This section is from the book "The London Medical Dictionary", by Bartholomew Parr. Also available from Amazon: London Medical Dictionary.
"After the operation, treat it as an ophthalmy; and a collyrium, of one part rectified spirit of wine, and ten parts of lukewarm water, will be as proper an application as any."
Mr. Daviel has the honour of having discovered the method of extracting the crystalline humour, but M de St. Yves practised it about sixty years before him. When the crystalline lens had passed through the pupil into the anterior chamber of the eye, both Mery and Petit extracted it; for then the depression is impracticable. When this mode of relief is employed, the following method is recommended.
Pass your knife through the cornea into the anterior chamber of the eye, about a line before the iris; for if it is not inserted there, the iris will perhaps be wounded: if you go too far on the cornea, the knife may pass between its lamina, and so not perforate into the chamber. After puncturing into the chamber, guide your knife, with the flat side perpendicular to the eye, through the aqueous humour horizontally, (being careful not to wound the iris,) and thrust it out at the opposite side and situation of the cornea to those in which you insert it; turning its edge obliquely and perpendicularly outwards, make an incision rather through the inferior half of the cornea; then lifting up the superior part of it, the crystalline humour will burst its capsule and drop out: but if it should stick at its exit through the wound, it shows that the capsula of the crystalline is not broken, on which you must puncture it with the knife, and then it will drop: but if the disease is in the aranea, or the capsule of the crystalline, you must extract it also with the forceps.
With respect to the nature of this disorder, or the state of the crystalline lens, whatever improvements have been made within the present century respecting its disordered state, many difficulties still attend. Mr. Pott observes, that, until about the year 1720, neither the state, nature, nor seat of this disease, was truly known, at least not to those who practised surgery. Accident, he adds, first proved it to be a distemper of the crystalline lens, and to be in general confined to it. Heister is the first writer who leads to any just idea on the subject. Mr. Pott seems to be the first who explains the true state of the crystalline humour, when a cataract is formed. He says, that the idea of a beginning or imperfect cataract being soft, and that of a mature or perfect cataract being hard, is erroneous; at least for the most part: that the natural sound transparent crystalline is very far from being uniform in its consistence through its whole substance; its external part is much softer, and more gelatinous than its internal, which, therefore, although equally transparent, may be said to form a kind of nucleus, and is always of a much firmer texture. He adds, if this known difference of consistence between the external and internal parts of the crystalline was duly attended to, it would solve many of the appearances in cataracts, which, for want of such attention, are either not at all or imperfectly understood. Among other phenomena, it would account for the very different colour which the different parts of the same cataract frequently bear; and which hath furnished the wildest conjectures. From this sound and natural state it is capable of several morbid alterations; it is capable of being dissolved, or of becoming a fluid, without losing any thing of its transparency. It hath been supposed, by very able anatomists, that the human crystalline has sometimes between its surface and its capsula, a small quantity of fine pellucid lymph, and consequently that there is no immediate connection between the body and its investing membrane. In many beasts, as well as fishes, this is known to be the case; but whether it be so in the human eye is not very easy to be known during life; though it sometimes happens from disease: that is, the whole crystalline is dissolved into a fluid, which still preserves its transparency; and this seems to form what is called the black cataract, which is a species of the gutta serena. Mr. Pott goes on to observe, that the crystalline humour is capable of being dissolved into an apparently uniform fluid of a gelatinous consistence, which will be more or less opake through the whole of it: it sometimes becomes opake while it undergoes a partial dissolution, which leaves or renders its different parts of very different degrees of consistence; and it now and then, though very rarely, becomes opake through its whole substance, and yet preserves its natural degree of firmness. From this variety of alteration, which the crystalline humour is capable of undergoing, proceeds that variety of appearance which our ancestors have called so many different kinds of cataracts. The idea of beginning cataracts being soft, and hardening as they become more perfect, hath had an unfortunate influence on practice. When the crystalline humour becomes softer than it should be, it is certainly distempered, and unfit for perfect vision, whether it be opake or not; but that this softened lens will ever be harder we have no more reason to think than we have evidences that an opacity is a proof of its induration. The most fluid cataracts are as opake as the most firm ones. If the early or unripe state be supposed an improper one for the operation, and that the patient must wait for a later or ripe one; it then becomes a matter of consideration, whether the patient shall or shall not continue blind for a very uncertain space of time, or perhaps be ever relieved. Besides the body of the crystalline lens, its capsula or investing membrane may be the seat of the disease; it may become opake, while its contents are clear and duly transparent. This may happen after the operation for depressing a harder cataract, or for discharging a softer one. When the capsula is the seat of the disease, and it takes place after depressing or extracting the crystalline lens, it sometimes vanishes in a few weeks, but occasionally requires an operation.
Respecting the operation of couching, Mr. Pott observes, that as in some instances the cataract remains always fluid, so in others it becomes instantly indurated; whence it follows, that there is no point of time for which we should wait; but at any time when, on other accounts, the object is a proper one, the surgeon may proceed. Previous to the operation, it is right to know the circumstances which render it likely or unlikely to succeed. That it may succeed, the crystalline humour should be opake, and all the other parts of the eye capable of performing their functions; the eye should be of its natural size: when, with the cataract, the globe of the eye is manifestly enlarged, the patient is incapable of perceiving light, or distinguishing betwixt light and darkness, in such a case, the operation must be omitted. The pupil ought to be capable of contracting and dilating. It hath been generally supposed, that when the pupil is immoveable it is useless to perform the operation, which is not in every instance true: the operation certainly should not be performed if the pupil is immoveable from a para. 3 B tysis of the part, nor if it adheres to the crystalline; as in these cases we could not operate with any success: but if it is immoveable, or almost so, from a distention of the crystalline humour, (which Mr. Pott thinks sometimes happens,) the operation may be performed: in these cases, however, on a very nice examination, the pupil will be found to have a very small degree of motion. The patient ought always to be able to distinguish light from darkness, and a white from a black body; if he is not, though you remove the cataract from the pupil, yet the retina is incapable of performing its office. In the following instances, success is hardly to be expected by either couching or extracting the crystalline body; viz. when the diseased crystalline is somewhat of the colour of brass, or of a bright yellow, or of a copper colour; the pupil being generally found immoveable, and the whole eye enlarged. When all the parts of the eye are enlarged, or when the crystalline protrudes through the pupil, the case is not proper for the operation.
Those who undertake to perform cither operation will, undoubtedly, have availed themselves of all the information given by the best writers on these subjects; and to those who wish for fuller directions, the subjoined writers are those from whom the whole of what art hath taught will be received.
See Celsus, Paulus Aetius, St. Yves on the Disorders of the Eyes, Heister's Surgery, Sharp's Operations, Med. Mus. vol. ii. p. 157, etc. and 412. vol. iii. p. 1. Warner and Pott on the Cataract. Bell's Surgery, vol. iii. p. 394. Medical Obs. and Inq. vol. vi. p. 250. Wallis's Nosology of the Eyes, p. 197, etc. Edinb. Med. Comment, vol. v. p. 275. White's Surgery, p. 236.