The secretory phenotypes of envenomed cells: Insights into venom cytotoxicity.

Snake envenomation is listed as Category A Neglected Tropical Diseases (NTD) by World Health Organization, indicates a severe public health problem. The global figures for envenomation cases are estimated to be more than 1.8 million annually. Even if the affected victims survive the envenomation, they might suffer from permanent morbidity due to local envenomation. One of the most prominent local envenomation is dermonecrosis. Dermonecrosis is a pathophysiological outcome of envenomation that often causes disability in the victims due to surgical amputations, deformities, contracture, and chronic ulceration. The key venom toxins associated with this local symptom are mainly attributed to substantial levels of enzymatic and non-enzymatic toxins as well as their possible synergistic actions. Despite so, the severity of the local tissue damage is based on macroscopic observation of the bite areas. Furthermore, limited knowledge is known about the key biomarkers involved in the pathogenesis of dermonecrosis. The current immunotherapy with antivenom is also ineffective against dermonecrosis. These local effects eventually end up as sequelae. There is also a global shortage of toxins-targeted therapeutics attributed to inadequate knowledge of the actual molecular mechanisms of cytotoxicity. This chapter discusses the characterization of secretory phenotypes of dermonecrosis as an advanced tool to indicate its severity and pathogenesis in envenomation. Altogether, the secretory phenotypes of envenomed cells and tissues represent the precise characteristics of dermonecrosis caused by venom toxins.

Biochemical and toxinological characterization of Naja sumatrana (Equatorial spitting cobra) venom

The lethal and enzymatic activities of venom from Naja sumatrana (Equatorial spitting cobra) were determined and compared to venoms from three other Southeast Asian cobras (Naja sputatrix, Naja siamensis and Naja kaouthia). All four venoms exhibited the common characteristic enzymatic activities of Asiatic cobra venoms: low protease, phosphodiesterase, alkaline phosphomonoesterase and L-amino acid oxidase activities, moderately high acetylcholinesterase and hyaluronidase activities and high phospholipase A2. Fractionation of N. sumatrana venom by Resource® S cation exchange chromatography (GE Healthcare, USA) yielded nine major protein peaks, with all except the acidic protein peak being lethal to mice. Most of the protein peaks exhibit enzymatic activities, and L-amino acid oxidase, alkaline phosphomonoesterase, acetylcholinesterase, 5'-nucleotidase and hyaluronidase exist in multiple forms. Comparison of the Resource® S chromatograms of the four cobra venoms clearly indicates that the protein composition of N. sumatrana venom is distinct from venoms of the other two spitting cobras, N. sputatrix (Javan spitting cobra) and N. siamensis (Indochinese spitting cobra). The results support the revised systematics of the Asiatic cobra based on multivariate analysis of morphological characters. The three spitting cobra venoms exhibit two common features: the presence of basic, potentially pharmacologically active phospholipases A2 and a high content of polypeptide cardiotoxin, suggesting that the pathophysiological actions of the three spitting cobra venoms may be similar.(AU)

The effect of light scattering on multifocal electroretinography.

PURPOSE: Unclear ocular media is a very common condition of older eyes characterized by significant light scattering and image degradation. The multifocal electroretinography (MERG) is a useful objective technique to measure retinal activity but its validity in the presence of cloudy ocular media remains unclear. We tested the MERG under controlled light scattering conditions using a liquid crystal diffuser (LCD) that simulated different degrees of image degradation. METHODS: The MERG were taken from 13 normal young subjects seated behind a LCD set under two conditions: scatter (visual acuity approximately 6/18) and non-scatter (visual acuity approximately6/6). The pupils had been dilated and the eyes were optically corrected for the working distance. The first-order kernel MERG response was analysed. Three subjects underwent MERG measurement with two additional intermediate light scattering levels (i.e. visual acuity approximately 6/9 and 6/12). RESULTS: The macular MERG response density was reduced (p < 0.001), but the peripheral MERG response densities were increased (p < 0.001) under the scattering condition. A similar trend was also observed with intermediate degrees of light scattering. Comparing the MERG waveforms without light scattering, a new retinal response was identified with a characteristic latency of about 60 ms (P60), but it was diminished in size under the scattering conditions. CONCLUSIONS: The veiling luminance might have caused the reduction in the macular MERG response and an elevation in the peripheral retina with light scatter. The functional suppression of P60 observed under the influence of light scatter may be related to retinal adaptation. Unclear optical media will affect the interpretation of MERG results.

Refractive errors in Singapore and Xiamen, China--a comparative study in school children aged 6 to 7 years.

PURPOSE: To compare and contrast the prevalence of myopia and other refractive errors in Xiamen city, Xiamen countryside (Southern China), and Singapore. METHODS: One hundred thirty-two schoolchildren aged 6 to 7 years from Xiamen city, 104 from Xiamen countryside, and 146 from Singapore city were recruited to join the study. Cycloplegic autorefraction, keratometry, and biometry measurements were performed on all children. RESULTS: The prevalence of myopia was 12.3% in Singapore city, 9.1% in Xiamen city, and 3.9% in Xiamen countryside. The prevalence of astigmatism was higher in Singapore compared with Xiamen. The rates of hyperopia and anisometropia were similar in all three locations. CONCLUSIONS: The myopia rate in Singapore city was higher than in Xiamen city; the lowest rates were found in Xiamen countryside. As the Chinese population from all three sites is of similar genetic stock (predominantly from Southern China), it is postulated that the differences in myopia rates in these three localities may be related to environmental factors.

Influence of age on the multifocal electroretinography.

The influence of age on the amplitude density (nV/sq deg) of the multifocal electroretinogram (ERG) was studied in 90 healthy subjects aged 18-52 years. Subjects were divided into three separate age groups; (i) 18-22 years (ii) 33-37 years and (iii) 48-52 years. Amplitude density of first order kernel of the multifocal ERG was measured for the three different age groups. When the whole response of the retina is considered, analysis of variance showed no significant differences in amplitude density between the three age groups. (ANOVA, df. 2, 87 F = 2.29, p = 0.11. However if the responses were segregated into a central area and concentric rings around the central area, analysis of variance showed that there were significant differences in responses between rings at different eccentricities and between different age groups (Anova F = 76.19, df. 17, 522, p = 0.00001). Post hoc analysis showed that the responses from the centre and the second ring around the centre of fixation for 48-52 year olds were significantly lower than those responses from the 33-37 year old and the 18-22 year old age groups. The decline in the multifocal ERG in the central retina of the 48-52 year olds could be associated with the decline of the number of photoreceptors as the eye ages. Student t test revealed no significant differences in amplitude density between males and females.

Radius of curvature of the posterior surface of the cornea.

The radius of curvature of the posterior surface of the cornea was measured in the vertical meridian for 120 children aged 6 to 17 years, using a Purkinje image method. The mean radius of curvature (+/-SD) was 6.42 +/- 0.31 mm, with a range from 5.62 to 7.22 mm. The ratio of anterior to posterior corneal radius was 1.210 +/- 0.045 or 0.827 +/- 0.029 when expressed as a reciprocal. There was a significant correlation between the anterior and posterior corneal radius (y = 0.798x + 0.228, r2 = 0.45). The study provides data that may be applied to a four-surface schematic eye.

Changes in ocular dimensions and refraction with accommodation.

The purpose of this study was to measure the changes in ocular dimensions with accommodation, with particular reference to the radius of curvature of the posterior surface of the crystalline lens. The increase in power of the eye with accommodation is considered to arise primarily from a decrease in the radius of curvature of the anterior surface of the lens, with the role of the posterior surface somewhat unclear. We measured the axial dimensions (A-Scan ultrasonography), corneal radius of curvature (keratometry), refractive error (auto-refractor) and radii of curvature of the lenticular surfaces (video phakometry) for 11 subjects, mean age 21.2 +/- 2.6 years, for five levels of ocular accommodation up to 8.00 D. At maximum accommodation the mean changes were a decrease in anterior chamber depth of 0.24 mm, an increase in lens thickness of 0.28 mm, a decrease in radius of curvature of the anterior surface of the lens of 4.95 mm and 1.34 mm for the posterior surface. The corresponding increase in power of the lenticular surfaces for an equivalent refractive index of 1.422 for the lens was 5.53 D and 3.10 D for the anterior and posterior surfaces respectively. No significant changes were recorded in axial length or vitreous chamber depth. We conclude that when crystalline lens power is calculated on the basis of an equivalent refractive index, changes in the posterior surface of the lens contribute around one third of the increase in lens power associated with 8.00 D of ocular accommodation.

The repeatability and variability of the multifocal electroretinogram for four different electrodes.

Multifocal electroretinograms were recorded from twelve subjects on three separate days using the Visual Evoked Response Imaging System (VERIS). The subjects were 18-40 years-of-age. Each recording session was separated by an interval of between one and 16 weeks. Four electrode types were compared: the JET contact lens electrode, the gold foil electrode, the DTL thread electrode and the carbon fibre (c-glide) electrode. The b-wave amplitude density (nV/sq.deg) recorded with each electrode was measured. The mean amplitude density recorded at each session for each subject and each electrode was calculated and compared. There were no significant differences in amplitude density for the ERGs recorded with each type of electrode over the three days. The coefficient of variation for each electrode and each subject was then calculated using the results for the three days. The coefficients of variation for each electrode showed significant differences (One-way ANOVA: F = 4.51, d.f. = 3.44, P < 0.008). The c-glide electrode results had the highest variability and post hoc tests showed that its coefficient of variation was significantly different from those of the JET and gold foil electrodes but not from that of the DTL thread electrode.

A new stereotest: the double two rod test.

A new stereoacuity test, the double two rod test, uses a two-alternative forced-choice (2AFC) paradigm. The subject's task is to state which pair of rods, the left or the right, contains depth information. The test gives repeatable results; comparison between the depth threshold measured binocularly and monocularly suggests that monocular cues, if present, provide only poor depth information, compared to the depth information arising from binocular disparity. As part of an investigation of stereoacuity and ageing, we tested stereoacuity as a function of viewing time and the number of comparisons made between the two pairs of rods. Stereoacuity was significantly reduced for viewing times less than 3 s while longer viewing times did not improve stereoacuity. The number of comparisons made between the two pairs of rods had no effect on stereoacuity.

Contrast and luminance as parameters defining the output of the VERIS topographical ERG.

The Visual Evoked Response Imaging System (VERIS I) topographical electroretinogram system (EDI Associates, San Francisco, CA) allows measurement of the response of large numbers of retinal areas simultaneously. This paper examines ERG responses derived with the VERIS system to changes in target contrast and to local reductions in luminance. There is a linear reduction of response with reductions of target contrast. Neutral density filters were placed over part of the display, to mimic the localised reductions in response which occur in glaucoma, age-related maculopathy or diabetic retinopathy. There is a definite reduction in response seen with a 0.4 ND filter, indicating that the system should have similar sensitivity in detection of retinal lesions to the commonly used visual field analysis systems.

Differences in visual acuity between the eyes: determination of normal limits in a clinical population.

We determined the difference in visual acuity between the right and left eyes of patients and also determined the maximal level of acuity expected in a group of visually normal individuals. Visual acuity was measured in the right and left eyes of 72 subjects aged from 16 to 67 years using Bailey-Lovie type charts. The chart was read until fewer than three letters were read on a line and acuities were based on each letter correct contributing -0.02 to the overall score. For 12 of these subjects, visual acuity was measured a further four times. Average visual acuities for right and left eyes were -0.137 and -0.126log MAR, respectively. The signed visual acuity difference was normally distributed and had a standard deviation of 0.050log MAR. The mean visual acuity difference for the 12 subjects for whom the measures were repeated was 0.033log MAR (SD of the signed visual acuity difference: 0.049log MAR). We conclude that if a patient has a difference in visual acuity between the two eyes of more than 5 letters on a Bailey-Lovie style chart, further investigation is indicated.

Ocular dimensions and refraction in Tibetan children.

A cross-sectional study of 404 Tibetan children (212 males, 192 females) aged 6 to 16 years was conducted in the Bouda region of Kathmandu, Napal in April, 1992. Examination procedures included retinoscopy (1% cyclopentolate HCl), keratometry A-scan ultrasonography, and video ophthalmophakometry. The mean refractive error was +1.11 D (SD: 0.56 D) at age 6 years decreasing to +0.63 D (SD: 0.34 D) at age 16 years with a prevalence of myopia in this group of 3.9%. Most children examined had low refractive errors, with 95.5% having errors in the range -0.50 to +1.50 D. Crystalline lens power decreased by 2.59 D, with an associated increase in its anterior radius of curvature of 1.98 mm and 0.49 mm in its posterior radius of curvature over the age range studied. Vitreous chamber depth increased by 0.69 mm, but no significant changes were recorded in anterior chamber depth, lens thickness, or corneal curvature. We conclude that the balance between the decrease in crystalline lens power and the increase in vitreous length is the major factor in maintaining the tendency to emmetropia in these children.

Effects of exposure to simulated altitudes on visual fields, contrast sensitivity, and dazzle recovery.

Previous studies have shown that visual performance may be impaired at altitudes above 12,000 ft when supplementary oxygen is not used. What is not known is whether there may be subtle changes in visual function at altitudes to which airline cabins are usually pressurized. In this study, we measured spatial and temporal contrast sensitivity, central visual field thresholds, and macular photostress recovery time in 12 male subjects at sea level and at simulated altitudes of 7000 ft and 12,000 ft. Our results showed insignificant changes in spatial and temporal contrast sensitivity, central visual field thresholds and dazzle recovery time with respect to simulated altitudes.

Age and the van Herick ratio in a Chinese population.

We derived estimates of the van Herick ratio or grading in a retrospective study using a Chinese clinical population. We found that the van Herick ratio decreased with age and increased with higher degrees of myopia. A lower van Herick ratio was found to be associated with higher intraocular pressure. There are significantly more patients with lower van Herick ratios or grades in our population than in populations described by others.

The repeatability of the noninvasive blue field entoptic phenomenon method for measuring macular capillary blood flow.

The speed of macular capillary blood flow can be estimated by using the blue field entoptic phenomenon. The technique uses a matching task in which the subject matches what is seen entoptically with a computer simulation of the phenomenon. In this study, we tested the repeatability of the leukocyte speed results obtained using this technique. Fourteen young subjects were tested on five different occasions. Group mean leukocyte speed did not vary significantly from one recording session to the next. However, readings for individuals varied substantially from one recording session to the next. This variability limits the usefulness of this technique for screening or monitoring macular blood flow in individuals.

Mechanical manipulation of the lids and tear break-up time measurements in Hong Kong Chinese.

We measured tear break-up time (TBUT) after lid-rubbing in a single masked experiment, and found that TBUT was unaltered. A further single masked experiment in which non-invasive tear break-up time (NITBUT) was measured after the lids were raised as if to apply fluorescein also showed no effect of this interference with the lids. An experiment in which fluorescein was applied either with the lid raised or not raised during fluorescein application, again with the experimenter masked with respect to treatment, also produced no significant difference in TBUT. When we measured TBUT with the lid raised so that it was not in contact with the cornea, there was no difference in TBUT for the group between the 'lifted' and 'non-lifted' eye; some subjects showed substantially shorter TBUT values, while others showed substantially longer TBUT values. These findings are surprising in view of the concerns expressed in the literature regarding the sensitivity of the tear film to mechanical interference, and suggest that the tear film is more resistant to disruption than has previously been thought.

Decrease in stereoacuity in the seventh decade of life.

We measured stereoacuity in 41 subjects with normal Snellen acuity in each eye, and normal ocular health. Patients were measured in each of the age ranges 21-28, 41-49, 51-59 and 60-70 years. Stereoacuity was reduced from about 16 sec arc for the three younger groups to about 27 sec arc for the older subjects. Since stereopsis has a cortical neural substrate, these data suggest that there may be cortical changes affecting the interaction of information from the two eyes with advancing age, but whether these changes result from loss of contrast sensitivity, instability of ocular alignment or binocular stress, all of which have been reported in elderly subjects, is not known.