Small-incision lenticule extraction is a relatively new surgical method for the treatment of myopia and myopic astigmatism.1 At present, the procedure is only available using the Visumax femtosecond laser platform (SMILE, Carl Zeiss Meditec AG). Although small-incision lenticule extraction has potential advantages over laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK), its safety and efficacy are comparable to those of the latter techniques.2 Moreover, the surgery requires more manipulation and is not free of complications.
To our knowledge, there has been 1 previous report of a retained lenticule, a disk-shaped piece of cornea, after femtosecond refractive lenticule extraction (FLEx, Carl Zeiss Meditec AG),3 and there is limited knowledge about residual lenticules after small-incision lenticule extraction and subsequent attempts to remove it.4,5 We present a patient who lost 3 lines of corrected distance visual acuity (CDVA) as a result of a residual lenticule after small-incision lenticule extraction and who had subsequent successful extraction of the residual lenticule 2 months after the first surgery. After the second surgery, clinical findings and patient complaints resolved. This case made us consider the reversibility of visual quality even in the case of a residual lenticule, and we are more comfortable about using the option of small-incision lenticule extraction surgery.
A 26-year-old woman attended our clinic for refractive surgery. She had no medical history of ocular disease or contact lens wear. The alteration in the refraction state in both eyes was less than 0.50 diopter for more than 2 years. The uncorrected distance visual acuity (UDVA) was 20/200 in both eyes. The manifest refraction (sphere, cylinder, and axis) was −3.75 −0.50 × 5 in the right eye and −3.75 −0.25 × 5 in the left eye. The CDVA was 20/20 in both eyes. The corneal topography and pachymetry maps showed regular anterior corneal curvature with a central corneal thickness of 562 μm. After having the routine evaluation procedure and discussing treatment options, the patient opted for small-incision lenticule extraction.
The Visumax femtosecond laser platform was used for the surgery with a near-infrared laser with 1053 nm wavelength and 140 nJ spot energy. Spot distances were set to 3 μm for lamellar cuts and to 2 μm for the side cut. Table 1 shows the treatment parameters. The surgical incisions were performed in 5 steps. First, a lamellar incision plane created the posterior surface of the lenticule that was to be extracted and separated it from the rest of the stroma. This incision was created from periphery to the center. After the lamellar incision was created, a 360-degree vertical incision was made to create the edge of the lenticule. After the edge incision was created, a cap incision was made from the center to the periphery to create the anterior surface of the lenticule. After the side-cut step, the lenticule that had been created between the base and cap incisions was removed (Figure 1). No complications occurred during incision creation with the femtosecond laser. A Stodulka double spatula (Rumex International Co.) was inserted from the side cut, and the anterior and posterior edges of the lenticule were identified. Then the anterior and posterior surfaces of the lenticule were dissected, and the lenticule was extracted using a McPherson forceps (design M. Blum, Geuder AG) at the 3.0 mm side cut.
One day postoperatively, the UDVA was 20/30 in the right eye and 20/20 in the left eye. Vision in the right eye did not improve with spectacle correction. Slitlamp examination indicated mild corneal edema. At the 1-week follow-up visit, the patient's left eye was fine; however, she reported blurry vision in the right eye. The patient's UDVA was 20/40 in the right eye and 20/20 in the left. The left eye had +0.50 −0.25 × 17 postoperative autorefractometer measurement. The CDVA in the right eye improved to 20/30 with a +1.00 −1.25 × 172. A through slitlamp examination (IS600 N, Topcon Europe Medical B.V.) showed a residual lenticule in the right eye (Figure 2, A). Corneal topography (Figure 2, B) findings were compatible with the residual lenticule seen during slitlamp examination. No surgical intervention was planned at that time because visual rehabilitation can be delayed after small-incision lenticule extraction; the recommended waiting time is 1 to 3 months. Two months after surgery, the patient was very satisfied with the left eye but still reported blurry vision in addition to halo and glare in the right eye. According to the patient, the right eye vision fluctuated on blinking and stabilized only after applying artificial tears. The UDVA was 20/20 in the left eye and 20/30 in the right eye and did not improve further, despite spectacle correction. Corneal topography at this time showed results similar to those on the 1-week postoperative topography. The lenticule was clearly visible on corneal optical coherence tomography (OCT) imaging (Spectralis HRA, Heidelberg Engineering GmbH), wherein the thickest part of the lenticule was observed to be its nasal part. The epithelium of the cap with the underlying residual lenticule was significantly thinner than the epithelium of the rest of the cap. After a discussion with the patient, a decision was made to perform surgery the next day to extract the residual lenticule (Figure 3).
A thin spatula was inserted from the original 3.0 mm incision site to the preexisting plane. No difficulty was encountered entering the interface. The spatula moved easily over the residual lenticule; hence, it was apparent that the anterior surface of the lenticule had been separated during the first operation. Although some resistance was encountered when the surgeon attempted to dissect the posterior surface, it was similar to the dissection performed during the primary operation. After all remaining tissue bridges were dissected, the lenticule was easily extracted.
One day after the extraction of the residual lenticule, the patient reported considerable improvement in her vision. The UDVA in the right eye had improved to 20/25. Corneal topography was still irregular but showed significant improvement. By 1 month after the extraction, the glare, halo, and blurry vision had resolved and the patient was happy with the vision in both eyes. The UDVA was 20/20 in both eyes. Slitlamp biomicroscopy showed a healthy eye, and the corneal topography was regular (Figure 4).
The two types of refractive lenticule extraction surgical methods available using the Visumax femtosecond laser platform are femtosecond lenticule extraction and small-incision lenticule extraction. In femtosecond lenticule extraction, a flap is cut over the lenticule and the lenticule is removed by lifting the flap. However, in small-incision lenticule extraction, an intrastromal lenticule is created instead of a flap and the lenticule is extracted from a 2.0 to 5.0 mm side cut.
Small-incision lenticule extraction is technically more challenging than femtosecond lenticule extraction, and lenticule dissection can be particularly challenging for new and inexperienced surgeons. Small-incision lenticule extraction also has advantages, such as improved biomechanics,6,7 better preservation of corneal nerves,8 and lack of flap-related problems. However, small-incision lenticule extraction is technically more challenging than LASIK, PRK, and femtosecond lenticule extraction and intraoperative complications, such as incomplete incisions and tears at the side-cut edges, can occur.
The most challenging aspect of small-incision lenticule extraction is the dissection of tissue bridges between the lenticule and the remaining stroma without creating a tear at the incision edges or damaging the cap stroma or lenticule. The lenticule can theoretically be torn during dissection or extraction, and a part of it might remain below the cap, resulting in irregular astigmatism and loss of CDVA. Although this is a possible complication, there are few reports of it. Dong and Zhou3 reported a case of retained lenticule resulting in irregular astigmatism and loss of CDVA after lenticule extraction. However, their method of extraction (ie, from an arcuate incision created on a 7.5 mm flap with a 45-degree superior hinge) is more suggestive of femtosecond lenticule extraction. Although their patient had irregular astigmatism in corneal topography and lost 2 lines of CDVA, the authors opted to follow the patient instead of performing a second surgery to remove the residual particle. Although they stated that the patient had UDVA of 20/25, they did not attempt a second surgery to remove the lenticule because of the uncertainty involved with the procedure and the resultant improvement in vision. Our speculation is based on the similar thoughts and doubts that we faced after realizing that when a tear occurred during surgery, a small part of the lenticule remained under the cap. Initially, we opted to wait for a few months but subsequently decided to intervene with a second procedure because our patient's vision did not improve and the corneal topography still showed irregular astigmatism.
To avoid such complications, surgeons should more carefully assess the integrity of the removed lenticule intraoperatively. This provides a chance to treat the remnant during the same surgical procedure. Based on this case, the timing of the intervention is not urgent because we successfully extracted the residual lenticule 2 months after the initial surgery. On the other hand, it seems that waiting 2 months does not benefit the patient because the presence of partial lenticule causing irregular astigmatism and decreased visual acuity will not subside with time. In our opinion, intervention should be performed as soon as possible.
Recently, Ganesh et al.4 reported a case series of eyes with residual lenticules. All the patients had surgical exploration for the extraction of the lenticules. The secondary intervention time ranged from 4 days to 9 months. They authors state that it is advisable to recognize and treat these cases promptly; however, based on their experience, it might be possible to extract retained lenticule fragments as late as 9 months after the primary surgery. Ng et al.5 also reported successful outcomes in 4 patients who had a secondary surgical procedure to remove a residual lenticule remnant.
In summary, the knowledge about residual lenticule management after small-incision lenticule extraction is limited. Our patient had a 3-line loss of CDVA and an irregular cornea for 2 months. However, her vision and topography findings improved significantly, returning to preoperative levels within 1 month after the small torn residual lenticule was extracted. The second surgery was straightforward and the dissection easy, even though the procedure was performed 2 months after the initial surgery. Extraction of retained lenticules or lenticule fragments restores visual acuity and the quality of vision and achieves the desired effect of the primary small-incision lenticule extraction procedure.
None of the authors has a financial or proprietary interest in any material or method mentioned.
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