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PubMed1989

Retinal damage thresholds from single-pulse laser exposures in the visible spectrum.

The risks of using lasers, particularly ocular hazards, have called for the definition of exposure limits. Our investigations involved the retinal effects of the laser beam in the visible spectrum and were directed toward verifying the limit values by defining the thresholds of retinal damage in experiments carried out on the rabbit and the monkey. The wavelengths emitted by the experimental set-ups were 593 and 532 nm, the pulse durations were 600 and 40 ns, and the retinal image diameter varied from approximately 30 to 570 microns. A direct ophthalmoscopic observation and a method using fluorescein angiography were employed to detect a pathologic change in the retina. The energy correlates of retinal lesions were statistically analyzed by a method of probit analysis. The results showed that determining funduscopic thresholds is chiefly a function of the investigation technique used and the delay in observation after the exposure. Our results obtained with fluorescein angiography extrapolated to the human eye support the exposure limit established for intrabeam viewing, but not for an extended source laser which corresponds to a probability of damage increasing with the retinal image diameter. The exposure limit related to the experimental retinal spot size of 285 and 570 microns corresponds to damage probabilities of 7% and 32%, respectively.

Animals↗
PubMed1992

[Cutaneous thermal-cooling and -warming detection thresholds in distal extremities of normal subjects].

The cutaneous thermal-cooling and -warming detection thresholds were evaluated on the dorsal side of the right distal forearm and on the dorsum of the right foot in 134 normal subjects (66 men and 68 women) without sensory symptoms and signs, aged from 11 to 87 years by using a Thermal Threshold Tester (Vickers Medical International, England). The normative data for the clinical evaluation of the severity and the pathologic process of the sensory disturbance of the patients were obtained. The data obtained included 1) the mean of each threshold and 2) its upper limit value of 95% confidence interval for each decade. The mean of each threshold was significantly increased with aging (P less than 0.0001). Therefore, the cutaneous thermal-cooling and -warming detection thresholds of the patients with sensory disturbances should be compared with the normative data adjusted for the age of each subject obtained in this study. Based on the evaluation, repeated six times for three weeks, of each threshold of six volunteers (ages from 21 to 66), high reliability of each threshold (intraclass correlation coefficient from 0.78 to 0.96) was observed.

Adolescent↗
PubMed1995

Orientation discrimination for bars defined by orientation texture.

A texture pattern consisting of short (0.2 deg) lines contained a 5.0 deg x 1.4 deg texture-defined bar. The bar was rendered visible by the difference in orientation (2 theta) between the lines inside the bar and outside the bar. Orientation-discrimination threshold for the texture-defined bar was a U-shaped function of 2 theta over the range 2 theta = 0 degree to 2 theta = 180 degrees. The lowest threshold was at 2 theta = 90 degrees, and was 0.57 degrees for both subjects tested. This threshold was little different from the lowest values of threshold for motion-defined bars, disparity-defined bars, and colour-defined gratings reported elsewhere. A luminance-defined bar was created by switching off all texture lines outside the texture-defined bar. Orientation-discrimination threshold fell to a limiting value as the luminance contrast of this bar was progressively increased. The lowest value of orientation discrimination for the luminance-defined bar (0.42 degrees and 0.35 degrees for the two subjects) was not greatly less than the lowest value for the texture-defined bar.

Adult↗
PubMed1984

Improvement in conditions at an amalgamation plant after an industrial hygiene survey.

After receipt of urine samples which showed higher than normal levels of mercury (Hg) from workers at a large goldmine, air samples were taken at the mine's amalgamation plant. These showed not only values higher than the threshold limit for Hg in air but also significant quantities of Hg on the worker's overalls. Recommendations were made for improvements and when these were completed samples were again taken at the plant. The mean Hg level in urine samples had dropped to one-third of its original value and concentrations in air were very much reduced.

Air Pollution↗
PubMedDate not supplied

Toxicological, medical and industrial hygiene aspects of glutaraldehyde with particular reference to its biocidal use in cold sterilization procedures.

Aqueous solutions of > or =5% glutaraldehyde (GA) are of moderate acute peroral toxicity and those of < or =2% are of slight toxicity. By single sustained skin contact, aqueous GA solutions of > or =45% are of moderate acute percutaneous toxicity, those of 25% are of slight toxicity and those of </=15% do not present an acute percutaneous hazard. Vapor generated at ambient temperature may cause sensory irritant effects to the eye and respiratory tract, but not acute respiratory tract injury. The 50% decrease in respiratory rate (rd(50)) is 13.86 ppm. A 0.1% solution of GA is not irritating to the eye; the threshold for conjunctival irritation is 0.2% and for corneal injury it is 1.0%. Eye injury is moderate at 2% and severe at > or =5%. Primary skin irritation depends on the duration and contact site, occlusion and solvent. By sustained contact, the threshold for skin irritation is 1%, above which erythema and edema are dose related. With 45% and higher, skin corrosion may occur. There is a low incidence of skin sensitizing reactions, with an eliciting threshold of 0.5% aqueous GA. However, GA is neither phototoxic nor photosensitizing. Subchronic repeated exposure studies by the peroral route show only renal physiological compensatory effects, secondary to reduced water consumption. Repeated skin contact shows only minor skin irritant effects without systemic toxicity. By subchronic vapor exposure, effects are limited to the nasal mucosa at 1.0 ppm, with a no-effect concentration generally at 0.1 ppm. There is no evidence for systemic target organ or tissue toxicity by subchronic repeated exposure by any route. A chronic drinking water study showed an apparent increase, in females only, of large granular cell lymphocytic leukemia but this was not dosage related. This is most likely the result of a modifying effect on the factor(s) responsible for the expression of this commonly occurring rat neoplasm. A chronic (2-year) inhalation toxicity/oncogenicity study showed inflammatory changes in the anterior nasal cavity but no neoplasms or systemic toxicity. In vitro genotoxicity studies--bacterial mutagenicity, forward gene mutation (HGPRT and TK loci), sister chromatid exchange, chromosome aberration, UDS and DNA repair tests--have given variable results, ranging from no effect through to weak positive. In vivo genotoxicity studies--micronucleus, chromosome aberration, dominant lethal and Drosophila tests--generally have shown no activity but one mouse intraperitoneal study showed bone marrow cell chromosome aberrations. Developmental toxicity studies show GA not to be teratogenic, and a two-generation study showed no adverse reproductive effects. Percutaneous pharmacokinetic studies showed low skin penetration, with lowest values measured in vitro in rats and human skin. Overexposure of humans produces typical sensory irritant effects on the eye, skin and respiratory tract. Some reports have described an asthmatic-like reaction by overexposure to GA vapor. In most cases this resembles reactive airways dysfunction syndrome, and the role of immune mechanisms is uncertain. Local mucosal effects may occur if medical instruments or endoscopes are not adequately decontaminated. Protection of individuals from the potential adverse effects of GA exposure requires that there be adequate protection of the skin, eyes and respiratory tract. The airborne concentration of GA vapor should be kept below the recommended safe exposure level (e.g. the threshold limit value) by the use of engineering controls. Those who work with GA should, through a training program, be aware of the properties of GA, its potential adverse effects, how to handle the material safely and how to deal with accidental situations involving GA. If effects develop in exposed workers, the reasons should be determined immediately and corrective methods initiated. (c) 2001 John Wiley & Sons, Ltd.

Administration, Inhalation↗
PubMed1997

Activation of Peptide ions by blackbody radiation: factors that lead to dissociation kinetics in the rapid energy exchange limit.

Unimolecular rate constants for blackbody infrared radiative dissociation (BIRD) were calculated for the model protonated peptide (AlaGly)(n) (n = 2-32) using a variety of dissociation parameters. Combinations of dissociation threshold energies ranging from 0.8 to 1.7 eV and transition entropies corresponding to Arrhenius preexponential factors ranging from very "tight" (A(infinity) = 10(9.9) s(-1)) to "loose" (A(infinity) = 10(16.8) s(-1)) were selected to represent dissociation parameters within the experimental temperature range (300-520 K) and kinetic window (k(uni) = 0.001-0.20 s(-1)) typically used in the BIRD experiment. Arrhenius parameters were determined from the temperature dependence of these values and compared to those in the rapid energy exchange (REX) limit. In this limit, the internal energy of a population of ions is given by a Boltzmann distribution, and kinetics are the same as those in the traditional high-pressure limit. For a dissociation process to be in this limit, the rate of photon exchange between an ion and the vacuum chamber walls must be significantly greater than the dissociation rate. Kinetics rapidly approach the REX limit either as the molecular size or threshold dissociation energy increases or as the transition-state entropy or experimental temperature decreases. Under typical experimental conditions, peptide ions larger than 1.6 kDa should be in the REX limit. Smaller ions may also be in the REX limit depending on the value of the threshold dissociation energy and transition-state entropy. Either modeling or information about the dissociation mechanism must be known in order to confirm REX limit kinetics for these smaller ions. Three principal factors that lead to the size dependence of REX limit kinetics are identified. With increasing molecular size, rates of radiative absorption and emission increase, internal energy distributions become relatively narrower, and the microcanonical dissociation rate constants increase more slowly over the energy distribution of ions. Guidelines established here should make BIRD an even more reliable method to obtain information about dissociation energetics and mechanisms for intermediate size molecules.

Journal Article↗
PubMedDate not supplied

Ion regulation in whitefish (Coregonus lavaretus L.) yolk-sac fry exposed to low pH and aluminum at low and moderate ionic strength.

Anadromous whitefish [Coregonus lavaretus (L.)] were exposed during the yolk-sac phase to combinations of pH values of 6.0, 5.5, 5.0, 4.5, and 4.0 and nominal Al concentrations of 0, 100, 200, and 400 micrograms liter-1 for 4 days. The test waters were: (1) lake water diluted 1:1 with ion exchanged water (DLW) and (2) artificial water (AW). The major differences were: [Ca2+] 0.069 mmol liter-1 in DLW versus 0.034 mmol liter-1 in AW, [Na+] 1.5 and [Cl-] 1.8 times higher in DLW, with no dissolved organic material in AW. The fry were sampled daily for the analysis of exchangeable body Na+ and Cl- contents, and the swimming activity and mortality were registered. Aluminum initially protected yolk-sac fry against acidic water at pH 4.0 both in DLW and in AW. Generally, however, an increase in [Al] and a decrease in pH increased the adverse effects, seen as decreased exchangeable body Na+ and Cl- content, decreased swimming activity, and increased mortality. The effects of Al were more pronounced in AW compared with DLW. In AW, the Na+ and Cl- content of the fry already decreased after 1 day of exposure to a level that predicts mortalities. There was a time trend in DLW toward decreasing exchangeable body Na+ and Cl- concentrations as a function of increasing acidity and [Al]. In DLW, mortalities occurred primarily at pH 4.0; at that pH value in AW, the mortality rate was even higher, and mortalities also occurred after 2 to 4 days at all other pH values. There was a threshold limit in exchangeable body Na+ and Cl- concentrations at which yolk-sac fry became passive; it was at approximately 0.3 mumol per fry in DLW and was slightly higher in AW. In the DLW control with moderate ionic strength, the Na+/Cl- ratio was above 1 from the second exposure day on but remained closer to 1 in soft AW control. The Na+/Cl- ratio was predominantly > 1 in AW when the fry were exposed to moderate acidities but approached 1 at pH values < 5.0. The Na+/Cl- ratio was mostly < or = 1 in DLW, irrespective of the exposure, indicating cation selectivity of ion leakage pathways in slightly harder water.

Acids↗
PubMed1996

Muscular disorders in tension-type headache.

In order to evaluate the diagnostic criteria for muscular disorders in tension-type headache, pericranial muscle tenderness and pressure pain thresholds were studied in a random sample population of 735 adults aged 25-64. In addition, quantitative EMGs were recorded in 547 of these subjects. The correlation between the three diagnostic tests was assessed and the discriminality and cut-off points were analysed using Receiver Operating Characteristics analysis. Local tenderness from the temporal muscles was closely related to the total tenderness scores from 14 pairs of muscles. In chronic tension-type headache, tenderness was positively related to EMG and inversely related to pain thresholds. In the episodic from the total tenderness score was inversely related to pain thresholds, whereas no significant relation to EMG was noted. The Receiver Operating Characteristics curves indicated that tenderness recorded by manual palpation was the most specific and sensitive test, whereas EMG and pain thresholds were of limited diagnostic value. Eighty-seven percent of subjects with the chronic, and 66% of subjects with the episodic form were found to have a "muscular disorder" defined as increased tenderness recorded by either manual palpation or pressure algometry and/or increased EMG levels. However, muscle tenderness increased significantly during pain, so the headache state should be considered in future studies. Suggestions for revision of the present diagnostic criteria for muscular disorders are given.

Adult↗
PubMed1987

Principles of the International Commission on Radiological Protection system of dose limitation.

The current recommendations of the International Commission on Radiological Protection (ICRP), published in 1977, identify two types of effect against which protection is required. "Stochastic" effects are those for which the probability of an effect occurring, rather than its severity, is regarded as a function of dose without threshold, whereas "non-stochastic" effects are those for which the severity varies with the dose and for which a threshold may occur. The system of dose limitation recommended by the ICRP is based on the prevention of non-stochastic effects and limitation of the probability of stochastic effects to levels deemed to be acceptable. The prevention of non-stochastic effects is achieved by setting dose-equivalent limits at values such that no threshold dose would be reached, even following exposure for the whole of a lifetime or for the total period of a working life. The limitation of stochastic effects is achieved by keeping all justifiable exposures as low as is reasonably achievable, economic and social factors being taken into account, subject to the constraint that reductions in collective exposure do not cause unacceptably large individual exposures. The formulation of a quantitative system of dose limitation based on these principles requires that judgments be made on several factors including: relationships between radiation dose and the induction of deleterious effects for a variety of endpoints and radiation types; acceptable levels of risk for radiation workers and members of the public; and methods of assessing whether the cost of introducing protective measures is justified by the reduction in radiation detriment which they will provide. In the case of patients deliberately exposed to ionising radiations, the objectives of radiation protection differ somewhat from those applying to radiation workers and members of the public. For patients, risks and benefits relate to the same person and upper limits on acceptable risks may differ grossly from those appropriate to normal individuals. For these reasons, and because of its historical relationship with the International Congress of Radiology, the ICRP has given special consideration to radiation protection in medicine and has published reports on protection of the patient in diagnostic radiology and in radiation therapy.

Animals↗
PubMed1997

Sensitivity and specificity of the neonatal brain-stem auditory evoked potential for hearing and language deficits in survivors of extracorporeal membrane oxygenation.

OBJECTIVE: We determined the sensitivity and specificity of neonatal brain-stem auditory evoked potentials (BAEP) as markers for subsequent hearing impairment and for developmental problems found later in infancy and childhood. METHODS: BAEP studies were performed before discharge in infants treated with extracorporeal membrane oxygenation (ECMO), and two specific abnormalities were analyzed: elevated threshold and delayed central auditory conduction. Behavioral audiometry was repeated during periodic follow-up until reliable responses were obtained for all frequencies, and standardized developmental testing was also conducted. The sensitivity and specificity of an elevated threshold on the neonatal BAEP for detecting subsequent hearing loss, and the relationship of any neonatal BAEP abnormality to language or developmental disorders in infancy, were calculated. RESULTS: Test results for 46 ECMO-treated infants (57.5%) were normal, and those for 34 infants (42.5%) were abnormal, with either elevated wave V threshold, prolonged wave I-V interval, or both on neonatal BAEP recordings. Most significantly, 7 (58%) of the 12 children with subsequent sensorineural hearing loss had left the hospital after showing normal results on threshold tests. There was no significant difference in the frequency of hearing loss between subjects with abnormal (5/21, or 24%) and those with normal BAEP thresholds (7/59, or 12%; Fisher Exact Test, p = 0.28). Therefore the sensitivity of neonatal BAEP testing for predicting subsequent hearing loss was only 42%. Neonatal BAEP specificity for excluding subsequent hearing loss was 76%. In contrast, on language development testing, 19 children demonstrated receptive language delay. Of these children, 12 (63%) had abnormal neonatal BAEP recordings and 7 (37%) had a normal BAEP threshold, normal central auditory conduction test results, or both (p = 0.04). CONCLUSIONS: Neonatal BAEP threshold recordings were of limited value for predicting subsequent hearing loss common in ECMO-treated survivors. However, an abnormal neonatal BAEP significantly increased the probability of finding a receptive language delay during early childhood, even in those with subsequently normal audiometry findings. Because neonatal ECMO is associated with a high risk of hearing and receptive language disorders, parents should be counseled that audiologic and developmental follow-up evaluations in surviving children are essential regardless of the results of neonatal BAEP testing.

Acoustic Impedance Tests↗
PubMed1995

Prevention of noise-induced hearing loss in the Canadian military.

A prospective study was undertaken to investigate the development of noise-induced hearing loss in Canadian military recruits, and to assess the effectiveness of the hearing conservation program currently in place. The participants were 134 men and women, 20 to 30 years of age, employed in four trades, three of these (infantry, artillery, and armour) associated with high noise levels. The data comprised audiometric measurements made at the time of entry and after 3 years of employment, and responses to a questionnaire mainly relating to noise exposure in the workplace and during leisure activities, and the utilization of personal hearing protective devices. The findings showed that group audiograms at entry and at the 3-year recall were characterized by a 6-kHz notch that was indicative of noise-induced hearing loss, although mean threshold values were within normal limits. By the 3-year recall, 11% of the infantry had sustained a mild-to-moderate hearing loss in the left ear, greater than 25-dB HL, that was consistent with the use of small-calibre weapons. Responses to the questionnaire indicated that, while subjects appreciated the potential benefit of wearing hearing protectors, instructions in their proper use and education on the hazards of noise exposure were poor. The results suggested methods to strengthen the existing scheme for hearing conservation to further minimize risk.

Adult↗
PubMed2001

Susceptibility differences in chemical carcinogenesis linearize the dose-response relationship: threshold doses can be defined only for individuals.

The debate on thresholds in dose-response relationships for chemical carcinogenesis concentrates on the question of mechanisms of action that come into play only at dose levels that overwhelm compensatory control mechanism, such as DNA repair or regulation of cell proliferation and death. In this article, individual susceptibility differences are introduced. It is postulated that one single threshold dose cannot be defined for a heterogeneous population because both the background rate of carcinogenesis and specific exposure-related effects differ between individuals. A threshold dose can therefore be defined only on an individual basis and for a given organ. Expressed as a time-to-tumor, the threshold dose results in tumor manifestation at exactly the end of the specified observation period. For those individuals who do not have cancer by the end of this period, the dose was below their individual threshold dose, for those who do have cancer, the dose was above their threshold dose. Based on this concept, a distinction between genotoxic and non-genotoxic carcinogens is no longer required; both types modulate time-to-tumor. Although the present analysis does not allow to define a threshold dose for a population, the setting of a "limit value" for regulatory purposes can be considered if regulators are aware of the fact that this splits a population at some percentile into a group for which the chosen standard is protective and a group for which it might not be. Investigation of factors that confer particular susceptibility to individuals is the key to an understanding of the dose-response relationship at low dose.

Animals↗
PubMed2000

Relations among hypoxemia, sleep stage, and bradyarrhythmia during obstructive sleep apnea.

BACKGROUND: Obesity, apneic hypoxemia, and rapid eye movement (REM) sleep are supposed to be the major causes for bradyarrhythmia in patients with obstructive sleep apnea. The aims of this study were to compare clinical findings and diagnoses in patients with obstructive sleep apnea with and without nocturnal bradyarrhythmia and to analyze the relations among hypoxemia, sleep stage, and bradyarrhythmia. METHODS: During a 17-month period 239 patients were found to have sleep apnea in an ambulatory study. Patients with nocturnal bradyarrhythmia were hospitalized for 3 days and polysomnographies were performed over 2 successive nights. A Holter electrocardiogram was recorded for 48 hours. RESULTS: Nocturnal episodes of bradyarrhythmia were identified in 17 (7%) of 239 patients. Body mass index (39 +/- 7 vs 31 +/- 5 kg/m(2)) and respiratory disturbance index (90 +/- 36 per hour vs 24 +/- 24 per hour) were significantly different (P <.01) between patients with (n = 17) and without bradyarrhythmia (n = 222). Bradyarrhythmia occurred significantly more often during REM than non-REM sleep (P <.01). There was a significant difference in end-apneic oxygen saturation in apnea/hypopnea episodes with and without bradyarrhythmia (71% +/- 9% vs 75% +/- 10%; P <.01). A linear relation between end-apneic oxygen saturation and number of sinus arrests and heart blocks could not be found. CONCLUSIONS: Patients with apnea-associated bradyarrhythmia are more overweight than patients without bradyarrhythmia. The higher respiratory disturbance index measurements found in these patients may be caused by this difference. Bradyarrhythmia occurs predominantly during REM sleep and occurred independently from decrease in oxygen saturation; a threshold value as an upper limit could not be found.

Adolescent↗
PubMed2002

Volatile organic compounds cytotoxicity and expression of HSP72, HSP90 and GRP78 stress proteins in cultured human cells.

The aim of this study was to determine whether overexpression of stress proteins (SPs) could be a sensitive biomarker for cell injury due to exposure to low doses of volatile organic compounds (VOCs) such as benzene, ethylbenzene, toluene, xylene, and chlorinated derivatives (ClB). Sublethal and cytotoxic threshold concentrations of the VOCs were determined by studying the growth rate of normal (fibroblasts) or tumor-derived human cell lines (A549, HepG2) exposed for 4 days to VOCs. Changes in SP expression as a function of concentrations were investigated by Western blotting.VOC toxicity was found to be correlated with their degree of chlorination and their hydrophobicity. Cytotoxic threshold concentrations (no-observed effect concentration, NOEC) were found to be similar for the three cell lines. It was observed that using a mixture of VOCs, each of them at concentration below the NOEC, resulted in an actual toxicity to the cells. This finding reveals a synergistic effect and should be taken into account when assessing threshold risk and exposure limit values in the worker's environment when several pollutants may be present. HSP72 and HSP90 expression levels were not affected whereas GRP78 expression was increased by all the VOCs. Taking into account the specific molecular function of GRP78, it suggests that VOC exposure results in misfolded or underglycosylated protein accumulation in the endoplasmic reticulum. GRP78 overexpression was closely related to the magnitude of growth inhibition due to increasing concentrations of each VOC. The overexpression was found to be significant for concentrations 5 to 30 times higher than NOEC, indicating that, under our experimental conditions, GRP78 expression cannot be considered as a sensitive biomarker of exposure to environmental VOCs.

Benzene↗
PubMed2003

Bioaerosol health effects and exposure assessment: progress and prospects.

Exposures to bioaerosols in the occupational environment are associated with a wide range of health effects with major public health impact, including infectious diseases, acute toxic effects, allergies and cancer. Respiratory symptoms and lung function impairment are the most widely studied and probably among the most important bioaerosol-associated health effects. In addition to these adverse health effects some protective effects of microbial exposure on atopy and atopic conditions has also been suggested. New industrial activities have emerged in recent years in which exposures to bioaerosols can be abundant, e.g. the waste recycling and composting industry, biotechnology industries producing highly purified enzymes and the detergent and food industries that make use of these enzymes. Dose-response relationships have not been established for most biological agents and knowledge about threshold values is sparse. Exposure limits are available for some contaminants, e.g. wood dust, subtilisins (bacterial enzymes) and flour dust. Exposure limits for bacterial endotoxin have been proposed. Risk assessment is seriously hampered by the lack of valid quantitative exposure assessment methods. Traditional culture methods to quantify microbial exposures have proven to be of limited use. Non-culture methods and assessment methods for microbial constituents [e.g. allergens, endotoxin, beta(1-->3)-glucans, fungal extracellular polysaccharides] appear more successful; however, experience with these methods is generally limited. Therefore, more research is needed to establish better exposure assessment tools and validate newly developed methods. Other important areas that require further research include: potential protective effects of microbial exposures on atopy and atopic diseases, inter-individual susceptibility for biological exposures, interactions of bioaerosols with non-biological agents and other potential health effects such as skin and neurological conditions and birth effects.

Aerosols↗
PubMed2001

Contribution of environmental factors to the risk of male infertility.

BACKGROUND: An increasing number of reports suggest that chemical and physical agents in the environment, introduced and spread by human activity, may affect male fertility in humans. We investigated the relationships between exposure to environmental agents and seminal characteristics, and the concentrations of reproductive hormones in the serum of men seeking infertility treatment. METHODS: We studied 225 male partners from consecutively recruited couples, who had their first infertility consultation between 1995 and 1998, in the Litoral Sur region of Argentina, one of the most productive farming regions in the world. RESULTS: A multivariate logistic regression model showed that exposure to pesticides and solvents is significantly associated with sperm threshold values well below the limit for male fertility. We also found that men exposed to pesticides had higher serum oestradiol concentrations, and that men exposed to solvents had lower LH concentrations than non-exposed men. All of these effects were greater in men with primary infertility than in men with secondary infertility. CONCLUSION: We have shown that environmental factors contribute to the severity of infertility, and that this may worsen the effects of pre-existing genetic or medical risk factors.

Agriculture↗
PubMed1997

Determination of the foveal cone spacing by ocular speckle interferometry: limiting factors and acuity predictions.

We have developed a high-resolution imaging technique, based on speckle interferometry, for the objective determination of the cone spacing in the living human fovea. The spatial resolution attained with this technique is theoretically diffraction limited by the pupil size. However, the highest frequency that we measure varies greatly among subjects, especially for fully dilated pupils. We have conducted several experiments (determination of the cutoff frequency of ocular speckle interferometry, the double-pass modulation transfer function, and the Stiles-Crawford effect) that indicate that, as expected, the resolution is not limited by the incoherent modulation transfer function. We found, though, a high correlation between the cutoff frequency and the width of the eye's Stiles-Crawford function. This implies that the resolution depends on the structural properties of the cone mosaic itself. In addition, we have compared the Nyquist frequency of the cone mosaic, determined objectively by our technique, with the grating visual acuity measured in the same eyes at the same foveal eccentricities. For our subjects, visual resolution nearly matches the Nyquist frequency within the fovea, except at the foveal center, where the optical transfer function of the eye attenuates the contrast of frequencies close to the Nyquist limit to a value below threshold.

Cell Count↗