The effect of humate as a feed additive on feed intake, production, and carcass parameters of Angus steers.

Humate may be a valuable livestock feed additive, with potential effects on nutrient utilisation and animal performance. Thus, the aim of this study was to investigate the effect of K Humate S 100R supplementation on the feed intake, liveweight gain, and carcass parameters of Angus steers. Within individual pens, 40 weaned steers were allocated to four treatment groups (n = 10/potassium humate K Humate S100R, Omnia Specialities Australia) for 100 days. The treatment groups included Group 1, 35 g K Humate S100R/animal/day; Group 2, 70 g K Humate S100R/animal/day; Group 3, 140 g K Humate S100R/animal/day; and Control Group, which were not supplemented with K Humate S100R (0 g K Humate S100R/animal/day). Chemical and mineral composition of the feed ingredients, dry matter intake (DMI), and average daily weight gains were recorded. The steers were slaughtered as a single group at a commercial Australian abattoir. Standard measures for hot standard carcass weight, eye muscle area, fat depth and coverage, marbling, ossification, meat and fat colour, dressing percentage and loin pH values at 24-hour postmortem were recorded. It was found that the steers allocated to Group 2 had higher DMI (P = 0.003) and feed conversion ratio (FCR) (P < 0.001) compared with those allocated to Group 1 and the Control Group. The MSA marbling score was lowest for steers allocated to the Control Group (P < 0.05) and comparable for those allocated to Groups 1, 2, and 3. Together, these results demonstrate that increased levels of K Humate S100R supplementation improved the carcass quality, via an increase in MSA. However, further research is warranted on the potential effects of humates supplementation on intramuscular fat associated qualities of beef.

A survey of producer practices and reproductive performance of containment and supplementary fed ewes.

Containment feeding, where ewes are fed complete rations, is used to maintain flock numbers in periods of inadequate pasture supply. Producer practices influence both the reproductive performance of ewes and the risk of health challenges. The aim of this study was to evaluate the reproductive, feeding and health management practices of producers using containment or supplementary feeding, and quantify any associations between practice and reproductive performance. An online survey of Australian producers was conducted in 2020. The number of responses (n = 43) allowed benchmarking but was insufficient to determine correlations between practice and performance. The reported pregnancy rate of adult Merino ewes was variable between respondents (78%-95%; n = 11), and lambs marked per ewe joined ranged from 60% to 110% (n = 9). In non-Merino flocks, lambs marked ranged from 82% to 161% (n = 4). Most respondents (9/11) fed cereal grain with hay or straw, either daily or two or three times a week. However, some respondents fed grain only or roughage only, such that the percentage of roughage in diets ranged from 0% to 100%. Ewes were most frequently separated into age groups for feeding, and shy feeders were only removed by 25% of respondents. Although generally the reported reproductive rate was high, wide variation indicates potential for improvement. Best practice management for containment remains unclear and requires further research given the diverse practices used. Veterinary practitioners should be aware that some of the practices used may contribute to reduced productivity or health issues in ewes.

Enhancing performance of berseem clover genotypes with better harvesting management through farmers' participatory research at smallholder farms in Punjab.

A field study was conducted on smallholder farmer fields between 2012 to 2014 to evaluate the performance of cv. Agaitti Berseem-2002, against local landraces exchanged between farmers (LBF1) or available from local markets (LBM1). The effects of genotype and harvesting regimen on forage production, quality and seed production were evaluated. Significant differences (P < 0.05) among genotypes and cutting treatments were recorded for forage and seed yields, and forage quality across all research sites in both years. Maximum cumulative fresh forage (89.7 t/ha) and dry matter (DM; 13.4 t/ha) yields were obtained with Agaitti Berseem-2002 when harvesting occurred five times over the season. However, maximum seed yield (1048 kg/ha) with higher 1000-seed weight (3.63 g) were obtained if forage was only harvested three times and the crop then left for seed set. Agaitti Berseem-2002 also produced forage with the higher crude protein content (27%), DM digestibility (69%), digestible organic matter (DM basis; 65%) and metabolizable energy content (10%) compared to the local landraces (LBF1 and LBM1). Therefore, the harvesting regimen for greatest economic return which produced optimum fresh and DM forage yields of highest nutritive values and maximum seed yield, were comprised of taking three forage cuts (at 65, 110 and 150 days after sowing) prior to seed harvest.

Treatment with potassium bromide mitigates ataxia and reduces tremor in lambs with perennial ryegrass toxicosis.

Aims: To assess the use of potassium bromide (KBr) as a therapeutic intervention for perennial ryegrass toxicosis (PRGT) in lambs fed ryegrass seed containing lolitrem B. Methods: Male lambs aged 10-12 months (n = 43) were assigned to receive ryegrass seed containing lolitrem B, at a dose of 0.16 mg/kg/day (Groups 2, 3 and 4), or lucerne chaff and molasses (Groups 1 and 5). Lambs in Groups 2 and 3 were observed for clinical signs and gait changes until defined signs of PGRT were observed, when they were transferred, with lambs in Group 1, to the Testing phase of the trial. Lambs in Group 3 were then treated with a single oral dose of 300 mg/kg bromide. Lambs in Groups 4 and 5 received KBr daily from the start of the trial (540 mg/kg bromide over 3 days then 20 mg/kg daily) and were transferred to the Testing phase after 18 days. Clinical examination and gait assessment, and surface electromyography of the triceps muscle, measuring root-mean-square (RMS) voltages, were carried out on Days 0, 1 and 2 of the Testing phase followed by necropsy, histopathology, measurement of concentrations of bromide in serum and CSF and faecal cortisol metabolites (FCM). Results: In Group 3 lambs, mean composite gait scores decreased between Testing phase Day 0 and Days 1 and 2 (p < 0.001), but increased in lambs in Group 2 between Day 0 and Day 2 (p = 0.015). Scores for lambs in Group 3 on Day 2 were lower than for lambs in Group 2 (p < 0.001). Mean RMS voltages on Day 2 were higher in lambs in Group 2 than Group 3 (p = 0.045). Mean concentrations of bromide in serum were >800 µg/mL in lambs in Groups 3 and 4 on Day 2. Concentrations of FCM were higher in lambs from Group 2 than in Groups 1 or 5, but were similar in Groups 2, 3 and 4. Histopathological findings in the cerebellum of lambs from Groups 2, 3 and 4 were similar, showing pyknosis of neurons within the granular layer of the cerebellum and Purkinje neuron proximal axonal spheroid formation. Conclusions and clinical relevance: A single oral dose of 300 mg/kg bromide in lambs with neurological signs of PRGT resulted in reduced composite gait scores and reduced RMS voltages, indicating a significant improvement in clinical signs of ataxia, movement disorder and muscle tremor associated with the neurotoxic effects of lolitrem B.

Development of a model for investigation of perennial ryegrass toxicosis in sheep.

AIMS To develop a clinical model of perennial ryegrass toxicosis (PRGT) based on feeding a known dose of lolitrem B and ergotamine, and to produce a consistent clinical presentation for assessment of disease pathophysiology, neurological changes and neurohistopathology. METHODS Male lambs, aged between 10-12 months, were randomly assigned to either Treatment (n=9) or Control (n=9) groups. Lambs in the Treatment group received feed containing a novel endophyte-infested perennial ryegrass seed, commencing on Day 0 of the Feeding phase with a low induction dose, then increasing after 3 days to provide 0.16 mg/kg live bodywight (LBW)/day of lolitrem B and 0.054 mg/kg LBW/day ergotamine. Lambs were examined daily and when defined signs of PRGT were observed they were transferred to the Testing phase. Neurological examinations, assessment of gait, surface electromyography (EMG) and mechanosensory nociceptive threshold testing were carried out and blood samples collected during both phases of the trial, with a full necropsy, histopathological examination and measurement of faecal cortisol metabolites (FCM) performed on Day 2 of the Testing phase. RESULTS Typical clinical signs of PRGT, including ataxia of vestibulocerebellar origin leading to stumbling, were observed in all Treatment lambs. The median interval from the start of the Feeding phase to entry into the Testing phase was 21 (min 18, max 34) days. Histopathological characterisation of neurological lesions included the presence of Purkinje cell vacuolation, pyknotic granular layer neurons and proximal axonal Purkinje cell spheroids. Lesions were most apparent within the vestibulocerebellum. Mean root-mean-square voltages from triceps EMG increased in Treatment lambs between Feeding phase Day 0 and Testing phase Day 2 (p<0.001). Daily water intake during the Testing phase for the Treatment group was less than in Control group lambs (p=0.002), and concentrations of FCM at necropsy were higher in Treatment compared to Control lambs (p=0.02). CONCLUSIONS AND CLINICAL RELEVANCE Lolitrem B and ergotamine dosing in feed on a live weight basis combined with neurological/gait assessment provides an effective model for investigation of PRGT and potential therapeutics. Assessment of gait changes using defined criteria and RMS voltages from EMG appear to be useful tools for the assessment of the severity of neurological changes.

Acute effects of sldenafil ctrate (Viagra) on intraocular pressure in open-angle glaucoma.

PURPOSE: To assess the acute effects of sildenafil citrate (VIAGRA) on the intraocular pressure (IOP) of patients with chronic open-angle glaucoma. DESIGN: This was a double-blind, randomized, placebo-controlled, crossover study, in which 15 patients received a single oral dose of sildenafil 100 mg or matching placebo on two separate occasions. METHODS: Fifteen subjects aged 63 +/- 14 years (mean +/- SD) with bilateral chronic open-angle glaucoma were administered a single oral dose of sildenafil 100 mg or matching placebo on two separate occasions at least 3 days apart. IOP was measured in both eyes by Goldmann ap-planation tonometry at baseline and then at 1-5 hours after dosing. Brachial artery systolic and diastolic blood pressures were determined by sphygmomanometry, and heart rate was also monitored at baseline and 1-5 hours after dosing. RESULTS: Compared with placebo, no statistically or clinically significant change in IOP was detected after a single dose of sildenafil 100 mg (P =.20). Moreover, no significant change in mean systemic blood pressure (P =.12) or heart rate (P =.72) was detected after treatment with sildenafil. CONCLUSION: At the maximum therapeutic dose of 100 mg, sildenafil did not produce any significant acute change in IOP in men with chronic open-angle glaucoma. This information is of importance for patients with glaucoma receiving sildenafil for treatment of erectile dysfunction.

Contralateral effect of topical beta-adrenergic antagonists in initial one-eyed trials in the ocular hypertension treatment study.

PURPOSE: To evaluate the magnitude of the contralateral effect of topically administered beta-blockers on intraocular pressure. METHODS: The Ocular Hypertension Treatment Study enrolled 1,636 subjects. Of these, 817 subjects were randomized to receive topical ocular hypotensive medication and 819 subjects were randomized to close observation (i.e., no topical medication). We compared the intraocular pressure of the contralateral eye of subjects at the baseline visit and after an initial one-eyed therapeutic trial of topical beta-blockers. We examined differences between baseline and follow-up intraocular pressure in untreated eyes of subjects randomized to close observation. RESULTS: The mean reduction in intraocular pressure in the beta-blocker-treated eyes was -5.9 +/- 3. 4 mm Hg (-22% +/- 12%; Student t test, P <.0001). In the contralateral eyes, mean intraocular pressure reduction was -1.5 +/- 3.0 mm Hg (-5.8% +/- 12%; P <.0001). Of the contralateral eyes, 35% showed a reduction of 3 mm Hg or more, and 10% showed a reduction of 6 mm Hg or more. The contralateral effect of the relatively selective beta-blocker betaxolol did not differ from that of any of the nonselective beta-blockers. Factors associated with the magnitude of the contralateral effect were the degree of intraocular pressure reduction in the treated eye and baseline intraocular pressure of the contralateral eye. In the close observation group, no significant reduction in intraocular pressure was noted between the baseline and follow-up visit. CONCLUSIONS: The contralateral effect is important in clinical practice and in clinical trials when the hypotensive effect of a topical beta-blocker is evaluated by means of a one-eyed therapeutic trial.

Computerized stereochronoscopy and alternation flicker to detect optic nerve head contour change.

PURPOSE/BACKGROUND: Stereochronoscopy, a technique previously explored but abandoned for glaucoma diagnosis, viewed optic nerve images acquired at separate points in time as if a stereo pair. Prior efforts to exploit this technique were impaired by a lack of superimposability for sequential optic nerve images. We investigated computerized registration techniques for aligning sequential, monoscopic optic disc images to facilitate sensitive detection of optic nerve head contour changes in glaucoma. DESIGN: Algorithm and software development. Comparisons with standard techniques. MATERIALS: Existing patient records from the Glaucoma Service, Scheie Eye Institute, University of Pennsylvania. METHODS: Two sets of optic disc photographs, separated in time by 1 to 18 years, of 25 eyes with and without glaucomatous optic disc progression were digitized. We developed custom software for accurate image alignment. Change in disc morphology was then judged by digital stereochronoscopy and user-controlled alternation flicker of superimposed, time-separated images on a computer monitor. Comparisons were made with standard stereoscopic comparison. MAIN OUTCOME MEASURE: Identification of change or no change in optic nerve head contour for images acquired at separate points in time. RESULTS: Image processing and registration permits accurate alignment of optic disc photographs. Alternation flicker of superimposed, sequential images facilitates image comparison and detection of change as indicated by change in vessel position, color, and other cues for contour change. A high concordance was found between standard stereoscopic comparison and alternation flicker. In several cases, reinspection of stereo comparison led to a revised judgment on the basis of disc changes rendered more obvious with alternation flicker. Digital stereochronoscopy was less concordant with standard techniques. CONCLUSIONS: Digital image processing techniques and alternation flicker provide a simple, sensitive, software-based method for detecting glaucomatous optic disc change.

Optic nerve blood flow in glaucoma: effect of systemic hypertension.

PURPOSE: To investigate optic nerve head blood flow in patients with glaucoma and to assess the effect of systemic hypertension. METHODS: This study included 24 eyes of 24 patients with primary open-angle glaucoma. Eleven of these patients had a history of systemic hypertension. Results in patients with glaucoma were compared with those of 13 eyes of 13 age-matched normal controls. Determinations of relative optic nerve head blood velocity, volume, and flow were obtained with laser Doppler flowmetry in the superotemporal and inferotemporal neuroretinal rim and also in the cup. Means of the velocity, volume, and flow of these three measurement sites were calculated for each subject. RESULTS: Mean overall optic nerve head blood flow was 29% lower in glaucoma patients than in normal controls (t test, P < .001). This decrease in flow was mainly caused by a decrease of 23% in mean blood velocity (P < .001). Mean flow in glaucoma patients without systemic hypertension was 26% lower than that of glaucoma patients with hypertension (Tukey honest significant difference test, P = .05). A significant direct correlation was observed between mean flow and mean blood pressure (R = 0.51, P < .02). CONCLUSIONS: Optic nerve blood flow is reduced in glaucoma patients. Glaucoma patients without systemic hypertension have lower optic nerve blood flow than those with hypertension. Our results raise concerns that treatment of systemic hypertension may further decrease optic nerve blood flow in glaucoma patients.

A false-positive Seidel test after Ahmed valve insertion.

An 80-year-old monocular man with long-standing primary open angle glaucoma underwent successful filtering surgery in his sighted right eye in 1980. He subsequently developed a cataract and had an uncomplicated clear cornea phacoemulsification with posterior chamber intraocular lens in 1996. Post-operatively, the filtration bleb remained very avascular but shallowed; the intraocular pressure increased and remained uncontrolled despite maximally tolerated medical therapy. His vision improved to 6/7.5 and automated perimetry revealed a less than 5 degrees small central island of vision. His left eye was phthisical with no light perception.

Optic nerve and choroidal circulation in glaucoma.

PURPOSE: To investigate the circulation of the optic nerve head and choroid in patients with glaucoma. METHODS: Laser Doppler flowmetry was used to determine optic nerve head relative blood velocity (ONVel), volume (ONVol), and flow (ONFlow) in 19 primary open-angle glaucoma patients and 15 age-matched healthy control subjects. In each subject, determinations were obtained from four sites on the neuroretinal tissue and from the center of the cup. A mean of the ONVel, ONVol, and ONFlow for these five measurement sites were calculated for each subject and defined as ONVel5, ONVol5, and ONFlow5. Circulatory parameters were correlated with measures of disease progression such as cup-to-disc ratio and Humphrey visual field indices. Measurements of relative choroidal blood velocity, volume, and flow were also obtained from the foveola. RESULTS: In glaucoma patients, mean ONFlow5 was significantly lower than in control subjects (24%; P = 0.001; independent, two-tailed Student's t-test). This decrease was caused by a significant decrease in ONVol5 (15%; P = 0.04) and a nonsignificant decrease in ONVel5 (10%; P = 0.07). In glaucomatous eyes, mean ONFlow was significantly reduced from normal, by 28% in the inferior temporal neuroretinal rim location (P = 0.001) and by 24% in the superior temporal location (P = 0.001). Although mean ONFlow was also decreased by 33% in the cup, the difference was not statistically significant after a Bonferroni correction was applied. No significant differences from normal were observed in the superior and inferior nasal rim tissues. In glaucoma patients, ONFlow5 was significantly and inversely correlated with the corrected pattern standard deviation (R = -0.53; P = 0.02) and with the cup-to-disc ratio (R = -0.65; P = 0.002). Choroidal blood flow measurements obtained in the foveola of glaucomatous eyes showed no statistically significant differences from normal. CONCLUSIONS: ONFlow5 is reduced by approximately 24% in glaucoma patients. In the inferior temporal rim, the area in which nerve bundle defects most commonly occur, blood flow is reduced by 28%. Patients with more advanced glaucomatous damage, as detected by visual field corrected pattern standard deviation and measurement of the cup-to-disc ratio, tend to have lower ONFlow5. These results suggest a decrease in optic nerve blood flow that is correlated with functional and morphologic measures of glaucomatous progression. However, from these results we cannot conclude whether this decrease in flow has a primary role in the etiology of glaucoma or whether it is the result of the loss of neural components caused by this disease.

The effect of nimodipine, a centrally active calcium antagonist, on visual function and mascular blood flow in patients with normal-tension glaucoma and control subjects.

PURPOSE: This study was performed to evaluate the effect of nimodipine, a centrally active calcium channel antagonist on automated Humphrey visual fields, Farnsworth-Munsell 100 (FM-100) hue color vision testing, and macular blood flow (blue field entoptic simulation technique) in patients with normal-tension glaucoma (NTG) and control subjects. METHODS: Thirteen patients with NTG and thirteen age- and sex-matched control subjects were studied in a prospective, placebo-controlled, double-masked, crossover protocol. On each of the two study dates, testing was performed at baseline and 90 minutes after administration of either two 30-mg nimodipine capsules or two identical appearing placebo capsules. Blood pressure and pulse were monitored throughout the study. RESULTS: Nimodipine administration resulted in a performance corrected improvement in Humphrey visual field mean deviation (patients with NTG and control subjects), corrected pattern standard deviation (patients with NTG), and macular sensitivity (the average of the foveal threshold and the four most central points of the visual field; patients with NTG). The FM-100 hue error scores significantly decreased after administration of nimodipine in patients with NTG and control subjects compared with baseline. There were no significant differences in baseline leukocyte velocity or density between patients with NTG and control subjects; no significant changes in leukocyte velocity or density were noted after administration of nimodipine in either group. CONCLUSION: Nimodipine caused a significant performance corrected improvement in visual field testing and a significant improvement in color vision. Nimodipine did not alter macular hemodynamics as measured using the blue field entoptic simulation technique, although results were hampered by high variability, particularly in the leukocyte density measurements.

Fenoldopam, a selective dopamine-1 receptor agonist, raises intraocular pressure in males with normal intraocular pressure.

Recent studies have suggested that intravenous infusion of fenoldopam, a selective dopamine-1 receptor agonist, elevates intraocular pressure (IOP) in man. This study evaluated the effect of intravenous fenoldopam on IOP, aqueous humor outflow facility and gonioscopy in 12 healthy human subjects. Three doses (0.2, 0.5 and 1.0 microg/kg/min) were infused for 120 minutes in a double masked, placebo controlled, four-way crossover design. IOP was measured every 20 minutes in the supine position and every 40 minutes while sitting during the drug and placebo infusions. Tonography and gonioscopy were performed at baseline and after 120 minutes of infusion. Compared to placebo, IOP increased by 3.5 mm Hg (32%) for the lowest dose, 5.8 mm Hg (46%) for the intermediate dose, and 6.9 mm Hg (55%) for the highest dose (p<0.05 for all three doses). IOP returned to baseline within 30 minutes of stopping the infusion. The outflow facility decreased from baseline by 26% after 120 minutes of infusion for all drug doses. In contrast, outflow facility increased from baseline by 11% during placebo infusion. Compared to placebo, the fenoldopam induced changes in outflow were statistically significant (p<0.05). There was no change in the gonioscopic appearance of the anterior chamber angle during the infusion. This study shows that systemic administration of a selective dopamine-1 receptor agonist causes a significant dose-dependent increase in IOP that can be explained in part by diminished outflow facility. These results support a role for the dopamine-1 receptor in the modulation of IOP in general and suggest modulation of aqueous humor outflow by dopaminergic receptors.

Nimodipine, a centrally active calcium antagonist, exerts a beneficial effect on contrast sensitivity in patients with normal-tension glaucoma and in control subjects.

BACKGROUND/PURPOSE: The use of calcium antagonists in patients with normal-tension glaucoma (NTG) currently is under investigation. The aim of this study is to evaluate the effect of an acute dose of oral nimodipine, a centrally active calcium antagonist, on spatial contrast sensitivity in patients with NTG and in age-matched control subjects. METHODS: Spatial contrast sensitivity was measured using the Pelli-Robson and the Vistech 6000 charts in 14 patients with NTG and in 17 control subjects. Testing was performed at baseline and at two subsequent sessions. Measurements were recorded 2 hours after oral administration of either nimodipine or placebo in a randomized, double-masked manner. Data were analyzed using unpaired, two-tailed Student's t test for between-group comparisons and repeated measures analysis of variance for within-group comparisons. RESULTS: Using the Pelli-Robson charts, baseline contrast sensitivity was significantly lower in patients with NTG compared with control subjects (P < 0.05, unpaired Student's t test). There was a significant increase in log contrast sensitivity after administration of nimodipine compared with baseline and placebo in patients with NTG (baseline, 1.39 +/- 0.38; placebo, 1.41 +/- 0.40; nimodipine, 1.51 +/- 0.39) and in control subjects (baseline, 1.62 +/- 0.11; placebo, 1.64 +/- 0.10; nimodipine, 1.81 +/- 0.14) (P < 0.05, repeated measures analysis of variance). A similar trend was observed using the Vistech charts. CONCLUSION: These results suggest that central visual function as measured by Pelli-Robson and Vistech contrast sensitivity is impaired in eyes with NTG. An acute, oral administration of nimodipine, a calcium antagonist, improved contrast sensitivity in patients with NTG and in control subjects. The mechanism of this improvement is not fully understood. Further studies are needed to evaluate the effect of long-term administration in glaucoma.

The use of subconjunctivally administered tissue plasminogen activator after trabeculectomy.

Blockage of aqueous flow in the early postoperative period can be devastating to the success of trabeculectomy. We used tissue plasminogen activator (tPA) subconjunctivally in an attempt to release a trabeculectomy flap that appeared to be adherent to its scleral bed. No change was noted 90 minutes after injection, but a highly elevated bleb was present on the first postoperative day. Subconjunctivally administered tPA may be useful in releasing the fibrin "glue" in cases with adherent trabeculectomy flaps.

Digoxin toxicity. Recognizing the varied visual presentations.

We report three cases of digoxin toxicity presenting with decreased visual acuity, unaccompanied by the classic visual symptom of xanthopsia. Visual function improved and symptoms diminished upon lowering of blood digoxin level. Electroretinographic (ERG) abnormalities in the first case were suggestive of a cone deficit, which supports recent electrodiagnostic and labeled tracer studies implicating retinal dysfunction in the pathogenesis of digoxin toxicity. The second patient presented with visual symptoms exclusively. Evaluation of the third case was hampered by advanced retinitis pigmentosa and the presentation was complicated by a syncopal episode. Digoxin toxicity is a potentially life-threatening condition. Ophthalmologists and neurologists may be the first physicians consulted. It must be considered in the differential diagnosis in patients with otherwise unexplained visual loss.

Effect of aging on retinal macular microcirculation: a blue field simulation study.

PURPOSE: Structural changes in the retina are known to occur with aging. This study was performed to investigate whether aging also affects the retinal macular microcirculation. METHODS: Healthy volunteers with ages ranging from 20 to 78 years (mean +/- SD, 49 +/- 19 years) were included in this study. The retinal macular microcirculation was assessed with the blue field simulation technique, based on the blue field entoptic phenomenon. Subjects were asked to match the velocity and density of computer-simulated particles displayed on a screen with those of their entoptically observed leukocytes. Ten matching trials were performed, and an average leukocyte velocity and density were calculated. RESULTS: Significant negative linear correlations were observed between velocity and age (P = 0.0001) and density and age (P = 0.009). Older subjects (50 to 78 years of age) had a significantly slower velocity (0.61 +/- 0.21 mm/s) and smaller density (90 +/- 43 particles per field of view) than younger subjects (0.92 +/- 0.12 mm/s and 135 +/- 65 particles, respectively; unpaired Student's t-test, P = 0.001 and P = 0.01, respectively). CONCLUSIONS: These results suggest that, in normal subjects, retinal macular blood flow decreases with age. The 20% decrease in average velocity with age is very similar to the age-related decrease in number of cells observed in the human foveal ganglion cell layer.

Vernier thresholds and alignment bias in control, suspect, and glaucomatous eyes.

Detection of vernier offsets requires integration of spatial information from many retinal receptive fields. It was postulated that diminution of the number of ganglion cells in glaucoma may diminish the spatial sampling grain, compromise these integrative processes, and raise vernier thresholds. To test this hypothesis, vernier thresholds were measured in 45 patients with primary open-angle glaucoma (POAG), 45 age-matched glaucoma suspects, and 45 age-matched controls. Alignment bias was measured in 43 subjects from each diagnostic group. Measurements were also obtained in an additional 29 control subjects to evaluate the effect of age on vernier thresholds. All subjects had acuities of 6/7.5 or better. Vernier thresholds were significantly greater in glaucomatous eyes and suspect eyes than in control eyes (p = 0.0002). Mean thresholds were increased by 64% in glaucomatous eyes and 47% in suspect eyes; however, there was significant overlap between the groups. A subgroup of 15 eyes with early glaucomatous damage without localized visual field defects also had vernier thresholds significantly greater than control eyes (p = 0.02). The variances of the alignment biases were significantly greater in the glaucomatous and suspect eyes than in controls eyes (p < 0.05). Our results demonstrate that significant deficits of vernier detection can be demonstrated in some glaucomatous eyes, even in the absence of defects on automated perimetry. Because of the overlap between diagnostic groups, measurement of vernier thresholds cannot be used to distinguish POAG from controls. However, elevation of vernier thresholds may serve as a marker for the early diffuse central dysfunction that occurs in some eyes with glaucoma. The significance of these findings in terms of the mechanisms of glaucomatous damage is discussed.

Endocytosis in the rat retinal pigment epithelium.

Endocytosis in the retinal pigment epithelium (RPE) of rats was studied using horseradish peroxidase, microperoxidase and ferritin tracers. Tracer uptake was mediated by coated pits and coated vesicles. Coated pits formed at two discrete regions at the RPE plasma membrane: that portion of basal membrane directly opposing Bruch's membrane, and at the bases of the apical lamellae and villi. Two populations of coated vesicles were identified and distinguished by size, location and function. Large coated vesicles (91.8 +/- 14.7 nm in diameter) were located near the cell surface and incorporated tracer. Small coated vesicles (64.5 +/- 15.7 nm diameter) located more deeply within the cell were not tracer-labeled, and were often fused with the endoplasmic reticulum or the Golgi apparatus. Observations of the endocytic pathway in rat RPE cells are presented. Tracer was also found in organelles of the lysosomal system, e.g. the multivesicular body, but was not identified in the smooth endoplasmic reticulum or Golgi apparatus.