Iris lens distance to predict the risk of intraocular pressure elevation after dark room provocative test

Purpose To investigate if a new ultrasound biomicroscopy (UBM) parameter, iris lens distance (ILD), and its model could predict clinically significant intraocular pressure (IOP) elevation after darkroom provocative test (DRPT). Methods Cases with a peripheral anterior chamber depth less than one-fourth corneal thickness were enrolled. All subjects underwent UBM examination and DRPT if possible. Anterior chamber depth (ACD) and ILD were measured in the central axis at different positions in dark (ACDD, ILDD) and bright (ACDB, ILDB). An IOP elevation over 5 mmHg and 8 mmHg was set as cutoffs for a positive DRPT result (positive-5 and positive-8). SAS 9.3 statistical software was used to manage and analyze data and calculate the linear probability model (LPM). Another 17 patients (34 eyes) were included to validate the model. Results Two hundred and ten (210) UBM images qualified for analysis. ILD was significantly less in the dark than in the bright and in patients with a positive DRPT result ( p < 0.001). The LPM for positive-5 and positive-8 were P = 1.14 + (− 0.49*ILDD) + (− 0.41*ACDD) ( n = 210, R 2 = 0.1079, AUC = 0.715), and P = 0.87 + (− 0.44*ILDD) + (− 0.35*ACDD) ( n = 210, R 2 = 0.1358, AUC = 0.807), respectively. Conclusions LPMs based on ILD could predict the risk of an IOP elevation over 5 mmHg or 8 mmHg. The LPM for positive-8 reached a good level of diagnostic accuracy.