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M. M. Muqit, J. C. B. Gray, G. R. Marcellino, D. B. Henson, L. B. Young, S. J. Charles, G. S. Turner, A. D. Dick, P. E. Stanga; Fundus Autofluorescence and Fourier-Domain Optical Coherence Tomography of Medium-Pulse Pascal versus Conventional Long-Pulse Photocoagulation: Study of Burn Morphology and Healing Responses. Invest. Ophthalmol. Vis. Sci. 2009;50(13):200.
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To investigate the evolution of medium-pulse duration Pattern scanning laser (Pascal: 10 ms, 20 ms) burns in comparison to long-pulse conventional (100 ms) photocoagulation using fundus autofluorescence (AF). To evaluate the AF characteristics using Fourier-Domain optical coherence tomography (FD-OCT) of the outer retina (OR).
Pilot study of consecutive patients with diabetic macular oedema and proliferative diabetic retinopathy that underwent macular and panretinal laser photocoagulation. Fundus photography (FP), FD-OCT (Topcon, 3D OCT-1000), and fundus camera-based AF (Topcon TRC-50DX, type IA) were performed in 20 eyes of 12 patients at 1 hour, 1 week, 2 weeks, 1 month, and one-year following laser.
Threshold laser burns were incompletely visible with colour and red-free FP one hour after laser. AF enabled visualization of complete Pascal arrays at one hour, with localized lack of AF at sites of burns. By observing laser tissue interactions via FD-OCT and AF, all Pascal burns are initially square-edged and displayed equivalent autofluorescence, localised to junction of inner and outer segments of photoreceptors and apical retinal pigment epithelium. With increasing duration of laser pulse, burn size increases with time with a contemporaneous diffuse increase in AF. Over time, Pascal burns reduced in size (100 µm 10 ms: 15% mean reduction; 400 µm 20 ms: 45% mean reduction) in comparison to conventional 100 ms pulse duration burns.
We report in vivo spatial localization and clinical correlations of medium-pulse Pascal and 100 ms burns using AF and FD-OCT. Ophthalmoscopically-invisible and threshold Pascal laser produces highly localized, well-circumscribed burns within OR. Longer-pulse durations produce more diffuse burns due to thermal blooming and greater collateral damage. AF may be used as a monitoring tool after laser photocoagulation, either to confirm successful placement of burns, to plan re-treatments, or when using subthreshold burns.
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