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BACKGROUND/OBJECTIVES: To analyze the ophthalmic characteristics of congenital prepapillary vascular loop (PVL) and to propose a new morphologic classification dividing the loops into six types. SUBJECTS/METHODS: Collaborative multinational multicentre retrospective study of PVL cases. RESULTS: There was a total of 49 cases (61 eyes), 37 unilateral (75.5%) and 12 bilateral (24.5%), 32 arterial type (65.3%) and 18 venous type (36.7%) (one patient had either kind in each eye). The mean number of loops per eye was 2.7 (range, 1-7). The loops were asymptomatic in 42 cases (85.7%). Other findings included: the presence of cilioretinal artery (14 cases), retinal vascular tortuosity (26 cases), amaurosis fugax (1 case), branch retinal artery occlusion (1 case) and vitreous haemorrhage (3 cases). Six morphologic loop types could be discerned based on elevation (flat vs. elevated), shape (figure of 8 or corkscrew with hyaline sheath), number (multiple or single), location (central or peripheral), lumen size (arterial vs. arteriolar) and presence of vascular tortuosity or vitreous traction. CONCLUSIONS: PVL are usually asymptomatic and can be divided into six morphologic types with different pathogenesis during early embryogenesis.

In this paper we obtain comparison results for the quasilinear equation − Δ p , x u − u y y = f with homogeneous Dirichlet boundary conditions by Steiner rearrangement in variable x, thus solving a long open problem. In fact, we study a broader class of anisotropic problems. Our approach is based on a finite-differences discretization in y, and the proof of a comparison principle for the discrete version of the auxiliary problem A U − U y y ≤ ∫ 0 s f , where A U = ( n ω n 1 / n s 1 / n ′ ) p ( − U s s ) p − 1 . We show that this operator is T-accretive in L ∞ . We extend our results for − Δ p , x to general operators of the form − div ( a ( | ∇ x u | ) ∇ x u ) where a is non-decreasing and behaves like | ⋅ | p − 2 at infinity.