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Cataracts are also formed in utero, and I have rarely observed in the subjects of congenital cataract other marks of deranged or defective organization. Some other and more subtle cause of opacity must therefore be admitted.
The cataracts of new-born children and of aged persons exhibit very opposite appearances. In congenital cases the opacity most frequently appears in the central nucleus, the interior denser structure demonstrated in the healthy lens by Petit, and is either stationary, or enlarges equally and slowly in a circle. This nucleus is sometimes not bigger than a pin's head in the centre of the transparent lens; but more commonly it is of the size of the contracted pupil, so that the child habitually knits his brows, or screens his eyes with his hand, to obtain that state of the pupil which he finds necessary to his vision. The fluid and capsular cataracts are exceptions to this observation. It is well known that adult subjects of cataract see better in moderate than in strong light, but in a much less degree; for the opacity is in them more diffused, so as very faintly, if at all, to exhibit a nucleus; and a dilatation beyond a natural one, I mean that obtained by the belladonna, though
I it enlarges somewhat the field of light, seldom permits of vision. The opacity commonly appears of equal consistency from the origin of the complaint, and in its progress the light is shut out from the whole sphere of the pupil. The hard cataract affords a partial exception to this remark, in which the nucleus, though imperfectly defined, is generally to be distinguished.
The opacity is sometimes simply capsular, which is known by the uniform nebulous tenuity of the opake membrane stretched over the transparent lens, and rendered more distinct by the dark tint reflected from the choroides. The cata
are familiar to our ordinary experience. Thus we see the matter of secretions altered, loose interstitial texture consolidated by excess of deposition, or obliterated by absorption; changes, which, in lymphatic glands, and parts framed for less nice and delicate purposes than the organ of vision, are less obvious, although equally subversive of their functions.
ract appears to be prominent in the pupil, which is sometimes slightly irregular. In this case, which is considered to be an incipient state of the cataract, as by the consequent opacity or absorption of the lens it becomes more dense and distinct, the quantity of light admitted is considerable.
More frequently the opacity is simply lenticular, which is known by the cataract appearing more dense, voluminous, and varied in its colour and texture, and in relation to the plane of the iris, deeper seated; by the circularity of the pupil, and the greater degree of blindness in the natural state of dilatation. The motions of the pupil being regulated by the quantity of light which is admitted to the retina, its size depends upon the texture and bulk of the opake lens, i. e. a very dense cataract keeps it dilated by excluding light from the retina; a very bulky one by mechanically distending it. In most cases of congenital cataract, and in some of mature age, the dilatation by belladonna discovers a defined margin to the opacity, and a transparent circle beyond it, and therefore adds considerably to the patient's perception of light. I have known patients in this state, who were of an age to judge for themselves, decline the operation, content with the vision they enjoyed by the use of the belladonna. In such cases, however, a tolerable vision has been previously enjoyed, owing to the smallness of the opake nucleus compared with the transparent portion of the lens. And in all cases the vision of near objects is confused, if not totally bedimmed, by the enlargement of the pupil with the belladonna, although that of distant ones is clear and distinct. Where a transparent circumference has been discovered after dilating the pupil by the belladonna, I have never seen the capsule opake, and I believe this black rim may be considered as diagnostic of the transparency of the capsule. Where the lenticular opacity is diffused, this sign of a transparent capsule is of course wanting.
The opacity is sometimes much deeper seated, so that you look at it through the transparent capsule and lens. It is here generally circumscribed, but irregularly shaped; and often, from its tenuity and depth of situation, escapes the observation even of oculists. This is usually considered to be a third seat of opacity, distinct from the former, viz. in the posterior covering of the lens. I do not find, upon repeated and strict examination, any proper capsule investing the lens, i. e. which admits of being removed with it. It may be necessary to a right understanding of this structure, briefly to describe it. The tunic of the vitreous humour advances to the ciliary body, there it separates into two laminæ, which, when contiguous to the margin of the crystalline, adhere closely to each other, forming the sacculated circle (canal godronné) described by Petit, which is capable of being inflated around the margin of the lens. This canal corresponds in breadth to the breadth of the ciliary processes, and is marked by them anteriorly. The anterior lamina, which is the more dense of the two, covers the crystalline in front; the posterior lines the fossula of the vitreous humour. There is no communication betwixt the canal of Petit, the vitreous humour, and the crystalline capsule. They are all distinct from each other, and must be inflated distinctly, if perfect. The crystalline, it will appear from this description, is incased in a duplicature of the vitreous capsule. The different texture of these laminæ adapted to their respective uses, (the one properly belonging to the crystalline, and supporting the whole lens in its place; the other proper to the vitreous, and covering a very small portion of the humour, which is sufficiently supported by the crystalline itself) and likewise the close investiture of the margin of the lens, which interrupts continuity, for it prevents the passage of air, explain why they are so seldom similarly affected in disease. The posterior opacity before described is therefore seated in the proper tunic of the vitreous humour. Thus much on the situations of the opacity forming cataract.
The varieties of consistency, colour, and figure, are numerous. With regard to consistency, we have the fluid or milky, the focculent or fleecy, the caseous or doughy, and the compact or hard cataract. The fluid lens is, I believe, rarely contained in a transparent capsule. The latter, in my expe. rience, has been partially opake, presenting a dotted or mottled surface. The capsule appears in contiguity with the margio of the pupil, and as if projecting in it, and the opake spots upon it are most distinguishable when it is viewed laterally. The second usually resembles, in appearance, flakes of snow irregularly heaped, being visibly of a loose and broken texture, and the larger masses intersected by semi-transparent lines: the arrangement is sometimes regular and uniform, being either foliated or radiated. The capsule is sometimes semi-opake, but more frequently transparent. The third is the cataract of greatest bulk, impeding the motions of the pupil, having a heavy and dense appearance, uniformly opake, a clouded not a fleecy whiteness, and sometimes a greenish or dirty white tinge. The fourth appears deep seated, of a brown yellow, or amber colour, most dense in the centre; if entirely opake, flat upon the surface, over which the iris plays freely. The second and third species are most commonly met with; the first and fourth are comparatively rare.
The description of such appearances is difficult, and might appear over minute; but to an eye much accustomed they admit of ready distinction, and the distinction is of the highest importance, as the operation should be selected accordingly. To the first and second species, formerly regarded as incurable on account of their softness, the operation performed by the late Mr. Saunders is admirably adapted. To the two latter, the operation of couching or extraction is best suited.
In the description given the capsular opacity is not included; for when the capsule is completely opake, we can hardly judge of the texture of the lens. But where the complete opacity of the capsule exists, the lens is commonly diminished in bulk; it undergoes a waste after the opacity of the capsule, so as in process of time to become a membranous cataract. This I conceive to be owing to the obliteration of the vessels of the capsule, from which those of the lens are derived. When the capsular opacity is congenital, it is either purely capsular, or
only a very small piece of lens remains. When the capsule turns opake from injury, the lens is soon greatly reduced in bulk, as appears from the falling in or concavity of the iris which loses its support, and is demonstrated in the operation. This observation renders the operation with the needle appropriate to the cataract in which the capsule is opake, in cases which are not very recent. When the capsule of the vitreous humour is the seat of the opacity, I have not observed that the lens undergoes any diminution, nor have I yet ascertained the remediableness of this case. The membranous or purely capsular cataract is a form of the disease which appears to me to require a somewhat different operation.
The fluid cataract commonly requires only the central aperture of the capsule; it flows out into the anterior chamber, and mixes with the aqueous humour, which, by the absorption of the opake particles, in a few days recovers its transparency. It is to be observed, however, that this form of cataract requires to be treated with caution. I have seen two instances in which the simple discharge of the fluid was followed by severe inflammation, by which the process of absorption was arrested, as appeared from the permanently turbid state of the humour. This does not happen where the whole substance of the lens is changed. The milk-like fluid in these cases concealed a solid bed of lens, which, by the free laceration of the capsule, was set at liberty, and oppressed the iris.
The flocculent cataract readily undergoes solution in the aqueous humour when the capsule is freely opened, and its texture broken down by the needle.*
* The attempt to procure a solution of the opake crystalline in the aqueous humour, was suggested by an accident, in which the crystalline being wounded, became opake, and was removed by this process. I have seen many examples of the same fact. Among the miracles recorded to have been wrought at the tomb of the Abbe Paris, is the gradual restoration of sight to a young man who became blind after a puncture of the eye with an awl, which caused the discharge of the aqueous humour. (See Paley's Evi. dences of Christianity, rol. I. p. 380.) This miracle admits of a more satisVOL. V.