The light reflected by an object must be focused on the retina so that the eyes can see the object clearly. The blurred vision caused by myopia is because the parallel light reflected by distant objects cannot focus on the retina, and the focus is in front of or behind the retina. Under normal circumstances, light enters the eye through the open pupil and reaches the retina through most of the cornea and lens.
Light passes through the cornea and lens periphery, causing ametropia and blurred vision. If only the light beam passing through the center of cornea and lens reaches the retina, any blurred vision caused by ametropia will be improved.
Aperture can just play this role, because it blocks the peripheral part of the beam, and it is the central part of the beam that enters the eye through the pupil, so any ametropia caused by cornea and lens is not so obvious. The pupil may be dilated, but the light beam received by the eyeball is only the central part. Although the light entering the eyes is a little dim, it is focused on the retina, so the image is very clear.
Extended data:
There are two kinds of pinhole glasses in the ophthalmic glasses box. One is 3 mm in diameter, close to the normal pupil size. One is the diameter1mm. Ophthalmologists use the former to understand the nature and degree of ametropia; The latter is used to determine the cause of vision loss.
When the mydriatic agent is dropped, the pupil is obviously enlarged. At this time, wearing a pinhole lens with a central aperture of 3 mm in front of your eyes, the measured vision is very close to the real vision without mydriasis (excluding accommodation). Ophthalmologists can know the nature and degree of each kind of ametropia (including true and false myopia, hyperopia, etc. ) Check your eyesight by dilating your pupils.