Prismatic reaction to glasses caused by inaccurate pupil distance

Wearing the exact prescription of glasses but often have visual fatigue, why do glasses also wear discomfort? In fact, we often encounter such a situation. We can think about this problem from several angles. One is the mirror angle of the glasses, the face bend of the lenses, etc. But the possibility of causing this phenomenon is unlikely; often, the pupil distance of glasses is not done accurately, beyond the pupil distance of our eyes, resulting in a prismatic reaction, leading to the appearance of our visual fatigue.
        Nowadays, most of the unqualified eyeglasses on the market have the phenomenon that the optical center distance and pupil distance of eyeglasses do not match, and the deviation of the optical center distance and pupil distance of eyeglasses can cause a series of uncomfortable symptoms to the wearer. In optometry, measuring the pupillary distance is the last procedure to complete the prescription of glasses, and the accurate pupillary distance is also an important basis for choosing frames and fitting glasses. The deviation of the optical center distance and pupil distance of the eyeglasses makes the glasses produce the trigeminal effect, which makes them uncomfortable to wear. The deviation of the optical center relative to the pupil, left or right, can be obtained trigeminal effect. Therefore, the optical center of the glasses worn must coincide with the visual axis of the eye; that is, the optical center of the glasses and the pupil correspond; otherwise, it is equivalent to wearing a pair of trigeminal lenses. So how do glasses with the wrong pupil distance produce prisms?
        For example, a pair of -8.00 degree glasses geometric optical center deviation of 2mm, can produce how much prism? We can calculate according to the formula: P=D×L/10, that is, the trigeminal prism = the number of diopters x the number of millimeters from the optical center/10), can produce P=8×2/10=1.6△ effect, in order to overcome the shift, the brain fusion center to use excessive regulation and produce visual fatigue, but also can cause the degree of deepening, and even strabismus. So in the process of processing our glasses, the pupil distance must be very precise. Generally speaking, because the pupil distance is too large, the occurrence of visual fatigue, glasses can not be worn, change to a smaller pupil distance after the symptoms disappear.
        The above can be seen. The size of the deviation between the optical center distance and the pupillary distance of the eyeglasses and the level of refraction has a great impact on the quality of optometry and prescription glasses. In order to prevent customers from wearing glasses with the negative effects of trigeminal lenses, it is necessary to accurately measure the pupil distance so that the smaller the deviation of the optical center of glasses, the better. We should not simply pursue low prices but should consider cheap glasses based on quality. In actual optometry, we often encounter some special problems, so we should do special treatment for special problems. From the perspective of vision protection and eye habits, the pupil distance of the new glasses and the old glasses should not exceed 2mm, so as to ensure the comfort of wearing and to ensure that the error of the pupil distance of the old and new glasses is within the standard range, which is perfectly feasible.