Biomedical subjects
Publications and source records attributed to J T Holladay.
We report a patient requiring keratoplasty who developed acute pulmonary edema following the administration of a retrobulbar block for anesthesia. A variety of factors that may have been implicated in the genesis of this complication are discussed.
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As part of the Prospective Evaluation of Radial Keratotomy (PERK) study, we examined the relationship between post-operative refractive error and visual acuity without correction. We included 394 eyes (one eye per patient) with refractive errors ranging from -3.00 to +3.00 diopters one year after radial keratotomy. Within each 1-D range of the spherical equivalent of the refractive error, the visual acuity spanned five to ten Snellen lines. For visual acuities of 20/16 to 20/50, the refractive error spanned 3 to 5 D. Additionally, operated eyes had a better average uncorrected visual acuity than unoperated eyes with a similar refractive error. Within the narrow range of refraction between -2.00 and -2.50 D, the mean uncorrected visual acuity was 20/125 for 56 unoperated eyes and 20/63 for 29 operated eyes, a difference of three Snellen lines.
The disparity between functional outdoor vision and the acuity measured in the standard refracting lane is well known among clinicians. A simple device, the brightness acuity tester (B.A.T.), was developed to predict a patient's functional outdoor acuity. The B.A.T. has an illuminated hemispheric bowl, 60 mm in diameter, with a 12-mm aperture. Fourteen normals and 50 patients with cataracts were tested using the B.A.T. and then tested outside in bright sunlight. The B.A.T. correlated extremely well (r = +0.84, P less than .0001) with the acuities measured outside. There was no decrease in visual acuity in the 14 normal patients, but there was a one to ten line decrease in vision among the cataract patients. Upon retesting, the B.A.T. scores did not vary, while outside testing scores did change due to variable outdoor ambient light levels on sunny days. The B.A.T. is a simple, repeatable, useful test for predicting functional outdoor acuity.
The resolution of 96 polymethylmethacrylate intraocular lenses with convexo-plano optics, ranging in power from 13 to 27 diopters, was measured in air and water. The resolution of each lens was expressed in linear units of resolving power, which is the maximum number of line-pairs that can be resolved per millimeter, as described in the current ANSI Standard Z80.7-1984. There was no clearly defined relationship between linear resolving power measured in air and that measured in water. Measurements on high power lenses (greater than 20 diopters) indicate that it is possible for an intraocular lens to meet the current 100 line-pair per millimeter standard for resolution and still be a limiting factor in a patient's best attainable visual acuity. An alternative method for evaluating lens resolution is to determine the resolution efficiency (the relative percentage performance of a lens compared to a diffraction-limited lens of the same dioptric power). Using these units, a consistent and predictable relationship from air to water was demonstrated. Our findings confirm that if a minimum standard of 30% resolution efficiency in air is established, in contrast to linear resolving power, the lens will perform near its diffraction limit when implanted in the eye. For intraocular lenses of materials other than polymethylmethacrylate, a minimum resolution efficiency in air other than 30% may be required.
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We reviewed the intraocular lens power calculations on 512 posterior chamber lens implantations and determined four ways to reduce the estimated 5% incidence of large postoperative refractive "surprises" (greater than 2 diopters [D]): First, preoperatively identify those patients who have greater than a 1-D difference between the theoretical and linear regression formulas. Second, repeat axial length and corneal power measurements in these patients to eliminate random error. Third, develop an individualized theoretical formula that accounts for constant bias. Fourth, encourage manufacturers to improve instrumentation for measuring corneal power and axial length. We also examined the disparity between the linear regression formula and the curvilinear theoretical formula.
Pterygia often induce with-the-rule astigmatism as they invade the cornea. Significant amounts of astigmatism occur long before a pterygium encroaches on the visual axis. We present an example in which a 3.3-mm pterygium resulted in 9 diopters (D) of with-the-rule astigmatism. Six weeks after the pterygium removal, the patient's cornea became spherical, but by three months the pterygium had recurred 2.2 mm onto the cornea and induced 4 D of with-the-rule astigmatism. Since the second removal and the application of beta irradiation, there has been no recurrence. The final correction was -1.00 + 1.00 X 127 degrees with a visual acuity of 20/20 +3. Characteristic keratoscopic photographs are shown and contrasted with surgically induced with-the-rule astigmatism.
A method is described for determining the power of an intraocular lens (IOL) within the eye by measuring the horizontal dimension of the corneal reflected image (Purkinje-Sanson I) and the anterior IOL reflected image (Purkinje-Sanson III) as seen through a standard slitlamp with a target positioned 68 mm anterior to the focal plane of the biomicroscope. The horizontal K-reading (at 180 degrees) and the anterior chamber depth are the two other parameters necessary to calculate the exact power of the IOL. Seven tables that use these four measurements have been provided, eliminating the need for complex calculations. To determine the accuracy of this technique, ten implanted IOLs ranging from 9 diopters (D) to 27 D were chosen and their powers calculated; these calculated values were then compared to the actual IOL powers. The largest error was 0.5 D and the average error was 0.17 D.
The optimal posterior capsulotomy diameter should be equal to the normal pupillary diameter in dark conditions to avoid glare and other undesirable optical aberrations. We studied 14 patients whose average pupillary diameter following cataract surgery was approximately 3.9 mm in scotopic conditions.
Complaints of light streaks, such as might be seen with a Maddox rod or Bagolini lens, are becoming more common with the trend toward extracapsular cataract surgery. The light streaks are usually a result of high plus cylinders somewhere in the patient's optical system. Windshields, spectacles, contact lenses, lashes, an excessive tear meniscus, intraocular lens scratches, and posterior capsular opacification are possible causes that can be easily identified and treated.
Analysis of data from four neodymium:YAG laser manufacturers submitted to the Food and Drug Administration (FDA) on over 17,000 cases indicate the procedure is safe and effective for cutting opaque posterior lens capsules. A successful opening in the pupillary membrane was achieved in 98% of the cases, and vision improved in 84% of the cases. Clinically significant risks include: a rise in intraocular pressure two to four hours after treatment, damage to the intraocular lens, and rupture of the anterior hyaloid face.
Clinical studies of intraocular lenses (IOLs) as investigational devices have been regulated in the United States by the Food and Drug Administration (FDA) since 9 February 1978. As of August 1982, data have been collected on more than one million IOLs implanted. During the last 12 months of the study, 409 000 IOLs were implanted. Visual acuity of 20/40 or better at one year after surgery was present in 85% of over 45 000 cases reviewed. Increasing patient age, surgical problems, postoperative complications, and adverse reactions were factors that reduced the visual acuity. The current trend in the USA is for implantation of posterior chamber and anterior chamber IOLs.
By averaging vertical and horizontal applanation readings from the Goldmann tonometer, we developed a simple technique that accurately measures intraocular pressure in patients with regular corneal astigmatism. This procedure eliminates the need for keratometry and oblique alignment of the applanator. When the applanator is oriented normally, with the mires displaced horizontally, intraocular pressure is underestimated for with-the-rule corneal astigmatism and overestimated for against-the-rule corneal astigmatism. The error is approximately 1 mm Hg for every 4 diopters of astigmatism. For oblique axis corneal astigmatism, the error is smaller and approaches zero when the axis is either 45 or 135 degrees.
Clinical studies of intraocular lenses (IOLs) as investigational devices have been regulated in the United States by the Food and Drug Administration (FDA) since February 9, 1978. As of August 1982, data have been collected on more than one million IOLs implanted. During the last 12 months of the study, 409,000 IOLs were implanted. Visual acuity of 20/40 or better at one year after surgery was present in 85% of over 45,000 cases reviewed. Increasing patient age, surgical problems, postoperative complications, and adverse reactions were factors that reduced the visual acuity. The current trend in the USA is for implantation of the posterior chamber and anterior chamber IOLs.
Twenty patients were evaluated by quantitative endothelial biomicroscopy and the resulting endothelial cell densities compared with those from a specular microscope. Estimated cell densities by this technique, when compared with the specular microscope, demonstrated a Pearson correlation coefficient of +0.977, an average error of -7% and an absolute error of 12%. There were no errors greater than 26% except for one extremely low cell density of 318 cells/mm2 for which the estimate was 476 cells/mm2. This rapid, inexpensive technique requires counting the number of endothelial cells seen across the horizontal diameter of the 0.2-mm projected spot beam of a standard biomicroscope. From this count and the known spot size the endothelial cell density may be accurately calculated. A simplified four-step technique for performing specular microscopy using only the standard biomicroscope and a method for accurately measuring the size of the projected slit lamp spot beam are explained.
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