If in terms of the type or degree of ametropia (defective vision) exists between the right and left eye, this is called anisometropia (inequality of vision). This is referred to when there is at least a 2.00 diopter difference.
What is anisometropia?
In anisometropia, the left and right eyes differ significantly in terms of the type or degree of optical refractive error. A wide variety of differences are possible. For example, one eye may be nearsighted and the other farsighted. Another possibility is that one eye is only very slightly farsighted and the other is very severely so. If a major anisometropia manifests itself in childhood, this can lead to a functional defective vision of the eye that is more severely defective. During this phase, which is very important for development, the eye is severely neglected by the brain, so it does not learn to see correctly. Even with later correction, this cannot be reversed. Therefore, anisometropia in childhood should definitely be treated.
Causes
There are numerous possible causes of anisometropia. The focal point of light rays incident on the eye is not located on the retina, but this is necessary for transmitting sharp image signals to the brain. In myopia, the focal point is located in front of the retina because the eye is either too long or the refractive power of the eye lens is too high. In farsightedness, the reverse is true: here, the eye is either too short or the refractive power of the lens is not sufficient. In both cases, the focal point lies behind the retina. The visual defects often occur in childhood and then persist throughout life. Other visual defects, on the other hand, develop with increasing age. Refractive anisometropia is caused by differences in the refractive power of the cornea and lens. Length anisometropia results from the fact that the eyeballs have different lengths. The absence of an eye lens is a special case of anisiometropia. It may be due to injury or removal of the lens.
Symptoms, complaints, and signs
Anisometropia is manifested by the fact that the spectacle values of both eyes are more than two diopters different. The affected person may be nearsighted and farsighted at the same time. For the brain this means an enormous load, since over the optic nerve constantly sharp, but also blurred pictures are transported at the same time into the brain. Objects close to the eye are displayed sharply by the nearsighted eye and blurred by the farsighted eye. With objects that are in the distance, it behaves the other way around. In a healthy person, two relatively identical images arrive in the brain. If anisometropia is present, the images are very different. In this case, the sharp images must be identified and the less good ones must be blanked out. In addition, those who suffer from severe anisometropia often complain of tired eyes and headaches.
Diagnosis and course
The ophthalmologist or optometrist can determine the exact extent of anisometropia by measuring visual acuity. A refractometer is usually used for this purpose. This device provides the sphere value (expressed in diopters) as well as other information as to whether a corneal curvature may be present. The visual aid is adjusted on the basis of the values collected. The visual acuity is determined separately for both eyes. Ultimately, both visual defects must be corrected. As a result, it is possible that convex lenses are used in one part of the eyeglasses and concave lenses in the other. Smaller deviations between the right and left eye are present in almost everyone. Anisometropia, if not treated, often leads to strabismus in young children. The reason for this is that the weaker eye is “switched off”, so to speak, by the brain. Anisometropia should therefore be treated before puberty sets in, if possible, as it cannot be successfully treated at a later stage.
When should you see a doctor?
Anyone who regularly suffers from tired eyes, headaches, or a feeling of pressure around the eyes should seek medical advice. The doctor can determine if it is anisometropia and consult an ophthalmologist or optometrist if necessary. In any case, anisometropia must be diagnosed and treated to avoid long-term vision limitations.If the visual disorder remains untreated, this can also lead to a reduced sense of well-being, chronic headaches and other complaints. Eyeglass and contact lens wearers should speak with an ophthalmologist if they experience migraine attacks or increasingly poor vision. Because anisometropia can worsen with age, the vision of both eyes should be checked regularly. In severe cases, the diopter strength must be adjusted annually or more often to ensure optimal vision. Therefore, even with diagnosed anisometropia, one must visit the ophthalmologist or optometrist regularly. If symptoms still occur, further examinations are recommended. Possibly, there is another disease of the eyes that requires treatment.
Treatment and therapy
If glasses are used in the case of anisometropia, there are some disadvantages: Correction produces retinal images of different sizes that are processed poorly or not at all by the brain. In addition, the eyes look very different behind the lenses and there is also a one-sided pressure load. There are limitations in wearing comfort as well as in the aesthetic effect. The optician generally has limits, so three diopters is the maximum difference between the right and left lenses. If the refractive error deviates more, perceptual disturbances are possible. Contact lenses are more suitable for correcting a large anisometropia. Surgical procedures are also available, but surgical correction of the eyes in children is controversial. In addition, in adults, anisometropia can be corrected by ophthalmic laser after adequate contact lens simulation.
Outlook and prognosis
Anisometropia does not have a good chance of improvement without ophthalmic therapy. Instead, symptoms can be expected to increase in the coming months and years. In the brain, information from the weaker eye is not adequately processed without corrective measures. Therefore, the nerve cord visibly atrophies. Strabismus sets in with these patients and in the long term the visual impairment is further intensified. A complete cure of anisometropia is not always possible even with early treatment with current medical options. It depends on the existing visual acuity. However, significant improvements exist with a good treatment plan that must be established and followed over many years. The visual acuity of the weaker eye can be trained more strongly by various methods, so that an increase in visual acuity develops in this eye. The vision of both eyes is thus adapted to each other in slow steps. Although the development of the eye is already finished at the age of 12 years, in case of anisometropia necessary treatments and therapies have to be taken even in adulthood. There is a very high risk of recurrence, which must be counteracted. Because of the possibility of recurrence, the patient rarely emerges from treatment as completely cured.
Prevention
The best way to avoid anisometropia is to actively do something yourself to maintain normal vision and prevent vision loss. It can already help to pay attention to the reading distance (not less than 30 centimeters), since too short a reading distance promotes myopia. If you work a lot on the computer, you should choose a large monitor and place it one meter away from you. During close-up work, it is advisable to look into the distance from time to time. In addition, care should be taken to ensure good lighting. A little vision training does not change the anatomical conditions of the eyes, i.e. the optics, but it does increase contrast sensitivity. To do this, even small activities such as always alternating wearing and taking off the visual aid will help.
Aftercare
Treatment of anisometropia usually does not bring a final cure. Adults, in particular, often relapse after successful therapy at a young age. Consequently, permanent vision correction becomes necessary, but medical treatment is only sought for acute symptoms. A refractometer is used to determine visual acuity. The patient can choose among vision aids for smaller dioptric differences between the right and left eye. In the case of large deviations, contact lenses should be used.It is scientifically recognized that the processing of images is comparatively strenuous for the brain. However, the perceptions of everyday life offer hardly any difficulties, so that there is a decent vision. Some patients opt for surgery, with which anisometropia is also treatable. Adults can strengthen their vision through small exercise sessions. These can easily be done at work or in private. A reading distance of at least 30 centimeters should be maintained. When working on a computer screen, people should prefer large displays and not stare at the monitor continuously. Looking into the distance increases contrast sensitivity.
This is what you can do yourself
Everyday life with anisometropia without appropriate correction is difficult to manage. Often, the brain turns off one eye, leaving the other untrained. Affected people can do nothing themselves for self-treatment, except to put themselves in the hands of an ophthalmologist. In most cases, the defective vision is corrected with contact lenses. Correction with glasses can lead to retinal aberrations (aniseikonia) of various sizes. These can be accepted by the brain only insufficiently or not at all. Further difficulties would arise due to the optical impression and the weight of the different lenses. Therefore, correction by means of contact lenses is the means of choice. This also makes everyday life easier, because the contact lenses lie directly on the eye and “send” the perceived images in the processable impression to the brain. This can now combine the two-sided impressions into a whole. Then a differing defective vision is no longer a problem. However, the visual defect should be checked by the ophthalmologist at regular intervals so that he can adjust the necessary lens strengths. Even after the adjustment by means of contact lenses, training is required. After all, the brain must first get used to receiving “normal” impressions. Then it is a matter of persevering with iron.
