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

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.

Two-dimensional micro-displacement measurement for laser coagulation using optical coherence tomography

“…Although these displacements decrease, it is not perfectly reversible. This reversibility is consistent with the previous report by Müller et al [10].…”

“…For instance, the laser-induced tissue displacement is expected to be less than a few micrometers between B-scans [10]. A future modification containing a protocol that would measure the displacement between successive B-scans, would overcome this limitation.…”

“…Another example is the use of optical coherence tomography (OCT) [8]. OCT is used to measure not only the depth-resolved scattering changes but also the tissue displacements that occur because of the thermal expansion induced by the laser coagulation with the help of phase-sensitive measurements [9,10].…”

“…Second, OCT visualizes a spatially-resolved structural change, which is necessary to observe localized tissue alteration. Third, OCT can directly monitor the thermal changes of the tissue including mechanical displacement, where such displacements can be measurable with the help of phase-sensitive measurements [9][10][11][12], speckle tracking [13], digital image correlation [14], and decorrelation [15,16]. Therefore, OCT is a promising tool for thermal expansion measurements.…”

In vivo optical imaging of physiological responses to photostimulation in human photoreceptors

“…Nonphysiologic effects, such as thermal expansion, would cause a direct decrease once the stimulus stops (22) and can therefore be ruled out. Also, we expect hemodynamic changes to last longer than a few 100 ms and not be as highly localized as observed here.…”