Macular thickness, as measured by OCT, is one of the key outcome measures used in most clinical trials, especially those on diabetic macular edema and AMD. Because Stratus TD-OCT was the most common commercially available OCT instrument in the past decade, most trials are designed based on Stratus OCT.
A percentile (or a centile) is a measure used in statistics indicating the value below which a given percentage of observations in a group of observations fall. For example, the 20th percentile is the value (or score) below which 20% of the observations may be found. The term percentile and the related term percentile rank are often used in the reporting of scores from norm-referenced tests.
A percentage point or percent point (pp) is the unit for the arithmetic difference of two percentages. For example, moving up from 40% to 44% is a 4 percentage point increase. In the literature, the percentage point unit is usually either written out, or abbreviated as pp or p.p.. After the first occurrence, some writers abbreviate by using just point or points.