Does the eye grow into focus?

Article Abstract:

The shape of the eyeball, whether its axis is too long or too short, will affect vision; those people with an elongated axis will be nearsighted (myopic) and have to be very close to an object to see it distinctly. The reason for this is that the image transmitted by the lens falls short of the retina, while it should just reach the retina. It has been theorized that the developing eye will most often form so that the image lies directly on the retina. But this development is sometimes imprecise, causing myopia or hyperopia (hyperopia is farsightedness, when the image focuses behind the retina). There is evidence that suggests that when the eye is deprived of a visual image it will overgrow and become myopic. Research with chicks has clearly demonstrated this phenomenon, which may be regulated by a type of nerve cell in the retina which is involved in regulating growth, called an amacrine cell. The neurotransmitter dopamine may also be involved, because stimulating the dopamine receptors in the retinal cells can prevent this myopia from developing. This research also showed that rearing chicks in darkness led to hyperopia. Both of these deprivation syndromes were reversed when the need to accommodate was removed. Eye growth seems to adapt to the visual needs of the animal in a particular environment, and the images being presented to the retina. This mechanism seems to be regulated within the eye itself, as myopia develops even when the optic nerve is cut, depriving the brain of all information about the image on the retina. (Consumer Summary produced by Reliance Medical Information, Inc.)

Development and progression, Eye diseases, Vision disorders

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Colour is what the eye sees best

Article Abstract:

Visual testing showed that the eye's primate retinal ganglion cells or P cells react more strongly to color as a stimulus than to luminance as a stimulus. A.B. Watson and colleagues found that luminance is what the eye is best able to perceive, but an expansion of their testing proves that color is the most powerful stimulus. The eye's marked reaction to color is probably due to the abundance, high chromatic gain and noise properties of the P cells.

Research, Retina, Color vision

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Stitch in time saves design

Article Abstract:

The vestibulo-ocular reflex (VOR) has been modeled as a simple electronic circuit by S.G. Lisberger and T.J. Sejnowski. The ideal VOR has the angular speed of the head equal to that of the eye's counter-rotation. In the model this is accomplished by setting the time constants of the input filter and the positive feedback loop equal, giving a gain of unity. This model reconciles the hypotheses of M.A. Ito and F.A. Miles.

Models, Vestibulo-ocular reflex

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