The RAF Rule provides a binocular gauge to measure objective and subjective convergence as well as accommodation in 1 mm increments.
The RAF Rule is a 50 cm long rule with a slider holding a rotating four-sided cube, each side with a different target. The first has a vertical line with a central dot for convergence fixation. The others provide a limited number of lines of near reading examples.
This instrument is used for determining the objective and subjective convergence points, examining the
accommodation and determining the master eye. The RAF Rule is useful for both diagnosis and treatment.