Opticians practice medicine

Eye refractometer

Eye refractometer, Device for the objective measurement of the refraction of the eye (refraction determination).

Manual refractometer use a measuring beam path to design test mark images on the retina of the eye, which must be viewed via an observation beam path and manually focused or manually brought into agreement (coincidence) (Fig. 1). The manual test mark shift is read on scales in dioptres (dpt) (minus values ​​for myopia, plus values ​​for clarity). The prerequisite is that the patient's eye is set remotely. The measured values ​​can also be output digitally and processed further.

Automatic refractometer, also called automatic refractometers, usually work with infrared light without any glare. Measuring light from an infrared source, which is arranged in connection with a grating or cutting diaphragm, hits the retina of the eye and is reflected there back to the diaphragm location. Sensitive sensor chips or CCD cameras now register the deviation of the reflected light from the diaphragm location, which is dependent on the respective ametropia (Fig. 2). An integrated microcomputer calculates the ametropia in dpt according to the sphere, cylinder and axis position of the cylinder. With some device types, factors for the transparency of the eye media are shown as additional services, deviations of the corneal center from the pupil center are displayed, the diameters of the cornea and pupil are measured and the interpupillary distance between the right and left eyes is recorded. In addition, the monitor of the observation beam path provides a clear and greatly enlarged image of the anterior segment of the eye, which gives a first impression of organic abnormalities in this area. More comfortable devices put the measured refraction values ​​in front of the test person as corrective glasses, through which he can observe an integrated eye test table and convince himself of the visual improvement achieved. This automatic rapid refraction is not a fully adequate substitute for the complete subjective lens determination. However, the acquisition of objective refraction data is very much appreciated as a basis for determining the lens.

A solution that is widely used is the data network between the automatic refractometer and the phoropter. The refraction values ​​objectively determined on the automatic refractometer are transmitted to the subjective test station and automatically set on the phoropter. The subjective fine-tuning of the values ​​can now be carried out here.

In combination with an automatic measuring device for the curvature of the cornea (keratometer), these devices are called auto-refractory keratometers.

Other automatic A. work according to the retinoscopy method, with photosensors evaluating the movement of the light reflex from the retina caused by a moving light source.