The PLR in healthy canine eyes can be elicited at very low light intensities using red and blue wavelengths of light, but in dogs with blindness caused by SARDS, the pupil reacts only to high-intensity blue wavelength light, implying loss of the rod-cone-mediated PLR and most likely the presence of intrinsic, melanopsin-mediated, retinal ganglion cell-mediated PLR.

Purpose To characterize the timing and extent of functional recovery in healthy canine eyes exposed to acute elevation of intraocular pressure (IOP). Methods Acute elevation of IOP was induced in 14 healthy Beagles by elevating IOP above the levels of systolic blood pressure for 60 min (average elevation was between 100 and 160 mmHg). Menace, dazzle and pupillary light reflexes (PLR) were tested at 1, 7, 14 and 28 days post elevation. Optical coherence tomography was used to evaluate retinal thickness preoperatively and at 15 and 30 days post elevation. Results One day post elevation all animals were blind in the operated eye (no positive menace), 5/14 had positive PLR and 10/14 had positive dazzle response. Seven days post elevation 4/14 animals had positive menace response and all animals (14/14) had positive dazzle and PLR responses. Fourteen and 28 days post elevation all animals had positive menace, PLR and dazzle responses. Optical coherence tomography analysis revealed significant thinning of the inferior retina (pre elevation: 156.3 ± 4.8 µ m; 15 days post elevation: 125 ± 10.4 µ m; 30 days post elevation 123 ± 11.9 µ m; P < 0.01,  ). The superior retina, however, did not show any detectable decrease in thickness compared to control eyes (pre elevation: 193.8 ± 2.6 µ m; 15 days post elevation: 176.9 ± 8.5 µ m; 30 days post elevation 176.9 ± 7 µ m; P = 0.057,  ). Conclusions Detailed functional and morphologic analysis revealed precise information about retinal damage after acute elevation of IOP. Canine retina has the capacity to recover at least some visual function even at 14 days after acute elevation of the IOP. More aggressive medical and surgical treatment of canine glaucomatous patients may be indicated despite complete loss of visual function, PLR and dazzle responses in early days after development of an acute glaucomatous attack.