Apraclonidine and anterior segment laser surgery. Comparison of 0.5% versus 1.0% apraclonidine for prevention of postoperative intraocular pressure rise.

PURPOSE: To compare the efficacy of 0.5% and 1.0% apraclonidine in preventing laser-induced intraocular pressure (IOP) elevation after trabeculoplasty, neodymium: YAG (Nd: YAG) iridotomy, and capsulotomy. METHODS: This is a prospective, masked, and randomized study of 83 patients undergoing trabeculoplasty, 62 patients undergoing iridotomy, and 57 patients undergoing capsulotomy. Surgical eyes received one drop of 0.5% or 1.0% apraclonidine immediately after surgery. RESULTS: Intraocular pressure reduced 2 hours after trabeculoplasty in the 0.5% (P = 0.028) and 1.0% (P = 0.004) groups. Intraocular pressure was higher than baseline in a greater number of eyes treated with 0.5% (12 of 39 eyes, 31%) compared with 1.0% apraclonidine (5 of 44 eyes, 11%) (P = 0.032). Intraocular pressure in eyes with a narrow chamber angle was reduced in 16 (85%) of 19 eyes treated with 0.5% and in 10 (84%) of 12 eyes treated with 1.0% apraclonidine after iridotomy. Of patients with chronic angle-closure glaucoma, IOP was similar to prelaser values in 11 (69%) of 16 eyes treated with 0.5% (P > 0.7) and 12 (80%) of 15 eyes treated with 1.0% apraclonidine (P > 0.3). In patients undergoing capsulotomy, pressure was significantly lowered in the 0.5% group (P = 0.04) but not in the 1.0% apraclonidine group. After capsulotomy, both treatment groups had similar (P > 0.3) numbers of eyes with an IOP less than baseline (83% for 0.5% apraclonidine and 81% for 1.0% apraclonidine). CONCLUSION: The single postoperative administration of 0.5% apraclonidine is as effective as the 1.0% concentration in preventing IOP elevation immediately after trabeculoplasty, iridotomy, or capsulotomy.

Analysis of variations in contrast-detail experiments.

Three sources of variability in a contrast-detail (CD) experiment have been quantitated: within-observer variance, between-observer variance, and sample variance. It is concluded that (1) it is more efficient to increase the numbers of replicated images and observers than to increase the number of readings; (2) sampling and between-observer variations are approximately equal; (3) one can expect approximately 10% standard errors in the measured value of threshold detail or threshold contrast in a CD experiment which employs four observers, four replicate image samples, and one reading per observer.

Relative dose efficiencies of antiscatter grids and air gaps in pediatric radiography.

The relative dose efficiencies (RDE) of various antiscatter grids and air gaps were determined for conditions simulating those found in pediatric radiography, using phantoms representing a newborn child, a 5-yr-old and a 10-yr-old child. Our data indicate than an air gap is best for the newborn, due to the low levels of scatter. The 8:1 fiber grid or 15.2-cm air gap without a grid can improve dose efficiency (DE) for the 5-yr-old child by 20%-25% relative to the 3.3-cm air gap and no-grid technique, while for the 10-yr-old child, DE can be improved by 40% with an 8:1 fiber grid.

Dose efficiency of screen-film systems used in pediatric radiography.

Twenty-one screen-film systems were examined using contrast-detail-dose methods in order to determine which were most dose-efficient for use in pediatric radiography. With a given screen, dose efficiency in the noise-limited region (contrast approximately equal to 0.05) was more or less constant (within the range of experimental error) with changes in film speed. When screens with decreased phosphor thickness were used, dose efficiency deteriorated markedly. For a given speed of up to two times Par, rare-earth phosphors offered no advantage over calcium tungstate systems with regard to low-contrast dose efficiency; however, they did increase the speed of the system. Anti-crossover film proved to be an effective means of improving high-contrast detail while maintaining low-contrast dose efficiency.