Source: 2020MagIn a study involving 83 patients who were given prisms to address double vision caused by fourth nerve palsy, 92.8% received permanent ground-in prisms, while initially, 38 patients were prescribed Fresnel prisms. Of these, 32 eventually switched to ground-in prisms, and 6 continued with Fresnel prisms.The satisfaction rate with prism use was 92%. Moreover, over a follow-up period ranging from 2 months to more than 6 years, 86% of the patients continued using prisms.Unlike standard eyeglasses, prism glasses require a more detailed assessment of vision and eye alignment. During the exam, the ophthalmologist may employ various tests to evaluate the need for prism correction. This may include:Hirschberg Test: An examination to check for strabismus, a condition where the eyes are misaligned. Using a pen light, the doctor observes the reflection in the eyes. If the reflection appears off-center, it may indicate strabismus.Krimsky Test: This test measures the degree of misalignment by using prisms. While focusing on a pen light, prisms of different strengths are introduced. The correct prism is determined when the reflection in each eye is brought to the center.Cover Tests: Cover tests come in three types. The cover/uncover test involves covering one eye and observing any movement in the uncovered eye. The prism and alternate cover test uses prisms and alternating covers to measure the offset between the eyes. The Maddox Rod test determines the type of double vision by assessing the offset between vertical or horizontal lines seen by each eye.If a prism correction is necessary, the doctor will incorporate it into the patient’s prescription.