Check vertex visibility in OpenGL ES 2.0

How can I check if vertex is visible in the most simple way?

If my vertex shader looks like:

void main(void) {
  vec4 glPosition = vec4(VTPosition.x * VTAspectRatio, VTPosition.y, VTPosition.z, 1.0);
  gl_Position = VTProjection * VTModelview * glPosition;
} 

Can I check visibility on CPU the same way ?

Vector4 vertex = {0.5, 0.5, -1.0, 1.0};

vertex = projectionMatrix * modelViewMatrix * vertex;

if vertex x and y value is in range -1.0 .. 1.0 (viewport coordinates) it is visible