Instrument myopia and the resting state of accommodation.

I measured the refractive errors of 210 eyes of 105 subjects by means of the Canon Autoref R-1 and by the Nikon autorefractometer NR7000. I also measured their dark focus of accommodation (DF) with the Canon instrument. Refractive errors had similar effects on the differences between the results produced by the two autorefractometers and on the changes in DF. The differences were statistically significant. Differences between the results produced by the two autorefractometers are thought to be mainly due to instrument myopia, which itself is strongly related to the resting state of accommodation. My results indicate a hyperopic shift in high hyperopes when they are observing through an instrument.