uneventful and the laser burns were fairly deep in the cornea, the inadvertent laser delivery may have contributed to the endothelial cell loss.
We conclude that surgeons should be aware of the intrinsic vulnerability of technology and its application in the trend toward the use of new technologies. We also propose more safeguard mechanisms, both human and technological, that will stop laser application when there is significant patient or eye movement, with or without loss of suction. With further advances and modifications to the laser system, the safety mechanism could be improved, enabling earlier detection of a suction break and automatic abortion of the laser. Although good visual acuity was achieved at the end of the surgery in the 3 reported cases, significant endothelial cell loss might have occurred as a consequence of the laser application, as seen in our case. Cataract surgeons should be aware of this uncommon complication of femtosecond laser-assisted cataract surgery and its potential consequences.