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MISCALIBRATION AND SEVERECOMPLICATIONS AFTER DIODE

LASERCYCLOPHOTOCOAGULATION:

TWO CASE REPORTS

T. ZEYEN*, K. VANDENBERGHE**

ABSTRACTBecause two similar transscleral cyclophotocoagu-lation diode lasers with identical power & durationsettings induced significantly different postopera-tive inflammation, we wanted to compare the realoutput of both lasers.Using a Power/ Energy Meter (Fieldmaster TM) wecompared the output of the two lasers (the Iridis [Qu-antel Medical] and the Iris Medical [OcuLight SLx])at different energy levels. At a setting of 600, 1000,1400, 1700, 2000 and 2500 mW, the measuredoutput for the Iridis and Iris Medical diode laser wererespectively 685 and 400 mW, 970 and 650 mW,1470 and 875 mW, 1700 and 1000 mW, and 1990

compared to 1000 mW.On the average the output of the Iridis laser was cor-rect and the output of the Iris Medical laser was 40%lower than the setting. Overtreatment and severecomplications occurred with the Iridis laser becausethe manufacturer recommended using wrong powersettings based on the Iris Medical laser, which wasundercalibrated.The calibration of cyclophotocoagulation diode la-sers should be performed prior to use when chang-ing to a new device and whenever over- or under-treatment is observed.

RSUM

Aprs lutilisation dun nouvel appareil de cyclopho-tocoagulation au laser diode, nous avons constat

une augmentation significative de linflammationpostopratoire avec de graves complications, et cemalgr un rglage identique celui de lappareil pr-cdemment employ.Nous avons donc voulu comparer la puissance rel-le gnre entre les deux lasers. A laide dun appa-reil de calibration (Fieldmaster TM), nous avons me-sur la puissance gnre par les deux lasers dio-de (lIridis [Quantel Medical] et lIris Medical [Ocu-light SLx]) et ce diffrents niveaux dnergie.Aux rglages de 600, 1000, 1400, 1700, 2000,et 2500 mW, nous avons mesur pour lIridis et lIrisMedical une puissance relle de respectivement 685et 400 mW, 970 et 650 mW, 1470 et 875 mW,1700 et 1000 mW, et de 1990 et 1000 mW.

La puissance gnre par lIridis tait correcte; lapuissance gnre par lIris Medical tait en moyen-ne de 40% infrieure au rglage annonc. Le sur-traitement et les complications svres qui se sontproduites avec lIridis taient dus au fait que le fa-bricant de cet appareil avait recommand demployerle mme rglage que celui propos par Iris Medical,appareil sous-calibr.Une calibration des lasers cyclophotocoagulationdevrait tre effectue avant lusage dun nouvel ap-pareil et lorsquun sous- ou surtraitement est observ.

KEY WORDS

Diode laser cyclophotocoagulation, refractory glau-coma, intraocular pressure, calibration, Iridis, Iris

Medical.

MOTS-CLS

Cyclophotocoagulation au laser diode,glaucome rfractaire, pression intra-oculaire,calibration, Iridis, Iris Medical.

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* Dpt. of Ophthalmology, U.Z. Leuven, Leuven.** Dpt. of Ophthalmology, St. Rembert Hospital,

Torhout.

received: 13.11.03accepted: 26.01.04

27Bull. Soc. belge Ophtalmol., 292, 27-30, 2004.

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INTRODUCTION

Cycloablative procedures are often used to treatpatients with uncontrolled high intraocular pres-sures in eyes with refractory glaucoma.Diode laser cyclophotocoagulation has provento be a safe and effective procedure comparedwith cyclocryodestruction. (1,2,9,11) Problemsassociated with the latter are uveitis, loss of vi-sual acuity, pain and phthisis bulbi. The pur-pose is to describe two patients who showedsigns of overtreatment and severe complica-tions after switching from one diode laser to an-other.

PATIENTS ANDMETHODS

CASE 1

A 67-year old female with severe diabetic re-tinopathy, first treated with conventional laser,developed neovascular glaucoma with an in-traocular pressure (IOP) of 56 mmHg in theright eye. Diode laser cyclophotocoagulationwith the Iris Medical (OcuLight SLx) was per-formed, followed by two sessions of peripheralcryocoagulation of the retina. Despite this treat-

ment, the intraocular pressure remained high(34 mmHg under maximum therapy) and theeye was painful. She underwent a second di-ode laser cyclophotocoagulation, this time witha different instrument, the Iridis from QuantelMedical, after which she developed a markedanterior chamber inflammatory reaction, a ma-ture cataract in two days and persisting highintraocular pressures (26 mmHg). This wastreated medically, followed by a cataractextrac-tion. For both diode lasers identical power set-tings were used as described below.

CASE 2

A 57-year old female with a history of chronicangle-closure glaucoma, who underwent a bi-lateral trabeculectomy, developed malignantglaucoma after a second trabeculectomy withMitomycin C in the left eye. For this reason theright eye was treated with diode laser cyclo-photocoagulation using the Iridis (Quantel Me-dical) diode laser. Postoperatively, she devel-oped a malignant glaucoma, rubeosis iridis, a

fibrinous anterior chamber reaction and a white

cataract. A vitrectomy combined with lensex-traction and endolasercoagulation of the reti-na was performed. Eventually the IOP normal-ized with medical treatment and a secondarylens implantation was performed.

Both patients were treated under retrobulbaranaesthesia using the same (recommended)protocol. First the conductivity of the probe wasroughly assessed by perforating a hole in black-ened printing paper at the following power set-tings: 1 second and 1000 mW. The probe wasthen carefully cleaned before the treatment wasinitiated. Subsequent laser applications were

spaced one width of the probe tip. We treated220 of the inferior circumference of the ciliarybody with 17-19 impacts of 2 seconds withgentle indentation. Applications started with apower of 1750 mW. If there was no tissue dis-ruption reaction (a pop or snap sound fromwithin the eye) during the first 2 applications,the power was increased to 2000 mW. If therewas a pop or snap during more than onesubsequent laser application, the power was re-duced back to 1750 mW. If a pop or snapsound occurred at 1750 mW during more thanone laser application, the power was reduced

to 1500 mW, and treatment completed at thispower (5,9). The probes of the two diode la-sers were slightly different. The fiber optic dia-meter of the Iris Medical is 600 with a pla-nar polished end protruding 0.7 mm from ahandpiece (G-probe), while the fiber optic dia-meter of the Iridis, also being 600 , has a bulbtip at the end (7,8). For both treatments withthe Iridis laser the power setting never exceeded1750 mW. Since over-treatment occurred us-ing the Iridis laser with the above mentionedpower settings, we decided to compare the out-put of both lasers at different energy levels (600,1000, 1400, 1700, 2000, 2500 mW), with

the Fieldmaster TM (Coherent). A new probewas used for each laser. The Fieldmaster is arugged, compact microprocessor driven, pow-er and energy meter with a unique combina-tion of an analog and digital meter for laser tun-ing, with a precise digital display of power orenergy on the LCD backplane. The Fieldmas-ter can be used with all lasers commonly man-ufactured today, simply by plugging the appro-priate sensor head into the console (4).

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RESULTS

Table 1 summarizes the results of the outputof both lasers at different settings.

The output of the Iridis laser varied from 14%higher to 3% lower than the setting power. Theoutput of the Iris Medical was lower for all set-tings, with an average of 38.9% deviation.

DISCUSSION

Ciliary ablation, first with cryotherapy and laterwith lasercoagulation has been used to reducethe IOP in patients with refractory glaucoma formany years. Diode laser cyclophotocoagula-tion is associated with less complications thancryocoagulation (1,2,9,11).

We describe two patients with severe compli-cations following cyclophotocoagulation usingthe Iridis diode laser. The first patient, treatedfor neovascular glaucoma, developed a markedinflammatory reaction and a rapid mature ca-taract. She received two diode laser sessions:the first, unsuccessful, with the Iris Medical la-ser, and the second with the Iridis laser usingidentical (recommended) power settings. Thesecond patient, with a history of malignant glau-coma after filtering surgery in the other eye, de-veloped the same complications as the first pa-tient in combination with malignant glaucomaand rubeosis iridis. She only received one di-

ode laser session using the Iridis laser. Thesefindings dont correlate with the outcome ofseveral studies suggesting cyclophotocoagula-tion to be a safe procedure with minimal in-flammatory reaction (2,9,10,13).Overtreatment and severe complications oc-curred with the Iridis laser because the manu-facturer recommended to use identical powersettings as used for the Iris Medical laser, nottaking into account that the output of the Iris

Medical laser might have been under-evaluat-

ed. The calibration of the two diode lasers withthe Fieldmaster confirmed the under-evalua-tion of the output of the Iris Medical laser withan average of 40% and a correct output of theIridis laser. Hence overtreatment with the Iri-dis laser at identical power settings. We shouldhave been aware of possible over-treatmentsince a pop was almost always heard at pow-er settings between 1500 and 1750 mW withthe latter instrument! The pop or snap isan audible alarm signal that warns for pos-sible over-treatment. Often it is accompaniedby excessive pigment dispersion. We dont thinkhowever that diode laser cyclophotocoagula-

tion can be performed solely on the base of apop or snap technique. Since the abovementioned complications we decreased the re-commended power settings of the Iridis laserwith 40% and obtained a good IOP loweringeffect without complications. We suggest us-ing the following power settings with the Iridisdiode laser: starting the applications at 1000mW and 2 seconds; if no pop or snap isheard during the first two applications, the pow-er is increased with increments of 100 mW upto a maximum of 1600 mW; if there is a popor snap during more than one subsequent la-

ser application, the power is reduced back withincrements of 100 mW down to a minimum of1000 mW. The above mentioned complica-tions, the calibration problem, and the suggest-ed new settings were communicated to bothmanufacturers.One might argue that the calibration with theFieldmaster could have been influenced by thedifferent shapes of the two probes. Indeed thefiber optic diameter of the Iris Medical is 600 with a planar polished end protruding 0.7 mmfrom a handpiece (G-probe), while the fiber op-tic diameter of the Iridis, also being 600 , hasa bulb tip at the end (7,8). Yet calibration with

the Fieldmaster was probably not influenced bythe two different shapes of the probe since la-ser energy is delivered as a coherent beam.Another point of concern in the calibration isthe repeated use of probes. A study of Tham etal resulted in an average decrease of 3% in la-ser energy delivered after repeated use of theG-probe with ethylene oxide sterilization in be-tween (12). Conversely, Buys et al found a slightincrease of energy transmission after repeated

Table 1

Setting mW Output Iridis mW(% compared to the setting) Output Iris Medical mW(% compared to the setting)

600 685 (+14%) 400 (33%)

1000 970 (3%) 650 (35%)

1400 1470 (+5%) 875 (37.5%)

1700 1700 (0% ) 1000 (41%)

2000 1990 (0.5%) 1230 (38.5%)

2500 2440 (2.4%) 1300 (48%)

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use and sterilization (3). As the influence of re-

peated use on the energy transmission of theprobe remains unclear and many clinicians re-use probes, it is important to find a methodwhich assesses the output of the G-probe be-fore use. Hossain et al found the assessmentof the cyclodiode G-probe using a grey scaletest to be a simple, quick and highly reproduciblemethod (6). They also recommended not re-using the probes more than 7 times.

CONCLUSION

Calibration of diode lasers is necessary whenchanging from one device to another, in be-

tween repeated use, and whenever signs of over-or under-treatment are observed.

REFERENCES

(1) BARTAMIAN M., HIGGINBOTHAM E.J. Whatis on the horizon for cycloablatio? Curr OpinOphthalmol 2001; 12: 119-123.

(2) BLOOM P., TSAI J.C., SHARMA K. Cyclo-diode: Trans-scleral diode laser cyclophoto-coagulation in the treatment of advanced re-fractory glaucoma. Ophthalmology 1997; 104:1508-1520.

(3) BUYS Y., TROPE G., CARRILLO M. Can trans-

scleral cyclophotocoagulation laser G-probesbe reused? Invest Ophthalmol Vis Sci 2003;44:E-Abstract 2193.

(4) FIELDMASTER TM COHERENT MANUAL: 1.(5) GAASTERLAND D.E., POLLACK I.P. Initial

experience with a new method of laser trans-scleralcyclophotocoagulation for ciliary abla-tion in severe glaucoma. Tr Am Ac Ophthal-mol 1992, 80 : 225-246.

(6) HOSSAIN P., GHOSH G., VERNON S.A. As-sessing the cyclodiode G-probe using a greyscale test: reproducibility and differences be-tween probes. Eye 2003 17, 167-176.

(7) IRIDIS VIRIDIS TWIN. Probe delivery sys-tems for 810 nm laser user manual. QuantelMedical; 2002: 10-14.

(8) IRIS G-ProbeTM. Chapter 12 In: IRIS OculightDiode Laser System operator manual. Moun-tain view, CA: Iris Medical Instruments; 1993.

(9) LINSEN M.C., MANNES K., ZEYEN T. Diodelaser cyclophotocoagulation in refractory glau-coma. Bull Soc belge Ophtalmol 1998; 270:69-73.

(10) SCHLOTE T., DERSE M., RASSMANN K., NI-CEAUS T., DIETZ K., THIEL HJ. Efficacy and

safety of contact transscleral diode laser cy-clophotocoagulation for advanced glaucoma. JGlaucoma 2001; 10: 294-301.

(11) SPENCER A.F., VERNON S.A. Cyclodio-de: results of a standard protocol. Br J Oph-thalmol 1999; 83: 311-6.

(12) THAM C., LAI J., FUNG P., CHUA J., POONA., LAM D. Physical effects of re-use and re-peated ethylene oxide sterilization on trans-scleral cyclophotocoagulation laser G-probes.J Glaucoma 2002; 11: 21-25.

(13) THRELKELD A.B., JOHNSON M.H. Contacttransscleral diode cyclophotocoagulation for re-fractory glaucoma. J Glaucoma 1999; 8: 3-7.

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Address for correspondence :Prof. Dr. T. ZeyenU.Z. Leuven, OogziektenKapucijnenvoer 33B-3000 Leuven

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