  Recent X-ray observations of microquasars and Seyfert galaxies reveal broad
emission lines in their spectra, which can arise in the innermost parts of
accretion disks. Simulations indicate that at low inclination angle the line is
measured by a distant observer as characteristic two-peak profile. However, at
high inclination angles ($> 85^0$) two additional peaks arise. This phenomenon
was discovered by Matt et al. (1993) using the Schwarzschild black hole metric
to analyze such effect. They assumed that the effect is applicable to a Kerr
metric far beyond the range of parameters that they exploited. We check and
confirm their hypothesis about such a structure of the spectral line shape for
the Kerr metric case. We use no astrophysical assumptions about the physical
structure of the emission region except the assumption that the region should
be narrow enough.
  Positions and heights of these extra peaks drastically depend on both the
radial coordinate of the emitting region (annuli) and the inclination angle. It
was found that these extra peaks arise due to gravitational lens effect in the
strong gravitational field, namely they are formed by photons with some number
of revolutions around black hole. This conclusion is based only on relativistic
calculations without any assumption about physical parameters of the accretion
disc like X-ray surface emissivity etc.
  We discuss how analysis of the iron spectral line shapes could give an
information about an upper limit of magnetic field near black hole horizon.
