Pinhole visual acuity
The pinhole is an eye shield with several small holes that allow light rays to reach the retina without the interference of optical problems of the eye. It is an excellent way to screen for uncorrected refractive errors and disorders of the ocular media. However, young children, elderly people, and mentally impaired individuals often have difficulty using it.
The possible result of Pinhole visual acuity test:
If the distance vision is less than 6/6 all patients should be asked to look through a pinhole and improvement if any in visual acuity should be recorded.
- A pinhole cuts off all the peripheral rays and allows an only central parallel beam of rays to enter the eye and visual improvement is seen in cases of refractive errors.
- If the cause for diminution of vision is not the refractive error like cataract then improvement in vision is not seen. The results of the pinhole test can be summarized as.
- Visual acuity improves with pinhole cause is the refractive error, which can be corrected by appropriate refraction and correction.
- No improvement in visual acuity with pinhole causes is corneal causes like corneal opacity, corneal oedema, and causes in the lens like a cataract.
- The decrease in visual acuity with pinhole the cause may be the central corneal opacity, central lens opacity, and macular pathologies.
Size of the pinhole:
The size of the pinhole is 1 mm.
How pinhole works?
|Fig showing how pinhole works|
Read more about: