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Jason C. Park, David W. Rhee, Ali S. Raza, Randy H. Kardon, Donald C. Hood; Assessing Rod and Cone Contributions to the Human Pupillary Light Reflex Using a Stiles Field Paradigm. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4908.
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© ARVO (1962-2015); The Authors (2016-present)
To better understand how the rods and cones control the sensitivity of the human pupillary light reflex (PLR) elicited with dim lights, the intensity of blue and red adapting field sensitivities were varied (Stiles field paradigm ).
Individuals with healthy vision participated. The PLR was measured with an eye tracker (Arrington Research) and the stimuli controlled with a Ganzfeld system (Espion E2, Diagnosys LLC), which generated the blue (467nm) and red (640nm) stimuli. Two 1-sec test lights were used: a low blue (-3 log cd/m2 above background) and a moderate blue (-1 log cd/m2 above background). A series of 2-min red and blue adapting background fields were presented and the PLR to the blue stimuli measured. The intensity of the red or blue adapting field increased from -3.2 log cd/m2 (for the low blue flash) or -2.2 log cd/m2 (for the moderate blue flash) to the level where incremental PLR to the blue flash was reduced to near zero.
As the intensity of the background increased, the incremental PLR became smaller. The normalized PLR amplitude vs. field intensity curves had similar shapes for the blue and red fields. For the low intensity blue flash, the separation of the curves for the blue and red adapting conditions was 2.4 log units. This was close to the 2.3 log unit separation predicted if only stimulation of the rods affected sensitivity. For the moderate intensity blue flash, the separation was 1.7 log units, implying that both rods and cones contribute to the field sensitivity.
The PLR to the 1 sec, -3 log cd/m2 blue light is rod driven and even red adapting fields appear to affect its sensitivity via rod pathways. For the -1 log cd/m2 blue flash, the adapting field is acting via both rod and cone pathways. The site of this rod-cone desensitization is probably due in large part to the compressive nonlinearity of the PLR, although a retinal contribution cannot be ruled out. As previously suggested, the PLR to a -3 log cd/m2 blue flash can be used as a clinical measurement of rod function. 1. Stiles, Doc Ophthalmol, 1949; 2. Kardon, et al., Ophthalmol, 2009; 3. Park et al., ARVO, 2010
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