There is more to accommodation of the eye than simply minimizing retinal blur.

Eyes of children and young adults change their optical power to focus nearby objects at the retina. But does accommodation function by trial and error to minimize blur and maximize contrast as is generally accepted? Three experiments in monocular and monochromatic vision were performed under two conditions while aberrations were being corrected. In the first condition, feedback was available to the eye from both optical vergence and optical blur. In the second, feedback was only available from target blur. Accommodation was less precise for the second condition, suggesting that it is more than a trial-and-error function. Optical vergence itself seems to be an important cue for accommodation.

Accommodation and the Stiles-Crawford effect: theory and a case study.

PURPOSE: Fincham (The accommodation reflex and its stimulus. Br. J. Ophthalmol. 35, 381-393) was the first to suggest that the Stiles-Crawford effect (Type I) might provide a stimulus for accommodation, but the possibility has not been investigated experimentally. The present paper outlines a theoretical basis for such a mechanism, and includes a case study on a subject with a nasally decentred Stiles-Crawford (S-C) function. METHODS: Accommodation to a monochromatic sine grating was monitored continuously with the natural S-C function intact, or with apodising filters imaged in the subject's pupil to neutralise, reverse or double the natural S-C function. RESULTS: Mean accommodative gain was not reduced significantly when the normal S-C function was either neutralised or reversed. CONCLUSIONS: For the present subject, the average S-C effect does not mediate the accommodation response to defocus, but more subjects should be examined. Other methods by which directionally sensitive cone receptors could detect light vergence are discussed.

Isolated short-wavelength sensitive cones can mediate a reflex accommodation response.

Both long- and middle-wavelength sensitive cones mediate the reflex accommodation signal but the contribution from the short-wavelength sensitive cones is unknown. A short-wavelength sensitive cone contribution could extend the range of the signed defocus signal from chromatic aberration. The aim was to determine whether isolated short-wavelength sensitive cones mediate reflex accommodation independently of long- and middle-wavelength sensitive cones. Accommodation was monitored continuously (eight subjects) to a sine-wave grating (3 cpd; 0.53 contrast) moving with a sum of sines motion in a Badal optometer. Two illumination conditions were used: a 'blue' condition that isolated short-wavelength sensitive cones, and a 'white' control condition that stimulated all three cone types. Of the eight subjects, two responded equally in the 'white' and 'blue' condition, four gave reduced responses in the 'blue' condition and two failed to respond in both conditions. The mean response in the 'blue' condition was reduced by 50% compared to the 'white' condition. Further analysis indicated that four of the eight subjects gave responses that were considerably greater than noise (S.D.>1.82) when short-wavelength sensitive cones were isolated. Some subjects can accommodate using only S-cones.

Accommodation to static chromatic simulations of blurred retinal images.

The eye's longitudinal chromatic aberration (LCA) is known to drive 'reflex' accommodation to moving objects, but the evidence is not as clear for stationary objects. The present study examined whether accommodation can be driven by static simulations of the effects of defocus and LCA. Accommodation was recorded continuously while each of 12 subjects viewed images (through a 0.75 mm pinhole) that simulated the appearances of blurred sine wave gratings (3.9 c.p.d.). In two experimental conditions, an eye with normal LCA was assumed and defocus of +1 D or -1 D was simulated. In a control condition, an eye with neutralised LCA was assumed and target defocus of 1 D was simulated. Subjects' accommodation responses were consistent with the hypothesis that LCA provides a stimulus to accommodation. Chromatic aberration drives accommodation to both moving and stationary objects, and thus is an important stimulus for accommodation in everyday situations. The study findings are discussed in relation to colour vision, visual display terminals and emmetropization.

Accommodation without feedback suggests directional signals specify ocular focus.

Accommodation was monitored continuously under open-loop conditions while subjects viewed a sinusoidally oscillating sine-wave grating (0.2 Hz; +/- 1 D; 2.7 c/d; 0.56 contrast) in a Badal optometer. The target was illuminated by monochromatic light (590 nm) or white light (3000 K) with longitudinal chromatic aberration (LCA) normal, doubled, neutralized and reversed. Subjects (12) accommodated well in white light with LCA normal and doubled (mean gains = 0.85 and 0.94), gain was reduced in the neutralized condition (0.54), in monochromatic light (0.43), and especially when LCA was reversed (0.30). The results suggest that accommodation responds to changes in the relative contrast of spectral components of the retinal image and perhaps to the vergence of light.

Accommodation to stationary and moving targets.

PURPOSE: To test the hypothesis that the contrast of spectral components of the retinal image specifies ocular focus and controls reflex accommodation. METHODS: Eight subjects viewed a stationary target at 0, 2.5, and 5 D in a Badal optometer, with longitudinal chromatic aberration (LCA) normal and reversed and in monochromatic (550 nm) light. Accommodation was monitored continuously during 40-s trials. Subjects also viewed the grating target as it moved sinusoidally (1.5 to 2.5 D) at 0.2 Hz under the same three conditions. RESULTS: Subjects accommodated relatively accurately at all distances in the normal condition; three subjects had difficulty accommodating in monochromatic light at 5 or 0 D, and seven subjects could not maintain focus with LCA reversed. The accommodative response differed significantly in the three chromatic conditions both for stationary and moving targets. CONCLUSIONS: Relative contrast of long-, middle-, and short-wavelength components of the retinal image specifies ocular focus and drives reflex accommodation.

Inhibitory effect of di-catechol rooperol on VCAM-1 and iNOS expression in cytokine-stimulated endothelium.

Induced expression of vascular cell adhesion molecule-1 (VCAM-1) and of nitric oxide synthase (iNOS) is believed to play a role in the pathogenesis of atherosclerosis, asthma, as well as other inflammatory disorders. In the current study we examined the effect of the di-catechol rooperol [(E)-1,5-bis (3',4'-dihydroxyphenyl) pent-4-en-1-yne] on the process of microvascular endothelial cell (MME) activation by TNF-alpha and IFN-gamma. We show that rooperol decreases VCAM-1 and iNOS mRNA levels in cytokine-activated MME with subsequent inhibition of VCAM-1 membrane expression as measured by adhesion of P815 cells to MME monolayers, and NO production, as reflected in the nitrite concentration in culture medium. The properties of rooperol now described suggest that rooperol may be an anti-inflammatory agent useful in the treatment of several inflammatory disorders.

Cytokine production in human and rat macrophages and dicatechol rooperol and esters.

The ability of dicatechol rooperol and esters to inhibit the production of cytokines in endotoxin-stimulated human alveolar macrophages, human blood monocyte/macrophages, histiocytic cell line U937, and rat alveolar macrophages was examined in vitro. Rooperol derivatives inhibited the production of tumour necrosis factor-alpha, interleukin-1 beta and interleukin-6. Of the esters tested on human cells, rooperol diacetate and tetraacetate were more potent inhibitors of cytokine production (IC50 in the range of 10-20 microM) than rooperol disulphate (IC50 in the range of 25-75 microM). The acetate esters also inhibited cytokine production in rat alveolar macrophages, whereas the sulphate had little effect. Rooperol and acetate esters, in the same concentration range, decreased the production of nitric oxide by rat alveolar macrophages stimulated by endotoxin. These concentrations of rooperol had no effect on cell viability, as indicated by incorporation of 14C-labelled leucine into macrophage proteins and their content of lactate dehydrogenase. The results obtained suggest that rooperol esters are potentially useful antiinflammatory agents.

Pharmacokinetic behaviour and cardiovascular effects of intravenously administered hypoxoside and rooperol.

This study concerns the pharmacokinetic behaviour and cardiovascular effects of rapid infusions of hypoxoside (CAS 83643-94-1) and rooperol (CAS 83644-00-2) in anaesthetised Chacma baboons. Institutional approval was obtained and animal care conformed to international guidelines. Hypoxoside (500 mg) and rooperol (240 mg) dissolved in isotonic saline were infused during 15 min. Concentration-time data from high performance liquid chromatography of arterial blood samples were subjected to non-linear curve-fitting to obtain two-compartment mammillary pharmacokinetic models. Mean values were: [Table: see text] Hypoxoside was eliminated without significant metabolite formation and it revealed no cardiovascular effects. Rooperol was metabolized rapidly with formation of nine metabolites of which the major three were the diglucuronide, disulphate and mixed glucuronide sulphate. Rooperol caused moderate, transient increased cardiac output, stroke volume and vascular pressures without increased heart rate or filling pressures, suggestive of increased myocardial contractility probably allied to its catechol structure.

Accommodation to monochromatic and white-light targets.

PURPOSE: The objective of the current study was to compare accommodation to targets illuminated with monochromatic light from different regions of the visible spectrum with accommodation to white-light targets. METHODS: One of 10 marrow-band interference filters (430, 450, 470, 500, 530, 550, 570, 590, 630, and 670 nm) was used to produce monochromatic light from a tungsten-halogen source to illuminate a Maltese cross-target in Maxwellian view. Luminance of each monochromatic light was matched by minimum border photometry against a standard white light (3000 K) that was maintained at 200 cd/m2. Chromatic difference of focus of the eye was minimized for all monochromatic targets by the use of an achromatizing lens. A white-light target also was used, and the subject's eye was achromatized or the eye had normal chromatic aberration. The target was moved sinusoidally toward and away from the eye at a temporal frequency of 0.2 Hz over a 1 D amplitude (peak to peak). Accommodation was monitored continuously by an infrared recording optometer, and responses were Fourier analyzed to obtain gain and phase lag at the temporal frequency of stimulation. RESULTS: Accommodative gain was highest and phase lag was smallest when the target was illuminated by white light in the presence of normal chromatic aberration. The achromatized white-light gain of accommodation was statistically similar to the gain for monochromatic targets, indicating that the presence of chromatic aberration facilitates accommodation. Significant intersubject variability was present in the accommodative tracking ability to monochromatic targets. CONCLUSIONS: Accommodation to monochromatic targets is not as accurate as accommodation to a white-light target, and this effect is related to the presence of ocular longitudinal chromatic aberration for the white-light target.

Small amounts of chromatic aberration influence dynamic accommodation.

The prevailing view of accommodation is that the eye changes focus to maximize luminance contrast by trial and error. Negative feedback is considered essential in this view because luminance contrast provides no directional information. Fincham proposed an alternate view in which longitudinal (axial) chromatic aberration (LCA) provides a directional stimulus for accommodation. For spatial frequencies above approximately 0.5 cpd contrast of the retinal image is different for long, middle, and short spectral waveband components of the image. We varied the amount of LCA in small steps (0.25 D) to determine how much LCA is needed to enhance or impair the response. An infrared optometer monitored accommodation continuously while subjects viewed a yellow/black square-wave grating (3.5 cpd) in a Badal stimulus system. The yellow/black grating was produced by superimposing red (600 nm) and green (520 nm) gratings, and LCA was increased, decreased, neutralized, and reversed by repositioning the red grating component along the axis of the optical system. Target vergence was modulated sinusoidally (0.2 Hz) over a 1 D range (1.5 to 2.5 D) and gain and phase-lag of the accommodation response were determined by Fourier analysis. Subjects accommodated well as long as a normal amount of LCA was present--0.5 D in the correct direction enhanced accommodative gain, and 0.25 D in the reverse direction markedly inhibited the response. We conclude that the contrast of the retinal image in different spectral wavebands specifies focus of the eye, and provides a powerful directional stimulus for reflex accommodation.

Morphological characterisation of the cell-growth inhibitory activity of rooperol and pharmacokinetic aspects of hypoxoside as an oral prodrug for cancer therapy.

Hypoxoside is the major diglucoside isolated from the corms of the plant family Hypoxidaceae. It contains an unusual E-pent-1-en-4-yne 5-carbon bridging unit with two distal catechol groups to which the glucose moieties are attached. It is non-toxic for BL6 mouse melanoma cells in tissue culture on condition that the fetal calf serum in the medium is heat-inactivated for 1 hour at 56 degrees C in order to destroy endogenous beta-glucosidase activity. The latter catalyses hypoxoside conversion to its cytotoxic aglucone, rooperol, which, when tested as a pure chemical, caused 50% inhibition of BL6 melanoma cell growth at 10 micrograms/ml. Light and electron microscopy revealed that the cytotoxic effect of rooperol manifested as vacuolisation of the cytoplasm and formation of pores in the plasma membrane. Indications of apoptosis were also found. Pharmacokinetic studies on mice dosed intragastrically with hypoxoside showed that it was deconjugated by bacterial beta-glucosidase to form rooperol in the colon. Surprisingly, no hypoxoside or rooperol was detectable in the serum. Only phase II biotransformation products (sulphates and glucuronides) were present in the portal blood and bile. In contrast, however, in human serum after oral ingestion of hypoxoside, the metabolites can reach relatively high concentrations. Rooperol metabolites isolated from human urine were non-toxic for BL6 melanoma cells in culture up to a concentration of 200 micrograms/ml. In the presence of beta-glucuronidase, which released rooperol from the metabolites, 50% growth inhibition was achieved at a 75 micrograms/ml metabolite concentration. The supernatant of a human melanoma homogenate could also cause deconjugation of the metabolites to form rooperol.(ABSTRACT TRUNCATED AT 250 WORDS)

The pharmacokinetic behaviour of hypoxoside taken orally by patients with lung cancer in a phase I trial.

OBJECTIVE: To study the pharmacokinetic behaviour of hypoxoside taken orally by 24 patients with lung cancer. DESIGN: Randomised open study with three single doses of 1,600, 2,400 and 3,200 mg standardised Hypoxis plant extract (200 mg capsules) and a multiple-dose study on the first 6 patients taking 4 capsules 3 times daily for 11 days. PARTICIPANTS AND SETTING: Patients with histologically proven squamous, large-cell or adenocarcinoma were hospitalised at the Radiation Oncology Ward, Karl Bremer Hospital, Bellville, W. Cape. METHODS: Blood was drawn at regular intervals up to 75 hours after single doses and the concentrations of metabolites of the aglucone of hypoxoside, rooperol, were measured with a high-performance liquid chromatography method. For the multiple-dose study blood was drawn before the first dose each day. Concentration-time relationships were analysed according to a conventional single open-compartment model and also by using the NONMEM digital computer programme. RESULTS: Neither hypoxoside nor rooperol appear in circulation. This is due to complete phase II biotransformation to diglucuronide, disulphate and mixed glucuronide-sulphate metabolites, of which the latter is the major component. Considerable interpatient variation in concentration-time relationships was found in the single-dose studies. It was due to an active enterohepatic recirculation in some patients and a distinct lag phase in others together with zero-order rate of formation of rooperol in the colon. Computer modelling indicated a single open-compartment model in which the mass of the patient did not influence volume of distribution and clearance because formation of the metabolites is dependent on the metabolising capacity of the patient. However, the elimination of the metabolites follows first-order kinetics with half-lives ranging from 50 hours for the major metabolite to 20 hours for the two minor metabolites. Multiple-dose studies also showed large interpatient variation. CONCLUSION: In order to reach metabolite levels near 100 micrograms/ml, which have been shown to be tumouricidal after enzymatic deconjugation to rooperol, maintenance doses need to be individualised for each patient. For most patients, however, a daily dose of 2,400 mg was sufficient.

A phase I trial of hypoxoside as an oral prodrug for cancer therapy--absence of toxicity.

OBJECTIVE: To assess the toxicity of hypoxoside taken orally by 24 patients with lung cancer. DESIGN: Open study with patients taking 1,200-3,200 mg standardised Hypoxis plant extract (200 mg capsules) per day divided in 3 doses in order to maintain metabolite blood levels near 100 micrograms/ml. PARTICIPANTS AND SETTING: Patients with histologically proven squamous, large-cell or adenocarcinoma were hospitalised initially at the radiation oncology ward, Karl Bremer Hospital, Bellville, W. Cape. Thereafter they returned every 2 weeks for full clinical examinations. METHODS: Routine biochemical and haematological measurements were done. Patients underwent regular full clinical examinations including radiographs and computed tomography scanning according to the discretion of the principal investigator. RESULTS: Nineteen patients on hypoxoside therapy survived for an average of 4 months with progression of their primary tumours and metastases, while 5 survived for more than a year. One of them survived for 5 years and histological examination of the primary lesion showed absence of cancer. No toxic effects, in clinical examinations or biochemical or haematological measurements, were found that could be ascribed to the ingestion of hypoxoside. Only one occasion of possible drug intolerance, with anxiety, nausea, vomiting and diarrhoea, was noted. CONCLUSION: The absence of toxicity warrants further investigation of hypoxoside as an oral prodrug, especially in patients with slow-growing necrotising tumours that are inoperable and have high concentrations of beta-glucuronidase and sulphatase as well as a high sensitivity for rooperol.

Accommodation responds to changing contrast of long, middle and short spectral-waveband components of the retinal image.

We simulated the effects of longitudinal (axial) chromatic aberration and defocus on contrast of the long-, middle- and short-wavelength components of the retinal image to determine whether the effects of chromatic aberration are sufficient to drive accommodation. Accommodation was monitored continuously while subjects (12) viewed a 3 c/deg white sine-wave grating (0.92 contrast) in a Badal stimulus system. The contrasts (amplitudes) of the red, green and blue components of the white grating changed independently to simulate a grating oscillating from 1 D behind the retina to 1 D in front of the retina at 0.2 Hz. Subjects responded strongly to the chromatic simulation but poorly to a luminance control. The results support the hypothesis that focus is specified by the contrast of spectral-wavebands of the retinal image, and that conventional color mechanisms, monitoring chromatic contrast at luminance borders (1-8 c/deg), mediate the signals that specify dioptric vergence.

Spectral bandwidth and ocular accommodation.

Previous studies have suggested that targets illuminated by monochromatic (narrow-band) light are less effective in stimulating the eye to change its focus than are black-white (broadband) targets. The present study investigates the influence of target spectral bandwidth on the dynamic accommodation response in eight subjects. The fixation target was a 3.5-cycle/deg square-wave grating illuminated by midspectral light of various bandwidths [10, 40, and 80 nm and white (CIE Illuminant B)]. The target was moved sinusoidally toward and away from the eye, and accommodation responses were recorded and Fourier analyzed. Accommodative gain increases, and phase lag decreases, with increasing spectral bandwidth. Thus the eye focuses more accurately on targets of wider spectral bandwidth. The visual system appears to have the ability to analyze polychromatic blur to determine the state of focus of the eye for the purpose of guiding the accommodation response.

Studies on hypoxoside and rooperol analogues from Hypoxis rooperi and Hypoxis latifolia and their biotransformation in man by using high-performance liquid chromatography with in-line sorption enrichment and diode-array detection.

Methanol extracts of the corms of Hypoxis rooperi and H. latifolia were studied for their hypoxoside content by an in-line sorption enrichment HPLC technique [Kruger et al., J. Chromatogr., 612 (1993) 191]. Hypoxoside is the trivial name for (E)-1,5-bis(3'-hydroxy-4'-O-beta-D-glucopyranosyl-phenyl) pent-1-en-4-yne and rooperol the aglucone obtained from beta-glucosidase treatment. Hypoxoside and rooperol analogues containing 4, 3 and 2 hydroxyl groups resolved as separate peaks with the proportion of the latter two markedly higher in H. latifolia than in H. rooperi. After oral ingestion of hypoxoside by humans, no hypoxoside or rooperol appeared in the serum. Only rooperol was present in the faeces. The serum and urine contained at least three phase II metabolite peaks. Selective enzyme hydrolysis showed that they represent the diglucuronide, disulfate and glucuronide-sulfate conjugates of all three rooperol analogues.

Spatiotemporal transfer function of human accommodation.

We have investigated the spatiotemporal transfer function of human "reflex" accommodation. An accommodative mechanism that is sensitive to an intermediate temporal rate of retinal image contrast change is proposed as the basis of the fine focus control hypothesis. To test the proposed mechanism accommodative responses were monitored by a dynamic infrared optometer while the subject focused on sinusoidal gratings (0.98-10.5 c/deg) which were moving sinusoidally at temporal frequencies in the range of 0.05-0.80 Hz over a 0.50 or 2.00 D peak-to-peak amplitude. The accommodative responses were best at 3 and 5 c/deg at both amplitudes of target motion. This result does not support the proposed mechanism or the fine focus control hypothesis for "reflex" accommodation. Fitting the data with first-order response functions showed little evidence of prediction. In addition, a second experiment found that the profile of the accommodative gain function is not altered by instruction at spatial frequencies above 5 c/deg in this type of dynamic accommodation experiment. The use of sinusoidally moving accommodative blur targets, particularly with careful instruction, seems to discourage voluntary accommodation in investigations of "reflex" control mechanisms of accommodation.

beta-Glucosidase activity in fetal bovine serum renders the plant glucoside, hypoxoside, cytotoxic toward B16-F10-BL-6 mouse melanoma cells.

By using p-nitrophenyl-beta-D-glucopyranoside as substrate, beta-glucosidase activity was observed in fetal bovine serum (FBS). This activity could be inhibited by heat inactivation of the serum. Gel chromatography of FBS indicated the presence of beta-glucosidase activity with an apparent molecular mass of 29 kDa. In McCoy's 5A medium supplemented with non-heat inactivated FBS, the diglucoside hypoxoside ([E]-1,5-bis[4'beta-D-glucopyranosyloxy-3'-hydroxyphenyl]pent-4-en - 1-yne) showed cytotoxicity toward B16-F10-BL-6 mouse melanoma cells. In incubations where the media were supplemented with FBS previously heat inactivated at 56 degrees C for 1 h or more, no cytotoxicity was observed in the presence of hypoxoside. The aglucone of hypoxoside, rooperol ([E]-1,5-bis[3',4'-dihydroxyphenyl]pent-4-en-1-yne), showed cytotoxicity regardless of whether the serum was heat inactivated or not. The kinetics of the heat inactivation of the beta-glucosidase activity in FBS coincided with the loss of apparent cytotoxicity of hypoxoside. High performance liquid chromatography analysis showed that rooperol could be generated by incubation of hypoxoside in non-heat inactivated FBS, but that this ability was lost in serum that was heat inactivated for 1 h or longer. Newborn bovine serum did not contain any beta-glucosidase activity whereas it was found in three different commercial sources of FBS. This observation is of practical importance because conventional heat inactivation of FBS at 56 degrees C for 30 min was not sufficient to inactivate the beta-glucosidase activity completely.

Therapeutic monitoring of antituberculosis drugs by direct in-line extraction on a high-performance liquid chromatography system.

A direct in-line pre-column extraction technique in which guanidinium and ammonium sulfate are used, followed by column switching, was employed to analyze serum, plasma and cerebrospinal fluid samples of patients treated for tuberculous meningitis. Resolution of a wide range of polar to non-polar xenobiotics was obtained on a C8 silica column by using a linear gradient from a binary system consisting of solvent A (0.05 M KH2PO4) and solvent B (acetonitrile-isopropanol, 4:1, v/v). Apart from the antituberculosis drugs (isoniazid, pyrazinamide, ethionamide and rifampicin) the patients received up to sixteen different medicines for prevention of complications and the treatment of symptoms. Qualitative resolution of all the drugs was obtained by the chromatographic system. Quantitation of pyrazinamide and ethionamide was achieved with high precision and low inter-sample variation.