What is the purpose of a pinhole disc in vision assessment?

The pinhole disc is primarily used in vision assessment to help identify refractive errors. When a patient looks through a pinhole, light rays entering the eye are directed in a manner that minimizes the impact of the eye's optical imperfections (such as those caused by uncorrected myopia or hyperopia). This allows the clinician to determine whether the patient's visual acuity improves with pinhole testing, indicating the presence of a refractive error. If vision improves when looking through the pinhole, it suggests that the patient's vision loss may be due to a refractive issue rather than other factors like pathology or retinal disease. Therefore, the main purpose of the pinhole disc is to effectively evaluate the eye's optical function in relation to refractive errors.