Star testing: a novel evaluation of intraocular lens optical quality.

BACKGROUND: Despite the importance of optical quality of an intraocular lens (IOL) on visual outcomes following cataract surgery, objective data on their optical quality are not readily available, and manufacturing standards are industry regulated. The star test is a classic test of optical quality based on examination of the Airy disc and expanded diffraction rings of a point source of light, used mainly for telescope and microscope objectives. METHODS: A physical model eye cell allowed star testing of IOLs under conditions similar to the optical environment in which they operate. 18 IOLs were tested and results compared to actual images produced by these lenses in the model eye cell. Quantitative measures of star testing performance were developed. RESULTS: The optical performance of the IOLs varied, some performing very poorly. Most lenses (13/17) performed better in reverse orientation, while aberrations induced by the haptics of foldable IOLs were also detected. There was excellent correlation between actual images formed and star testing parameters. CONCLUSION: Star testing IOLs was a novel biomedical application of a centuries old, inexpensive method. A concerning variation of optical quality was found, suggesting IOL optical performance data should be more readily available. Independent, authority mandated IOL optical quality standards should be developed, and results readily available to ophthalmologists.

Digital imaging of the human cornea in vivo with ultraviolet light.

We have a developed a novel and practical method of imaging the cornea under ultraviolet (UV) light using a digital medium. Wavelengths of 336-371 nm were used to illuminate the cornea. Images were recorded using a UV Nikkor lens and a digital charged coupled device (CCD). Images obtained showed ferritin lines not visible under white light. This study concluded that 336-371 nm is comparable to shorter wavelengths for the imaging of ferritin in the cornea and that a digital image capture system was comparable to that of film.

Characterization of the mouse thrombomodulin gene and functional analysis of the 5' flanking region in F9 teratocarcinoma cells.

The mouse thrombomodulin (TM) gene was examined and shown to be a single copy gene lacking introns. Two different clones each containing the entire mouse TM gene were isolated and the nucleotide sequence of a 1.4 kb fragment comprising the 5' untranslated region and 1.2 kb of flanking sequences was determined. The transcriptional initiation site was located 30 bp downstream from a classical TATA motif within this fragment. This site was used in BALB/c 3T3 cells constitutively expressing TM, and when TM expression was induced in F9 teratocarcinoma cells in response to retinoic acid (RA) and dibutyryl cAMP (dbcAMP). A reporter construct consisting of the 1.4 kb fragment fused to the chloramphenicol acetyl transferase (CAT) gene was used to examine promoter function in F9 cells. CAT activity was induced on exposure to RA and dbcAMP and mimicked the pattern of expression of the endogenous TM gene. Induction of CAT activity did not depend on a sequence resembling a palindromic retinoic acid/thyroid hormone response element. We conclude that the 1.4 kb fragment contains the mouse TM promoter together with elements that control the induction of TM expression in differentiating F9 cells.

The minimum precorneal oxygen tension to avoid corneal edema.

One eye of each of eight subjects was exposed to gases containing oxygen concentrations of 1.0%, 2.5%, 4.9%, 7.5%, 10.1%, and 21.4% (oxygen partial pressures ranging from 8 to 158 mmHg) for 8 hr. The precorneal oxygen concentration required to avoid corneal edema for the group as a whole was 10.1% (an oxygen tension of 74 mmHg). There was considerable individual variation both in the corneal swelling response with each of the various oxygen concentrations and in the atmospheric oxygen concentration required to avoid edema: one subject required 7.5%, four subjects required 10.1%, and three subjects required 21.4% oxygen concentration. The results of this study suggest that the cornea requires higher levels of atmospheric oxygen than previously considered necessary for normal function.

Interocular transfer of the movement aftereffect in central and peripheral vision of people with strabismus.

PURPOSE: To compare binocularity in central and peripheral vision of people with early-onset strabismus and people with normal binocular vision. METHODS: Ten subjects with early-onset strabismus, and nine subjects with normal binocular vision were tested. To assess binocularity, interocular transfer (IOT) of a rotary movement aftereffect (MAE) was measured. The MAE stimuli were either confined to the central 2.8 degrees of the visual field or were presented 10 degrees into peripheral vision. RESULTS: In peripheral vision, there was no significant difference in IOT for the two groups of subjects. In central vision, there was a significant decrease of IOT in subjects with early-onset strabismus. Their IOT was, however, significantly greater than zero. CONCLUSIONS: Early-onset strabismus appears to spare binocularity in peripheral vision but reduces it in central vision. It does not abolish binocularity assessed by IOT of MAE, suggesting that some binocular connections survive early-onset strabismus, even in central vision.

A comparison of RT-PCR, in-situ hybridisation and in-situ RT-PCR for the detection of rhinovirus infection in paraffin sections.

We describe an in-situ RT-PCR method for the amplification of rhinovirus (RV) in fixed, paraffin-embedded HeLa cells employed as a model for human respiratory epithelium. HeLa cells were infected in-vitro with inocula of rhinovirus-16 ranging from 10(2) to 10(6) 50% tissue culture infective doses (TCID50), incubated for 18 h then fixed and processed into paraffin blocks. Sections of the cell preparation were subjected to standard RT-PCR, in-situ hybridisation (ISH) or in-situ RT-PCR using specific oligonucleotide primers or probes directed against the 5' non-coding region of RV RNA. RT-PCR was found to be capable of detecting RV16 RNA in one 8 microns-thick section of cells infected with the lowest virus titre. ISH using digoxigenin labelled oligonucleotide probes located RV16 signal in the majority of HeLa cells at the highest virus titre, but in few or no cells with the lowest virus titre. In contrast, in-situ RT-PCR detected RV16 in the majority of cells infected with this amount of RV16. There was a slight loss of morphology and fine localisation associated with the in-situ thermal cycling process. However, the sensitivity of in-situ RT-PCR is comparable to standard RT-PCR and greater than ISH for the detection of RV. In-situ RT-PCR has wide applications for sensitive localization of low copy viral and RNA sequences within cells to investigate the role of viruses in a variety of clinical conditions.

A multiplex RT-PCR for the detection of parainfluenza viruses 1-3 in clinical samples.

Parainfluenza viruses (PIV) are an important cause of respiratory morbidity. Conventional diagnostic methods for detection of PIV are time consuming or lack sensitivity. A multiplex PCR that detects PIV 1-3 was developed using novel primers for PIV viruses 1 and 2 and primers for PIV 3 described previously. Following RNA extraction a single multiplex reverse transcription was undertaken using antisense primers specific for each virus type. This was followed by a 40-cycle multiplex PCR using primers directed towards the haemagglutinin-neuraminidase coding region of each virus type. Products were probed with type-specific fluorescein labelled internal probes and detected by chemiluminescence. Cultured PIV viruses were detectable to a sensitivity of 1 TCID50. The technique was applied to 57 nasal aspirates taken from children presenting with various acute respiratory conditions and analysed previously by culture, immunofluorescence and/or serology. It was possible to detect PIV 1, 2 or 3 in 13/13 samples found previously positive for PIV by tissue culture, 13/15 found previously positive by immunofluorescence and 6/10 that coincided with positive serology. None of the samples found previously positive for other viruses (26) or negative to virus detection (6) were found positive by RT-PCR. It is concluded that this method is as sensitive as combined immunofluorescence and tissue culture for the detection of the PIV viruses 1-3 and should be useful for rapid diagnosis of PIV 1-3 infections.

Rhinovirus identification by BglI digestion of picornavirus RT-PCR amplicons.

Rhinoviruses are the main cause of the common cold and precipitate the majority of asthma exacerbations. RT-PCR followed by internal probe hybridisation or Southern blotting, or nested PCRs are currently the most sensitive methods for their identification. However, none of the published techniques can differentiate satisfactorily rhinoviruses from other picornaviruses. Examination of the restriction maps of sequenced rhinoviruses, revealed a highly conserved BglI restriction site (GCCnnnnnGGC), located exactly in the middle of the 380-bp amplicon generated with the OL26-OL27 primer pair, which has been used extensively in the past to identify picornaviruses. Such a site was either not present, or positioned differently in other picornaviruses of known sequence. It was, therefore, considered that digestion of rhinovirus amplicons with this enzyme would result in two equal length fragments, generating a single 190-bp band in gel electrophoresis. In contrast, either one undigested 380-bp band or a double-band pattern would appear in amplicons from other picornaviruses. To test this hypothesis, Bgl digestions of OL26-OL27 amplicons from cultured and wild-type rhinoviruses, whose identity was confirmed by acid lability, as well as from echo, polio and coxsackie viruses were carried out. All rhinovirus samples were digested successfully generating single bands. Among the other picornaviruses, only 6.6% presented a single band pattern, while the rest were as predicted from the model. With a sensitivity of 100% and a specificity over 90%, the method described, which is rapid and remarkably easy to perform, can be used to distinguish rhinoviruses from other picornaviruses to a considerable extent.

Apparent accommodation and depth of field in pseudophakia.

PURPOSE: To assess depth of field in phakic and pseudophakic eyes to explain good distance and uncorrected near visual acuity in pseudophakic eyes. SETTING: Department of Ophthalmology, University of Otago Medical School, Dunedin, New Zealand. METHODS: Depth of field was measured in pseudophakic (n = 10) and phakic (n = 10) eyes for both near and distant targets. Test conditions included cycloplegia and a constant pupillary aperture using a soft contact lens with a central artificial pupil diameter of 2.5 mm. RESULTS: There was no statistically significant difference between phakic and pseudophakic eyes for any test. Depth of field for near visual acuity was +/-0.85 diopters (D), but amplitude of legibility was +/-1.94 D. Depth of field for distance visual acuity was between 0.25 and 0.50 D in 85% of eyes. CONCLUSION: In the absence of astigmatism and disease, a pseudophakic eye with -0.75 D of myopia can expect to achieve 20/30 uncorrected distance acuity and read N5 unaided if the pupil is approximately 2.5 mm.

Sarcocystis kirkpatricki n. sp. (Apicomplexa: Sarcocystidae) in muscles of raccoons (Procyon lotor) from Illinois.

Sarcocysts of Sarcocystis kirkpatricki n. sp. (Apicomplexa: Sarcocystidae) are described from the skeletal and heart musculature of 66 (66%) of 100 raccoons (Procyon lotor) from Illinois. Histologic examination of muscle tissues from tongue, diaphragm, esophagus, and heart revealed that 61%, 47%, 32%, and 2%, respectively, contained sarcocysts of this species. Juvenile raccoons (less than 1 yr old) were more likely (P less than 0.01) to have sarcocysts in the tissues examined (52/60 or 87%) than were adults (14/40 or 35%). Histologically, sarcocysts in the 4 tissues were similar: the cyst wall was 2-3 microns thick, PAS negative, and had fine hairlike surface projections; interior septa were indistinct. Ultrastructurally, sarcocyst walls had short (mean = 2.8 microns), straight to sloping, villuslike projections. Longitudinal tubular filaments inside these projections extended from the tips to the base, where they terminated in a granular electron-dense layer of the primary cyst wall. Thin septa were within the sarcocysts. Feeding experiments utilizing dogs and cats as potential definitive hosts were negative.

Clinical bronchography in the horse: development of a method using barium sulphate powder.

A method for performing bronchography in standing nonanaesthetized horses was developed. Bronchography was performed by insufflating the previously intubated trachea with a mixture of 120 to 200 g of finely powdered barium sulphate mixed with 3 to 7 g of powdered methyl cellulose. The mixture was delivered from an ether vaporiser into which compressed air was blown. Premedication with atropine sulphate immediately before insufflation minimised bronchoconstriction. Satisfactory bronchograms with contrast visible down to the seventh and eighth bronchial divisions were obtained in 80 per cent of the 26 horses tested. Poor results were obtained if there were delays in taking exposures. Total clearance of the barium sulphate from the lung fields was extremely rapid, averaging 4 h. No significant clinical side effects were noted and histology of the lungs, in animals sacrificed sequentially over a period of 2 weeks, demonstrated a minimal cellular response. In one clinical case, with chronic bronchitis, loss of parallelism of the bronchial walls and moderate bronchial dilatation between branches was demonstrated. It was concluded that although the value of bronchography as a diagnostic procedure in equine radiology has yet to be proven, the method of powder insufflation with barium sulphate provides a safe and accurate means of investigating bronchial conditions in the horse.

Effects of lead, iron, and bismuth alloy shot embedded in the breast muscles of game-farm mallards.

Effects of five lead (Pb), iron (Fe), or bismuth (Bi)/tin (Sn) alloy shot embedded in the breast muscles of game-farm mallards (Anas platyrhynchos) were studied from 28 March 1994 through 27 March 1995. We detected no differences in the mean survival times, mean hematocrits, or mean body weights among the three shot types. Connective tissue encapsulated Pb and Bi/Sn shot but only slight changes occurred in tissues surrounding the shot. Recovered Pb and Bi/Sn shot were essentially unchanged in appearance and weight. A thin zone of "oxide" surrounded Fe shot with a slight inflammatory response and a small amount of scarring adjacent to the embedded shot. Fe shot decreased slightly in weight while embedded. Bacterial infections were absent in all dosed ducks. Mean weights of kidneys, livers, and gonads did not vary by type of shot. Kidneys and livers of Bi-dosed ducks had higher concentrations of Bi than in Pb- and Fe-dosed ducks. Muscle and blood showed no differences in Bi concentrations among doses. We found no histological dose-related effects in kidneys, liver, and gonads from the embedded shot.

Influence of diet on the hematology and serum biochemistry of zinc-intoxicated mallards.

Changes in hematological and serum biochemistry parameters in female zinc (Zn)-dosed farm-raised mallards (Anas platyrhynchos) fed four different diets were examined. Sixty ducks received an average dose of 0.97 g of Zn in the form of eight, 3.30-mm diameter shot pellets containing 98% Zn and 2% tin, and another 60 ducks were sham-dosed as controls. Fifteen ducks from each of the two dosing groups were assigned to one of four dietary treatments: corn only, corn with soil, commercial duck ration only, or commercial duck ration with soil. Shot-pellet dissolution rates ranged from 7 mg/Zn/day to 27 mg/Zn/day. Regardless of diet, the Zn dose resulted in mortality; incoordination; paralysis and anorexia; decreased body, liver, pancreas, gonad, and gizzard weight; increased kidney weight; and macroscopic lesions. Zn-dosed ducks had a lower mean erythrocyte packed cell volume (PCV), higher mean reticulocyte count, and a greater number of individuals with immature and/or abnormal erythrocytes, than did control mallards. Mean total leucocyte counts were higher in Zn-dosed ducks than in controls. Zn-dosed ducks that had soil available had higher leucocyte counts than those without soil. Zn-dosed ducks were characterized by a marked heterophilia and relative lymphopenia. In Zn-dosed ducks, the mean lymphocyte count was highest in those provided a commercial duck ration, and lowest in those fed corn. In control ducks, the mean lymphocyte count was highest in ducks fed corn, and lowest in those provided soil along with a commercial duck ration. Zn-dosed mallards had higher serum aspartate aminotransferase and amylase levels, and lower alkaline phosphatase activities than control ducks. Serum phosphorus and uric acid concentrations were higher, and calcium, glucose, and total protein levels lower, in Zn-dosed ducks than in control ducks. Diet did affect serum calcium, phosphorus, total protein, and uric acid concentrations. Differences in erythrocyte and leucocyte parameters, serum enzyme activities, and metabolite concentrations were associated with dose and diet effects. Diets high in protein and other organic matter and calcium and phosphorus did not prevent or substantially alleviate Zn toxicosis in farm-raised mallard ducks.

Community study of role of viral infections in exacerbations of asthma in 9-11 year old children.

OBJECTIVE: To study the association between upper and lower respiratory viral infections and acute exacerbations of asthma in schoolchildren in the community. DESIGN: Community based 13 month longitudinal study using diary card respiratory symptom and peak expiratory flow monitoring to allow early sampling for viruses. SUBJECTS: 108 Children aged 9-11 years who had reported wheeze or cough, or both, in a questionnaire. SETTING: Southampton and surrounding community. MAIN OUTCOME MEASURES: Upper and lower respiratory viral infections detected by polymerase chain reaction or conventional methods, reported exacerbations of asthma, computer identified episodes of respiratory tract symptoms or peak flow reductions. RESULTS: Viruses were detected in 80% of reported episodes of reduced peak expiratory flow, 80% of reported episodes of wheeze, and in 85% of reported episodes of upper respiratory symptoms, cough, wheeze, and a fall in peak expiratory flow. The median duration of reported falls in peak expiratory flow was 14 days, and the median maximum fall in peak expiratory flow was 81 l/min. The most commonly identified virus type was rhinovirus. CONCLUSIONS: This study supports the hypothesis that upper respiratory viral infections are associated with 80-85% of asthma exacerbations in school age children.

Short- and long-term academic predictors of medical student performance.

The relationship between entry qualifications and performance throughout the medical course was studied in individual cohorts of students admitted in the years 1977 to 1981. A modest but significant relationship with overall initial qualifications was found throughout the course. Students without biology showed a marked disadvantage in the first year but the effect did not persist. There were quite marked variations in all these effects between cohorts; studying only a single cohort could lead to inappropriate conclusions.