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Editors Selection IGR 13-4

Anterior Segment Imaging: Angle measurement: Visante versus SL-OCT

Comment by Lisandro Sakata & Tin Aung on:

21765 Anterior chamber angle measurement with anterior segment optical coherence tomography: a comparison between slit lamp OCT and Visante OCT, Leung CK; Li H; Weinreb RN et al., Investigative Ophthalmology and Visual Science, 2008; 49: 3469-3474

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Anterior segment optical coherence tomography (AS-OCT) is a new technology capable of obtaining real-time images of the anterior chamber angle in a non-contact fashion. Two commercially available AS-OCT devices are currently available ‐ Visante-OCT (Carl-Zeiss Meditec, Dublin/CA, USA) and Slit-Lamp-OCT (SL-OCT, Heidelberg Engineering, Heidelberg, Germany). Although both devices rely on the principle of low coherence interferometry, there are some differences in the way each instrument acquires and processes the anterior segment images. Leung et al. (1061) evaluated the agreement and inter-observer reproducibility of angle measurements obtained with Visante and SL-OCT. Images of the nasal and temporal angles were obtained in 49 eyes of healthy normal subjects. Pupil diameter, angle opening distance, trabecular-iris space area, trabecular-iris angle were measured by two experienced observers using semi-automated analysis software unique for each instrument. These consisted of a computer program developed by the author for Visante-OCT images, and the SL-OCT built-in analysis software.

Clinicians should be aware of the potential differences in angle measurements obtained with different anterior segment OCTs

The study observed that both AS-OCT devices demonstrated good inter-observer reproducibility for angle measurements. However, most of the participants included in their study had open angles on gonioscopy, with a mean Shaffer grading of 3.71 ± 0.46 for the nasal angle and 3.46 ± 0.54 for the temporal angle. The reproducibility of angle measurements in eyes with narrow angle was not assessed and this may not be as good as in open angles. As the location of the scleral spur is less detectable in narrow angles, the variability of these angle measurements is also likely to increase in such eyes. Interestingly, when the authors compared the anterior-segment parameters measured by Visante-OCT and SL-OCT, they found poor agreement between the two devices. Differences in imaging acquisition (state of accommodation, exact scan location, scanning speed) and in imaging processing (algorithms for image dewarping, resolution of the scans) between Visante-OCT and SL-OCT may explain this finding. Clinicians should thus be aware of the potential differences in angle measurements obtained with these instruments.

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