title: Fresnel prism on hess screen test.
abstract: A 65-year-old male patient complained of diplopia after a cataract surgery. He had esotropia of 18 prism diopters (PDs) at distant and near deviation, and therefore, we performed the Hess screen test to identify any abnormal eye movement. However, the indicator was found to be out of bounds, and therefore, the test could not be completed. Therefore, the test was subsequently performed with a 20 PD base-out Fresnel prism, and an abduction deficit was observed in the right eye, but not in the left eye. Therefore, we speculated that the patient had abducens nerve palsy in the right eye. The results obtained in the present study imply that performing the Hess screen test with the Fresnel prism may be very useful in diagnosing ambiguous abnormalities in patients with extraocular movement. The Hess screen test can be performed for patients with a strabismus of greater than 15 PD by using a Fresnel prism. Thus, a Fresnel prism may be useful for performing both the Hess screen test and Lancaster screen test.
authors.affiliation: Department of Ophthalmology, Kim's Eye Hospital, Youngdeungpo 4th 156, Youngdeungpo-gu, Seoul 150-034, Republic of Korea.
authors.forename: Kyung Min
authors.initials: KM
authors.lastname: Koh
authors.forename: Ungsoo
authors.initials: U
authors.lastname: Samuel Kim