Opposing Roles of OPN3 and OPN5 Affecting the Intrinsic Pupillary Light Reflex of the Mammalian Iris

Purpose: The pupillary light reflex (PLR) can be divided into processes regulated by the brain and by the iris sphincter muscle. This study aimed to unravel potential roles of opsin 3 (OPN3) and OPN5 for the intrinsic iris-regulated PLR. Methods: Opn3, Opn4, and Opn5 expression in the mouse and human iris was analyzed by reverse-transcription quantitative polymerase chain reaction (RT-qPCR). The intrinsic PLR was studied in enucleated eyes from wild-type (WT) and Opn3, Opn4, or Opn5 knockout (KO) mice in response to specific wavelengths of blue light (440, 460, and 480 nm) or ultraviolet A light (380 nm) by ex vivo PLR recordings. Enucleated eyes were either dark adapted only or challenged with short light flashes before PLR recordings. Results: Opn3, Opn4, and Opn5 are expressed in the iris of mice and humans. Opn3 KO enucleated mouse eyes challenged with short light flashes before dark adaptation, followed by 10 minutes (min) of 440 nm light exposure, remained significantly more constricted in the sustained contraction phase compared to Opn3 WT eyes. Exposure to 460 or 480 nm did not change the PLR between Opn3 WT and KO eyes. Moreover, Opn5 KO challenged eyes exposed to 10 min 380 nm light remained significantly less constricted in the sustained contraction phase compared to Opn5 WT eyes. Conclusions: This study shows that OPN3 and OPN5 affect the intrinsic PLR in opposing manners, with increased iris contraction in Opn3 KO challenged eyes and decreased iris contraction in Opn5 KO challenged eyes, respectively. The study also provides evidence that OPN3, OPN4, and OPN5 are expressed in human iris.