GEN. I. SPEC. III.

6 P. longin

Unalterable

com

long-sight. Singular plicated with paralysis of muscles. the adjoining

mirably described by Dr. Wells in the Philosophical Transactions, in an interesting case of a young person about thirty-five years of age, whose retina was as sensible qua paretica. to the stimulus of light as ever; yet who, from a paresis, or permanent dilatation of the pupil, saw near objects with considerable confusion, but remote objects with perfect accuracy. The power of moving the upper eye-lid was also lost. It was an extreme case of the disease before us, complicated with partial paralysis of the adjoining muscles, and may be imitated by applying the tincture of belladonna. 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.

How imitated.

How re

medied.

tutis.

of age.

The THIRD VARIETY or that produced by old age, y P. longinconstitutes the presbytia, and presbyopia of medical quenewriters, from @pέobus, 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 trans

parency.

writers.

plan.

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.

SPECIES IV.

PAROPSIS PROPINQUA.

Short-sight.

GEN. I. SPEC. IV. Mostly an opposite disease to

the former:

and hence to

be remedied

VISION ONLY ACCURATE WHEN THE OBJECT IS NEAR.

THIS is in most respects an opposite disease to the preceding; for it not only produces an opposite effect, but proceeds, in the main, from an opposite cause. In the 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 the present it is too convex or polarized. The best palliative, therefore, is spectacles of an opposite character to those recommended under the preceding species; and with these we must satisfy ourselves till age brings us a natural relief, by taking off the entony and depressing the cornea. Unfortunately, however, this is a relief that only cured 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.

by opposite

means.

Cured by age;

but often

Called myo

piasis, as mice

Mice are said to have this kind of vision naturally, and are supposed hence one of the technical names for it is myopia or myoto possess it piasis, literally "mouse-sight".

naturally.

Great con

common

In the common technical terms for the present and the fusion in the preceding species, there is the same kind of confusion in 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.

technical terms.

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

GEN. I. SPEC. IV. Paropsis

objects;” while p. propinqua, the short-sight of the common idiom, is the amblyopia, or dyopia dissitorum of 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.

SPECIES V.

PAROPSIS LATERALIS.

Skew-sight. Sight Askew.

VISION ONLY ACCURATE WHEN THE OBJECT IS PLACED
OBLIQUELY.

GEN. I. SPEC. V.

Disease explained.

How to be distinguish

ed from

or squinting.

In this species the patient can only see in an oblique direction, in consequence of some partial obfuscation of the cornea (usually perhaps from scratches or slight scars) or of the humours through which the light is transmitted, or from a partial paralysis of the retina. This must not be confounded with strabismus, or squinting, as it sometimes 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 the judgement is formed from the strongest eye alone. 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.

sometimes follows.

GEN. I. SPEC. VI.

a P. illusoria phan

tasmatum. Ocular

spectres.

Dark spots. The muscæ volitantes of various authors.

Cause.

Apparent change of position accounted

for.

SPECIES VI.

PAROPSIS ILLUSORIA.

False-sight.

IMAGINARY OBJECTS FLOATING BEFORE THE SIGHT;
OBJECTS. APPEARING WITH IMAGINARY

OR REAL

QUALITIES.

THIS species, thus defined, clearly includes two varieties as follow:

a Phantasmatum.

Ocular spectres.

B Mutationis.

Ocular transmuta

tions.

Appearances of objects before

the sight that have no real existence.

Real objects apparently changed in their natural qualities.

Both these varieties offer a very numerous family of distinct illusory perceptions, which require to be noticed in their order.

Of the OCULAR SPECTRES, constituting the FIRST VARIETY, one of the most frequent forms is that of DARK SPOTS. These are the muscæ volitantes of authors; many and "are sometimes," says Dr. Young "if not always occasioned by an opacity of some of the vessels of the vitreous humour near the retina. They are seen in a full light, and cannot, therefore, as Sauvages has justly remarked, be caused by any thing in the anterior part of the eye; and they may often be observed to change their form with the motions of the eye; which they could not do if they did not depend on some floating substance. 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” *.

Delius, Diss. Phantasmata ante oculos volitantia, affectus oculorum singularis. Erlang. 1751.

GEN. I.

SPEC. VI.

a P. illuso

tasmatum.

If, however, these phantasmata depended upon vascular opacity of any kind, it is difficult to account for their mobility. And hence Demours is, perhaps, nearer ria phanthe mark in ascribing them to small portions of Mor- Ocular gagni'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 coincides +.

the humor

Morgagni

and Guthrie.

Ocular

Another form these ocular spectres exhibit is that of by Demours NET-WORK; hence called suffusio reticularis by Sauvages, and visus reticularis by Plenck. This is some- spectres of times permanent; sometimes transitory; and is probably, as conjectured by Sauvages, produced by a morbid affec- reticularis. tion of the arteriole of the retina.

net-work :

or visus

A third form is that of SPARKS; and hence called by Sparks or Sauvages suffusio scintillans. It proceeds generally from

a blow or excess of light.

suffusio

The eye is also troubled with an imaginary sense of Dazzling or DAZZLING, constituting the myrmaryge of the Greek myrmaryge. writers. Its usual cause is supposed to be a plethora of the minute vessels of the eye.

suffusio

Sometimes from the same cause the ocular spectres Irridescent assume an IRRIDESCENT APPEARANCE; or exhibit, in spectres, or 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.

+ Lectures on the operative Surgery of the Eye, p. 211. 8vo. 1823.