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Connie Yeh, Kristin L Koehl, Christine Harman, Simone Iwabe, Jose Guzman, Simon M Petersen-Jones, Andras M Komaromy; Assessment of rod, cone, and intrinsically photosensitive retinal ganglion cell (ipRGC) contribution to the canine chromatic pupillary response. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5569.
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© ARVO (1962-2015); The Authors (2016-present)
The objective of this study was to develop a chromatic pupillometry protocol for specific functional assessment of canine rods, cones, and ipRGCs by evaluating both normal dogs and dogs with well-defined retinal and optic nerve (ON) disease phenotypes.
Thirty five dogs with different stages of primary loss of rod- (mutations in CNGB1, PDE6A, PDE6B, RD3), cone- (CNGB3 - achromatopsia), combined rod/cone- (RPE65, STK38L, IQCB1, RPGR), and optic nerve function (ON head coloboma) were tested and compared to normal animals (n=5). Chromatic pupillometry was performed bilaterally under isoflurane general anesthesia using a Q450 Ganzfeld stimulator (Roland Consult). This system also contained a computerized pupillometer to record the movement of the pupil. After 20 min of dark adaptation, the eyes were stimulated with a 1-sec dim (1 cd/m2) and bright (400 cd/m2) blue light stimulus (470 nm). Following 5 min of light adaptation to a blue background (480 nm, 25 cd/m2) the eyes were stimulated with a 1-sec bright red (640 nm, 400 cd/m2) light.
The median constriction amplitude (%) induced by the dim blue, bright blue, and bright red light stimuli in normal dogs were 18% (range: 6.7-41.2%), 58.9% (23.8-67.6%), and 18.6% (9.3-32.2%) respectively. In dogs with loss of rod function, the pupillary response to dim blue light stimulus was absent, followed by a decrease in bright red light response with retinal disease progression. In dogs with achromatopsia, an absent pupil response to bright red light stimulus but well-preserved response to blue light stimulus was observed. Except for the animal with ON disease, in which all pupillary responses were absent, the melanopsin response was maintained in all dogs, even when rod- and cone-mediated retinal function was not detectable. Characteristic for ipRGC function, the melanopsin response was sustained for several minutes (median: 7 min 36 sec, range: 50 sec-17 min 46 sec) after the offset of the bright blue light stimulus.
Pupil responses elicited by light stimuli of different color and intensity allow functional assessment of canine rods, cones and ipRGCs. Chromatic pupillometry offers an effective diagnostic tool for retinal and ON diseases in both clinical and research settings.
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