DARK FOCUS OF ACCOMMODATION AND UNCORRECTED VISUAL-ACUITY

We compared the dark focus of accommodation in 33 healthy children, 19 eyes with good uncorrected visual acuity (1.0 or more) vs. 14 with poor uncorrected visual acuity (below 1.0). The two groups were matched for age and cycloplegic refractive error. Cycloplegic refractive error ranged from +0.15 to +1.75 D in the good visual acuity group and from +0.25 to +1.87 D in the poor visual acuity group. The dark focus was defined as the difference between the refractive error in the dark and the refractive error under cycloplegia. Initially, visual acuity was measured subjectively. Next, refractive error in the dark was measured using the Nidek Autorefractometer AR1600 with its optical target light off. Refractive error under cycloplegia was measured 40 min after the instillation of cyclopentolate hydrochloride using the same autorefractometer. There was a significant correlation between the dark focus and the cycloplegic refractive error (r = -0.53, p < 0.01). Despite an equal refractive error under cycloplegia the dark focus was significantly larger in the eyes with good uncorrected visual acuity than in those with poor uncorrected visual acuity (p < 0.01). Tonic accommodation may influence uncorrected visual acuity.