Long-term stability of the dark focus of accommodation.

For 1 year we monitored the stability of the accommodative state assumed in darkness (the dark focus) of five subjects. Our results are similar to previously reported individual mean values. The magnitude and pattern of the variability in the dark-focus also demonstrate individual differences. Despite this individual variability, all five subjects oscillated around a stable mean dark-focus value throughout their respective measurement periods. This study indicates the feasibility of using the dark-focus as a basis for correcting the anomalous myopias, in particular night and empty-field myopia.