Imaging thermal expansion and retinal tissue changes during photocoagulation by high speed OCT

Heike H Müller,Reginald Birngruber,Kerstin Schlott,Christina Debbeler,Marco Bever,Ralf Brinkmann,Stefan Koinzer,Gereon Hüttmann,Lars Ptaszynski

doi:10.1364/boe.3.001025

Abstract

Visualizing retinal photocoagulation by real-time OCT measurements may considerably improve the understanding of thermally induced tissue changes and might enable a better reproducibility of the ocular laser treatment. High speed Doppler OCT with 860 frames per second imaged tissue changes in the fundus of enucleated porcine eyes during laser irradiation. Tissue motion, measured by Doppler OCT with nanometer resolution, was correlated with the temperature increase, which was measured non-invasively by optoacoustics. In enucleated eyes, the increase of the OCT signal near the retinal pigment epithelium (RPE) corresponded well to the macroscopically visible whitening of the tissue. At low irradiance, Doppler OCT revealed additionally a reversible thermal expansion of the retina. At higher irradiance additional movement due to irreversible tissue changes was observed. Measurements of the tissue expansion were also possible in vivo in a rabbit with submicrometer resolution when global tissue motion was compensated. Doppler OCT may be used for spatially resolved measurements of retinal temperature increases and thermally induced tissue changes. It can play an important role in understanding the mechanisms of photocoagulation and, eventually, lead to new strategies for retinal laser treatments.

Highlights

Since the introduction of the photocoagulation in 1959 [1], it had become one of the most successful laser therapies in medicine and the standard therapy for diabetic retinopathy [2, 3], branch vein occlusion [4] and central retinal vein occlusion [5]
Series of laser exposures with decreasing irradiance were applied under Optical coherence tomography (OCT) imaging to the retina of the enucleated eyes
Optical coherence tomography is essential for the diagnosis of retinal diseases

Summary

Introduction

Since the introduction of the photocoagulation in 1959 [1], it had become one of the most successful laser therapies in medicine and the standard therapy for diabetic retinopathy [2, 3], branch vein occlusion [4] and central retinal vein occlusion [5]. The laser spots are manually positioned by the physician, who sets the irradiation parameters, i.e the spot size, the applied radiant power, and the irradiation time, according to the subjective evaluation of the appearance of previous lesions. Strength and extension of the coagulated lesions do depend on the irradiation parameters, and on the transmission of the ocular media and the pigmentation of the retina, which both vary between patients. Earlier attempts to use the increase of tissue scattering in the retina [11] or autofluorescence [12] were not successful

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Conclusion