Anatomy.-The crystalline lens is a transparent, bi-convex, solid body that is inclosed in a transparent capsule and rests just behind the iris in a depression in the vitreous humor. The measurements of the lens at different periods of life were most carefully made by Priestley Smith, Trans. Ophthal. Soc. vol. iii, 1883. who examined one hundred and fifty-six lenses and found the diameters to vary from 8.25 mm. to 10 mm. The antero posterior diameter was not systematically measured, but he believes that the measurement of 3.7 mm. attributed to this axis of the lens in the schematic eye is too small even for the young adult, and that in elderly people he has found the axial thickness of the lens to be as high as 6.5 mm. His experiments also show that the healthy lens increases in weight and volume throughout the whole of life, adding from the twenty-fifth to the sixty-fifth year of life one-third to its weight, one-third to its volume and one-tenth to its diameters. Lenses which are becoming cataractous are as a rule smaller than healthy lenses. The lens in the young is perfectly colorless, but becomes yellowish later in life, at the same time it becomes flatter and less elastic. The shape of the lens is, therefore, more globular in early life, and, from its greater elasticity at this period, it has a greater amplitude of accommodation.
The substance of the lens is made up of long fibres or cells and interstitial cementing substance. The fibres are band-like structures having an oval nucleus and are arranged in concentric lamellae, each lamella consisting of a single layer of fibres. Each lens-fibre runs from the anterior to the posterior surface in a meridional direction, the ends meeting at the poles of the lens in such a manner as to form a stellate figure. The result of this arrangement is to divide the mass into sectors. The fibres toward the centre of the lens are more compressed than the peripheral ones, and hence the centre of the lens is spoken of as the nucleus and the more peripheral portion as the cortex. The refractive index of the lamellae increases from the periphery toward the centre. In the young the superficial fibres have about the same index of refraction as the aqueous; but, as the refracting power increases with age, the difference causes an abrupt change which creates a reflection of light from the surface of the lens in old people and causes the grayish or semi-opaque appearance of the pupil so frequently seen in the aged.
The capsule of the lens is a highly elastic homogeneous membrane, thicker in front than behind. The anterior capsule is lined with a single layer of transparent, hexagonal cells which are supposed to govern the nutrition of the lens. The posterior capsule has no epithelial lining, but is in close contact with both the substance of the lens and the vitreous.
The lens is held in position by the zonule of Zinn or suspensory ligament of the lens, which is a continuation of the membrane limitans of the retina. This membrane is firmly attached to the ciliary processes, and, as it passes to the border of the lens, divides into two layers, to be inserted into both the anterior and posterior capsule. The small space left by the separation of this membrane is called the canal of Petit and is supposed by some to convey the nourishment to the lens. The function of the zonule is Zinn of probably to maintain the lens in situ and to control its accommodative changes.
Cataract.-Opacity may occur in the lens or its capsule, or both.
PATHOLOGY.-The pathological changes in cataract have been especially studied in senile cataract. It commences by the separation of the lens-fibres at spots so that spaces containing fluid (spheres of Morgagni) are produced. These spaces are first formed between the nucleus and the cortex and are supposed to be due to sclerosis and shrinking of the nucleus. The liquid within the spaces, which is at first transparent, coagulates and becomes cloudy. The lens-fibres then become cloudy and contain in their interior minute drops of a fatty substance. The lens-fibres swell up in spots and finally break down, so that from the lens tissue there is formed a pultaceous mass composed of drops of fat, spheres of Morgagni, remains of lens-fibres, and an albuminous liquid. As the lens-fibres break down liquid collects between the lens and capsule, loosening the intimate connection that normally exists.
The nucleus remains unchanged in the midst of the disintegration cortex. There may later be a gradual resorption of the pultaceous lens-masses resulting in some clearing up of the opacity.
Capsular Cataract is due to a deposit upon the inner surface of the capsule, between it and the lens, and results from a proliferation of the capsular epithelium. There is formed a multiple layer of these cells from which, by the growth of the epithelial into elongated fibres, there is formed a sort of fibrous tissue which causes a distinct elevation on the anterior surface of the lens.
In Soft Cataract the fibres are swollen and varicose; they become degenerated and destroyed. There is an increased amount of fluid, the fibres containing molecules, and debris of fat are thrown off between the fibres. The Traumatic Cataract is due to an injury, causing a rupture in the capsule, allowing the entrance of the aqueous, which causes a swelling and disintegration of the lens fibres. In Diabetic Cataract Kamocki Archiv. Ophthal., vol. xvii., 1, 1888. describes the pathological changes in the lens as follows: Commencing with proliferation of the intra-capsular cells, together with the formation of vesicle cells, and, finally, the absorption of water by the lens nucleus, with resulting loosening of its fibres, and drops of water forming in the spaces made by the separation of its fibres.
SYMPTOMS.-There is at first the appearance of motes before the eye and a slowly progressing dimness of vision which causes some obscuration of distant objects and, from the swelling of the lens, the refraction of the eye increases so that the tendency is to cause myopia of a low degree. The opacity in the lens will also often produce astigmatism or alter an already existing irregularity. The extent of the loss of vision will depend upon the situation and extent of the opacity and will be different in different cases;some will be greatly affected by the presence of a few striae, while in others we are often surprised at the acuity of vision that will be possessed by an eye in which the fundus will be almost obscured by the numerous striae. As the lens becomes more and more opaque the acuity of vision is gradually reduced until only perception of light remains. Photophobia and phosphenes are sometimes complained of and in some cases pain and asthenopic symptoms will be experienced on attempting to use the eyes. There is occasionally from the strain on using the eyes slight conjunctival hyperaemia. In ripe cataract the pupil will appear gray or white in color, excepting in some cases of so-called “black cataract,” when it will appear dark; the pupil may also be small and sluggish. The anterior chamber is sometimes a little shallow from swelling of the lens.
The use of the ophthalmoscope, together with the oblique illumination, renders the diagnosis of cataract not at all difficult. Dilatation of the pupil either with homatropine or preferably cocaine renders the examination more thorough. With the oblique illumination the opacity, if immature, appears as white as gray streaks or dots. The ophthalmoscope is used by the direct method and with a weak illumination. The patient is then made to look in all directions so as to bring all parts of the periphery into view. The most frequently seen opacities in cataracts are in the form of streaks or spiculae running from the periphery toward the centre of the lens, and which appear black with the ophthalmoscope. Particles may be seen in any part of the lens and the remainder of the lens are perfectly transparent. Thus the nucleus may be involved and the periphery clear, or the periphery may be affected all around or at one spot and the nucleus and balance of the lens remain clear. If the opacity involves the whole substance of the lens, there will be no reflex from the fundus. In some cases the undilated pupil will give no reflex, but, upon using some mydriatic, the periphery of the lens will give the reflex, showing that the cataract is still immature and that the extreme periphery has not become entirely opaque.
COURSE.-Simple senile cataract, as a rule, follows a progressively increasing course from incipiency to full maturity; but, according to some authorities, an immature cataract may in some cases remain stationary for many years. The period of time required for the development of mature cataract from its incipiency is most variable, as in some cases the cataract will progress rapidly and blindness ensue within a few months, while others will go on for several years before the cataract will become fully matured. Some idea of the rapidity of the progress may be formed in the striated variety of the cataract from the appearance of the striae, as the thin, narrow striae are of much slower course than are the broad and thick striae. Opacities occurring as dark, flocculent masses usually advance more rapidly than do those commencing as striae. Opacities showing both the striae of the cortex and the haziness of the nucleus as well, as spoken of a mixed cataracts and are usually more rapid in their progress. After reaching maturity the cataract may proceed to the condition of “over-ripeness of Morgagnian cataract, in which the cortical substance becomes liquified and the nucleus displaced. Other changes sometimes met with in over matured cataracts are calcareous and fatty degenerations of either the lens or its capsule. Spontaneous absorption may take place in diabetic cataracts, and has been reported as occurring in the ordinary senile cataract.
Professor of Ophthalmology in the College of the New York Ophthalmic Hospital; Surgeon to the New York Ophthalmic Hospital. Visiting Oculist to the Laura Franklin Free Hospital for Children; Ex-President American Homoeopathic Ophthalmological, Otological and Laryngological Society. First Vice-President American Institute of Homoeopathy : President Homoeopathic Medical Society of the State of New York ; Editor Homoeopathic Eye. Ear and Throat Journal : Associate Editor. Department of Ophthalmology, North American Journal of Homoeopathy, etc.