Refractive surgery is ever evolving with new technologies such as the femtosecond laser creating a paradigm shift in surgeons' ability to perform refractive correction. Small-incision lenticule extraction (SMILE, Carl Zeiss Meditec AG) is the latest advancement that involves the creation of 4 sequential cuts to form an intrastromal lenticule, which is subsequently removed to offer a refractive correction. Initial enhancement modalities after small-incision lenticule extraction included surface ablation or implantable phakic intraocular lenses in eyes wherein the residual stroma was inadequate for photoablation. The Circle software (Carl Zeiss Meditec AG) allows the creation of a lamellar ring posterior, anterior, or adjacent (Pattern B, C, or D, respectively) to the previous small-incision lenticule extraction pocket cut for conversion to a flap and enhancement after small-incision lenticule extraction (Figure 1).1 We describe the use of the Circle software (Pattern D) to manage a case of suction loss with incomplete cap side-cut formation in small-incision lenticule extraction. To our knowledge, a similar use has not yet been reported in literature.
A 20-year-old male presented to the Centre for Sight, New Delhi, India, seeking correction for a myopic refractive error of −2.0 diopters (D) and −2.5 D in the right and left eye, respectively, with a corrected distance visual acuity of 20/20 in both eyes. Standard candidacy criteria for keratorefractive procedures were met. Anterior segment and fundus evaluations were unremarkable. Corneal tomography was within normal limits with a thinnest pachymetry of 554 μm and 547 μm in the right eye and left eye, respectively. Small-incision lenticule extraction was planned.
The procedure was performed using a femtosecond-laser system (Visumax, Carl Zeiss Meditec AG) with a targeted cap depth of 120 μm and an optical zone of 6.5 mm (spot distance, 3 μm for lenticule cut and 2 μm for side cut; energy 150 nJ). The cap side cut was formed with a circumferential length of 3.0 mm, with the incision positioned at 90 degrees with a side-cut angle of 90 degrees.
The patient's eye was centered and docked with the curved interface before initiation of suction. Treatment in the right eye was completed successfully. During the treatment in the left eye, the posterior refractive cut and lenticule side cut were completed successfully. During the anterior lenticule cut, an unstable suction was noted, although it was adequate to allow progress of laser delivery. Toward the end of the treatment, conjunctival encroachment under the curved interface prevented transmission of the femtosecond delivery and a subsequently unformed cap side cut. Because the laser was delivered for the entire duration of the treatment, the software registered a complete laser delivery. This prevented a retreatment option, allowing completion of the incomplete side cut only. Attempts at gaining access to the interface with manual dissection failed.
At this juncture, the treatment option included surface ablation at a later date. The Circle software (Pattern D) was used to create a lamellar ring to convert the cap into a flap. The intended depth of the flap cut was 120 μm with a planned flap diameter of 8.1 mm. A spatula (Sielbel, Rhein Medical GmbH) was inserted under the flap, which was subsequently separated and reflected. The separation was performed posterior to the lenticular surface because an anterior dissection posed the risk for a potential false passage creation between the junction of the initial cap and subsequent flap (junction cut). The lenticule was then subsequently separated from the underlying flap surface and peeled off. The interface was washed, and the flap was repositioned (Video 1).
The postoperative treatment regimen included topical steroids (loteprednol etabonate 0.5% ophthalmic suspension) in tapering doses and lubricating drops (carboxymethylcellulose 0.5% ophthalmic drops). A well-centered flap was noted with an uncorrected distance visual acuity of 20/20 in both eyes at the first postoperative visit and at subsequent follow-ups up to 6 months.
Small-incision lenticule extraction is the latest advancement in the field of keratorefractive surgery. Small-incision lenticule extraction entails the use of the femtosecond laser to create 4 sequential cuts to form an intrastromal lenticule, which is subsequently separated from the surrounding corneal stroma to provide myopic correction.
Suction loss is an associated complication, with an incidence ranging from 0.8% to 2.1% in large cohorts.2,3 Risk factors include a narrow palpebral fissure, excessive eyelid squeezing during laser delivery, sudden eye movement, and fluid ingress between the contact glass suction ports and the cornea.3 In addition, the femtosecond-laser system used for small-incision lenticule extraction is a low-pressure system with an intraocular pressure rise of 35 mm Hg during laser delivery.4 The increased time requirement for laser completion in comparison to femtosecond flap5 and the obscuration of the fixation target after a posterior lenticule cut increase the risk for suction loss during anterior lenticule cuts and cap side cuts.6 The recommendation for management of suction loss during a cap side cut entails repeating the cap side cut only with decreased size.A
In our case, the encroachment of the superior conjunctiva underneath the contact interface occurred at the stage of the cap side cut. Subsequent interference with femtosecond laser delivery resulted in uncut corneal tissue. However, because the treatment was registered as being completed successfully, we were unable to proceed with a repeat cap side cut only.
The Circle software allows the conversion of the small-incision lenticule extraction cap into a flap for subsequent excimer ablation.1 We describe the use of pattern D to form a flap to gain access to the lenticule, allowing successful removal and refractive correction. To our knowledge, the use of the Circle software for management of suction loss in small-incision lenticule extraction has not been described previously.
None of the authors has a financial or proprietary interest in any material or method mentioned.
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Wong CW, Chan C, Tan D, Mehta JS. Incidence and management of suction loss in refractive lenticule extraction. J Cataract Refract Surg 2014; 40:2002-2010
Ang M, Mehta JS, Chan C, Htoon HM, Koh JC, Tan DT. Refractive lenticule extraction: transition and comparison of three surgical techniques. J Cataract Refract Surg 2014; 40:1415-1424
OTHER CITED MATERIAL
Carl Zeiss Meditec AG. FLEx Option. In: Visante Operation Manual. Jena, Germany; 2011:24-25