Purpose:
To investigate real-time optical coherence tomography (OCT) scan for the detection of standard and non-visible sub-threshold laser irradiation.
Methods:
An integrated platform composed of a slit lamp, a digital camera, a slit-lamp mounted OCT and a 532 nm laser photocoagulator (Topcon inc., Tokyo, Japan) was used. The laser aiming beam and the OCT beam were aligned for obtaining a real-time tomographic imaging of the irradiated area during laser exposure. Standard and sub-threshold laser irradiation and simultaneous OCT acquisition were tested in artificial and biological samples. Laser testing cards were chosen as artificial samples. Freshly enucleated pig eyes were used for iris irradiation.
Results:
Two parallel rows of ophthalmoscopically visible reference burns were placed on the laser testing cards with the following parameters: spot size 300 µm, power 800 mW, exposure time 100 msec. Then, a series of laser spots with the same size and duration were placed between the reference burns. Powers ranged from 100 mW to 500 mW. OCT scan could detect non ophthalmoscopically-visible irradiation of the artificial sample at a power of 200 mW. Ophthalmoscopically and OCT visible lesions were produced using a power of 400 mW. Similarly, reference burns were placed on the iris using the following parameters: spot size 400 µm, power 1,500 mW, exposure time 100 msec. Subsequently, irradiation was conducted at powers ranging from 500 mW to 1,200 mW. Changes in the iris optical properties as detected with real-time OCT in the absence of visible end-points were produced with a power of 860 mW.
Conclusions:
Real-time OCT scanning of laser irradiation can detect non ophthalmoscopically visible lesions both in artificial samples and in pig iris. The proposed method could be used as dosimetry during less invasive sub-threshold laser treatment modalities.
Keywords: laser • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)