ILM Peeling and Multifocal IOLs

Visualization can be difficult to obtain in such cases.

STEVE CHARLES, MD, FACS, FICS

Surgeons have expressed theoretical concerns about visualization when vitreomacular surgery is performed in the presence of multifocal intraocular lenses since these IOLs were first approved. As is often the case, the issues are far more complex than visualization issue.

ILM PEELING

Internal limiting membrane peeling was first described for full-thickness macular hole surgery, but the indications have dramatically expanded over the past two decades. Wollensak et al¹ showed that ILM peeling in an experimental setting increased the compliance of the retina by more than 50%.

Basically, ILM peeling causes the retina to become highly flexible instead of taut. A more flexible retina enables the interfacial surface tension effect of a gas bubble to reapproximate the edges of a macular hole. In addition, ILM peeling ensures that all posterior vitreous cortex remnants, as well as epiretinal membrane traction, have been removed.

I have previously noted that the gas bubble prevents fluid flow into the retina, which in turn results in the resolution of the edema surrounding the hole, as well as through the hole, facilitating closure by interfacial surface tension. I have stressed the importance of ILM peeling when operating on symptomatic partial-thickness macular holes, as well as the necessity of using SF₆ to restore normal or near normal foveal architecture in these cases.

Kampik and colleagues² emphasized the importance of ILM peeling in epimacular membrane surgery because it reduced recurrence rates, presumably because the ILM acts as a basement membrane attachment site for the modified astrocytes implicated in glial recurrence.

I have emphasized that ILM peeling also results in intraoperative elimination of retina striae because the ILM is an elastic structure that maintains retinal folding once it occurs. Air or gas surface-tension agents have no place in epimacular membrane surgery.

In my opinion, ILM peeling is necessary in vitreomacular traction syndromes and particularly macular schisis cases to increase retinal compliance. ILM peeling is especially crucial in the presence of a posterior staphyloma, to allow the retina to stretch sufficiently to conform to the retinal pigment epithelium in the staphyloma.

Recently, I have utilized ILM peeling to manage macular folds caused by inadequate technique when performing fluid-air exchange and internal drainage of subretinal fluid in rhegmatogenous retinal detachment surgery.

This technique has been effective in a small number of cases and does not require redetachment of the retina, liquid perfluorocarbon, or gas. ILM peeling has also been used to treat hypotony maculopathy with excellent results in a large series from Spain.³

VISUALIZATION

The ILM is approximately 3 µm thick, transparent, acellular, and colorless. It is adherent to the anterior surface of transparent, colorless retina, varying from 200 µm to more than 1,000 µm in thickness with certain disease processes.

The stereo resolving power of the operating microscope is barely sufficient to determine the z-axis (depth) location of the ILM on the anterior surface of the retina. Multifocal IOLs make visualization of the ILM somewhat more difficult.

Optimal choice of intraoperative visualization methods makes ILM peeling safer and more effective in all cases, but especially in multifocal IOL cases. Unfortunately, many surgeons still utilize noncontact visualization for vitreomacular surgery.

Unlike noncontact visualization, surgical contact lenses eliminate all corneal asphericity, which is exceptionally common because of prior cataract surgery, LASIK, photorefractive keratectomy, radical keratotomy limbal relaxing incisions, penetrating keratoplasty, Descemet’s membrane epithelial keratoplasty, corneal lacerations, and pterygium surgery.

Contact lens–based visualization should be used for all macular surgery and diabetic traction retinal detachment surgery; the modulation transfer function is far superior to noncontact visualization.

Although staining of the ILM was introduced to determine the presence or absence of ILM in the plane of the retina, I have made the point that a significant advantage of staining is identifying the z-axis location of the transparent ILM to enable precise depth positioning of ILM forceps tips.

Brilliant blue G (BBG) has been shown to be the only safe and effective stain by Kampik and colleagues,² as well as Farah and Maia’s group.³ Unfortunately, many surgeons still use indocyanine green staining, although numerous papers have shown it to be toxic, presumably because BBG is not FDA-approved.

BBG is clearly off-label, and it must be prepared by a compounding pharmacy. Many surgeons simply do not have access to BBG because of the off-label status. BBG is safe because it is dissolved in balanced saline solution, while ICG is dissolved in water; BBG is not fluorescent, so there is less risk of phototoxicity. It has a stable pH and optimal osmolarity, and there is no need to infuse under air. Most importantly, with BBG, the surgeon can stain the ERM and then stain again, multiple times if necessary, to peel the ILM.

Triamcinolone acetonide is not a stain; it is a particulate marking agent developed to enhance visualization of the vitreous. It does not stain the ILM; the presence or absence of particles simply tells whether something has been peeled. Use of triamcinolone for ILM peeling increases the likelihood that ILM will be left behind.

REFRACTIVE ISSUES AND VISUAL FUNCTION

New technology IOLs, refractive surgery in general, small-incision cataract surgery, and femtosecond laser–assisted cataract surgery have all raised patients’ expectations with regard to being spectacle-free. Extensive marketing by both surgeons and industry, as well as patient payment for advanced technology IOLs, have created increasing pressure for spectacle-free outcomes with excellent visual function.

Figure 1. Alcon ILM forceps

Figure 2. If a PVD is not present, one is made using the suction-only mode of the vitreous cutter.

A-scan ultrasound cannot accurately determine axial length in the presence of macular hole, epimacular membrane, macular schisis, macula edema, submacular fluid, or VMT syndrome.

Measurement of axial length using the Haag Streit Lenstar LS 900 (Köniz, Switzerland) or the Carl Zeiss Meditec Zeiss Humphrey IOLMaster (Dublin, CA), which measure from the RPE, is absolutely necessary in the presence of any macular disease, to reduce refractive surprises. This can be a crucial issue if the patient has paid for a multifocal IOL.

Figure 3. The ILM is peeled in a circumferential fashion

Figure 4. Air/gas exchange is performed at the end of the case.

Fragmentation of care between preoperative examiners and the cataract surgeon, the cataract surgeon’s lack of focus on macular disease, and cataract itself, which limits visualization, often result in the cataract surgery patient having inadequate macular assessments before surgery is performed.

Preoperative OCT, particularly physician-interpreted spectral-domain OCT, has the potential of reducing this widespread problem. Pseudocolor and three-dimensional mapping reduce, rather than enhance, the ability of the physician to interpret macular OCT. Examination of all gray-scale slices by the physician should be mandatory, not an image selected by technicians and incorporated into the EHR database.

Multifocal IOLs reduce contrast sensitivity, and patients with any macular disease require the greatest possible image quality to achieve optimal visual performance. It is probably unwise to use multifocal IOLs in patients with intermediate or placoid drusen because of the likelihood of future AMD and the lack of an approved treatment for dry AMD.

Visual performance after any macular surgery increases incrementally over 12-18 months, and today’s patients are very impatient. Màny surgeons are not aware that cones and rods adaptively realign to point toward the nodal point, apparently to restore the Stiles-Crawford effect over 12-18 months. This is less than the resolution of the best swept-source OCT machines and even adaptive optics.

SUMMARY

BBG staining and repeat staining and contact lens–based visualization are the optimal techniques for ILM peeling, especially in the presence of a multifocal IOL. Preoperative SD-OCT and axial length measurement from the RPE not using A-scan ultrasound are crucial prior to refractive cataract surgery. RP

REFERENCES