Physiological optics, being an essay contributed to the American encyclopedia of ophthalmology - Softcover
Synopsis
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1918 Excerpt: ...the periphery of the retina. At a certain distance from the axis the green spot will appear white, hence the object will be seen but no notion of its hue would be forthcoming unless the image had been initially received on the center of the retina. It is, of course, to be noted that the brightness of the color and the size of the spot cause variations in the angle at which the color disappears. If the brightness be feeble and the angle which the colored disc subtends on the retina be very small, a shift of the axis of the eye by a very few degrees will suffice to render the spot colorless. This simple experiment is worthy of consideration as it shows that the retina is most sensitive to color in the region which the axis of the eye cuts and that there is a gradual diminution in sensitiveness to color though not necessarily to light as the periphery is approached. This is what would be expected if the eye has followed the laws of evolution. Every individual, therefore, is color-blind though not light blind in the outer retinal regions. The most difficult color (exclusive of white, which should be considered a combination color) to cause to disappear is the blue. 232. These color-blind conditions in the peripheral regions are of considerable interest to the physicist, physiologist and the psy chologist; to the ophthalmologist they are of particular interest only when contracted or abnormal color fields are found, for these are an aid in the diagnosis of disease. We shall confine our attention here to the normal eye when pure spectral colors are used, the eye being dark adapted. Sir William Abney describes in his book on Researches on Color Vision two forms of special apparatus for plotting the color fields. The first is a perimeter of ordinary form but modifi...
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