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First Author: V.Bo ITALY
Co Author(s): D. Venzano R. Scotto C. Traverso
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To describe a technique for the differential diagnosis among angle closure (AC) mechanisms through digital scans combined with a new dynamic test.
Anterior segment Optical Coherence Tomography (AS-OCT) was performed using the RT 100-2 (Optovue Inc., Freemont, CA, USA). We used a scleral depressor (Heine, Germany) to perform a corneal indentation. Corneal anaesthesia was induced with with Oxibuprocaine 0,4%.
54 eyes of 33 patients (8 males, 25 females) were enrolled in the study and divided in 2 groups: group 1 comprised eyes with irido-corneal angle width less than 25Ḟ width in both the nasal and temporal sectors (n=51), while group 2 comprised patients with a previous acute angle closure attack in the fellow eye (n=3). The Irido-corneal angle was graded using the Spaeth system. AS-OCT was performed and angle width was measured in the nasal and temporal quadrants. After topical anaesthesia corneal indentation was performed on central cornea; a scleral depressor to increase pressure in the anterior chamber and move aqueous towards the iris; angle width was recorded again during indentation. A cut-off value of 25Ḟ was taken to identify the angles to be classified as narrow", and the width variations from this value were recorded while indentation was performed. The main value of the nasal and temporal sector was used for statistical analysis. Two-tailed T-test was used both to verify the significance of changes in angle width before and during corneal indentation.
In group 1, an increase in angle width reaching the cut-off value of 25Ḟ was observed in 20 eyes (39%) in at least one sector during corneal indentation (mean width during indentation 28.3Ḟḟ5.6; P<0.0001); among the remaining 31 eyes (61%), a significant increase was observed in 25 (49%) but did not reach the cut-off value (15.6Ḟḟ5.3; P<0.0001), while in 6 eyes (12%) a reduction in angle width was observed (6.7Ḟḟ7.0; P=0.23). Two eyes of group 2 (66.6%) showed an increase in angle width over 25Ḟ (25.8Ḟḟ4.5), while in the remaining eye a smaller increase was measured (9.4Ḟ). In group 1 the mean difference in angle width before and during corneal indentation was 7.5Ḟḟ6.5; in subjects widening to 25Ḟ during indentation (subgroup A) the angle width was enlarged by 13.2Ḟḟ5.8 (P=0,0005). This was larger than in subgroup B (4.9Ḟḟ3.0; P=0,021); the differences between subgroup A and B are statistically significant (P<0.0001).
Angle-closure glaucoma is a leading cause of irreversible blindness. Diagnosis and treatment are intrinsically related to angle assessment techniques. Purpose of gonioscopy is to determine the topography of the anterior chamber angle and is indicated to establish the possible mechanism of obstacles to aqueous outflow. Dynamic indentation gonioscopy is valuable for examining eyes with narrow or closed angles and to differentiate optical from either appositional or synechial closure, as well as for measuring the extent of angle-closure; however this method requires specific training and has some subjective interpretation. Anterior segment optical coherence tomography (AS-OCT) provides a rapid method for the quantitative recording of angle features and gives supplemental information useful to understand the mechanism for angle closure. Our technique of DOCTAA is able to identify modifications like plateau iris, appositional or synechial closure, and to have a dynamic evaluation. In eyes with phacomorphic angle closure, during indentation, there were no posterior movements of the iris; in these cases phacoemulsification is an option that must be taken into consideration. In plateau-iris configuration there was little or no movements of the peripheral iris and the angle recess remained narrow; miotic topic treatment or laser peripheral iridoplasty could reduce the crowding of the angle. If a pupillary block, due to peripheral anterior synechia (PAS), is present the adherent area remained attached to the outer wall of the angle, and LPI would be indicated to equalize the pressure in the anterior and posterior chamber. In conclusion, according with our data, DOCTAA could be an useful tool to better understand cases which are not clear-cut with gonioscopy, offering also the possibility of quantitative recording. Thereby therapeutic action could be chosen with a smaller margin of error.