Cataract is a pathology of the refractive structure of the eye – lens, characterized by its opacity and loss of natural transparency. Cataract is manifested by “blurred” vision, deterioration of night vision, weakening of color perception, sensitivity to bright light, diplopia. Ophthalmological examination for cataracts includes visometry, perimetry, ophthalmoscopy, biomicroscopy, tonometry, refractometry, ophthalmometry, ultrasound scanning of the eye, electrophysiological studies. Conservative therapy is performed to slow the progression of cataracts; cataract removal is performed by microsurgical intervention with the replacement of the lens with an intraocular lens.
Cataract (from Greek. katarrhaktes – waterfall) – clouding or discoloration of part or all of the lens, leading to a decrease in its light conductivity and a decrease in visual acuity. According to WHO, half of the cases of blindness worldwide are caused by cataracts. In the age group of 50-60 years, cataracts are detected in 15% of the population, 70-80 years – in 26%-46%, over 80 years – in almost everyone. Cataract also occupies a leading position among congenital eye diseases. The high prevalence and social consequences of the disease make cataract one of the most pressing problems of modern ophthalmology.
The lens is part of the dioptric (light-conducting and light-refracting) apparatus of the eye, located posteriorly from the iris, opposite the pupil. Structurally, the lens is formed by a capsule (bag), capsular epithelium and lens substance. The lens surfaces (anterior and posterior) have a spherical shape with a different radius of curvature. The diameter of the lens is 9-10 mm. The lens is a vascular-free epithelial formation; nutrients enter it by diffusion from the surrounding intraocular fluid.
By its optical properties, the lens is a biological biconvex transparent lens, the function of which is to refract the rays entering it and focus them on the retina of the eye. The refractive power of the lens is heterogeneous in thickness and depends on the state of accommodation (at rest – 19.11 dptr; in the state of tension – 33.06 dptr).
Any change in the shape, size, position of the lens leads to significant violations of its functions. Among the anomalies and pathology of the lens, aphakia (absence of the lens), microphakia (reduction in size), coloboma (absence of a part of the lens and its deformation), lenticonus (protrusion of the surface in the form of a cone), cataract are found. The formation of a cataract can occur in any of the layers of the lens.
The etiology and mechanisms of cataractogenesis – the development of cataracts are explained from the standpoint of several theories, but none of them gives an exhaustive answer to the question of the causes of the disease.
In ophthalmology, the theory of free radical oxidation has become the most widespread, which explains the mechanism of cataract formation in terms of the formation of free radicals in the body – unstable organic molecules with an unpaired electron that easily enter into chemical reactions and cause severe oxidative stress. It is believed that lipid peroxidation – the interaction of free radicals with lipids, especially unsaturated fatty acids, leads to the destruction of cell membranes, which causes the development of senile and diabetic cataracts, glaucoma, microcirculation disorders in brain tissues, hepatitis. The formation of free radicals in the body is primarily promoted by smoking and ultraviolet radiation.
An important role in the mechanism of cataract development is played by an age-related decrease in antioxidant protection and a deficiency of natural antioxidants (vitamins A, E, glutathione, etc.). In addition, the physico-chemical properties of the protein fibers of the lens, which make up more than 50% in its structure, change with age. Impaired lens metabolism and the development of opacities may be associated with changes in the composition of intraocular fluid in recurrent inflammatory diseases of the eye (iridocyclitis, chorioretinitis), as well as dysfunction of the ciliary body and iris (Fuchs syndrome), terminal glaucoma, pigmented degeneration and retinal detachment.
In addition to age-related involution, deep general exhaustion after severe infectious diseases (typhus, malaria, smallpox, etc.), starvation, anemia, excessive insolation, exposure to radiation, toxic poisoning (mercury, thallium, naphthalene, ergot) predispose to the development of cataracts. Risk factors for the development of cataracts are endocrinopathies (diabetes mellitus, tetany, muscular dystrophy, adiposogenital syndrome), Down’s disease, skin diseases (scleroderma, eczema, neurodermatitis, poikiloderma Jacobi). Complicated cataracts can occur with mechanical and contusion injuries of the eye, eye burns, eye surgeries, dysfunctional heredity for cataracts in the family, high degree myopia, uveitis.
Congenital cataract in most cases is caused by toxic effects on the embryo during the laying of the lens. Among the causes of congenital cataracts are infections suffered by a pregnant woman (influenza, rubella, herpes, measles, toxoplasmosis), hypoparathyroidism, corticosteroids, etc. Congenital cataracts can occur with hereditary syndromes and be combined with malformations of other organs.
In ophthalmology, cataracts are divided into two large groups: congenital and acquired. Congenital cataracts, as a rule, are limited in area and stationary (do not progress); with acquired cataracts, changes in the lens progress.
Among the acquired cataracts, depending on the etiology, there are senile (senile, age-related – about 70%), complicated (with eye diseases – about 20%), traumatic (with eye wounds), radiation (with damage to the lens by X-ray, radiation, infrared radiation), toxic (with chemical and medicinal intoxications), cataracts associated with common diseases.
According to the localization of opacity in the lens , there are:
- anterior polar – located under the capsule in the area of the anterior pole of the lens; the opacity has the appearance of a round spot of whitish and grayish color;
- posterior polar – located under the capsule of the posterior pole of the lens; similar in color and shape to the anterior polar cataract;
- fusiform – located on the anteroposterior axis of the lens; has the shape of a spindle, looks like a thin gray ribbon;
- nuclear – located in the center of the lens;
- layered (zonular) – located around the core of the lens, with cloudy and transparent layers alternating;
- cortical (cortical) – located along the outer edge of the lens shell; has the appearance of whitish wedge-shaped inclusions;
- posterior subcapsular – located under the capsule behind the lens;
- complete (total) is always bilateral, characterized by turbidity of the entire substance and the capsule of the lens.
Among congenital cataracts, all of these morphological forms are found; among acquired ones, nuclear, cortical and complete.
In its maturation, the cataract goes through 4 stages, in connection with which there are initial, immature, mature and overripe cataracts.
At the stage of initial maturation of the cataract, there is a hydration of the lens, characterized by the accumulation of excess fluid between the fibers of the cortical layer with the formation of so-called “water gaps”. Opacities in the initial cataract are localized in the cortex, on the periphery, outside the optical zone of the lens, therefore they do not affect visual acuity.
The stage of immature cataract is characterized by the progression of opacities that affect the central optical zone of the lens. Biomicroscopic examination reveals lens opacities interspersed with transparent areas. At this stage of cataract maturation, there is a noticeable decrease in visual acuity.
At the stage of mature cataract, there is a compaction and complete clouding of the lens substance. The nucleus of the lens and its posterior cortical layers are not visible during biomicroscopy of the eye. An external examination reveals a milky-white or gray pupil. Visual acuity in mature cataracts varies from 0.1-0.2 to the level of light perception.
At the stage of overripe cataract, the crystalline fibers disintegrate, the cortical substance of the lens dilutes, and the capsule shrinks. The bark becomes a homogeneous milky-white shade. The core, having lost its support, falls down. The lens becomes like a pouch filled with a cloudy liquid, with a nucleus lying at the bottom. Such an overripe cataract is called a morganian cataract. Complete blindness corresponds to this stage.
Overripe cataract can be complicated by phacogenic (phacolytic) glaucoma associated with clogging of the natural outflow pathways of intraocular fluid by macrophages and protein molecules. In some cases, a rupture of the lens capsule may occur and the release of protein detritus into the eye cavity, which entails the development of phacolytic iridocyclitis.
The maturation of cataracts can be rapidly progressive, slowly progressive and moderately progressive. In the first variant, 4-6 years pass from the initial stage to extensive clouding of the lens. Rapidly progressive cataract develops in about 12% of cases. Slow maturation of cataracts occurs within 10-15 years and occurs in 15% of patients. Moderate progression of cataracts in 70% of cases occurs over a period of 6-10 years.
The severity of clinical manifestations depends on the stage of cataract. Visual acuity in the initial cataract may not suffer. Early signs of the disease may be double vision of objects (diplopia), flashing of “flies” before the eyes, blurred vision (“like in a fog”), staining of visible objects in a yellowish hue. Patients with cataracts note difficulties when writing, reading, working with small details.
The cataract clinic is characterized by increased sensitivity of the eyes to light, deterioration of night vision, weakening of color perception, the need to use bright lighting when reading, the appearance of a “halo” when looking at any light sources. Vision in cataracts changes towards nearsightedness, so patients with severe farsightedness sometimes suddenly discover that they see perfectly up close without glasses. The visible image blurs before the eyes, but it is not possible to correct it with glasses or contact lenses, despite the change in the level of diopters.
In the stage of immature and especially mature cataracts, visual acuity decreases sharply, objective vision is lost, only light perception remains. During the maturation of the cataract, the pupil color becomes milky white instead of black.
Cataract detection is performed by an ophthalmologist on the basis of a number of standard and additional examinations.
Routine ophthalmological examination for suspected cataracts includes visometry (visual acuity check), perimetry (determination of visual fields), color testing, tonometry (measurement of intraocular pressure), biomicroscopy (examination of the eyeball using a slit lamp), ophthalmoscopy (examination of the fundus). Together, a standard ophthalmological examination can reveal such signs of cataract as decreased visual acuity, impaired color perception; to investigate the structure of the lens, to assess the localization and magnitude of opacity, to detect dislocation of the lens, etc. If it is impossible to examine the fundus, with pronounced clouding of the lens, they resort to the study of entopic phenomena (mechanophosphene and the phenomenon of autophthalmoscopy), which allow us to judge the state of the neuroreceptor apparatus of the retina.
Special examination methods for cataracts include refractometry, ophthalmometry, ultrasound scanning of the eye in A- and B-mode, ultrasound biomicroscopy, etc. Additional methods allow an ophthalmologist to calculate the strength of an intraocular lens (artificial lens), determine the optimal operating technique.
To assess the functional state of the retina, optic nerve and central parts of the visual analyzer in cataract, electrophysiological studies are carried out: electrooculography, electroretinography, registration of visual evoked potentials.
In the initial stages of senile cataracts, conservative therapy is used, including instillation of eye drops (azapentacene, pyrenoxine, combined preparations with cytochrome C, taurine, etc.). Such measures do not lead to the resorption of lens opacities, but only slow down the progression of cataracts.
The meaning of the so-called substitution therapy is the introduction of substances, the lack of which leads to the development of cataracts. Therefore, the composition of eye drops includes amino acids, vitamins (riboflavin, nicotinic acid, ascorbic acid), antioxidants, potassium iodide, ATP, and other substances. The drug azapentacene has a different mechanism of action – due to the activation of proteolytic enzymes, it contributes to some extent to the resorption of opaque protein structures of the lens.
Conservative treatment of cataracts is ineffective, so the only method of eliminating pathology and restoring vision is microsurgical surgery – removal of the altered lens and its replacement with an intraocular lens. The possibilities of modern eye microsurgery eliminate the need to wait for the full maturation of the cataract to remove it.
Medical indications for surgical treatment include: swelling cataract, overripe cataract, subluxation or dislocation of the lens, detection of secondary glaucoma, concomitant pathology of the fundus requiring treatment (diabetic retinopathy, retinal detachment, etc.). Additional indications for the surgical treatment of cataracts are determined by professional and household needs to improve the quality of vision. In case of bilateral cataract, an eye with a lower visual acuity is operated on first.
In modern cataract surgery, several methods are used to remove clouded lens: extracapsular and intracapsular cataract extraction, ultrasound and laser phacoemulsification.
The method of extracapsular cataract extraction consists in removing the lens nucleus and lens masses; at the same time, the posterior capsule of the lens remains in the eye, separating the anterior and posterior segments of the eye. In the process of intracapsular cataract extraction, the lens is removed together with the capsule. Both operations are quite traumatic, because they require a large incision of the cornea and suturing.
The modern standard of cataract surgery is ultrasound phacoemulsification with IOL implantation. At the same time, an ultrasonic tip of a phacoemulsifier device is inserted through an incision of about 3 mm into the anterior chamber of the eye, under the action of which the lens substance turns into an emulsion and is aspirated from the eye. A similar algorithm is used for laser phacoemulsification of cataracts, during which a laser emitter is used to crush the lens.
Numerous variants of cataract phacoemulsification allow simultaneously solving related tasks: correcting corneal astigmatism (phacoemulsification with soft toric IOL), presbyopia (phacoemulsification with multifocal IOL), simultaneous surgical treatment of glaucoma (phacoemulsification of cataracts with IOL + antiglaucomatous surgery), etc.
Prognosis and prevention
Despite the speed and relative safety of cataract extraction, in 1-1.5% of observations in the postoperative period, inflammatory reactions (uveitis, iridocyclitis), an increase in intraocular pressure, IOL displacement, hemorrhage into the anterior chamber of the eye, retinal detachment, secondary cataract may develop. When the IOL is completely displaced, vitrectomy and suture fixation of the dislocated IOL are performed.
The most serious prognosis for visual function is associated with congenital cataract, since in this case, as a rule, there are changes in the neuro-receptor apparatus of the eye. Surgical treatment of acquired cataracts, in most cases, leads to the achievement of acceptable visual acuity, and often – and the restoration of the patient’s ability to work.
Prevention of congenital cataracts requires the prevention of viral diseases during pregnancy, the exclusion of radiation effects. To prevent the development of acquired cataracts, especially at a young age, antioxidant protection of the body is necessary, earlier treatment of concomitant general and ophthalmological pathology, prevention of eye injuries, annual professional examinations by an ophthalmologist.