Highlights d Photoreceptor degeneration leads to retinal ganglion cell hyperactivity d Hyperactivity is triggered by overproduction of retinoic acid (RA) d Blocking the RA receptor with drug or gene therapy reduces hyperactivity d RA receptor blockade augments light-evoked behaviors in vision-impaired mice

Phenol red thread test and STT are both valid methods to measure tear production; however, a separate baseline must be determined for each species using these methods, as the results of one method cannot be extrapolated to the other. Due to significant differences observed within diurnal and nocturnal species, it appears that a more intricate division should be used when comparing these parameters for raptors, and the classification of diurnal or nocturnal holds little significance in the baseline of these data.

Tear pH in all 3 species differed from that of published blood pH values and the pH of common topically administered ophthalmic medications. These fndings may have implications for variations in ocular flora and defense mechanisms, susceptibility to ocular disease, and success or comfort of topical treatment.

Lateral inhibition in the vertebrate retina depends on a negative feedback synapse between horizontal cells (HCs) and rod and cone photoreceptors. A change in pH is thought to be the signal for negative feedback, but its spatial profile in the synaptic cleft is unknown. Here we use three different membrane proteins, each fused to the same genetically-encoded pH-sensitive Green Fluorescent Protein (GFP) (pHluorin), to probe synaptic pH in retina from transgenic zebrafish (Danio rerio) of either sex. We used the cone transducin promoter to express SynaptopHluorin (pHluorin on vesicle-associated membrane protein (VAMP2)) or CalipHluorin (pHluorin on an L-type Ca 2ϩ channel) and the HC-specific connexin-55.5 promoter to express AMPApHluorin (pHluorin on an AMPA receptor). Stimulus light led to increased fluorescence of all three probes, consistent with alkalinization of the synaptic cleft. The receptive field size, sensitivity to surround illumination, and response to activation of an alien receptor expressed exclusively in HCs, are consistent with lateral inhibition as the trigger for alkalinization. However, SynaptopHluorin and AMPApHluorin, which are displaced farther from cone synaptic ribbons than CalipHluorin, reported a smaller pH change. Hence, unlike feedforward glutamatergic transmission, which spills over to allow cross talk between terminals in the cone network, the pH change underlying HC feedback is compartmentalized to individual synaptic invaginations within a cone terminal, consistent with private line communication.

On the basis of this small series, presumed topical CAI-associated keratitis in dogs appeared to be an uncommon immune-mediated disease that was not responsive to corticosteroid treatment. Affected patients improved rapidly, but only after discontinuation of CAI treatment. In dogs with glaucoma, clinicians should consider the development of punctate keratopathy and severe diffuse keratitis as potential adverse effects related to topical administration of CAIs, even after previously uneventful long-term use.

To evaluate the outcome of eyes with a confirmed iridociliary epithelial tumour (ICET) following biopsy. Forty-two specimens were selected from the Comparative Ocular Pathology Laboratory of Wisconsin database, including 11 globes enucleated following ICET biopsy and 31 iridociliary biopsies with a confirmed ICET. Histopathology was performed for all specimens. When identified, the corneal surgical wound was examined in enucleated globes. Tumour type and margins were determined for biopsy specimens and follow-up was obtained when possible. Biopsies were performed for diagnosis, debulking or excision. 30/31 biopsies had dirty margins, and iridociliary adenomas were indistinguishable from adenocarcinomas by biopsy. Upon biopsy submission 5/23 biopsies were reported as incisional and 18/23 as excisional. Follow-up information was obtained for 14/18 of those reported as excisional. 8/14 had documented recurrence within 5.0±5.6 months and 6/14 had no recurrence at 21.5±13.6 months postoperatively. Three enucleated globes were diagnosed with iridociliary adenocarcinomas and eight with iridociliary adenomas. The corneal surgical wound was sampled in 8/11 globes. There was a synechia to the surgical wound in 3/8 globes, and in 3/8 globes there were neoplastic cells within or adjacent to the surgical wound. The postoperative success of ICET excision is highly variable; complete excision is rarely achieved and recurrence is common. Biopsy effects on ocular tissues may result in synechia and other surgical complications. ICET can be diagnosed by biopsy, but adenomas are indistinguishable from adenocarcinomas.

Papillomas of the conjunctival surface in people can be of viral or nonviral origin and are found in high association with human papillomavirus. Canine conjunctival papillomas are seldom described, and published accounts have mostly been associated with canine oral papillomavirus infection. Here, we describe conjunctival squamous papillomas that do not express papillomavirus proteins and compare them with papillomavirus-associated conjunctival papillomas. Conjunctival squamous papillomas presented a distinct histopathologic profile and lacked the cytopathic effects seen in viral papillomas. They appeared as exophytic, papilliferous, pedunculated lesions with delicate fronds and angular terminal margins. Squamous papillomas presented with a delicate fibrovascular core and were associated both clinically and grossly with a feeder vessel. Pigmentation was variable within the epithelium and stroma of these lesions, and inflammatory infiltrates were characteristically minimal. Conjunctival squamous papillomas resembled squamous papillomas of the skin; however, they lacked significant hyperkeratosis. Compared with conjunctival viral papillomas, these masses occurred in older dogs and were smaller and solitary. Furthermore, polymerase chain reaction and immunohistochemistry failed to demonstrate papillomavirus genetic material and antigens in conjunctival squamous papillomas. Both viral and nonviral conjunctival papillomas were considered benign.

Protozoal keratitis and conjunctivitis without systemic involvement appears rare and may be associated with chronic preexisting ocular surface disease treated with long-term immunosuppression. Based upon clinical appearance, lesions could be confused with neoplasia. This is the first report of amoebic keratoconjunctivitis in dogs and of L. mexicana in dogs in the United States.