Pharmacological mydriasis and optic disc examination

Aim-To determine whether pharmacological mydriasis leads to a significant d ifference in interobserver agreement of optic disc measurement compared wit h examination without mydriasis. Method-A cross sectional study was performed with a pair of observers exami ning the optic disc of two randomised groups of patients, one group before diagnostic mydriasis, and the other afterwards. Horizontal and vertical dis c diameters and cup/disc ratios were measured with a 78 dioptre lens. The s tudy was repeated with another observer pair and two further groups of pati ents. Results-In study A 86 subjects were examined in total (52 without and 34 wi th mydriasis). In study B 87 subjects were examined (45 without and 42 with mydriasis). The 95% limits of agreement of the cup/disc ratio measurement differences were significantly larger without mydriasis (p<0.001 for all st udies (F test)). For both studies examination after mydriasis gave signific antly greater agreement for vertical and horizontal cup/disc ratios. The ca ses with good agreement (0.1 difference or better) for vertical cup/disc ra tios were 37/52 (72%) and 34/45 (76%) without mydriasis and 33/34 (97%) and 40/42 (95%) respectively with mydriasis. Similar differences were recorded for horizontal cup/disc ratios. Disc diameter measurement results showed s imilar differences in study A but were not affected by mydriasis in study B . Conclusions-Examination of the optic disc without pharmacological mydriasis gives significantly poorer interobserver agreement. In this study, the mea n 95% limits of agreement values for all cup/disc ratio values were 0.27 fo r examination without mydriasis and 0.13 for examination with mydriasis. A measure outside these limits would suggest a real difference. This study in dicates that mydriasis is important for reproducible clinical examination i n glaucoma.