A

Because intra-ocular pressure in the 100 patients is approximately normally distributed, about 95 % of individual values are expected to lie within ±2 standard deviations of the mean. 2 × SD = 2 × 1 = 2 mm Hg; therefore the lower 95 % limit is 30 – 2 = 28 mm Hg. [Altman, 2005, PMID 16303711]