Self-assembly in escin-nonionic surfactant mixtures: From micelles to vesicles.

HYPOTHESIS: Saponins are a class of plant derived surfactants which are widely used in food related foams and emulsions, aerated drinks, and in pharmaceuticals and cosmetics. As a potential biosourced and renewable ingredient in a wider range of surfactant based formulations their potential is intimately associated with their mixing with synthetic surfactants. As such the nature of the mixed saponin-surfactant self-assembly is an important characteristic to investigate and understand. The unconventional structure of the saponins compared to the conventional synthetic surfactants poses some interesting constraints on the structures of the mixed aggregates. EXPERIMENTS: Small angle neutron scattering, SANS, is used to investigate the structure of the saponin, escin, mixed with a range of nonionic surfactants with different ethylene oxide groups, from triethylene glycol monododecyl ether, C12E3, to dodecaethylene glycol monododecyl ether, C12E12. FINDINGS: The scattering data reveal a complex evolution in the solution self-assembled structure with varying escin / nonionic composition and ethylene oxide chain length. The rich structural development comprises of the evolution from the elongated micelle structure of escin to the micelle structure of the nonionic surfactant. At the intermediate solution compositions the structure is predominantly planar, comprising mostly of planar / micellar mixed phases. The nature of the planar structures depend upon the ethylene oxide chain length and the solution composition, and include lamellar, bilamellar vesicle, multilamellar vesicle, and nanovesicle structures, in common with what is observed in other surfactant mixtures.

Adsorption and self-assembly properties of the plant based biosurfactant, Glycyrrhizic acid.

There is an increased interest in the use of natural surfactant as replacements for synthetic surfactants due to their biosustainable and biocompatible properties. A category of natural surfactants which are attracting much current interest is the triterpenoid saponins; surface active components found extensively in a wide range of plant species. A wide range of different saponin structures exist, depending upon the plant species they are extracted from; but regardless of the variation in structural details they are all highly surface active glycosides. Greater exploitation and application requires a characterisation and understanding of their basic adsorption and self-assembly properties. HYPOTHESIS: Glycyrrhizic acid, extracted from Licorice root, is a monodesmosidic triterpenoid saponin. It is widely used in cosmetic and pharmaceutical applications due to its anti-inflammatory properties, and is an ingredient in foods as a sweetener additive. It has an additional attraction due to its gel forming properties at relatively low concentrations. Although it has attracted much recent attention, many of its basic surface active characteristics, adsorption and self-assembly, remain relatively unexplored. How the structure of the Glycyrrhizic acid saponin affects its surface active properties and the impact of gelation on these properties are important considerations, and to investigate these are the focus of the study. EXPERIMENTS: In this paper the adsorption properties at the air-water interface and the self-assembly in solution have been investigated using by neutron reflectivity and small angle neutron scattering; in non-gelling and gelling conditions. FINDINGS: The adsorption isotherm is determined in water and in the presence of gelling additives, and compared with the adsorption behaviour of other saponins. Gelation has minimal impact on the adsorption; apart from producing a rougher surface with a surface texture on a macroscopic length scale. Globular micelles are formed in aqueous solution with modest anisotropy, and are compared with the structure of other saponin micelles. The addition of gelling agents results in only minimal micelle growth, and the solutions remain isotropic under applied shear flow.

Mixing Natural and Synthetic Surfactants: Co-Adsorption of Triterpenoid Saponins and Sodium Dodecyl Sulfate at the Air-Water Interface.

Saponins are highly surface active glycosides, derived from a wide range of plant species. Their ability to produce stable foams and emulsions has stimulated their applications in beverages, foods, and cosmetics. To explore a wider range of potential applications, their surface mixing properties with conventional surfactants have been investigated. The competitive adsorption of the triterpenoid saponin escin with an anionic surfactant sodium dodecyl sulfate, SDS, at the air-water interface has been studied by neutron reflectivity, NR, and surface tension. The NR measurements, at concentrations above the mixed critical micelle concentration, demonstrate the impact of the relative surface activities of the two components. The surface mixing is highly nonideal and can be described quantitatively by the pseudophase approximation with the inclusion of the quadratic and cubic terms in the excess free energy of mixing. Hence, the surface mixing is highly asymmetrical and reflects both the electrostatic and steric contributions to the intermolecular interactions. The relative importance of the steric contribution is reinforced by the observation that the micelle mixing is even more nonideal than the surface mixing. The mixing properties result in the surface adsorption being largely dominated by the SDS over the composition and concentration range explored. The results and their interpretation provide an important insight into the wider potential for mixing saponins with more conventional surfactants.

Surfactant/biosurfactant mixing: Adsorption of saponin/nonionic surfactant mixtures at the air-water interface.

Saponins are naturally occurring biosurfactants present in a wide range of plant species. They are highly surface active glycosides, and are used to stabilise foams and emulsions in foods, beverages and cosmetics. They have great potential for an even wider range of applications, especially when mixed with different synthetic surfactants. Understanding those mixing properties are key to the exploitation of saponins in that wider range of potential applications. The surface adsorption properties of the saponin, escin, with two conventional nonionic surfactants, polyethylene glycol surfactants, have been studied at the air-water interface using neutron reflectivity, NR, and surface tension, ST. Although the saponin and polyethylene glycol, CnEOm, surfactants are both nonionic the disparity in the relative surface activities and packing constraints result in non-ideal mixing. Comparison with the predictions of the pseudo phase approximation requires the inclusion of the quadratic, cubic and quartic terms in the expansion of the excess free energy of mixing to explain the variations in the surface composition. For escin/pentaethylene glycol monododecyl ether, C12EO5, the interaction is attractive and close to ideal. For escin/octaethylene glycol monododecyl ether, C12EO8, it is repulsive and close to the criteria for demixing. The differences in mixing behaviour are attributed to greater packing constraints imposed by the larger ethylene oxide headgroup of the C12EO8 compared to C12EO5.

Adsorption of Bovine Serum Albumin (BSA) at the Oil/Water Interface: A Neutron Reflection Study.

The structure of the adsorbed protein layer at the oil/water interface is essential to the understanding of the role of proteins in emulsion stabilization, and it is important to glean the mechanistic events of protein adsorption at such buried interfaces. This article reports on a novel experimental methodology for probing protein adsorption at the buried oil/water interface. Neutron reflectivity was used with a carefully selected set of isotopic contrasts to study the adsorption of bovine serum albumin (BSA) at the hexadecane/water interface, and the results were compared to those for the air/water interface. The adsorption isotherm was determined at the isoelectric point, and the results showed that a higher degree of adsorption could be achieved at the more hydrophobic interface. The adsorbed BSA molecules formed a monolayer on the aqueous side of the interface. The molecules in this layer were partially denatured by the presence of oil, and once released from the spatial constraint by the globular framework they were free to establish more favorable interactions with the hydrophobic medium. Thus, a loose layer extending toward the oil phase was clearly observed, resulting in an overall broader interface. By analogy to the air/water interface, as the concentration of BSA increased to 1.0 mg mL(-1) a secondary layer extending toward the aqueous phase was observed, possibly resulting from the steric repulsion upon the saturation of the primary monolayer. Results clearly indicate a more compact arrangement of molecules at the oil/water interface: this must be caused by the loss of the globular structure as a consequence of the denaturing action of the hexadecane.

Performance of the compensation comparison method for retinal straylight measurement: effect of patient's age on repeatability.

AIM: The assessment of repeatability and reproducibility of retinal straylight measurements with the C-Quant straylight meter (Oculus AG, Germany) and the effect of patient's age on the instrument performance are tested with a series of experiments. METHODS: First, 20 eyes from 20 subjects (mean age 26.9 (SD 2.7) years, mean refractive error -1.34 (2.72) D) were examined with the C-Quant straylightmeter, taking 10 consecutive readings. Five subjects were also examined on five consecutive days to assess reproducibility. Additionally, repeated measures of straylight from 84 subjects of ages ranging from 19 to 86 years (mean (SD): 42.4 (24.0) years) were retrospectively analysed to assess the effect of patient's age on repeatability. RESULTS: The results failed to show significant differences between the readings taken within the same session (mean (0.07), p>0.05) or between sessions (mean (0.05), p>0.05). Variability of intrasession measurements was not significant for subjects of different age (p = 0.094). CONCLUSION: It may be concluded that the C-Quant straylightmeter is repeatable and reliable for the assessment of retinal straylight in human eyes. Age of the patient does not decrease repeatability, even though they feel more insecure about their ability to perform the test.

First-line therapy with latanoprost 0.005% results in improved ocular circulation in newly diagnosed primary open-angle glaucoma patients: a prospective, 6-month, open-label study.

PURPOSE: To evaluate the effect of latanoprost 0.005% on the optic nerve head (ONH) and retinal circulation of newly diagnosed and previously untreated primary open-angle glaucoma (POAG) patients. METHODS: Twenty-two newly diagnosed and previously untreated POAG patients (mean age+/-SD: 68.38+/-11.92 years) were included in this longitudinal open-label study. Patients were treated with latanoprost 0.005% once a day. Intraocular pressure (IOP), systemic blood pressure (BP), mean ocular perfusion pressure (MOPP), and ocular perfusion parameters 'volume', 'velocity', and 'flow' measured at the optic nerve head (ONH) and retina by means of Heidelberg Retina Flowmeter system were evaluated during a 6-month follow-up period. RESULTS: Treatment with latanoprost 0.005% resulted in a significant decrease in IOP (P<0.0001) and increase in MOPP (P<0.0001). After correcting for changes in MOPP, the blood velocity measured at the ONH level was significantly higher after 6 months of treatment than at baseline (P=0.0310). In addition, blood volume and flow measured at the peripapillary retina level improved after 3 and 6 months of treatment (P=0.0170; P=0.0260, and P=0.0170; P=0.0240 respectively). CONCLUSION: Previously untreated POAG patients exhibit reduced IOP, increased MOPP and improved ocular perfusion at the ONH and retina levels when treated with Latanoprost 0.005%. These effects could be beneficial for glaucoma patients suffering from ocular vascular dysregulation.

Beneficial effects of small-incision cataract surgery in patients demonstrating reduced ocular blood flow characteristics.

PURPOSE: To investigate intraocular pressure (IOP) and ocular haemodynamics following small incision cataract surgery. METHODS: Systemic and ocular haemodynamics, and IOP, were measured pre-operatively and 1 month post-operatively, in 25 eyes of 25 patients (mean age 72.6+/-7.9 years) scheduled for small incision cataract surgery and intraocular lens implantation; these values were compared to an untreated age-matched healthy group (n=25, mean age 72.3+/-5.0 years). For each eye, the Ocular Blood Flow Analyser (OBFA, Paradigm Inc., UT, USA) was used to obtain measurements of IOP, pulsatile ocular blood flow (POBF), pulse volume (PV), ocular pulse amplitude (PA), and pulse rate (PR). Systemic blood pressure measurements were obtained at each visit. Pre- and post-operative values for the cataract group were compared using repeated measures analysis of variance, and compared to the normal group using analysis of variance. RESULTS: Pre-operatively, IOP was significantly higher in the cataract group compared to the age-matched normal control group (P<0.001). Cataract surgery resulted in a significant 16.7% reduction in IOP (P=0.001). Consequently, the post-operative IOP in the cataract group was similar to that of the normal group (P>0.05). Both pre- and post-operative POBF and PV values for the cataract group were significantly lower than for the normal age-matched group (P<0.0125). Small incision cataract surgery led to an 8.3% post-operative increase in POBF (P=0.0118) and 15.5% increase in PV (P<0.001). No changes in PA or PR were evident. CONCLUSION: These data suggest that cataract patients exhibit higher IOP and reduced ocular perfusion characteristics compared to an age-matched normal healthy group. Following cataract surgery, IOP reduced and ocular pulsatility improved.

Corneal pachymetry in normal and keratoconic eyes: Orbscan II versus ultrasound.

PURPOSE: To compare corneal thickness measurements using Orbscan II (OII) and ultrasonic (US) pachymetry in normal and in keratoconic eyes. SETTING: Eye Department, Heartlands and Solihull NHS Trust, Birmingham, United Kingdom. METHODS: Central corneal thickness (CCT) was measured by means of OII and US pachymetry in 1 eye of 72 normal subjects and 36 keratoconus patients. The apical corneal thickness (ACT) in keratoconus patients was also evaluated using each method. The mean of the difference, standard deviation (SD), and 95% limits of agreement (LoA = mean +/- 2 SD), with and without applying the default linear correction factor (LCF), were determined for each sample. The Student t test was used to identify significant differences between methods, and the correlation between methods was determined using the Pearson bivariate correlation. Bland-Altman analysis was performed to confirm that the results of the 2 instruments were clinically comparable. RESULTS: In normal eyes, the mean difference (+/- 95% LoA) in CCT was 1.04 microm +/- 68.52 (SD) (P>.05; r = 0.71) when the LCF was used and 46.73 +/- 75.40 microm (P =.0001; r = 0.71) without the LCF. In keratoconus patients, the mean difference (+/- 95% LoA) in CCT between methods was 42.46 +/- 66.56 microm (P<.0001: r = 0.85) with the LCF, and 2.51 +/- 73.00 microm (P>.05: r = 0.85) without the LCF. The mean difference (+/- 95% LoA) in ACT for this group was 49.24 +/- 60.88 microm (P<.0001: r = 0.89) with the LCF and 12.71 +/- 68.14 microm (P =.0077; r = 0.89) when the LCF was not used. CONCLUSIONS: This study suggests that OII and US pachymetry provide similar readings for CCT in normal subjects when an LCF is used. In keratoconus patients, OII provides a valid clinical tool for the noninvasive assessment of CCT when the LCF is not applied.

Ocular haemodynamic responses to induced hypercapnia and hyperoxia in glaucoma.

AIM: To determine the ocular haemodynamic response to gas perturbations in glaucoma. METHODS: Intraocular pressure (IOP), systemic systolic and diastolic blood pressure (SBP and DBP), and retrobulbar blood flow velocities, measured by colour Doppler imaging (CDI), were recorded at two visits. CDI was used to measure peak systolic and end diastolic velocities (PSV and EDV) and resistance index (RI) in the ophthalmic artery (OA), central retinal artery (CRA), and short posterior ciliary arteries (SPCAs). At the first visit, measurements were taken at baseline (B1: breathing room air) and during isoxic hypercapnia (end tidal PCO(2) increased 15% above baseline) in 16 normal subjects and 12 patients with glaucoma. On another day, measurements were repeated at a second baseline (B2) and during hyperoxia (100% oxygen breathing) for 15 normal subjects and 13 glaucoma patients. Baseline systemic data were compared using paired t tests; REANOVA was performed to compare group differences at baseline and to determine the vessel response to each condition. Fisher's LSD was used for post hoc comparison. RESULTS: Baseline OA PSV was lower for the glaucoma than for the normal group (p = 0.047); the groups were otherwise similar at baseline. IOP demonstrated no response to hypercapnia, but reduced during hyperoxia for both the normal subjects (p<0.0001) and glaucoma patients (p = 0.04). During hypercapnia, SBP increased in normal subjects (p = 0.03) and glaucoma patients (p = 0.01); DBP increased in normal subjects (p = 0.021). There was a corresponding increase in ocular perfusion pressure (OPP) for normal subjects (p = 0.01) and glaucoma subjects (p = 0.028), and as a result OPP was included as a covariate in the REANCOVA model. Hypercapnia resulted in increased PSV in the CRA of normal subjects (p = 0.035) and increased PSV and EDV in the SPCAs of glaucoma patients (p = 0.041 and p = 0.030 respectively). Hyperoxia resulted in reduced PSV and EDV in the ophthalmic arteries of normal subjects only (p = 0.001 and 0.031 respectively). CONCLUSIONS: These findings suggest the presence of relative vasoconstriction in glaucoma patients, which is at least partially reversed by hypercapnia.

Contrast sensitivity improves after brimonidine therapy in primary open angle glaucoma: a case for neuroprotection.

AIMS: To determine the visual outcome following initiation of brimonidine therapy in glaucoma. METHODS: 16 newly diagnosed previously untreated glaucoma patients were randomly assigned to either timolol 0.5% or brimonidine 0.2%. Visual acuity, contrast sensitivity (CS), visual fields, intraocular pressure (IOP), blood pressure, and heart rate were evaluated at baseline and after 3 months. RESULTS: IOP reduction was similar for both groups (p<0.05). Brimonidine improved CS; in the right eye at 6 and 12 cpd (p=0.043, p=0.017); in the left eye at 3 and 12 cpd (p=0.044, p=0.046). Timolol reduced CS at 18 cpd in the right eye (p=0.041). There was no change in any other measured parameters. CONCLUSION: Glaucoma patients exhibit improved CS on initiation of brimonidine therapy.

Epilepsy patients treated with vigabatrin exhibit reduced ocular blood flow.

BACKGROUND/AIM: Reduced cerebral blood flow and decreased glucose metabolism have been identified in epilepsy patients receiving vigabatrin. It is likely that such a change may extend to the eye and may be linked to previously reported irreversible visual field defects. The aim of this study was to determine whether patients who have undergone anti-epileptic drug (AED) therapy with vigabatrin have altered ocular haemodynamics. METHODS: The study cohort comprised 11 normal subjects (mean age 42.6 (SD 12.7) years and 17 epilepsy patients, of which 10 were either currently or previously treated with vigabatrin (38.6 (11.7) years) and seven were treated with AEDs excluding vigabatrin (46.0 (9.8) years). The three groups were matched at baseline for pulse rate, diastolic and systolic blood pressure, and intraocular pressure (IOP). At a single visit, the ocular blood flow analyser (OBFA; Paradigm Medical Instruments Inc, UT, USA) was used to measure pulsatile ocular blood flow (POBF) and pulse amplitude (PA) in each eye of all subjects. One way ANCOVA (with age as a covariate) was used to identify differences in POBF and PA between the groups. For the vigabatrin group only, Pearson's product moment correlation coefficient was used to explore potential interactions between ocular blood flow parameters and cumulative vigabatrin dose, duration, and maximum dose. RESULTS: Both the vigabatrin treated epilepsy group and conventionally treated epilepsy group exhibited significantly reduced POBF (p=<0.001, p=0.040) and PA (p=<0.001, p=0.005) compared to normal subjects. Patients treated with vigabatrin exhibited a further reduction in POBF (p=0.046) and PA (p=0.034) compared to conventionally treated epilepsy patients. No significant correlations were found between drug dosage and POBF and PA for the vigabatrin treated epilepsy group. CONCLUSIONS: A significant reduction in POBF and PA is apparent in epilepsy patients treated with AEDs when compared to normal subjects. A further reduction in POBF and PA is apparent between vigabatrin treated and conventionally treated patients. The reduction in ocular perfusion, which is more pronounced in patients previously treated with vigabatrin, may have implications in the impairment of visual function associated with the drug.

Effect of senescence on ocular blood flow in the retina, neuroretinal rim and lamina cribrosa, using scanning laser Doppler flowmetry.

PURPOSE: To determine the effects of age on blood flow measurements obtained using the scanning laser Doppler flowmeter (SLDF). METHOD: Using SLDF (Heidelberg retina flowmeter, Heidelberg Engineering, Germany) three 10 degrees images were taken of the superior temporal retina and three further images of the superior temporal neuroretinal rim in 15 young, healthy subjects (mean age 27.9 years +/- 6.2 years) and 15 mature, healthy subjects (mean age 65.2 years +/- 13.7 years). In addition, measurements were taken of the lamina cribrosa in 12 of the volunteers from each subject group (mean age 27.1 +/- 6.3 years and 64.8 +/- 13.2 years respectively). Using a 10 x 10 pixel measurement frame, blood flow readings were obtained at a predetermined position on the retina, neuroretinal rim and lamina cribrosa. Student's two-tailed unpaired t-tests were used to compare measures of blood flow, volume and velocity between the two subject groups (P < 0.05). In addition, linear regression analysis was used to assess the relationship between age and blood flow, volume and velocity at the retina, neuroretinal rim and lamina cribrosa. RESULTS: Retinal blood volume measured at the retina was significantly lower in the mature compared with the young subject group (P = 0.01). Mature subjects also exhibited reduced blood flow and velocity at the neuroretinal rim (P = 0.01 for both parameters) and lamina cribrosa (P = 0.008 and P = 0.01 respectively). Regression analysis revealed negative trends for all blood flow parameters in each of the anatomical areas with advancing age. Significant negative correlations were obtained for retinal blood volume (r = -0.455, P < 0.05), neuroretinal rim blood velocity (r = -0.359, P < 0.05) and lamina cribrosa blood volume (r = -0.475, P < 0.05). CONCLUSION: Capillary blood flow in the retina, neuroretinal rim and lamina cribrosa decreases with advancing age. This may be of consequence in the progression of chronic ocular diseases such as glaucoma, and should be considered in the longitudinal determination of change in disease monitoring.

Application of a local search strategy improves the detection of blood flow deficits in the neuroretinal rim of glaucoma patients using scanning laser Doppler flowmetry.

BACKGROUND/AIM: Blood flow measures acquired using the scanning laser Doppler flowmeter (SLDF) are known to be highly susceptible to spatial and temporal variations of physiological origin. The purpose of this study was to evaluate a local search strategy intended to overcome these intrinsic variations, thereby improving the detection of blood flow defects resulting from glaucoma. METHODS: The sample consisted of one eye of each of 15 glaucoma patients (aged 69.1 (SD 6.6) years) and 15 normal subjects (aged 65.2 (13.7) years). Three 10 degree images of the superior temporal retina and three images of the superior temporal rim were acquired using the Heidelberg retina flowmeter (HRF). Standard analysis was performed using a 10 x 10 pixel frame. For the search strategy the same frame was located within a 15 x 15 pixel window and manually repositioned in order to identify the highest and lowest local values of blood flow. Student's paired t test was used to identify differences between groups for the two methods (p<0.05). RESULTS: The standard strategy revealed no significant differences in blood flow measures between the subjects at either the retina or neuroretinal rim. With the search strategy there was also no difference in blood flow measures at the retina. At the neuroretinal rim, the search strategy demonstrated that the highest measured blood flow, volume, and velocity values were significantly lower for the glaucoma patients (p = 0.002, 0.02, and 0.002 respectively) while comparison of the lowest flow values showed that glaucoma patients had lower blood flow and velocity only (p = 0.023 and 0.021 respectively). CONCLUSIONS: Glaucoma patients exhibit reduced ocular blood flow at the neuroretinal rim, which seems to affect high velocity flow more profoundly than low velocity flow. When analysing perfusion images a local search strategy is recommend to identify the highest local blood flow values in order to optimise the ability to differentiate between subject groups.

Hypercapnia invokes an acute loss of contrast sensitivity in untreated glaucoma patients.

BACKGROUND/AIM: It is widely accepted that hypercapnia results in increased retinal, choroidal, and retrobulbar blood flow. Reports of a visual response to hypercapnia appear mixed, with normal subjects exhibiting reduced temporal contrast sensitivity in some studies, while glaucoma patients demonstrate mid-peripheral visual field improvements in others. This suggests that under hypercapnic conditions a balance exists between the beneficial effects of improved ocular blood flow and some other factor such as induced metabolic stress; the outcome may be influenced by the disease process. The aim of this study was to evaluate the contrast sensitivity response of untreated glaucoma patients and normal subjects during mild hypercapnia. METHODS: 10 previously untreated glaucoma patients and 10 control subjects were evaluated for contrast sensitivity and intraocular pressure while breathing room air and then again during mild hypercapnia. RESULTS: During room air breathing, compared with normal subjects, glaucoma patients had higher IOP (p = 0.0003) and lower contrast sensitivity at 3 cycles/degree (cpd) (p = 0.001). Mild hypercapnia caused a significant fall in contrast sensitivity at 6, 12, and 18 cpd (p < 0.05), only in the glaucoma group. CONCLUSION: Glaucoma patients with early disease exhibit central vision deficits as shown by contrast sensitivity testing at 3 cpd. Hypercapnia induces further contrast loss through a range of spatial frequencies (6-18 cpd) which may be predictive of further neuronal damage due to glaucoma.

Detector sensitivity influences blood flow sampling in scanning laser Doppler flowmetry.

PURPOSE: To establish the effect of photodiode sensitivity on the DC (brightness) value and the resultant blood flow measurements of retina and rim tissue using a scanning laser Doppler flowmeter (SLDF). METHODS: The sample consisted of one eye of each of 15 healthy subjects (mean age 27.8 +/- 6.1 years). Using the Heidelberg Retina Flowmeter (HRF), three 10-deg images of the superior temporal retina and three further images of the superior temporal rim were acquired for each of five DC bands: band 1: 30-70; band 2: 70-110; band 3: 110-150; band 4 150-190; band 5: 190-230. Retinal blood volume, flow and velocity were determined for each image using a 10 x 10 pixel square grid located at a predetermined location on the retina and rim for each subject. Following image acquisition, the DC values corresponding to each pre-assigned retinal or rim location were determined. The mean and standard deviation were determined for the blood flow parameters within each DC band for each subject in both locations. Analysis of variance was used to identify significant change in the data as a function of the DC value (P<0.05). RESULTS: Analysis of variance revealed that retinal blood flow measures acquired within DC band 5 resulted in significantly lower measures of blood flow and velocity (P=0.035 and P=0.049 respectively) than at lower DC values. Band 5 values of flow, volume and velocity in the neuroretinal rim were also significantly low (P=0.016, P= 0.003 and P=0.026 respectively). Peak neuroretinal rim blood flow was recorded when the DC value was between 70 and 110. For blood flow measurement at the retina and neuroretinal rim the DC value should not exceed 190. CONCLUSION: Photodiode sensitivity as indicated by the DC value affects measurements of ocular blood flow using the HRF.

Long-term fluctuation in short-wavelength automated perimetry in glaucoma suspects and glaucoma patients.

PURPOSE: To determine the magnitude of the homogeneous, LF(Ho), and the heterogeneous, LF(He), components of the long-term fluctuation (LF) in glaucoma suspects and in stable primary open angle glaucoma (POAG) patients undergoing short-wavelength automated perimetry (SWAP) and to compare the magnitude of the SWAP LF components with those elicited by standard white-on-white (W-W) perimetry. METHODS: The sample comprised 33 glaucoma suspects and 17 patients with early-to-moderate stable POAG who underwent W-W perimetry and SWAP at each of six visits over a mean period of 12.75 months (SD, 2.29). The LF(Ho), LF(He), and error components of the long-term fluctuation were determined between the third and seventh visual field examinations. The intervening visual field examinations and the optic nerve head parameters, derived both by stereo observation and by the Heidelberg Retinal Tomograph, were used to confirm stability over the follow-up period. RESULTS: The LF(Ho) and LF(He) components were larger in the POAG patients than in the glaucoma suspects for both W-W perimetry and SWAP; the magnitude was independent of the depth of defect and of the short-term fluctuation. All three components of long-term fluctuation were greater for SWAP than for W-W perimetry, both in the glaucoma suspects and in the POAG patients. CONCLUSIONS: SWAP exhibits greater long-term fluctuation than white-on-white perimetry. The usefulness of SWAP will be limited if the extent of this variability is not overcome in future statistical procedures developed to detect progressive visual field loss.

The influence of contour line size and location on the reproducibility of topographic measurement with the Heidelberg Retina Tomograph.

BACKGROUND: The recommended contour line (CL) location with the Heidelberg Retina Tomograph (HRT) is on the inner edge of Elschnig's scleral ring. This study investigated HRT parameter reproducibility when: (i) the CL size is altered relative to Elschnig's ring; (ii) the CL is either redrawn or imported between images. METHODS: Using the HRT, seven 10 degrees images were acquired for 10 normal volunteers and 10 primary open angle glaucoma (POAG) subjects. A CL was drawn on one image for each subject using Elschnig's scleral ring for reference and imported into subsequent images. The CL diameter was then (a) increased by 50 microns; (b) increased by 100 microns; and (c) decreased by 50 microns. To investigate the effect of the method of contour line transfer between images a CL was: (1) defined for one image and imported to 6 subsequent images; (2) drawn separately for each image. RESULTS: Parameter variability improved as the size of the CL increased for the normal group relative to Elschnig's ring but was unchanged in the POAG group. The export/import function (method 1) resulted in better parameter reproducibility than the redrawing method for both groups. CONCLUSIONS: The exporting and importing function resulted in better parameter variability for both subject groups and should be used for transferring CLs across images for the same subject. Increasing the overall CL size relative to Elschnig's scleral ring improved the reproducibility of the measured parameters in the normal group. No significant difference in parameter variability was observed for the POAG group. This suggests that the reproducibility of HRT images are affected more by the variation in topography between images than change in CL definition.

Regional differences in retinal vascular reactivity.

PURPOSE: Although glaucomatous visual field defects are more common in the superior field than in the inferior field, microaneurysms are more frequent in the superior than in the inferior retina in diabetic retinopathy. The authors hypothesized that differences in vascular hemodynamics in the two areas might contribute to these phenomena. METHODS: The blood flow response to hyperoxia and hypercapnia was evaluated in peripapillary retinal tissue superior and inferior to the optic nerve head using confocal scanning laser Doppler flowmetry. In 14 young, healthy persons, blood flow was measured while breathing room air and during isocapnic hyperoxia (100% O2 breathing) and isoxic hypercapnia (PCO2 increased 15% above baseline). Histograms were generated from pixel-by-pixel analysis of retinal portions of superior and inferior temporal quadrants of the entire image. RESULTS: Baseline blood flow in the inferior temporal quadrant was significantly greater than in the superior temporal quadrant (P < 0.05). However, the inferior region failed to increase in perfusion during hypercapnia and experienced significant mean blood flow reduction; flow reduction in the pixels at the 25th, 50th, 75th, and 90th percentile of flow; and an increased percentage of pixels without measurable flow, during hyperoxia (each P < 0.05). In contrast, in the superior temporal region, hyperoxia failed to reduce blood volume, velocity, or flow, whereas hypercapnia significantly increased mean flow; increased flow in the pixels at the 25th, 50th, 75th, and 90th percentile of flow; and reduced the percentage of pixels without measurable flow (each P < 0.05). CONCLUSIONS: The inferior temporal quadrant of the peripapillary retina is, in comparison with the superior temporas region, less responsive to vasodilation and more responsive to vasoconstriction. These differences could contribute to different susceptibility to visual field defect or vascular dysfunction in the superior and inferior retina.

Comprehensive assessment of retinal, choroidal and retrobulbar haemodynamics during blood gas perturbation.

BACKGROUND: A study was performed to evaluate the effect of isoxic hypercapnia on ocular haemodynamics using colour Doppler imaging (CDI), scanning laser Doppler flowmetry (SLDF) and ocular blood flow (OBF) tonography. METHODS: Measurements were taken for one eye of each of 14 healthy subjects (mean age 27 +/- 6 years) during breathing of room air and then during isoxic hypercapnia (breathing CO2 and room air). Using CDI, blood flow velocities and resistance indices were determined for the ophthalmic artery (OA), central retinal artery (CRA) and short posterior ciliary arteries (SPCAs). Using SLDF a 10 x 10 pixel frame was used to measure blood flow, volume and velocity in each quadrant of the peripapillary retina. Pulsatile ocular blood flow (POBF) was measured using the OBF tonograph. RESULTS: Using CDI, peak systolic and end diastolic velocities increased and resistance index decreased significantly in the SPCAs during hypercapnia. Using SLDF, blood flow, volume and velocity increased significantly during hypercapnia in the superior temporal quadrant of the peripapillary retina. No significant difference was observed between baseline and hypercapnia for POBF. CONCLUSIONS: Isoxic hypercapnia resulted in an increase in peripapillary retinal and SPCA blood flow parameters as determined by SLDF and CDI respectively. This implies the presence of autoregulatory activity in these vasculatures. These findings may be of significance in the pathogenesis of ocular disease such as glaucoma where autoregulation is thought to be compromised.