**12. ILM peeling technique**

### **12.1 Initiation**

The creation of an ILM flap is a crucial step in ILM peeling. The ideal starting point has been suggested as about 1000 microns above or below the fovea. A small ILM tear is created on the retinal surface by scraping the retinal surface with a diamond-dusted or using picks, bent MVR blades or with dedicated ILM forceps using a pinch and peel technique. Many surgeons utilise custom-designed micro forceps to pinch and lift the ILM and create a small flap to then grasp and customise the direction and shape of the desired flap (**Figure 10**).

### **12.2 Flap creation**

Vitreoretinal forceps and the diamond-dusted membrane scraper are valuable tools for flap creation [54]. The majority of surgeons tend to peel an ILM area of about one disk diameter around the fovea, releasing enough retinal tissue in order to allow macular hole closure (**Figure 11**). A broader area of ILM up to 3 disk diameters may be removed to improve retinal compliance and subsequent retinal closure but it is still unclear regarding the exact dimension of ILM removal needed.

**Figure 10.** *The finesse SHARKSKIN ILM forceps.*

**Figure 11.** *ILM flap folded over the macular hole.*

## **12.3 Side effects**

ILM peeling is one of the most demanding procedures in ophthalmic surgery requiring a high level of manual dexterity. Retinal damage can occur at the initial ILM flap creation point resulting in retinal haemorrhages and nerve fibre layer damage as well as iatrogenic eccentric retinal holes have been reported [55]. A peculiar retinal alteration in the area where the ILM is removed has been described as Disassociated

Optic Nerve Fibre Layer (DONFL) with a characteristic change in inner retinal morphology and appears related to Muller cell end plate damage [56–58].

#### **12.4 ILM peeling variants**

#### *12.4.1 Foveal sparing peeling*

This technique entails ILM removal but sparing a circular area of 400 microns around the MH rim. In a study by HO [59] foveal sparing resulted in better visual acuity and postoperative anatomy, based on the concept that Muller cells are important for maintaining foveal architecture. Muller cells may improve light transmission to the photoreceptors [60]. In a study by Morescalchi [61], a total of 46 eyes had macular hole surgery and were randomly allocated to complete or foveal-sparing peeling. The latter group demonstrated a greater increase in foveal sensitivity following surgery. Muller cells preservation may therefore provide a better functional outcome after macular hole surgery [62, 63].

#### *12.4.2 ILM abrasion*

Mahajan [64] reported a different procedure to reduce trauma during ILM removal by using a diamond-dusted membrane scraper (DDMS) in circumferential and centripetal motions around the MH. This procedure was thought to encourage glial cell activation, losing ILM attachment to the underlying retinal tissue and ultimately encouraging MH closure.

ILM peeling was initially described in 1997 by Eckardt [25]. The rationale for ILM peeling was the removal of residual adherent vitreous cortex remnants, thereby increasing retinal compliance. ILM serves as a scaffold for cellular proliferation, and its removal should encourage MH closure. Peeling the ILM ensures the thorough removal of any tangential tractional components implicated in the development of macular holes. The removal of a potential scaffold for the re-proliferation of myofibroblasts may reduce the possibility of late reopening of surgically closed holes. Furthermore, peeling off the ILM is also believed to stimulate wound healing at the macula, possibly by inducing local expression of growth factors that promote glial repair (**Video 1**, http://bit.ly/433B3XW).

The Cochrane database of systemic reviews concluded in 2013 that there was enough evidence to support the positive effects of ILM peeling for stages 2–4 idiopathic MH's to improve the primary anatomical hole closure rate, although no clear benefit was found for small holes [24].

ILM peeling increases the likelihood of successful macular hole closure, but it has been suggested that the extra manipulation of this membrane at the time of surgery could be harmful to the retina.

Swelling of the arcuate nerve fibre layer after internal limiting membrane peeling was described by Clark [65]. Electrophysiologic studies using focal macular electroretinogram showed a delayed recovery of the b-wave 6 months after macular hole surgery in eyes that underwent ILM peeling compared to those without peeling [66].

Although anatomical closure achieved after complete ILM peeling was associated with improved visual outcomes, the rate of anatomic closure was inversely correlated with the extent of ILM peeling actually achieved. It was suggested that excessive unsuccessful attempts at ILM peeling might enhance anatomic success (possibly

through enhanced promotion of glial healing) at the expense of poorer visual outcomes, presumably resulting from damage to inner retinal elements [67].

Inner limiting membrane peeling appears to improve the rate of anatomical closure, but its effect on visual outcome is less predictable and unsuccessful attempts to peel the ILM are associated with poor visual outcome. While ILM peeling may be performed for full-thickness macular holes of any stage, it is more commonly reserved for stage 3 or 4 holes, long-standing holes, those that have failed to close, or those that have re-opened following conventional surgery.

ILM peeling is thought to be beneficial for macular hole closure and in particular for large holes, however, it may also cause side effects on retinal anatomy and functionality. Retinal changes described after ILM peeling included inner retinal dimpling [68], dissociated retinal nerve fibre layer (RNFL), [69] and reduced parafoveal retinal thickness [70].

#### **13. Internal limiting membrane peel extension**

ILM peeling has improved surgical success in MH surgery. The ILM can be removed using forceps, diamond dusted scraper or other surgical tools and it has been suggested that at least 2 disc diameter (DD) of ILM should be removed around the fovea. Different surgeons perform this delicate procedure using peel radii from 0.5 to 3 DD. Bae et al. [71] compared peel sizes of 0.75 DD versus 1.5 DD and showed that a larger ILM peel lessens postoperative metamorphopsia. Modi et al. [72] have shown similar results in MH closure rates with 3 mm versus 5 mm peel sizes. No consensus on optimal peel width exists, but case reports of wide peels having success in large MHs have led many surgeons to peel ILM up to the arcades [73].

#### **13.1 Macular holes >400 microns**

In macular holes <400 microns conventional ILM peeling provided better functional outcomes compared with the inverted flap technique and should be advocated [74].

FTMH above 400 microns have a reduced rate of success with standard surgery, and other techniques such as ILM flaps and retinal expansion may be preferred for these macular holes [7]. Vitrectomy with the inverted ILM flap technique seems to be effective surgery for large idiopathic and myopic MHs, improving both functional and anatomical outcomes in a study by Rizzo [75] and surgical closure in all patients is reported in a study by Yamashita [76].

The practice of using the ILM on top of a macular hole has many effects, such as a bandage, isolating the retinal hole from the vitreous fluids, as a scaffold stimulating glial tissue proliferation, and will all encourage hole closure. In a study by Michalewska et al. [19] the use of ILM flap increased the rate of MH closure up to 98% for large MHs. This technique has also resulted in a 100% macular hole closure rate in myopic MH's reported in some studies [77, 78].

ILM flaps can be divided into two groups, inverted and non-inverted flaps: Inverted flaps


These flaps require the presence of ILM still hinged around the hole or near the hole in order to prevent displacement of ILM in the vitreous cavity. Michalewska [79] describes a procedure where the ILM is engaged with ILM forceps and removed almost in its entirely around the macular hole but a tiny residual attachment is left in place. Folded ILM is then packed inside the MH rather than a flap covering it. ILM is massaged into the MH from all sides until it becomes inverted and may be described as an 'ILM plug'. At a microscopic level, the presence of this plug may hamper outer retinal layer healing and prevent visual acuity recovery by interfering with photoreceptor reconstitution [80]. ILM tissue however is also known to work as a scaffold for tissue proliferation, promoting photoreceptors restoration and providing guidance for the correct positioning of the cells [81]. Rossi [82] stated that by using the fill technique, the ILM acts as a filler, glue, and scaffold all at the same time.

Shin [83] first introduced a true flap technique (single-layered flap of the ILM) for covering MH's (larger than 400 μm) with the assistance of perfluoro-n-octane (PFO) in 2014. Perflurocarbon liquid allows ILM flap stabilisation during fluid-air exchange by reducing dislocation or flap loss.

The temporal inverted internal limiting membrane flap was described by Michalewska [79]. The nasal ILM was left in place to protect the tissue from surgical trauma and lessen the occurrence of dissociated optic nerve fibre layer (DONFL).

The opposite approach has also been described and named the "Texas taco" [84]. This procedure involves peeling the nasal ILM and then it is folded temporally to cover the MH.

Ghassemi et al. [85] investigated the results of different ILM flap directions. The techniques used were a hemi circular ILM peel with a temporally hinged inverted flap, a circular ILM peel with a temporally only hinged inverted flap and a circular ILM peel with a superior inverted flap. Similar results were obtained with all flap directions.

Aurora [86] described the Cabbage Leaf Inverted Internal Limiting Membrane Flap technique. Three inverted ILM flaps sealed the hole looking like cabbage leaves. These flaps were connected to the edge of the MH, trimmed and flipped over the MH, one above the other like seen with cabbage leaves.

In cases when the central ILM had already been removed during previous surgery, Tabandeh [87] described the SWIFT flap procedure. An ILM flap is fashioned from superior residual ILM then a narrow strip of residual ILM forms the base of the flap, which is positioned horizontally. The ILM flap is inverted over the macular hole and covers the MH and the retina inferior to the MH **Figures 12** and **13**.

Leisser [88] described a technique where a temporal ILM flap was prepared while the residual ILM around the MH was peeled to the rim of the MH, after which the ILM flap was positioned in an inverted fashion over the MH (**Figures 14** and **15**).

The pedunculated flap technique creates an ILM flap that covers the macular hole from the border of the previous ILM peel. The flap should be large enough to cover the region of the pre-existing ILM peel as well as the macular hole.

**Figure 12.** *SWIFT (superior wide-based FLAP transposition) FLAP.*

**Figure 13.** *Macular holes covered with inverted ILM.*
