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Multispot andMultiwavelength Lasersfor Diabetic Retinopathy
Advanced laser technology allows less damaging, more efficient treatment delivery.
By Manish Nagpal, MS, DO, FRCS; Chaitanya Shukla, DNB;
and Kartikey Kothari, MSS

ince the ETDRS, panretinal photocoagulation(PRP) or macular laser in the form of focal or grid
treatments have been the standard of care fortreating patients with diabetic retinopathy. The
first lasers were argon and krypton gas in blue-green
wavelengths.1,2 Their use was limited because they had
short wavelengths, caused light scatter, used high levelsof energy, induced photochemical damage, and led toacceleration of cataracts.3 Tunable dye lasers were thenext development in laser technology and were available in yellow (577 nm), orange (597 nm to 622 nm), andred wavelengths (622 nm to 680 nm). Maintaining thetunable lasers, however, was expensive and difficult, andsome of the dyes were carcinogenic.4 Further research
resulted in the introduction of infrared (532 nm) andgreen (810 nm) wavelengths. The benefits of these lasers
include reduced scatter, ease of delivery in dense ocular
media, lower cost, and reduced maintenance.5
Further development of solid-state technology
brought about the production of 577-nm wavelength
lasers.4 The combined absorption by both melanin andoxyhemoglobin of 577 nm causes less scatter comparedwith 532 nm or other yellow wavelengths (561 nm or
568 nm), allows better selective treatment of vasculature, and compensates for the reduction in absorption
by retinal pigment epithelium (RPE) melanin comparedwith 532 nm. The energy concentration to a smaller
volume allows use of lower powers and shorter pulse
durations. This wavelength provides greater transmittance through some corneal or lenticular opacities,6 andit falls occurs outside the absorption spectrum of retinal
xanthophylls, potentially allowing treatment close to thefovea.6 High choriocapillaris absorption should also help

Figure 1. Right eye fundus photograph of a patient treatedwith green, yellow, and red laser. Three rows of laser burns
are seen inferior to the macula in a region of diabetic edema.

to provide more uniform effects in patients with lightor irregular fundus pigmentation.7 Studies have shown ahigher likelihood that green laser might lead to submacular fibrosis or choroidal neovascularization. Thus, 577-nm
wavelength has been described as optimal for macular
photocoagulation and treatment of vascular lesions andsubretinal vascular proliferations.7,8Laser light absorbed by melanin of the RPE leads todestruction of mitochondria-rich, and therefore oxygendemanding, photoreceptors. The resulting mitochondriadeficient glial scars facilitate oxygen diffusion directlyfrom the choroid to the inner retina by reduced oxygen
consumption in the outer retina. Relief of inner retinal
hypoxia reduces production of VEGF receptors, whichlimits neovascularization.9,10
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cover storyAABCFigure 2. Optical coherence tomography (OCT) image ofgreen laser burns shows increased reflectivity, subretinal
fluid, and intraretinal vacuoles (A). OCT image of yellow laserburns shows a uniform effect with minimal disruption of thesurrounding tissue (B). OCT image of red laser burns showsincreased disruption of the outer retinal layers (C).

Multispot Lasers
Standard laser photocoagulation is performed using
single spots with pulse durations of 100 to 200 ms in acontinuous mode. The sessions are lengthy and taxing
for both patient and surgeon.11 Also, treatments such as
PRP carry risk of complications such as macular edema.12
Limitations include the inability to apply laser spots inpatterns in the periphery and the tedious burn placementwith appropriate spacing.
The multispot laser bypasses some of these limitations.12 Multiple uniform laser burns delivered simultaneously by a single footpedal depression in a variety ofpatterns using proprietary software create adjustablepredetermined square arrays, arcs, and grids with variable
spot sizes and variable distance between spots, all controlled through an intuitive interface.11 This defines newstrategies in terms of power, software, and hardware technology to formulate safer macular laser applications.10
These devices save time, streamline patient flow for the
retina practice, and reduce discomfort from long laser
sessions.13,14 These conclusions were drawn from a prospective randomized clinical trial performed to compare
the efficacy, collateral damage, and convenience of PRP
for proliferative diabetic retinopathy or severe nonpro70 Retina Today April 2014

B

Figure 3. Optical coherence tomography images showing
the involution of the yellow laser burn marks at days 1 (A)and 30 (B).

liferative diabetic retinopathy with a 532-nm solid-state
green laser (GLx) compared with a 532-nm pattern-scanlaser.15 The latter laser showed less collateral damage andsimilar regression of retinopathy compared with GLx, wasless time consuming, and was less painful for patients.16-18
The PASCAL laser (Topcon) uses a proprietary,
semiautomated pattern generation technique thatallows rapid delivery of laser pulses in a predeterminedsequence, with durations of 10 ms to 20 ms at each spot,
as opposed to 150 ms to 200 ms with conventional laser.
The fluence is only a quarter of that delivered by conventional laser (30 J/cm2 vs conventional, 127 J/cm2). It
might be thought that treatment effect would be diminished because of the reduction in fluence, but investigators have not found this to be the case.19
Precision control, safety, and efficiency of the photocoagulation procedure is combined with optimized patient
comfort and convenience.20-22
Patient satisfaction questionnaires state a preference
for multispot laser over conventional laser with the experience with conventional laser being described as tiringand painful.11,18

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B

B

Figure 4. Optical coherence tomography images showing theinvolution of red laser burn marks at days 1 (A) and 30 (B).

Figure 5. Optical coherence tomography images showing theinvolution of green laser marks at days 1 (A) and 30 (B).

The efficacy of the PASCAL
laser in the macular area has
been supported by thePETER PAN study.

ruption to the rest of the layers. In the argon lase-treatedarea, the elevation and destruction of the receptors
around the treatment area were greater.11,22,25-27
The efficacy of the PASCAL laser in the macular area
has been supported by the PETER PAN study, in whichbarely visible subthreshold laser has been shown to beeffective in the macular area or as PRP.22,28

In our experience comparing multispot laser in 1 eyeand conventional laser in the contralateral eye, weobserved less field loss in all eyes treated with multispot
laser. Improved ease in treating the extreme periphery
was also observed.11
Frequency-domain optical coherence tomography has
confirmed that burns from the multispot lasers are confined and localized to the outer retina, and fundus autofluorescence has confirmed the presence of burns thatare not always visible on fundus biomicroscopy.23,24
In our experience, comparison of burns in lapine eyeswith half the fundus lasered with PASCAL and the otherhalf with argon using the same power revealed small
blisters in the PASCAL-treated tissue, with minimal dis-Combination of Multispot andMulti-wavelength
The 577-nm wavelength and the multispot delivery
mode combination facilitates lower required energy
levels than that of conventional 532-nm laser, resulting
in less pain and a milder inflammatory response for thepatient.18 Treatment grids are homogeneous and evenly
spaced, and similarly intense spot patterns are adjustablefor individualized treatment needs. The rapidity of thedelivery significantly reduces effects of patient movement.14 The longest bursts last 0.5 seconds, but thoseconsisting of 9 spots are practically instantaneous andavoid the effect of most eye movements.12
A combination of benefits of multispot and multiwavelength lasers is seen with the MC-500 Vixi
Multicolor Scan Laser Photocoagulator (Nidek), whichApril 2014 Retina Today 71

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allows the user to select from 3 wavelengths either alone
or in combination: 532-nm green, 577-nm yellow, and647-nm red. This enables the user to select the necessary
color combination to increase efficiency of treatment fora specific indication.6
The Vixi laser includes 8 preprogrammed scan patterns with a memory function for up to 14 patterns.
Available patterns include a single spot, squares, circles,arcs of various dimensions, triple arcs, macular grids,triangles, lines, and curves. The most frequently usedscan patterns can be recalled from memory for futureuse. The scan spot size is continuously variable from50 µm to 500 μm in single mode and from 100 µm
to 500 μm in scan and automanipulation mode.
Automanipulation mode delivers repeated laser emissions with variable interval times and conventional
coagulation settings in a selectable scan pattern. It
allows the surgeon to continue laser emission while
confirming spot placement. The scan mode is usedfor repeated laser emissions with a fixed interval time,high power, and instantaneous speed. It saves time byrequiring fewer sessions,14 consumes less energy, andprovides more versatility than conventional models.6
Compared with green wavelength, yellow wavelength
enables more efficient photocoagulation throughopaque media such as cataract. In eyes with retinal
hemorrhage, better penetration is achieved with the red
wavelength. Hence, with this multi-wavelength, multispot laser, treatment may be started with a particularcolor and continued with a different color. The laser canbe used with existing slit lamps, transforming them intoa stage for scanning laser treatments. All units incorporate the safety optics with low impact on cornea (SOLIC)
optical design, which ensures low-energy density on thecornea and lens even with large spot sizes.7
In our experience, this laser saves time by requiring fewer sessions, consumes less energy, and provides
greater versatility. Laser output can be limited to a single
wavelength or modulated to a combination of colors for
specific treatments.
Study on Effects of DifferentWavelengths
We compared the 3 wavelengths in patients with diabetic macular edema who were scheduled for a grid laser
treatment. In the area of thickened retina we placed 3
sequential line patterns of laser marks, 1 each with red,green, and yellow wavelength using similar power settings (Figure 1). Following the laser treatment, a spectraldomain optical coherence tomography (SD-OCT) scanusing the Spectralis (Heidelberg) was taken through thearea containing these 3 rows of laser. The comparative
72 Retina Today April 2014

We compared the 3 wavelengths
in patients with diabetic macularedema who were scheduled
for a grid laser treatment.
scans of each are shown in Figure 2, which shows thatthe green wavelength burn tends to cause more collateral damage as compared with yellow, and that red
tends to produce a deeper burn. We further carried out
repeat scans in the same area after 1 month to examine
the involution of these laser burns. The least amount ofcollateral damage was seen with the yellow wavelength(Figures 3-5).
Based on these findings, we conducted a study
comparing the morphologic effects of the yellow andgreen wavelengths using the Vixi laser for patients
undergoing laser for diabetic retinopathy.29 Fifty-sixeyes of 28 patients received PRP in this prospective
study. The green laser was applied to the right eye andyellow to the left. The study areas were imaged on thesame day and after 1 month with color fundus photography and SD-OCT.
We found more morphologic changes in the retinal layers in the form of hyperreflectivity, subretinal
fluid, and intraretinal vacuoles on OCT scans of theright eyes. At 1 month, SD-OCT scans of the right eyes
showed greater alteration in the form of hyperreflectivity involving the RPE and neurosensory retina comparedwith the left eyes. Hence, yellow was seen to cause lesscollateral damage to the neuroretina and permit a levelof reorganization in the outer retina.15
Summary
The pattern scan yellow laser uses less power anddecreases patient discomfort.18,22,30 The treatment isdelivered in minimal time with a gentle effect on thetargeted area; there is minimal effect on the surrounding
retinal tissue and an absence of late scarring. Treatment
can be delivered through opaque media, and we believe
there is potential synergy when combined with intravitreal anti-VEGF therapies.31 nManish Nagpal, MS, DO, FRCS, is a vitreoretinal consultant at Retina Foundation inAhmedabad, India. Dr. Nagpal is a consultant
for Nidek and Topcon. Dr. Nagpal may bereached at drmanishnagpal@yahoo.com.

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Chaitanya Shukla, DNB, is a fellow atRetina Foundation in Ahmedabad, India.
Dr. Shukla may be reached atdrchaitanyashukla@gmail.com.
Kartikey Kothari, MS, is a fellow atRetina Foundation in Ahmedabad, India.
Dr. Kothari may be reached at
drkartikeykothari@gmail.com
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