Asthenopia and the dark focus of accommodation.

To study asthenopia, we compared the dark focus of accommodation of 54 symptomatic and 56 asymptomatic control subjects. The two groups were matched for age and cycloplegic refractive error. Symptomatic subjects were defined as those who complained of asthenopia daily even though their refractive error had been corrected. Subjects with other eye diseases that could produce asthenopia such as strabismus or aniseikonia were excluded. Using a Nidek Autorefractometer AR1600, we first measured non-cycloplegic refractive error (Non-Cyclo R) in a bright room, then the dark refractive state (Dark R) in complete darkness using the instrument with the optical target light extinguished and, finally, determined the cycloplegic refractive error (Cyclo R) after instilling cyclopentolate hydrochloride. The difference between Dark R and Cyclo R was defined as DFcus (Cyclo R) and that between Dark R and Non-Cyclo R as DFcus (Non-Cyclo R). We found both DFcus (Cyclo R) and DFcus (Non-Cyclo R) to be smaller in the symptomatic than in the asymptomatic subjects, indicating that asthenopia is associated with a low rather than a high level of tonic accommodation.