Multi-spot laser coagulation with the VISULAS 532s VITE : A comparative study of 101 procedures

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Bruno Norman
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1 Multi-spot laser coagulation with the VISULAS 532s VITE : A comparative study of 11 procedures A single-center clinical study comparing treatment workflow and patient comfort of multi-spot laser photocoagulation with the new VISULAS 532s VITE laser versus singlespot laser photocoagulation with the conventional green coagulation laser VISULAS 532s Antje Röckl, MD, Marcus Blum, MD, Department of Ophthalmology, Helios Kliniken Erfurt, Germany ABSTRACT BACKGROUND VISULAS 532s VITE is a 532nm photocoagulation laser which is able to operate both in classic single-spot treatment modes as well as in a new, semi-automated multispot treatment mode. In the latter mode, the laser fires a predetermined linear spot sequence at high speed, released with the joystick trigger button of the laser slit lamp. The authors report their early experience with the system and compare the new multi-spot with the conventional single-spot functionality in terms of treatment time and pain felt during the procedure. sequence, the overall treatment time of an average PRP session is decreased by up to 2/3. Whereas 46.% of patients of single-spot group A have reported feeling some degree of pain during laser treatment, only 1.3% of the patients in multi-spot Group B have reported feeling pain during their treatment. On a scale from 1 to 1, the average pain value in the single-spot coagulation Group A was 2.1. In the multispot coagulation Group B, the average pain value was only.1. No adverse events were noted in either of the two groups. METHODS Patients of 18 years and above requiring pan-retinal photocoagulation to treat their retinal condition were recruited into the study. The procedures done were divided into two groups: Group A - Classic single-spot photocoagulation with the conventional VISULAS 532s, and Group B - Multi-spot photocoagulation using the new functionality of the VISULAS 532s VITE. RESULTS Compared with the single-spot treatment group, multispot coagulation with the VISULAS 532s VITE requires half a minute less time per 1 applied laser shots in an average PRP session. Depending on the number of laser spots per multi-spot INTRODUCTION Laser photocoagulation remains the gold standard in the therapy of many retinal vascular disorders. For more than 3 years, it has been known that panretinal laser photocoagulation (PRP) is effective in treating proliferative retinopathy in a wide variety of underlying conditions, of which diabetic retinopathy is the most common indication. The most frequently used photocoagulation settings are still based on the original recommendations of the 1978 Diabetic Retinopathy research Study (DRS) /1/. Classic photocoagulation conditions of pulse widths from 1 to ms and laser powers from to 4 mw are still widely recommended although commercially available photocoagulation lasers have been capable of delivering 1

2 both shorter pulse widths as well as higher laser power for years. For instance, the VISULAS 532s from Carl Zeiss delivers laser pulses with pulse durations from 1 ms up to continuous wave, offering a maximum laser power of 1.5 W (mea sured at the cornea). Recently, Zeiss has implemented the concept of fast and flexible multi-spot cascades in the new VITE option of the VISULAS 532s photocoagulation laser. The purpose of this study was to compare the new multi-spot photocoagulation to the traditional single-spot photocoagulation of the VISULAS 532s VITE. One goal was to investigate if and how the improved VITE functionality accelerates photocoagulation workflow in daily clinical practice in comparison to classic single-spot operation. The second goal was to evaluate if and how patient compliance is influenced by the change in the modus operandi. METHODS PATIENTS Patients 18 years and above requiring pan-retinal photocoagulation to treat their retinal condition were recruited into the study. There were no exclusion/inclusion criteria associated with patient gender or ethnicity. Patients with tremors, cataract, cloudy vitreous or acute ocular inflammation were excluded from the study. Patients who received a laser treatment with less than 35 burns were retrospectively excluded. In Group A (single-spot group), pan-retinal photocoagulation was done for the following conditions: 28 (8%) were treated for Proliferative Diabetic Retinopathy, 4 (11%) for Central Retinal Artery Occlusion, and 3 (9%) for Central Retinal Vein Occlusion. 7 (%) of Group A treatments were initial first treatments, and 28 (8%) retreatments (including a second and third PRP session and re-filling procedures). In Group B (multi-spot group), pan-retinal photocoagulation was done for the following conditions, 5 (76%) were treated for the following conditions: 28 (8%) were treated for Proliferative Diabetic Retinopathy, 7 (1%) for Central Retinal Artery Occlusion, and 9 (14%) for Central Retinal Vein Occlusion. 15 (23%) of Group B treatments were initial first treatments, and 51 (77%) re-treatments (including both a second / third PRP session and re-filling procedures). Group A (non-vite) Single-spot [1 15 ms] Group B (VITE) Multi-spot [ ms] Number of Procedures Patient Gender Female Male Patient Age Standard Deviation Diagnosis Diabetic Retinopathy Central Retinal Artery Occlusion Central Retinal Vein Occlusion Laser Therapy First treatment Re-treatment 49% [17] 51% [18] % [28] 11% [4] 9% [3] % [7] 8% [28] 33% [22] 67% [44] % [5] 14% [9] 1% [7] 23% [15] 77% [51] Table 1: Distribution of patient demographics and laser treatment LASER TREATMENT PROCEDURE The VISULAS 532s VITE is a frequency-doubled, neodymium-doped yttrium aluminum garnet (Nd:YAG) solid-state laser operating at 532nm wavelength. Besides the classical single-spot treatment mode, the VISULAS 532s VITE is capable of delivering multi-spot sequences at a single press of the release button on the slit lamp joystick. Based on the concept of flexible treatment multi-spot cascades, linear, circular or customized coagulation strategies can be pursued (see Fig. 1). Linear spot sequences of variable orientation consisting of 3 to 8 single laser spots are most suitable for pan-retinal photocoagulation. Semi-automated parallel movement of the slit lamp field and the laser beam in the multi-spot mode allows individual application of several spots consecutively in fast linear sequences to fill in a large retinal area. During the normal retina consultation hours in the Helios Kliniken Erfurt, 11 consecutive procedures were randomly allocated to Group A or Group B to receive laser treatment. In both treatment groups, a single quadrant of the retina was treated with about 5 peripheral laser spots. In Group A, shots of scatter laser photocoagulation using conventional laser parameters in the single-spot operation mode were applied: a spot size of µm, exposure times between 1 and 15 ms, and laser power values sufficient to cause moderate blanching of the ret- 2

Fig. 1: Possible, multi-spot treatment strategies with the VISULAS 532s VITE Color fundus image of a multi-spot laser treatment with linear cascades of the VISULAS 532s VITE ina were used.

patient operation mode with a pulse duration of ms. There- left from the chair after treatment.

3 Fig. 1: Possible, multi-spot treatment strategies with the VISULAS 532s VITE Color fundus image of a multi-spot laser treatment with linear cascades of the VISULAS 532s VITE ina were used. In Group B, laser treatment was also per- on a co-observation tube, was switched on when the formed with µm spot size, but this time in multi-spot patient took a seat, and switched off when the patient operation mode with a pulse duration of ms. There- left from the chair after treatment. The treatment time fore, higher laser power values had to be used in order to was defined as the time from the first to the last applied provide a similar visible laser effect in both study groups. laser pulse in a treatment session. It was measured after For the VITE Group B we used straight, linear spot se- treatment on the basis of the acquired video data. Fun- quences of variable orientation. We decided to use 3 to dus images were acquired after laser treatment with an 6 individual laser spots per sequence with a spacing of a FF45 fundus camera from Carl Zeiss in order to compare single spot diameter. treatment regimens regarding the spatial regularity, homogeneity and intensity of the applied laser spots of the Group A Non-VITE treatment Single-spot [1 15 ms] Group B VITE treatment Multi-spot [ ms] Laser spot diameter [μm] two treatment regimens. At the end of the laser treatment, patients were asked to mark on a visual analog, linear scale the severity of the pain experienced for the two treatment regimens with (= no pain) to 1 (= most severe pain ever experienced). Laser power [mw] Standard deviation Pulse duration [ms] Standard deviation Number of laser burns Standard deviation The results were presented in terms of mean pain scores and analyzed in terms of standard deviations. RESULTS and DISCUSSION During the study period, 142 procedures were performed. Of these, 41 procedures had less than 35 spots and were excluded from the analysis. The final set of data included 11 procedures, with 35 done in single-spot treatment mode (Group A, non-vite group), and 66 in Table 2: Treatment parameters the multi-spot treatment mode (Group B, VITE group). The procedures done on all patients were recorded on The average laser pulse of the 35 conventional treat- video in order to compare treatment times between ments in the single-spot treatment mode (= Group A, Groups A and B. The video camera, which was placed non-vite group) had a duration of 116 ms and a laser 3

4 power of 157 mw. The average non-vite treatment consisted of 59 laser burns. The average laser pulse of the 66 treatments in the multi-spot treatment mode (= Group B, VITE group) had a duration of ms and a laser power of 286 mw. The average VITE treatment consisted of 555 laser burns. r Power [mw] Average Laser Pulse Duration [ms] Fig. 2: Average laser power values used depending on laser pulse duration Fig. 2 displays the average values of the mean laser power values for all applied pulse durations. The applied laser power values in the multi-spot treatment group B had been chosen in such a way that the visible clinical endpoint (the burns ) in this group corresponds to the clinical outcomes in group A. Fig. 2 illustrates that shorter laser pulse durations have to be compensated for with higher laser power values. Because of the relatively gentle laser powers we used in our single-spot therapy regimen, this compensation for the shorter ms multi-spot pulses did not cause any clinical side-effects at all. It should be noted that physicians who already coagulate with higher laser powers in conventional treatment may also use 3, 4, or 5 ms pulse durations with the multispot option VITE, which requires less compensation in the applied laser power. We extracted the individual treatment times from the recorded videos of all laser treatments. Based on the individual treatment times we calculated a normalized treatment time value which represents the individual treatment time normalized to the application of 1 laser pulses. Group A (non-vite group) Group B (VITE group) Number of procedures Treatment time (normalized to 1 burns) Standard deviation 73.4 sec 9.6 sec sec Mann Whitney U-Test P < sec 14 sec sec Table 3: Normalized treatment time statistics in both study groups Comparing the normalized treatment times in the two study groups, a treatment with 1 laser shots in singlespot treatment Group A takes an average of 73.4 seconds, whereas a treatment with 1 laser shots in multi-spot treatment Group B takes only 49.4 seconds on average. This corresponds to a time saving of 24. seconds per 1 applied laser shots or a relative time saving of 33% in the multi-spot VITE Group B. In order to take into account an initial learning curve when the operator has to become accustomed to the system and gain experience with the new multi-spot sequences, we divided the VITE group B into two subgroups: Group B1 contains all multi-spot treatments within the first 8 weeks after installation of the system (June and July 9). Group B2 contains all multi-spot treatments after week 8 from installation of the same operator (September and October 9). Group B1 (VITE group <8 weeks) Group B2 (VITE group >8 weeks) Number of procedures Treatment time (normalized to 1 burns) Standard deviation 55.5 sec 17. sec sec Mann Whitney U-Test P < sec 9.9 sec sec Table 4: Normalized treatment time statistics in both B subgroups 4

5 Comparing the normalized treatment times between the two B sub-groups, a treatment with 1 laser shots within the learning phase of 8 weeks takes 55.5 seconds on average; after an learning phase it shortens to an average of 44.8 seconds. In other words: on average, a skilled operator of Group B2 saves half a minute per 1 applied laser shots with the multi-spot option VITE compared to a skilled single-spot treatment operator. This corresponds to a relative time saving of 4%. Comparing the standard deviation values of the normalized treatment times of Groups A, B1 and B2 from tables 3 and 4, these values suggest that after the learning phase of 8 weeks (with a treatment of approximately 5 eyes), the operator in multi-spot Group B2 has achieved a similar skill level compared to single-spot reference Group A operator several years of experience with the VISULAS 532s laser. The normalized treatment time values for all the treatments within this clinical study are displayed in Fig. 3. The shortest normalized treatment times of about 25 seconds per 1 shots were achieved in both B sub-groups. The initial normalized treatment time of about 95 seconds in Group B1 was significantly reduced to about 6 seconds in Group B2 after the learning phase of 8 weeks. Therefore, the linear interpolation curve of the normalized treatment values of Groups B2 shows an identical slope to the line of single-spot Group A, demonstrating similar skill levels of the operator in both groups. Both the faster individual treatments (left-hand side of the graph) and the slower individual treatments (right-hand side of the graph) of multi-spot treatment Group B2 show the same time saving of half a minute in comparison with a comparable treatment procedure in single-spot treatment Group A. 1 t time for 1 laser shots Normalized treatment Patient Number Group A (skilled) Group B1 (< 8w) Group B2 (> 8w) Linear (Group A (skilled)) Linear (Group B1 (< 8w)) Linear (Group B2 (> 8w)) Fig. 3: Comparison of the normalized treatment times of groups A, B1 and B2 Generally, initial PRP sessions on patients with good compliance take the shortest normalized treatment times, whereas re-filling procedures and patients with poor compliance slow down the PRP treatment workflow. When working with the multi-spot option VITE, even the most demanding treatments have a comparable or shorter normalized treatment time than with fastest single-spot treatment regimen. The therapy workflow can be flexibly adjusted to the individual patient case by variation of the spot sequence length. Table 5 shows the statistics of spot sequence lengths used within the treatment group B2: 5

6 Number of laser spots per spotsequence Patients 3 only 3 % [1] 3 and 4 3 % [1] 4 only 11 % [4] 4 and 5 8 % [3] 5 only 53 % [] 5 and 6 3 % [1] 6 only 8 % [3] More than 2 changes between 3, 4, 5, 6 spots (mostly re-filling) 11 % [4] Table 5: Distribution of applied multi-spot sequences in Group B after 8 weeks Based on these statistics, Fig. 4 shows the dependency of the normalized treatment time from the length of the applied spot-sequence. In this figure, we have considered treatments with a single sequence length value as well as treatments where we switched between two length values. Preferably, we treated with 5 spots per sequence in order to have a similar confidence level and control as we did in the past with single-spot laser treatment. Sequences of 2 spots only result in minor workflow acceleration. Large sequences of 7 or 8 spots could be beneficial for initial PRP treatments. In our study, however, we stayed with our very controlled way of operation, which makes it more comfortable and easy both for the operator as well as for the patient. The linear interpolation curve of Fig. 4 shows a clear trend: The larger the spot sequence length, the shorter the normalized treatment time. Treatments which alternated between two spot sequence lengths required slightly longer normalized treatment times because of the need to switch between the different spot sequence length values. Therefore, they are generally situated above the interpolation line. Although not experimentally proven in this study, an extrapolation of the linear regression line to the largest available spot sequence length value of 8 spots suggest that it may be possible to shorten the normalized treatment time to an average of to 25 seconds per 1 applied laser spots. alized treatment time laser shots Average norm per , 2, 3, 4, 5, 6, 7, 8, Laser spots per spot sequence Fig. 4: Correlation between average normalized treatment time and the length of a multi-spot sequence Pain perception during laser photocoagulation varies among patients and also depends on the treated area on the retina. However, discomfort remains a significant cause of unsatisfactory treatment sessions for both patient and physician. Strategies to make the treatment more comfortable include changing of the laser treatment parameters. In a small study, Friberg et al. (1995) showed that patients found shorter exposure, higher power laser treatment much more comfortable than conventional settings, with no apparent reduction in visible endpoint /2/. A more recent study on patients by Al-Hussainy et al. (8) has clearly proven that reducing the exposure time and increasing the laser power reduced pain significantly without compromising the long-term results of the laser therapy /3/. Shorter duration laser burns may be less painful due to the thermal conduction effects in the treated tissue. Short-duration burns cool off more rapidly in comparison with the longer duration burns, in which adjacent tissues become heated and the energy reaches the pain-sensitive region in the deeper retinal and choroidal layers. When applying multi-spot sequences either by the press of the laser slit lamp joystick or the footswitch pedal, the overall treatment time of a sequence should not significantly exceed half a second in order to avoid interference with eye movements of the patients. Therefore, when using multi-spot sequences with the VISULAS 532s VITE, the pulse duration of the individual laser pulses within a sequence is limited to 5 ms. In our clinical study, we used significantly shorter pulse durations in multispot group B than in single-spot Group A, which had to be compensated for by higher laser power (see Table 1). 6

7 In order to evaluate the pain perception among the different laser treatment regimens in both groups, we used a graphical linear scale with increments of perceived pain from (= no pain) to 1 (= severe pain). Right after the laser treatment the patients were given this scale and they were asked to score the perceived pain value. 16 (46.%) out of the 35 patients of group A scored a value greater than zero, which indicates some degree of pain during the laser treatment. The distribution of the pain response of the single-spot treatment group A is shown in figure 5. Only 2 (1.3%) of the 66 patients of group B reported pain during treatment with the multi-spot option VITE, with one patient scoring a value of 3 and one a value of 4. All other patients of group B had no pain at all during the multi-spot treatment. atients Number of pa Pain score Fig. 5: Pain score distribution of single-spot treatment group A The results confirm the findings of Al-Hussainy et al (8) /3/ that reducing the exposure time and increasing the laser power can significantly reduce pain without compromising the results of the treatment. Due to the shorter pulse duration, there is a reduced thermal diffusion to adjacent retinal and choroidal layers which prevents a heating of the pain-sensitive areas. CONCLUSION In this study, we performed 35 pan-retinal photocoagulation procedures in single-spot treat ment mode with the VISULAS 532s and 66 pan-retinal photocoagulation procedures with the new multi-spot treatment option of the VISULAS 532s VITE. Compared to conventional single-spot photocoagulation, laser treatment with the VISULAS 532s VITE significantly reduces the overall treatment time while shorter pulse durations improve patient s pain perception. Our results suggest that after a learning phase of 8 weeks with a VITE multi-spot treatment of approximately 5 eyes, an operator can achieve the same level of efficiency as a skilled single-spot operator with more than 4 years of experience. Compared with the single-spot treatment group, multispot coagulation with the VISULAS 532s VITE saves half a minute per 1 applied laser shots in an average PRP session. Depending on the number of laser spots per multispot sequence, up to 2/3 of the overall treatment time of an average PRP session can be saved. Although rapid laser treatment with multi-spot cascades requires short individual pulse durations, which have to be compensated for with higher laser power, no adverse events have been observed during the multi-spot treatment sessions with the VISULAS 532s VITE. On the contrary, only 2 patients (1.3%) treated with the VISULAS 532s VITE in the multi-spot group reported feeling pain, whereas 16 patients (46.%) patients treated in the conventional way reported feeling pain during the laser treatment. 7

8 REFERENCES /1/ The Diabetic Retinopathy Study Research Group: Photocoagulation treatment of proliferative diabetic retinopathy: The second report from the Diabetic Retinopathy Study. Arch Ophthalmol 1978; 85: /2/ Friberg et al.: Alteration of pulse configuration affects the pain response during diode laser, Lasers Surg Med 16, 1995, /3/ Al-Hussainy et al.: Pain response and follow-up of patients undergoing pan-retinal laser photocoagulation with reduced exposure times, Eye 22, 8, Publication No: , LAS.2979 The contest of the brochure may differ from the current status of approval of the product in your country. Please contact our regional representative for mor information. Subject to change in design and scope of delivery and as a result of ongoing technical development. Printed on elemental chlorine-free bleached paper. S O M M E R VI/1 1 by Carl Zeiss Meditec AG. All copyrights reserved. Carl Zeiss Meditec AG Goeschwitzer Str Jena GERMANY Phone: Fax: info@meditec.zeiss.com Carl Zeiss Meditec Inc. 516 Hacienda Drive Dublin, CA USA Phone: Fax: info@meditec.zeiss.com 8

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