ILM peeling with epiretinal membrane removal
Epiretinal membrane is a disease of the eye in response to changes in the vitreous humor or more rarely, diabetes. It is also called macular pucker. Sometimes, as a result of immune system response to protect the retina, cells converge in the macular area as the vitreous ages and pulls away in posterior vitreous detachment (PVD). PVD can create minor damage to the retina, stimulating exudate, inflammation, and leucocyte response. These cells can form a transparent layer gradually and, like all scar tissue, tighten to create tension on the retina which may bulge and pucker (e.g., macular pucker), or even cause swelling or macular edema. Often this results in distortions of vision that are clearly visible as bowing when looking at lines on chart paper (or an Amsler grid) within the macular area, or central 1.0 degree of visual arc. Usually it occurs in one eye first, and may cause binocular diplopia ordouble vision if the image from one eye is too different from the image of the other eye. The distortions can make objects look different in size (usually larger = macropsia), especially in the central portion of the visual field, creating a localized or field dependent aniseikoniathat cannot be fully corrected optically with glasses. Partial correction often improves the binocular vision considerably though. In the young (under 50 years of age), these cells occasionally pull free and disintegrate on their own; but in the majority of sufferers (over 60 years of age) the condition is permanent. The underlying photoreceptor cells, rod cells and cone cells, are usually not damaged unless the membrane becomes quite thick and hard; so usually there is no macular degeneration.
Several surgical techniques exist for the treatment of EMM. However, 3 basic stages of treatment exist.
- Pars plana vitrectomy is performed to excise the posterior and central vitreous in phakic patients and the remainder of the anterior vitreous in aphakic and pseudophakic patients. This step is especially important in cases where marked adherence of the vitreous to the macula is present.
- Lately, questions have been raised regarding the need for vitrectomy in EMM peeling, especially in those cases where no significant PVR exists.
- The main advantages of doing a vitrectomy are the prevention of vitreous contraction and elimination of vitreous traction on the macula. In addition, removal of the vitreous is believed by many to increase the safety of the mechanical aspects of the membrane removal.
- The main disadvantages of vitrectomy include cataractogenesis and increased possibility of creating iatrogenic retinal breaks. Vitrectomy has been shown to increase the rate of cataract formation through unclear mechanisms.
- Studies have shown that a 3-fold increase in the rate of significant cataract formation exists in patients that have undergone vitrectomy after a follow-up period of only 6 months.
- Some surgeons feel that the effectiveness of membrane peeling is negated significantly by the cataract formation such that they have foregone vitrectomy in selected cases, opting to perform no-infusion/no-vitrectomy membrane peelings. The main disadvantage of this technique is the persistence of floaters postoperatively, which may be very bothersome to some patients. Furthermore, some surgeons have seen no significant difference in either cataractogenesis or development of retinal breaks/detachments in their series comparing vitrectomizing and nonvitrectomizing techniques.
- While the vitrectomy can be performed using the standard 20-gauge system, surgeons are also using smaller gauge vitrectomy systems (eg, 23 gauge, 25 gauge) for surgical management of EMM.[6, 7]These systems are transconjunctival with the potential to create self-sealing wounds. Complications appear low while affording the potential for more rapid surgical and visual recovery.
Epiretinal membrane peeling
- From the time Machamer developed the concept of membrane peeling in the mid 1970s, several variations and refinements in both technique and instrumentation have been developed.
- This procedure basically involves identifying the outer edge of the membrane and creating a dissection plane with the use of a blunt-tipped pick or a bent needle.
- Once the edge of the membrane is seen, it may be gently lifted off the retinal surface with the use of a pick or fine forceps.
- The membrane should be lifted in a tangential rather than an anteroposterior fashion so as not to pull on the underlying retina and create tears. This maneuver is relatively straightforward if the edge of the membrane is visible.
- Charles developed a maneuver that approaches the membrane from inside out in cases where the edge is difficult to identify. It involves creating a slit on the thickest part of the membrane with a straight microvitreoretinal blade and using this opening as the edge with which to start the peeling. The peeling is performed moving the forceps in a circular fashion similar to capsulorrhexis. The freed membrane should be removed either by pulling it out with the forceps through the sclerotomy or by using the vitreous cutter.
Internal limiting membrane (ILM) peeling
- Removal of the ILM at the time of EMM peeling is a current controversy.
- Vital stains, such as indocyanine green (ICG) dye and Trypan blue dye, have been used to assist ILM and EMM peeling. Dyes that stain the ILM highlight foci of EMM and potentially reduce the risk of recurrence or the persistence of symptoms.
- Similar to its use in macular hole surgery, the use of ICG has proponents and detractors on the basis of its potential toxic effects. Haritoglou et al suggested that ICG-assisted ILM peeling may adversely affect the functional outcome of surgery for EMM.[9, 10]
- Hillenkamp et al prospectively evaluated the effect of ICG dye in the setting of EMM surgery. No difference or evidence of ICG toxicity was observed. Both visual function and macular morphology improved in patients with and without ICG dye use.
- However, Garweg et al suggested that ILM peeling with ICG dye, but not with trypan blue dye, may result in loss of the central visual field over time. No difference in visual acuity was noted. This study suggests that the ICG dye, not necessarily the ILM peeling, may have an adverse effect following EMM surgery.
Management of retinal breaks
- Once the membrane is removed, it is imperative for the surgeon to look for any breaks in the retina, both in the posterior pole and in the periphery.
- Any maneuvers completed to remove the membranes, no matter how elegant, become irrelevant if the retina detaches because of missed breaks.
- Careful scleral depression of the anterior retina combined with indirect ophthalmoscopy should be performed to detect breaks in the periphery.
- Breaks without subretinal fluid accumulation can be treated by laser retinopexy or cryoretinopexy.
- The presence of significant amounts of subretinal fluid necessitates internal drainage under air, retinopexy, and gas tamponade.