Assessment of Anterior Chamber Changes after Laser Peripheral Iridotomy using Anterior Segment OCT

Joshua C. Teichman, MDRichard Lee, MD

Andrea Butler, BScThomas B. Klein, MD FRCSC

Iqbal Ike K. Ahmed, MD FRCSC

Department of OphthalmologyUniversity of Toronto

Financial Disclosure: None of the authors have any financial interest in the contents of this poster.

Background

Gonioscopy is the gold standard for evaluating angle anatomy, and the results of laser peripheral iridotomy (LPI)• Subjective, semi-quantitative, affected by

pressure and lighting, and difficult to perform

Anterior segment OCT (AS-OCT) may offer a precise, objective, non-contact alternative to gonioscopic evaluation

Purpose

To compare the anatomical changes that occur in the anterior chamber after laser peripheral iridotomy (LPI) using anterior segment optical coherence tomography (AS-OCT)

Methods

Using AS-OCT 74 patients with closed or occludable angles, as determined clinically, were imaged before and after LPI

Low resolution scans of the horizontal and vertical meridians were obtained, as well as high resolution scans of all four quadrants

Scans were conducted in the dark

Patients who had previous surgery that would alter angle anatomy were excluded

Data Measures

Data Measures

Iris convexity (IC)

Lens rise (LR:AC)

Anterior chamber depth (ACD)

Results - Division into Groups

Patients could be divided into two groups• Angles opened significantly after LPI,

defined as a change in TIA of > 4°• Angles did not open significantly after LPI,

defined as a change in TIA of < 4°

There were 37 patients in each group

Pre and Post LPI Images

Significant change inangle after LPI

Minimal change in angleafter LPI

Group with ImprovementPreoperatively

Postoperatively

ACD* (p<0.05)

2.213mm 2.253mm

AOD500* (p<0.0001)

79um 189um

TIA* (p<0.0001)

7.8° 19.3°

IT1000 (p=0.47)

418um 425um

IC* (p<0.0001)

324um 132um

LR:AC (p=0.15)

0.253 0.243

Group without Improvement

Preoperatively

Postoperatively

ACD (p=0.21)

2.209mm 2.242mm

AOD500 (p=0.94)

89um 89um

TIA (p=0.45)

10.4° 10.7°

IT1000 (p=0.97)

392um 390um

IC* (p<0.0001)

290um 167um

LR:AC (p=0.47)

0.267 0.264

Conclusions

In the group of patients whose angles opened significantly after LPI (change in TIA of > 4°):• AOD500 increased significantly • IC decreased significantly

In the group of patients whose angles did not open significantly after LPI (change in TIA of < 4°):• No significant change in AOD500 • IC decreased significantly

This may demonstrate that their narrow angles are likely due to a combined mechanism of pupil block and plateau iris

Conclusions

AS-OCT was useful in the objective measurement of iridocorneal angles before and after LPI

AS-OCT appears to be helpful in differentiating mechanisms of narrow angles:

Pupil block

Lens-related

Plateau iris

AS-OCT may be useful in predicting the effect of LPI preoperatively