In addition to checking direct and consensual constriction of the pupil to light, the swinging flashlight test is performed to detect a relative afferent pupillary defect (RAPD; also known as a Marcus Gunn pupil), the presence of which indicates extensive retinal disease or optic nerve dysfunction. (See also BCSC Section 5, Neuro-Ophthalmology.) Although the vision of a patient with RAPD in the cataractous eye may improve after cataract surgery, the visual outcome may be limited by optic nerve dysfunction. The patient must be made aware of the possibility of less than complete restoration of vision.
It is important to measure the size of the pupil under different lighting conditions, because this information may affect selection of the IOL. For example, small-optic lenses may be inappropriate for a patient who has a large pupil in moderate or dim illumination. The edge of the optic can fall inside the pupil border, allowing light to pass around the optic edge, with resultant glare or dysphotopsias. Also, the function of a multifocal IOL may be affected by a pupil that is small, atonic, or eccentric. It is helpful to assess pupil size before and after dilation, because the risk of surgical complications is higher in small pupils that do not dilate adequately (eg, in patients with diabetes mellitus, posterior synechiae, pseudoexfoliation syndrome, a history of opioid use, or a history of systemic α1-adrenergic antagonist or long-term topical miotic use); in such cases, the surgeon may need to use expansion devices. These devices are discussed in Chapter 12.
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.