Enablers and barriers to implementing obesity assessments in clinical practice: a rapid mixed-methods systematic review.

OBJECTIVES: This systematic review aims to improve our knowledge of enablers and barriers to implementing obesity-related anthropometric assessments in clinical practice. DESIGN: A mixed-methods systematic review. DATA SOURCES: Medline, Embase and CINAHL to November 2021. ELIGIBILITY CRITERIA: Quantitative studies that reported patient factors associated with obesity assessments in clinical practice (general practice or primary care); and qualitative studies that reported views of healthcare professionals about enablers and barriers to their implementation. DATA EXTRACTION AND SYNTHESIS: We used random-effects meta-analysis to pool ratios for categorical predictors reported in ≥3 studies expressed as pooled risk ratio (RR) with 95% CI, applied inverse variance weights, and investigated statistical heterogeneity (I2), publication bias (Egger's test), and sensitivity analyses. We used reflexive thematic analysis for qualitative data and applied a convergent integrated approach to synthesis. RESULTS: We reviewed 22 quantitative (observational) and 3 qualitative studies published between 2004 and 2020. All had ≥50% of the quality items for risk of bias assessments. Obesity assessment in clinical practice was positively associated with patient factors: female sex (RR 1.28, 95% CI 1.10 to 1.50, I2 99.8%, mostly UK/USA), socioeconomic deprivation (RR 1.21, 95% CI 1.18 to 1.24, I2 73.9%, UK studies), non-white race/ethnicity (RR 1.27, 95% CI 1.03 to 1.57, I2 99.6%) and comorbidities (RR 2.11, 95% CI 1.60 to 2.79, I2 99.6%, consistent across most countries). Obesity assessment was also most common in the heaviest body mass index group (RR 1.55, 95% CI 0.99 to 2.45, I2 99.6%). Views of healthcare professionals were positive about obesity assessments when linked to patient health (convergent with meta-analysis for comorbidities) and if part of routine practice, but negative about their role, training, time, resources and incentives in the healthcare system. CONCLUSIONS: Our evidence synthesis revealed several important enablers and barriers to obesity assessments that should inform healthcare professionals and relevant stakeholders to encourage adherence to clinical practice guideline recommendations.

Development and internal validation of the Edmonton Obesity Staging System-2 Risk screening Tool (EOSS-2 Risk Tool) for weight-related health complications: a case-control study in a representative sample of Australian adults with overweight and obesity.

OBJECTIVE: Excess weight and related health complications remain under diagnosed and poorly treated in general practice. We aimed to develop and validate a brief screening tool for determining the presence of unknown clinically significant weight-related health complications for potential application in general practice. DESIGN: We considered 14 self-reported candidate predictors of clinically significant weight-related health complications according to the Edmonton Obesity Staging System (EOSS score of ≥2) and developed models using multivariate logistic regression across training and test data sets. The final model was chosen based on the area under the receiver operating characteristic curve and the Hosmer-Lemeshow statistic; and validated using sensitivity, specificity and positive predictive value. SETTING AND PARTICIPANTS: We analysed cross-sectional data from the Australian Health Survey 2011-2013 sample aged between 18 and 65 years (n=7518) with at least overweight and obesity. RESULTS: An EOSS≥2 classification was present in 78% of the sample. Of 14 candidate risk factors, 6 (family history of diabetes, hypertension, high sugar in blood/urine, high cholesterol and self-reported bodily pain and disability) were automatically included based on definitional or obvious correlational criteria. Three variables were retained in the final multivariate model (age, self-assessed health and history of depression/anxiety). The EOSS-2 Risk Tool (index test) classified 89% of those at 'extremely high risk' (≥25 points), 67% of those at 'very high risk' (7-24 points) and 42% of those at 'high risk' (<7 points) of meeting diagnostic criteria for EOSS≥2 (reference). CONCLUSION: The EOSS-2 Risk Tool is a simple, safe and accurate screening tool for diagnostic criteria for clinically significant weight-related complications for potential application in general practice. Research to determine the feasibility and applicability of the EOSS-2 Risk Tool for improving weight management approaches in general practice is warranted.

Clinical Obesity Services in Public Hospitals in Australia: a position statement based on expert consensus.

We aimed to describe the current state of specialist obesity services for adults with clinically severe obesity in public hospitals in Australia, and to analyse the gap in resources based on expert consensus. We conducted two surveys to collect information about current and required specialist obesity services and resources using open-ended questionnaires. Organizational level data were sought from clinician expert representatives of specialist obesity services across Australia in 2017. Fifteen of 16 representatives of current services in New South Wales (n = 8), Queensland (n = 1), Victoria (n = 2), South Australia (n = 3), and the Australian Capital Territory (n = 1) provided data. The composition of services varied substantially between hospitals, and patient access to services and effective treatments were limited by strict entry criteria (e.g. body mass index 40 kg/m2 or higher with specific complication/s), prolonged wait times, geographical location (major cities only) and out-of-pocket costs. Of these services, 47% had a multidisciplinary team (MDT), 53% had an exercise physiologist/physiotherapist, 53% had a bariatric surgeon and 33% had pharmacotherapy resources. Key gaps included staffing components of the MDT (psychologist, exercise physiologist/physiotherapist) and access to publicly funded weight loss pharmacotherapy and bariatric surgery. There was consensus on the need for significant improvements in staff, physical infrastructure, access to services, education/training in obesity medicine and targeted research funding. Based on the small number of existing, often under-resourced specialist obesity services that are located only in a few major cities, the vast majority of Australians with clinically severe obesity cannot access the specialist evidence based treatments needed.

Greener neighbourhoods, slimmer children? Evidence from 4423 participants aged 6 to 13 years in the Longitudinal Study of Australian children.

OBJECTIVES: There is a growing belief that green space (for example, parks) help prevent obesity. There is evidence of an inverse association between green space and childhood body mass index (BMI); however, the majority of these studies are cross-sectional. Longitudinal studies that track change in BMI across childhood in relation to levels of green space proximity would improve the quality of evidence available for decision making. METHODS: Objectively measured BMI was obtained every 2 years between 2006 and 2012 for 4423 participants initially aged 6-7 years in the Longitudinal Study of Australian Children (LSAC). The LSAC is a nationally representative study on a range of health and socio-demographic measures. Using Australian Bureau of Statistics mesh block data, which classify small scale land areas based on the main usage, each participant was assigned an objective measure of green space availability within their Statistical Area (level 2) of residence. Gender-stratified multilevel linear regression was used to estimate BMI growth curves across childhood in relation to green space availability. Family income, Australian Indigenous status, mothers' education and language spoken were used to adjust for socio-economic confounding. RESULTS: Age was found to be an effect modifier of associations between green space and BMI for boys (P=0.005) and girls (P=0.048). As children grew older, an inverse patterning of BMI by green space availability emerged. These findings held after adjustment for socio-economic circumstances for boys (P=0.009), though were less robust for girls after this adjustment (P=0.056). CONCLUSION: A beneficial effect of green space on BMI emerges as children grow older. However, there was little additional benefit after a modest amount of green space was met. Further research is needed to understand whether the drivers of this effect are from age-specific mechanisms, or whether the benefit of living in a greener neighbourhood is accumulated through childhood.

Neighborhood walkability, fear and risk of falling and response to walking promotion: The Easy Steps to Health 12-month randomized controlled trial.

In older adults the relationships between health, fall-related risk factors, perceived neighborhood walkability, walking behavior and intervention impacts are poorly understood. To determine whether: i) health and fall-related risk factors were associated with perceptions of neighborhood walkability; ii) perceived environmental attributes, and fall-related risk factors predicted change in walking behavior at 12 months; and iii) perceived environmental attributes and fall-related risk factors moderated the effect of a self-paced walking program on walking behavior. Randomized trial on walking and falls conducted between 2009 and 2012 involving 315 community-dwelling inactive adults ≥ 65 years living in Sydney, Australia. Measures were: mobility status, fall history, injurious fall and fear of falling (i.e., fall-related risk factors), health status, walking self-efficacy and 11 items from the neighborhood walkability scale and planned walking ≥ 150 min/week at 12 months. Participants with poorer mobility, fear of falling, and poor health perceived their surroundings as less walkable. Walking at 12 months was significantly greater in "less greenery" (AOR = 3.3, 95% CI: 1.11-9.98) and "high traffic" (AOR = 1.98, 95% CI: 1.00-3.91) neighborhoods. The intervention had greater effects in neighborhoods perceived to have poorer pedestrian infrastructure (p for interaction = 0.036). Low perceived walkability was shaped by health status and did not appear to be a barrier to walking behavior. There appears to be a greater impact of, and thus, need for, interventions to encourage walking in environments perceived not to have supportive walking infrastructure. Future studies on built environments and walking should gather information on fall-related risk factors to better understand how these characteristics interact.

Learning chronobiology by improving Wikipedia.

Although chronobiology is of growing interest to scientists, physicians, and the general public, access to recent discoveries and historical perspectives is limited. Wikipedia is an online, user-written encyclopedia that could enhance public access to current understanding in chronobiology. However, Wikipedia is lacking important information and is not universally trusted. Here, 46 students in a university course edited Wikipedia to enhance public access to important discoveries in chronobiology. Students worked for an average of 9 h each to evaluate the primary literature and available Wikipedia information, nominated sites for editing, and, after voting, edited the 15 Wikipedia pages they determined to be highest priorities. This assignment (http://www.nslc.wustl.edu/courses/Bio4030/wikipedia_project.html) was easy to implement, required relatively short time commitments from the professor and students, and had measurable impacts on Wikipedia and the students. Students created 3 new Wikipedia sites, edited 12 additional sites, and cited 347 peer-reviewed articles. The targeted sites all became top hits in online search engines. Because their writing was and will be read by a worldwide audience, students found the experience rewarding. Students reported significantly increased comfort with reading, critiquing, and summarizing primary literature and benefited from seeing their work edited by other scientists and editors of Wikipedia. We conclude that, in a short project, students can assist in making chronobiology widely accessible and learn from the editorial process.

Healthcare resource use and medical costs for the management of oesophageal cancer.

BACKGROUND: This study examined the interaction between natural history, current practice patterns in diagnosis, monitoring and treatment of oesophageal cancer, and associated health resource utilization and costs. METHODS: A cost analysis of a prospective population-based cohort of 1100 patients with a primary diagnosis of oesophageal cancer was performed using chart review from the Australian Cancer Study Clinical Follow-Up Study. The analysis enabled estimation of healthcare resources and associated costs in 2009 euros by stage of disease and treatment pathway. RESULTS: Most patients (88·5 per cent) presented with stage II, III or IV cancer; 61·1 per cent (672 of 1100) were treated surgically. Overall mean costs were €37,195 (median €29,114) for patients undergoing surgery and €17,281 (median €13,066) for those treated without surgery. Surgery contributed 66·4 per cent of the total costs (mean €24,697 per patient) in the surgical group. In the non-surgical group, use of chemotherapy was more prevalent (81·9 per cent of patients) and contributed 61·1 per cent of the total costs. Other important cost determinants were gastro-oesophageal junction tumours, treatment location and tumour stage. Mean costs of those monitored for Barrett's oesophagus (7·3 per cent of patients) were lower, although about one-third still presented with advanced-stage cancer. CONCLUSION: Overall costs for managing oesophageal cancer were high and dominated by surgery costs in patients treated surgically and by chemotherapy costs in patients treated without surgery. Radiotherapy, treatment location and cancer subtype were also important. Monitoring for Barrett's oesophagus and earlier-stage detection were associated with lower management costs, but the potential net benefit from surveillance strategies needs further investigation.

Source of level dependent minima in rabbit distortion product otoacoustic emissions.

Sharp level dependent minima (commonly called nulls or notches) in the distortion product otoacoustic emissions (DPOAEs) have been postulated to be due to two different mechanisms. It is shown here that the level dependent nulls in rabbit 2f(1)-f(2) DPOAEs carry the signature of the mixing of a third order nonlinear term with a fifth order nonlinear term. This suggests that the minima are not due to the mixing of signals from two different physical sites of origin, but rather are due to the nature of the nonlinearity itself. Model simulations show that null production is indifferent to several properties of nonlinear input/output functions.

Mechanism for bandpass frequency characteristic in distortion product otoacoustic emission generation.

It is commonly observed that the levels of the 2f1-f2 and the other mf1-nf2 (m = n + 1 = integer) distortion product otoacoustic emissions (DPOAEs) initially increase in level for fixed f2 as fl -->f2, starting at f1

Long-term survival of surgically treated hip fracture in an Australian regional hospital.

This study was undertaken to identify factors influencing outcome in elderly patients operated for hip fracture. In particular, this study examined factors related to mortality at least 30 months post-fracture. Hospital records and death registrations were analysed for 463 patients aged 60 or more years treated for hip fracture at a Queensland regional hospital between 1997 and 2001. The overall mortality for surgically treated patients was 13.7% at 100 days and 24.9% at one year Patient factors including age, gender, health status and place of residence were the predominant influences on mortality. Non-patient and process factors including delay to surgery, type of operation and type of anaesthetic had minimal impact on mortality. No major determinants of length of hospital stay were identified. Patient health status was the main determinant for surgical delay. Our results confirm the persistently high mortality in this group of patients, and suggest that the main determinants of outcome are patient- rather than process-related.

Planning research in rural and remote areas.

INTRODUCTION: In order to set a regional research agenda, an interactive research workshop was planned by the joint University of Queensland and University of Southern Quennsland Centre for Rural and Remote Area Health (CRRAH), in which researchers and regional organisations would meet together to discuss and prioritise local research needs, then formulate constructive ideas and activities. METHODS: Selection of Participants: Organisations representing all key consumer, academic and health professionals within the Toowoomba, Queensland, Australia region were sent a letter inviting them to attend and to send at least one representative, resulting in a total of 75 workshop participants from 45 organisations representing 20 separate entities. The Design of the Workshop: The workshop was planned as an interactive research workshop, with a preliminary brainstorming to identify and prioritise topics, followed by facilitated small group discussions, and finally presentations to the reassembled total group. RESULTS: Forty three topics were put forward by participants during the plenary session, in which the following 12 major themes were evident: (1) health professional development and support; (2) mechanisms for identifying regional/local needs; (3) mental health; (4) health and interaction with the environment; (5) management of common conditions of which little is known; (6) post acute/aged care; (7) evidence based practice; (8) health workforce including volunteers; (9) indigenous health; (10) access to health service delivery; (11) economic impact of new programs; and (12) outcomes impact of research partnerships. Five subject areas from four of these themes were chosen for further small group discussion. A summary of the views, ideas and conclusions of each group, which were presented to a plenary session of reassembled participants over a 10-15 minute period by each group facilitators, are discussed below. Following each presentation, a 5-10 minute question session was provided after each topic. CONCLUSION: A workshop, enabling rural and remote organisations and regional researchers to meet and identify local research needs attracted strong local support. Although the final benefits of the workshop remain to be determined, a number of new collaborative research avenues are now being actively explored within the region, by a number of the participants.

General practitioners' perceptions of after hours primary medical care services: a Toowoomba, Queensland, Australia study.

INTRODUCTION: This article reports on a project, undertaken in 2002 in the regional city of Toowoomba, Queensland, Australia, that investigated the viability of establishing an after-hours primary medical care (AHPMC) service. OBJECTIVES: To ascertain GPs' perceptions of the adequacy of AHPMC services in Toowoomba. DESIGN: Thirty GPs were randomly selected to participate in face-to-face interviews using a semi-structured interview tool. SETTING: Toowoomba, Australia is the largest inland non-capital city in Australia. It is located approximately 130 km west of Brisbane, the State capital city and is a referral centre for patients from the rural and remote communities of south-west Queensland. PARTICIPANTS: 15 male and 15 female GPs. RESULTS: While the majority of participants believed the current provision of AHPMC in Toowoomba was adequate, they stated that the provision of AHPMC services was onerous and, given a choice, they would prefer to refer all patients seeking care between 2200 and 0800 hours to an Emergency Department (ED). Similar to GPs who work in rural and remote areas of Australia, they believed that AHPMC work was poorly remunerated, had an adverse effect on their lifestyle and could endanger their personal and their patient's safety. CONCLUSION: The findings of this study confirm previous studies into the perceptions of GPs to the provision of AHPMC in a regional city. Additionally, while the GPs in Toowoomba have the options of referring after-hours patients to an ED and being part of a large GP after hours cooperative, their opinions on after-hours work did not differ significantly from those expressed by GPs working in rural and remote areas of Australia. The GPs in this study, given the option, would prefer not to undertake an AHMPC service provision between 2200 and 0800 and many had chosen not to do so, instead directing their patients at this time to one of the two EDs located in Toowoomba.

Effects of light adaptation on contrast processing in bipolar cells in the retina.

Effects of light adaptation on contrast processing in the outer retina were investigated over nearly four decades of background illumination by analyzing the intracellular responses of 111 bipolar cells, 66 horizontal cells, and 22 cone photoreceptors in the superfused eyecup of the tiger salamander (Ambystoma tigrinum). Light adaptation had striking and similar effects on the average contrast responses of the hyperpolarizing (Bh) and depolarizing (Bd) classes of bipolar cells: Over the lower two decades of background illumination, the contrast gain increased 7-fold to reach values as high as 20-30, the dynamic range and the half-maximum contrast decreased by about 60%, the total voltage range increased some 40%, and contrast dominance changed from highly positive to more balanced. At higher levels of background, most aspects of the contrast response stabilized and Weber's Law then held closely. In this background range, the contrast gain of bipolar cells was amplified some 20X relative to that of cones whereas the corresponding amplification in horizontal cells was about 6X. Differences in the growth of contrast gain with the intensity of the background illumination for cones versus bipolar cells suggest that there are at least two adaptation-dependent mechanisms regulating contrast gain. One is evident in the cone photoresponse such that an approximately linear relation holds between the steady-state hyperpolarization and contrast gain. The other arises between the voltage responses of the cones and bipolar cells. It could be presynaptic (modulation of cone transmitter release by horizontal cell feedback or other mechanisms) and/or postsynaptic, that is, intrinsic to bipolar cells. Contrast gain grew with the background intensity by a larger factor in horizontal than in bipolar cells. This provides a basis for the widely held view that light adaptation increases the strength of surround antagonism in bipolar cells. On average, the effects of light adaptation and most quantitative indices of contrast processing were remarkably similar for Bd and Bh cells, implying that both classes of bipolar cells, despite possible differences in underlying mechanisms, are about equally capable of encoding all primary aspects of contrast at all levels of light adaptation.

Nonlinear interactions that could explain distortion product interference response areas.

Suppression and/or enhancement of third- and fifth-order distortion products by a third tone that can have a frequency more than an octave above and a level more than 40 dB below the primary tones have recently been measured by Martin et al. [Hear. Res. 136, 105-123 (1999)]. Contours of iso-suppression and iso-enhancement that are plotted as a function of third-tone frequency and level are called interference response areas. After ruling out order aliasing, two possible mechanisms for this effect have been developed, a harmonic mechanism and a catalyst mechanism. The harmonic mechanism produces distortion products by mixing a harmonic of one of the primary tones with the other primary tone. The catalyst mechanism produces distortion products by mixing one or more intermediate distortion products that are produced by the third tone with one or more of the input tones. The harmonic mechanism does not need a third tone and the catalyst mechanism does. Because the basilar membrane frequency response is predicted to affect each of these mechanisms differently, it is concluded that the catalyst mechanism will be dominant in the high-frequency regions of the cochlea and the harmonic mechanism will have significant strength in the low-frequency regions of the cochlea. The mechanisms are dependent on the existence of both even- and odd-order distortion, and significant even- and odd-order distortion have been measured in the experimental animals. Furthermore, the nonlinear part of the cochlear mechanical response must be well into saturation when input tones are 50 or more dB SPL.

Contrast rectification and distributed encoding By ON-OFF amacrine cells in the retina.

The encoding of luminance contrast by ON-OFF amacrine cells was investigated by intracellular recording in the retina of the tiger salamander (Ambystoma tigrinum). Contrast flashes of positive and negative polarity were applied at the center of the receptive field while the entire retina was light adapted to a background field of 20 cd/m(2). Many amacrine cells showed remarkably high contrast gain: Up to 20-35% of the maximum response was evoked by a contrast step of only 1%. In the larger signal domain, C50, the contrast required to evoke a response 50% of the maximum, was often remarkably low: 24 of 25 cells had a C50 value of < or =10% for at least one contrast polarity. Across cells and contrast polarity, the dynamic ranges varied from extremely narrow to broad, thereby blanketing the range of reflectances associated with objects in natural environments. Although some cells resembled "contrast rectifiers," by showing similar responses to contrasts of opposite polarity, many did not. Thus for contrast gain and C50, individual cells could show a strong preference for either negative or positive contrast. In the time domain, the preference was strong and unidirectional: for equal contrast steps, the latency of the response to negative contrast was 20-45 ms shorter than that for positive contrast. The present results, when compared with those for bipolar cells, suggest that, on average, amacrine cells add some amplification, particularly for negative contrast, to the high contrast gain already established by bipolar cells. In the time domain, our data reveal a striking transformation from bipolar to amacrine cells in favor of negative contrast. These and further observations have implications for the input and output of amacrine cell circuits. The present finding of substantial differences between cells reveals a potential substrate for distributed encoding of luminance contrast within the ON-OFF amacrine cell population.

Preferential pulmonary retention of (S)-albuterol after inhalation of racemic albuterol.

The (R)-enantiomer of racemic albuterol produces bronchodilation, whereas the (S)-enantiomer may increase airway reactivity. After oral or intravenous administration of racemic albuterol, the (R)- enantiomer is metabolized several times faster than the (S)-enantiomer; however, enantiomer disposition after inhaling racemic albuterol with a metered-dose inhaler (MDI) is not known. Accordingly, 10 healthy subjects inhaled racemic albuterol with a MDI alone and with a MDI and holding chamber. We measured plasma levels of unchanged (R)- and (S)-albuterol before and up to 4 h after inhalation of racemic albuterol, and determined the unchanged R/S ratio in urine before and at 0.5, 4, 8, and 24 h later. The disposition of albuterol's enantiomers with a MDI and holding chamber was similar to that with a MDI alone. The area under the curve (AUC) of the plasma levels over time was significantly lower for the (S)- than for the (R)-enantiomer-395.5 +/- 141.0 (SE) versus 882.7 +/- 126.4 ng. ml(-)(1). min (p < 0.05)-indicating preferential retention of (S)-albuterol in the lung. The R/S ratio in urine at 0. 5 h after albuterol was > 1, reflecting the higher plasma level of the (R)-enantiomer. In conclusion, preferential retention of the (S)- compared with the (R)-enantiomer in the lung could lead to accumulation of the (S)-enantiomer after long-term use of racemic albuterol.

Reconciling in vitro and in vivo measurements of aerosol delivery from a metered-dose inhaler during mechanical ventilation and defining efficiency-enhancing factors.

We attempted to resolve the discrepancies in reported data on aerosol deposition from a chlorofluorocarbon (CFC)-propelled metered-dose inhaler (MDI) during mechanical ventilation, obtained by in vivo and in vitro methodologies. Albuterol delivery to the lower respiratory tract was decreased in a humidified versus a dry circuit (16.2 versus 30.4%, respectively; p < 0.01). In 10 mechanically ventilated patients, 4.8% of the nominal dose was exhaled. When the exhaled aerosol was subtracted from the in vitro delivery of 16.2% achieved in a humidified ventilator circuit, the resulting value (16.2 - 4.8 = 11.4%) was similar to in vivo estimates of aerosol deposition. Having reconciled in vitro with in vivo findings, we then evaluated factors influencing aerosol delivery. A lower inspiratory flow rate (40 versus 80 L/min; p < 0.001), a longer duty cycle (0.50 versus 0.25; p < 0.04), and a shorter interval between successive MDI actuations (15 versus 60 s; p < 0.02) increased aerosol delivery, whereas use of a hydrofluoroalkane (HFA)-propelled MDI decreased aerosol delivery compared with the CFC-propelled MDI. A MDI and actuator combination other than that designed by the manufacturer altered aerosol particle size and decreased drug delivery. In conclusion, aerosol delivery in an in vitro model accurately reflects in vivo delivery, providing a means for investigating methods to improve the efficiency of aerosol therapy during mechanical ventilation.

Contrast enhancement and distributed encoding by bipolar cells in the retina.

Responses of bipolar cells, cone photoreceptors, and horizontal cells were recorded intracellularly in superfused eyecup preparations of the tiger salamander (Ambystoma tigrinum). Contrast flashes of positive and negative polarity were applied at the center of the receptive field while the entire retina was light adapted to a background field of 20 cd/m2. For small contrasts, many bipolar cells showed remarkably high contrast gain: up to 15-20% of the bipolar response was evoked by a contrast step of 1%. There was considerable variation from cell to cell but, on average, no striking differences in contrast gain were found between the depolarizing (Bd) and hyperpolarizing (Bh) bipolar cells. Quantitative comparisons of contrast/response measurements for cone photoreceptors and cone-driven bipolars suggest that the high contrast gain of bipolars is the consequence of a 5-10 x amplification of small signals across the cone-->bipolar synapse. Bipolar cells had a very restricted linear range of response and tended to saturate at stimulus levels that were within the linear range of the cone response. The contrast/response of horizontal cells was similar to that of cones and differed markedly from that of Bh cells. For steps of equal contrast, the latency of the Bh cells was approximately 20 ms shorter than that of the Bd cells regardless of the contrast magnitude. For both bipolar cells and cones, the effect of contrast polarity on latency seems largely due to the absolute value of the light step, delta L. In the large signal domain, properties of the contrast responses of bipolar cells varied appreciably, both within and between the Bd and Bh classes. Cells of either class could be positive- or negative-contrast dominant. These and additional results show that in the light-adapted retina, the bipolar population is functionally diverse and has the potential to provide a rich substrate for distributed encoding of visual images.