Effect of Pulse Duration on Size and Character of the Lesion in Retinal Photocoagulation

Department of Ophthalmology, Stanford University, Stanford, CA 94305-5308, USA.
Archives of Ophthalmology (Impact Factor: 4.4). 01/2008; 126(1):78-85. DOI: 10.1001/archophthalmol.2007.29
Source: PubMed


To systematically evaluate the effects of laser beam size, power, and pulse duration of 1 to 100 milliseconds on the characteristics of ophthalmoscopically visible retinal coagulation lesions.
A 532-nm Nd:YAG laser was used to irradiate 36 retinas in Dutch Belt rabbits with retinal beam sizes of 66, 132, and 330 mum. Lesions were clinically graded 1 minute after placement, their size measured by digital imaging, and their depth assessed histologically at different time points.
Retinal lesion size increased linearly with laser power and logarithmically with pulse duration. The width of the therapeutic window, defined by the ratio of the threshold power for producing a rupture to that of a mild coagulation, decreased with decreasing pulse durations. For 132- and 330-mum retinal beam sizes, the therapeutic window declined from 3.9 to 3.0 and 5.4 to 3.7, respectively, as pulse duration decreased from 100 to 20 ms. At pulse durations of 1 millisecond, the therapeutic window decreased to unity, at which point rupture and a mild lesion were equally likely to occur.
At shorter pulse durations, the width and axial extent of the retinal lesions are smaller and less dependent on variations in laser power than at longer durations. The width of the therapeutic window, a measure of relative safety, increases with the beam size.
Pulse durations of approximately 20 milliseconds represent an optimal compromise between the favorable impact of speed, higher spatial localization, and reduced collateral damage on one hand, and sufficient width of the therapeutic window (> 3) on the other.

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    • "Shorter laser exposure was limited to RPE and photoreceptors and thus caused less damage to the nerve fiber layer by decreasing the axial spread of heat toward the inner retinal layer and providing better spatial confinement of the lesion in an animal study [13]. Defect areas after laser photocoagulation were known to be the junction of the inner and outer segments of photoreceptors and apical RPE regardless of pulse duration [12,18]. "
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    ABSTRACT: Purpose To evaluate the effect of pattern scan laser (PASCAL) photocoagulation on peripapillary retinal nerve fiber layer (RNFL) thickness, central macular thickness (CMT), and optic nerve morphology in patients with diabetic retinopathy. Methods Subjects included 35 eyes for the PASCAL group and 49 eyes for a control group. Peripapillary RNFL thickness, cup-disc area ratio and CMT were measured before PASCAL photocoagulation and at 2 and 6 months after PASCAL photocoagulation in the PASCAL or control groups. Results The average RNFL thickness had increased by 0.84 µm two months after and decreased by 0.4 µm six months after PASCAL photocoagulation compared to baseline, but these changes were not significant (p = 0.83, 0.39). The cup-disc area ratio was unchanged after PASCAL photocoagulation. CMT increased by 18.11 µm (p = 0.048) at two months compared to baseline thickness, and partially recovered to 11.82 µm (p = 0.11) at six months in the PASCAL group. Conclusions PASCAL photocoagulation may not cause significant change in the peripapillary RNFL thickness, CMT, and optic nerve morphology in patients with diabetic retinopathy.
    Full-text · Article · Oct 2014 · Korean Journal of Ophthalmology
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    • "Retinal damage can be reduced by changing some of these parameters. Pascal technology utilises an exposure time of 10 ms for macular photocoagulation and 20 ms for PRP (Jain et al., 2008). Our study revealed that this brief exposure requires a higher power to achieve the desired therapeutic lesion. "
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    ABSTRACT: To compare the safety and efficacy of Pascal laser photocoagulation in comparison with the conventional laser photocoagulation in the treatment of diabetic retinopathy. A prospective randomized case series study was done on 120 procedures done in 120 patients divided into two main groups, group A, patients undergoing focal or modified grid macular laser and group B, patients undergoing panretinal photocoagulation (PRP). Each of the two groups were subdivided into two subgroups randomly in the first we used conventional laser photocoagulation (groups A1 and B1) and in the other we used Pascal laser photocoagulation (groups A2 and B2). Procedures in groups A1,2 and in groups B1,2 had successful outcomes. Significantly higher powers were required with the Pascal (groups A2 and B2) than with conventional laser (groups A1 and B1) (p < 0.001) in eyes that underwent PRP and focal/modified grid macular treatment with both systems. No adverse events were noted in all groups. The Pascal photocoagulator is safe, rapid, effective, with rapid learning and had short exposure time. Although the shorter pulse duration of the Pascal necessitates the use of a higher power, it is not associated with adverse effects.
    Full-text · Article · Apr 2011 · Saudi Journal of Ophthalmology
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    • "Retinal photocoagulation using 10- to 30-ms pulse duration may be less destructive and initiate healing responses within the retina (Jain et al. 2008). The localization of medium pulse duration burns has recently been reported in humans (Muqit et al. 2008). "
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    ABSTRACT: Purpose: To establish safe laser parameter standards for 10–30 ms Pascal® laser in clinical practice and to evaluate clinical and visual outcomes using this 532-nm multi-spot photocoagulation system. Methods: Retrospective observational case series of 313 patients treated between 2006 and 2008. Evaluation of eight groups: A – panretinal photocoagulation (PRP) for proliferative diabetic retinopathy (PDR); B – focal laser treatment for clinically significant diabetic macular oedema; C – grid laser for diffuse diabetic macular oedema; D – sector PRP for ischaemic branch retinal vein occlusions (I-BRVO); E – full PRP for ischaemic central retinal vein occlusions (I-CRVO); F – macular laser treatment for macular oedema secondary to non-ischaemic BRVO; G – full PRP for rubeosis iridis and/or neovascular glaucoma (NVG) secondary to I-BRVO, I – CRVO or PDR; H – laser retinopexy for retinal breaks/degenerations. Results: Mean LogMAR visual acuity for all procedures improved postlaser (p = 0.065), and laser prevented visual loss in 85% eyes. Topical anaesthesia was only required. At mean follow-up of 5 months, 72% procedures had a successful clinical outcome. Significantly higher powers were required for PRP using Pascal® compared to conventional laser (p = 0.001) in PDR, I-BRVO, I-CRVO and NVG. Sixty-seven per cent of patients (15/20) were successfully treated with single-session 20-ms PRP using a mean 1952 burns. There were no laser-associated adverse effects or ocular complications associated with multi-spot PRP or macular Pascal® arrays. Conclusions: The clinical efficacy using 10- to 30-ms pulse duration Pascal® laser is comparable to conventional standard protocols used for the treatment of vascular retinal disorders. Higher power, 10- to 30-ms pulse duration laser may be safely and effectively used in clinical practice.
    Full-text · Article · Feb 2010 · Acta ophthalmologica
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