When a patient has a vision of less than 1, which improves when examining with a stenopeic opening, there is presence of a refractive error. It is not clear yet whether this concerns myopia or hypermetropia. For this, diagnostic refractioning must be perfomed.
A lens with strength -1D and one of +1D is required [Figure 20].
Figure 20
Procedure
- The patient looks through lens +1D. A myopic patient will exhibit even stronger myopia and their sight will deteriorate. For a hypermetropic patient, there will be no effect (apart from accommodation being released) on their vision, or vision will improve.
- The patient then looks through lens -1D. A myopic eye will see better with this lens. However, for a hypermetropic eye, there will be no difference (it will accommodate slightly more than it already did) or it will see worse, depending on the severity of the hypermetropia.
Please Note: This is only a coarse method for determining if myopia or hypermetropia is present. If astigmatism is mainly present, this test will not give a definite answer. It is not a method for determining correction.