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Biomedical subjects

M J Lynn

Publications and source records attributed to M J Lynn.

At least 55 records · Page 3Linked to original sources
PubMed1987

Three-year results of the Prospective Evaluation of Radial Keratotomy (PERK) Study.

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center clinical trial of a standardized technique of radial keratotomy in 435 patients who had simple myopia with a preoperative refractive error between -2.00 and -8.00 diopters (D). The authors report results for one eye of each patient. The surgical technique consisted of eight incisions using a diamond micrometer knife with the blade length determined by intraoperative ultrasonic pachymetry and the diameter of the central clear zone determined by the preoperative refractive error. At 3 years after surgery, 58% of eyes had refractive error within 1.00 D of emmetropia; 26% were undercorrected and 16% were overcorrected by more than 1.00 D. Uncorrected visual acuity was 20/40 or better in 76% of eyes. The operation was more effective in eyes with a preoperative refractive error between -2.00 and -4.37 D. Between 1 and 3 years after surgery, the refractive error changed by 1.00 D or more in 12% of eyes, indicating a lack of stability in some eyes. In the 435 eyes, there was a small number of complications including six eyes that lost two or three lines of best-corrected acuity, 16 that experienced vascularization of the incisions, 2 that had delayed bacterial keratitis, and 4 that had recurrent epithelial erosions.

Follow-Up Studies↗
PubMed1985

Results of the prospective evaluation of radial keratotomy (PERK) study one year after surgery.

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center, self-controlled clinical trial of a standardized technique of radial keratotomy in 435 patients who had physiologic myopia with a preoperative refraction between -2.00 and -8.00 diopters. The surgical technique consisted of eight incisions using a diamond micrometer knife with blade length determined by intraoperative ultrasonic pachymetry and the diameter of central clear zone determined by preoperative refraction. At one year after surgery, myopia was reduced in all eyes; 60% were within +/- 1.00 diopter of emmetropia; 30% were undercorrected and 10% were overcorrected by more than 1.00 diopter (range of refraction, -4.25 to +3.38 D). Uncorrected visual acuity was 20/40 or better in 78% of eyes. The operation was most effective in eyes with a refraction between -2.00 and -4.25 diopters. Thirteen percent of patients lost one or two Snellen lines of best corrected visual acuity. However, all but three eyes could be corrected to 20/20. Ten percent of patients increased astigmatism more than 1.00 diopter. Disabling glare was not detected with a clinical glare tester, but three patients reduced their driving at night because of glare. Between six months and one year, the refraction changed by greater than 0.50 diopters in 19% of eyes.

Adult↗
PubMed1984

Stellate iron lines in the corneal epithelium after radial keratotomy.

Biomicroscopic examinations of the corneal epithelium of 54 patients who had consecutive radial keratotomy operations in the National Eye Institute Prospective Evaluation of Radial Keratotomy (PERK) study showed that abnormal stellate epithelial iron lines had appeared at the junction of the middle and inferior thirds of the cornea in 13 of 16 eyes (81%) examined six months after surgery, in 43 of 50 eyes (86%) examined 12 months after surgery, and in seven of nine eyes (78%) examined 24 months after surgery. The density and pattern of the deposits varied from a faint tan horizontal iron line studded with small branches to a dense yellow-brown deposit with eight radiating arms that extended between all of the incisions. Analysis of the configuration of the iron line and the central keratometric readings 12 months after surgery showed that the greater the reduction in the central keratometric measurement postoperatively, the more prominent the iron line. We attribute the occurrence and variation of the stellate epithelial iron line to irregularities in the surface of the cornea present in the first year after radial keratotomy.

Adult↗
PubMed1983

Three types of alpha-melanocyte-stimulating hormone: bioactivities and half-lives.

Three types of alpha-melanocyte-stimulating hormone (alpha MSH) that differ in the acetyl status of the N-terminal serine have been found in the neurointermediate lobe of the pituitary gland and in the brain: desacetyl alpha MSH, which lacks an acetyl group; monoacetyl alpha MSH, in which the amino group of the serine is acetylated; and diacetyl alpha MSH, in which both amino and hydroxy groups of the serine are acetylated. We compared the lipolytic and melanotropic actions of these three peptides, and their rates of disappearance from plasma, both in vitro and in vivo. The following differences were found. a) For in vitro lipolytic actions on rabbit adipose tissue slices, the potencies differed according to the order diacetyl = monoacetyl greater than desacetyl. On rabbit isolated adipocytes, however, the three peptides were equipotent. b) For in vivo lipolytic action in the rabbit, not only potency but also kinetics differed. Diacetyl alpha MSH had the slowest onset, longest duration, and greatest potency. The desacetyl variant had the quickest onset, shortest duration, and least potency. c) The half-life for elimination from rabbit plasma both in vitro and in vivo was shortest for the desacetyl form and longest for the diacetyl peptide. d) For in vitro melanotropic effect on frog skin, kinetics of action were the same for all three peptides, but potency differed according to the order diacetyl = monoacetyl greater than desacetyl. Thus acetylation of alpha MSH alters lipolytic and melanotropic potencies in vitro and lipolytic potency and kinetics in vivo. These differences result in part from the fact that acetylation slows the degradation of the tridecapeptide both inside and outside the circulation.

Adipose Tissue↗
PubMed1983

Effects of opioid peptides and opiate alkaloids on insulin secretion in the rabbit.

In pentobarbital-anesthetized rabbits, iv injection of 9 nmol (31 micrograms) human beta-endorphin (beta h-endorphin)/kg BW caused a significant (P less than 0.05) increase in serum glucose and a significant decline in serum insulin during the subsequent 60 min. When 9 nmol/kg BW beta h-endorphin were injected simultaneously with 0.7 g glucose/kg BW, the clearance of serum glucose and the expected glucose-stimulated rise in serum insulin were both inhibited. The threshold dose for the insulinopenic effect of beta h-endorphin in the anesthetized, glucose-loaded rabbit was 0.09 nmol/kg BW. Threshold doses/kg BW were determined for six structurally related peptides found to possess insulinopenic activity: camel beta-endorphin, 0.09 nmol; N-arg-beta h-endorphin, 0.09 nmol; D-ala2-beta h-endorphin, 0.09 nmol; leu5-beta h-endorphin, 0.09 nmol; met-(O)5-beta h-endorphin, 0.9 nmol; and beta h-endorphin1-27, 0.9 nmol. Threshold dose/kg BW for somatostatin was 9 nmol. The following compounds were inactive at 9 nmol/kg BW: N-acetyl-beta h-endorphin; N-acetyl-arg-beta h-endorphin; beta h-endorphin2-31; beta h-endorphin6-31; beta h-endorphin(((1-5 + 6-31))); beta h-endorphin1-18 (gamma-endorphin); beta h-endorphin1-17 (alpha-endorphin); beta h-endorphin1-5 (met-enkephalin); leu5-beta h-endorphin (leu-enkephalin); met-NH2(5)-beta h-endorphin1-5 (met-enkephalinamide); D-ala2-leu5-beta h-endorphin1-5; D-ala2-N-me-phe4, met-(O)5-ol-beta h-endorphin1-5; and D-ala2-D-leu5-beta h-endorphin1-5. Ninety nmoles per kg BW of naloxone did not alter the insulinopenic effect of 0.9 nmol/kg BW beta h-endorphin. As little as 2.9 X 10(-10) molar beta h-endorphin inhibited glucose-stimulated release of insulin by rabbit pancreas slices in vitro. The capacities of the peptides and alkaloids to inhibit insulin secretion in vitro followed the same general order as the in vivo insulinopenic capacities. Naloxone at 2.9 X 10(-6) M did not reduce the antisecretagogue effect of 2.9 X 10(-8) M beta h-endorphin. These findings, when compared with previously described structure-activity relationships for opioid receptors, indicate the presence of a novel receptor for beta-endorphin in rabbit pancreas, the activation of which inhibits glucose-stimulated secretion of insulin.

Amino Acids↗
PubMed1981

Energy malabsorption: measurement and nutritional consequences.

Fecal energy (FE) loss was measured using bomb calorimetry in 30 patients; 14 had a history of malabsorption, while 16 had no history of intestinal dysfunction. Average digestibility (and range) of energy and FE loss were 73% (48 to 91%) and 493 kcal/day (177 to 927 kcal/day) in the group with malabsorption, compared to 96% (89 to 99%) and 74 kcal/day (8 to 146 kcal/day) in the group without malabsorption, respectively. Metabolizable energy supplied by the diet (intake kcal -- (fecal kcal + urinary kcal) was below the calculated daily energy requirement in five of seven patients with malabsorption; in three of these five subjects the combination of decreased energy intake and increased FE loss produced negative energy balance, while in the remaining two patients malabsorption alone caused negative energy balance. Inadequate metabolizable energy in these five patients was associated with weight loss and protein-energy malnutrition. The usual clinical laboratory tests applied to the study of malabsorption, including fecal fat, fecal nitrogen, and stool weight, were poor predictors of FE loss. These tests were also of limited value in assessing the effects of dietary modification on energy malabsorption. Contrastingly, bomb calorimetry provided a simple and accurate alternative in quantitatively assessing FE loss in the patient with malabsorption.

Calorimetry↗
PubMed1981

Total parenteral nutrition as an adjunct to chemotherapy of metastatic colorectal cancer.

A randomized study was performed in advanced cancer to test the effectiveness of total parenteral nutrition (TPN) in maintaining and improving nutrition, to examine the effects of TPN on tumor growth, and to determine if TPN altered chemotherapy response rates, treatment tolerance, and survival. Forty-five patients on identical chemotherapy were randomized to TPN versus ad libitum feeding. TPN was well tolerated. No clinical or tumor marker evidence suggesting neoplastic growth stimulation was obtained. Chemotherapy-related complications and chemotherapy responses did not differ between the two groups. TPN had little effect on performance status. TPN patients gained an average of 2.8 kg before chemotherapy, but triceps skinfold and mid-arm muscle area did not change significantly during TPN. Survival did not improve with TPN. We conclude that current techniques of TPN are of limited benefit in advanced colon cancer. A small subset of patients with short-gut malabsorption may be helped. Further study is needed to determine the mechanisms of cancer undernutrition and to refine nutritional supplementation techniques on the basis of these mechanisms.

Adenocarcinoma↗
PubMed1981

Effect of total parenteral nutrition on survival in advanced colon cancer.

To determine if total parenteral nutrition (TPN) with constant infusion of hypertonic glucose and amino acids by central vein (35 kcal/kg/day) would influence survival in advanced colorectal carcinoma, 50 patients were randomized to receive either chemotherapy alone or the same drugs plus TPN for 14 days before treatment and a variable period thereafter. Overall median survival was significantly decreased in the TPN patients (79 vs 305 days, P = 0.03). Survival was significantly decreased in the TPN patients who had lost the least percentage of premorbid weight (0-6%) (66 vs 398 days, P = 0.02), and in all TPN males (61 vs 209 days, P = 0.03), when compared to similar controls. TPN did not increase survival in any patient subcategory. Catheter-related and metabolic complications were uncommon. We conclude that TPN as used in this study did not prolong median survival in the group as a whole, and may have shortened survival in males and in patients with little or no prior weight loss.

Adolescent↗
PubMed1979

Relationship between survival and histologic type in small cell anaplastic carcinoma of the lung.

Survival and histologic subtype were compared in 61 patients with small cell anaplastic lung cancer. Patients with lymphocyte-like (oat cell) and fusiform histologies treated with chemotherapy had longer median survivals than the polygonal and other varieties on the same treatment. Likewise, when detectable disease was confined to the chest and supraclavicular nodes, the patients with lymphocyte-like and fusiform types lived longer. The improved survival in the lymphocyte-like and fusiform categories accounted for most of our improved overall median survival rates with the COPP regimen in small cell lung cancer. Survival in the polygonal and other types was not appreciably different from that seen in non-small cell lung cancer (squamous and adenocarcinoma). It may be possible to refine treatment plans on the basis of cell type so as to further increase survival in small cell anaplastic lung carcinoma.

Antineoplastic Agents↗
PubMedDate not supplied

Age-related refractive shifts in simple myopia.

BACKGROUND: An understanding of physiologic age-related shifts in myopic refractive errors is important to the refractive surgeon for the interpretation of long-term results, surgical planning, and patient counseling. This study characterizes the refractive stability of adult simple myopia with a retrospective study of 413 eyes. METHODS: Approximately 74,000 patient records were analyzed to identify 208 adults with -1.00 to -6.00 diopters (D) of myopia who were followed for more than 20 years at the Spokane Eye Clinic. Amounts of myopic shift (increase in myopia) and hyperopic shift (decrease in myopia) were identified and analyzed within the population. The results were compared to long-term studies of radial keratotomy. RESULTS: The mean changes per patient age decade were: 20s, -0.60 D; 30s, -0.39 D; 40s, -0.29 D; 50s, +0.28 D; 60s, +0.41 D. Reanalyzed Prospective Evaluation of Radial Keratotomy (PERK) study 10-year postoperative data demonstrated progressively increasing hyperopic shifts per decade, at least to age 50. CONCLUSION: The normal adult population with simple myopia differs from the general population and consists of a population subgroup that is relatively stable and other subgroups that experience significant refractive shift. The hyperopic shift after radial keratotomy appears to be surgically induced and may be larger than previously thought.

Adult↗
PubMedDate not supplied

Serum lipoprotein levels fail to predict postangioplasty recurrent coronary artery stenosis.

A prospective study to explore the role of serum lipoproteins in the development of recurrent stenosis after percutaneous transluminal coronary angioplasty was conducted on serum samples from 103 patients. Serum was collected at the time of angioplasty and evaluated for total cholesterol, total triglycerides (TG), high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, very low-density lipoprotein cholesterol, and apolipoproteins A1 and B. In addition, LDL cholesterol/HDL cholesterol ratios and apolipoprotein B/A1 ratios were calculated for each sample. Information was then gathered from four years of follow-up after angioplasty, which was sufficient to establish the presence or absence of recurrent stenosis in 87 patients (68 males and 19 females). Stenosis recurred in 31 of the 87 patients (36%); the rate was similar for males (35%) and females (37%). Univariate analysis of the total patient population revealed no statistically significant difference in values for any of these lipoprotein parameters between success and recurrence groups. Likewise, multivariate analysis revealed no combination of lipoprotein values to be associated with success or recurrence. Findings were similar for the males alone and the total group of males and females. The female group was too small for separate statistical analysis. The power of this study to detect meaningful differences in each of these parameters except TG was at least 80%. These results do not support the hypothesis that lipoprotein factors influence the development of recurrent stenosis in patients undergoing coronary angioplasty.

Angioplasty, Balloon↗
PubMedDate not supplied

Stability of refraction and visual acuity during 5 years in eyes with simple myopia. The PERK Study Group.

BACKGROUND: Normal ranges of variability of refraction and visual acuity in adult myopic eyes are needed as a reference standard for assessing the stability of refractive corneal surgery. METHODS: We measured the changes in spectacle-corrected visual acuity and cycloplegic refraction during 5 years for the unoperated eye of 82 patients aged 21 to 57 years in the Prospective Evaluation of Radial Keratotomy Study. The changes were compared for contact lens and non-contact lens wearers. We also compared the 5-year cycloplegic and manifest refractions for these unoperated eyes. RESULTS: Of 77 eyes, 44% gained or lost one Snellen line and 48% experienced no change in spectacle-corrected visual acuity between baseline and 5 years. Only one eye (1%) lost two lines, and 7% gained two lines. The refractive change was less than 1.00 D for 84% of the 37 non-contact lens wearing eyes. Only 13% became more myopic by at least 1.00 D (maximum increase in myopia, 2.00 D), and 3% became less myopic by 1.00 D. Of 45 contact lens wearing eyes, 38% became more myopic by at least 1.00 D. The 5-year manifest refraction was 0.50 D to 1.50 D more myopic than the cycloplegic refraction for 37% of eyes. CONCLUSIONS: We recommend using two or more Snellen lines as the standard for a meaningful change in spectacle-corrected visual acuity in operated eyes, and 1.00 D as a meaningful cutoff for stability of refraction. The wearing of contact lenses can confound the results of stability studies. The difference between the cycloplegic and manifest refractions suggests that the cycloplegic refraction should be used in planning for refractive surgery.

Adult↗
PubMedDate not supplied

A comparison of corneal stromal edema induced from the anterior or the posterior surface.

BACKGROUND: Many differences between the anterior and posterior corneal stroma have been reported. The physiological and mechanical properties of the cornea are a summation of these properties across each of the corneal regions. This article investigates corneal stromal swelling that is experimentally induced through each surface. METHODS: Corneal stromal swelling was induced in human and rabbit corneas through either the anterior or posterior surface. The rate of stromal swelling was analyzed with a linear regression model. RESULTS: Swelling in the rabbit stroma was 3.65 x faster when induced through the posterior surface than through the anterior surface (p less than .0001), while the human stroma swelled 13.1 x faster through the posterior surface (p less than .0001). The hydration of the stroma increased during swelling through the posterior surface, but paradoxically decreased during swelling through the anterior surface. CONCLUSIONS: These experiments showed that stromal swelling occurs more rapidly through the posterior corneal surface than through the anterior surface. These results may have implications for the refractive surgeon performing laser ablative procedures on the anterior surface of the cornea.

Animals↗
PubMedDate not supplied

Combining refractive error and uncorrected visual acuity to assess the effectiveness of refractive corneal surgery.

Residual refractive error and uncorrected visual acuity are two frequently measures used to assess the effectiveness of refractive corneal surgery. Nordan and colleagues have suggested a Visual Function Index which combines these two measures in one quantitative measure. This article presents a Visual Function Score for radial keratotomy which includes a set of qualitative categories (excellent, good, fair, poor) and specifies the clinical values for refractive error and visual acuity in each category. There was substantial agreement among ophthalmologists who reviewed the category definitions, and we think that the Visual Function Score improves our ability to objectively assess surgical outcome. Application of the score to the Prospective Evaluation of Radial Keratotomy (PERK) Study data yielded closer agreement with refractive error results than with visual acuity values. The Visual Function Score lowered the classification of eyes that were hyperopic but had sufficient accommodation to overcome so that a high visual acuity result could be achieved. The inclusion of astigmatism values would be an important next step in the development of composite measures for the assessment of refractive surgery. In the future, a multifactorial index or score may be used to estimate the outcome of reported surgical procedures.

Adult↗
PubMedDate not supplied

Three year results of the Prospective Evaluation of Radial Keratotomy (PERK) study.

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center clinical trial of a standardized technique of radial keratotomy in 435 patients who had simple myopia with a preoperative refractive error between -2.00 and -8.00 diopters (D). We report results for one eye of each patient. The surgical technique consisted of eight incisions using a diamond micrometer knife with the blade length determined by intraoperative ultrasonic pachymetry and the diameter of the central clear zone determined by the preoperative refractive error. At three years after surgery, 58% of eyes had refractive error within one diopter of emmetropia; 26% were undercorrected, and 16% were overcorrected by more than one diopter. Uncorrected visual acuity was 20/40 or better in 76% of eyes. The operation was more effective in eyes with a preoperative refractive error between -2.00 and -4.37 diopters. Between one and three years after surgery, the refractive error changed by 1.00 diopter or more in 12% of eyes, indicating a lack of stability in some eyes.

Astigmatism↗
PubMedDate not supplied

Symmetry of refractive and visual acuity outcome in the Prospective Evaluation of Radial Keratotomy (PERK) study.

In the Prospective Evaluation of Radial Keratotomy (PERK) study, the symmetry of refractive and visual acuity outcome was analyzed in 269 patients with bilateral radial keratotomy with a single operation in each eye. Patients were required to wait 1 year after surgery on the first eye before having surgery on the second eye. At 1 year after surgery on the second eye, 98% of patients had 3.00 diopters or less difference between their two eyes in the spherical equivalent of the cycloplegic refraction (100% before surgery), and 96% of patients had 3.00 D or less difference between their two eyes in the amount of refractive power in the vertical meridian (100% before surgery). Thus, surgically induced refractive anisometropia was not a major complication in the PERK study. However, 14% of patients had four to eight Snellen lines difference in the uncorrected visual acuity between their two eyes (1% before surgery), emphasizing that induced asymmetry of refraction is a potential clinical problem for some patients.

Adult↗