The eye test involves an examination and determination of visual acuity, or so-called visual acuity, and is a fundamental component of every ophthalmologic examination. Visual acuity is defined as the resolving power in angular minutes at which the human eye can just perceive two points as separate objects. A visual acuity of 1.0 (100%) corresponds to normal visual acuity; with increasing age, the visual acuity decreases and falls below 1.0. The visual acuity test is mandatory for every driver’s license applicant in classes A, A1, B, BE, M, L or T. For driver’s licenses in classes C, C1, CE, C1E, D, D1 or E, a certificate is required to test the visual field, spatial vision, ocular motility, twilight vision and color vision. In principle, an eye test can detect any visual acuity (visual acuity) loss; however, the causes of most conditions are complex and require extensive further diagnostic testing. Common causes of visual acuity (visual acuity reduction) include:
- Myopia – nearsightedness
- Hyperopia – farsightedness
- Amblyopia – amblyopia, functional visual impairment due to strabismus (squint), for example.
- Hemianopia – hemifacial blindness due to disorders of the visual pathway (nerve pathway that directs sensory input to the central nervous system for processing).
Indications (areas of application)
- Ablatio retinae (synonyms: amotio retinae; retinal detachment).
- Amaurosis fugax – short-term mostly unilateral blindness due to occlusion of the central retinal artery.
- Acute optic neuropathies – e.g., circulatory disturbance of the optic nerve, which leads to visual acuity loss.
- Age-related macular degeneration – reduction in function of the sensory cells in the yellow spot of the retina.
- Diabetic maculopathy – damage to the eye, as a result of diabetes mellitus, affecting the site of sharpest vision on the retina, the macula.
- Vitreous hemorrhage
- Glaucoma (glaucoma)
- Cataract (cataract)
- Presbyopia (presbyopia)
- Refractive errors – nearsightedness, farsightedness.
- Disorders in the visual pathway or in the visual center of the central nervous system.
The procedure
The subject is shown various visual signs, or so-called optotypes, which must be recognized. These include:
- Landolt rings – Black ring open in eight different directions, the patient must recognize the opening.
- Letters
- Numbers
- Snellen hook – this visual sign is a large Latin E that points in four different directions.
The sight signs can be used in different ways. Either the examiner moves the visual signs further and further away from the subject, so that the subject has to recognize them from a greater distance, or the signs on the visual chart become smaller and smaller in logarithmic increments. The latter method is the more common. The vision chart is usually located 5-6 meters away from the subject when testing distance visual acuity. If the subject does not recognize the largest visual sign at this distance, the distance can be reduced. When testing near visual acuity, which is important for reading ability and should be performed with the patient in a physiological body or head position if possible, the visual chart is approximately 40 cm away. During the examination, each eye is tested individually, and then retested if necessary with corrected visual acuity (e.g., with glasses). The visual acuity is usually then taken from a table previously calculated on the basis of the visual signs and distances. Determining visual acuity in children is much more complex, as perception and recognition are age-dependent and vary according to experience gained:
- 6-16 months of age – Preferential-looking method: children are shown two surfaces with a striped pattern and an equivalent shade of gray; the pattern is more interesting to children, so they are more likely to look at it with interest. The better the visual acuity, the finer the stripe pattern that the children can recognize.
- 16 months of life to 3.-4 years of age – fixation tests and control of eye position replace the stripe patterns, which are now no longer interesting enough.
- Age 3 to 4 – Children need to recognize simple symbols such as a circle, triangle or cross.
The eye test is used to quickly and reliably detect a reduction in visual acuity, so that further therapy can be optimally planned. Especially for many professions, as well as to obtain a driver’s license of any class, an eye test is required.
