Biomedical subjects

J A Weerheim

Publications and source records attributed to J A Weerheim.

6 recordsLinked to original sources

PubMed1992

Methionine intake in rainbow trout (Oncorhynchus mykiss), relationship to cataract formation and the metabolism of methionine.

Young rainbow trout were given diets containing graded levels of methionine for 16 wk. Analysis of the weight gain and food efficiency data showed the methionine requirement to be not more than 0.76% of the diet (1.9% of dietary protein). Activities of regulatory enzymes of the transulfuration pathway, methionine adenosyltransferase and cystathionine synthase in trout liver were not altered by changes in methionine intake. Concentrations of free serine in liver and plasma of the trout were high at low levels of methionine intake but fell as dietary methionine increased. This implied decreased flux through cystathionine synthase at low methionine intakes. Large increases in liver and plasma taurine occurred at high methionine intakes, implying enhanced transulfuration activity. Liver ornithine decarboxylase activity was reduced at the lowest level of dietary methionine used but the activity of S-adenosylmethionine decarboxylase was unchanged. Eye lenses of the trout given these diets were examined by a scanning lens monitor. Analysis of focal length variability with this equipment demonstrated that, if abnormality of the lens is to be avoided, a higher concentration of dietary methionine (0.96% or 0.6% methionine + 0.36% cystine) is needed than that required to maximize growth.

Amino Acids↗

PubMed1992

Scanning laser measure of optical quality of the cultured crystalline lens.

An apparatus has been designed to automate the laser measuring technique and make it possible to monitor lens refractive function (spherical aberration) as well as change in lens transmittance during lens culture. A scanning laser beam (helium-neon) is used so that a number of beams pass through different spots on the lens to determine lens spherical aberration compared over time. Each refracted beam, received by two video cameras (X and Y directions), is digitized. The system first locates the optical centre of the lens by determining the beam position providing the least deflection for both the X and Y directions. The beam is then moved in predetermined steps on either side of the centre, and focal lengths are determined relative to the optic axis for each position. A measure of beam scatter is noted from post-refraction pixel excitation for each beam position. Improvements to the scanning laser system have led to greater accuracy and speed as well as to improved culture cells. Accuracy was increased by using high resolution (1 micron) stepping motors to move the scanning helium-neon laser. A new alignment process involving the superposition of the incident beam reflected on itself ensures that the incident beam is perpendicular to the lens equatorial axis. Scanning speed has been improved through a variety of hardware and software changes. Scanning time for a lens, including locating the optical centre and measuring focal length for 20 lens positions along the X and Y directions, takes about 60 seconds. Long-term studies on the degradation of lens optical performance frequency yield diffuse beams of very low intensity.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1991

UV-B radiation and the optical properties of cultured bovine lenses.

The effect of UV-B radiation on the crystalline lens was examined by subjecting bovine lenses in culture to varying low exposures at 300 nm. Lens optical quality was monitored on a long-term basis (to 1000 hrs.) with an automated scanning laser system that recorded both change in relative scatter and focal length across each lens. Data were collected for 20 lens positions at each scan. Radiant exposure levels consisted of 0.5, 0.25, 0.125, 0.06 and 0.03 Jcm-2. Twenty irradiated lenses were compared to twelve untreated controls. All of the irradiated lenses showed changes in scatter and focal length relative to the controls. Most (about 75%) of the treated lenses showed significant increases in scatter (200-400%) and focal length (10-20%) at 40 to 60 hours after exposure. A similar time frame for lens damage was noted by visual inspection. Exposure to UV-B at the above doses did not affect culture longevity.

Animals↗

PubMed1991

Lens optical quality is a direct function of lens sutural architecture.

We analyzed the structural and functional relationship between lens sutures and lens optical quality (focal length variability) by correlative scanning electron microscopy (SEM) and laser scan analysis. Twenty-two rabbit lenses (8 pigmented and 14 albino) were used in this study. Lenses were initially scanned by a low-power helium-neon laser beam that was passed either at an acute angle to a lens suture or along a lens suture. The results of laser scan analysis with the incident beam passed at an acute angle to a lens suture showed that generally, rabbit lenses were well corrected for spherical aberration. Subsequent SEM analysis showed that areas of lenses scanned that produced the least amount of focal variability were characterized by uniform fiber cells arranged in parallel, radial cell columns. In contrast, the results of laser scan analysis with the incident beam passed along a lens suture showed that there was significant focal length variability, i.e., spherical aberration at the lens sutures. Subsequent SEM analysis showed that the areas of lenses scanned that produced the greatest amounts of focal variability (lens sutures) were characterized by nonuniform fiber cell ends arranged as erratic suture branches in single growth shells and collectively as erratic suture planes formed between growth shells extending from the embryonic nucleus to the lens periphery. Furthermore, the amount of focal variability was directly proportional to the degree of structural disorder at the lens sutures. This is the first study to unequivocally show that the relationship between lens optical quality and specific parameters of lens morphology (lens sutures) can be quantified. These findings may help to elucidate the pathologic changes that lead to presbyopia and cortical cataractogenesis because these lenses are characterized by asymmetrical suture patterns and planes.

Animals↗

PubMed1989

Role of the lens and vitreous humor in the refractive properties of the eyes of three strains of goldfish.

Certain strains of goldfish are characterized by large bulging eyes which have been shown to be extremely myopic. Such myopia has been hypothesized to have its origin in enlargement of the posterior chamber of the eye. The focal length of the lens was found to be similar for paraxial and marginal lens zones in common, Chinese Black Moor and Celestial goldfish, thus providing indirect support of that hypothesis. Freeze-sectioning study of intraocular dimensions shows that the axial length of the vitreous chamber of the common goldfish eye is about 37% of total axial length. In contrast, it becomes more than 70% of axial length in Chinese Black Moors and Celestials. An examination of vitreous protein concentration indicates that ocular enlargement in Chinese Black Moors and in Celestials is related to an increase in vitreous quantity, and is accompanied by vitreous dilution. The fact that similar findings are reported in the case of experimental myopia in chicks, suggests the existence of a fundamental mechanism of refractive development for the vertebrate eye.

Animals↗

PubMed1989

Bilateral experimental myopia in chicks.

Substantial amounts of myopia can be induced in chicks by depriving the eye of clear vision for a period of 2 weeks after hatching. Previous work has primarily involved unilateral visual deprivation. Experiments described here include bilateral visual deprivation involving an opaque goggle over one eye and a translucent goggle over the other. The results indicate that although myopia is induced bilaterally, the eye under the translucent goggle becomes more myopic than the contralateral eye or the unilateral deprivation condition. Lens focal characteristics are not affected by the level of myopia. The fact that deprivation of one eye can affect the refractive development of the contralateral eye has implications related to the question of central vs. peripheral neural control of refractive development.

Animals↗