I would like to ask the community for a reference on the following subject: is there some thing as an equivalence between the definitions of Uniform Visibility manifolds and Gromov $\delta$-hyperbolic manifolds? Or even an implication. By visibility I mean:


A Riemannian manifold $(M,g)$ with riemannian distance $d$ is said to be a *visibility manifold* if given $p\in M$ and $\varepsilon>0$ there exists $r=r(p,\varepsilon)>0$ with this property: if $\sigma:[a,b]\longrightarrow M$ is a geodesic segment such that $d(p,\sigma)\geqslant r$, then $\sphericalangle\_p(\sigma(a),\sigma(b))\leqslant\varepsilon$, where $\sphericalangle\_p(\sigma(a),\sigma(b))$ is the angle between the tangent vectors of the minimizing geodesics joining $p$ to $\sigma(a)$ and to $\sigma(b)$.


The manifold is said to be *uniform visibility manifold* if $r$ doesn't depend on $p$.


I already know, based on the work of Morse, that the $\delta$-hyperbolic condition implies some sort of shadowind property of quasi-geodesics. Also, based on the work of Bonk, we see that the shadowing property implies $\delta$-hyperbolicity (Bonk, M.: *Quasi-geodesic segments and Gromov Hyperbolic Spaces*). I'm trying to understand the relation (if there exists some) between visibility, Gromov hyperbolicity and the shadowing property.


Thanks in advance.



Visibility spaces and Gromov hyperbolicity
For Cartan-Hadamard manifolds the equivalence of uniform visibility and Gromov hyperbolicity is proved in the following [paper](http://www.ams.org/mathscinet-getitem?mr=1293874) by Kaimanovich, Theorem 2.9. 


