Lens anomalies are malformations, less often acquired pathologies in which the ability to accommodate, light transmission or light refraction is impaired. Common symptoms for most forms are impaired visual functions, the appearance of “fog” or “shroud” in front of the eyes. Diagnostics includes external examination, biomicroscopy, gonioscopy, visometry, ultrasound in In-mode, OCT. Treatment tactics depend on the type of lens abnormalities. Conservative correction of visual acuity with glasses is possible only with ectopia. Surgical treatment of lens anomalies is reduced to phacoemulsification or implantation of an intraocular lens.
Q12 Congenital anomalies [malformations] of the lens
Lens anomalies are a heterogeneous group of diseases in clinical ophthalmology characterized by changes in the shape, size, transparency or ectopia of the lens. Congenital variants of pathologies, as a rule, are diagnosed during the newborn period or in early childhood. In children, cataracts occur with a frequency of 5:100,000. In old age, this disease causes almost 50% of all cases of blindness, and after the age of 60, a certain degree of lens opacity is determined in every second patient. Anterior lenticonus is often diagnosed in males, posterior – in women. Lens anomalies can develop in isolation or be one of the manifestations of genetic syndromes (dislocation of the lens in Marfan or Markezani syndrome).
Violation of the embryonic period of development can lead to such anomalies of the lens as primary or secondary aphakia, coloboma, lenticonus, ectopia of the lens, etc.
- Causes of aphakia. In the primary variant of the disease, complete aplasia of the lens is observed. The trigger mechanism is a decrease in the expression of the PAX6 and BMP4 genes, which are responsible for the process of differentiation of the embryonic rudiment of the lens and its separation from the external ectoderm. The cause of the development of the secondary form is intrauterine inflammation or idiopathic rupture of the lens capsule. With a delay in differentiation or a violation of the reverse development of the capsule vessels, bifacia occurs.
- Causes of coloboma. The reason for the development of a congenital variant of this lens anomaly is complete or partial aplasia of the ciliary girdle. The trigger of the acquired form may be the mechanical pressure of a cyst or a pathological neoplasm on an already formed ciliary girdle.
- Causes of lenticonus. An etiological factor in the development of anterior lenticonus is a violation of lens separation caused by low resistance of the lens capsule. The absence or pathological attachment of zonular fibers also contributes to the occurrence of this lens anomaly. The appearance of the posterior lenticonus is due to pronounced tension or rupture of the posterior capsule. The triggering factor is the reverse development of the artery of the gelatinous body at the stage of embryogenesis.
- Causes of ectopia of the lens. Ectopia is one of the genetically determined anomalies of the lens. The type of inheritance is autosomal dominant. The etiology of the disease is associated with a mutation in the FBN1 gene, which is responsible for the synthesis of fibrillin. This protein is part of many body tissues, which explains the high prevalence of dislocations and subluxations of the lens in Marfan syndrome. However, family cases of isolated development of ectopias of the lens are described.
- Causes of micro- and macrofacies. Lens anomalies associated with a change in its size (micro-, macrofacia) occur in patients with a change in the structure of the ciliary ligament, degeneration or stretching of glycoprotein fibers.
Symptoms of lens abnormalities
A specific symptom of microphakia is the trembling of the iris, which develops when the eyeballs move. With this anomaly of the lens, ametropia occurs, which is associated with a discrepancy between refraction and the length of the visual axis. Due to a violation of the ability to accommodate patients, visual functions are sharply impaired. Lens anomaly often complicates the course of Weill-Markezani syndrome. With macrofacia, an increase in the lens leads to an increase in intraocular pressure, which also causes visual dysfunction and a high risk of secondary glaucoma.
In primary aphakia, the biological lens is completely absent in the structure of the eyeball. The presence of an underdeveloped lens or its parts is characteristic of the secondary form. With this lens anomaly, patients complain of decreased visual acuity, iridodon and asthenopic manifestations. With bifacia, due to the double elastic formation in the eyeball cavity, the refraction function changes dramatically.
The number of lens defects include anterior, posterior or internal lenticonus, in which one of its parts changes its configuration. With this anomaly of the lens, the clarity of vision is significantly impaired. The anterior form of the disease is characterized by a marked decrease in visual acuity. The posterior lenticonus is characterized by a monocular lesion.
A coloboma can develop as an isolated lens anomaly. Less often, the disease is combined with microphthalmia, ectopia of the cornea or the pupillary membrane. If this pathology is accompanied by clouding of the lens, patients complain of the appearance of “fog” or “shroud” in front of the eyes.
Dislocation of the lens
Dislocation of the lens is often complicated by secondary glaucoma or uveitis. A specific symptom complex of subluxation: trembling of the iris, lens and a decrease in the size of the anterior chamber of the eye.
The diagnosis of lens anomalies is based on anamnestic data, the results of external examination, biomicroscopy, gonioscopy, visometry, tonometry, ultrasound examination (ultrasound) in In-mode, optical coherence tomography (OCT).
Diagnosis of micro- and macrofacies
During external examination of patients with microphakia, mydriasis is observed. The method of biomicroscopy reveals an anomaly of the lens, in which the size, as well as the ciliary ligaments do not correspond to the reference values. The depth of the anterior chamber of the eye increases, the walls become uneven, which is visualized during gonioscopy.
In patients with macrofacia, a significantly enlarged lens is found on OCT. The size of the anterior chamber of the eye of this lens anomaly is decreasing. The tonometry method determines the increase in intraocular pressure. Both micro- and macrofacies are accompanied by a violation of accommodation. This leads to a decrease in visual acuity, which is confirmed during visometry.
Diagnosis of aphakia
With primary aphakia by biomicroscopy, there is a complete absence of the lens in the eyeball cavity. For differential diagnosis with a secondary form of the disease, OCT. Unlike primary aphakia, the secondary one visualizes an underdeveloped lens or parts of it. In 30% of patients with coloboma, the turbidity of the biological lens is determined during biomicroscopy. A triangular, crescent-shaped or ellipsoid defect is detected in the lower quadrant. With lens anomalies manifested by dislocation (dislocation, subluxation), part of the biological lens is shifted to the anterior chamber of the eye, which is diagnosed by gonioscopy.
Diagnosis of lenticonus
With lenticonus, the biomicroscopy method determines the protrusion of one of the walls of the lens with complete preservation of transparency. In patients with an anterior variant of this lens anomaly, the anterior capsule becomes thinner, the number of epithelial cells decreases with the cortex of the anterior layer bulging. The lens has the form of a ball or cone. The movement of the eyeballs is accompanied by dislocation of the anterior lenticonus in the same direction. With the posterior form of this lens anomaly, there is a shift in the opposite direction. The method of biomicroscopy reveals the thinning of the posterior capsule with an abnormal structure of the nucleus. With internal lenticonus, the external structure of the lens corresponds to the norm, but the fibers have a cone-shaped shape.
Treatment of lens anomalies
Treatment tactics are determined by the form of the lens anomaly. Surgical intervention in microphakia is indicated for patients with a decrease in visual acuity of less than 0.2 diopters. At the first stage, an operational micro-incision is performed, followed by capsulorexis. With the help of special ultrasound equipment, fragmentation and aspiration of the lens is carried out. The next stage is the implantation of an intraocular lens of the required size. To correct visual acuity, contact lenses or glasses are used only in patients with minor changes in visual acuity. Surgical intervention is recommended in adolescence. Macrofacia is also an indication for the removal of the lens with further implantation of a special lens.
Conservative treatment is recommended for mild ectopia of the lens, lenticonus or aphakia. In case of dislocations of a biological lens or binocular aphakia (dislocation, subluxation), vision correction is carried out using glasses. The monocular absence of the lens is an indication for the appointment of contact methods of correction of visual acuity. In case of low efficiency, surgical intervention is recommended. Among the methods of surgical treatment of lens anomalies, in particular, cataracts, phacoemulsification with subsequent implantation of an intraocular lens is the most common.
Prognosis and prevention
There is no specific prevention of lens anomalies. Non-specific preventive measures for the development of congenital forms are reduced to reducing the teratogenic effect of medications, chemicals on the fetal body. During pregnancy planning, a woman is shown to conduct special tests for a group of TORCH infections, because their course leads to a violation of the formation of the organ of vision at the stage of embryogenesis. All patients with congenital or acquired lens abnormalities should be examined by an ophthalmologist 2 times a year. The prognosis for life in this group of diseases is favorable. However, with ineffective treatment, most forms are accompanied by a decrease in visual acuity and disability.