Lasers in Surgery and Medicine 12:604408 (1992)

Immediate Retinal Adhesion by C02 Laser Irradiation Using a Fiberoptic Intraocular Probe Ari DeRowe, MD, Elisha Bartov, MD, Giora Treister, MD, Michael Belkin, MD, and Abraham Katzir, PhD Department of Applied Physics, Raymond and Beverly Sackler Faculty of Exact Science School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (A.D.,A.K.), and Goldshlagger Eye Institute, Tel-Hashomer Hospital, Ramat-Gan 52671 (E.B.,G.T.,M.B.), Israel

Using an experimental fiberoptically guided CO, laser system, we produced lesions on fresh bovine retinas. These lesions were shown to achieve immediate measurable chorioretinal adhesion. This model provides preliminary data on the use of a fiberoptic CO, laser probe to produce chorioretinal lesions and possible future use in intraocular surgery for retinal detachment. The advantages of using CO, laser energy are minimal damage surrounding desired lesion and its versatility as a coagulator and cutter. With modifications, COP endolaser may have a role in intraocular surgery. 0 1992 Wiley-Liss, Inc. Key words: bovine eyes, endolaser, intraocular surgery, retinal detachment

sue mainly consists of water, and the CO, laser radiation is highly absorbed in water. Therefore, The goal of retinal detachment surgery is to when a lesion is produced by the CO, laser most of obtain approximation of the retina to the layers the energy is immediately absorbed and the dambelow and t o prevent further detachment and loss age to the surroundings is minimal [31. This is a of vision. distinct advantage when treating the delicate retBy inserting into the eye a fiberoptically ina. Also, the absorption of energy is not depenguided probe capable of delivering laser energy to dent on pigment as with argon laser. This is esa spot on the retina, photocoagulation can be perpecially important in areas of the retina that are formed resulting in the adhesion of the retina to devoid of pigment or are avascular. the choroid below. Such a system utilizing argon The ability t o work at different power levels, laser energy (488,514.5nm wavelength) has been in continuous wave or pulsed mode, adds to the developed and is in widespread clinical use [1,21. versatility of the CO, laser. The same system can Although useful to the surgeon, there are disadcoagulate, cut, vaporize, and “weld” tissue. vantages inherent in the wavelength of the argon However, it is difficult working in a fluid laser when applied t o adhesion of retinal detachmedium due t o high absorption of C 0 2 laser enments. It is dependent on the presence of pigment ergy in water. Also, there is yet no dependable for its energy to be absorbed, and thus fibrous or flexible delivery system. avascular areas of the retina cannot be treated. Our group, at the applied physics departAlso, in the presence of bleeding, its energy is ment of Tel-Aviv University, is currently develabsorbed by hemoglobin and not at the desired area of treatment. What makes argon laser attractive is a reliable fiberoptic delivery system, Accepted for publication May 4, 1992. made of fused silica. Address reprint requests to Ari DeRowe, Applied Physics CO, laser radiation (10,600 nm wavelength) Group, School of Physics and Astronomy, Tel-Aviv Univerhas certain potential advantages. Biological tis- sity, Ramat-Aviv, Tel Aviv 69978, Israel. INTRODUCTION

0 1992 Wiley-Liss, Inc.

605

Retinal Adhesion by COz Laser TABLE 1.0.6 Watts, Time (Sec)/Force (mg) Time (sec)

Eye 1

Eye 2

Eye 3

Eye 4

Eye 5

Eye 6

0 2 4 6 8 10 12 14 16 18

86 NA 102 134 102 118 224 256

102 118 102 102 160 176 160 192 160 NA

118 134 102 134 118 240 240 224 240 NA

54 70 70 102 102 134 134 240 160 160

70 70 70 70 102 160 160 134 134 192

NA NA

2S.D.

86 NA NA 70 102 192 192 240 192 240

Mean 86.0 98.0 89.2 102.0 114.3 170.0 185.0 214.3 177.2 197.3

118 86 118 176 225 192 176 NA

Mean 96.7 88.7 99.3 126.7 164.7 179.7 163.7 155.0

?S.D. 11.9 11.9 11.0 41.2 30.5 34.5 15.1 45.7

20.7 28.6 15.7 26.1 21.2 39.8 37.5 41.0 36.4 32.9

TABLE 2.0.9 Watts, Time (SecVForce (mer) ~~

Time (sec) 0 0.5 1 2

3 4 5 6

Eye 1 102 86 86 102 160 208 176 NA

Eye 2

86 102 102 86 176 160 176 208

Eye 3 86 102 86 102 134 176 160 118

86 70 102 102 134 118 134 102

oping a fiberoptic delivery system capable of transmitting CO, laser energy [41. Presented here are a series of experiments utilizing our flexible fiberoptic system designed to study its potential for effecting immediate adhesion of the retina to the choroid. MATERIALS AND METHODS Laser

The optical fiber was coupled to the Apollo Laser inc. (Chatsworth, CA) CO, laser model 580 using the continuous wave mode. Delivery System

The optical fiber is a silver halide fiber of 50 cm length and 0.9 mm diameter. Throughout the experiments maximal energy loss was approximately 5% per meter as measured by power meter. The fiberoptic could be bent to a radius of 2 cm. without significant energy loss. The probe used in this experiment was designed as a prototype for future intraocular surgery. It consists of a 19 G needle closed at the tip by an infra-red window, transparent t o CO, laser radiation. The fiberoptic was inserted into the probe. Energy loss due to reflection from the surface was approximately 30%.

102 86 102 192 160 224 160 192

Distance of the probe from the retina was 2 mm. Lesion diameter was 1.5-2.0 mm. Experimental Model

We used bovine eyes taken immediately after slaughter and saved on ice. Eyes were used for experiments within 6 hours of slaughter. The posterior segment was divided from the other parts of each eye. The vitreous was carefully removed. Lesions were produced approximately 1-2 cm from the optic disk. Different energy outputs, of 0.6, 0.9, and 1.2 watts as measured at tip of probe by a power meter, were used to produce lesions on the retinas. A range of exposure times were used at each energy output. The tensile strength attained by the lesion was measured as previously described by Foulds and others [5-71. In short, an analytical scale was balanced. On one side the sclera was tacked t o a board with the retina and lesion facing up. A 5-0 silk suture was glued to the retina with cyanoacrylate and attached to the arm of the scale. A petri dish was placed on the other side. Drops of water were slowly placed on the dish using a 25 G insulin syringe. Each drop measured 16 k 0.5 mg. Drops were added causing increasing force eventually leading to the detachment of the retina.

200

200

l/y+

150

150

I

-

-

a]

i 50

0

0

Fig. 1. 0.6 watts, time/force.

I

I

I

I

I

I

Fig. 2. 0.9 watts, time/force.

in adhesion reaching maximal adhesion strength of 179.7 k 34.5 mg using a 4 second exposure. Again, there was decreased adhesion due to charring thereafter. Table 3 and Figure 3 show the results with a 1.2 watt output. The baseline retinal adhesion was 79.3 ? 17.7 mg. As in the previous measureRESULTS ments, there was an increase in the tensile Table 1 shows the adhesion strength at- strength of adhesion with increasing exposure 53.2 mg was tained at different exposure times with 0.6 watt time. Maximal adhesion of 186 attained with a 3 second exposure. As in previous output. For every timed exposure a number of of adhesion after 3 seconds was graphs, decline measurements were made and the force required due to charring. for detachment was measured. The average force Figure 4 Compares the results of the three and standard deviation were calculated and are different energy outputs. Although 14 seconds at presented in Figure 1 as force (mg) versus time 0.6 watts gave the strongest adhesive force, such (seconds).The baseline retinal adhesion (when no a long exposure time is impractical for intraoculesion was produced) was 86 20.7 mg. With increasing exposure times there was an increase in lar surgery. Only a minor difference was noticed adhesion. Maximal retinal adhesion was 214.3 ? between 0.9 and 1.2 watts. 41 mg using an exposure time of 14 seconds. Adhesion strength declined thereafter due t o charDISCUSSION ring. Table 2 and Figure 2 represent the same In this study, measurable immediate adhewith a 0.9 watt output. The baseline retinal ad- sion of the retina to the pigment epithelium and hesion was 96.7 +- 11.9 mg. With increasing ex- choroid ex vivo using a fiberoptically guided C 0 2 posure times there was a corresponding increase laser probe was attained.

The adhesion strength was measured as the number of drops necessary to cause detachment of the retina. A constant slice (1.5 x 5 mm) of retina was used. A total of 156 lesions were produced and measured.

*

*

Retinal Adhesion by C 0 2 Laser

607

TABLE 3. 1.2 Watts. Time (Sec)/Force (me) ~~

Time (sec) 0

Eye 1 86 86 118 208 160 134 NA NA

0.5 1 1.5 2 3 4 5

Eye 2 54 70 86 134 118 208 118 NA

Eye 3 70 70 70 86 86 288 176 NA

Eye 4 86 102 102 86 208 192 192 70

Eye 5 102 86 118 70 102 134 224 134

200

200

150

150

100

100

50

50

0

0 -1

0

1

2

3

4

5

8

Time (sec.)

Eye 6 54 54 70 102 86 160 160 208

-1 1 3 5

Mean 75.3 78.0 94.0 114.3 126.7 186.0 174.0 137.3

7

-cS.D. 17.7 15.3 20.1 46.3 44.2 53.2 35.1 56.4

9 11 13 15 17 19

Time (sec.)

Fig. 3. 1.2 watts, timeiforce.

Fig. 4. Summary: graphs 1-3.

There has been a considerable amount of research on the role of low power CO, laser as a tissue welder. Local heating appears to cause changes in the collagen matrix creating a “glue” that can hold tissue together [8]. Studies comparing the strength of microanastomosis of blood vessels using laser tissue welding and conventional suturing have been made yielding similar results between the two [9]. To our knowledge this is the first time that the strength of CO, laser tissue welding was measured on the retina. Other modalities have been tested such as argon laser, cryopexy, and cyanoacrylate glue. Zauberman measured the tensile strength at-

tained by chorio-retinal lesions made by photocoagulation, diathermy, and cryopexy [6]. Measurements were made days and weeks following induction so that no immediate effect can be determined. Baseline adhesion without lesion was 60-90 mg similar to our result of 54-118 mg. McCuen compared the adhesion of cyanoacrylic glue and cryopexy, immediate and late [71. Immediate adhesion of cryopexy lesions was 34-87 mg. Cyanoacrylate lesions measured 59-261 mg. Maximal adhesion of lesions made with our CO, laser system was 134-236 mg at 0.6 watts for 14 seconds. However, comparison is difficult because no data for baseline adhesion were given.

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DeRowe et al.

Can the adhesion attained ex vivo reflect on surgical results in vivo? Retinal attachment depends on dynamic and structural forces [lo]. In retinal detachment these forces are canceled as they are postmortem [ll]. Therefore, the model we used approximates the adhesion that may be attained in retinal reattachment surgery. There have been other experimental reports of hollow guide and fiberoptically guided CO, laser beams in intraocular surgery [12-151. So far none have achieved routine clinical use status. In those studies lesions were not tested for adhesion force. We wish to point out the importance of measuring the optimal parameters that induce adhesion. For example: at 0.9 watts a lesion can be observed with an exposure of 1 second. At 1 second the adhesion force was an average of 99.3 mg, almost identical with the baseline adhesion of 96.7 mg. However maximal adhesion occurred at 4 second exposure with a force of 179.7 mg, almost double the baseline. Therefore a lesion seen is not necessarily that which will achieve adherence. This must be remembered before clinically applying any laser photocoagulation system. The advantages of using a CO, laser over other modalities are due to its high absorption in water. This causes minimal damage to tissue surrounding the lesion. Also, the versatility of a system that can be both a photocoagulator and a phototransector makes its potential use in intraocular surgery appealing. However, the same high absorption in water causes difficulties in the delivery of the energy into the eye and working in the fluid medium of the eye. Further development of this fiberoptic probe will hopefully solve the problem of delivery. As t o transmitting energy in a fluid medium, intra-ocular surgery can be performed after exchanging the liquid vitreous with gas. Also, in other experiments a “cavitation effect” using pulsed CO, laser t o “dig” a hole through water has been proven [16]. Liquid medium used in retinal surgery such as silicon oil is more viscous than water and in preliminary experiments we found it much easier t o attain a cavitation in silicon oil than in water. Further experiments are needed to prove the feasability in CO, laser photocoagulation utilizing the “cavitation effect.” FiberoDticallv guided CO, laser radiation

appears to be a promising tool in intraocular surgery. However, further experimental work including in vivo studies are necessary for exact definition of optimal in vivo irradiation parameters. REFERENCES 1. Fleischman JA, Swartz M, Dixon JA. Argon Laser endophotocoagulation. Arch Ophthalmol 1981; 99:16101612. 2. Acheson RW, Capon M, Cooling RJ, Leaver PK, Marshal J, Mcleod D. Intraocular argon laser photocoagulation. Eye 1987; 1:97-105. 3. Bridges TJ, Strand AR, Patel CKN, Karlin DB. Interaction of carbon dioxide laser radiation with ocular tissue. IEEE J Quant Elect QE-20. 1984; 12:1449-1458. 4. Katzir A, Ariel R. Long wavelength infrared optical fibers. J Non Cryst Solids 1982; 47(2):149-158. 5 . Foulds WS. A method for measuring the relative strengths of induced chorio-retinal adhesions. Med Prob Ophthalmol 1969; 8:436-439. 6. Zauberman H. Tensile strength of chorioretinal lesions produced by photocoagulation, diathermy, and cryopexy. Br J Ophthalmol 1969; 53:749-752. 7. McCuen BW, Mida T, Sheta SM, Isbey I11 EK, Mahn DK, Hickingbotham D. Experimental transvitreal cyanoacrylate retinopexy. Am J Ophtalmol 1986; 102:199-207. 8. Schober R, Urlich F, Gonder J, Durselen H, Hesel S. Laser-induced alteration of collagen substructure allows microsurgical tissue welding. Science 1986; 232:14211422. 9. Fleming AFS, Coller MJ, Gulliaroti R, Brough MD, Bown SG. Laser assisted microvascular anastomosis of arteries and veins: laser tissue welding. Br J Plast Surg 1988; 41:378-388. 10. Machemer R. The importance of fluid absorption, traction, intraocular currents and chorioretinal scars in the therapy of rhegmatogenous retinal dettachments. Am J Ophthalmol 1984; 98(6):681-693. 11. Zauberman H, DeGuillebon H. Retinal traction in vivo and post mortem. Arch Ophthalmol 1972; 87:549-554. 12. Miller JB, Smith MR, Pincus F, Stockert M. Intraocular carbon dioxide laser photocautery 1. Animal experimentation. Arch Ophthalmol 1979; 97:2157-2162. 13. Miller JB, Smith MR, Pincus F, Stockert M. Intraocular carbon dioxide laser photocautery 2. Preliminary report of clinical trials. Arch Ophthalmol 1979; 97:2123-2127. 14. Miller JB, Smith MR, Pincus F, Stockert M. Transvitreal carbon dioxide laser photocautery and vitrectomy. Ophtalmology 1978; 85:1195-1200. 15. Karlin D, Jakobiec F, Harrison W, Bridges T, Patel CKN, Strnad AR, Wood I1 0. Endophotocoagulation in vitrectomy with a carbon dioxide laser. Am J Ophthalmoll986; 1011445-450. 16. Sa’ar A, Gal D, Wallach R, Akselrod S, Katzir A. Transmission of pulsed laser beams through “opaque” liquids by a cavitation effect. Appl Phys Lett 1982; 50(22):15561558.