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Faraday's Eyesight and the Blind Spot


UNDER the heading “Science News a Century Ago” a paragraph headed “Faraday's Eyesight” appeared in NATURE of January 12, p. 77. The note referred to an entry in Faraday's “Diary” of date January 15, 1835, in which Faraday stated he had noticed “a slight obscurity of the sight of my left eye”. Dr. Frank Marsh, writing from the Pathological Laboratory, c/o Anglo-Iranian Oil Co., Ltd., Masjid-i-Sulieman, via Ahwaz, South Iran, suggests that the quotation in NATURE indicates that “Faraday had discovered his ‘blind spot’, that is, the optic disc, the place of exit of the optic fibres from the retina, which exists in the retina of every normal person”. We have consulted a leading authority on ophthalmology upon Dr. Marsh's suggestion, but he thinks that the explanation of the blur in Faraday's vision as being due to his blind spot is not satisfactory for several reasons. Faraday describes it as a “slight obscurity of the sight”, that is, it was a definite blur—in ophthalmological phrase, a positive scotoma. The blind spot causes a hiatus in vision, but no positive blur; in other words, causes a negative scotoma. Apparently the blur was first noticed when Faraday used both eyes in reading, though it is not definitely stated that the right eye was open. If both eyes were being used, the blind spot would not be noticed in reading. Moreover, the size of the scotoma (“about half an inch in diameter”) does not correspond with the visual angle subtended at the nodal point of the eye by the normal blind spot. Faraday's description is meticulously accurate, as one would expect from him, and it is unlikely that he would write “to the right and below the axis of the eye” if the true projection were to the left, as would be the case for the blind spot. It is probable that Faraday had a temporary retinal lesion, possibly a small retinal haemorrhage, and that this accounted for the obscurity he described. In concluding his letter, Dr. Marsh asks whether Faraday's entry was “the earliest reference to observations on the physiological ‘blind spot’ “. It was certainly not; for in the second volume of the Philosophical Transactions it is recorded that Mariotte demonstrated the blind spot ‘to the Royal Society before King Charles II in 1668.

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Faraday's Eyesight and the Blind Spot. Nature 136, 542 (1935).

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