Centres of Excellence -> Ophthalmology -> Prescribing glasses

Prescribing glasses

Ophthalmological examination of diopter determination

The examination to determine the diopter of glasses begins with the measurement of eye parameters with a computerized refractorkeratometer. Refractokeratometer is a device that automatically determines the refraction of the eye and the refractive power and curvature of the cornea in each of its meridians.

The refraction of the human eye means the dioptric state of refraction of light rays at rest (without accommodation). Deviation from regular refraction is called a refractive error of the eye (farsightedness, nearsightedness, astigmatism).

Determining the diopter of vision
Ophthalmological examination to determine the diopter of vision

How is eye refraction determined subjectively?

After recording with a refractorkeratometer, the refraction of the eyes is determined by subjective and objective methods. In the subjective determination of eye refraction, the patient reads letters or numbers from the optotype (board with symbols). The examiner uses spherical lenses (in case of nearsightedness and farsightedness) or cylindrical lenses (in case of astigmatism) to correct his refractive error and thus determine the diopter that achieves a visual acuity of 1.0. If this acuity is not achieved, one should suspect low vision or an organic eye disorder.

The examination lasts 15 - 30 minutes and you should take with you previous medical documentation, glasses or contact lenses, so that you can compare the previous and current refractive correction and continuously monitor the change, that is, the stability of the refractive state of the eye.

How is eye refraction determined objectively? 

The objective determination of the refraction of the eye is performed using the skiascopy method, as the most common, cheapest and simplest method. After paralyzing the ciliary muscle by performing cycloplegia (dilation of the pupils and instillation of mydriatic drops four times in 15 minutes), the refractive error of both eyes is determined.

Cylindro-skiascopy is performed with the use of a trial frame and glasses from a trial set, where the point of neutralization is determined for the spherical and/or cylindrical part of the refractive error, while recording the refraction on a refractometer with wide pupils can also give an objective amount of the refractive error. The prescription of glasses follows the subjective and objective determination of the refraction of the eye. The glasses are a synthesis of all examinations, but also the experiences of doctors. The indications for prescribing glasses are different, but the most common reason is a decrease in visual acuity as a result of the refractive error of both eyes.

For children of preschool and school age, the goal of prescribing glasses is often not only to improve visual acuity, but also part of the therapeutic protocol. After the examination, a prescription for glasses is made according to which new eyeglass lenses are made in the optician or old ones are changed and which must contain basic information about the aid (diopter, sphere, cylinder, axes, pupillary distance, vertex distance, instructions for use, etc.).

If you have noticed changes in your vision, react promptly and book an appointment for an ophthalmological examination.

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