Vitreoretinal Surgery Assisted by the 193-nmExcimer Laser

Itzhak Hemo* Daniel Palanker,^ Igor Turovets,^ Aaron Lewis,^ and Hanan Zauberman*

Purpose. Ablating and cutting vitreoretinal membranes using a 193-nm excimer laser-basedmicrosurgical system.

Methods. A 193-nm microsurgical system enables delivery of the beam into a fluid medium tocut preretinal and subretinal membranes. Two patients with proliferative diabetic retinopathyand one patient with proliferative vitreoretinopathy were treated with this new device.

Results. Gentle ablation and cutting of the preretinal and subretinal membranes withoutexerting any traction on or apparent damage to the neighboring tissue was achieved.

Conclusions. The technology is applicable to a variety of intraocular vitreoretinal surgicalprocedures. Invest Ophthalmol Vis Sci. 1997;38:1825-1829.

A roliferative vitreoretinopathy is the most commoncause of failure in surgical procedures designed totreat retinal detachment. The pathogenesis of prolif-erative vitreoretinopathy involves proliferation of vari-ous cell types forming contractile membranes on theanterior and the posterior surfaces of the detachedretina. The removal of these membranes requires pre-cise surgical intervention. The current procedures ofchoice for the removal of such membranes are me-chanical segmentation, peeling, or delamination. Themechanics of membrane removal are such that a de-gree of traction is usually exerted on the tissue thatcan damage the internal limiting layer and cause iatro-genic tears and bleeding.1

To circumvent the associated problems of me-chanical membrane removal, several approaches havebeen investigated to accomplish tractionless removalof vitreoretinal membranes, using various types of la-sers.2"6 The approach of using the CO22 and Hol-mium:YAG3 lasers that are strongly absorbed in watercauses collateral effects of the laser on the sur-rounding healthy tissue. In both these cases, the retinawas damaged when the laser probe was located ~1.5to 2 mm from the retinal surface. In the first applica-

* From the Department of Ophthalmology, Hadassah University Hospital, and thef Laser Center, Hadassah University Hospital and Division of Applied Physics, TheHebrew University of Jerusalem, Israel.Submitted for publication August 9, 1995; revised August 5, 1996; accepted March14, 1997.Proprietary interest category: P.Reprint requests: Itzhak Hemo, Department of Ophthalmology, Hadassah UniversityHospital, PO Box 12000, 91120 Jerusalem, Israel.

tion of the Erbium:YAG laser (in a normal spikingmode)4 to vitreoretinal membrane cutting, the retinawas also damaged at approximately the same distanceas it was in the previous studies. Recent research onthe application of this laser to vitreoretinal membraneremoval,5 using tips of improved configuration, gener-ated data of considerably better quality. Membranesthat were in contact with die retina and those located~0.2 mm and 0.5 mm from the retina were cut withthese tips. Thermal damage or hemorrhage of theretina was detected in 7 of the 18 cuts.5 The 308-nm XeCl excimer laser was also reported able to cutvitreoretinal membranes,6 but this wavelength is haz-ardous to cornea, lens, and retina.7 As a result, theseapproaches have failed to achieve their objective ofreplacing mechanical instrumentation with laser re-moval of the interfering membranes.

Another technology, that of dielectric breakdownby a tightly focused laser beam, has also been triedfor vitreoretinal membrane photodisruption. A pico-second NeodymiumrYAG laser was focused by a highnumeric aperture lens placed in front of the eye.8

The membranes were cut successfully, but the retinalinjuries were frequently detected up to 2 mm fromthe focal point of the laser. However, these injurieswere detectable only in experiments in vivo using flu-orescein angiography. The retinal damage was proba-bly a result of laser absorption in the retinal pigmentepithelium under the irradiated area,8 because a sig-nificant part of the radiation penetrates through thefocal spot of the laser beam and reaches the underly-

Investigalive Ophthalmology & Visual Science, August 1997, Vol. 38, No. 9Copyright © Association for Research in Vision and Ophthalmology 1825

1826 Investigative Ophthalmology & Visual Science, August 1997, Vol. 38, No. 9

ing tissue. In addition, the laser beam cannot betightly focused in the peripheral part of the eye globe,which complicates, or makes impossible, the applica-tion of such a technique in these areas. Furthermore,the noninvasive nature of this procedure has no advan-tage for retinal membranes, because the actual re-moval of the cut membranes requires an invasive pro-cedure.

We have developed a microsurgical system basedon the 193-nm ArF excimer laser.910 In the past, theapplication of this laser has been limited to such rela-tively dry tissues as the cornea, because of its compli-cated delivery problems in transmission through opti-cal fibers11 and through biologic fluids. We have re-solved these problems by designing an articulated armand a specialized tip that permit the transmission ofthe 193-nm radiation in the eye and allow the tip toreach almost all regions of the eyeball. In preliminarystudies with animal models, we demonstrated preciseand reproducible cutting of membranous tissue in thefluid environment of an eye in vivo.10

Herein we describe the first applications of thisdevice to three patients with vitreoretinal proliferativedisease in whom intravitreal, preretinal, and subreti-nal membranes were ablated with the 193-nm excimerlaser.

METHODS

All patients described were treated according to thetenets of the Declaration of Helsinki after written, in-formed consent was obtained.

A model 103 MSG Lambda Physik (Gottingen,Germany) ArF excimer laser with 193-nm wavelengthand a ~20-nsec pulse duration was used. The laserbeam was directed with a specially designed articu-lated arm.910 The excimer laser probes, with outerdiameter of 1.5 mm and tip diameter 0.28 ± 0.03 mm,were inserted through the sclerotomy in all proce-dures. The total energy transmitted through the tipswas calibrated before the sterilization by an OphirDGX energy meter (Jerusalem, Israel) with an 03APhead. In all surgical procedures, the total energy was0.12 ± 0.02 mj/pulse. For effective ablation and cut-ting, it was necessary to touch the tissue gently withthe laser tip during the surgical procedure.

RESULTS

The three patients described illustrate different tech-niques of vitreoretinal surgery with the ArF laser-basedmicrosurgical system: direct ablation or removal, gen-tle lift with tangential cutting, and cutting of subreti-nal membrane fibers through small holes created inthe retina.

Patient 1

A 61-year-old woman, with known diabetes of 15 years'duration, had proliferative diabetic retinopathy. Sheunderwent panretinal photocoagulation with theargon laser and thereafter had several episodes of re-current vitreous hemorrhage in the right eye. Preoper-ative examination revealed that visual acuity in theright eye was limited to perception of hand move-ments only. A mature cataract and dense intravitrealhemorrhage completely obscured the fundus. Echo-graphic examination showed an attached retina withepiretinal membranes in the posterior pole.

Under general anesthesia, the cataract was re-moved by phacoemulsification, and a pars plana vitrec-tomy was performed. After the vitreous was cleared,we could observe an attached retina, a pale optic disc,and an epiretinal fibrous tissue remnant (1.5 mm X1 mm) in the posterior pole. We decided to removethis tissue to prevent a traction retinal detachmentfrom developing. We chose the excimer laser to re-move the membrane by direct ablation at a repetitionrate of 10 to 20 Hz (Fig. 1). The laser probe was passedover the tissue, in near contact, scalping the tissuelayer by layer. It took several scans before the tissuewas completely removed. In spite of the very closelocation of the fibrous clump to the retina, no appar-ent damage in the underlying retina was detected aftertissue removal (Fig. 2). The technique enabled us toremove such tissue without pulling the retina and thusprevented a retinal break.

At a follow-up visit 14 months after the procedure,the visual acuity in the patient's right eye had recov-ered to 20/500, and the retina was attached.

Patient 2

A 65-year-old woman had proliferative diabetic reti-nopathy for 20 years. During the last 5 years, she hadundergone panretinal photocoagulation by argon la-ser in both eyes, but her vision had declined. Examina-tion revealed no light perception in the right eye be-cause of neovascular glaucoma, whereas the vision inher left eye was limited to perception of hand move-ments because of mature cataract and tractional reti-nal detachment.

Under general anesthesia, she underwent a pha-coemulsification procedure and pars plana vitrec-tomy. After the vitrectomy was completed, a large fi-brovascular epiretinal membrane covering the poste-rior pole and a traction-localized retinal detachmentwere revealed (Fig. 3). Removing such a large mem-brane by "direct ablation" as described in the firstpatient is very time consuming. Therefore a gentle-lifttechnique was employed. The large membrane wasfirst segmented into five parts by passing the laser tipover the membrane from the edge of the optic disc

Vitreoretinal Surgery With the 193-nm Excimer Laser 1827

FIGURE l. Patient 1. Epiretinal fibrous tissue remnant (anoiu)in patient with proliferative diabetic retinopathy before abla-tion by excimer laser. Laser tip is touching the tissue. Theshadow of the tip can be seen on the retinal surface.

FIGURE 4. Patient 2. Excimer laser cutting the fibrotic con-nections between the membrane and the retina.

FIGURE 2. Condition of patient 1 after removal of epiretinalfibrous tissue. No apparent damage can be observed on theretina under the removed clump,

FIGURE 5. Patient 2. One month after ablation of preretinalmembranes with the excimer laser.

FIGURE 3. Patient 2. Proliferative diabetic retinopathy withfibrovascular membranes (arroius) covering the posteriorpole and preretinal bleeding.

FIGURE 6. Patient 3. Cutting of a subretinal fibrotic band andthe overlying reuna with the laser tip. The arrow indicateswhere the fibrotic band was cut.

1828 Investigative Ophthalmology & Visual Science, August 1997, Vol. 38, No. 9

to the peripheral areas of the retina and performingfull-thickness cuts in the membrane. The edges of thesmall, segmented membranes were gently lifted up byforceps, revealing the fine fibrotic connections at-taching the retina to the membrane. The laser tip wasbrought into near contact with these fine connections(Fig. 4) and cut with a few laser pulses, thereby fullyreleasing the membrane, which could then be re-moved with forceps or a vitrectome without associatedretinal damage. Because there was no retinal tear, sili-cone oil or gas exchange was not needed. The opera-tion was completed by argon endolaser.

In follow-up examination 14 months later, the ret-ina was flat (Fig. 5), and the patient's visual acuity inthe treated eye was 20/600.

Patient 3

A 62-year-old man with myopia underwent a circling-buckling procedure with cryopexy for retinal detach-ment in his left eye. Four months later he appearedwith total retinal detachment in that eye. Examinationrevealed total retinal detachment, with subretinalbands forming a triangular pattern in the midperi-phery retina and peripheral retinal folds causing trac-tional retinal detachment. No retinal break was seen.

Under general anesthesia, he underwent a parsplana vitrectomy followed by heavy fluid (decalin) in-jection into the posterior pole to flatten it and tostabilize the retina. The peripheral retina remaineddetached because of the subretinal bands. To cutthese bands the laser tip was brought in proximity tothe point in the retina at which the subretinal bandswere located. Using a few pulses of the laser, a smallhole approximately 0.4 mm in diameter was made inthe retina, and the underlying bands were cut (Fig.6). When the tension of the bands was released, theretina immediately flattened.

The peripheral retinal folds were treated by pass-ing the laser tip through the space between the foldswhere the fine, transparent epiretinal membraneswere located. The membranes were ablated with lowenergy without visible damage to the retina itself, andthe wrinkled retina was freed. Once the retina wasfree, heavy fluid-silicone oil exchange was performedto complete the flattening of the retina.

In follow-up examination 13 months after the op-eration, the retina was still attached, and the patient'svisual acuity was 20/200.

DISCUSSION

Ideally, a technique for the removal of epiretinal mem-branes should avoid undue displacement of the retinaand thermal or other damage in the surrounding tis-sues. Today, even with the finest intraocular instru-

mentation, mechanical traction of the epiretinal tissuecan induce complications.

The unique capabilities of the ArF laser microsur-gical instrument that we have developed allows tissueto be cut and removed in a gradual and controlledmanner without tissue displacement. The mechanismof such tissue cutting is associated with the generationof fast-expanding cavitation bubbles. The dynamics ofthese bubbles have been studied in model systems,12

and the results have shown10 that the 193-nm excimerlaser is capable of cutting retinal tissue in vivo to adepth of approximately 25, 50, and 120 //m/pulsewhen the total energy at the ablating tip is varied inthe range of 0.075, 0.11, and 0.17 mj/pulse, respec-tively, for a tip diameter of 0.25 mm. Epiretinal mem-branes were cut with approximately the same pulserate as the retina.10

The biologic medium screens the tissue from the193-nm radiation caused by absorption when the tip isheld at some distance from the surface. This screeningeffect determines1 the minimum distance allowed foroperation of the laser without damaging the underly-ing tissue while holding the tip in near contact withthe tissue during the cutting.13 At a distance from thetip to the tissue surface exceeding 60 /xm, cavitationbubbles are not generated at the energies used inthese surgical procedures; thus, no cutting occurs.13

This feature provides the surgeon with good distancecontrol for the cutting of vitreoretinal membrane.Concerning possible photochemical effects of the la-ser on the underlying retina after tissue removal, re-sults of studies in vitro have shown13 that, beyond 250fim from a cellular surface, no alterations even in thecellular membrane permeability are seen.

Three techniques of vitreoretinal surgery with theArF excimer laser were demonstrated. First, a methodof "direct ablation," which causes the lowest degreeof trauma to the underlying tissue. In this method,dissection and removal could be done in a precisemanner with the removal depth depending on thelaser energy. With such a technique, layer-by-layer re-moval could be accomplished.

Second, a gentle-lift technique was applied toareas of large and thick membranes that were adher-ing tightly to the retina and in which direct ablationwould be time consuming. In this procedure, the laserprobe was applied first to segment the large mem-brane. Then, the small membrane segments werelifted gently while the fibrotic connections attachingthe membrane to the retina were cut tangentially withthe laser, as an additional precaution against retinalinjury.

Third, a method of subretinal membrane cuttingwas employed to cut subretinal bands through smallholes made in the retina. The diameter of these holesslightly exceeded the tip diameter that was, in our

Vitreoretinal Surgery With the 193-nm Excimer Laser 1829

patient, ~0.28 mm. For this method, especially finetips can be used to decrease the dimensions of theretinal damage.

During the application of the laser in all the pa-tients there were no observable anatomic effects indi-cating inadvertent retinal damage, hemorrhage, andother complications. This was true during the opera-tion and in the extended follow-up period after thesurgery. The absence of any complications in our pa-tients is probably related to the choice of optimal irra-diation conditions, which were selected on the basisof our previous investigations in vivo and in vitro.10'12'13

The main difficulties associated with our micro-surgical system are of a technical nature. The articu-lated arm is rather cumbersome—heavy and not flex-ible enough. The energy stability on the exit of thearm should be improved. An additional disadvantageis the need for a sclerotomy diameter of ~1.5 mm,larger than the standard. Among the limitations ofthe method is the minimal safe distance at which thelaser can be applied. Future developments may permiton-line control of tip-to-surface distances.

The 193-nm excimer laser-based ultramicrosurgi-cal system for vitreoretinal applications, developed atthe Hadassah University Hospital Laser Center, hasseveral attractive features and advantages when com-pared with other methods: Membranes are removedwithout any traction (this feature is characteristic ofall laser-based approaches and is one of the main ad-vantages of such techniques when compared with me-chanical peeling); cutting occurs only when the tiptouches the tissue, a feature that makes it much saferthan lasers that are absorbed in water (er:YAG, CO2)or those that penetrate deeply in biologic fluids (XeClexcimer, Nd:YAG); and a variety of techniques allowsthe surgeon the flexibility to choose die best way fortotal membrane removal with minimal damage to thesurrounding tissue.

From our experience in the three patients de-scribed, it appears that the 193-nm excimer laser-based ultramicrosurgical system could become an im-portant technical auxiliary in patients with severe vi-treoretinal proliferative disease that require surgicalintervention.

Key Words

193-nm excimer laser, epiretinal membrane, laser ablation,subretinal membrane, vitreoretinal surgery

References

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