PURPOSE. To determine the spatial properties of stimuli that elicit photophobi a (PP) in normal subjects: Does PP exhibit spatial summation? Are different para foveal quadrants (superior, inferior, temporal, and nasal) of the retina differe ntially sensitive in PP) What is the relationship between PP sensitivity and ret inal eccentricity? What is the relationship between the spatial properties of PP and the spatial distribution of macular pigment (MP)? METHODS. A Maxwellian-vi ew optical system with a xenon light source was used to present the stimuli. Fou r normal subjects viewed stimuli of various sizes, retinal locations, and one of two chromatic contents: xenon-white and a broadband orange. The intensity of t he test stimulus was increased between trials until the PP threshold was reached . The squinting response corresponding to PP was assessed by electromyography an d used as an objective criterion of PP. Three parameters were examined: stimulus size, parafoveal retinal locus (superior, inferior, temporal, and nasal), and r etinal eccentricity (extending into the perifovea). Spatial profiles of MP were measured psychophysically using heterochromatic flicker photometry (HFP). RESULTS. Spatial summation for PP was found essentially to adhere to Pipers law(radiance proportional to square root of stimulus area). The PP response was greater to centrally than peripherally viewed targets. In this regard, MP acted as a spatially integrated filter in the attenuation of PP. CONCLUSIONS. The degr ee of spatial summation found for PP indicates that an increase of 1.0 log unit in field area results in an approximately 0.57-log-unit decrease in the radian ce required to elicit PP. PP appears to serve the function of retinal photoprote ction. PURPOSE. To determine the spatial properties of stimuli that elicit photophosphoryla (PP) in normal subjects: Does PP exhibit spatial summation? Are different para foveal quadrants (superior, inferior, temporal, and nasal) of the retina differently susceptible in PP) What is the relationship between PP sensitivity and ret in eccentricity? What is the relationship between the spatial properties of PP and the spatial distribution of macular pigment (MP)? METHODS. A Maxwellian-vi ew optical system with a Xenon light source was used to present the stimuli. Fou r normal subjects viewed stimuli of various sizes, retinal locations, and one of two chromatic contents: xenon-white and a broadband orange. The intensity of t he test stimulus was increased between trials until the PP threshold was reached. The squinting response corresponding to PP was assessed by electromyography an d used as an objective criterion of PP. Three parameters were examined: stimulus size, parafoveal retinal locus (su perior, inferior, temporal, and nasal), and r etinal eccentricity (extending into the perifovea). Spatial profiles of MP were measured psychophysically using heterochromatic flicker photometry (HFP). RESULTS. Spatial summation for PP was found essentially to adhere to Piper ’ s law (radiance proportional to square root of stimulus area). The PP response was greater to centrally than peripherally viewed targets. In this regard, MP acted as a spatially integrated filter in the attenuation of PP. CONCLUSIONS. The degr ee of spatial summation found for PP indicates that an increase of 1.0 log unit in field area results in an approximately 0.57-log-unit decrease in the radiance ce required to elicit PP. PP appears to serve the function of retinal photoprotection.