Eye specialists conduct eye exams and vision screenings to detect vision impairments and eye diseases before they become too problematic for the patient. The pinhole test is one simple but vital element of a comprehensive exam.
The pinhole test helps to differentiate between two types of blurred vision. A patient's blurred vision might be caused by a focusing problem, which can be corrected by glasses or contacts, or it may be caused by a disease. A properly conducted pinhole test will pinpoint the source of the problem.
A pinhole test is very simple but very useful; it can even be conducted at home with a piece of cardboard material perforated with a pin tip to create a pinhole about 2mm in diameter. The person suffering from blurred vision should select and focus on a distant object. Then, with one eye at a time, she should focus on that same distant object through the pinhole in the card.
If the distant object appears sharper through the pinhole, then the subject likely has a simple focusing problem that can be addressed with corrective lenses. However, if the distant object is still blurry through the pinhole, the subject should contact an eye doctor immediately, as this could be an indicator of disease.