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Biomedical subjects

S Norrby

Publications and source records attributed to S Norrby.

At least 19 recordsLinked to original sources
PubMed2002

Spherical and irregular aberrations are important for the optimal performance of the human eye.

Contrast sensitivity measured psychophysically at different levels of defocus can be used to evaluate the eye optics. Possible parameters of spherical and irregular aberrations, e.g. relative modulation transfer (RMT), myopic shift, and depth of focus, can be determined from these measurements. The present paper compares measured results of RMT, myopic shift, and depth of focus with the theoretical results found in the two eye models described by Jansonius and Kooijman (1998). The RMT data in the present study agree with those found in other studies, e.g. Campbell and Green (1965) and Jansonius and Kooijman (1997). A new theoretical eye model using a spherical aberration intermediate between those of the eye models described by Jansonius and Kooijman (1998) and an irregular aberration with a typical S.D. of 0.3-0.5 D could adequately explain the measured RMT, myopic shift, and depth of focus data. Both spherical and irregular aberrations increased the depth of focus, but decreased the modulation transfer (MT) at high spatial frequencies at optimum focus. These aberrations, therefore, play an important role in the balance between acuity and depth of focus.

Adaptation, Ocular↗
PubMed2001

Multicenter biometry study of 1 pair of eyes.

PURPOSE: To assess the accuracy of biometry for intraocular lens (IOL) power calculation. SETTING: Six ophthalmic surgery centers in Europe and 1 in the United States. METHODS: Biometry was done as if in preparation for cataract surgery in 2 eyes of the same person with 10 combinations of operator and instrument. Data analysis followed a standardized procedure to assess repeatability (within-center variability) and reproducibility (between-center variability) of the test methods. RESULTS: The reproducibility of the corneal radius measurement was 0.06 mm. The use of different keratometric indices made conversion to K-values less reliable. The repeatability of the axial length (AL) measurement of 0.30 mm and the reproducibility of 0.66 mm converted to a calculated IOL power of 0.75 diopter (D) and 1.65 D, respectively. Thus, this potential patient runs the risk of a refractive surprise of up to 1.10 D purely as a result of a measurement error within a center and up to 2.30 D if the patient goes to the worst-case center. CONCLUSIONS: The biometry results show that the measured corneal radius can be used with confidence. Reproducibility errors in AL determination require personalization of formula constants or correction at the source by proper calibration.

Biometry↗
PubMed2001

Injectable intraocular lens materials based upon hydrogels.

The possibilities to develop an injectable hydrogel lens were investigated. Aqueous solutions of reactive polymers in combination with a water-soluble blue light photoinitiator were transformed into hydrogels by irradiation with blue light. Poly(ethylene glycol) diacrylates (PEGDA) with low molecular weights and an acrylate modified copolymer of N-vinylpyrrolidone and vinyl alcohol with a high molecular weight were used as reactive polymers. A copolymer of (4-vinyl-2,6-dimethylbenzoyl)diphenylphosphine oxide and dimethylacrylamide was used as a water-soluble blue light photoinitiator. PEGDA showed high reactivity and the hydrogels were more transparent than the natural lens. The mass loss and the additional swelling of the hydrogel were 1.0 and 4.0%, respectively. The refractive index of these hydrogels was 1.40, lower than that of natural lens. The viscosity of the solutions before cross-linking was too low for injection into the capsular bag. Hydrogels based upon the copolymer had a transmission comparable to a 25-year-old natural lens. The materials showed no mass loss and the additional swelling after curing was less than 1%. The refractive index was comparable to that of the natural lens (1.42). The viscosity of the polymer solutions was sufficient for injection into the capsular bag without leakage.

Adult↗
PubMed2001

Hydrophilic polymeric acylphospine oxide photoinitiators/crosslinkers for in vivo blue-light photopolymerization.

Three vinyl-functionalized phosphine oxide photoinitiating monomers have been synthesized: 4-vinylbenzoyldiphenylphosphine oxide (VBPO), 2,6-dimethyl-4-vinylbenzoyldiphenylphosphine oxide (DMVBPO), and 2,4,6-trimethylbenzoylphenyl-4-vinylphenylphosphine oxide (TMBVPO). VBPO was copolymerized with vinylpyrrolidone or vinyl acetate (PPI-1a) and dimethylacrylamide (PPI-1b). DMVBPO and TMBVPO were both copolymerized with dimethylacrylamide (PPI-2 and PPI-3, respectively). The choice of vinylphosphine oxide and comonomer(s) had a significant influence on the properties of the resulting PPI. PPI-1a was not stable in solution in 2-hydroxyethyl methacrylate (HEMA), whereas the VBPO-dimethylacrylamide (DMA) copolymer (PPI-1b) was stable in HEMA but not stable in aqueous solutions. PPI-2 was both soluble and stable in water up to 22 months. PPI-1a was as effective as trimethylbenzoyldiphenylphosphine oxide (TPO, BASF Lucirin). PPI-2 was more effective in the polymerization of HEMA/water mixtures than PPI-3. PPI-2 and PPI-3 acted as self-cross-linking species, resulting in the formation of hydrogels; PPI 3 was more effective in this. PPI-2 was very effective in forming hydrogels based on poly(ethylene glycol) diacrylate.

Biocompatible Materials↗
PubMed2000

Age-related changes of defocus-specific contrast sensitivity in healthy subjects.

To investigate the effect of defocus on contrast sensitivity as a function of age in healthy subjects, the through focus contrast sensitivity was measured in 100 healthy subjects aged 20-69. Defocus-specific changes in contrast sensitivity reflect age-related changes in the optics of the eye. Tests were performed in cycloplegic eyes varying artificial pupil size (2, 4 and 6 mm), defocus (-1 to +2 D), and spatial frequency (1-16 cpd). Integrated contrast sensitivity was taken as a measure for the total amount of visual information transferred by the optical media. At optimal focus, integrated contrast sensitivity and log contrast sensitivity at 8 cpd showed a significant age-related decline. The log contrast sensitivity at 1 cpd appeared to be independent of age. The depth of focus for a 4-mm pupil increased significantly with age, even though contrast sensitivity at +2 D defocus decreases with age too, but not as much as the contrast sensitivity at optimal focus. Our study indicates that the effect of defocus on contrast sensitivity decreases with age; this was attributed to age-related changes in the optical media.

Adult↗
PubMed1999

Average optical performance of the human eye as a function of age in a normal population.

PURPOSE: To determine the average optical performance of the human eye, in terms of the modulation transfer function (MTF), as a function of age. METHODS: An apparatus was constructed to measure the ocular MTF, based on the recording of images of a green, 543-nm laser-point source after reflection in the retina and double pass through the ocular media. MTFs were computed from the average of three 4-second-exposure double-pass images recorded by a slow-scan, cooled charge-coupled device camera. The ocular MTF was measured for three artificial pupil diameters (3 mm, 4 mm, and 6 mm) with paralyzed accommodation under the best refractive correction in 20 subjects for each of three age categories: young subjects aged 20 to 30 years, middle-aged subjects aged 40 to 50 years, and older subjects aged 60 to 70 years. The selected subjects passed an ophthalmologic examination, excluding subjects with any form of ocular or retinal disease, spherical or cylindrical refractive errors exceeding 2 D, and corrected visual acuity lower than 1 (0.8 in the older age group). RESULTS: The average MTF was determined for each age group and pupil diameter. A two-parameter analytical expression was proposed to represent the average MTF in each age group for every pupil diameter. The ocular MTFs declined as age increased from young to older groups. The SD of the MTF results within age groups was lower than the differences between the mean for each group. CONCLUSIONS: The average optical performance of the human eye progressively declines with age. These MTF results can serve as a reference for determining mean ocular optics according to age.

Adult↗
PubMed1997

After-cataract and ocular growth in newborn rabbit eyes implanted with a capsule tension ring.

PURPOSE: To examine after-cataract and eye growth in lensectomized newborn rabbits implanted with capsule tension rings of different sizes. SETTING: S:t Eriks Eye Hospital, Karolinska Institute, Stockholm, Sweden. METHODS: Two groups of 24-day-old rabbits were used. In Group 1 (n = 9), lensectomy was performed in both eyes. In one randomly selected eye, an open poly(methyl methacrylate) (PMMA) capsule tension ring with a 7.0 mm diameter and 0.13 mm thickness was implanted in the capsular bag. The other eye was left aphakic. In Group 2 (n = 10), an open PMMA capsule tension ring with a 10.0 mm diameter and 0.13 mm thickness was implanted in one randomly selected eye, and the other eye was left aphakic. Axial length, corneal diameter, corneal thickness, and intraocular pressure (IOP) were measured in all eyes preoperatively and 1, 2, and 3 months after surgery. The wet mass of the after-cataract was measured at 3 months. Three Group 1 eyes and four Group 2 eyes developed secondary glaucoma and were excluded from the study. RESULTS: Axial growth did not differ significantly between the eyes implanted with the 7.0 mm ring and the aphakic eyes (mean difference 0.01 mm; F3;15 = 0.02; P > .25). Corneal diameter also did not differ (two-way analysis of variance [ANOVA]). Axial length growth was less in the eyes implanted with the 10.0 mm ring than in the aphakic eyes (mean difference 1.05 mm; F3;15 = 2.06; P < .25). The average decrease in corneal diameter growth was 1.0 mm in the implanted eyes. Growth in the eyes with the 10.0 mm ring was significantly less than in the eyes with the 7.0 mm ring (P = .05, Wilcoxon rank-sum test). Corneal thickness and IOP did not differ significantly between eyes (F3;15 = 0.6; P > .25; two-way ANOVA). Amount of after-cataract did not differ significantly between the aphakic eyes and the eyes implanted with the 7.0 mm ring. It was significantly less in the eyes with the 10.0 mm ring than in those with the 7.0 mm ring (Wilcoxon signed-rank test) and in the aphakic eyes (P < .025, Wilcoxon rank-sum test). CONCLUSION: In the young rabbit eye, a 10.0 mm capsule ring reduced the eye growth compared with both the aphakic eye and the eye implanted with a 7.0 mm ring. The 10.0 mm ring also inhibited the production of after-cataract compared with the production in the aphakic eye and the eye implanted with the 7.0 mm ring.

Animals↗
PubMed1988

Duration of T-tube drainage after exploration of the common bile duct.

The optimal duration of T-tube drainage after choledochotomy is not known. In a randomized study, comparison was made between early (postoperative day 4) and late (day 7) removal of the T-tube. The evaluation was made on 62 patients, after exclusion of 20 because of retained stones, technically inadequate postoperative cholangiography, cholangitis or failed T-tube removal. The T-tube was removed on day 4 in 28 cases and on day 7 in 34. There were no clinically significant complications, but two patients with early and two with late removal had transient pyrexia. The mean postoperative stay in hospital was significantly shorter for the patients with early T-tube removal (8.2 vs. 9.8 days). The corresponding figures for the patients younger than 50 years were 7.1 vs. 9.1 days and for those older than 50 they were 8.7 vs. 10.1 days--both differences significant. The results indicated that early removal of choledochal T-tube drain does not increase postoperative morbidity and can significantly shorten the hospital stay.

Adult↗
PubMed1986

Decreasing incidence of gallstone disease in a defined Swedish population.

The number of operations for biliary stone disease in Sweden has decreased. To assess the changing incidence of gallstone disease, the numbers of gallstone operations and positive and negative cholecystograms occurring in a defined population over a 10-year period were studied. Both investigations showed a highly significant decrease; the cholecystectomy rate was reduced to 57% of that at the beginning, and the proportion of pathological cholecystograms to 35%. The proportion of normal X-ray findings increased over the 10-year period, and a larger proportion of the patients with radiologically confirmed gallstone disease were operated on. The incidence of pathological cholecystograms is considered to be of particular significance with regard to prediction of the incidence of symptomatic cholelithiasis. It is concluded that the incidence of symptomatic gallstone disease decreased during the period studied.

Adolescent↗
PubMed1986

Pancreatic trauma in a defined population.

In a 20-year period, 378 of a 390,000 population were laparotomized following abdominal trauma, and pancreatic injury was found in 27. Together with two nonsurgically treated patients, these gave an average annual incidence of 0.4 cases of pancreatic trauma/100,000 population. Ten of the injuries occurred in the first and 19 in the second decade of the study. The cause was traffic accident in 18 cases and penetrating wound in only two. The patients' median age was 17 years, and 23/29 were males. The pancreatic injury was the only important intraabdominal lesion in 17 patients, but 12 had associated, potentially lethal lesions. The main pancreatic duct was injured in 11/29 patients, most commonly in those with impaired circulation on admission. Six patients died, 5/11 with, and 1/18 without injury to the main pancreatic duct. Mortality was also related to defective preoperative and intraoperative diagnosis. Clinical recognition of isolated pancreatic injury is difficult, as pain and tenderness may be initially minimal. In two of the six fatal cases and four of the 11 with injured main pancreatic duct, the abdominal status was first judged to be normal.

Adolescent↗
PubMed1985

Intravenous cholecystography and ultrasonography in the diagnosis of acute cholecystitis. A prospective comparative study.

In a consecutive series of 120 patients with clinically suspected acute cholecystitis, intravenous cholecystography and gray scale sonography were performed for comparative evaluation in a prospective study. Acute cholecystitis was diagnosed in 71 patients and gallstones without signs of acute cholecystitis in 12, while in 37 patients no gallstone disease could be detected. Intravenous cholecystography could not be performed in 28 cases because of jaundice, iodine allergy or pregnancy, and in ten other patients there was no proof of hepatic excretion of the contrast medium. Though the results in the cases with interpretable cholecystograms were excellent, the clinical usefulness was only 68%. Ultrasonography was feasible in all cases and the accuracy was 93%. Ultrasonography has the additional advantages of noninvasiveness and no irradiation problems. Sonographic findings such as thickening of the gallbladder wall, distension, and tenderness on compression of the gallbladder were diagnostically helpful in acalculous cholecystitis and in distinguishing between acute and chronic gallbladder disease. Ultrasonography is recommended as the initial screening procedure in suspected acute cholecystitis.

Acute Disease↗
PubMed1985

Ineffectiveness of vitamin A therapy in severe Crohn's disease.

In Crohn's disease there are changes in the ultrastructure of the intestinal epithelium, not only in the inflammatory tissue but also in non-ulcerated areas and in non-involved resection margins. Vitamin A is known to influence the metabolism and differentiation of epithelial tissue and has also been reported to normalize the number of stools after ileocaecal resection for Crohn's disease. We gave vitamin A (150 000 U daily) for 2 weeks to 8 patients with severe but not acute Crohn's disease. Various clinical parameters and the mucosal permeability to different-sized polyethyleneglycols were investigated before and after the administration of vitamin A. Disappointingly, no patient derived any benefit from the vitamin A ingestion as regards subjective manifestations, clinical signs, or mucosal permeability. However, some patients with Crohn's disease have low plasma concentrations of vitamin A and should be offered replacement therapy.

Administration, Oral↗
PubMed1985

Acute cholecystitis. Frequency of stones in the common duct and predictive value of liver function tests.

Two hundred and forty-three patients aged under 75 years with acute calculous cholecystitis treated by early surgery were studied with a view to investigating the frequency of choledocholithiasis and the predictive value of routine liver function tests (bilirubin, alkaline phosphatase, alanine aminotransferase). 7% had stones in the common duct, but 33% had hyperbilirubinaemia. In less than 10% of the latter could be hyperbilirubinaemia be attributed to common bile duct stones. It was concluded that the frequency of common bile duct stones in acute cholecystitis was low, and that patients often had signs of impaired liver function which was of no help in diagnosing the presence of stones in the common duct.

Adult↗
PubMed1983

Perforated duodenal ulcer--long-term results following simple closure.

Perforated duodenal ulcer was treated with suture plication in 77 patients. Only one-third of the operations were performed within six hours of the onset of perforation symptoms. The postoperative morbidity and mortality were related to the duration of the perforation and the age of the patient. The postoperative mortality rate was 6.5%. Fifty-three of the patients could be followed up after a mean period of 7.5 years. The long-term results were unsatisfactory in 84% of the patients who had had ulcer symptoms for more than three years prior to perforation, but in only 18% of those with symptoms for less than three years. Simple closure thus seems to be the treatment of choice for perforated duodenal ulcer when the patient's general health is poor or when the history of ulcer symptoms is short. A definitive operation, consisting of selective proximal vagotomy with or without drainage, should be considered for good-risk patients with pre-perforation ulcer symptoms for more than three years.

Acute Disease↗
PubMed1981

Intravenous cholecystography is a reliable method in the diagnosis of acute cholecystitis.

To evaluate the reliability of intravenous cholecystography in the diagnosis of acute cholecystitis, 186 consecutive patients with a clinical suspicion of acute cholecystitis were investigated. The contrast medium was administered as an intravenous infusion. The gall-bladder was not visualized in 110 patients (59%), suggesting acute cholecystitis. In 105 of these patients acute cholecystitis was confirmed at operation, or by a characteristic clinical course and/or oral cholecystography done later. There were 5 false positives; four of these patients were operated on, and proved to have other serious disease of the biliary tract. Filling of the gall-bladder was obtained in 76 cases (41%). One of these patients developed acute cholecystitis with perforation of the gall-bladder, diagnosed at laparotomy. In most other patients with filling of the gall-bladder diagnoses other than acute cholecystitis were verified. Intravenous cholecystography has proved highly reliable in the diagnosis of acute cholecystitis, and can contribute to reducing the incidence of misdiagnosis.

Acute Disease↗
PubMed1980

Altered gallbladder bile composition in gallstone disease. Relation to gallbladder wall permeability.

The possible role of conjugated bile salts in the induction and mediation of acute aseptic cholecystitis has been assessed. Using an experimental model, we determined the passive permeability to fluorescently labelled dextran in the gallbladder wall when exposed to different bile salts, alone or together with lecithin. Both taurocholate (20 mM) and, in particular, taurodeoxycholate (20 mM) markedly increased the transmural passage of dextran, but this effect was inhibited by lecithin (50 mM). Bile from patients with cholesterol gallstones contained relatively more deoxycholates (19.4% +/- 8.6%) and less lecithin (35 +/- 20 mmol/l) than did bile from patients with uncomplicated gastric disease (14.1 +/- 6.0% deoxycholates and 53 +/- 26 mmol lecithin/l). Since deoxycholates are more inflammation-promoting than cholates in several systems, and lecithin is considered necessary for protection against the devastating effects of bile salts, these findings should not be overlooked in current hypotheses on the pathogenesis of acute calculous cholecystitis.

Adult↗