The subject invention utilizes the characteristics of in vivo tissue impedances to provide an embodiment of a retinal rake capable of providing a visible and/or preferably an audible signal to a surgeon that more clearly indicates which type of tissue(s) is in contact with the retinal rake. A preferred embodiment comprises a handheld, battery operated retinal rake having two electrodes, wherein at least one electrode is the modified retinal rake. Upon contact with different optical tissues, e.g., epiretinal membranes, retinal tissue, vitreous humor, etc., the electrodes detect varying impedances which are translated by onboard circuitry into various signals that indicate what type of tissue, fluid, structure, etc. is in contact with the retinal rake.