Biomedical subjects
T A McMillan
Publications and source records attributed to T A McMillan.
Analysis of diode, argon, and Nd: YAG peripheral iridectomy in cadaver eyes.
We compared semiconductor diode, neodymium (Nd): YAG and argon laser iridectomies performed in 14 cadaver eyes using Miyake videographic, histologic and scanning electron analysis. We found that the diode laser created an iridectomy in < 10 applications in blue, hazel and brown irides using 1000-1200 mW over 0.5 seconds. In hazel and blue irides the argon laser created iridectomies at parameters similar to the diode, but required multiple low energy burns in brown irides. Scanning electron microscopy showed pigment epithelial loss with the diode and Nd:YAG laser, and heaped up epithelium at the iridectomy site with the argon laser. Nd:YAG laser had the greatest iridectomy size. This study suggests a possible clinical advantage of diode versus argon laser iridectomies in reduced applications in brown irides and in preventing postoperative pigment occlusion. However, diode laser demonstrated no definite advantage over Nd:YAG laser.
Comparison of diode and argon laser trabeculoplasty in cadaver eyes.
PURPOSE: To evaluate differences in the effects of diode and argon trabeculoplasty on cadaver eye trabecular meshwork. METHODS: The argon laser was used at a 50 mu spot size, 500 to 100 mW of power, and a 0.1 second time interval, and the diode laser was used at a 0.1 to 0.2 second time interval, 100 mu spot size, and 400 to 1200 mW of power. Analysis was performed using videography, microscopy, and scanning electron microscopy. RESULTS: This study found grossly that burns with the argon laser caused tissue blanching and pigment dispersion, whereas no reaction was observed with the diode laser. The diode laser made no observable histologic alterations, but the argon caused fragmentation and coagulation of trabecular beams. Scanning electron microscopy showed that the diode laser caused an area of trabecular beam coalescence measuring 50 to 100 mu in diameter with energies > or = 0.12 J. A surrounding zone of more superficial trabecular beam fragmentation measuring 200 to 400 mu in diameter also was observed. Similar energy levels from the argon laser caused hole formation 200 to 400 mu in diameter. Lower argon energy levels (0.05 J) caused inconsistent coalescence 50 to 100 mu in diameter similar to the diode laser. CONCLUSIONS: This study suggests that in the trabecular meshwork the diode laser causes a reaction at, but not at less than, energy levels shown previously to produce a clinical ocular hypotensive effect. Also, at similar energy per area, the tissue effects of the diode and argon laser are comparable.
Conjunctival structure and cell counts and the results of filtering surgery.
We evaluated perioperative conjunctival biopsy specimens in 28 consecutive patients with primary open-angle glaucoma undergoing trabeculectomy who had not undergone previous intraocular surgery. We found six months postoperatively that the number of goblet cells was significantly greater (6.40 +/- 5.40 vs 1.68 +/- 1.60 per field of view; P = .004, Student's t-test) in patients with easier postoperative intraocular pressure control (intraocular pressure < or = 15 mm Hg with zero to two glaucoma medications) than in patients with more difficult intraocular pressure control (> 15 mm Hg with three or more glaucoma medications). No statistical differences between groups were observed in mast cells, neutrophils, eosinophils, macrophages, plasma cells, lymphocytes, or fibroblasts (P > .05). Also, no statistical difference between groups existed in conjunctival structure, including mucopolysaccharide and collagen composition, vascular density, or epithelial thickness (P > .05). This study suggests that the number of conjunctival goblet cells may be related to intraocular pressure control after trabeculectomy.
The influence of age upon inflammatory cell counts and structure of conjunctiva in chronic open-angle glaucoma.
We evaluated the influence of age upon conjunctival structure and number of inflammatory cells by studying perioperative conjunctival biopsies from 54 consecutive primary open-angle glaucoma patients undergoing initial filtering surgery (trabeculectomy alone or combined cataract extraction and trabeculectomy). All patients had received chronic topical glaucoma therapy for > 1 year. We divided the patients into three age groups for analysis: 40-60 (n = 10), 61-74 (n = 28), and > 75 (n = 16) years. We found no statistical difference (p > 0.05, chi-square) in cell counts of neutrophils, eosinophils, mast cells, macrophages, fibroblasts, lymphocytes, plasma cells and goblet cells across the three age groups. In addition, no statistical differences were observed between age groups in vascular density, epithelial thickness as well as mucopolysaccharide and collagen composition (p > 0.05, chi square). This study suggests that conjunctival structure and inflammatory cell counts change little with advancing age in primary open-angle glaucoma patients.
Association of reliability with reproducibility of the glaucomatous visual field.
We studied 207 glaucoma patients (207 eyes) who had two successive visual tests on the Humphrey Field Analyzer to determine the association of unreliability (> 10% incidence of a missed catch trial test) with threshold variation. We found that in patients where one visual field showed > 30% false negative or positive errors, and the other visual field also was unreliable, a significant increase in the variance of the mean defect existed from reliable patients (p < 0.05). Of patients who had only one of two visual fields which was unreliable (from false negative errors), only those with marked glaucomatous visual field loss (< -15 dB depth of defect) showed a greater variance in mean defect between examinations over reliable patients (p < 0.05). In total, 41 patients (19.8%) had unreliable visual fields associated with statistically increased threshold variation. This study suggests that patient reliability should be considered when interpreting changes in threshold between automated visual field examinations.
The effect of varying wavelength on subconjunctival scleral laser suture lysis in rabbits.
We studied laser suture lysis of subconjunctival scleral sutures in a rabbit eye using selected wavelengths from a dye and diode laser to determine which wavelength caused the least conjunctival damage. We found an oval shaped area of coagulation necrosis surrounding the suture track in the conjunctival substantia propria measuring in depth 61.0 mu for 488 + 514 nm (blue-green), 105.7 mu for 514 nm (green), 148.3 mu for 630 nm (red), and 29.0 mu with 780 + 830 nm (infrared) wavelengths. No observable damage was noted with 585 nm (yellow) or 610 nm (orange) wavelengths. The energy intensity required for suture lysis was similar across each wavelength studied. No damage was observed in the sclera or conjunctival epithelium. These findings suggest that using the yellow or orange wavelength, when performing laser suture lysis clinically, potentially may limit conjunctival damage.
Histologic differences in the conjunctiva of black and white glaucoma patients.
We compared perioperative conjunctival biopsy specimens from 31 consecutive trabeculectomy patients to determine if there were any histologic differences between black and white glaucoma patients. We found a statistically significantly greater mean and distribution of mast cells and neutrophils in the white patients. No significant difference was found in the mean number of goblet cells, eosinophiles, macrophages, fibroblasts, plasma cells, or lymphocytes; or in thickness of the epithelium, vascular density, or collagen or mucopolysaccharide staining. We conclude that histological conjunctival factors that could be evaluated preoperatively probably are not related to the poor results in black patients of filtration surgery noted by some investigators.
Conservation of central nervous system glutaryl-coenzyme A dehydrogenase in fruit-eating bats with glutaric aciduria and deficient hepatic glutaryl-coenzyme A dehydrogenase.
The adult fruit-eating bat, Rousettus aegypticus, excretes massive amounts of glutaric acid in the urine (20-70 mumol/mg creatinine) comparable to those of humans affected with the inherited metabolic disorder, glutaric aciduria type I. Glutaric acid was quantified by sequential liquid partition chromatography and gas chromatography. Oral loading with the amino acid precursors of glutaric acid, L-lysine and L-tryptophan, resulted in significant increases in glutaric acid excretion above the base-line values. Glutaryl-CoA dehydrogenase activity was assayed in adult bat tissues and compared with the same tissues in the rat using methods of 14CO2 evolution from 1,5-[14C]glutaryl-CoA. A severe deficiency of glutaryl-CoA dehydrogenase activity was found in the bat liver and kidney, whereas brain and spinal cord levels were similar to those in the rat. Reverse phase high performance liquid chromatography analysis of the metabolites in the assay mixture showed negligible hydrolysis of [14C]glutaryl-CoA to free [14C]glutaric acid and complete conversion of the product [14C]crotonyl-CoA to 3-hydroxy[14C]butyryl-CoA. The adult bat, with its huge glutaric acid excretion and deficient liver glutaryl-CoA dehydrogenase, metabolically mimics patients affected with glutaric aciduria type I. The bat does not, however, display the neurologic manifestations seen in patients. This may be explained by conservation of glutaryl-CoA dehydrogenase activity in the central nervous system of the bat.
Interlaboratory proficiency survey of cholesterol and high-density lipoprotein cholesterol measurement.
We conducted a proficiency survey of cholesterol and high-density lipoprotein (HDL) cholesterol analysis in local clinical laboratories to determine whether increased national emphasis on cholesterol measurement had resulted in changes in performance from previous surveys. Sets of frozen aliquots of plasma and HDL supernate pools were sent to nine laboratories for analysis; results were compared with Northwest Lipid Research Center values, and relationships were determined by linear regression. Of all the cholesterol measurements, 81% were considered acceptable (i.e., within 9% of the NWLRC value), and 61% of the HDL cholesterol measurements were considered acceptable (within 50 mg/L of NWLRC values). These data represented no improvement over previous surveys. Workload had increased significantly: 79% for cholesterol and 284% for HDL cholesterol. On a bias plot, six of the laboratories demonstrated inaccuracy greater than the +/- 3% recommendation within the critical range of 2000-2400 mg/L for total cholesterol. For HDL cholesterol, two laboratories demonstrated bias greater than 10% at the critical point of 350 mg/L, with three additional laboratories displaying strong bias outside the decision point. The survey results indicate that apparently further improvements must be made for laboratories to achieve acceptable performance in cholesterol analysis.