Correction of poor vision

Correction of poor vision is based on enhancing the visual image by:

• improving image quality;
• magnification of the image on the retina;
• expansion of the field of vision.

The means of assistance are selected individually, depending on the nature of the pathology of the visual organ, anatomical and optical characteristics and other ophthalmological parameters.

Expansion of the "tunnel" field of vision is effective with sufficiently high central visual acuity; it is carried out using reverse telescopes and negative lenses of high refraction.

Improvement of image quality is achieved by correcting ametropia and astigmatism, using diaphragms, spectral filters, and creating optimal illumination levels. In case of ametropia, which is observed in 98% of visually impaired children, glasses or contact lenses are used for distance correction. Special therapeutic light filters are effective in 95% of cases. They protect the eye structures from the damaging effects of UV radiation, provide increased visual acuity and contrast, create optimal illumination levels, reduce light scattering in the eye environments, and help prevent the development of visual complications. They are used with glasses for distance vision and for reading, when working with a computer. The choice of the optimal filter is influenced not only by the main but also concomitant ophthalmopathology, the type of visual work, and lighting conditions.

Diaphragm devices increase the resolving power of the eye in non-obscuring opacities of optical media. The use of chromatic spectacle correction and a diaphragm can significantly increase visual acuity, but in most cases it is insufficient for the most difficult visual task - reading.

The main way to improve the perception of a visual image is to increase its retinal image in order to involve the functioning paracentral and peripheral areas of the retina in the work.

Distant objects are better distinguished with the help of afocal telescopic systems of Galilean or Keplerian type of different power, which are divided into telescopic glasses, monoculars and binoculars. Children prefer to use portable monoculars of 2.5-5x magnification, focusing objects from infinity to 1 m. The need to improve distant vision arises mainly during the period of receiving general or special education, during orientation.

The most difficult visual task is reading. Magnifying devices used to improve near vision: hyperocular glasses of mono- and binocular use, magnifying glasses of various powers and designs, telescopic glasses and electronic video magnifiers.

Hyperoculars - glasses with positive spherical or spheroprismatic lenses (so-called magnifying glasses) - are one of the main means of helping children with low vision, with the exception of people with myopia. Leaving hands and workspace free, they can magnify the observed object up to 5 times. With visual acuity above 0.15, glasses often serve as the most popular magnifying means.

Loupes of various design solutions with magnification of 1.5-12x have wider indications for use. In case of weak accommodation, aphakia, overhead or support loupes are preferable. However, the higher the magnification, the narrower the diameter of the lens and, accordingly, the fewer letters in the field of view. To expand the visible field, two types of magnifiers are combined: hyperoculars (which can also be used for writing) and loupes.

Children do not use telescopic glasses that are more difficult to use due to significant limitations of the field of vision, an unaesthetic appearance, and significant dimensions; glasses are also not effective in cases of oculomotor pathology (nystagmus, strabismus).

Modern electronic video magnifiers have many attractive characteristics for the visually impaired: a large size of the visible field, sufficient depth of field, stable working distance and clear focusing. A wide range of magnifications (5-40 times) allows you to distinguish book font with a visual acuity of 0.01-0.02. When working, you can use contact and spectacle correction, light filters, maintain correct posture, perform eccentric fixation of the gaze, connect the worse-seeing eye to reading. Inversion of the image of letters, adjustable brightness, contrast provide comfortable conditions for both people with photophobia and those requiring increased levels of illumination. In cases of different visual acuity in both eyes, the device can provide acceptable conditions for the second eye to perceive information. However, the reading speed is limited by the limited number of letters on the monitor screen (although their number in the field of view is greater than when using magnifying glasses of equal magnification). The reading speed is reduced by the delay in the appearance of a clear image of letters on the monitor when moving the camera along the line; discoordination of eye movements when reading (from left to right) and the "running" line on the screen (from right to left); time spent on manually translating text from line to line. In this regard, video magnifiers are recommended for children with a significant decrease in vision: from 0.02 to 0.1-0.12, with a reading speed of no more than 500-600 characters per minute.

Children easily adapt to new situations and quickly learn to use optical devices. In addition to correcting visual acuity, it is necessary to improve oculomotor activity and develop eye-hand coordination. A thorough examination of the central zone of the visual field can help in choosing the most optimal position of the book with the fixation of the text by the area of the retina with the highest resolution or with a sufficiently wide field. The appointment of various means of special assistance, in addition, depends on the age of the child, his somatic pathology, the presence and severity of psychoneurological disorders. Children under 5-6 years mainly need means to improve the quality of the image: glasses, contact, intraocular lenses, spectral filters; to examine close objects, you may need second glasses, 2-4 diopters stronger than glasses for distance. The help of parents, caregivers, and teachers is important. When entering school, other magnifying devices are also used: support or overhead magnifying glasses of large diameter. In addition to improving the perception of small objects, magnifying glasses prevent the reduction of the working distance, which is important for the prevention of chest and spine deformation in children. The need for magnifiers increases throughout the entire school period: visual load increases, the educational font decreases, the disease may progress. In adolescence, children more often use telescopes for distance, age-related decrease in the volume of accommodation requires more powerful magnifiers when reading and writing. They use the computer more actively, when working with which they often use bifocal glasses. Teenagers show more personal initiative in mastering magnifying means to expand communication, receive various visual information.

Special correction of low vision is effective throughout the life of a child with a disability and serves as one of the main components of a complex of rehabilitation measures for obtaining an education, rational employment and improving the standard of living.

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