Quantitative AS-UBM (Q-UBM)
Standard Q-UBM analysis
The basic Q-UBM analysis includes:
1. RTR – spur to spur distance (scleral spur)
2. RD – spur depth
3. ITI – IPE to IPE distance (peripheral end of iris pigment epithelium)
4. ID –iris root depth or IPE depth
5. XTX – apex to apex distance (apex of ciliary processes)
6. XD – apex depth
7. ACD – anterior chamber depth
8. CA – ciliary angle
9. IA – iris angle
10. IH – iris vault height
The basic AS-UBM imaging is recommended in dilated eye. It is more repeatable as it reduces the need for control of far/near focus and lighting conditions and it is more practical in clinical setting after it is determined that the dilated patient is a candidate for cataract surgery. Additional AS-UBM in near focus, distance focus or pilocarpine state settings could be performed at the second patient visit.
In contrast with the anterior segment optical coherence tomography (AS-OCT) and other AS optical imaging methods, anterior segment ultrasound biomicroscopy (AS-UBM) also comprises the images of structures behind the iris, such as the ciliary body and processes, peripheral lens or the haptics of the intraocular lens. Basic quantitative analysis (Q-UBM) developed by our center measures the entire anterior segment in horizontal plane and includes two contralateral anterior angles at 0 and 180 degrees.
This is in contrast to classical UBM imaging from 1980’s that we call Anterior angle UBM (AA-UBM) to distinguish it from AS-UBM, because it analyzed the dimensions of only one anterior angle and not the whole anterior segment with both contralateral angles. Quantitative analysis of one AA-UBM image angle was first described by Pavlin in 1980’s using parameters such as angle opening distance (AOD), angle recess area (ARA) and trabecular space area (TISA). These parameters represented only one out of 360 degrees of the iridocorneal angle and were used mainly for the classification of narrow angle glaucoma. The reference plane was the tangential line to scleral surface at the point of the vertex of the anterior angle. AS-UBM uses as reference plane the frontal plane.