OCT could assist in laser tissue bonding of corneal incisions

A laser tissue bonding apparatus integrated with an optical coherence tomography (OCT) probe is a plausible instrument that allows for temperature-controlled laser bonding of incisions in the cornea, according to Israeli researchers. The OCT probe can provide real-time feedback of structural change of the corneal tissue, and indicate the progress and end point of the bonding.

Reporting in The International Society for Optics and Photonics’ Proceedings of SPIE, the researchers noted that laser tissue bonding offers several desirable attributes compared to suturing, including water-tight closure, non-contact application, reduced scarring, and faster healing.

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The researchers added that when a corneal incision is made and then sutured, substantial surgical ability is needed to ensure that the shape of the cornea is not changed at the end of the healing process. Such unplanned geometric changes in the shape of the cornea may cause significant reductions in patients’ visual acuity.

The researchers performed a bond strength experiment on 51 freshly enucleated bovine eyes, using a temperature-controlled laser bonding system, and analyzed both the rate of successful bonding and the burst strength of the successful bonds.

They found that the bond strength of the successful operations peaked at 80°C. They also noted that the bond strength showed a steady increase as a function of the operating temperature. This decreased slightly at very high temperatures, although this decrease was usually irrelevant because of high thermal damage. “This means that although the procedure fidelity decreases as we increase the temperature past the peak, the incisions which are successfully joined using higher temperatures do display a stronger bond in comparison to those which succeeded in the ‘optimal’ setting,” the researchers wrote.

The researchers then conducted an experiment on 40 freshly enucleated bovine eyes to assess the thermal effects of laser tissue bonding on the corneal tissue using OCT imaging, histological section evaluations, and tensile strength measurements.

Next: Change of tissue structure

The tissue structure of the cornea is changed by the heat generated to obtain the bonding; this change presents as a bowl-shaped lesion around the heated spot. In their experiment, the researchers use OCT as the modality for the assessment of these lesions, and used the histological section evaluations and tensile strength measurements for validation. Using a dedicated image-processing algorithm, the researchers produced a quantitative analysis of the lesions’ attributes.

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The researchers noted that lesion depth is the most effective measure to assess the extent of the tissue’s reaction to heat. Their analysis of lesion depth produced by different heating profiles found a linear dependence on both the temperature of the laser tissue bonding and the exposure time. They also evaluated the bond strength for several temperatures at the same heating time (20 seconds), and found 70°C to be the optimal value.

According to the researchers, the OCT output proved to be extremely suitable for measuring the tissue reactions to the laser tissue bonding process by providing a non-destructive, fast method for detecting denaturation of cells and allowing them to be distinguished from non-affected areas.

“This validation was one of the main goals and achievements of this research, and is an important stepping stone for further LTB research using OCT,” the researchers wrote. “This method requires far less skill and time than histological analysis, which is the main technique used today in this type of research, making the OCT more accessible, appropriate for large data sets, and significantly cheaper in the long run. Moreover, since the OCT imaging is non-destructive, it allows for in vivo research, which opens up a whole new set of possibilities regarding the tracking of healing, which had been unavailable in the past.”

The researchers added that, theoretically, a 3D scanning apparatus built specifically to support laser tissue bonding operations could allow a physician to actually see the bonding of the incision in real time.

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“This proves the viability of the idea that was the trigger to this experiment, which consisted of the incorporation of an OCT probe into the physician’s LTB utensil via an optical fiber,” the researchers concluded. “Such a contraption would advance the feedback concept  . . . in LTB to a new level. The idea being that through a correlation between denaturation and bond strength, it could be possible to design a feedback mechanism, showing the depth of the reaction, indicating to the physician to move to the next point, and automatically stopping irradiation of the affected points to avoid unintended heating.”