Greater Pupillary Escape Differentiates Central from Peripheral Visual Field Loss Oliver Bergamin, MD, Randy H. Kardon, MD, PhD Objective: To test whether pupil escape observed during a constant light stimulus was greater in eyes with central visual field loss compared to eyes with peripheral visual field loss and normal eyes. Design: Comparative, observational case series. Participants: Twenty-seven normal subjects, 5 patients with central field loss, 11 patients with peripheral field loss, and 8 patients with combined loss (central and peripheral visual field loss) were tested. Methods: A dual-channel infrared pupillograph was used to simultaneously record the right and left pupil diameters at a rate of 60 Hz to characterize the initial, phasic pupil contraction, and the sustained, or prolonged, pupil contraction in response to a 5-second light stimulus. Full-field light stimuli with a diameter of 30° were presented to each eye at seven different intensities. Main Outcome Measures: The amplitude of the phasic pupil contraction was compared with the amplitude of the sustained pupil contraction at the four brightest intensities (slope of phasic versus sustained contraction) in the normal eyes and in eyes with visual field loss in the center and the periphery. Results: The sustained pupillary contraction showed a statistically greater reduction in proportion to the phasic component in eyes with central field loss compared to those with peripheral field loss, combination central and peripheral field loss, and normal eyes. Conclusions: Afferent neurons from the central retina normally contribute a substantial component to the sustained pupil response. Eyes with central field loss can be distinguished from eyes with peripheral field loss by a relatively greater loss of the sustained response, causing greater pupil escape. This study showed that pupil movements in response to a nonperimetric full-field light stimulus may provide some degree of mapping of retinotopic sensitivity. This information may be of use in interpreting the pupillary movements during the swinging flashlight test and may help predict the pattern of visual field loss. Ophthalmology 2002;109:771–780 © 2002 by the American Academy of Ophthalmology. The use of the pupil light reflex in clinical practice is important for objectively assessing afferent damage to the visual system. 1 In the swinging flashlight test, the light input of the two eyes is compared by monitoring the dynamics of pupil movement as a light is alternated between the two eyes to estimate the presence and extent of a relative affer- ent pupil defect. 2–7 The log unit value of the relative affer- ent pupil defect can be quantified using neutral density filters and has been shown to correlate with the degree of visual field asymmetry. 8 –11 Besides its usefulness in objec- tive detection of asymmetric damage, it is also clinically useful for following the course of disease and response to treatment. However, a difference of opinion exists among clinicians as to what aspect of the dynamic behavior of the pupil light reflex is best for detecting and quantifying the relative afferent pupil defect. Some clinicians use the initial con- traction of the pupil (phasic response) to compare the two eyes as the light is alternated. 12 Others have found that the amount of sustained pupil contraction that occurs with a continuous light stimulus is a sensitive indicator of dam- age. 13–15 A lack of sustained pupil constriction in the pres- ence of a continuous light has been termed pupil “escape” (an example of the time course of the pupillary response to the onset and duration of a constant light stimulus is shown in Figure 1, identifying the phasic and sustained compo- nents of the response and the pupil escape). Pupillary escape can also be seen in a normal eye, especially at lower stimulus intensities, and is thought to represent a type of adaptation to the continuous light. In many patients, there seems to be less of a sustained pupil contraction (more pupil escape) when a light stimulus is presented to their damaged eye compared with when light is shined in their fellow, normal eye, but this difference in Originally received: June 4, 2001. Accepted: August 8, 2001. Manuscript no. 210369. From the Department of Ophthalmology and Visual Sciences, Veterans Administration and University of Iowa Hospitals and Clinics, Iowa City, Iowa. Presented at The Pupil Colloquium, Asilomar, Pacific Grove, California, September 7, 2001 to September 11, 2001. Supported by the Swiss National Science Foundation, the Freiwillige Akademische Gesellschaft, Basel, Switzerland; the Roche Research Foun- dation, Basel, Switzerland; an unrestricted grant from Research to Prevent Blindness, New York, New York; a grant from Zeiss-Humphrey Corpo- ration, Dublin, California; and a Merit Review and Career Development Award from the Veterans Administration, Washington, DC (Dr. Kardon). RHK is the recipient of a Lew Wasserman Scholar Award (Research to Prevent Blindness). Reprint requests to Randy Kardon, MD, PhD, Department of Ophthalmol- ogy and Visual Sciences, University of Iowa Hospitals and Clinics, PFP, 200 Hawkins Drive, Iowa City, IA 52242-1091. 771 © 2002 by the American Academy of Ophthalmology ISSN 0161-6420/02/$–see front matter Published by Elsevier Science Inc. PII S0161-6420(01)01026-0