Lawrence S. Evans

Comparison of three methods of estimating the parameters of the Naka-Rushton equation

The Naka-Rushton equation empirically describes the amplitude R of the darkadapted electroretinogram b-wave, as a function of stimulus luminance L, asR/Rmax = Ln/(Ln +Kn). Estimating the three parametersRmax,n, andK of this function from electroretinogram data is of both experimental and clinical interest. Several different approaches have been developed to accomplish this analysis, but these approaches may derive different estimates of the three parameters. To examine this possibility, we compared the results of three methods of fitting the Naka-Rushton equation to data sets obtained from 30 normal subjects. Two methods were nonlinear curve-fitting programs; the third method involved fitting a regression line to transformed data. The results indicate that solutions provided by these methods have consistent differences, which may be an important consideration when comparing results reported in studies that used different curve-fitting methods.

Increased Intraocular Pressure in Severely Burned Patients

Six eyes of three patients with severe body burns had intraocular pressure ranging from 37.2 to 81.7 mm Hg. Because of extreme orbital congestion, lateral canthotomies were performed, which caused abrupt decrease in intraocular pressure (range, 17.6 to 49.0 mm Hg). None of the patients had a history of glaucoma, narrow angles, or any precondition for a pupillary block mechanism. Two patients survived and neither had optic nerve damage or increased intraocular pressure after hospital discharge. Tonometry should be performed in patients with severe burns and orbital congestion, especially in those patients receiving large amounts of intravenous fluids. Lateral canthotomies may be of benefit to relieve potentially damaging high intraocular pressure.

Effects of topical suprofen and flurbiprofen on the miosis produced by anterior chamber irrigation with cholinergic agonists

ABSTRACT Pretreatment with topical nonsteroidal anti‐inflammatory drugs is common practice to maintain maximal pupil dilation for cataract surgery. Most surgeons also inject a cholinergic agent intracamerally for miosis after intraocular lens insertion. We evaluated the effects of topical suprofen and flurbiprofen on the miosis induced by anterior chamber irrigation with either acetylcholine or carbachol. One eye of 30 pigmented rabbits was dilated with cyclopentolate HCl and phenylephrine HC1. Three groups, each composed of ten eyes, received flurbiprofen, suprofen, or a control. In each group, five eyes received acetylcholine by anterior chamber irrigation and five received carbachol. Pupil diameters were measured with calipers before and five minutes after irrigation by an observer unaware of the treatment regimen. Irides irrigated with carbachol constricted less than those irrigated with acetylcholine (P = .016). In anterior chambers irrigated with carbachol, suprofen was associated with less miosis than either tears (P = .005) or flurbiprofen (P = .0091; however, if the infusion was performed with acetylcholine, no differences between the three groups were noted (P = .44).