[Optical coherence tomography: from retina imaging to intraoperative use - a review]

Optical coherence tomography (OCT) is new diagnostic procedure that has rapidly evolved in the last years. The recently developed spectral domain OCT allows one to increase the imaging speed by a hundred times compared to the first generation time domain OCT and enables three-dimensional imaging as well as real-time imaging of fast moving structures. Volumetric imaging improves the quantitative measurement of morphology and the evaluation of temporal changes. In addition, an exact correlation with images acquired with other imaging modalities is possible. Real-time imaging enables also the use of OCT during examinations with the slit-lamp and during ophthalmological surgery.

A spectral domain OCT was adapted to a slit lamp. 70 patients (91 eyes) were examined at the anterior or posterior segment of the eye. Images of healthy structures and different pathologies were compared to OCT images obtained with Stratus 3, Spectralis, and the SL-OCT. To demonstrate the feasibility of OCT during surgery, spectral domain OCT devices working with 20,000 and 210,000 A scans per second were coupled by specially developed optics to the camera port of a surgical microscope. The device was tested with phantoms and enucleated pig eyes.

A 5 kHz spectral domain OCT can image the retina during slit lamp-based indirect ophthalmoscopy with a quality similar to that of the Stratus 3. In addition, relevant structures of the anterior segment were imaged. Here, compared to commercially available devices, the imaged field was smaller and the angle of the anterior chamber was not directly visible due to the 830 nm wavelength, which had to be used for retinal imaging. Through the surgical microscope, a volumetric imaging of epithelium, Bowman's, Descemet's membranes, limbus, iris, lens, conjunctiva and sclera was demonstrated with several tens of centimetre working distance. Instruments and incisions in the cornea were visualised with 20 microm precision. Real-time imaging and visualisation of volumetric OCT data were also demonstrated. In principle, all technical problems of an intraoperative use of OCT have been solved and a clinical trial will start in the near future. OCT has the potential to improve the precision of surgical interventions and may even enable new interventions.