Anterior Segment Optical Coherence Tomography
Anterior segment OCT (AS-OCT) enables high-resolution imaging of the anterior segment, including the anterior chamber angle (Fig 13-4). Compared with UBM, a major limitation of AS-OCT is that it does not allow visualization of the ciliary sulcus and ciliary body. As with UBM, AS-OCT does not always yield images that allow reliable identification of angle landmarks. Moreover, neither modality can differentiate between appositional and synechial angle closure—a distinction that is possible only with dynamic gonioscopy. In contrast, AS-OCT is a noncontact modality that can be performed relatively rapidly.
Table 4-2 Anterior Segment Par ameters Obtained From Anterior Segment Imaginga
Figure 4-13 An example of an anterior segment OCT scan that demonstrates iridotrabecular contact.
(Courtesy of Angelo P. Tanna, MD.)
Gonioscopy remains the reference standard method for evaluating the anterior chamber angle, but it has limitations. A skilled examiner and patient cooperation are required, and the results are inherently subjective. The illumination required to obtain an adequate view of the angle structures can cause miosis, resulting in the relative opening of the angle compared to its status at lower levels of ambient light. These limitations are largely obviated with AS-OCT; however, correct identification of the scleral spur is not always possible, complicating the interpretation of the degree of angle crowding.
AS-OCT has the potential to add meaningful information to aid in the detection of angle-closure disease. Both time-domain and spectral-domain OCT, operating at various wavelengths, have been studied and seem to have similar diagnostic performance. The principles for evaluation of the angle are similar to those previously described for UBM, as are many of the quantitative parameters (see Table 4-2 and Fig 12-4). As with UBM, automated quantitative analysis is available on some platforms.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.