When patients have poor corrected vision, there may be two reasons. One is uncorrected ametropia and the other is ophthalmic diseases affecting vision. Pinhole lens can distinguish the two. The principle of pinhole lens (a small hole with a diameter of about 1 mm) is to increase the focal depth, so as to reduce the size of blurred spots on the retina caused by defocused light.People feel that they can see more clearly.

Picture 1-2-1 Pinhole Lens

Picture 1-2-2

Parallel light enters the eyeball. Due to myopia, the light focuses on point a in front of the retina, and a blurred light class arrives at the retina. Its size is shown by the arrow in picture 1-2-2.

Picture 1-2-3

Assuming that the eyes in picture 1-2-3 have the same size and diopter as those in picture 1-2-2, add the pinhole lens in front of the eyes, so only the central part of the parallel light can pass through the small hole. Due to myopia, the light focuses on point a in front of the retina, and a fuzzy spot reaches the retina, and its size is shown by the arrow in picture 1-2-3. It can be seen that the blurred spots in picture 1-2-3 are significantly smaller than those in picture 1-2-2. At this time, people will feel that their eyesight is more‘clear’， which is the role of pinhole lens.

When the patient's corrected eyesight is lower than 0.6, insert a pinhole lens. If the patient's eyesight improves, it indicates that the poor eyesight  is caused by ametropia. If the eyesight  does not improve, it indicates that the poor eyesight  is caused by ophthalmic diseases.

Visual acuity chart, pinhole lens hand occluder.

① Patients wear their original prescription or new optometry.

② Open the visual acuity chart, cover one eye, and generally measure it first.Measure the left eye after the right eye.

③ The pinhole lens is added in front of the patient to measure pinhole vision.It is consistent with the far vision measurement method. If there is a significant improvement in vision, it indicates that the diopter is wrong before, it is necessary to re optometry. If the visual acuity is not improved or decrease, it indicates that poor vision is caused by eye disease, and the patient is further treated by the blink department. 

④ Result recording: pinhole vision was recorded after the visual examination results.

If the pinhole vision is not improved, it is recorded as phni (pinhole no improvement). VAcc OD: 0.3 PH: 0.7 + 2 or VAccOS: 0.6 PHNI

Pinhole vision can be used in both corrected and uncorrected states. It can distinguish whether poor vision is caused by ametropia. Pinhole vision is mainly measured when looking far.