Glasses are methods of correcting refractive errors. They provide the patient with the appropriate optical correction and offer the necessary visual comfort. Glasses vary depending on the disorder detected, so to find out from how many diopters you should wear glasses, it is necessary to go for an ophthalmological examination in a specialized clinic.
Stay with us to learn more about diopters and refractive errors, and how the latter can be corrected with glasses.
What is the diopter?
Before you can find out from how many diopters you need glasses, you should first know what the role of diopters is and how they can affect your visual acuity. In optics, the diopter is the measurement unit of the refraction of the lens and the eye. It is based on the power of the lens at a focal length of one meter.
Depending on the vision problems observed during investigations, the patient may need positive, negative, or both positive and negative diopters. In this respect, the lenses of the glasses may also differ:
- Spherical lenses
- Cylindrical lenses
- Spherocylindrical lenses
- Prismatic lenses
- Convergent lenses
- Diverging lenses
How many types of diopters can there be?
Diopters can be positive or negative. In order to determine the right type of correction, it is essential to diagnose the disorder.
- Myopia is corrected with minus diopters. In this case, the patient cannot see clearly at a distance.
- Hypermetropia is corrected with plus diopters. Here, the patient cannot see well at close range and the quality of vision at distance also decreases with ageing.
- Astigmatism can be corrected with plus and also minus diopters. In this case, it is more complicated, as the patient is faced with double image and the quality of near and also distance vision can be poor.
- Presbyopia can be corrected with the help of plus diopters. The most frequent cases occur after the age of 40, when the quality of near vision declines. It is considered a normal phenomenon of ageing.
What diopters do you need, depending on your ophthalmological disorder?
For myopia
Myopic patients cannot see clearly at a distance. This is because the focus of the light rays is in front of the retina, in the vitreous body. Myopia can be refractive, curvature myopia (in these cases, it occurs as a result of the cornea or lens being too bulging) or axial myopia (as a result of the eyeball being too long).
Up to 3 diopters, myopia is considered low. It usually occurs during childhood or adolescence as a physiological response of the eye to intensive reading and writing. Also called “school myopia”, it stops progressing around the age of 25. At the opposite pole is pathological myopia. It is more common in women, progresses rapidly and lasts for a long time. In this case, the eye elongates excessively, the eye wall becomes thinner, the fundus changes and there is a risk of the retinal detachment.
Between 3 and 6 diopters, myopia is average. Between 6 and 9 diopters, it is high, and anything over 9 diopters is considered very high. Most patients have low or medium myopia.
Myopia can be corrected with minus diopters or diverging contact lenses. These are designed to shift the focus of the image from the front of the retina to the retina, giving patients the ability to see clearly also at a distance. Other options for myopia correction are:
- Through lens implant
- By means of laser surgeries – Excimer or RelEX Smile
For hypermetropia
Studies show that 75% of babies are hypermetropic at birth, but emmetropization of the eyes (normal elongation of the eyeball) occurs in the first 3 years of life.
In patients with hypermetropia, the focus of the image is behind the retina and the image of objects close to the retina is blurred. This disorder can also be of curvature, refractive (when the radius of curvature of the cornea or lens is flatter) and axial (the anterior-posterior axis of the eye is too short).
Up to 3 diopters hypermetropia is low. These patients are able to identify objects close to them, using the compensatory mechanism of accommodation at distance. However, permanent bulging of the lens leads to visual fatigue, especially when the effort is made over a longer period of time (e.g. reading, writing). In children under the age of 3, hypermetropia can lead to convergent strabismus (when one or both eyes move inwards).
Hypermetropia is considered medium if it is between 3 and 6 diopters, and high if it is more than 6 diopters.
This refractive error can be corrected with positive diopters or converging contact lenses, which bring the image focus from behind the retina to the retina. Other methods of correction are:
- Laser surgery
- Lens implant surgery
For astigmatism
Astigmatism involves corneal ovalization and leads to a cylindrical error in image formation on the retina. Astigmatism can be simple – when incident light rays are focused outside the retina into a single image focus (behind the retina – hypermetropic astigmatism, in front of the retina – myopic astigmatism) – or compound and mixed, when incident light rays are focused into at least two different image focal points.
Patients suffering from astigmatism may have blurred and tilted vision. Correction of the refractive error can be achieved by means of positive or negative diopters, and cylindrical (in the case of simple astigmatism) or spherocylindrical (in the case of compound and mixed astigmatism) lenses. Other correction possibilities are:
- RelEX Smile laser intervention
- Excimer laser surgery
- Lens implant
For presbyopia
This ophthalmological disorder is frequent with ageing. Typically, after the age of 40, the accommodative ability of the lens decreases for near vision and patients are unable to see clearly at a distance of about 30 cm. They feel the need to resort to a compensatory method, moving the object a little further away in order to see it clearly at close range.
If the patient already suffers from hypermetropia, there is a risk that presbyopia may develop before the age of 40, whereas myopic patients can live without glasses for a longer period of time.
Presbyopia is corrected with positive diopters and converging contact lenses. Their value increases at an interval of about 5 years, until the age of 65. Other options for correcting the refractive error are:
- Presbyond Laser Blended Vision laser surgery
- Lens implant surgery
If you feel visual discomfort when looking far away or up close, don’t hesitate to make an appointment with a specialist. The Dr. Holhoș ophthalmology network is waiting for you in its clinics to provide you with the best services and the best care.