Predictability of Morphological Changes of the Anterior Chamber Angle after Laser Iridotomy by Ultrasound Biomicroscopy

 

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Abstract

Background: Laser peripheral iridotomy is a useful method in primary angle-closure eyes to prevent angle-closure attack and development of glaucomatous optic nerve damage. The aim of this study was to quantify morphological changes after LPI and their impact on intraocular pressure, and to evaluate predictive parameters for enlarging the anterior chamber angle after laser peripheral iridotomy. Patients and Methods: Ultrasound biomicroscopy images and intraocular pressure before and after laser peripheral iridotomy from 62 eyes of 34 patients with primary angle-closure were retrospectively analysed. Anterior chamber angle, anterior chamber depth, lens thickness, iris curvature and a newly defined parameter, the end-iris-lens vault were measured. Results: In each quadrant anterior chamber angle was on average significantly larger (at 12 oʼclock: from 10.1° to 15.0°; at 3 oʼclock: from 13.4° to 19.8°; at 6 oʼclock: from 12.2° to 18.5°; at 9 oʼclock: from 12.9 to 17.9°; p < 0.001) and iris curvature significantly smaller (at 12 oʼclock: from 0.26 mm to 0.10 mm; at 3 oʼclock: from 0.21 mm to 0.08 mm; at 6 oʼclock: from 0.25 mm to 0.08 mm; at 9 oʼclock: from 0.21 mm to 0.08 mm; p < 0.001) after laser peripheral iridotomy. Anterior chamber depth, lens thickness and end-iris-lens-vault did not significantly change. Anterior chamber angle in each quadrant (p < 0.05), and iris curvature at 3 and 6 oʼclock positions (p < 0.05) were highly predictive for the enlargement of the anterior chamber angle after laser peripheral iridotomy. Intraocular pressure was slightly lower after laser peripheral iridotomy (from 16.6 mmHg to 16.1 mmHg). Conclusion: In primary angle-closure eyes, laser peripheral iridotomy enlarges the angle and flattens the iris significantly. This study demonstrated that a small anterior chamber angle and a large iris curvature are predictive parameters for a greater enlargement of the anterior chamber angle after laser peripheral iridotomy. These new findings underline the importance of the ultrasound biomicroscopy and may help in counselling patients about laser peripheral iridotomy.

Zusammenfassung

Hintergrund: Die periphere Laser Iridotomie ist eine nützliche Methode bei Augen mit primärem Engwinkel, um einen Winkelblock und einer glaukomatösen Optikusnervenschädigung vorzubeugen. Das Ziel dieser Studie war es, morphologische Veränderungen des Vorderabschnittsegments nach peripherer Laser-Iridotomie und ihren prädiktiven Einfluss sowie auf die Öffnung des Kammerwinkels und auf den Augeninnendruck zu beurteilen. Patienten und Methoden: Ultraschallbiomikroskopie Bilder und Augeninnendruck wurden vor und nach peripherer Laser-Iridotomie von 62 Augen von 34 Patienten mit primärem Engwinkel retrospektiv analysiert. Der Kammerwinkel, die Vorderkammertiefe, die Linsendicke, die Iriskurve sowie ein neuer Parameter, der End-Iris-Lens-Vault, wurden gemessen. Ergebnisse: In jedem Quadranten war der vordere Kammerwinkel signifikant größer (bei 12 Uhr: von 10,1° zu 15,0°; bei 3 Uhr: von 13,4° zu 19,8°; bei 6 Uhr: von 12,2° zu 18,5°; bei 9 Uhr: von 12,9 zu 17,9°; p < 0,001) und die Iriskurve war signifikant kleiner (bei 12 Uhr: von 0,26 mm zu 0,10 mm; bei 3 Uhr: von 0,21 mm zu 0,08 mm; bei 6 Uhr: von 0,25 mm zu 0,08 mm; bei 9 Uhr: von 0,21 mm zu 0,08 mm; p < 0,001) nach Laser Iridotomie. Die Vorderkammertiefe, die Linsendicke und der End-Iris-Lens-Vault hatten keine signifikante Veränderung. Der Kammerwinkel war signifikant prädiktiv in jedem Quadranten (p < 0,05), und die Iriskurve war signifikant prädiktiv an der 3-Uhr- und der 6-Uhr-Position (p < 0,05) für die Öffnung des vorderen Kammerwinkels nach peripherer Laser-Iridotomie. Der Augeninnendruck war geringfügig niedriger nach peripherer Laser-Iridotomie (von 16,6 mmHg zu 16,1 mmHg). Schlussfolgerungen: In Augen mit primärem Engwinkel öffnet sich der Winkel und verflacht sich die Iris nach peripherer Laser-Iridotomie signifikant. Diese Studie konnte aufzeigen, dass ein kleiner Kammerwinkel und eine große Iriskurve prädiktive Parameter für eine größere Kammerwinkelöffnung nach Laser-Iridotomie sind, und unterstreicht den Stellenwert der Ultraschallbiomikroskopie in der Beratung von Patienten über periphere Laser-Iridotomie.

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