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R. Regler, A. Walter, P. Prahs, D. Theisen-Kunde, C. Alt, R. Brinkmann, C. Framme; Structural Changes of the Retina After Conventional Laser Photocoagulation and Selective Retina Treatment (SRT) in Spectral Domain OCT. Invest. Ophthalmol. Vis. Sci. 2009;50(13):207.
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High resolution optical coherence tomography (OCT) in patients can be achieved using spectral domain OCT. This may allow a first-time evaluation of the extent of damage to the retinal pigment epithelium (RPE) and the neurosensory retinal layer after conventional laser photocoagulation and selective retina treatment (SRT), which only targets the RPE while sparing the photoreceptors.
In a retrospective observation spectral domain OCT was used to evaluate the appearance of 175 conventional retinal laser lesions (CRL) lasting 1 hour up to 4 years after treatment in ten patients with diabetic maculopathy and 91 SRT lesions in 9 patients with central serous retinopathy, geographic atrophy and diabetic maculopathy lasting 1 hour up to 2 years. CRL lesions were applied with an ophthalmoscopically slightly whitish-gray appearance (Nd:YAG laser at 532nm wavelength; power: 100-200mW; retinal spot diameter: 100µm; pulse duration: 100ms), while the only angiographically visible SRT lesions were applied with a Nd:YLF (527nm; pulse duration: 200ns [30 pulses at 100Hz]; energy : 100-200µJ/pulse; retinal spot diameter: 200µm).
All CRL lesions revealed high reflectivity throughout the full-thickness neurosensory tissue one hour after irradiation suggesting complete neurosensory coagulation. In contrast, the neural retina appeared unaffected immediately after SRT. For both lesion types the RPE appeared to be thinner immediately after treatment. Within a period of four weeks both lesion types showed a thickening of the RPE layer indicating RPE proliferation. While neurosensory retina appeared unaffected in SRT lesions during the follow-up period, within seven days a full-thickness strong contraction and an increased reflectivity of the neurosensory layers was observed for CRL lesions. CRL lesions of about one year and older revealed RPE atrophy combined with significant changes in the neurosensory tissue whereas SRT lesions one year and older presented unaffected neurosensory structures and a firm RPE layer.
Spectral domain OCT can clinically be used to exactly follow the extent of laser induced lesions over time. For both, CRL and SRT laser lesions a postoperative RPE proliferation process was observed with subsequent appearance of atrophy only in CRL lesions whereas the neurosensory retina appeared unaffected following SRT. This underlines the selective effect of SRT also in humans.
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