Internal limiting membrane (ILM) removal is recognized as a useful surgical approach for treatment of different macular surface diseases. The surgical technique, however, for ILM peeling is demanding in terms of time and skill. Challenges include poor visibility of the thin transparent membrane and the small dimensions and the sensitivity of the macular tissue, which increase the risk of iatrogenic damage from surgical manipulation. These factors increase the risk of iatrogenic damage.
INDICATIONS FOR ILM PEELING
The indications for ILM peeling have been expanded
to many different macular conditions. The primary indications
include idiopathic macular hole and macular
pucker (primary or secondary). Recently, studies and
reports have described the effectiveness of ILM removal
in pseudo-hole cases in myopic eyes,1 chronic diabetic
macular edema (DME),2-8 and vein occlusive diseases
such as central retinal vein occlusion (CRVO) or branch
retinal vein occlusion (BRVO).3-14
It has been recommended that ILM peeling be performed after silicone oil removal to prevent late postoperative complication such as secondary macular pucker.15
PATHOGENESIS
The mechanical and degenerative theories of macular
surface pathologies have been investigated in many centers
worldwide. Newly formed collagen and glial cells,
macrophages, myofibroblasts, fibrocytes, retinal pigment cells, and fibrous astrocytes are responsible for the tangential
traction and have been identified on the ILM and the
epiretinal membrane (ERM) surface.16-18 The collagen formation
and cellular matrix cause wrinkling of the ILM and
increase in tangential traction to the foveal tissue. This
traction, originating in the acellular prefoveal vitreous,
appears to be the initial cause of anterior-posterior traction
that leads to hole formation. Further hole enlargement
is due to myofibroblastic contraction on the ILM.
The sophisticated development of optical coherence tomography (OCT) technology has revolutionized our understanding of the nature of these degenerative conditions. The OCT has become the gold standard in clinical evaluation of the disease's staging and a reliable method of estimating surgical outcomes.
Since the initial report of vitreous surgery for idiopathic macular hole by Wendel et al,19 different ILM peeling techniques have been described that improve the anatomic closure of the macular hole.
I have developed the one-drop technique, which uses a minimal amount of staining for visualization and a minimal amount of surgical manipulation.
PHACOEMULSIFICATION/IOL
IMPLANTATION
All cases in this report were performed under local
anesthesia and general sedation with combined phacoemulsification
and three-port 23-gauge microincisional
vitrectomy surgery (MIVS). I prefer to insert the
23-gauge transconjunctival ports prior to beginning
phacoemulsfication. Special attention must be paid to
secure the infusion cannula within the vitreous, and we
use conjunctival displacement to construct sclerotomies
with watertight architecture (Figure 1). A oneor
two-step sclerotomy technique can be employed.
For cataract removal, I create a clear corneal incision
(Figure 2) and after phaco I implant a posterior-chamber
IOL. The IOL must be positioned behind the anterior
capsulorrhexis edge to prevent dislocations or malpositioning,
especially in macular hole cases, in which
we will be using a gas bubble and having the patient
posture postoperatively (Figure 3). I do not fill the
anterior chamber with an ophthalmic viscosurgical
device. I recommend slight hydration of the corneal incision to maintain an appropriate anterior chamber
depth during the posterior segment portion of the surgery.
I suture our corneal incisions only if there is significant
leakage and flattening of the anterior chamber. I
use a coating on the cornea to maintain visual clarity
to the posterior pole.
VITRECTOMY
Before beginning vitrectomy, I recommend rechecking
the position of the infusion cannula to ensure that it is
stable within the vitreous cavity.
I start the core vitrectomy using a moderate cutting rate and high vacuum (Figure 4). If a posterior vitreous detachment (PVD) exists, I do not force with shaving the vitreous base to enhance the removal of posterior hyaloid; in the absence of PVD, I induce a PVD by using my cutter for posterior hyaloid separation. Posterior hyaloid removal requires good visualization of the retinal periphery and adequate machine settings—I use high cut rates and low vacuum to reduce the mechanical stress on the surface. To reduce sclerotomy-associated vitreous incarceration and postoperative retina detachment or endophthalmitis, I am careful to remove all visible vitreous fibers with the cutter from trocars until I get free passage of balanced salt solution. Bimanual scleral indentation can be used to detect any retinal breaks or holes in the periphery, with special attention paid to areas of thinning or lattice dystrophies. For areas that are suspect, I apply endolaser.
The 3D settings on the Accurus Surgical System (Alcon Laboratories, Inc.) are effective in reducing surgical time and surgically induced trauma to ocular tissues when combined with good footpedal balance and eye-hand coordination.
ILM REMOVAL
ILM removal can be divided into two stages. The first
is dependent on the vitrectomy system in terms of its
ability to cut and remove the vitreous and posterior
hyaloid membrane. The second, and most important,
stage of ILM removal almost always relies on the manual
skills of the surgeon. After completing the vitrectomy,
I perform fluid-air exchange with passive aspiration
using the Charles Flute cannula (BD Visitec, Waltham,
MA). I introduce the dye to the surface of the macula
carefully with one drop, mixing either Mono Blue 0.25%
(trypan blue; Arcad Ophtha, Launac, France) or Brilliant
Peel (trypan blue; Geuder, Heidelberg, Germany) with a
small amount of residual balanced salt solution (Figure
5). Gentle rotational movements can be applied to
encourage the dye to spread over the surface of the
macula, painting the area between the vascular arcades
(Figure 6). Using passive aspiration, the dye can be easily
removed after 10 to 15 seconds without reducing the
quality of visualization. The coating that is applied to
the cornea, along with the use of a disposable central
contact lens, provides 3D high definition of the macular
structures.
STEPS IN THE SURGICAL TECHNIQUE
After the dye is removed and air-fluid exchange is
performed, the ultrastructures are exposed and, with
the help of an MVR blade, the first flap or strip of the
ILM or ERM can be gently manipulated and dissected
(Figure 7). This first flap must be made temporally or
diagonally parallel to the axons in the parafoveal area. I
grip the most visible edge of the ILM with Eckhardt forceps
(DORC, Zuidland, Netherlands) which are
designed to grasp the ILM with minimal contact with
the underlying retinal surface. The light source must be
adjusted away from the fovea in an angled manner to
minimize phototoxicity. Additionally, the angulation of
light creates a better shadow for visualization of the distance
between the retina and the instruments. The various
divergence angles can also be used for spot or
floodlight effect—wide illumination produces more
uniform contrast (Figure 8).
Grasping the ILM by the edge, as noted above, allows me to slow the movement (Figure 9). It is crucial to grasp the proximal edge (the edge nearest to the retina surface) of the flap and to guide the movement away from the retina; it is also important not to tear the flap (Figure 10). By controlling the speed with which the ILM is peeled and the direction of movement, it is easier to maintain control over the shape and diameter of the macularrhexis with minimal touch to the retinal layer. During ILM removal, one must avoid the small areas of preretinal bleeding that will appear. As peeling progresses, it becomes easier to identify the stained ILM from the naked retinal surface. The gentle manipulation of the ILM tissue without tearing gives the opportunity to complete the peel in one strip. If some residual ILM material is attached to the macular hole edge, it is important that it not be forced because the macular tissue may be torn radially. The best approach is to cut it with the vitrector or curved scissors. I do not recommend aspirating with the cannula because this can lead to a permanent defect in the retinal pigment epithelial (RPE) layer.
In cases of macular pucker, the ERM edges can be easy to identify and begin to grasp and peel. Peeling both the ERM and the underlying ILM is possible to perform using the same technique. If the ERM is separated from the ILM, dye staining can be repeated. In cases of diffuse DME, the adhesion of the ILM to the macula is stronger, and the manipulation must be more delicate. Repeated staining may be indicated. At the close of the procedure, I recommend removing the trocars one by one and using a gentle massage technique. I switch off the infusion before removing the last cannula (Figure 11). I apply an injection of antibiotic mixed with steroid deep into the sub-Tenon space (Figure 12).
SPECIAL SURGICAL CONSIDERATIONS
Following are some points for consideration using the
one-drop technique:
- The visualization of ILM vs ERM can depend on the degree of retinal pigmentation; it has been noticed by many surgeons that ILM removal is easier in dark pigmented eyes.
- Some surgeons have reported green light illumination to be beneficial, but I have no experience with this technique.
- Indocyanine—green (ICG)-assisted ILM peeling remains the gold standard worldwide, but this has proved to be toxic to the retinal ganglion cells and the RPE.
- Blood- and triamcinolone-assisted ILM peeling have not been proved superior to ICG.
- A diamond-dusted sweeper is an effective device to peel strong adhesive ILM, particularly in cases of DME and young patients.
- In the majority of cases, we have noticed that peeling can cause insignificant axon edema, which results in two different shades of colors in the naked retina and the remaining membrane. These color differences can provide valuable feedback regarding the peeled area's zone, shape, and diameter.
- Several experts recommend that peeling should begin temporally at least two disc diameters outside the parafoveal zone, especially in cases of macular hole with elevated edges seen on OCT. Peeling must be performed away from the hole, outside the maculopapillary bundle, and preferably not over the large retinal vessel.
- The diameter of the macularrhexis must include the area between the arcades to release the mechanical traction. Hypothetically, a large diameter will relieve the macular surface, and the micro-migration of the tissue will cause the anatomic closure of the hole.
ADVANTAGES/DISADVANTAGES
Using dye under air has the following advantages: 1)
only a small amount of dye is required; 2) the dye needs
to stay in the eye for only a short duration of time; 3) it
is easy to inject and easy to remove; 3) it can be placed
selectively above the zone that will be peeled; 4) there is
minimal penetration of the dye into the retinal tissues;
5) it is easy to spread over the macular surface; 6) there
is no incidence of staining the lens capsule or loss of visualization; 7) it has low toxicity and lowers the risk of
phototoxicity; and 8) the dye makes is easy to identify
the edges of the ILM.
The possible disadvantages of this technique include: 1) in some cases, more than one or two drops is required; 2) if the staining is found to be inadequate, a repeat procedure will be necessary; and 3) after air-fluid exchange some air bubbles may escape above the anterior hyaloid, necessitating an anterior vitrectomy and the reduction of dye concentration above the macular surface.
The one-drop technique requires careful manual dexterity, but the learning curve is relatively short for the experienced vitreoretinal surgeon. There are studies suggesting trypan blue has a less toxic effect on retinal cells compared with ICG staining.20,21 By minimizing the duration of exposure and the amount we use, however, any residual harmful effects of trypan blue to the retinal ganglion cells, retinal pigment epithelium, and photoreceptors can be minimized.
CONCLUSION
The goals of macular hole surgery are to achieve
anatomic closure of the hole and to achieve good functional
results. Minimizing the use and duration of use of
staining dye can dramatically reduce the toxic chemical
damage to the retinal ganglion cells and RPE. The correct
use of the illumination in terms of its intensity and
angulation can minimize the phototoxicity to sensitive
photoreceptors. It is important to correctly understand
forceps design, the multiple grasp-and-peel technique,
and how to guide the speed and direction to skillfully
manipulate the ILM and ERM with the least iatrogenic
trauma to the retinal surface. This technique will provide
better safety and lower toxicity, and it my hope
that ICG be retired permanently from retinal surgery.
I would like to express my thanks to Zoran Tomic MD, for his scholarship and to the surgical staff at Eye Clinic, Uppsala University, Sweden. I would also like to thank Samer Saher, MD, for his generous review and valuable comments.
Wamidh Simawi, MD, is a cataract and vitreoretinal surgeon who has practiced at Uppsala University Eye Clinic, Sweden. He performs his current refractive and cataract surgeries at Capio Medocular AB in Uppsala. Dr. Simawi has no financial interests regarding any products mentioned in the article. He can be reached via e-mail at wamidh.simawi@capio.se; or wamidh.simawi@ste.ki.se.
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