How can I put an optional value in this condition?

How can I put an optional value in this condition?

func mapView(mapView: MKMapView, regionDidChangeAnimated animated: Bool) {

    if var annotations = mapView.annotations {
        for annotation in annotations  {
            if let a = annotation as? MKPointAnnotation {
                encontrarEnderecoPara(a)
            }
        }
    }
}