Aphakia is a pathological condition of the organ of vision, which is characterized by the absence of a lens in the eyeball. Clinically, the disease is manifested by a decrease in visual acuity, trembling of the iris, loss of the ability to accommodate and asthenopic complaints. Diagnosis of aphakia includes visometry, gonioscopy, biomicroscopy, ophthalmoscopy, refractometry and ultrasound examination of the eye. Conservative therapy consists in correcting aphakia with the help of contact lenses and glasses. The tactics of surgical treatment is reduced to the implantation of an artificial lens (intraocular lens) in the aphakic eye.
Aphakia, or lack of a lens, is an eye disease of congenital or acquired genesis, which is accompanied by refraction pathology, decreased visual acuity and inability to accommodate. Congenital aphakia is one of the orphan diseases, the frequency of its development in the population has not been studied enough. At the same time, the number of postoperative aphakias resulting from cataract extraction increases every year. The risk of developing an acquired form of the disease increases dramatically after the age of 40. An increase in the number of acquired forms of the disease is predicted in economically prosperous countries. The development of both congenital and acquired forms of pathology is not affected by race and gender.
Causes of aphakia
The clinical classification of aphakia includes congenital and acquired forms of the disease. In ophthalmology, there are two types of congenital aphakia: primary (due to lens aplasia) and secondary (develops with intrauterine resorption of the lens). Depending on the prevalence, the absence of the lens can be monocular (unilateral) and binocular (bilateral).
A key role in the development of congenital aphakia is played by a violation of the development of the lens at the stage of embryogenesis. In the primary form of congenital malformation, the separation of the crystalline vesicle from the external ectoderm does not occur. PAX6 and BMP4 genes are normally responsible for this process. Depending on the degree of decrease in the expression of these genes at certain stages of embryonic development, the formation of anterior lenticonus, anterocapsular cataract and Peters anomaly, combined with the absence of a lens, is possible. It has been experimentally proved that the delay in the development of eyeball structures at the stage of corneal-lens contact leads to the primary form of congenital aphakia.
The cause of the secondary form of the disease is idiopathic absorption of the lens, which occurs spontaneously. One of the theories of its development is considered to be spontaneous mutation, which provokes a violation of the formation of the basement membrane, from which a lens capsule should form during embryogenesis.
In the etiology of acquired aphakia, the main role is given to surgical cataract extraction, dislocation and subluxation of the lens. Also, the causes of this disease can be penetrating wounds and contusions of the eyeball.
Symptoms of aphakia
A specific symptom of aphakia is iridodon (trembling of the iris), which develops when the eyes move. During the examination, patients have a decrease in visual acuity and the ability to accommodate. In prognostic terms, the most unfavorable is the unilateral form of the disease, since the clinical picture is complicated by aniseiconia. The anomaly induced by organic pathology is accompanied by a difference in the size of the image on the retina of the eyes, as a result of which binocular vision deteriorates sharply.
The congenital form of pathology is characterized by a progressive decrease in visual acuity with relative stability of other clinical manifestations. Lack of timely treatment can cause blindness. The postoperative form of aphakia is characterized by the stages of the course of the underlying disease, which caused the surgical intervention to remove the lens. The clinical picture of traumatic aphakia is characterized by a progressive increase in symptoms, the early manifestations of which are an intense pain syndrome with an increase in local edema and a progressive decrease in visual acuity.
From asthenopic complaints in patients with aphakia, the appearance of fog in front of the eyes, low ability to fix and double image is noted. Nonspecific manifestations of the disease are headache, general weakness, increased irritability.
The congenital form of aphakia or removal of the lens in childhood is complicated by microphthalmia. In the complete absence of the lens capsule, the vitreous body is limited only by the boundary membrane. This causes the formation of a vitreous hernia. In case of rupture of the boundary membrane, the contents of the vitreous body exit into the anterior chamber of the eye. At the same time, contact correction is a provoking factor in the development of keratitis, scarring on the cornea, in the corneal-scleral region and limb.
For the diagnosis of “aphakia”, it is advisable to conduct such research methods as visometry, gonioscopy, biomicroscopy of the eye, ophthalmoscopy, refractometry and ultrasound of the eye. With the help of visometry, it is possible to determine the degree of visual acuity reduction. This research method is shown to all patients before the correction. With gonioscopy, there is a pronounced deepening of the anterior chamber of the eye. Ophthalmoscopy is necessary to identify concomitant pathology and to choose further treatment tactics. In addition to scarring in the retina and choroid, aphakia often reveals central chorioretinal retinal dystrophy, partial atrophy of the optic nerve and peripheral chorioretinal foci.
The technique of refractometry in the unilateral form of the disease allows you to detect a decrease in refraction by 9.0 – 12.0 diopters on the aphakic eye. Hypermetropia is detected in children after extraction of congenital cataracts and averages 10.0 – 13.0 diopters. The development of microphthalmos in congenital aphakia also contributes to hyperopia. The optical section of the lens cannot be visualized by biomicroscopy. In rare cases, capsule residues are detected. When studying Purkinje-Sanson figures, there is no reflection from the back and front surfaces of the lens.
Treatment of aphakia
Correction of aphakia is carried out with the help of glasses, contact and intraocular lenses. The indication for eyeglass vision correction is a bilateral form of the disease. With unilateral aphakia, glasses are recommended only if contact correction methods are intolerant. The choice of glass for an emmetropic eye is difficult, because even a glass of +10 diopters is not comparable to the refractive power of the lens, which is equal to 19 diopters. This is due to the fact that the refractive index of the liquid that surrounds the lens is higher than the air environment surrounding the glass.
The optical power of a glass lens depends on the refraction of the patient. With hypermetropia, it is necessary to choose glasses with stronger optics than with myopia. There is no need to prescribe vision correction methods to patients with a high degree of myopia before lens removal. Due to the lack of ability to accommodate, the patient should be assigned glasses for working at close range 3.0 diopters stronger than for long-range vision.
Contact or intraocular vision correction is indicated for patients with monocular aphakia. Prescribing glasses to patients with this form of the disease will aggravate aniseiconia. During the surgical intervention (intraocular correction), an artificial lens with an individually selected optical power is implanted. The most preferred treatment option is the use of posterior chamber lenses, because being localized at the location of the natural lens, they provide high quality vision. Congenital aphakia with the help of this technique can be corrected only after the child reaches the age of two.
Prognosis and prevention
The prognosis for life and working capacity with the correct correction of aphakia is favorable. In the absence of timely treatment, there is a high risk of complete loss of vision, which subsequently leads to disability.
In ophthalmological practice, there are no specific measures for the prevention of congenital aphakia. To prevent the development of acquired forms of the disease, it is necessary to undergo an annual examination by an ophthalmologist. This will help to diagnose in a timely manner those diseases that can lead to the operative removal of the lens. Persons who are at risk of eye injuries due to the peculiarities of the profession, it is necessary to use protective glasses or masks during working hours.