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mirably described by Dr. Wells in the Philosophical Ges. I.
Spec. III. Transactions, in an interesting case of a young person 6 P. longinabout thirty-five years of age, whose retina was as sensible qua paretica.
Unalterable to the stimulus of light as ever ; yet who, from a paresis, long-sight. or permanent dilatation of the pupil, saw near objects with Singular considerable confusion, but remote objects with perfect
plicated with accuracy. The power of moving the upper eye-lid was paralysis of also lost. It was an extreme case of the disease before us,
of the disco hefore the adjoining complicated with partial paralysis of the adjoining muscles, How imiand may be imitated by applying the tincture of bella- tated.
m ala How redonna. It was easily remedied by the use of spectacles with convex glasses, by means of which the patient was able to read without difficulty in a printed book, whose letters he was scarcely able to distinguish from each other before the spectacles were applied. The Third VARIETY or that produced by old age, g P. longin
qua senecconstitutes the presbytia, and presbyopia of medical dutis. writers, from wpécbus, senex; and here the hebetude and Long-sight relaxation, while short of paralysis, extend usually through
The presthe retina, iris, and, indeed, every part of the complicated bytia of organ of the eye; on which account the cornea becomes many less convex in its form and less pellucid in its transpareney.
In the present, as in the other varieties of this affec- Remedial tion of the eyes, the best remedy for supplying the deficient convexity of the cornea, as well as the deficient irritability of the iris, is convex spectacles ; adapting their power to the precise demand of the eye and increasing it as the demand grows more urgent.
VISION ONLY ACCURATE WHEN THE OBJECT IS NEAR.
the former :
and hence to
Gen. I. This is in most respects an opposite disease to the preSpec. IV. Mostly an ceding; for it not only produces an opposite effect, but opposite proceeds, in the main, from an opposite cause. In the disease to
former the iris is for the most part relaxed and weakly; here it is sound, often too much contracted : in the former
the cornea is, in almost all cases, too much flattened, in
to the present it is too convex or polarized. The best palbe remedied by opposite liative, therefore, is spectacles of an opposite character
to those recommended under the preceding species; and Cured by with these we must satisfy ourselves till age brings us a age;
natural relief, by taking off the entony and depressing the but often
cornea. Unfortunately, however, this is a relief that temporarily. does not always continue for many years; since the excess
of tone becomes too much lowered as the age advances,
and the sight grows imperfect from this cause. Called myo Mice are said to have this kind of vision naturally, and piasis, as mice are supposed hence one of the technical names for it is myopia or myoto possess it piasis, literally "mouse-sight”. naturally. Great con
In the common technical terms for the present and the fusion in the preceding species, there is the same kind of confusion in technical
respect to the colloquial terms by which these diseases are distinguished as we have already shown to exist between the technical and colloquial names of the first and second species.
Thus paropsis longinqua, the long-sight of the common idiom, is the amblyopia, or dyopia proximorum of Sauvages and Cullen, literally “ morbid sight of near
objects ;" while p. propinqua, the short-sight of the com- Gen. I. mon idiom, is the amblyopia, or dyopia dissitorum of Precs is. the same writers ; literally “morbid sight of objects far propinqua. off". In the terms now offered the technical and collo-short-sight. quial ideas run parallel.
Skew-sight. Sight Askew.
VISION ONLY ACCURATE WHEN THE OBJECT IS PLACED
In this species the patient can only see in an oblique Gen. I.
Spec. V. direction, in consequence of some partial obfuscation of Disease irection, 1..consequence of some the cornea (usually perhaps from scratches or slight scars) plained. or of the humours through which the light is transmitted, or from a partial paralysis of the retina. This must not How to be
distinguishbe confounded with strabismus, or squinting, as it some- ed from times has been, but which proceeds from a different strabismus cause, and is accompanied with different phænomena. In skew-sight or lateral vision, the axis of the eye affected usually coincides with that of the sound eye, though it runs somewhat obliquely to avoid the obstruction in the tunic. In strabismus. the two axes do not coincide, and Strabismus
sometimes the judgement is formed from the strongest eye alone. follows. If, however, in lateral vision, the obstruction be such as to make the optical axis of the affected eye at variance with that of the sound eye, squinting must be a necessary consequence of the disease.
IMAGINARY OBJECTS FLOATING BEFORE THE SIGHT;
OR REAL OBJECTS. APPEARING WITH IMAGINARY
This species, thus defined, clearly includes two varieties
as follow :
a Phantasmatum. Appearances of objects before Ocular spectres. the sight that have no real
existence. B Mutationis.
Real objects apparently changed Ocular transmuta in their natural qualities.
tions. Both these varieties offer a very numerous family of distinct illusory perceptions, which require to be noticed
in their order. a P. illuso- Of the oculAR SPECTRES, constituting the FIRST VAria phan- RIETY, one of the most frequent forms is that of DARK
spots. These are the muscæ volitantes of many authors;
and “ are sometimes,” says Dr. Young “ if not always Dark spots, The muscæ occasioned by an opacity of some of the vessels of the volitantes vitreous humour near the retina. They are seen in a of various authors.
full light, and cannot, therefore, as Sauvages has justly Cause. remarked, be caused by any thing in the anterior part of Apparent
the eye; and they may often be observed to change their
the eve: and th change of
form with the motions of the eye; which they could not position accounted do if they did not depend on some floating substance. for.
Their apparent change of position, when we attempt to follow them with the eye, is a necessary consequence of the motion of the eye itself which contains them”*.
tasmatum. Ocular spectres.
• Delius, Diss. Phantasmata ante oculos volitantia, affectus oculorum singularis. Erlang. 1751.
If, however, these phantasmata depended upon vas- Gen. I. cular opacity of any kind, it is difficult to account for
a P. illusotheir mobility. And hence Demours is, perhaps, nearer ria phanthe mark in ascribing them to small portions of Morgagni’s humour that have acquired an increase of density, spectres. weight, and refractile power without losing their trans- Supposed to parency *. And in this view of their formation Mr. Guthrie be seated in
the humor coincides t.
Morgagni Another form these ocular spectres exhibit is that of by Demours
and Guthrie. NET-WORK; hence called suffusio reticularis by Sau- Ocular vages, and visus reticularis by Plenck. This is some- spectres of times permanent; sometimes transitory; and is probably,
Yr or visus as conjectured by Sauvages, produced by a morbid affec- reticularis. tion of the arteriolæ of the retina.
A third form is that of SPARKS; and hence called by Sparks or Sauvages suffusio scintillans. It proceeds generally from scintillans. a blow or excess of light.
The eye is also troubled with an imaginary sense of Dazzling or DAZZLING, constituting the myrmaryge of the Greek" writers. Its usual cause is supposed to be a plethora of the minute vessels of the eye.
Sometimes from the same cause the ocular spectres Irridescent assume an IRRIDESCENT APPEARANCE; or exhibit, in splendid succession, all the colours of the rainbow. This coloris. Sauvages calls suffusio coloris. It is occasionally a regularly intermittent affection, or returns at stated periods, and particularly in the evenings; and occasionally the morbid appearance is confined to a single colour. Dr. Heberden has given a curious example of an affection of this kind in a lady of advanced age, who took lodgings on the eastern coast of Kent in a house that looked immediately upon the sea, and was of course very much exposed to the glare of the morning sun. The curtains of the bed in which she slept, and of the windows, were of white linen, which added to the intensity of the light. When she had been there about ten days, she observed
* Traité des Maladies des Yeux, p. 409.