Emmetropia describes the condition in which no refractive error is present. In order to see clearly, the focal point of the incoming light must fall precisely on the retina. Ideally, the incoming light rays are bent by the cornea and the crystalline lens of the eye in such a way that they meet exactly on the fovea and produce a sharp image.
Myopia is a refractive error of the eye in which the focal point—and thus the sharp image—lies in front of the retina. High myopia of more than -6.0 diopters is more likely lead to pathological changes in the retina.
In myopia, the refractive power of the eye is too high for the length of the eye.
In axial myopia, the mismatch occurs because the eye grows too long but the refractive power is normal. In refractive myopia, the refractive power of the cornea and/or crystalline lens is too high with normal eye length.
Nearby objects are seen clearly, while objects further away appear blurred and out of focus.
Other symptoms may include headaches, squinting to see distant objects clearly, excessive blinking and rubbing of the eyes.
The degree of myopia is determined in dioptres with the aid of a refraction test.
The aim of correcting myopia is to reduce the refractive power of the eye to produce a sharp image on the retina.
There are different options, depending among other factors on the degree of myopia:
Corrective glasses with negative power.
Soft or rigid contact lenses with negative power.
Rigid Ortho-K lenses that specifically reshape the cornea overnight so that no visual aids are needed during the day.
Corneal reshaping through refractive surgery such as LASIK, LASEK or PRK.
Implantation of an artificial lens into the eye (ICL), in addition to the body's own lens.
Replacement of the body's own lens with an artificial intraocular lens (IOL).
There are also specialist glasses, contact lenses and eye drops, which have been shown to slow down the progression of myopia in some children. By slowing down the growth of the eye and therefore limiting the amount of myopia in adulthood, the risk of complications associated with myopia is reduced.
In myopia, the refractive power of the eye is too high for the length of the eye.
In axial myopia, the mismatch occurs because the eye grows too long but the refractive power is normal. In refractive myopia, the refractive power of the cornea and/or crystalline lens is too high with normal eye length.
Hyperopia is a refractive error of the eye in which the focal point—and thus the sharp image—lies behind the retina.
In hyperopia, the refractive power of the eye is too low in relation to the length of the eye.
In axial hyperopia, the eye is too short with normal refractive power. In refractive hyperopia, the refractive power of the cornea and/or crystalline lens is too low with normal eye length.
Objects appear blurred and out of focus at all distances, although distance vision can be compensated for to a certain extent by using some of the ability of the lens to change focus (accommodation), but this limits the focusing power available for normal near vision.
Headaches and eye strain may be additional symptoms.
The degree of hyperopia is determined in diopters with the aid of a refraction test.
The aim of correcting hyperopia is to increase the refractive power of the eye to produce a sharp image on the retina.
There are many options, depending among other factors on the degree of hyperopia:
Corrective glasses with plus power.
Soft or rigid contact lenses with plus power.
Refractive surgery such as LASIK, LASEK or PRK.
Implantation of an artificial lens into the eye (ICL), in addition to the body's own lens.
Replacement of the body's own lens with an artificial intraocular lens (IOL).
In hyperopia, the refractive power of the eye is too low in relation to the length of the eye.
In axial hyperopia, the eye is too short with normal refractive power. In refractive hyperopia, the refractive power of the cornea and/or crystalline lens is too low with normal eye length.
Astigmatism is a vision disorder that causes blurred or distorted vision.
Due to an irregular curvature of the cornea—or, less commonly, the crystalline lens of the eye—light entering the eye does not focus on a single point on the retina, resulting in blurred vision.
Astigmatism is often present from birth. The extent of astigmatism can vary throughout life and depends on ethnicity, genetic predisposition, changes in the shape of the eyelids, cornea and crystalline lens.
Eye diseases such as keratoconus, amblyopia, eye surgery and injuries can also influence the severity.
The symptoms of astigmatism vary depending on its severity. The most common symptoms include distortion and blurred, unfocused vision. Increased strain on the eyes can cause headaches, fatigue and discomfort.
A refraction test is used to determine visual acuity and the degree of refractive error, including astigmatism.
Further examinations include keratometry and corneal topography.
Astigmatism can be corrected using the following methods:
Toric glasses with plus or minus power.
Toric soft or rigid contact lenses with plus or minus power.
Rigid night lenses (Ortho-K lenses) that specifically reshape the cornea overnight so that no visual aids are needed during the day.
Refractive surgery such as LASIK, LASEK, or PRK.
Astigmatism is often present from birth. The extent of astigmatism can vary throughout life and depends on ethnicity, genetic predisposition, changes in the shape of the eyelids, cornea and crystalline lens.
Eye diseases such as keratoconus, amblyopia, eye surgery and injuries can also influence the severity.
Presbyopia is a natural age-related process of the crystalline lens, which increasingly makes it difficult to see nearby objects or letters.
Lens fibers are continuously produced in the crystalline lens, making it thicker and stiffer over time. As a result, it loses its flexibility and ability to change curve. This restricts accommodation—the ability to focus on near objects—and makes it impossible with advancing age.
Presbyopia is usually noticed in the mid-40s. From then on, near vision steadily becomes more blurred.
Colors appear paler and sensitivity to glare increases. Straining the eyes can cause headaches.
To diagnose presbyopia, a refraction test is performed for distance and near vision.
Presbyopia can be corrected with glasses (progressive lenses, bifocals, reading glasses) or contact lenses (multifocal, monovision). Special intraocular lenses (multifocal IOLs) can also correct presbyopia and are used in combination with cataract surgery.
Lens fibers are continuously produced in the crystalline lens, making it thicker and stiffer over time. As a result, it loses its flexibility and ability to change curve. This restricts accommodation—the ability to focus on near objects—and makes it impossible with advancing age.
