Removal of Retained Descemets Membrane Using Femtosecond Laser.

We present a unique method of retrocorneal membrane removal with a femtosecond laser (FSL). A 22-year-old male who had undergone penetrating keratoplasty had a retained retrocorneal membrane and a double anterior chamber postoperatively. The membrane was dissected completely with the FSL and the free-floating membrane was removed. Histopathological evaluation confirmed the diagnosis of retained Descemets membrane (DM). There was improvement in uncorrected visual acuity from 20/300 to 20/50. Central corneal endothelial cell count was 810 cells/mm(2) preoperatively and 778 cells/mm(2) postoperatively. Inadvertent retention of DM may be safely treated with the FSL. Clarity and viability of the existing graft can be maintained.

INTRODUCTION

Femtosecond laser is a near infrared laser (1053 nm wavelength) with a very short pulse duration (10−{15} s) that is being used for a variety of applications in ophthalmology. It can be focused precisely at different depths within the anterior chamber to create incisions by photodisruption. Femtosecond laser was originally used in refractive surgery in 2001 for the creation of laser in situ keratomileusis flaps. Recently, the femtosecond laser has been approved for use in cataract surgery including the creation of corneal wounds, astigmatic keratectomy, capsulotomy and nuclear fragmentation of the crystalline lens. In this report, we discuss the novel use of femtosecond laser in a case of retrocorneal membrane after penetrating keratoplasty.

CASE REPORT

A 22-year-old male underwent penetrating keratoplasty for keratoconus in his left eye at another facility. He underwent intracameral air injection in his left eye at 1-week and 6-weeks postoperatively for an assumed diagnosis of DM detachment. Ten months later, the patient presented to our clinic with blurry vision in the left eye. On examination, his uncorrected visual acuity was 20/300 and intraocular pressure was 17 mmHg. Slit lamp microscopic examination indicated a clear graft with few folds and pigmented keratic precipitates. The anterior chamber showed mild flare and no cells. There were peripheral anterior synechiae and a mild fibrotic membrane over the crystalline lens [Figure 1a]. The patient was diagnosed with a retrocorneal membrane that gave the appearance of a double anterior chamber.

Figure 1

(a) Slitbeam microscopic image shows attached, clear penetrating keratoplasty graft with old pigmented keratic precipitates. A retrocorneal membrane with folds and a “double anterior chamber” is apparent. (b) Anterior segment optical coherence tomography image shows a retrocorneal membrane with apparent double anterior chamber. (c) A centered and round membranotomy in a retrocorneal membrane is apparent postoperatively. (d) Anterior segment ultrasound biomicroscopy image shows peripheral segments of retained Descemets membrane postoperatively

Further work up included specular microscopy and anterior segment optical coherence tomography (OCT). Endothelial cell count was 850 cells/mm2. The anterior segment OCT showed a retro-corneal membrane with double anterior chamber [Figure 1b].

Extensive discussion occurred with the patient regarding the diagnosis as well as potential treatments. The use of the femtosecond laser was discussed. The patient was fully aware that the femtosecond laser was not indicated for such procedures and the proposed treatment was considered off-label and experimental. In addition, the patient was informed that the risks of femtosecond laser treatment for retrocorneal membrane were not fully understood. The patient consented to proceed with femtosecond laser-assisted surgical intervention for removal of the retrocorneal membrane. An informed consent was obtained from the patient.

Removal of the retrocorneal membrane with femtosecond laser was planned. The patient was taken to the femtosecond laser machine (LenSx®, Alcon Inc., Fort Worth, Texas, USA). The anterior capsulotomy was the only mode selected on the laser. After preparation of the patient with topical anesthetic and povidone-iodine solution, docking with good suction was achieved. The laser software automatically recognized the anterior lens capsule. The laser beam was manually changed and moved anteriorly to focus the laser spots on the retrocorneal membrane instead of the anterior capsule.

Dissection of the membrane was assumed to require more energy than a lens capsulotomy. Thus, the total energy was increased to 15 μJ. The laser settings were adjusted as follows: Circumference was 5.5 mm, spot separation was 3 μm, and line separation was 2 μm. Gates were set at 325 μm up and 375 μm down.

After completion of laser treatment, the left eye was prepped and draped in the usual sterile fashion for ophthalmic surgery. The patient was transferred to the operating microscope. A 2 mm limbal corneal incision was made. An ophthalmic viscoelastic device (OVD) was injected into the anterior chamber. The retrocorneal membrane was removed with capsulorhexis forceps. The membrane was completely dissected and no tags were present. The OVD was removed from the anterior chamber with an irrigation and aspiration cannula. The wound was closed with a 10-0 nylon suture.

Postoperatively, the patient was prescribed topical prednisolone acetate (1%) and moxifloxacin hydrochloride (0.5%) 4 times a day.

On the first postoperative day, UCVA was 20/125 and intraocular pressure was 16 mmHg. Slit lamp microscopy indicated a clear corneal graft; a well-centered 5.5 mm opening in the retrocorneal membrane, a deep anterior chamber with occasional cells and a clear lens. On the third postoperative week, UCVA improved to 20/50 and the intraocular pressure was 16 mmHg. The corneal graft was clear and the anterior chamber showed no cells or flare [Figure 1c].

Postoperative investigations included tissue histopathology that established the diagnosis of retained DM. Ultrasound biomicroscopy showed retained segments of peripheral DM [Figure 1d]. Specular microscopy showed a minimal decrease in endothelial cell count to 778 cells/mm2.

DISCUSSION

Retained DM is an uncommon complication of penetrating keratoplasty. It has been postulated that edematous recipient cornea facilitates separation of DM, which predisposes to incomplete trephination and retained DM.12

Retained DM can threaten graft viability and clarity by compromising the endothelial cells either by direct contact or by limitation of aqueous nutrient diffusion.23 Removal of retained DM is indicated when it threatens the graft viability or jeopardizes visual acuity through opacification. There are some reports in the literature describing different techniques to remove the retained DM by surgical excision. Such techniques involve more intraocular manipulation and potentially more damage to the corneal endothelium.456

There are reports of the use of the neodymium-doped yttrium aluminum garnet (Nd: YAG) laser to create an opening within the membrane over the visual axis to restore vision.78 Such openings are typically rather small. Further, it has been reported that Nd: YAG laser capsulotomy and iridotomy affect the corneal endothelium.9 If the Nd: YAG laser is moved closer to the endothelium, the expected damage could increase, especially for peripheral laser application.10 Reports of Nd: YAG laser treatment for retrocorneal membrane do not report a comparison of pre- and post-operative endothelial cell count.

In our case, the femtosecond laser was used to create an opening within the retained DM, which was easily removed with forceps. Advantages of this technique are: Precise and controlled diameter of membranotomy, reduced surgical manipulation, which reduces endothelial cell damage, and rapid visual recovery. The disadvantages compared to Nd: YAG capsulotomy include the higher cost and intraocular surgery with the attendant potential complications.

To our knowledge, this is the first report of removal of retained DM by femtosecond laser. In addition, this is the first report that compares pre- and post-operative endothelial cell counts. Membrane opacification due to DM retention have been reported to decrease visual acuity postoperatively.3 This may be due to fibroblastic activity of the keratocytes in response to the remaining stroma that is adherent to the DM.

CONCLUSION

The FSL can be used to safely remove retained DM. It results in a perfectly centered and round membranotomy, with minimal effect on the corneal endothelial cells. The major advantages of the FSL over manual removal of retained DM are reduced operative time and reduced intraocular time. This may reduce the stress on the endothelial cells as well as postoperative inflammation. However, other studies have not reported on pre- and post-operative endothelial cell count for objective comparison of the two techniques. Additionally, only one peripheral corneal incision was needed in our case as compared to 2–3 incisions for manual techniques. The lower number of incisions may reduce the opportunity for bacterial ingress into the eye and thus lessen the risk of postoperative infection. Furthermore, the lower intraocular manipulation in this young phakic patient avoided the risks of potentially violating the anterior lens capsule or the endothelial cells of the graft. The disadvantage of the FSL-assisted DM removal to manual technique is the added equipment and costs associated with the FSL. The FSL can be safely used to remove a postoperative retrocorneal membrane.

Financial support and sponsorship

Unrestricted grant from the Michael O’Bannon Foundation.

Conflicts of interest

There are no conflicts of interest.