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Biomedical subjects

D D Koch

Publications and source records attributed to D D Koch.

At least 109 records · Page 6Linked to original sources
PubMed1992

Visual results and complications following posterior iris-fixated posterior chamber lenses at penetrating keratoplasty.

We retrospectively reviewed the records of 13 patients with pseudophakic bullous keratopathy who had undergone penetrating keratoplasty combined with suturing of a posterior chamber intraocular lens (PC-IOL) with angulated haptics to the posterior iris using the four optic positioning holes. Corneal endothelial decompensation was associated with anterior chamber IOLs in nine cases, with iris-fixated lenses in three cases, and a subluxated PC-IOL in one case. Visual acuity was 20/40 or better in 46%, 20/50 to 20/100 in 31%, and 20/200 or worse in 23%. These visual results are comparable with those reported for other similar surgical series. In four of seven eyes that had preoperative peripheral anterior synechiae (PAS), postoperative extension of at least 2 clock hours occurred; progressive angle-closure glaucoma developed in two of the four. In all four eyes, the extension occurred in the region directly overlying the lens haptics. The angulated haptics of iris-sutured PC-IOLs may predispose to extension of PAS and development of progressive angle-closure glaucoma.

Aged↗
PubMed1992

Comparison of plastic vs. glass evacuated serum-separator (SST) blood-drawing tubes for common clinical chemistry determinations.

We evaluated a plastic evacuated blood-drawing tube containing an integral serum-separating barrier gel, by direct comparison with a glass counterpart. The plastic tube demonstrated no differences when compared for common clinical chemistry analytes with multiple types of instruments and systems. A total of 260 such different combinations were studied with emphasis on tests sensitive to drawing and handling indexes such as lactate dehydrogenase and potassium. A total of six separate blood drawings were tested with no significant differences noted in these tests. The total study included subjective evaluations of the plastic tube's use as a blood-drawing device and objective studies based on quantitative test results from normal and hospitalized patients and use of the primary sampling tubes (both plastic and glass) for 48-h storage.

Blood Specimen Collection↗
PubMed1991

Surface analysis of surface-passivated intraocular lenses.

We analyzed the surfaces of six different types of poly(methyl methacrylate) intraocular lenses using electron spectroscopy for chemical analysis (ESCA), static secondary ion mass spectroscopy (SIMS), and two techniques for determining surface energies. The tested lenses were (1) Ioptex lathe-cut surface-passivated, (2) Ioptex lathe-cut, (3) another manufacturer's lathe-cut, (4) cast-molded, (5) polyfluorocarbon-coated, and (6) polyvinylpyrrolidone-grafted. The ESCA testing revealed marked differences in the chemical composition of the surfaces of the polyfluorocarbon-coated and polyvinylpyrrolidone-grafted lenses compared to the other four. Minute amounts of silicon were present on the cast-molded and surface-passivated lenses. Static SIMS testing revealed the presence of siloxane contaminants on the three lathe-cut and the cast-molded lenses; a statistically smaller amount of siloxane was present on the surface-passivated lenses. Contact angle and surface energy analysis revealed statistically lower surface energies for the polyfluorocarbon-coated materials and statistically higher surface energies for the polyvinylpyrrolidone-grafted; we found no differences in the contact angles and surface energies among the surface-passivated, lathe-cut, and cast-molded lenses.

Biocompatible Materials↗
PubMed1991

Pupillary size and responsiveness. Implications for selection of a bifocal intraocular lens.

The authors measured the pupil sizes of 132 subjects and correlated these to selected designs of annular bifocal intraocular lenses (IOLs). Pupils were measured under five different testing conditions that simulated representative visual tasks: (1) driving at night, (2) reading in dim illumination, (3) reading in bright illumination, (4) distant viewing in indirect sunlight, and (5) distant viewing in direct sunlight. Pupil size diminished with age and with increased illumination. Because of accommodative pupillary constriction, there was little difference in pupil size measured while reading in bright indoor illumination and distant viewing in indirect sunlight. Evaluating a patient's pupil size permits the individualized estimation of the eye's bifocal function following implantation of each of the annular-design bifocal IOLs.

Accommodation, Ocular↗
PubMed1991

Determination of maximal incision length for true small-incision surgery.

We studied induced astigmatism in cadaver eyes to determine how small a limbal incision must be to avoid a long-term corneal flattening induced by limbal incisions along the meridian of the incision. We performed scleral pocket incisions (2.0 to 5.5 mm in 0.5-mm increments) on 12 fresh human cadaver globes, recessing the incisions 0.5 mm to simulate the natural wound sliding that causes corneal flattening. We found that with increasing incision length there was a nearly linear increase in corneal flattening. The maximal incision length that minimized induction of corneal flattening in excess of 0.25 diopters was 3.0 mm.

Astigmatism↗
PubMed1990

Posterior polar cataracts: a predisposition to intraoperative posterior capsular rupture.

We performed phacoemulsification or planned extracapsular cataract extraction on posterior polar cataracts in 31 eyes of 22 patients and experienced eight cases of posterior capsular rupture (26%). Capsular rupture occurred during removal of the posterior polar opacity or during cleaning of the posterior capsule after the opacity had been removed. We believe that excessive adherence of the opacity to the posterior capsule and unusual thinness of the capsule predisposed these eyes to posterior capsular rupture.

Adult↗
PubMed1990

Multilamellar hydrodissection in phacoemulsification and planned extracapsular surgery.

Multilamellar hydrodissection is the injection of balanced salt solution into multiple lamellae of the lens, cleaving it into a small nucleus and multiple layers of cortex. In phacoemulsification, the smaller nucleus reduces phacoemulsification time, and the thicker bed of cortex provides greater protection for the posterior capsule. In extracapsular extraction, the smaller nucleus can be more readily extracted, which is particularly advantageous when capsulorhexis is performed. Creation of multiple cortical lamellae facilitates their aspiration, either with the phacoemulsification or irrigation/aspiration tips. Multilamellar hydrodissection increases the predictability and safety of phacoemulsification and planned extracapsular cataract extraction.

Cataract Extraction↗
PubMed1990

Survey of the clinical use of glare and contrast sensitivity testing.

In August 1988, we surveyed a random 10% sample of the members of the American Society of Cataract and Refractive Surgery about their use of contrast sensitivity and glare testing. Of 396 surveys mailed, 214 were returned for a response rate of 54.3%. Thirty-six percent of respondents used glare testing alone; 5.6% used contrast sensitivity testing alone; 23.4% used both test modalities; 35% used neither. The most common uses of glare and contrast sensitivity testing were to evaluate visual function in patients who have cataracts, secondary cataracts, and/or intraocular lens problems.

Cataract↗
PubMed1990

Predicting effects of quality-control practices on the cost-effective operation of a stable, multitest analytical system.

The cost-effective operation of an analytical system depends on quality-control (QC) practices such as the QC procedure itself (control rules, number of control measurements); the batch size or the run length; and the use of bracketed, nonbracketed, or pre-control modes of operation. Predictive value models that predict the defect rate and test yield of each test, as well as of the system as a whole, have been used to study these practices and to develop strategies for improving the quality and productivity of a multitest analyzer. Quality was optimized for most tests by achieving high error detection and low false rejection by the QC procedures. For a few tests where ideal QC performance could not be achieved, predictive models indicate that high quality is achieved, predictive models indicate that high quality is achieved as long as the observed stabilities (low frequencies of errors) of the measurement procedures are maintained. In our laboratories, productivity gains of 2.9% ($17,400/year) were achieved by changing QC procedures. Predictive models indicate that further gains are possible by increasing batch size and changing from bracketed to nonbracketed control operation. In general, the common practice of bracketed control on stable analytical systems may need to be re-examined owing to its effect on the cost of operation.

Chemistry, Clinical↗
PubMed1990

Selection of medically useful quality-control procedures for individual tests done in a multitest analytical system.

Quality-control (QC) procedures (i.e., decision rules used, numbers of control measurements collected per run) have been selected for individual tests of a multitest analyzer, to see that clinical or "medical usefulness" requirements for quality are met. The approach for designing appropriate QC procedures includes the following steps: (a) defining requirements for quality in the form of the "total allowable analytical error" for each test, (b) determining the imprecision of each measurement procedure, (c) calculating the medically important systematic and random errors for each test, and (d) assessing the probabilities for error detection and false rejection for candidate control procedures. In applying this approach to the Hitachi 737 analyzer, a design objective of 90% (or greater) detection of systematic errors was met for most tests (sodium, potassium, glucose, urea nitrogen, creatinine, phosphorus, uric acid, cholesterol, total protein, total bilirubin, gamma-glutamyltransferase, alkaline phosphatase, aspartate aminotransferase, lactate dehydrogenase) by use of 3.5s control limits with two control measurements per run (N). For the remaining tests (albumin, chloride, total CO2, calcium), requirements for QC procedures were more stringent, and 2.5s limits (with N = 2) were selected.

Autoanalysis↗
PubMed1990

Effect of transscleral neodymium: YAG cyclophotocoagulation on intraocular lenses.

A neodymium: YAG laser operating in the thermal mode was used to irradiate isolated intraocular lenses (IOLs) and to perform transscleral cyclophotocoagulation on pseudophakic autopsy eyes to investigate the potential damage to IOL haptics such irradiation may cause. In the isolated IOLs, 70 mJ of energy deformed and partially melted both polymethylmethacrylate (PMMA) and polypropylene haptics. One of the capsular-fixated PC-IOL haptics in an autopsy eye partially melted when irradiated with the maximum energy level (8.8 J), with the aiming beam focused 1 mm posterior to the limbus and maximal posterior focus offset.

Humans↗
PubMed1989

Refractive complications of cataract surgery after radial keratotomy.

Four patients underwent cataract extraction with posterior chamber lens implantation several years after radial keratotomy. All four patients experienced an initial hyperopic shift caused by an early postoperative corneal flattening of greater than or equal to 1 diopter. This flattening partially regressed, leaving the patients with a mean of 0.42 diopter of persistent corneal flattening. We found the Binkhorst and the Holladay intraocular lens calculation formulas to be more accurate than the SRK II for these patients. Corneal curvature measured with the keratometer was less accurate for intraocular lens calculations than was a value derived by subtracting the refractive change induced by the radial keratotomy from the patients' keratometric measurements obtained before radial keratotomy.

Cataract Extraction↗
PubMed1989

Axial myopia increases the risk of retinal complications after neodymium-YAG laser posterior capsulotomy.

We conducted a retrospective analysis of Q-switched neodymium-YAG laser capsulotomies performed in 122 eyes between April 1984 and June 1987. Retinal complications occurred in 3 (2.5%) of 121 eyes followed up for 1 year and in 2 (3.6%) of 55 eyes followed up for 2 years. Four eyes developed rhegmatogenous retinal detachments and 1 developed an acute symptomatic retinal tear. No patients developed clinical cystoid macular edema (visual acuity 20/30 or worse). These retinal complications were significantly correlated with axial myopia, preexisting vitreoretinal disease, male gender, younger age, vitreous prolapse into the anterior chamber, and spontaneous extension of the capsulotomy.

Adolescent↗
PubMed1989

Glare and contrast sensitivity testing in cataract patients.

I measured contrast sensitivity and glare in 51 cataract patients who had Snellen visual acuities of 20/60 or better. The VCTS contrast sensitivity plates, the Miller-Nadler glare tester, Baylor visual function tester, and the Stereo Optical glare tester were used. Patients indicated that the Baylor visual function tester most closely reproduced their daytime glare symptoms and that the Stereo Optical glare tester most closely reproduced their nighttime glare symptoms. Scores on the Stereo Optical glare tester and VCTS contrast sensitivity chart statistically were most strongly correlated with patients' complaints and the severity of their lens opacities. Contrast sensitivity and glare testing are important adjuncts in evaluating patients who have visual complaints and yet have good Snellen acuities.

Cataract↗
PubMed1989

Improved resolution of specular micrographs.

The purpose of specular photomicrography of the corneal endothelium is to depict fine cellular morphology and to determine total cell density. The use of silver-based photographic films to record the cells and generate enlarged paper prints yields the highest resolution currently possible. Previously, the quality of these prints was diminished when the highly resolved cell image was combined with the standardized grid used for quantification, since the sub-optimal quality of the grid's plastic substrate caused optical aberrations. We present a prototype device and a modified technique that enables the full resolution of the microscope to be represented on photographic prints and allows highly detailed views of the endothelial mosaic to be depicted with or without the standardized grid.

Endothelium, Corneal↗
PubMed1989

Endogenous endophthalmitis with lenticular abscess caused by Enterobacter agglomerans (Erwinia species).

We report for the first time a case of metastatic endophthalmitis caused by the gram-negative organism Enterobacter agglomerans (Erwinia species). One day following internal hemorrhoidal ligation, the patient developed anterior uveitis that progressed to panophthalmitis with a lenticular abscess and a necrotic retina. Despite aggressive surgery and appropriate antibiotic therapy, the affected eye lost useful vision.

Abscess↗