Depth-resolved measurement of lesion formation process during retinal laser photocoagulation by using phase sensitive optical coherence tomography

Abstract

Purpose : Retinal laser photocoagulation requires dosage management to control the severity of laser lesion. High-sensitivity, depth-resolved tissue deformation measurement might be a promising technology for the dosage management. Retinal lesion formation due to photocoagulation was investigated by local tissue deformation measurement based on phase sensitive optical coherence tomography (OCT).

Methods : Seven ex vivo enucleated porcine eyes were involved in the experiment. The 1-μm wavelength spectral-domain OCT system combined with coagulation laser (GYC-1000, Nidek Co., Ltd., Japan) was used. Laser illumination with 20 configurations (5 powers times 4 durations) were applied to each eye. During the laser illumination, an M-mode OCT scan was acquired at the illumination point. Depth-localized optical path length (LOPL) change which derives local tissue deformation was computed by phase analysis of the M-mode OCT. A deformation metric was computed by integrating the absolute of the LOPL change. In addition to the M-mode scan, OCT volumes were acquired before and after photocoagulation. The existence of laser lesion was determined by the hyper-scattering spot appearance in the en face slice of the post-coagulation OCT at the outer nuclear layer.
The maximum deformation metric and laser power and duration were compared to laser lesion existence by using multiple logistic regression analysis.

Results : Time-resolved LOPL change measurement revealed the tissue deformation during photocoagulation. The start time of tissue coagulation was measured as abrupt change of LOPL. After this time, the deformation metric is significantly increased. The regression model with the maximum deformation metric and laser power and duration is good to explain the laser lesion generation (McFadden's pseudo-R² = 0.91). Wald test indicates that the deformation metric is only one statistically significant (p < 0.01) factor to explain laser lesion formation.

Conclusions : Tissue deformation measurement by using OCT will be a good investigation and monitoring method of laser lesion formation.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

A representative experimental result of one porcine eye with 400 mW power and 100 ms duration of coagulation laser. (a) Time-resolved LOPL change rate of the porcine retina. (b) The deformation metric at the corresponding time point of (a). OCT cross sections (c) before and (d) after the laser coagulation.