The +1.00 blur test is one of the most commonly used procedures for checking the spherical correction at the end of a subjective refraction (Bennett & Rabbetts 1998, Elliott 1997, Fletcher & Still 1998). It involves adding a +1.00DS lens to the distance refractive correction and remeasuring the distance VA. Textbooks suggest that VA should reduce with a +1.00DS from 6/5 to 6/12 or 6/18 (Elliott 1997), 6/6 to 6/18 (Bennett & Rabbetts 1998, Fletcher & Still 1991) or 6/5 to 6/18 (O’Leary 1988). In a patient with normal VA (using the Snellen chart, this is typically the bottom line of the chart as the measurements provide truncated data), a visual acuity with the +1.00DS better than 6/18, say 6/9, is taken to indicate that the refractive correction may have been under-plussed (or over-minused) and should be rechecked. As underplussing or over-minusing a refractive correction is typically due to insufficient relaxation of accommodation during the subjective refraction, the test is principally used in pre-presbyopic patients.