A comparison of survey method efficiencies for estimating densities of zebra mussels (Dreissena polymorpha).

Abundance surveys are commonly used to estimate plant or animal densities and frequently require estimating detection probabilities to account for imperfect detection. The estimation of detection probabilities requires additional measurements that take time, potentially reducing the efficiency of the survey when applied to high-density populations. We conducted quadrat, removal, and distance surveys of zebra mussels (Dreissena polymorpha) in three central Minnesota lakes and determined how much survey effort would be required to achieve a pre-specified level of precision for each abundance estimator, allowing us to directly compare survey design efficiencies across a range of conditions. We found that the required sampling effort needed to achieve our precision goal depended on both the survey design and population density. At low densities, survey designs that could cover large areas but with lower detection probabilities, such as distance surveys, were more efficient (i.e., required less sampling effort to achieve the same level of precision). However, at high densities, quadrat surveys, which tend to cover less area but with high detection rates, were more efficient. These results demonstrate that the best survey design is likely to be context-specific, requiring some prior knowledge of the underlying population density and the cost/time needed to collect additional information for estimating detection probabilities.

Resampling-based methods for biologists.

Ecological data often violate common assumptions of traditional parametric statistics (e.g., that residuals are Normally distributed, have constant variance, and cases are independent). Modern statistical methods are well equipped to handle these complications, but they can be challenging for non-statisticians to understand and implement. Rather than default to increasingly complex statistical methods, resampling-based methods can sometimes provide an alternative method for performing statistical inference, while also facilitating a deeper understanding of foundational concepts in frequentist statistics (e.g., sampling distributions, confidence intervals, p-values). Using simple examples and case studies, we demonstrate how resampling-based methods can help elucidate core statistical concepts and provide alternative methods for tackling challenging problems across a broad range of ecological applications.

Radar quantifies migrant concentration and Dawn reorientation at a Great Lakes shoreline.

BACKGROUND: Millions of flying migrants encounter the Great Lakes and other large water bodies on long-distance flights each spring and fall, but quantitative data regarding how they traverse these obstacles are limited. Shorelines are known areas of migrant concentration due to the ecological barrier effect, but details on the magnitude of this concentration and the flight behaviors causing it are largely unknown and difficult to quantify. Mobile avian radar can provide a unique view of how birds and bats move across landscapes by tracking thousands of individual migrants moving through a sample volume that extends multiple kilometers in radius. RESULTS: During the spring of 2014 we used two avian radar units to compare migration patterns at shoreline (1.5 km from the shore) and inland (20 km from the shore) sites along the eastern shoreline of Lake Michigan in the north-central US. We found shoreline activity to be 27% greater than inland activity over all time periods, and 132% greater during the hour surrounding dawn. An analysis of flight directions found that migrants flew to the north and northwest during dusk and night, with many heading out over the lake, but shifted direction towards the east at dawn, as those flying over water reoriented towards land. This shift in direction, which was most intense at the shoreline, may contribute to the higher concentrations of migrants observed at shorelines in this study and others. CONCLUSIONS: These findings help confirm and quantify the phenomenon of nocturnal migrant reorientation at dawn, and also stress the functional importance of coastal regions for aerial migrants. The high use of coasts by migrants highlights the importance of conserving shoreline stopover habitat, which often competes with anthropogenic uses. We suggest using a high degree of caution when assessing potential impacts from development in these sensitive environments, and encourage protection of these high-use areas.

Predictors of Current and Longer-Term Patterns of Abundance of American Pikas (Ochotona princeps) across a Leading-Edge Protected Area.

American pikas (Ochotona princeps) have been heralded as indicators of montane-mammal response to contemporary climate change. Pikas no longer occupy the driest and lowest-elevation sites in numerous parts of their geographic range. Conversely, pikas have exhibited higher rates of occupancy and persistence in Rocky Mountain and Sierra Nevada montane 'mainlands'. Research and monitoring efforts on pikas across the western USA have collectively shown the nuance and complexity with which climate will often act on species in diverse topographic and climatic contexts. However, to date no studies have investigated habitat, distribution, and abundance of pikas across hundreds of sites within a remote wilderness area. Additionally, relatively little is known about whether climate acts most strongly on pikas through direct or indirect (e.g., vegetation-mediated) mechanisms. During 2007-2009, we collectively hiked >16,000 km throughout the 410,077-ha Glacier National Park, Montana, USA, in an effort to identify topographic, microrefugial, and vegetative characteristics predictive of pika abundance. We identified 411 apparently pika-suitable habitat patches with binoculars (in situ), and surveyed 314 of them for pika signs. Ranking of alternative logistic-regression models based on AICc scores revealed that short-term pika abundances were positively associated with intermediate elevations, greater cover of mosses, and taller forbs, and decreased each year, for a total decline of 68% during the three-year study; whereas longer-term abundances were associated only with static variables (longitude, elevation, gradient) and were lower on north-facing slopes. Earlier Julian date and time of day of the survey (i.e., midday vs. not) were associated with lower observed pika abundance. We recommend that wildlife monitoring account for this seasonal and diel variation when surveying pikas. Broad-scale information on status and abundance determinants of montane mammals, especially for remote protected areas, is crucial for land and wildlife-resource managers trying to anticipate mammalian responses to climate change.

Prioritizing Avian Species for Their Risk of Population-Level Consequences from Wind Energy Development.

Recent growth in the wind energy industry has increased concerns about its impacts on wildlife populations. Direct impacts of wind energy include bird and bat collisions with turbines whereas indirect impacts include changes in wildlife habitat and behavior. Although many species may withstand these effects, species that are long-lived with low rates of reproduction, have specialized habitat preferences, or are attracted to turbines may be more prone to declines in population abundance. We developed a prioritization system to identify the avian species most likely to experience population declines from wind facilities based on their current conservation status and their expected risk from turbines. We developed 3 metrics of turbine risk that incorporate data on collision fatalities at wind facilities, population size, life history, species' distributions relative to turbine locations, number of suitable habitat types, and species' conservation status. We calculated at least 1 measure of turbine risk for 428 avian species that breed in the United States. We then simulated 100,000 random sets of cutoff criteria (i.e., the metric values used to assign species to different priority categories) for each turbine risk metric and for conservation status. For each set of criteria, we assigned each species a priority score and calculated the average priority score across all sets of criteria. Our prioritization system highlights both species that could potentially experience population decline caused by wind energy and species at low risk of population decline. For instance, several birds of prey, such as the long-eared owl, ferruginous hawk, Swainson's hawk, and golden eagle, were at relatively high risk of population decline across a wide variety of cutoff values, whereas many passerines were at relatively low risk of decline. This prioritization system is a first step that will help researchers, conservationists, managers, and industry target future study and management activity.

Environmental variability and population dynamics: do European and North American ducks play by the same rules?

Density dependence, population regulation, and variability in population size are fundamental population processes, the manifestation and interrelationships of which are affected by environmental variability. However, there are surprisingly few empirical studies that distinguish the effect of environmental variability from the effects of population processes. We took advantage of a unique system, in which populations of the same duck species or close ecological counterparts live in highly variable (north American prairies) and in stable (north European lakes) environments, to distinguish the relative contributions of environmental variability (measured as between-year fluctuations in wetland numbers) and intraspecific interactions (density dependence) in driving population dynamics. We tested whether populations living in stable environments (in northern Europe) were more strongly governed by density dependence than populations living in variable environments (in North America). We also addressed whether relative population dynamical responses to environmental variability versus density corresponded to differences in life history strategies between dabbling (relatively "fast species" and governed by environmental variability) and diving (relatively "slow species" and governed by density) ducks. As expected, the variance component of population fluctuations caused by changes in breeding environments was greater in North America than in Europe. Contrary to expectations, however, populations in more stable environments were not less variable nor clearly more strongly density dependent than populations in highly variable environments. Also, contrary to expectations, populations of diving ducks were neither more stable nor stronger density dependent than populations of dabbling ducks, and the effect of environmental variability on population dynamics was greater in diving than in dabbling ducks. In general, irrespective of continent and species life history, environmental variability contributed more to variation in species abundances than did density. Our findings underscore the need for more studies on populations of the same species in different environments to verify the generality of current explanations about population dynamics and its association with species life history.

Patterns in diurnal airspace use by migratory landbirds along an ecological barrier.

Migratory bird populations and survival are affected by conditions experienced during migration. While many studies and conservation and management efforts focus on terrestrial stoppage and staging areas, the aerial environment through which migrants move also is subjected to anthropogenic impacts with potential consequences to migratory movement and survival. During autumn migration, the northern coastline of Lake Superior acts as an ecological barrier for many landbirds migrating out of the boreal forests of North America. From 24 observation points, we assessed the diurnal movements of birds throughout autumn migration, 2008-2010, within a 210 × 10 km coastal region along the northern coast of Lake Superior. Several raptor species showed patterns in airspace associated with topographic features such as proximity to the coastline and presence of ridgelines. Funneling movement, commonly used to describe the concentration of raptors along a migratory diversion line that either prevents or enhances migration progress, occurred only for Bald and Golden Eagles. This suggests a "leaky" migration funnel for most migratory raptors (e.g., migrating birds exiting the purported migration corridor). Passerines migrating during the late season showed more spatial and temporal structure in airspace distribution than raptors did, including funneling and an association with airspace near the coast. We conclude that (1) the diurnal use of airspace by many migratory landbirds is patterned in space and time, (2) autumn count sites situated along ecological barriers substantially underestimate the number of raptors due to "leakage" out of these concentration areas, and (3) the magnitude and structure of diurnal passerine movements in airspace have been overlooked. The heavy and structured use of airspace by migratory landbirds, especially the airspace associated with anthropogenic development (e.g., buildings, towers, turbines) necessitates a shift in focus to airspace management and conservation attention for these animals.

Population dynamics of Amur tigers (Panthera tigris altaica) in Sikhote-Alin Biosphere Zapovednik: 1966-2012.

In 2010, the world's tiger (Panthera tigris) range countries agreed to the goal of doubling tiger numbers over 12 years, but whether such an increase is biologically feasible has not been assessed. Long-term monitoring of tigers in Sikhote-Alin Biosphere Zapovednik (SABZ), Russia provided an opportunity to determine growth rates of a recovering population. A 41-year growth phase was followed by a rapid decline in tiger numbers. Annual growth rates during the growth phase averaged 4.6%, beginning near 10% in the earliest years but quickly dropping below 5%. Sex ratio (females per male) mirrored growth rates, declining as population size increased. The rapid decline from 2009 to 2012 appeared to be tied to multiple factors, including poaching, severe winters and disease. Reproductive indicators of this population are similar to those of Bengal tiger populations, suggesting that growth rates may be similar. These results suggest that, first, tiger populations likely in general grow slowly: 3-5% yearly increases are realistic and larger growth rates are likely only when populations are highly depressed, mortality rates are low and prey populations are high relative to numbers of adult females. Second, while more research is needed, it should not be assumed that tiger populations with high prey densities will necessarily grow more quickly than populations with low prey densities. Third, while growth is slow, decline can be rapid. Fourth, because declines can happen so quickly, there is a constant need to monitor populations and be ready to respond with appropriate and timely conservation interventions if tiger populations are to remain secure. Finally, an average annual growth rate across all tiger populations of 6%, required to reach the Global Tiger Initiative's goal of doubling tiger numbers in 12 years, is a noble but unlikely scenario.

Behavior of bats at wind turbines.

Wind turbines are causing unprecedented numbers of bat fatalities. Many fatalities involve tree-roosting bats, but reasons for this higher susceptibility remain unknown. To better understand behaviors associated with risk, we monitored bats at three experimentally manipulated wind turbines in Indiana, United States, from July 29 to October 1, 2012, using thermal cameras and other methods. We observed bats on 993 occasions and saw many behaviors, including close approaches, flight loops and dives, hovering, and chases. Most bats altered course toward turbines during observation. Based on these new observations, we tested the hypotheses that wind speed and blade rotation speed influenced the way that bats interacted with turbines. We found that bats were detected more frequently at lower wind speeds and typically approached turbines on the leeward (downwind) side. The proportion of leeward approaches increased with wind speed when blades were prevented from turning, yet decreased when blades could turn. Bats were observed more frequently at turbines on moonlit nights. Taken together, these observations suggest that bats may orient toward turbines by sensing air currents and using vision, and that air turbulence caused by fast-moving blades creates conditions that are less attractive to bats passing in close proximity. Tree bats may respond to streams of air flowing downwind from trees at night while searching for roosts, conspecifics, and nocturnal insect prey that could accumulate in such flows. Fatalities of tree bats at turbines may be the consequence of behaviors that evolved to provide selective advantages when elicited by tall trees, but are now maladaptive when elicited by wind turbines.

A comprehensive analysis of small-passerine fatalities from collision with turbines at wind energy facilities.

Small passerines, sometimes referred to as perching birds or songbirds, are the most abundant bird group in the United States (US) and Canada, and the most common among bird fatalities caused by collision with turbines at wind energy facilities. We used data compiled from 116 studies conducted in the US and Canada to estimate the annual rate of small-bird fatalities. It was necessary for us to calculate estimates of small-bird fatality rates from reported all-bird rates for 30% of studies. The remaining 70% of studies provided data on small-bird fatalities. We then adjusted estimates to account for detection bias and loss of carcasses from scavenging. These studies represented about 15% of current operating capacity (megawatts [MW]) for all wind energy facilities in the US and Canada and provided information on 4,975 bird fatalities, of which we estimated 62.5% were small passerines comprising 156 species. For all wind energy facilities currently in operation, we estimated that about 134,000 to 230,000 small-passerine fatalities from collision with wind turbines occur annually, or 2.10 to 3.35 small birds/MW of installed capacity. When adjusted for species composition, this indicates that about 368,000 fatalities for all bird species are caused annually by collisions with wind turbines. Other human-related sources of bird deaths, (e.g., communication towers, buildings [including windows]), and domestic cats) have been estimated to kill millions to billions of birds each year. Compared to continent-wide population estimates, the cumulative mortality rate per year by species was highest for black-throated blue warbler and tree swallow; 0.043% of the entire population of each species was estimated to annually suffer mortality from collisions with turbines. For the eighteen species with the next highest values, this estimate ranged from 0.008% to 0.038%, much lower than rates attributed to collisions with communication towers (1.2% to 9.0% for top twenty species).

Habitat selection and ranges of tolerance: how do species differ beyond critical thresholds?

Sensitivity to habitat fragmentation often has been examined in terms of thresholds in landscape composition at which a species is likely to occur. Observed thresholds often have been low or absent, however, leaving much unexplained about habitat selection beyond initial thresholds of occurrence, even for species with strong habitat preferences. We examined responses to varying amounts of tree cover, a widely influential measure of habitat loss, for 40 woodland bird species in a mixed woodland/grassland landscape in eastern North Dakota, USA. We used LOESS smoothing to describe incidence for each species at three scales: within 200, 400, and 1200 m around sample locations. For the 200-m scale, we also calculated the most-preferred range of tree cover (within which at least half of observations were predicted to occur) for each species. Only 10 of 40 species had occurrence thresholds greater than about 10% tree cover. After initial occurrence, species showed three general patterns: some increased monotonically with tree cover; some increased up to an asymptote; some peaked at intermediate amounts of tree cover and then declined. These patterns approximate selection for interior woodlands and for edge-rich environments, but incidence plots provide greater detail in landscape-scale selection than do those categories. For most species, patterns persisted at larger scales, but for some, larger scales had distinctly different patterns than local scales. Preferred ranges of tree cover varied from <20% tree cover (common grackle, Quiscalus quiscula) to >60% (veery, Catharus fuscescens). We conclude that incidence patterns provide more information on habitat selection than do threshold measures for most species: in particular, they differentiate species preferring concentrated woodlands from those preferring mixed landscapes, and they show contrasting degrees of selectiveness. [Correction added on 16 October 2012, after first online publication: the Abstract section has been reworded].

Conserving migratory land birds in the new world: do we know enough?

Migratory bird needs must be met during four phases of the year: breeding season, fall migration, wintering, and spring migration; thus, management may be needed during all four phases. The bulk of research and management has focused on the breeding season, although several issues remain unsettled, including the spatial extent of habitat influences on fitness and the importance of habitat on the breeding grounds used after breeding. Although detailed investigations have shed light on the ecology and population dynamics of a few avian species, knowledge is sketchy for most species. Replication of comprehensive studies is needed for multiple species across a range of areas, Information deficiencies are even greater during the wintering season, when birds require sites that provide security and food resources needed for survival and developing nutrient reserves for spring migration and, possibly, reproduction. Research is needed on many species simply to identify geographic distributions, wintering sites, habitat use, and basic ecology. Studies are complicated, however, by the mobility of birds and by sexual segregation during winter. Stable-isotope methodology has offered an opportunity to identify linkages between breeding and wintering sites, which facilitates understanding the complete annual cycle of birds. The twice-annual migrations are the poorest-understood events in a bird's life. Migration has always been a risky undertaking, with such anthropogenic features as tall buildings, towers, and wind generators adding to the risk. Species such as woodland specialists migrating through eastern North America have numerous options for pausing during migration to replenish nutrients, but some species depend on limited stopover locations. Research needs for migration include identifying pathways and timetables of migration, quality and distribution of habitats, threats posed by towers and other tall structures, and any bottlenecks for migration. Issues such as human population growth, acid deposition, climate change, and exotic diseases are global concerns with uncertain consequences to migratory birds and even less-certain remedies. Despite enormous gaps in our understanding of these birds, research, much of it occurring in the past 30 years, has provided sufficient information to make intelligent conservation efforts but needs to expand to handle future challenges.

Cerebrospinal fluid pressure is decreased in primary open-angle glaucoma.

PURPOSE: To compare cerebrospinal fluid (CSF) pressure in patients with primary open-angle glaucoma (POAG) with that in nonglaucomatous patients. DESIGN: Case-control study. PARTICIPANTS: Thirty-one thousand, seven hundred and eighty-six subjects underwent lumbar puncture (LP) between 1996 and 2007 at the Mayo Clinic, Rochester, Minnesota. Of these, 28 patients who had POAG and 49 patients who did not have POAG were analyzed. METHODS: Retrospective review of medical records. Comparison of the 2 groups and factors associated with CSF pressure were analyzed by univariate and multivariate analyses. MAIN OUTCOME MEASURES: Demographics (age and gender), medical history, medication use, indication for LP, intraocular pressure (IOP), optic disc cup-to-disc ratio, visual field assessment, and CSF pressure. RESULTS: The mean CSF pressure +/- standard deviation was 13.0+/-4.2 mmHg in nonglaucoma patients and 9.2+/-2.9 mmHg in POAG patients (P<0.00005). The CSF pressure was lower in POAG patients regardless of indication for LP or age. Linear regression analysis showed that cup-to-disc ratio correlated independently with IOP (P<0.0001), CSF pressure (P<0.0001), and the translaminar pressure difference (P<0.0001). Multivariate analysis demonstrated that larger cup-to-disc ratio (P<0.0001) was associated with lower CSF pressure. CONCLUSIONS: Cerebrospinal fluid pressure is significantly lower in POAG patients compared with that in nonglaucomatous controls. These data support the notion that CSF pressure may play an important contributory role in the pathogenesis of POAG.

Mechanism of action of bimatoprost, latanoprost, and travoprost in healthy subjects. A crossover study.

PURPOSE: To study the effects of 3 prostaglandin analogs, bimatoprost, latanoprost, and travoprost, on aqueous dynamics in the same subjects and to compare techniques of assessing outflow facility. DESIGN: Experimental study (double-masked, placebo-controlled, randomized paired comparison, 4-period crossover). PARTICIPANTS: Thirty healthy adult subjects. METHODS: Bimatoprost, latanoprost, travoprost, or a placebo was administered to the left eye once a day in the evening for 7 days, after a minimum 4-week washout period between each session. Tonographic outflow facility was measured by Schiøtz tonography and pneumatonography on day 7. On day 8, the aqueous humor flow rate and fluorophotometric outflow facility were measured by fluorophotometry. Uveoscleral outflow was calculated from the aqueous humor flow rate and outflow facility using the Goldmann equation. MAIN OUTCOME MEASURES: Facility of outflow, aqueous humor flow rate, intraocular pressure (IOP), and calculation of uveoscleral outflow. RESULTS: All medications lowered IOP relative to a placebo. None of the drugs affected aqueous humor production. All medications increased outflow facility compared with placebo when measured by Schiøtz and 2-minute pneumatonography (P< or =0.02); the apparent increase of outflow facility measured with fluorophotometry and 4-minute pneumatonography did not reach statistical significance. In contrast, uveoscleral outflow was significantly increased by all medications when calculated from 4-minute pneumatonography data, and fluorophotometry and Schiøtz data at higher episcleral venous pressures. The apparent increase found with 2-minute pneumatonography did not reach statistical significance. These differing results in the same patients indicate that differences in measurement techniques, and not differences in mechanism of action, explain previous conflicting published reports on the mechanism of action of the prostaglandins. CONCLUSIONS: Bimatoprost, latanoprost, and travoprost have similar mechanisms of action. All 3 drugs reduce IOP without significantly affecting the aqueous production rate. All drugs increase aqueous humor outflow, either by enhancing the pressure-sensitive (presumed trabecular) outflow pathway or by increasing the pressure-insensitive (uveoscleral) outflow, but the assessment of the amount of flow through each pathway depends upon the measurement technique.

Circadian variation of aqueous dynamics in young healthy adults.

PURPOSE: Recent research indicates that intraocular pressure (IOP) does not decrease significantly during the nocturnal period, although aqueous humor flow decreases by 50% or more at night. This study was undertaken to investigate whether changes in outflow facility, episcleral venous pressure, or uveoscleral flow at night could account for the nocturnal IOP. METHODS: Sixty-eight eyes of 34 healthy subjects (age, 18-44 years; mean, 29) were studied. Aqueous humor flow rate, IOP, and outflow facility were measured with pneumatonometry, anterior chamber fluorophotometry, and Schiotz tonography respectively, in each eye during the mid-diurnal (2-4 PM) and mid-nocturnal (2-4 AM) periods. Nocturnal IOP, flow rate, and outflow facility were compared to the same variables during the diurnal period. Mathematical models based on the modified Goldmann equation were used to assess the conditions under which these results could be reconciled. RESULTS: Supine IOP decreased slightly from 18.9 +/- 2.7 mm Hg in the mid-diurnal period to 17.8 +/- 2.5 mm Hg in the mid-nocturnal period (mean +/- SD, P = 0.001). Aqueous flow rate decreased from 2.26 +/- 0.73 to 1.12 +/- 0.75 microL/min (mean +/- SD, P < 0.001). There was a nonsignificant trend toward a nocturnal decrease of outflow facility (diurnal, 0.27 +/- 0.11 microL/min/mm Hg; nocturnal, 0.25 +/- 0.08 microL/min/mm Hg; mean +/- SD, P = 0.13). CONCLUSIONS: Outflow facility measured by tonography does not decrease enough during the nocturnal period to compensate for the decreased aqueous humor flow rate. Modeling results indicate that the experimental results could be reconciled only if nocturnal changes in episcleral venous pressure and/or uveoscleral flow occurred.

Durable, safe, multi-gene lentiviral vector expression in feline trabecular meshwork.

Multiple disease-specific considerations have led to interest in the potential of gene therapy to permanently correct elevated intraocular pressure (IOP), the main causal risk factor for primary open angle glaucoma (POAG). Since IOP elevation results from abnormal resistance to aqueous humor outflow from the eye through the trabecular meshwork (TM), a means to genetically modify this specialized outflow organ permanently and safely is a prioritized goal. Here we tested different lentiviral vector designs and doses for long-term transgene expression in a large animal model, and investigated whether exogenously introduced myocilin proteins influenced IOP. The anterior chambers of 18 domestic cats (36 eyes) were injected with dual-gene feline immunodeficiency virus (FIV) vectors. Substantial, well-tolerated green fluorescent protein (GFP) expression was achieved in TM and monitored non-invasively in vivo for 1.2-2.3 years, using both 5' cap-translation and internal ribosome entry site (IRES)-translation. In all 36 eyes, post-mortem examination revealed substantial TM transgene expression (which often greatly exceeded that observable non-invasively during life). However, co-expression with enhanced GFP of myocilin or a juvenile glaucoma-associated mutant myocilin did not elevate IOP. These results demonstrate a safe, long-term single and dual gene expression in TM and establish an experimental system for testing candidate therapeutic transgenes for POAG.

Prostaglandins increase trabecular meshwork outflow facility in cultured human anterior segments.

PURPOSE: To determine the effect of latanoprost free acid and prostaglandin E1 (PGE1) on outflow facility in cultured human anterior segments. Clinical studies find prostaglandin treatment increases uveoscleral outflow, but do not agree whether trabecular outflow increases. Cultured anterior segments eliminate the uveoscleral pathway and enable a direct assessment of trabecular outflow. DESIGN: Laboratory investigation. METHODS: One anterior segment of an eye pair was placed in perfusion organ culture and received a continuous infusion of drug while the fellow anterior segment received vehicle. Histologic changes were assessed. Zymography and Western blots were used to analyze matrix metalloprotease (MMP) activity. Scleral hydraulic conductivities were measured. RESULTS: Latanoprost significantly increased outflow facility (67% +/- 11% vs control 6% +/- 10%, P < .001). Facility changes occurred within one hour of receiving drug, reaching a new baseline by 24 hours. Facility changes were reversible, requiring about 48 hours to return to pre-drug values. PGE1 caused less facility change (13% +/- 17% vs control 1% +/- 11%, P = .02). Prostaglandin treated anterior segments had regions of focal detachment and loss of Schlemm canal endothelial cells, with loss of extracellular matrix underlying some areas. MMPs were not consistently increased in Western blots, zymography, or immunohistochemistry. Scleral hydraulic conductivity increased, but not enough to account for total facility increase. CONCLUSIONS: Prostaglandins increase outflow facility in perfusion organ culture of human anterior segments. MMP activity was not consistently increased, and scleral hydraulic conductivity was not increased sufficiently to account for total facility increase. The histologic changes suggest a direct trabecular meshwork effect.

Histologic findings after argon laser trabeculoplasty in glaucomatous eyes.

The purpose of the study was to determine histologic findings after successful laser trabeculoplasty in eyes with glaucoma. Previous studies have examined eyes in which laser did not lower intraocular pressure, or examined only the region of the laser burn itself. Nineteen autopsy eyes from 14 donors with either primary open angle or pseudoexfoliative glaucoma that had undergone laser trabeculoplasty during life were studied. Clinical records were used to determine the effect of laser in lowering intraocular pressure (IOP). For comparison, 49 glaucomatous eyes that had not undergone laser, and 55 normal eyes were studied as control eyes. Histologic sections from multiple quadrants of each eye were studied by light microscopy, selecting regions between laser spots when the spots were visible. Meshworks from lasered eyes frequently had regions of an expanded juxtacanalicular region associated with numerous superimposed giant vacuoles partially filling Schlemm's canal. This finding was more common in eyes fixed by posterior chamber perfusion, occurring in 90% (9/10) of lasered eyes, while it was found in only 20% (3/15) of glaucomatous control eyes (p=0.01) and 33% (14/43) of normal eyes (p=0.01). The mean decrease in IOP caused by laser was 34%+/-14%, with mean follow-up time before death of 2.7+/-1.7 years. In eyes fixed by immersion the expanded JCT finding was less common, occurring in 22% (2/9) of lasered eyes, but only 9% (3/34) of glaucomatous control eyes and 8% (1/12) of normal eyes. The mean decrease in IOP in these eyes was 39%+/-10%, with mean follow up of 2.3+/-1.0 years until death. Downgrowth of Descemet's membrane over the meshwork was observed in portions of two of the 19 lasered eyes. In conclusion, laser trabeculoplasty associated with decreased IOP appears to cause a remodeling of the juxtacanalicular region of the meshwork. This may be a dynamic, flow dependent finding, as it was more common in eyes fixed by perfusion. Downgrowth of Descemet's membrane over the meshwork was uncommon.

The risk of glaucoma in pseudoexfoliation syndrome.

PURPOSE: To determine the conversion rate of pseudoexfoliation syndrome (PEX) to pseudoexfoliative glaucoma or treated ocular hypertension. METHODS: Retrospective community-based study of newly diagnosed cases of PEX syndrome in all residents of Olmsted County, Minnesota between 1976 and 1991. The end point was considered the initiation of therapy, which included patients with glaucoma (optic disc damage or visual field defects), or with elevated intraocular pressure (IOP) >21 mm Hg in the presence of risk factors; the subsequent development of damage in the latter group was also determined. RESULTS: Two hundred fifty-five patients (318 eyes) had newly diagnosed PEX over the 15-year interval. Mean age was 73+/-10 years; 78% (199/255) were female. Of all PEX patients, 16% were placed on therapy at the time of initial diagnosis of PEX. In the remaining PEX patients, the probability of being placed on therapy was 44% at 15 years. Bilateral PEX was present in 25% at initial diagnosis and developed in another 29% by 15 years. Of those not placed on therapy, 16% (23/142) had IOP increase 5+ mm Hg during follow-up, with 11% (16/142) reaching 22 mm Hg or more. The strongest risk factors for converting to therapy were IOP at initial diagnosis of PEX and bilateral involvement. CONCLUSIONS: In a geographically defined population of PEX patients, 16% required treatment upon presentation. Of the remaining PEX patients, 44% received therapy over the next 15 years.