Theory of Colours — trans. Charles Lock Eastlake (1840)

We now proceed to speak of morbid and other extraordinary affections of the retina, by which the eye may be susceptible of an appearance of light without external light, reserving for a future occasion the consideration of galvanic light.

115.

If the eye receives a blow, sparks seem to spread from it. In some states of body, again, when the blood is heated, and the system much excited, if the eye is pressed first gently, and then more and more strongly, a dazzling and intolerable light may be excited.

116.

If those who have been recently couched experience pain and heat in the eye, they frequently see fiery flashes and sparks: these symptoms last sometimes for a week or fortnight, or till the pain and heat diminish.

117.

A person suffering from ear-ache saw sparks and balls of light in the eye during each attack, as long as the pain lasted.

118.

Persons suffering from worms often experience extraordinary appearances in the eye, sometimes sparks of fire, sometimes spectres of light, sometimes frightful figures, which they cannot by an effort of the will cease to see: sometimes these appearances are double.

119.

Hypochondriacs frequently see dark objects, such as threads, hairs, spiders, flies, wasps. These appearances also exhibit themselves in the incipient hard cataract. Many see semi-transparent small tubes, forms like wings of insects, bubbles of water of various sizes, which fall slowly down, if the eye is raised: sometimes these congregate together so as to resemble the spawn of frogs; sometimes they appear as complete spheres, sometimes in the form of lenses.

120.

As light appeared, in the former instances, without external light, so also these images appear without corresponding external objects. The images are sometimes transient, sometimes they last during the patient's life. Colour, again, frequently accompanies these impressions: for hypochondriacs often see yellow-red stripes in the eye: these are generally more vivid and numerous in the morning, or when lasting.

121.

We have before seen that the impression of any object may remain for a time in the eye: this we have found to be a physiological phenomenon (23): the excessive duration of such an impression, on the other band, may be considered as morbid.

122.

The weaker the organ the longer the impression of the image lasts.
The retina does not so soon recover itself; and the effect may be
considered as a kind of paralysis (28).

123.

This is not to be wondered at in the case of dazzling lights. If any one looks at the sun, he may retain the image in his eyes for several days. Boyle relates an instance of ten years.

124.

The same takes place, in a certain degree, with regard to objects that are not dazzling. Büsch relates of himself that the image of an engraving, complete in all its parts, was impressed on his eye for seventeen minutes.

125.

A person inclined to fulness of blood retained the image of a bright red calico, with white spots, many minutes in the eye, and saw it float before everything like a veil. It only disappeared by rubbing the eye for some time.

126.

Scherfer observes that the red colour, which is the consequence of a powerful impression of light, may last for some hours.

127.

As we can produce an appearance of light on the retina by pressure on the eyeball, so by a gentle pressure a red colour appears, thus corresponding with the after-image of an impression of light.

128.

Many sick persons, on awaking, see everything in the colour of the morning sky, as if through a red veil: so, if in the evening they doze and wake again, the same appearance presents itself. It remains for some minutes, and always disappears if the eye is rubbed a little. Red stars and balls sometimes accompany the impression. This state may last for a considerable time.

129.

The aëronauts, particularly Zambeccari and his companions, relate that they saw the moon blood-red at the highest elevation. As they had ascended above the vapours of the earth, through which we see the moon and sun naturally of such a colour, it may be suspected that this appearance may be classed with the pathological colours. The senses, namely, may be so influenced by an unusual state, that the whole nervous system, and particularly the retina, may sink into a kind of inertness and inexcitability. Hence it is not impossible that the moon might act as a very subdued light, and thus produce the impression of the red colour. The sun even appeared blood-red to the aëronauts of Hamburgh.

If those who are at some elevation in a balloon scarcely hear each other speak, may not this, too, be attributed to the inexcitable state of the nerves as well as to the thinness of the air?

130.

Objects are often seen by sick persons in variegated colours. Boyle relates an instance of a lady, who, after a fall by which an eye was bruised, saw all objects, but especially white objects, glittering in colours, even to an intolerable degree.

131.