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Donna Nguyen, Nicholas Bell, Lauren Blieden, Laura Baker, Alice Chuang, Robert Feldman; Effect of Laser Peripheral Iridotomy on Trabecular-Iris Surface Area Over 360 Degrees in Primary Angle Closure. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4812. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Trabecular-iris surface area 750 (TISA750) is a measurement commonly used to characterize the anterior chamber angle depth. By using Swept Source Fourier domain anterior segment optical coherence tomography (FD ASOCT), TISA750 can now be calculated every 1.4 degrees over the entire circumference of the anterior chamber angle. Clinically, it is believed that the entire angle deepens after laser peripheral iridotomy (LPI); however, this has never been quantitatively measured. The purpose of this study is to evaluate the effect of LPI on TISA750 over the entire angle circumference in primary angle closure (PAC) eyes.
Thirteen consecutive eyes with PAC and Spaeth gonioscopy grades A or B scheduled for LPI were included. LPIs were placed temporally. Eyes were imaged in both 2D and 3D modes using the Angle Analysis Scan on the CASIA SS-1000 ASOCT (Tomey, Nagoya, Japan) preoperatively and 3 months postoperatively. An experienced reader using the Anterior Chamber Analysis and Interpretation software (ACAI, Houston, Texas) identified the scleral spur landmarks (SSLs) on the higher resolution 2D images (both horizontal and vertical scans). The ACAI software automatically transferred the SSLs to the same location on the 3D images and then interpolated SSLs for the rest of the angle. These were confirmed or adjusted by the reader. Average TISA750 was calculated for each location at each time point based on these SSLs.
Thirteen eyes of 7 patients were evaluated. The average age was 59.4 (± 10.6) years. Eight of the LPIs were within 20 degrees inferotemporal to the horizontal meridian and 5 were within 20 degrees superotemporal to the horizontal meridian. Overall, average TISA750 increased from 0.033 mm2 to 0.062 mm2 post-LPI and was greater than the pre-LPI TISA750 at all locations except 30-40 degrees below the horizontal meridian. Figure 1 shows the average TISA750 pre- and post-LPI.
The clinical impression of circumferential angle deepening after LPI is confirmed quantitatively. TISA750 increases over the entire circumference of the angle with the exception of 30-40 degrees below the horizontal meridian. We hypothesize that the lack of deepening in this location may be related to post-LPI iris thickening inferior to the area of the LPI. This deserves further study.
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