Contact vision correction: indications and contraindications

Contact correction is widely used in myopia. It is known that patients with high degree myopia, especially with anisometropia, do not tolerate a full score correction, and the resulting optical aberrations are not compensated for by spectacles. Contact lenses are well tolerated in myopia of almost any degree and myopic anisometropia with any differences in the refraction of both eyes. They contribute to the restoration of binocular vision, improve the condition of the accommodation apparatus of the eye and ensure high visual performance, while wearing glasses it is necessary to be content with only a tolerable correction (with a difference in the optical power of spectacle lenses of not more than 2.0 D).

Thus, myopia is the kind of ametropia in which contact lenses have absolute advantages over glasses.

Relative indications for contact correction of sight can be considered hypermetropia and hypermetropic anisometropia. If the minus glass glasses reduce the size of the image on the retina, then the plus ones, on the contrary, increase, so patients with hypermetropia worse adapt to contact lenses, which, as is known, do not change the size of the image.

When astigmatism is not always possible to achieve maximum visual acuity with the help of spectacle correction. Contact lenses successfully compensate for corneal deformities. When using lenses, patients do not complain about asthenopia. Toric soft contact lenses and gas-permeable hard contact lenses give a clear, high-contrast image.

Contact lenses are also used to correct aphakia.

With keratoconus, the average visual acuity of patients using contact lenses is approximately 2 times higher than with spectacle correction. In addition, patients who wear contact lenses have stable binocular vision. For correction of vision in the initial stages of keratoconus, gas-tight rigid contact lenses are used. With severe deformation of the cornea, the selection of contact lenses is difficult, and if this can be done, their tolerability is reduced. In this case, keratoplasty is indicated.

Cosmetic masking contact lenses are successfully used in congenital and post-traumatic eye lesions. In the case of an iris or aniridia cola, contact lenses with a colored peripheral zone and a transparent pupil not only produce a cosmetic effect, but also reduce light scattering on the retina, eliminate photophobia and increase visual acuity.

For correcting presbyopia, hard contact lenses are used, but in recent years bifocal and multifocal soft contact lenses have appeared.

Contact correction is used in the treatment of amblyopia. To this end, designate cosmetic contact lenses with a colored (opaque) pupillary zone or a lens of high optical power to turn off a better seeing eye. This creates conditions for connecting the amblyopic eye to visual work.

Contact lenses can be applied with therapeutic purposes for various diseases of the cornea. Practice shows that soft contact lenses saturated with drugs are very effective in the treatment of eye diseases and injuries (with bullous keratopathy, non-healing corneal ulcers, dry eye syndrome to maintain the humidity of the cornea, for the rehabilitation of patients after keratoplasty and eye burns).

However, there are objective medical contraindications to contact correction. First of all, these are inflammatory diseases of the anterior part of the eye. Wearing contact lenses causes the worsening of patients with parasitic eye diseases (especially with common tick-borne blepharitis - demodecosis). With special care, contact lenses should be prescribed to patients with dry eyes. In this case, it is better to use highly hydrophilic soft contact lenses (with a moisture content of more than 55%), and also use special moisturizing drops when wearing lenses.

Contact lenses are contraindicated for lacrimal obstruction and dacryocystitis.

With iterigium and pingvecula, the selection of contact lenses is difficult due to mechanical obstacles to their movement along the cornea. In these cases, it is recommended to perform a surgical treatment beforehand.

Finally, the absolute general contraindication to wearing contact lenses is mental illness.

Basic principles of contact lens selection and their features. The main criteria for preference for hard contact lenses in front of soft contact lenses are the presence of severe astigmatism (more than 2.0 D), a small eye gap, a small diameter of the cornea, intolerance of soft contact lenses. It should be emphasized that caring for hard contact lenses is easier, they cause fewer complications, they can be used for a longer period of time.

To select the optimal parameters for corneal hard contact lenses, it is necessary to determine the overall diameter of the lens, the diameter of the optical zone, the optical power of the lens, and the shape of its inner surface. When choosing the overall diameter of hard contact lenses, account for the size of the eye gap, the position and tone of the eyelids, the degree of the eyeballs, the diameter and shape of the cornea. The total diameter of hard contact lenses should be 1.5-2 mm below the horizontal diameter of the cornea. The inner surface of the corneal hard contact lenses has three zones: a central, or optical, slip zone and an edge zone. The diameter of the optical zone of the lens should be greater than the width of the pupil determined by diffuse light, so that the lens shift at blinking does not lead to an appreciable shift of the optical zone of the lens beyond the pupil. The gliding zone should correspond as much as possible to the shape of the cornea at this site and is designed to hold rigid contact lenses on the cornea due to the forces of capillary attraction. The smaller the pressure of the lens on the cornea in the slip zone, the higher the lens tolerance. The shape of the edge of the lens is determined empirically. It should provide the formation of a meniscus tear fluid and not cause the patient unpleasant sensations. To maintain the lens on the eye due to capillary forces, the gap between the lens and the cornea should be sufficiently small, close in thickness to the natural lacrimal film.

The optical force of the contact lens is determined from the results of a clinical eye refraction study: it is equal to the spherical refractive component + 1/2 of the value of the cylindrical component. Finally, the optical power of the lens is established with a trial lens, whose optical power is closest to the value of clinical refraction. To the trial lens

Attach different glasses from the set to get the maximum visual acuity. When correcting myopia, choose a glass of minimal dioptric power to obtain the greatest visual acuity, and when correcting hypermetropia and aphakia, the glass is the maximum dioptric force.

To calculate the refraction of the contact lens to the optical power of the trial lens, the optical power of the spectacle glass with which the patient has the maximum visual acuity is added. The success of the selection of contact lenses depends on the following factors: the correspondence of the inner surface of the lens to the shape of the cornea, the centering of the lens and its mobility.

When selecting rigid contact lenses, they strive for maximum correspondence of the inner surface of the lens to the shape of the cornea, taking into account the preservation of a certain thickness of the tear fluid layer between the lens and the cornea in various zones. The lacrimal liquid is tinted with a 0.5% fluorescein solution, and the slit lamp in the light of the blue filter measures the fluorescein distribution under the test lens and determines the need for changes in the design of the individually manufactured lens.

It is extremely important to investigate the sensitivity of the cornea, the condition of lacrimal organs, the production of tear fluid, and the time of rupture of the tear film. Then determine the size of the ocular neck, the turgor of the eyelids and the diameter of the pupil.

After a routine ophthalmological study, they begin to choose the shape of the lens and its optical power. Using an ophthalmometer determine the radius of curvature of the cornea in the main meridians and decide on the choice of the type of lens.

Under local anesthesia (0.5% solution of dicain), hard contact lenses are put on the eye from a test set of lenses whose optical strength and design parameters (total diameter, diameter of the optical zone and the shape of the inner surface) correspond most closely to the parameters of the eye being corrected. Assess the position of the lens on the eye, its mobility, the distribution of fluorescein under the lens. If the design of the lens selected from the test kit is optimal, an individual rigid contact lens is manufactured.

For the final confirmation of the correctness of the selection of gas-permeable rigid contact lenses, it is necessary to observe the patient for 2-3 days, gradually increasing the time of wearing the lens daily. In the adaptation period, the lens can be modified. At the end of the trial period, the manufactured lens is given to the patient, instructing him about the rules of use and the wearing regime.

Spherical soft contact lenses, due to their elasticity, are effective only in the absence of significant changes in the shape of the cornea, since they are more often repeated in the wrong shape (for example, when astigmatism exceeds 2.0 D). The choice of soft contact lenses is quite simple and is based on the results of ophthalmometry. There are special tables for corneal radii and refractions, the optical power of spectacle lenses and soft contact lenses. The thickness of soft contact lenses is chosen taking into account the individual characteristics of the eye. With moderate astigmatism or reduced production of tear fluid, thicker soft contact lenses are prescribed (thin, highly hydrophilic soft contact lenses are dehydrated faster and do not correct astigmatism). After the initial selection of soft contact lenses, the position of the lens on the eye, its mobility and subjective sensations of the patient are evaluated.

The correct position of the lens can be checked with a "blending test" when the lens is moved along the cornea by 1/3 to 1/2 of its diameter: with a good fit, the lens should slowly return to the center position.

The recommended duration of wearing soft contact lenses for the adaptation period: in the first 3 days - 1-2 hours a day, for the next 3 days - up to 3 hours a day, from the 2nd week - for 4 days for 4 hours a day, then 3 days for 5 hours a day, from the 3rd week daily increase the time of wearing soft contact lenses for 1 hour, bringing it up to 12 hours a day.

[1], [2], [3], [4], [5]