Vitrectomy and Gas Tamponade with Internal Limiting Membrane Peeling for Myopic Tractional Maculopathy

Myopic Tractional Maculopathy (MTM) with foveal detachment, also known as myopic foveoschisis, is a condition that occasionally occurs in highly myopic eyes with posterior staphyloma [1,2]. The unique anatomical features of the highly myopic eyes, the presence of a traction induced by epiretinal membrane (ERM) and vitreomacular traction (VMT), and the rigidity of the internal limiting membrane have been presented as major causes [1-6] and have been confirmed in histologic studies [7,8]


Introduction
Myopic Tractional Maculopathy (MTM) with foveal detachment, also known as myopic foveoschisis, is a condition that occasionally occurs in highly myopic eyes with posterior staphyloma [1,2]. The unique anatomical features of the highly myopic eyes, the presence of a traction induced by epiretinal membrane (ERM) and vitreomacular traction (VMT), and the rigidity of the internal limiting membrane have been presented as major causes [1][2][3][4][5][6] and have been confirmed in histologic studies [7,8] In symptomatic patients with reduced vision or central metamorphopsia, various combinations of pars plana vitrectomy (PPV), internal limiting membrane (ILM) peeling, and gas tamponade have been shown to result in the resolution of myopic tractional maculopathy with visual improvement with different success rates [3][4][5][6]9,10]. The purpose of this study is to evaluate the outcome of vitrectomy and gas tamponade with ILM peeling for the treatment of highly myopic eyes with symptomatic visual impairment as a result of myopic tractional maculopathy.

Patients
The study adhered to the tenets of the Declaration of Helsinki and was approved by the Ethics Committee of Tehran University of Medical Sciences Eye Research Center (TUERC). This study and accumulation of data were in conformity with all country laws, and informed consent was obtained from all patients.
From September 2007 to June 2008, patients who underwent vitrectomy for MTM were consecutively included in the study. Inclusion criteria were progressive visual loss over the past 6 months presumably due to MTM associated with high myopia,metamorphobsia, absence of retinal tears, and absence of macular hole observed by optical coherence tomography (OCT). Exclusion criteria included age less than 18 years, myopia of less than 6 diopters, or presence of macular hole documented on OCT. The follow-up period was six months.

Surgical procedure
All surgeries were performed by one author (M.A). All patients underwent standard three-port PPV with 20 gauges. Phacoemulsification with implantation of intra-ocular lens was performed in patients with age greater than 50 years and patients with more than 2+ nuclear sclerosis cataracts. Posterior vitreous detachment (PVD) was routinely performed by using active aspiration. Any visible epiretinal membrane was gently removed with using intra-ocular forceps after visualization with triamcinolone. The ILM of 2-3 disk diameters was peeled after dying with Brilliant blue (BBG [Germany, DORC]) and triamcinolone. Finally, vitreous cavity was replaced with air and gas tamponade using 20% sulfur hexafluoride (SF6). Patients were instructed to maintain prone position postoperatively for one week.

Data Collection
Preoperative data included patients' demographics, duration of symptom, lens status, refractive error, and axial length. Preoperative and postoperative BCVA were measured by a certified optometrist with standard Snellen chart. Snellen BCVA was converted to logarithm of the minimum angle of resolution (logMAR) for statistical analysis. Intra-operative data included the presence or absence of posterior detachment and epiretinal membrane. Preoperative and postoperative OCT (Stratus OCT, Carl Zeiss Meditec, Dublin, CA) was performed using the default setting, which scans 6 mm vertically and horizontally on the retina; six "radial lines" scans centered on the fovea, one scan every 30 degrees, for complete evaluation of posterior pole. The height of foveal detachment defined as the distance between the inner surface of retinal pigment epithelium and the outer surface of the neural retina at the fovea was measured on the vertical scan mode using the retinal thickness mode of OCT application.

Statistical analysis
Statistical analyses were performed by computer (SPSS for Windows, ver.13.0). Normality was tested using the Kolmogorov-Smirnov test, and paired t-test was used for comparison of the groups. Data are expressed as mean ± SD. Differences were considered statistically significant when p < 0.05.

Patient's demographics
A total of eighteen eyes from 15 patients were recruited (Table 1). There were fourteen eyes from female patients (78%) and four eyes from males (22%). The mean duration of symptoms as described by the patients was 8.3 months (range, 3 to 30 months); preoperative symptoms included blurring of vision in 14 eyes and metamorphopsia in 4 eyes. Sixteen eyes were phakic before surgery and two eyes were psudophakic.

Intraoperative data
Pars plana vitrectomy combined with phacoemulsification and implantation of intraocular lens (IOL) [acrysof Alcone medical] was performed in eleven eyes (61%). Intraoperatively, eight cases had incomplete PVD and active aspiration to induction of PVD was done. An epiretinal membrane was found and removed in eleven (61%) eyes. No serious intraoperative complication including macular hole, peripheral retinal break or intraocular hemorrhage occurred.

Visual and anatomical outcomes
Postoperatively, thirteen (72%) eyes had improvement in BCVA at the last follow-up and four (22%) eyes remained unchanged; vision was decreased in one eye. Eight eyes (50%) had at least four lines improvement in the Snellen chart. Four (22%) eyes had a final BCVA of 20/80 or better, compared with no eye preoperatively. There was a statistically significant improvement in the mean BCVA from 1.3 ± 0.29 logMAR preoperatively to 1± 0.60 logMAR postoperatively (P <0.05, Table 1 and Table 2).
Postoperative OCT showed resolution of foveal thickness in all of the eyes. Complete resolution was seen in fourteen eyes (78%), and the remaining four eyes (22%) had partial resolution with reduction in the height of foveal detachment. The mean of foveal thickness decreased from 478 ± 226 microns preoperatively to 219 ± 79 microns postoperatively (P<0.0001, Table 1).

Postoperative complications
One patient (case #12) developed full thickness macular hole 2 months after surgery but did not progress to retinal detachment during follow-up period and no intervention was done. One patient (case # 8) developed retinal detachment three months after surgery and she underwent PPV with silicone oil tamponade. After two months she developed postoperative refractory glaucoma and filtration surgery with silicone removal was performed. Finally, glaucoma was controlled with retinal reattachment but visual acuity remained at hand motion at 2 ft.

Discussion
The mechanism of foveal thickening and MTM in highly myopic   [1] reported the presence of an epiretinal traction exerted by ERM or VMT in almost half of the patients with highly myopia. In their study one third of patients were presented with a form of retinal damage; macular schisis in 58% of cases followed by retinal thickening, lamellar hole, and shallow detachments.
They explained that ERM and vitreomacular adhesions generate a centripetal and/or internal traction which is greatly enhanced by the force exerted by staphyloma and progressive scleral stretching in highly myopic eyes. In another study, Ishida et al. [7] performed a pathologic examination on the epiretinal membranes harvested from highly myopic eyes. They reported that the ERM consisted of cortical vitreous and fibrous astrocytes as the major cellular compartment. The newly formed collagen in the cortical vitreous was suggested to be the source of the tangential traction on the retina.
The role of the epiretinal traction in the pathogenesis of this condition is also supported by a case report by Polite et al. [11] in which vitreofoveal separation resulted in the resolution of retinoschisis in an eye with myopia. Similarly, Takano and kishi [2] in a study on 32 highly myopic eyes with posterior staphyloma have pointed out the causal effect of tangential contraction of the premacular vitreous cortex and the contributory role of posterior staphyloma especially at the site of non-extensible retinal vessels.
Surgical release of this traction has resulted in favorable and stable anatomical results as well as improvement in the visual acuity, suggesting its pathogenic role in MTM (see below). In our study, complete or partially reattachment rate was nearly 95% and visual improvement rate was about 72%, although some may attributed to the cataract extraction which may be one of the limitation of this study; the final outcomes were almost similar with the previous studies. Kanda et al. [6] reported anatomical and visual improvements after PPV with ILM peeling and gas tamponade in two myopic foveoschisis. Kobayashi and Kishi [3] carried out a prospective study to evaluate the use of PPV with ILM peeling in patients with myopic foveoschisis. Foveal reattachment was achieved in eight eyes (89%) of nine eyes after surgery; one eye developed a micro hole at the macula during brushing of retinal surface with silicone tipped canula for removal of premacular vitreous cortex. All eyes had visual improvement postoperatively. In our study, during the vitrectomy after separation of posterior cortical vitreous the height of fovea dramatically decreased and after ILM peel which was thicker than normal ,the radiating folds stained by triamcinolone disappeared (Figure 1, Figure 2).One case developed a full thickness macular hole post operatively ( Figure 3) that did not progress to retinal detachment during follow-up. In another study conducted by Ikuno et al. [5] vitrectomy with ILM peeling was performed in six patients with myopic foveoschisis, five eyes (83%) had complete resolution of myopic foveoschisis and one eye had partial resolution. Although there was a lack of complete foveal reattachment in all cases, all cases had visual improvement postoperatively. In Pannozo and Mercanti study [4], they performed PPV with ILM peeling without gas tamponade in 24 eyes with MTM, 23 eyes (96%) had complete resolution and mean visual improvement was 2.5 Snellen lines and five eyes (21%) developed a macular hole. Dr. Pannozo has mentioned that this traction is generated by sheets of posterior vitreous cortex that adheres to the retina and bridges the borders of staphyloma in the presence of both false and true PVD.
In a small (9 eyes) case series by Kwok et al. [10]vitrectomy was performed without ILM peeling followed by gas tamponade. Patients were followed for 6 months and according to their report, results were comparable with other studies in which ILM was removed. Recently, Yeh et al. [9] reported similar results in a case report on 3 patients followed for more than 12 months. However, Futagami et al. [12] in their recent case report reattached the retina by ILM peeling for a patient with recurrent myopic foveoschisis after 3 years of an initial vitrectomy without ILM removal. They stated that peeling the ILM   may not only resolve the retinoschisis but also be effective to prevent a recurrence. In addition, a pathologic examination by Bando et al. [8] on ILM specimen excised from patients with myopic foveoschisis has found significantly more collagen fibers and cell debris compared to samples from eyes with idiopathic macular hole. Accordingly, ILM peeling seems to be an effective procedure to remove any residual epiretinal membrane, premacular vitreous cortex, collagen fibers and cellular compartments in order to relieve the macular traction more reliably.
In summary, vitrectomy and ILM peeling with gas tamponade appears to have favorable visual and anatomical outcome for treating MTM with posterior staphyloma and it may be recommended for highly myopic patients with recent visual acuity loss or metamorphobsia and signs of MTM on OCT images. Further prospective controlled studies in the future will be useful in demonstrating the effects of ILM peeling and gas tamponade on the outcome of vitrectomy for MTM.