A study was made of the phenomenon of mechanophosphene (phosphene induced by pressure on eyeball) in 190 patients with retinal detachment, glaucoma, opaque optica media attended with pigmental retinitis, and high myopia. Besides subjective registration of mechanophosphene some patients underwent an objective one by recording a mechanoelectroretinogram using a specially designed device, which made it possible to judge quantitatively as to the mechanical sensitivity of the retina in different sectors of its periphery. Determination of the 'field of vision' with the aid of mechanophosphene enabled one to roughly judge the functional integrity of the retinal periphery, starting from its extreme portion and up to 30 to 40°. Mechanophosphene is unquestionably of diagnostic and prognostic value in cases of retinal detachment, and in deciding as to the expediency of an operative intervention in cases of glaucoma in combination with a cataract. A simultaneous control effected by ophthalmoscopy, biomicroscopy, ultrasonic echography and mechanoelectroretinography confirmed the reliability of mechanophosphene as an approximate indicator reflecting the functional activity of the retinal periphery.