According to a first aspect of the present invention, background light on the seeming invisible (for example, and red / or substantially has a wavelength greater than 580nm, or, at a wavelength of light bleaching, for rods Some), and the target light on the seeming visible (for example, and a green / or substantially in excess of 400nm at 580nm is less than, for example, has a wavelength of about 514nm +/- 50nm for the rod, Alternatively, a device that is arranged to provide one) is the wavelength, target light and the background light and / or is suitable for stimulating the dominant rod) to (co, target light and the background light and are superimposable on each other, using an apparatus where it is devoted to the subject, the target light is incident to the foveal region of the retina of the subject, the target light to the eye characteristics of the subject A method for measuring, by using a) the bleaching light stimulates the retina of the subject in breach of a low level after starting the bleach above b), is maintained at a substantially constant background light While adjusting the target light with initial brightness modulation of the target light is not recognized by the subject then when the subject recognizes the modulation of light target the d) increase the brightness of the target light according to the regulation c) reduces the intensity of the target light and after the input of the e), according to the adjustment received in, indicating a threshold associated with the rod, the input from the subject and, e from step c) f) The above method) the method comprising determining a threshold set by repeating, is associated with the rod over a predetermined period of time is provided.本発明の第1の特徴によれば、ブリーチ光、桿体に対して見せ掛け上不可視の背景光(例えば、実質的に赤で、そして/又は、580nmを超える波長を有し、又は、波長であるもの)、及び、桿体に対して見せ掛け上可視の標的光(例えば、実質的に緑で、そして/又は、580nm未満で400nmを超える、例えば、約514nm+/-50nmの波長を有し、又は、波長であるもの)を提供するように配置された装置であって、前記背景光及び/又は標的光は(共同して)桿体優勢の刺激に適しており、前記背景光及び標的光は相互に重ね合わせ可能であり、そして、前記標的光は被験者に当てられて、前
