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Biomedical subjects

M G Harris

Publications and source records attributed to M G Harris.

At least 19 recordsLinked to original sources
PubMed2006

Treated incidence of first-episode psychosis in the catchment area of EPPIC between 1997 and 2000.

OBJECTIVE: To identify the treated incidence of psychosis in catchment of the Early Psychosis Prevention and Intervention Centre (EPPIC), Melbourne, Australia. METHOD: Cases were aged 15-29 years with a first episode of a psychotic disorder accepted into EPPIC between 1997 and 2000. Age- and sex-specific incidence rates per 10,000 person-years were calculated in 5 year age bands. Rate ratios were used for age group comparisons. RESULTS: The age-specific treated incidence of first-episode psychosis in 15-29-year old individuals was 16.7 per 10,000 person-years in males, and 8.1 per 10,000 person-years in females. The incidence was highest in 20-24-year-old males and in 15-19-year-old females. For both sexes, incidence rates were significantly lower in the 25-29-year age group. CONCLUSIONS: The incidence of psychosis in the catchment of EPPIC was higher than previously reported, especially in female teenagers. Peak rates in 15-24 year olds suggest a youth model approach to early psychosis may be indicated.

Adolescent↗
PubMed2001

Broad direction bandwidths for complex motion mechanisms.

Growing evidence from psychophysics and single-unit recordings suggests specialised mechanisms in the primate visual system for the detection of complex motion patterns such as expansion and rotation. Here we used a subthreshold summation technique to determine the direction tuning functions of the detecting mechanisms. We measured thresholds for discriminating noise and signal+noise for pairs of superimposed complex motion patterns (signal A and B) carried by random-dot stimuli in a circular 5 degrees field. For expansion, rotation, deformation and translation we found broad tuning functions approximated by cos(d), where d is the difference in dot directions for signal A and B. These data were well described by models in which either: (a) cardinal mechanisms had direction bandwidths (half-widths) of around 60 degrees; or (b) the number of mechanisms was increased and their half-width was reduced to about 40 degrees. When d=180 degrees we found summation to be greater than probability summation for expansion, rotation and translation, consistent with the idea that mechanisms for these stimuli are constructed from subunits responsive to relative motion. For deformation, however, we found sensitivity declined when d=180 degrees, suggesting antagonistic input from directional subunits in the deformation mechanism. This is a necessary property for a mechanism whose job is to extract the deformation component from the optic flow field.

Discrimination, Psychological↗
PubMed2001

Obstetric risk factors for postnatal depression in urban and rural community samples.

OBJECTIVE: The objective of this study was to examine obstetric risk factors for postnatal depression in an urban and rural community sample, with concurrent consideration of personality, psychiatric history and recent life events. METHODS: This was a prospective study with women planning to give birth in one of the four participating hospitals recruited antenatally. Obstetric information was obtained from the New South Wales Midwives Data Collection, completed shortly after delivery. Personality, psychiatric history and life-events information were obtained from a questionnaire, administered within 1 week postpartum. Depression status was assessed at 8 weeks postpartum using the Edinburgh Postnatal Depression Scale. RESULTS: Complete data were obtained from 490 women. Several non-obstetric risk factors for the development of postnatal depression at 8 weeks postpartum were reported including: sociodemographic (up to technical college level education, rented housing, receiving a pension/benefit), personality (those who described themselves as either nervy, shy/selfconscious, obsessional, angry or a worrier), psychiatric history (familial history of mental illness, personal history of depression or anxiety or a history of depression in the participant's mother) and recent life-events (major health problem, arguments with partner and friends/relatives). None of the obstetric variables were significantly associated with increased risk for postnatal depression, but several showed marginally significant increases (multiparous women, antepartum haemorrhage, forceps and caesarean section deliveries). CONCLUSIONS: The results emphasize the importance of psychosocial risk factors for postnatal depression and suggest that most obstetric factors during pregnancy and birth do not significantly increase risk for this depression. Early identification of potential risk for postnatal depression should include assessment of sociodemography, personality, psychiatric history and recent life events, as well as past and present obstetric factors.

Adolescent↗
PubMed2001

Is optic flow used to guide walking while wearing a displacing prism?

Rushton et al (1998 Current Biology 8 1191 - 1194) recently showed that walkers wearing displacing prisms follow curved trajectories determined by the perceived direction of their target. This suggests that optic flow is not important in guidance, since flow cues are unaffected by the prism and should allow a straight, direct trajectory. We replicated Rushton et al's result but also tried to rule out an important artifact associated with the prism. Prisms restrict the field of view and, particularly, access to the foreground optic flow that is likely to be important in providing guidance cues. We found that performance did not improve when walkers directed their gaze to include the foreground flow, suggesting that Rushton et al's results were not due to this artifact. On the other hand, performance did reliably improve when subjects reduced their viewing height by crawling towards the target. This improvement may be due to coarsening of the visual texture or to increased salience of alignment and motion-parallax cues. Whatever its cause, the improvement demonstrates that guidance is not determined only by perceived target direction and that, under some conditions, flow may be important.

Adolescent↗
PubMed2001

Independent detectors for expansion and rotation, and for orthogonal components of deformation.

It is well known that optic flow--the smooth transformation of the retinal image experienced by a moving observer--contains valuable information about the three-dimensional layout of the environment. From psychophysical and neurophysiological experiments, specialised mechanisms responsive to components of optic flow (sometimes called complex motion) such as expansion and rotation have been inferred. However, it remains unclear (a) whether the visual system has mechanisms for processing the component of deformation and (b) whether there are multiple mechanisms that function independently from each other. Here, we investigate these issues using random-dot patterns and a forced-choice subthreshold summation technique. In experiment 1, we manipulated the size of a test region that was permitted to contain signal and found substantial spatial summation for signal components of translation, expansion, rotation, and deformation embedded in noise. In experiment 2, little or no summation was found for the superposition of orthogonal pairs of complex motion patterns (eg expansion and rotation), consistent with probability summation between pairs of independent detectors. Our results suggest that optic-flow components are detected by mechanisms that are specialised for particular patterns of complex motion.

Differential Threshold↗
PubMed2000

Coarse-grained information dominates fine-grained information in judgments of time-to-contact from retinal flow.

To investigate the relative importance of fine- and coarse-grained structure in the analysis of retinal flow, subjects made estimates of time-to-contact from random dot kinematograms depicting movement towards a flat, sparsely textured surface. Individual display elements moved smoothly away from each other while expanding smoothly in size. By artificially manipulating the rate at which the individual elements expanded we showed that this cue has only a small effect upon performance. When individual elements were replaced by small clusters of dots, expansion of the clusters had a similarly small effect upon performance. However, estimates of time-to-contact were possible when a single expanding cluster was presented in isolation. We conclude that both types of information are available to the subject but that estimates of time-to-contact are based primarily on coarse-grained changes in the position of image elements and that fine-grained changes in element size or position play only a minor role.

Biomechanical Phenomena↗
PubMed2000

Ultraviolet transmittance of the Vistakon disposable contact lenses.

With increasing scientific evidence demonstrating the harmful effects of ultraviolet (UV) radiation on different ocular tissues, contact lens manufacturers are incorporating UV blocking monomers into their contact lenses. This study evaluated the transmittance spectra of Vistakon's disposable soft contact lenses (1 Day Acuvue, Acuvue, Surevue, and Vistavue). All except Vistavue contain a UV blocking agent. Transmittance for each lens was recorded from 200 to 400 nm on a Shimadzu UV 160U Dual Beam Recording Spectrophotometer. The results indicate that lenses which incorporate the UV blocking monomer significantly reduced the transmission of W radiation while untreated lenses did not. Our findings indicate that 1 Day Acuvue, Surevue, and Acuvue meet the American National Standards Institution (ANSI) Standard Z80.20 for Class 2 UV blockers: a maximum of 30% transmittance of UVA wavelengths and 5% transmittance of UVB wavelengths. In contrast, the Vistavue lens demonstrated negligible UV blockage. Our technique, in which contact lenses were placed directly in front of a measuring beam, was accurate and simpler than previously reported methods and may be useful in future studies. We found that UV blocking soft contact lenses can be a viable alternative for spectacles in protecting internal ocular structures from UV radiation. However, the external structures of the eye remain at risk and would continue to benefit from the use of UV blocking sunglasses or spectacle lenses.

Journal Article↗
PubMed2000

Legal responsibilities when fitting minors with contact lenses.

BACKGROUND: Practitioners must understand their legal responsibilities in fitting minors with contact lenses, which include informed consent, contractual obligations, and the Statute of Limitations. Minors are children and teenagers who have not yet reached voting age in their state--generally 18 years of age. Informed consent requires permission from the patient before a practitioner performs any treatment. For these young people, this consent generally can only be given by a parent or legal guardian. Minors can repudiate contracts made with them; therefore, the contractual obligation to pay for a contact lens fitting should be established with a parent or legal guardian. In most states, minors have additional time beyond the usual Statute of Limitations to bring a lawsuit. If practitioners recognize their legal responsibilities in caring for these special patients, fitting youngsters with contact lenses can be a rewarding part of practice.

Adolescent↗
PubMed2000

Why don't we have enough cornea donors? A literature review and survey.

BACKGROUND: Organ donation provides a second chance for those who have experienced severe disease or injury. Unfortunately there is a huge discrepancy between the supply and demand of transplantable organs, despite the existence of sufficient numbers of potential donors. Through a review of the literature and a survey of optometry students, this article provides insight into the reasons for the shortage of corneal donors and how more corneal donors might be obtained. METHOD: A survey of 200 optometry students at the University California, Berkeley, School of Optometry was conducted to augment the literature review. Seventy-six students (38% of those surveyed) completed the survey process. RESULTS: Results of the survey indicated that 64.5% of who responded were willing to donate body organs, while 31.6% were not. Of those not willing to donate organs, 11.8% cited religious reasons. Other personal reasons included: fear (4%), respect for the human body (7.9%), and parental disapproval (6.4%). Only 46.1% of respondents had donation stickers on their driver's licenses. CONCLUSION: The literature review and survey indicate that age, religion, culture, personality characteristics, views on death and mortality, body image, and humanitarian concerns are among the many factors that influence people's opinion concerning organ donations. Education of the public and health care professionals' awareness of the importance of obtaining corneas for donation is crucial to end the shortage of organ donors.

Cornea↗
PubMed1999

Major concerns and needs of breast cancer patients.

Between 1989 and 1991, 102 breast cancer patients completed a questionnaire survey on concerns and needs at their first visit to the University Clinic after they were diagnosed or treated for breast cancer at other clinics. Their major concerns and needs were health, family, finances, work, the future, self-esteem, counseling and support for themselves and their family. Married women and those younger than 50 years were more likely to have concerns about their family. Nonwhites had more concerns about finances and work than white women, with an odds ratio (OR) of 6.58. Older women and those married, however, had less concerns about finances and work than younger women and those not married, with ORs of 0.96 and 0.34, respectively. Fewer nonwhite than white patients expressed concerns about their future (OR = 0.31). Young women were more concerned about self-esteem than older women. More nonwhites than whites and more married than unmarried women expressed needs for family counseling and support (OR = 3.58 and 3.68, respectively). Help for interpreting information was required more frequently by nonwhites than whites (OR = 7.25, 95% confidence interval [CI] = 2.19-24.00). Nonwhite women also tended to require more referrals than whites. In summary, major concerns and needs varied among patients of different demographic characteristics, especially those of age, race, and marital status.

Adaptation, Psychological↗
PubMed1999

Transmittance of tinted and UV-blocking disposable contact lenses.

PURPOSE: Tinted and ultraviolet (UV)-blocking disposable contact lenses have become increasingly popular over the last decade. Wearers of UV-blocking contact lenses could benefit greatly by protecting their eyes from potential UV radiation damage. A Uvikon 930 dual beam spectrophotometer was used to measure three enhancement-tinted lenses (royal blue, evergreen, and aqua), two types of UV-blocking lenses, and two types of non-UV-blocking lenses. Enhancement-tinted lenses did show a decrease in transmittance at certain wavelengths on the visible spectrum, but they did not reduce the transmittance of UV radiation to the extent of the UV-blocking lenses designed specifically for this purpose.

Contact Lenses, Hydrophilic↗
PubMed1998

The Australian health system: continuity and change.

The health of Australians, with the exception of Aboriginals and Torres Strait Islanders, compares favourably with other industrialised nations. Since 1984, universal access for citizens to medical and public hospital services has been achieved under a national Health Insurance Scheme called Medicare, partially funded by a 1.4 percent levy on all taxpayers. Medicare found early widespread support from the electorate but continues to be buffeted by a minority coalition of some medical associations, private health insurers, and conservative "libertarian" politicians. Over the decade since its inception, Medicare has provided stability in maintaining total health costs around 8 percent of GDP. This has been largely due to capping hospital costs via Commonwealth-State agreements. Medicare has failed in the past five years to contain medical costs which have increased proportionally with increases in the medical workforce. This article examines the structure and performance of Medicare and its role within Australia's overall health system. Benefits of a universal access insurance program are outlined together with challenges associated with inequities in health status, geography, aging of the population, burgeoning technology, ideological diversity, and an economic climate requiring cost containment and favouring privatisation and the role of the market. It can be concluded that, despite these challenges, universal access to health care is here to stay. Australia's Medicare program has become popular with the electorate.

Australia↗
PubMed1997

Computation of surface slant from optic flow: orthogonal components of speed gradient can be combined.

In previous work [Meese et al. (1995). Vision Research, 35, 2879-2888)] we showed that one-dimensional (1D) speed gradients are sufficient to produce a compelling impression of surface slant. Summing a 1D vertical shearing gradient or, less intuitively, a 1D horizontal shearing gradient with a random field of horizontally translating dots produces perceived slant about a horizontal axis. Similarly, a 1D vertical or horizontal compression gradient produces perceived slant about a vertical axis. Appropriately combining orthogonal 1D shears or compressions produces a purely deforming flow pattern. Here we asked whether both the vertical and horizontal components in such a stimulus contribute to perceived slant. Using a matching technique we found that for surfaces inclined about a vertical axis, this was indeed the case and that horizontal and vertical compression gradients contributed roughly equally to perceived slant. Similarly, for surfaces inclined about a horizontal axis, both vertical and horizontal shearing gradients contributed to the perceived slant, though here the horizontal gradient was given less weight than the vertical. We conclude that under appropriate conditions, the human visual system combines orthogonal speed gradients prior to the computation of slant from retinal flow.

Humans↗
PubMed1996

On the relationship between deformation and perceived surface slant.

A compelling impression of surface slant is produced by random dot displays depicting deformation and translation alone. A simple model of slant estimation based upon deformation is shown to capture quantitatively both the perceived slant in this situation and the distortion in perceived slant produced when constant deformation is added to random dot displays depicting moving slanted surfaces. The results confirm that deformation provides a simple account of perceived slant.

Humans↗
PubMed1996

The pH of multi-purpose soft contact lens solutions.

Contact lens patient discomfort has been linked to the pH of lens care solutions differing from that of tears. To determine if this is a potential problem with multi-purpose soft contact lens solutions, we used a Fisher Scientific Accumet 950 pH/ion meter (accuracy +/- 0.05 pH units) to measure the pH of 3 multi-purpose solutions-Alcon's Opti-One, Allergan's Complete, and Bausch & Lomb's ReNu. The resulting pH values were compared to the threshold for ocular awareness, which is outside the zone of 6.6 to 7.8, and the pH value of tears of 7.45. Each solution was dispensed and measured daily over a 23- to 36-day period using 15-ml increments to simulate the amount used on a daily basis. The average pH of solutions tested were 7.18 +/- 0.02 for ReNu, 6.97 +/- 0.02 for Opti-One, and 7.55 +/- 0.02 for Complete. The highest and lowest pH values of all three multi-purpose solutions were found to be within the zone of ocular comfort and remained within a narrow value range throughout the testing period. Therefore, pH-induced discomfort is unlikely to occur when using these solutions on a daily basis. Nonetheless, practitioners should select lens care products carefully to ensure that the prescribed regimen meets the patient's needs.

Contact Lens Solutions↗
PubMed1996

Fitting characteristics of 1-day and 14-day Acuvue disposable contact lenses.

The fitting characteristics of 1-day Acuvue disposable soft contact lenses (SCLs) [base curve (BC) 9.0 mm, diameter 14.2 mm] and 14-day Acuvue disposable SCLa (BC 8.8 mm, diameter 14.0 mm) were evaluated and compared with respect to lens centration and post-blink movement in primary gaze and in upgaze. In this double-blind study 25 successful daily wearers of either the 1-day lens or the 14-day lens with the same parameters were randomly fit with three 1-day lenses and three 14-day lenses for a total of 6 lenses per eye. The lene fit was evaluated 5 min after insertion. Lens centration was assessed by measuring temporal, nasal, superior and inferior limbal coverage, and then comparing the net horizontal centration (temporal minus nasal coverage) and the net vertical centration (superior minus inferior coverage) of the 1-day and 14-day lenses. There was no significant difference between the two lenses in terms of temporal, superior, and inferior limbal coverage (p > 0.05). However, the 1-day lens showed statistically more nasal coverage (p < 0.05). No statistically significant difference in movement or in horizontal and vertical differences in centration were found (p > 0.05). Although our findings indicate a subtle statistical difference in fitting characteristics, clinically the two lenses should provide similar fits.

Adult↗
PubMed1996

Survival of contaminating bacteria in over-the-counter artificial tears.

BACKGROUND: The use of OTC artificial tears is becoming increasingly widespread. Unintentional contamination of artificial tear products potentiates a risk of developing bacterial keratitis or exacerbating an existing eye infection. Presently, no published study has investigated recovery from bacterial contamination of artificial tear products. METHODS: Four different over-the-counter (OTC) artificial tear products were contaminated with two types of bacteria. Staphylococcus aureus and pseudomonas aeruginosa were analyzed for the survivability of the microorganisms at various times following contamination. RESULTS: In this cross-sectional study, it was found that all the preserved brands showed a significant recovery rate from contamination compared to the preservative-free brand. After 9 hours, the preservative-free brand did not completely regain sterility after contamination with either bacteria. CONCLUSIONS: This study indicates that preserved artificial tears recover from bacterial contamination at a significantly faster rate than preservative-free products. It is likely that the recovery from bacterial contamination is not solely attributed to the preservative, but that other variables may contribute.

Colony Count, Microbial↗