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R. Ritch, S.K. Dorairaj, C. Tello, J.M. Liebmann; Why Is The Superior Angle Narrower Than The Inferior Angle In Eyes With Narrow Angles? . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5470.
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In patients with narrow angles, the superior angle is usually narrowest and peripheral anterior synechiae generally form first superiorly, but no explanation for this has ever been provided. We investigated patients with uniocular asymmetric angle grades to determine the cause of this phenomenon.
Asymmetric angles differed by two or more Shaffer grades (appositionally closed, slit, 1, 2, or 3) between superior and inferior angles in the sitting position by 4–mirror gonioscopy without pressure on the cornea. Ultrasound biomicroscopy (UBM) was performed supine in light and dark using the Paradigm model P–40 UBM. The superior and inferior angles of eyes developing appositional closure between light and dark were graded as S–type (apposition beginning at Schwalbe’s line) and B–type (apposition beginning at the angle apex (Sakuma T, et al: J Glaucoma 1997;6:165). The Y intercept, the apparent distance from scleral spur to iris insertion was measured using UBM pro 2000 software program.
The slit–lamp grading difference between superior and inferior angles was 2 grades in 14/15 (93.3%) and 3 grades in 1/15 (6.6%) eyes. Nine eyes developed appositional closure by UBM. Of these, 8 had a B–type angle and one had an S–type angle superiorly. Four of these eyes also had apposition inferiorly, one with a B–type angle and 3 with S–type angles. From light to dark, the Y–intercept (apparent distance from scleral spur to iris insertion) decreased from 24.03 to 8.58 µm in superior angles, while that in the inferior angle paradoxically increased from 30.80 to 52.52 µm. Ciliary body position did not differ between the superior and inferior angles.
Asymmetry of angle narrowing appears to occur primarily on the basis of asymmetry of iris insertion distance rather than asymmetry of position of the ciliary body (e.g. different degrees of plateau iris). Whether this asymmetry of angle insertion is hereditary or acquired remains to be determined.
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