Pain Responses of Pascal

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Pain responses of Pascal 20 ms multi-spot and
100 ms single-spot panretinal photocoagulation:
Manchester Pascal Study, MAPASS report 2
M M K Muqit,
1,2
G R Marcellino,
3
J C B Gray,
1
R McLauchlan,
1
D B Henson,
1,2
L B Young,
1
N Patton,
1
S J Charles,
1
G S Turner,
1
P E Stanga
1,2
ABSTRACT
Aims To evaluate pain responses following Pascal 20 ms
multi-spot and 100 ms single-spot panretinal
photocoagulation (PRP).
Methods Single-centre randomised clinical trial. 40 eyes
of 24 patients with treatment-naive proliferative diabetic
retinopathy randomised to 20 and 100 ms PRP under
topical 0.4% oxybuprocaine. A masked grader used
a pain questionnaire within 1 h (numerical pain score
(NPS)) and 1 month after treatment (numerical
headache score (NHS)). Primary outcome measure was
NPS immediately post-PRP. Secondary outcome
measures were mean NHS scores and levels of
photophobia reported within 4 weeks of primary PRP.
Results Mean laser fluence was significantly lower
using 20 ms PRP (4.8 J/cm
2
) compared to 100 ms PRP
(11.8 J/cm
2
;p<0.001). Mean NPS scores for treatment
were 2.4 (2.3) (mild) for 20 ms PRP group compared to
4.9 (3.3) (moderate) in 100 ms PRP groupda significant
difference (95% CI 4.3 to 0.68; p¼0.006). Mean NHS
score within 1 month was 1.5 (2.7) in 20 ms PRP group
compared to 3.2 (3.5) in the 100 ms PRP group
(p<0.05). The median duration of photophobia after
20 ms PRP was 3 h, and significantly less compared to
100 ms PRP after which 72 h of photophobia was
reported (p<0.001).
Conclusions Multi-spot 20 ms PRP was associated with
significantly lower levels of anxiety, headache, pain and
photophobia compared to 100 ms single-spot PRP
treatment. Possible reasons include lower fluence,
shorter-pulse duration, and spatial summation of laser
nociception with multi-spot Pascal technique.
Laser panretinal photocoagulation (PRP) standards
for treating proliferative diabetic retinopathy (PDR)
were established by the Diabetic Retinopathy
Study 20 years ago.
1
The conventional long-pulse
durations (100e200 ms) used for PRP may be
associated with significant pain and laser intoler-
ance by patients.
2
A number of pre-laser injection strategies have
been investigated. Subconjunctival and sub-Tenon
injections may be effective, but sharp needle peri/
retrobulbar anaesthesia is rarely used due to
potential sight-threatening complications.
2e5
Oral acetaminophen, diazepam, diclofenac,
mefenamic acid and paracetamol have all been
studied.
467
Entonox and intramuscular ketorolac
tromethamine have also been studied pre-laser.
48
To date, oral diclofenac has been shown to be
effective in reduction of post-laser pain response.
6
Randomised trials of pretreatment analgesia for
PRP using pain scales report mean placebo group
pain scores that range from 37.3 to 53.1.
46910
Pain
scores of 31e69 fall within the moderate range of
pain.
11
Recently, clinicians have undertaken conven-
tional laser PRP parameters with reduced 50 ms
pulse duration.
12
Reductions in pain response have
been reported with different pulse waveforms and
20 ms pulse duration PRP.
13 14
The Pascal (Pattern
Scanning Laser) Photocoagulator uses a brief
pulse duration combined with rapid raster scan
that allows effective multi-spot applications.
15 16
Furthermore, this technique may be less damaging
to the inner retina, with reduced collateral thermal
diffusion.
17
The conception of this study was based on the
following observations: pain may reduce laser
uptake during photocoagulation, pain-related
anxiety post-PRP may reduce compliance and
further delay application of laser in sight-threat-
ening diabetic retinopathy, and reduced pulse laser
may reduce pain.
The primary aim of this study is to compare the
pain responses under topical anaesthesia of multi-
spot 20 ms PRP and single-spot 100 ms PRP burns
in PDR. Our secondary aims included an evaluation
of the characteristics of pain responses, subjective
responses post-laser and evaluation of patient’s
experiences related to laser-induced inflammation.
MATERIALS AND METHODS
A prospective, randomised clinical trial was carried
out with patients treated at Manchester Royal Eye
Hospital (MREH) over a 1-year period. The study
protocol received research ethics committee
approval, and informed written consent was
obtained from all participants. Data and safety
monitoring was provided by an independent panel
at the University of Manchester and the Research
Office at MREH. The inclusion and exclusion
criteria are outlined in box 1.
Literature searches were carried out in the
PubMed and MEDLINE databases between January
1993 and June 2009 to uncover all previously
published articles describing pain modification
techniques for PRP using the search terms “panre-
tinal photocoagulation”,“laser photocoagulation”,
“pain”and “laser pulse duration”.
The randomisation sequence was generated using
randomly permuted blocks, and a randomisation
table was created for the 40 subjects. After
a computerised randomisation procedure, sequen-
tially numbered, opaque, sealed envelopes were
1
Manchester Royal Eye
Hospital, Manchester, UK
2
Faculty of Medicine, University
of Manchester, Manchester, UK
3
OptiMedica Corporation, Santa
Clara, California, USA
Correspondence to
Paulo E Stanga, University of
Manchester, Manchester Royal
Eye Hospital, Oxford Road,
Manchester, M139WL, UK;
retinaspecialist@btinternet.com
This work was presented in
May 2009 at the Royal College
of Ophthalmologists Annual
Congress, Birmingham, UK, and
presented in October 2009 at
the joint American Academy of
Ophthalmology and
Pan-American Association of
Ophthalmology Annual Meeting.
Accepted 31 January 2010
Published Online First
16 June 2010
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generated by the masked trial statistician. The treatment allo-
cation envelopes remained concealed until interventions were
assigned. Once a participant consented to the study, a research
trial coordinator who was blinded to the treatment opened the
sealed envelope and assigned participants to each group. The
treatment was not blinded to the treating investigator or study
participant. Patients underwent either unilateral or bilateral PRP
according to randomisation treatment allocation. In cases of
bilateral study eye eligibility, the right eye was randomised first
with treatment allocation, followed by independent random-
isation and allocation of the left eye. Eyes were randomised into
one of two groups, 20 ms PRP or 100 ms PRP.
The primary efficacy endpoint was the NPS score for each
group immediately post-PRP. Main secondary efficacy endpoints
included duration of pain responses during PRP, NHS score at
1 month, affective changes post-treatment and levels of photo-
phobia post-PRP.
Safety endpoints included all adverse events reported spon-
taneously by study participants, elicited by investigators or
observed by investigators. Adverse events were graded as mild,
moderate or severe, and were assessed as being either related to
the laser intervention or unrelated to the laser treatment. We
recorded all serious adverse events whether deemed related to
the treatment or not, as per ethical and good clinical practice.
Pre-laser anaesthesia used up to five drops of topical 0.4%
oxybuprocaine hydrochloride applied over 5 min. Photocoagu-
lation was applied using techniques outlined in table 1 with
a Mainster 165 PRP lens. Before trial commencement, two
experienced retinal specialists at MREH externally validated the
laser technique of the treating investigator (MM), and laser
training was certified according to the study laser protocol and
good clinical practice guidelines. Threshold laser burn intensity
was standardised for all eyes, and this was checked at 1 h post-
laser using fundus photographs.
This pain assessment was part of MREH guidelines for nurses
and was adapted from McGill Pain Questionnaire.
18
This
measurement tool has been externally validated previously and
is routinely used at MREH as a reliable and sensitive measure of
pain responses.
16 19
An examiner, masked to the treatment, used
a standard questionnaire to assess the pain responses, charac-
teristics of responses and levels of affect.
Participants were asked to rate the level of pain related to the
treatment session using the numerical pain scale (NPS). The
NPS allows the patient to rate the pain intensity on a numbered
scale, from 0 to 10. Zero is absence of pain, 1e3 is mild pain, 4e6
is moderate pain and 7e10 is severe pain. In subjects undergoing
multiple-session PRP, we recorded the mean NPS score over three
treatment sessions. The duration of pain responses was reported
using a three-point scale: first half of treatment, second half of
treatment and full duration of treatment.
The laser illumination lamp intensity was adjusted to mini-
mise unnecessary photophobia or discomfort. For patients
receiving bilateral PRP, the first eye was treated followed by pain
assessment; after a delay, the second eye was treated followed by
pain assessment. This method ensured that treatment of second
eyes did not elicit an exaggerated or diminished pain response
depending on the nature and fluence of the first eye’s treatment.
At 1 month post-PRP, the same masked examiner carried out
a second questionnaire-based interview to assess headache
responses, and used a numerical headache scale (NHS), analo-
gous to the NPS. Patients were asked about the presence of
photophobia, photopsia and affective responses (anxiety, mood
disturbances) within the preceding 4 weeks. The responses were
recorded as increased, reduced or unchanged compared to the
day of primary PRP laser. We scored these responses using the
ratio of increased versus decreased responses as the (I/R) ratio.
We performed statistical analyses using STATISTICA version
6 (StatSoft, Inc). We used the two-tailed t test to explore mean
NPS and NHS scores, and duration of photophobia following
Box 1 Study eye major inclusion and exclusion criteria
Inclusion criteria
<Older than 18 years of age
<Male or female patients with diabetes mellitus type I or type 2
who meet the WHO or ADA criteria for diabetes
<ETDRS visual acuity between 35 and 85 letters (Snellen
equivalent of 6/60 or better).
<Newly diagnosed PDR
<Mean CRT of less than 300
m
m as measured by OCT scans
with absence of intraretinal and/or subretinal fluid
<Adequate pupil dilatation and clear media to perform laser
photocoagulation, digital photography and OCT scans
<Ability to perform accurate Humphrey visual field test
<If both eyes are eligible, then both will be randomised as per
protocol and treated independently
Exclusion criteria
<Recent (last 6 months) or ongoing poor glycaemic control.
HbA1C greater than 10.0 mg/dl
<Uncontrolled hypertension. Blood pressure greater or equal to
180/110 mmHg
<History of chronic renal failure or renal transplant for diabetic
nephropathy
<Lens opacity/cataract that could influence vision and results
<Any previous surgical or laser treatment to the study eye or
fellow eye
<Planned YAG peripheral iridotomy
<Previous laser photocoagulation or macular laser treatment to
study eye or fellow eye
<History of DME in study or fellow eye
<Any previous ocular condition that may be associated with
a risk of macular oedema
<Active lid or adnexal infection
<Previous retinal treatment: laser, drug or surgery
<Planned intra-ocular surgery within 1 year
ADA, American Diabetic Association; CRT, retinal thickness within
central subfield; DME, diabetic macular oedema; ETDRS, Early
Treatment Diabetic Retinopathy Study; HbA1C, glycosylated
haemoglobin; OCT, optical coherence tomography; PDR, prolifer-
ative diabetic retinopathy; YAG, yttrium aluminium garnet.
Table 1 Pascal laser parameters
Single-session group Multiple-session group
No of sessions One Three
Day 0 Day 0, day 14, day 28
No of burns 1500 500 per session (total 1500)
Type of laser Pascal (532 nm) Pascal (532 nm)
Type of laser spot Pattern-spot Single-spot
535, 434 arrays
Spot size 400
m
m 400
m
m
Pulse duration 20 ms 100 ms
Laser burn spacing 1.5 burn-widths 1.5 burn-widths
Laser burn intensity Grade 2+, 3+ ETDRS Grade 2+, 3+ ETDRS
Mild gray-white Mild gray-white
ETDRS, Early Treatment Diabetic Retinopathy Study.
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treatment at specified time points. The null hypothesis was
rejected for p values less than 0.05.
The sample size was based on the following assumptions: the
test of significance should be two-sided, with a significance level
of 5%. Using an SD of 2.0, if the true difference in the mean NPS
response of matched pairs is 1.5, we will need to study 20 pairs
of subjects (20 experimental and 20 control subjects) to be able
to reject the null hypothesis that this response difference is zero
with probability (power) 0.8. The type I error probability asso-
ciated with this test of this null hypothesis is 0.05. A 1.5-point
mean NPS difference was chosen since this represented a realistic
value within the ranges of pain scores published in the literature
for laser PRP studies to achieve significance.
67910
RESULTS
A total of 40 eyes of 24 patients (20 in each arm) were studied
between 23 June 2008 and 10 July 2009 (figure 1). Complete data
capture from study questionnaires were obtained for 40 eyes all
visits. The age profiles were similar in both groups, with mean
46 years. No patient required additional PRP treatment within
1 month of the primary PRP. Patient demographics and laser
parameters are presented in table 2.
Examples of threshold laser burn intensities at 1 h are shown
in figure 2. Laser fluence was significantly greater in 100 ms PRP
compared to 20 ms PRP (average values 11.8 and 4.8 J/cm
2
;
p¼0.0001); however, the intensity of photocoagulation burns
was equivalent in both groups.
The mean NPS score immediately post-laser was 2.4 (2.3) for
the 20 ms PRP group, compared to 4.9 (3.3) for the 100 ms PRP
group, categorised as moderate severity of pain (figure 3).
11
The
pain following multi-spot 20 ms PRP was mild, and this was
significantly lower than the single-spot 100 ms PRP (95% CI 4.3
to 0.68; p¼0.006). The mean NHS score within 1 month of
treatment was 1.5 (2.7) in the 20 ms PRP group compared to 3.2
(3.5) in the 100 ms PRP group (figure 4). The difference in NHS
scores between groups was significant (95% CI 3.7 to 0.3;
p¼0.045).
During treatment, the mean contact-lens-related NPS score
was three in four eyes (20%) for the 20 ms PRP group, and mean
NPS was six in four eyes (20%) for the 100 ms PRP group. Pain
related to the laser contact lens was reported in 20% total study
eyes, and this source of pain was reported as either a “gritty”or
“foreign-body”sensation in all cases. The characteristics of side
effects related to pain responses are presented in table 3. As
Figure 1 Consort flow chart of study.
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shown in table 3, subjects in the 100 ms PRP group reported
significantly increased levels of anxiety compared to Pascal
20 ms PRP treatment (p<0.05). At 1 month, patients in both
arms reported equivalent anxiety and mood changes, related to
apprehension regarding the future beneficial outcomes of laser
treatment rather than any pain responses.
Pain responses reported by the 20 ms PRP group occurred
during the first half of treatment in 11 (55%) eyes and during the
full duration in 3 (15%) eyes. In the 100 ms PRP group, pain
responses were reported to last the full duration of treatment in
16 (80%) eyes. The remainder did not report any pain during
treatment (30% 20 ms PRP, 20% 100 ms PRP).
The data for levels of photophobia reported within 1 month
of PRP in both groups were skewed, and median values were
analysed for comparison to achieve a better central tendency
than arithmetic mean scores. Median duration of photophobia
after 20 ms PRP was 3 h, and this was significantly less
compared to 100 ms PRP (72 h, p<0.001). The effects of PRP on
driving and work performance, reading ability, watching televi-
sion and navigation during night-time did not show any
significant differences or results between either group (table 4).
There were no significant differences in physiological responses
designated by I/R ratios for either treatment group.
There were no ocular complications during the immediate or
short-term, and no reported adverse or serious adverse events. In
the 20 ms PRP group, there were no signs of intraretinal
haemorrhage or blood vessel damage from photocoagulation
burns.
DISCUSSION
Our results have demonstrated that single-session, multi-spot
20 ms PRP using topical 0.4% oxybuprocaine is significantly
more comfortable for patients with PDR compared to conven-
tional multiple-session 100 ms PRP.
Although the retina is devoid of pain sensitivity, ocular pain
and photophobia are frequently reported post-laser. Laser-
induced eye nociception may be related to thermal effects
within choroid, stimulation of ciliary nerves within supra-
choroidal spaces, thermal diffusion to nerve fibre layer or
perhaps direct photocoagulation of the long posterior ciliary
nerve.
20
Laser photocoagulation may produce a thermal increase in
outer retina. Leukocyteeendothelial cell interactions can lead to
inflammatory maculopathy post-PRP in animal models, with
increased cytokine release and retinal capillary hyper-
permeability.
21
Recent work with rabbit retina demonstrated
that 100 ms pulse duration burns produced full-thickness retinal
injury on pathological sections.
22
Laser photocoagulation may stimulate ocular nociception
through inflammatory, mechanical and thermal stimulation. A
significantly higher fluence was required for 100 ms PRP that
will produce higher levels of intraretinal inflammation. Longer
standard pulse duration was associated with higher pain scores
and greater photophobia post-laser. Local ocular inflammatory
responses may enhance outer retinal neurogenic inflammation in
ocular nociceptive terminals and higher order neurons.
20
The conventional 100 ms PRP produced pain for the full
duration of PRP, whereas the multi-spot Pascal 20 ms pattern
arrays triggered pain responses during the first half of PRP. This
temporal aspect of pain may be related to spatial summation of
pain associated with shorter-pulse Pascal. A 20 ms pulse reduces
Table 2 Demographics for each group
Single session Multiple session
Pascal 20 ms 100 ms
Mean age (SD), years 45.7 (9.7) 45.8 (10.5)
Male-to-female ratio (% men) 14:6 (70%) 13:7 (65%)
Mean total laser power (SD), mW 287 (71) 142 (22)
Mean laser fluence, J/cm
2
4.8 11.8
Figure 2 Appearances of threshold
laser photocoagulation burns at 1 h
post-laser. (A) Pascal single-session
with 434 array, and (B) single-spot
multiple-session panretinal
photocoagulation laser applications.
Figure 3 Numerical pain scale scores immediately after treatment. y-
axis: numerical pain scale (0e10). Grade of pain scores: 0, absent; 1e3,
mild; 4e7, moderate; 8e10, severe.
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the time required for intraretinal tissue thermal changes to
occur. Better localisation of 20 ms burns within outer retina will
minimise heat diffusion towards the retinal nerve layer and
choroid.
17
Furthermore, the 1.5 burns spot-spacing means each
20 ms burn within the array is applied to the retina in a scatter
technique. The Pascal rapid raster application of multiple spots
may lead to habituation of pain associated with the laser arrays
during PRP. The interactions between these spatial summation
and temporal aspects of repetitive noxious stimulation have
been studied in skin.
23
A shorter stimulus duration has been
shown to reduce nociceptor activation times and produce
a stronger spatialetemporal summation at central synapses.
24
The pain scores reported by Al-Hussainey and co-workers
14
were better than our NPS scores for 20 and 100 ms photocoag-
ulation, although far less laser burns were used in their study
and a single eye received two different types of laser that would
confound the overall perception of pain by the patient. The
mean age of patients and the laser power parameters for the
100 ms group was higher compared to our study. We found no
correlation between NPS and NHS scores and age or sex. Higher
fluence laser in an older age group with less retinal pigmentation
may explain the differences between pain scores in both studies.
The pain responses demonstrated in our study are more closely
related to clinical practice, as 1500 burn PRP is within Early
Treatment Diabetic Retinopathy Study recommendations
for treatment. Previous PDR studies have not as yet studied
physiological, psychological and spatial-temporal effects of
retinal laser photocoagulation at different pulse durations.
Our study did not demonstrate any significant effects or
differences between 20 and 100 ms PRP on physiological aspects of
pain. Depressed mood and anxiety was reported in 10e20%
of patients in both laser groups, and photopsia was problematic in
25% cases following 100 ms PRP. At home, patients reported no
significant impairment of reading and televisiontasks, with similar
and equivalent responses when either navigating at night or
driving. Our small sample size may explain the difficulty in asso-
ciating any physiological responses with different PRP techniques.
The main limitations of our study include the absence of
conventional argon laser (514 nm) PRP as a comparative group.
However the Pascal system (532 nm) allows 100 ms burns in
single-spot mode, and we used a single laser system with stan-
dard illumination and optical apparatus for both arms of the
study. The exact source of pain during the laser treatments may
be questionable. Patients reported any discomfort from the laser
illumination source at the onset of laser titration before the PRP
had commenced, and light intensity was adjusted accordingly
until patients were comfortable and able to fixate with the other
eye during the PRP. There were no reports of increased
discomfort or pain associated with the multiple aiming beams of
the multi-spot Pascal raster patterns. Pre-laser topical anaes-
thesia minimised any surface discomfort from the contact lens,
and pain related to contact lens was reported in only 20% of all
eyes.
Multi-spot 20 ms PRP laser under topical 0.4% oxybuprocaine
is associated with significantly lower levels of anxiety, headache,
pain and photophobia compared to single-spot 100 ms PRP
treatment. This may be explained by a combination of lower
fluence, shorter-pulse duration and spatial summation of laser
nociception.
Acknowledgements This research was supported by the Manchester Academic
Health Sciences Centre and National Institute for Health Research Manchester
Biomedical Research Centre.
Funding Optimedica Corporation, Santa Barbara, USA.
Competing interests GRM is an employee of Optimedica Corporation. PES has
received financial support from Optimedica Corporation.
Ethics approval This study was conducted with the approval of the Stockport Ethics
Committee.
Contributors There are 10 authors involved in this work. All authors contributed in the
recruitment of patients, investigations, treatment, analysis and writing of the paper.
Provenance and peer review Not commissioned; externally peer reviewed.
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MAPASS report 2
photocoagulation: Manchester Pascal Study,
ms single-spot panretinal and 100 ms multi-spot Pain responses of Pascal 20
B Young, N Patton, S J Charles, G S Turner and P E Stanga
M M K Muqit, G R Marcellino, J C B Gray, R McLauchlan, D B Henson, L
doi: 10.1136/bjo.2009.176677
2010 2010 94: 1493-1498 originally published online June 16,Br J Ophthalmol
http://bjo.bmj.com/content/94/11/1493
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