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Biomedical subjects

T L Lewis

Publications and source records attributed to T L Lewis.

At least 55 records · Page 3Linked to original sources
PubMed1992

The development of the temporal and nasal visual fields during infancy.

We used static perimetry to measure the development of the monocular visual field during infancy. Infants from birth to 6 months of age, and adults, were shown a 3 or 6 degrees flashing light at various locations between 15 and 120 degrees in the temporal and nasal visual fields. We assumed that subjects could see a light if they moved their eyes toward it more often than they looked in the same direction on blank control trials. For both the 3 and 6 degrees lights, the visual field expanded with age from the center out, and development in the nasal visual field lagged behind development in the temporal visual field. Possible reasons for these findings are discussed.

Adult↗
PubMed1992

Vision in the "good" eye of children treated for unilateral congenital cataract.

PURPOSE: The authors examined linear acuity and contrast sensitivity in the "good" (fellow) eye of children treated for unilateral congenital cataract to determine (1) whether there were subtle deficits like those described for the good eye of patients with strabismic amblyopia and (2) whether any deficits were related to the degree to which the good eye had been patched. METHODS: The authors tested patients treated for unilateral congenital cataract who had a well-documented history of patching. The good eye was physically normal with minimal refractive error. The measures were linear acuity at far (n = 15) and contrast sensitivity (n = 9). RESULTS: Compared with age-matched control subjects, the good eyes of patients had subtle deficits in linear acuity and in contrast sensitivity at high spatial frequencies. These deficits occurred even in eyes that had received minimal patching, and their severity was not related systematically to the duration of patching, which varied widely across the group. CONCLUSION: The visual sensitivity of the good eye of children treated for unilateral congenital cataract is, on average, slightly reduced, even in cases of minimal patching. Consequently, any deficits discovered after aggressive patching may not have been caused by occlusion amblyopia.

Adolescent↗
PubMed1991

Detection of BVD viruses using synthetic oligonucleotides.

This study examined synthetic oligonucleotide probes as potential diagnostic tools for bovine viral diarrhea virus (BVDV). Six 20-base sequences from across the genome were selected by homology analysis of the published genomic sequences of the NADL and Osloss isolates of BVDV. RNA was extracted from 22 BVDV isolates propagated in bovine turbinate (BT) cells, blotted, and probed with 32P end-labeled oligonucleotides. The stringency conditions used were such that more than a single base mismatch would result in no hybridization. The probe originating nearest the 5' end of the viral RNA, ND001, detected 86% of the viral isolates while the other probes detected from 19% to 57%. Both cytopathic and noncytopathic isolates were detected by these synthetic probes. A cocktail of these probes were used to specifically detect BVDV RNA extracted directly from tissues of cattle either persistently or acutely infected.

Animals↗
PubMed1991

Antigenic and genomic comparison between non-cytopathic and cytopathic bovine viral diarrhoea viruses isolated from cattle that had spontaneous mucosal disease.

Antigenic and genomic relationships between five pairs of non-cytopathic and cytopathic bovine viral diarrhoea (BVD) viruses isolated from cattle with mucosal disease were examined. Antigenic similarity was evaluated by studying the binding characteristics of 10 monoclonal antibodies (MAbs) directed against the gp53 BVD virus glycoprotein. The MAb binding match between members of the same virus pair ranged from 10/10 to 7/10. The genomic relationships was evaluated by studying the hybridization characteristics of two cDNA probes and six complementary 20 base oligomer probes with virus DNA, selected on the basis of conservation between published BVD virus sequences; cDNA probes were hybridized at two stringencies (60 degrees C and 45 degrees C). The match of hybridization results between members of the same virus pair ranged from 4/4 to 1/4 with the cDNA probes and from 6/6 to 3/6 with the oligomer probes. The results indicate that members of the same virus pair can differ at both the antigenic and genomic levels.

Animals↗
PubMed1991

A new look at an old disease.

Despite 200 years of effort, much about glaucoma remains a mystery, and numerous critical questions remain unanswered. Are there subgroups of primary open-angle glaucoma, with different etiologies, risk factors, clinical presentations, and prognoses? What criteria should be adopted for important diagnostic tests, such as automated perimetry, to reduce the likelihood of variability? Is medical management of the disease truly efficacious? Should laser trabeculoplasty become the initial surgery of choice? Current answers to these and other important questions are reviewed in this survey of the many new research efforts exploring this old disease.

Electrophysiology↗
PubMed1989

Optokinetic nystagmus in normal and visually deprived children: implications for cortical development.

Ten years ago we proposed that the limitations on young infants' vision might be caused by an immature Y-pathway through the cortex, while their abilities might be mediated by an X-pathway to the cortex and by Y- and/or W-pathways to the superior colliculus and pretectum (Maurer & Lewis, 1979). Although that explanation was too simple overall, it fits well with what is known about asymmetrical optokinetic nystagmus, viz. the difficulty in eliciting OKN to patterns moving from the nasal field toward the temporal field. In this paper, we describe the development of symmetrical OKN, its alteration by early deprivation from cataract, and its physiological basis. We then suggest that, for primates, an explanation based on projections through the magnocellular versus parvocellular layers of the lateral geniculate nucleus may be more appropriate than one based on X-, Y-, and W-cells.

Animals↗
PubMed1989

A new test of luminous efficiency for babies.

We used the minimum motion method devised by Anstis and Cavanagh (1983) to measure the luminous efficiency of red and green and of yellow and blue for "normal" 1- 3-month-old babies and for one 3-month-old boy destined to be color-deficient because of a deutan mother. Subjects watched a display which created apparent motion, the direction of which depended on the relative luminance of the colors. To determine the equiluminant points, we observed the optokinetic nystagmus elicited by the display as the relative luminance of the colors was varied. The equiluminant points of the normal mothers and their infants were similar to each other but different from those of the deutan mother and her son. Our new method demonstrates the early maturation of input from red and green cones into achromatic pathways. It can also be used to identify some color-deficient infants.

Color Perception↗
PubMed1988

Pleiotropic mutations in Saccharomyces cerevisiae affecting sterol uptake and metabolism.

Sterol uptake control mutants (upc-) have been isolated via ethylmethanesulfonate mutagenesis from wild-type Saccharomyces cerevisiae. These mutants are heme and sterol competent but possess the ability to accumulate exogenous sterol(s) under aerobic conditions. Previous studies demonstrate sterol uptake only in a hem-, erg- background; however, the Upc- strains described here are Hem+ and do not require exogenous sterol for growth. We were unable to obtain viable hem+, erg-, upc+ recombinants; such combinations appear to be lethal. Isolates of Upc mutants demonstrated different levels of sterol uptake, and sterol analysis revealed a broad phenotypic range with regard to amounts and accumulation of ergosterol and non-ergosterol sterols. Assays of acyl CoA: ergosterol acyltransferase and sterol ester hydrolase showed no apparent difference in activity between Upc mutants and the wild type.

Cholesterol↗
PubMed1987

Detection of latency-related viral RNAs in trigeminal ganglia of rabbits latently infected with herpes simplex virus type 1.

Using a combination of in situ hybridization and Northern (RNA) blot analysis, we investigated herpes simplex virus type 1 (HSV-1) transcriptional activity in an ocular rabbit model of HSV-1 latency. Radioactively labeled cloned fragments, representing virtually the entire HSV-1 genome, were individually hybridized to RNA in sections of trigeminal ganglia taken from rabbits during the latent phase of infection with HSV-1 (McKrae). Our results suggest that two discrete latency-related RNAs (LR-RNAs) may be present. The LR-RNAs were localized mainly in the nuclei of neurons. The more abundant LR-RNA was detected in approximately 3% of all neurons examined and was designated major LR-RNA. The other LR-RNA, designated minor LR-RNA, was detected in approximately 0.3% of neurons from latently infected rabbits. The genes for the LR-RNAs mapped in the vicinity of the immediate-early gene ICP0 (also designated IE110). The gene for the major LR-RNA partially overlapped the left (3') end of the ICP0 gene. In situ hybridization with single-stranded RNA probes showed that this LR-RNA was of complementary sense to that of ICP0 mRNA. Northern blot analysis gave an approximate size for this LR-RNA of 1.8 to 2.2 kilobases. The minor LR-RNA mapped to or near the right (5') end of the ICP0 gene. The detection of LR-RNAs suggests the possibility that these RNAs or their products may play significant roles in the initiation and/or maintenance of HSV-1 latency.

Animals↗
PubMed1986

Preferential looking as a measure of visual resolution in infants and toddlers: a comparison of psychophysical methods.

We used preferential looking to estimate the monocular visual resolution of children 6-36 months old and compared results from 3 psychophysical methods: Taylor and Creelman's PEST staircase, our modification of the PEST procedure, and the method-of-constant stimuli. Estimates of visual resolution for 48 children tested with the original and modified PEST procedures and for 50 children tested with the method-of-constant stimuli and the modified PEST procedure showed excellent agreement across procedures, with the modified PEST procedure requiring the fewest trials and the least time. Results from the modified PEST procedure for 168 children with normal eye alignment and minimal refractive errors indicated that monocular visual resolution improves from 6.5 min at 6 months to 1.2 min at 36 months. Preferential looking combined with the shortened PEST procedure should be useful for testing the visual resolution of preverbal children with eye problems.

Child Development↗
PubMed1986

Effects on perceptual development of visual deprivation during infancy.

We measured three aspects of vision in children treated for unilateral congenital cataract: visual resolution, the symmetry of optokinetic nystagmus (OKN), and peripheral vision. Good visual resolution was achieved by children who had had the earliest treatment and who had had the normal eye patched close to 50% of the waking time throughout early childhood. All children treated for unilateral congenital cataract showed a marked asymmetry of OKN regardless of the age of treatment. One child with early treatment who could be tested with the Goldmann perimeter also showed especially poor sensitivity in the nasal visual field of her aphakic eye. We found no such deficits in the vision of children who had had normal visual experience during early infancy and then later developed cataracts in one or both eyes. The limitations observed in children treated for congenital cataract are similar to those reported in normal human infants, in normal kittens, and in cats which were visually deprived early in life.

Adolescent↗
PubMed1985

The development of young infants' ability to detect stimuli in the nasal visual field.

We compared infants' ability to detect single lines of varying width in the temporal and nasal visual fields. The smallest lines detected by 1-month-olds at 20 degrees in the nasal visual field were more than eight times wider than those detected at 30 degrees in the temporal visual field. In contrast, 2-month-olds detected smaller lines at 20 degrees in the nasal visual field than at 30 degrees in the temporal visual field. Converging evidence suggests that the observed improvement between 1 and 2 months in detection in the nasal visual field reflects the maturation of a projection from the retina through the visual cortex to the superior colliculus.

Eye Movements↗
PubMed1985

Outcome of pregnancy following induced abortion. Report from the joint study of the Royal College of General Practitioners and the Royal College of Obstetricians and Gynaecologists.

A total of 1590 general practitioners and 795 gynaecologists in England, Scotland and Wales are participating in a long-term, prospective study concerning the sequelae of induced abortion. In the present report a comparison is made between the outcome of the first post-index pregnancy in 745 women whose index pregnancy ended in an induced abortion (cases) and that in 1339 women who had an unplanned index pregnancy but were not referred for induced abortion (controls). There were no statistically significant differences between cases and controls. The increased relative risk which was found amongst the induced abortion group of non-viable outcome, low birthweight and shortened gestation, could have arisen by chance. Further analysis of a larger number of pregnancies is required to permit confident interpretation of these observations. The present data provide no reason for alterations in the current management of induced abortion, or the subsequent pregnancy.

Abortion, Induced↗
PubMed1984

Effects of fasting, pancreatectomy, and hypophysectomy in the yellow eel, Anguilla rostrata.

Metabolic effects of pancreatectomy and hypophysectomy are investigated in the yellow American eel, Anguilla rostrata, fasted for 6 months. The results are compared with the findings in freshly captured eels subjected to the same operations. In intact animals, fasting causes a statistically significant decrease in serum amino acid nitrogen (AAN), serum urea, and relative liver weight, and an increase in serum free fatty acids (FFA), serum cholesterol, and tissue hydration. Serum glucose, liver and muscle glycogen, liver and muscle fatty acids, and abdominal fat stores do not show significant alterations. The absence of diabetes mellitus after pancreatectomy, seen in previous studies, is confirmed. However, pancreatectomy affects fewer parameters in fasting eels than in fed ones. After hypophysectomy, the situation is similar; only serum AAN shows an impact of the operation in fasted eels. As in freshly captured eels, surgical stress seems to affect almost all metabolic parameters. It appears that the smaller impact of both pancreatectomy and hypophysectomy in fasted eels reflects the reduced role of hormones in the state of lowered metabolism.

Amino Acids↗
PubMed1983

Peripheral vision and optokinetic nystagmus in children with unilateral congenital cataract.

The vision of cats which were monocularly deprived during early infancy, of kittens, and of young human infants shares two limitations: detection in the nasal visual field is far poorer than detection in the temporal visual field, and optokinetic nystagmus (OKN) is difficult to elicit when a pattern moves nasally to temporally. Here we report similar limitations on the vision of children who had a dense central cataract in one eye during early infancy. Extensive static perimetry with one of these children whose visual acuity was good in both eyes revealed that her threshold for detection all along the horizontal meridian was higher in her aphakic than in her normal eye, with this difference much more pronounced in the nasal visual field than in the temporal visual field. Three children who developed cataracts after 6 months of age showed no such discrepancy between thresholds in the temporal and nasal fields. We tested the symmetry of OKN in 12 children treated for unilateral congenital cataract. In every test of an aphakic (n = 4) or normal eye (n = 12), OKN occurred significantly more often when stripes moved temporally to nasally than when they moved nasally to temporally. In contrast, no asymmetry was observed in any of 13 children treated for traumatic cataracts incurred after 3 years of age. We conclude that children treated for unilateral congenital cataract, like young human infants and monocularly deprived cats, show asymmetric OKN and relatively poor detection in the nasal visual field.

Animals↗