Purpose:  To determine the relationship between the morphology and electrophysiological properties of the inner retina in patients with retinitis pigmentosa (RP), because most of recent clinical trials for RP depend on the inner retinal function.

Methods:  Typical RP patients whose visual acuities were better than 0.7 in decimal unit were studied.  The ganglion cell complex (GCC) and the photoreceptor inner/outer segment (IS/OS) junction within the central 10 degrees were examined by spectral-domain OCT.  The amplitude of P1 and multifocal photopic negative response (mfPhNR) of the mfERGs within the central 10 deg were assessed.  Eyes were divided into two groups according to the length of the IS/OS junction: Group A, length <3 mm; and Group B, length ≥3 mm.

Results:  The mean GCC thickness was significantly thicker in Group B (P<0.01).  The mfERGs were recordable in 21 eyes (68%) in Group A, and 19 eyes (95%) in Group B.  The mean P1 amplitude was significantly larger in Group B (P<0.01).  There was no significant difference in either the mfPhNR amplitude or the mfPhNR/P1 ratio between the two groups.  There was a significant correlation between the GCC thickness and the mfPhNR amplitude in Group A (P=0.02) but not significant in Group B.

Conclusions:  The significant correlation between the thinning of the inner retina and the shortening of the IS/OS junction indicates the RP patients have not only alterations of the photoreceptors but also the inner retina.  The significant correlations between the amplitudes of mfPhNR and the thickness of GCC in Group A indicate that the electrophysiological properties of inner retina are dependent on the morphology of inner retina in the RP patients with severely damaged outer retina.