Blue-green Range Research Articles

Induced color blindness in goldfish: A behavioral and electrophysiological study

To answer the question whether, like man, ethambutol treated fish would become color-blind, wavelength discrimination was measured behaviorally in goldfish, preceding, during and after ethambutol treatment. The results are that of the three high discrimination abilities at around 400, 500 and 600 nm, ethambutol affected the latter one. Red-green discrimination is lost reversibly leaving the discriminations in the blue-green and violet range unaffected. This red-green discrimination deficiency cannot be accounted for by a loss of long wavelength cones since the ERG and luminosity functions remain unaffected. Intracellular horizontal cell recordings in goldfish show that ethambutol hyperpolarizes all three types of cone driven horizontal cells and changes their color coding such that their spectral characteristics become cone-like as is the case in dark adapted retina. So, the initial effect induced by ethambutol seems to be an adaptation deficiency in color vision related tasks. Human wavelength discrimination and increment threshold spectral sensitivity functions obtained at low luminance levels are compared to behavioral functions in ethambutol treated goldfish. The high similarity between the ethambutol effects in man and goldfish, and the effects observed in the horizontal cell responses in goldfish are highly indicative that horizontal cells play a key role in color vision. So far their function has been puzzling.

Lasers in rectosigmoid cancers: factors affecting immediate and long-term results

Surgical segmental resection offers the best chance of cure in patients with rectosigmoid cancer. It is also the most effective form of palliation of local symptoms. Unfortunately, it can cause excessive morbidity and mortality in patients who have severe concomitant medical illness. For these patients, alternative methods of removing cancer are being studied for efficacy and risk. One important method of destroying rectosigmoid cancer uses laser energy. Laser is an acronym for light amplification of stimulated emission of radiation. The energy is monochromatic, coherent and collimated. It can be delivered through a quartz fibre passed down the instrument channel of an endoscope to focus the beam on a well demarcated area of tissue. At an appropriate intensity, laser energy creates heat in the tissue resulting in cell death at moderate temperatures and tissue vaporization at higher temperatures. The amount of heating depends on the wavelength, the irradiance, the pulse sequence and the spot size. The goal in laser ablation of cancer is to destroy the cancer cells while avoiding deeper injury to the intestinal wall which could result in perforation. The two most commonly used lasers for gastrointestinal tumour ablation are the argon laser and the Nd:YAG laser. The argon laser emits several wavelengths from 4W514 nm which is in the blue-green range of the visible light spectrum. Absorption is high in tissue and this results in superficial destruction without deeper injury. It is most useful in destroying smaller amounts of tissue with a high degree of precision. The Nd:YAG laser has an invisible wavelength of 1064nm and is poorly absorbed. There is much more penetration and diffusion of heat with the Nd:YAG laser than with the argon laser. The Nd:YAG laser is therefore more useful for destroying larger intraluminal areas of tumour. Rectosigmoid cancers which invade only superficially into the submucosa

Soft apertures for lasers emitting visible radiation

It was found that an Al2O3:Ti3+ crystal grown by the Verneuil method can be used in the fabrication of soft apertures for lasers emitting in the blue–green range. The experimental results indicated equalization of the intensity of the radiation across the laser beam and also polychromatic lasing when apertures made of Al2O3:Ti3+ were placed inside the resonator cavity.

Changes induced in spectral sensitivity and form of retinal action potential of the cockroach eye by selective adaptation

The relative spectral sensitivity and the shape of the slow monophasic action potential of the compound eye of the cockroach, Periplaneta americana L., were investigated using monochromatic light for stimulation and adaptation. It was demonstrated that different areas of this eye differ in function. Ventral parts show a one-peak spectral sensitivity curve (maximum at about 507 mμ) which is unaltered by the state of adaptation. Spectral sensitivity of areas at the upper edge of the eye shows the same maximum as a result of dark adaptation, but the sensitivity curve rises towards violet wavelengths. Adaptation with monochromatic light changes the relative spectral sensitivity considerably. Colour specific differences in the shape of the action potential are seen in the latter areas only. The results indicate that two receptor systems exist in the cockroach eye, which differ in spectral sensitivity and which may mediate true colour vision, at least in the blue-green and violet range of the spectrum. The meaning of the different time course of potentials following stimulation with different colours is discussed.