An exploratory subgroup analysis found that lesions with a greatest linear dimension 4 mm ( the size of the treatment zone ) and a macular volume greater than the median ( 7.4 mm ( 3 ) ) were more responsive to SRT , with 3.9 PRN injections versus 7.1 in comparable sham-treated participants ( P = 0.001 ) and mean BCVA 4.4 letters superior to sham ( P = 0.24 ) .