The most constant and critical finding in retinitis pigmentosa is

Typical electrophysiological changes in retinitis pigmentosa appear early in the disease before the subjective symptoms or the objective signs (fundus changes) appear and are most constant and critical finding. Electroretinogram (ERG) is initially subnormal (scotopic affected before photopic; b-waveaffected before ;a wave) and eventually extinguished. Electro-oculogram {EOG) is subnormal with an absence of light peak. Bony spicules are not seen in all cases. Tubular visual field can occur due to other causes as well like open angle glaucoma.