Minus dioptre, plus dioptre, cylindrical dioptre – these are all terms that we often hear in eye optics and surgeries, but also in everyday life. The fact is that often even the wearers of glasses or contact lenses do not know what their dioptre represents. In the following, we will explain what diopter is, which glasses are best for a certain diopter, and how to read the diopter reading.
What is a dioptre and how to read a dioptre reading?
Minus dioptre, plus dioptre, cylindrical dioptre – these are all terms that we often hear in eye optics and surgeries, but also in everyday life. The fact is that often even the wearers of glasses or contact lenses do not know what their dioptre represents. In the following, we will explain what diopter is, which glasses are best for a certain diopter, and how to read the diopter reading.
What is a diopter?
A dioptre is a unit for measuring the strength of refraction of rays of light, i.e. refraction. It represents the refractive error of the eye, i.e. the inability to focus the image. Refractive error means that the eye does not refract light rays in the correct way, resulting in a blurred image. The main types of refractive errors are nearsightedness (myopia), farsightedness (hypermetropia), astigmatism (cylinders) and senile farsightedness (presbyopia).
In an emmetropic eye (an eye without diopters), the incoming light rays are directed onto the retina by the cornea and the natural lens of the eye, creating a sharp image that is transmitted to the brain. The lens is elastic and the ciliary muscles adjust the shape of the lens to properly focus the image on the retina.
“Refractive error or diopter is actually the eye’s inability to accurately focus images on the retina.“
Dioptric symptoms
The main and basic symptom of dioptria is blurred and blurred vision. Sometimes excessive strain of the ciliary muscle in the eye can cause headaches. Prolonged squinting and frowning can also lead to headaches and pressure in the frontal area of the head. Over-focusing can dry out the surface of the eye, causing eye irritation, fatigue, itching, foreign body sensation and redness. Frowning when reading and excessive blinking or eye rubbing are symptoms of diopter in children.
The most common symptoms of diopter are:
- Blurred vision
- Squinting
- Eye strain
- Glare or halos in bright lights
- Double vision
- Headaches
What dioptre exists and how to distinguish it?
There are three types of diopters: minus , plus and cylinders for correcting astigmatism. The causes of the main types of refractive errors of the eye are described below:
Short-sightedness or myopia (near objects are clear and distant objects are blurry). Myopia is corrected with a minus dioptre. It is usually inherited and is often discovered in childhood. Myopia often progresses during the teenage years, when the body is growing rapidly.
Farsightedness or hypermetropia (near objects are dimmer than distant objects). Farsightedness is corrected with a dioptre plus. It can also be inherited. Children often have a plus dioptre, which can decrease as the child grows. In mild hypermetropia, far vision is clear while near vision is blurred. With high hypermetropia, vision can be blurred at all distances.
Age-related farsightedness or presbyopia (weakening of near vision that comes with a decrease in the elasticity of the eye lens). Presbyopia is corrected with a diopter plus. After the age of 40, the lens of the eye becomes less flexible and does not bend easily. As a result, the eye loses its ability to focus and it becomes increasingly difficult to read at a closer distance. This natural aging process of the eye lens can be combined with myopia, hypermetropia or astigmatism.
Astigmatism usually occurs when the front surface of the eye, the cornea, has an asymmetrical curvature. Astigmatism is corrected with a cylindrical diopter marked “cyl”, which can have a plus or minus sign. In ideal circumstances, the cornea is equally curved in all directions, and the light entering the cornea is equally directed in all planes or in all directions.
In astigmatism, the front surface of the cornea is curved more in one direction than the other. This abnormality can lead to vision that is similar to looking into a distorted, wavy mirror. Astigmatism usually causes blurred vision at all distances.
How is diopter diagnosed?
Diopters can be determined by an optometrist or ophthalmologist during a routine eye examination. The diopter is usually first measured objectively with the help of an autorefractometer (computer control), and then the final result is determined subjectively with the help of changing the glasses in the trial frame and reading the letters on the optotypes.
How to read the dioptric reading?
The diopter reading usually contains 3 values:
Dsph or Sph – the first number, indicates the strength of the required spherical correction, a minus sign for nearsightedness or a plus sign for farsightedness.
Dcyl or Cyl – the second number, indicating the strength of the cylindrical correction, can be written with a minus or plus sign.
Axis or Os – the third number indicates the axis of the cylinder, i.e. the degrees of the cylinder.
Dsph indicates the dioptric power of each eye separately. In this example, the diopter of the right eye is -1.75 dsph, and the left eye -1.25 dsph. Visual acuity with correction is 1.0 bilaterally, which indicates 100% vision. Pupil distance 32/32 can also be written as 64 mm.
How is diopter “treated”?
First, it should be emphasized that diopter is not an eye disease, but a refractive error of the eye.
Diopter is not treated, but is corrected with the help of dioptric glasses, contact lenses or refractive surgery.
Nearsightedness and farsightedness are corrected with spherical lenses. Concave lenses are used to correct myopia; diopter minus (divergent). Convex lenses are used to correct farsightedness; diopters plus (convergent). Astigmatism is corrected with cylindrical lenses.
Diopter glasses are the simplest and safest way to correct diopters. They can be monochromatic, bifocal or progressive , depending on your needs. When determining the diopter, your ophthalmologist or optometrist will recommend the best option for you.
Contact lenses are sometimes a better option than glasses, depending on the diopter height and lifestyle. People who wear contact lenses have a wider field of vision, and often clearer and more “natural” vision than with prescription glasses. Soft contact lenses are extremely practical for sports activities, as they will not break like prescription glasses. It is extremely important to follow the instructions on hygiene and lens cleaning, as this minimizes the possibility of infection. Along with contact lenses, you should always have prescription glasses, so that you can occasionally rest your eyes from the lenses.
Laser dioptre correction offers the possibility of permanently eliminating the need for dioptre glasses or contact lenses. With the help of a special laser, the surgeon changes the shape of the cornea of the eye, thereby improving the ability of the eye to precisely focus light rays on the retina. Everyone who is interested in the procedure should undergo a comprehensive ophthalmological examination, because not everyone is an ideal candidate for laser vision correction.
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