import math


def zangle(points, eye_radius):
    """Determines the Z depth and angle-from-Z axis of an SVG feature
    (ostensibly a circle, polygonalized by get_points()); for example,
    the depth of the iris, or the start and end angles for the curve
    that's lathed to form the sclera. Pass point list and eye radius."""
    xdist = points[0][0]
    ydist = points[0][1]
    radius = math.sqrt(xdist * xdist + ydist * ydist)  # R of SVG feature
    z_depth = math.sqrt(eye_radius * eye_radius - radius * radius)
    angle = math.atan2(radius, eye_radius) * 180.0 / math.pi

    return (z_depth, angle)