A Conventional Laser burns appears to be larger and

A significant difference between two groups
was the spot size within the first month: Conventional Laser group had larger
lesion size than PASCAL group which was expected considering PASCAL system has shorter
pulse duration (10-30 ms) when applying laser burns whereas Conventional Laser
burns are generally delivered with ranging spot size (100-500 µm) and longer
pulse duration (100-200 ms).  In 1999, Mainster
suggested that lesion size decreases with decreased pulse duration in pulsed
lasers and both small lesion size and short pulse duration was associated with
less pain (121).  Jain et al. conducted a
study to observe the effect of pulse duration in size and character of lesion
using 532-nm Nd:YAG
laser in Dutch Belt rabbits. They compared the effects of various laser powers
and pulse durations  on the histologic
character and size of the retinal lesion and described size
of the retinal lesion increased linearly with laser power and logarithmically
with pulse duration (99).  

Generally the PASCAL laser burns seemed to
be smaller and regular in size and were more precisely spaced and more uniform;
whereas Conventional Laser burns appears to be larger and irregular (122).

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Previously the morphological changes were
described by other studies using OCT to evaluate techniques, clinical benefits,
side effects (119, 120, 123-125). Studies
of retinal healing after photocoagulation demonstrated significant reduction in
the size of retinal lesions and contraction of the damage zone in
photoreceptors layer in lesions (100, 119, 123, 124, 126).  

Paulus et
al. reported the histopathologic findings after application of laser burns with
PASCAL system in Dutch Belt rabbits and at all pulse durations, the size of the
retinal lesions decreased over time (100).  In their study, Muqit
et al. described the morphology of different laser burns made by PASCAL system
in human subjects using OCT and found a 50% decrease in laser spot size at month
six compared to 1-hour after treatment (124).  In their study Lavinsky et al. provided a
detailed evaluation of long-term changes in retinal photocoagulation lesions
produced with various spot sizes, pulse durations and clinical grades in
patients, using OCT. They found that relative residual area at 12 months,
compared with the initial lesion size, was 12-33% for 20 ms pulse duration and
50% for 100 ms pulse duration with 200µm spot size (123).  In consistent with the
above mentioned studies, our study showed that at 6 months laser spots
contracted to 47-51% of their initial size at baseline diameter. In contrast
however, Maeshima et al. researched the areas of laser scars from panretinal photocoagulation
with different types of lasers including conventional laser over a long period
of follow-up time (36-122 months) and they found that 89.5% laser scars expands
over time (127). 

It was
suggested that this significant reduction in size was
associated with migration of photoreceptors from the non-photocoagulated
surrounding areas, filling in the damaged outer part of retina over time (99, 100, 123, 126).  

Mirshahi et al. compared the pain scores of
patients underwent conventional laser (100ms) photocoagulation and single-spot
short pulse duration (20ms) photocoagulation. They found that short pulse
duration photocoagulation was less painful compared to conventional laser and as
effective as conventional laser photocoagulation (128).  It provides a better side effect profile
compared to conventional laser (11).  Pulse duration is one of
the differences between Conventional Laser and PASCAL (129).  Because of the short pulse durations, small
sized laser burns can be applied. As Paulus et al. and Lavinsky et al.
suggested laser burns produced by shorter pulses and with smaller spot sizes
can heal much more completely than the conventional larger and more aggressive
lesions (100, 123). This
healing process means fewer side effects for patients such as scotomata and
scarring after panretinal photocoagulation. 
 Studies have proven that PASCAL
is superior to the conventional laser when it comes to patients comfort and
less side effects (11, 90, 91, 128).  In our study we also attempted to see
whether there are other factors effecting laser spot size such as age, gender,
and laser energy setting besides laser device. We found that age had a weak but
positive effect on the laser spot size, meaning older patients tented to have
larger spot size after treatment. Although we did not find a statistically
significant effect of laser energy on laser spot size or their atrophy zones
over observed period of time; in 2008 Jain et al. suggested that laser power
had an effect on laser burn size and demonstrated that lesion size increases
with laser power (99).

Beginning from the first month, the 33% of laser
spots were surrounded by an atrophy zone which was described as a loss of
photoreceptor segment layer by Kriechbaum et al. (119, 120).  Throughout the months the PASCAL atrophy zone
size shrunk and on the sixth month after treatment it decreased 16% of the
original measurement. Whereas the Conventional Laser atrophy zone size first
expanded and then on the sixth month it decreased 5% of the original atrophy
zone size. This decrease in size might be explained by migrating RPE cells,
replacing the atrophic photoreceptor layer as suggested by Kriechbaum et al. (119).  At Month 1, 56% of
Conventional Laser lesions developed atrophy zone whereas for PASCAL lesions
this was 18%. Afterwards Conventional Laser lesions continued to increase in
percent and at Month 6, 74% of laser burns developed atrophy zone. In PASCAL
group the percentage also increased until the third month up to 32%. However at
the sixth month it decreased compared to the third and we saw that 27% of
lesions were surrounded by atrophy zone.

One of the complications of conventional
photocoagulation is the laser burns spreading with enlargement of the atrophic
area, which might lead to loss of visual field; night vision and RPE atrophy (123, 127, 130). Lavinsky
et al. suggested that minimally damaging photocoagulation can be done by
avoiding inner retinal damage (123). Although a larger number of burns should be applied to treat the
same area, minimal damaging photocoagulation, which can protect the retina from
the feared side effects, is a better option (90).  Our study showed us both
laser devices damaged not only the laser burn spot but also surrounding area.  However, not only PASCAL atrophy zones
decrease in size more than conventional laser atrophy zones at month six but
also atrophy zone development was much higher with 74 % in Conventional Laser
group than PASCAL group which might mean that PASCAL laser system is more tissue
protective and minimal damaging option compared to Conventional Laser.

In this study the frequency of the
archway-formation was also analysed and we saw that one week after treatment archway
figures were formed between the laser burns. This archway figure is the outer
nuclear layer being replaced with a downward shift of the inner layers (119).  At the first week the frequency
of archway formation was over 50% for both laser groups, however at the sixth
month after treatment the frequency drops to 24-39% in both groups which can be
explained by the realignment of the layers as a part of the healing process
after photocoagulation.  Nonetheless,
there was no significant difference between two groups within the 6 months
follow-up.

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