Night Myopia and Dark Focus of Accommodation

Influence of an Imaginary Target on the State of Accommodation Under Scotopic Conditions

Shifts in accommodation at decreasing luminance levels are considered as principle cause for night myopia. Previous studies with laser optometers quantified the dark focus of accommodation up to 3 D. In addition to the measurement of dark focus, the aim of this study was to investigate the influence of an imaginary target at finite distances on the state of accommodation at scotopic luminance.

Accommodation was measured by using an open-field autorefractor (WAM 5500, GRAND SEIKO). Full corrected right eyes of 39 subjects aged from 18 to 40 years were investigated in this randomized, cross-sectional study. Accommodation measurements in photopic luminance were taken for 6 m of empty field and for optotype fixation at 2 m, 1 m and 0.5 m. At scotopic luminance, dark focus of accommodation was examined directly after darkening and after 10 min of dark adaptation. After adaptation, subjects had to visualize imaginary targets in the four distances while accommodation was measured.

Inclusion Criteria:

• age 18 - 44
• visual acuity at least 0.8 (5/6)

Exclusion Criteria:

• medication with an impact on the visual system
• visual disease or disease with an impact on the visual system
• pregnancy or other hormonal variances
• drug usage
• overfatigue at the period of investigation
• mental handicap