On the vision of objects on and in the eye / by William Mackenzie.

  • William Mackenzie
Date:
1845
Catalogue details

Licence: Public Domain Mark

Credit: On the vision of objects on and in the eye / by William Mackenzie. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    56/64 (page 56)
    § 37. Persistent spectra. Fixed muscce. There is reason to believe, not only that fixed muscce, as they are termed, bear, in some instances, a resemblance to the spectra of which we have been speaking, (§ 35, 36,) in their form and in the sort of affection of the retina upon which they sometimes de- pend, but that they are in certain cases nothing else than persis- tent spectra, the consequences of over-excitement of the nerve of vision, and exhaustion of its sensorial power. Buffon’s own case may be quoted as an instance of this kind. “ I have seen,” says he, “ black points for more than three months, in so great a number that I was very uneasy about them. I had apparently fatigued my eyes in making and too often re- peating the preceding experiments, [on accidental colours,] and in looking sometimes at the sun, for the black points appeared at that very time, things which I had never seen before. At last they annoyed me so much, especially when in broad day-light I looked at objects strongly illuminated, that I was obliged to turn my eyes away; yellow especially was insupportable to me, and I was obliged to change the yellow curtains in the room which I occupy, and to put up green ones. As 1 avoided looking at all colours which were very strong, and at all brilliant objects, gra- dually the number of black points diminished, and at present 1 am no more troubled with them. What convinced me that those black points arose from too strong an impression of light, is that after looking at the sun, I always saw a coloured image which for a certain time covered all objects, and watching with attention the different gradations of this coloured image, I observed that it lost its colours by degrees, so that at last I saw upon objects only a black blotch, at first pretty large, but which gradually di- minished, and ultimately was reduced to a black point.”* Some fifteen years after the attack above described, Buffon, who studied much and was very short-sighted, had another, com- mencing with photopsia, followed by the spectrum of a dark ring or disk before his left eye, covering all objects and preventing him from reading. After a day and two nights it grew less, so as to allow him to see objects to the right and below. For fifteen days he could not see the pen with which he wrote. His eyes then became inflamed, which obliged him to give them rest, and after the space of some months, the spectrum broke up into frag- ments, and his sight was restored.f § 38. Various appearances of retinal or fixed muscce. Fixed muscae are sometimes single; often more numerous. They are of different sizes, and present a great variety of forms. * Mem. de l’Academie Royale des Sciences, pour 1743, p. 156. Paris, 1746. *J- Histoire de l’Academie Royale des Sciences, pour 1760, p. 55. Paris, 1766.