[Instrument myopia as a possible source of error in nyktometer examinations].

In comparative studies covering 142 eyes a "night myopia" of 0.5 to 1.5 D was found in 33 eyes with the Nyktometer (Rodenstock) and in 23 eyes with the Mesoptometer I (Oculus). In 17 eyes the same degree of "night myopia" was determined with both instruments, while in 16 eyes it was found to be more severe when measured with the Nyktometer than with the Mesoptometer. In one eye this myopia was only found with the Mesoptometer. This more severe "night myopia" measured with the Nyktometer is probably attributable to "instrument myopia."