Projection optometry is a kind of objective optometry, which utilizes the illumination system of the projection lens to illuminate the inside of the eyeball, the light will change after passing through the refractive system of the eye, and the refractive state of the eye will be judged by the change of the light reflected back to the eye.
The general procedure is as follows: dilate the pupil of the patient, then examine the shadow in a dark room, the observation distance is about 1 meter, the inspector will project the light of the detector lens to the patient’s dilated pupil area, and move the detector lens to observe the direction of the light reflected from the retina to the pupil area in the eye, so as to determine the existence of refractive error, and, if suffering from refractive errors, to check the nature and extent of the refractive error.
In general, the image of an orthopic eye is immobile, the image of a hyperopic eye is paracentric, and the image of a myopic eye is retrograde.