Pathology in Practice.

In collaboration with the American College of Veterinary Pathologists.

Zebrafish models of alx-linked frontonasal dysplasia reveal a role for Alx1 and Alx3 in the anterior segment and vasculature of the developing eye.

The cellular and genetic mechanisms that coordinate formation of facial sensory structures with surrounding skeletal and soft tissue elements remain poorly understood. Alx1, a homeobox transcription factor, is a key regulator of midfacial morphogenesis. ALX1 mutations in humans are linked to severe congenital anomalies of the facial skeleton (frontonasal dysplasia, FND) with malformation or absence of eyes and orbital contents (micro- and anophthalmia). Zebrafish with loss-of-function alx1 mutations develop with craniofacial and ocular defects of variable penetrance, likely due to compensatory upregulation in expression of a paralogous gene, alx3. Here we show that zebrafish alx1;alx3 mutants develop with highly penetrant cranial and ocular defects that resemble human ALX1-linked FND. alx1 and alx3 are expressed in anterior cranial neural crest (aCNC), which gives rise to the anterior neurocranium (ANC), anterior segment structures of the eye and vascular pericytes. Consistent with a functional requirement for alx genes in aCNC, alx1; alx3 mutants develop with nearly absent ANC and grossly aberrant hyaloid vasculature and ocular anterior segment, but normal retina. In vivo lineage labeling identified a requirement for alx1 and alx3 during aCNC migration, and transcriptomic analysis suggested oxidative stress response as a key target mechanism of this function. Oxidative stress is a hallmark of fetal alcohol toxicity, and we found increased penetrance of facial and ocular malformations in alx1 mutants exposed to ethanol, consistent with a protective role for alx1 against ethanol toxicity. Collectively, these data demonstrate a conserved role for zebrafish alx genes in controlling ocular and facial development, and a novel role in protecting these key midfacial structures from ethanol toxicity during embryogenesis. These data also reveal novel roles for alx genes in ocular anterior segment formation and vascular development and suggest that retinal deficits in alx mutants may be secondary to aberrant ocular vascularization and anterior segment defects. This study establishes robust zebrafish models for interrogating conserved genetic mechanisms that coordinate facial and ocular development, and for exploring gene--environment interactions relevant to fetal alcohol syndrome.

Clinical and pathologic evaluation of chorioretinal lesions in wild owl species.

OBJECTIVE: Investigate histopathology and spectral-domain optical coherence tomography (OCT) imaging of wild owls with chorioretinitis and identify any potential correlation with an infectious etiology. MATERIALS AND METHODS: Ophthalmic examination and retinal OCT imaging were performed on fifteen great horned (Strix varia) and barred (Bubo virginianus) owls (30 eyes) with chorioretinitis and five owls with normal eyes (10 eyes). Testing to investigate the presence of potential infectious diseases included a complete blood count, biochemistry, protein electrophoresis, West Nile virus (WNV) plaque reduction neutralization test, Toxoplasma gondii modified direct agglutination test, WNV RT-PCR, and Avian Influenza RT-PCR. A necropsy was performed on all owls, including ocular histopathology. RESULTS: Fundus lesions included retinal detachment (7/15 owls), depigmented lesions (12/15), pigment clumping (8/15), and retinal tear (4/15). All birds were negative for WNV and Avian Influenza on RT-PCR. Of the owls with chorioretinitis, 3/15 were seropositive for WNV and 7/15 for T. gondii. Optical coherence tomography of 25/30 affected eyes revealed outer retinal lesions (19/25 eyes), retinal detachment (16/25), and retinal tears (3/25). Histopathological examination revealed outer nuclear layer atrophy (19/30 eyes), retinal detachment (18/30), retinal tears (7/30), suprachoroidal hemorrhage (12/30), scleral rupture (3/30), and ossicle fracture (3/30). CONCLUSIONS: Although 20% of birds were seropositive for WNV and 46.6% for T. gondii, histopathologic findings supported that the posterior segment lesions in the study group were likely due to blunt ocular trauma rather than an infectious etiology. The results of OCT imaging and histopathology documented retinal changes most consistent with blunt ocular trauma.

Pathology in Practice.

In collaboration with the American College of Veterinary Pathologists.

Changing the Wound: Covalent Immobilization of the Epidermal Growth Factor.

Re-epithelialization of wounds is a critical element of wound closure. Growth factors have been used in combination with conventional wound management to promote closure, but the method of delivery has been limited to the topical application of ointment formulations. Cytoactive factors delivered in this way have short resident times in wounds and have met with limited success. Here, we demonstrate that methods used to covalently immobilize proteins on synthetic materials can be extended to immobilize cytoactive factors such as the epidermal growth factor (EGF) onto the wound beds of genetically diabetic mice that exhibit impaired healing. Full-thickness splinted excisional wounds were created in diabetic (db/db) mice with a well-defined silicone splint to limit wound contracture. Wound surfaces were treated with a reducing agent to expose sulfhydryl groups and subsequently treated with EGF modified with a heterobifunctional crosslinker. This allowed for the covalent immobilization of the EGF to the wound surface. The conjugation chemistry was validated in vitro and in vivo. In a separate group of mice, wounds were topically treated twice daily with soluble EGF. The mice were evaluated over 11 days for wound closure. This covalent immobilization strategy resulted in EGF being retained on the wound surface for 2 days and significantly increased epithelial wound closure by 20% compared to wounds treated with topical EGF or topical vehicle. Covalent immobilization was not only therapeutically effective but also delivered a markedly reduced load of growth factor to the wound surface compared to topical application (when only 180 ng of EGF was immobilized onto the wound surface in comparison with 7200 ng of topically applied EGF over a period of 11 days). No adverse effects were observed in treated wounds. Results obtained provide proof of concept for the effectiveness of covalent immobilization in the treatment of dysregulated wounds. The covalent immobilization of cytoactive factors represents a potentially transformative approach to the management of difficult chronic wounds.

Ocular anatomy and correlation with histopathologic findings in two common octopuses (Octopus vulgaris) and one giant Pacific octopus (Enteroctopus dofleini) diagnosed with inflammatory phakitis and retinitis.

PURPOSE: Review octopus ocular anatomy and describe the histopathologic findings in three octopuses diagnosed with phakitis and retinitis. ANIMALS: Two common octopuses (Octopus vulgaris) and one giant Pacific octopus (Enteroctopus dofleini) with a history of ophthalmic disease. METHODS: A literature search was performed for the ocular anatomy section. Both eyes from all three octopuses, and two control eyes, were submitted for histopathologic evaluation. Hematoxylin and eosin stain was used for standard histopathologic evaluation; GMS stain was used to screen for fungi, gram stain for bacteria; and Fite's acid fast stain for acid fast bacteria. RESULTS: Anatomically, the anterior chamber of the octopus has direct contact with ambient water due to an opening in the dorsal aspect of a pseudocornea. The octopus lens is divided into anterior and posterior segments. The anterior half is exposed to the environment through the opening into the anterior chamber. Neither part of the lens has a lens capsule. The retina is everted, unlike the inverted vertebrate retina, and consists of just two layers. Histopathology revealed inflammatory phakitis and retinitis of varying severity in all six eyes of the study animals. No intraocular infectious organisms were recognized but one common octopus eye had clusters of coccidian parasites, identified as Aggregata sp., in extraocular tissues and blood vessels. CONCLUSION: We describe inflammatory phakitis and retinitis in two species of octopuses. The underlying cause for the severe intraocular response may be direct intraocular infection, water quality, an ocular manifestation of a systemic disease, or natural senescence.

Atypical free-floating iridociliary pigmented epithelial cysts and secondary glaucoma in a caiman (Caiman latirostris).

We describe a case of chronic ocular trauma that resulted in fixed and free-floating, pigmented epithelial iridociliary cysts, inflammation, and secondary glaucoma in a caiman (Caiman latirostris). A 20- to 25-year-old male caiman was presented with phthisis bulbi in the right eye, and congested episcleral vessels, corneal leukoma, disorganized anterior chamber, multifocal anterior synechia, and elevated intraocular pressure in the left eye. Ocular ultrasound of the left eye revealed round structures dispersed in the anterior and posterior chambers and vitreous cavity. Bilateral enucleation was performed, and gross pathology of the left eye revealed multiple pigmented cysts attached to the iris and posterior corneal surface causing marked distortion of the anterior uvea, and free-floating in the vitreous cavity. Histopathology demonstrated heavily pigmented cystic structures of iridociliary epithelium origin carpeting the anterior segment surfaces and causing obstruction of the iridocorneal angles, leading to secondary glaucoma. To the authors' knowledge, this is the first report of iridociliary cysts in wildlife species.

Ocular porcupine quilling in dogs: Gross, clinical and histopathologic findings in 17 cases (1986-2018).

The objectives of this retrospective study were to evaluate the histopathologic changes associated with porcupine ocular quill injuries in dogs, to discuss the various methods of quill detection when quills are not grossly visible, and to discuss the pathogenesis of delayed ocular quill injuries in dogs. Seventeen globes sustaining ocular quilling injuries from 17 dogs (1986-2018) were identified in the COPLOW archives and the gross and histologic changes tabulated and compared. All cases were dogs, with one whole globe submitted from each patient. Sixteen of 17 cases had known or suspected porcupine encounters in the weeks or years preceding enucleation. Histopathologic findings included retinal detachment, hyphema, cataract, granulomatous to pyogranulomatous inflammation (uveitis, endophthalmitis, panophthalmitis), lens capsule rupture, suppurative phakitis, scleral perforation, stromal keratitis, breaks in Descemet's membrane, preiridal fibrovascular membrane, anterior and posterior synechia, Schnabel's cavernous atrophy, and periorbital fibrosis. Quill-associated ocular trauma can have a significant deleterious effect on vision and result in enucleation. The time from initial quilling to the manifestation of ocular signs may be prolonged (weeks to years). Any dog presenting for ocular signs with a history of a previous porcupine encounter should be carefully checked for quill migration into the globe as the source of ocular disease. Quills may not be visible grossly, and ancillary imaging techniques can be utilized with various rates of success.

Management of corneal epithelial defects in a population of mature chuck-will's-widows (Antrostomus carolinensis) in South Florida.

PURPOSE: To describe ocular clinical findings, gross/histopathologic findings, and treatment regimens in a series of migratory chuck-will's-widows (Antrostomus carolinensis) (CWW) with corneal epithelial defects. METHODS: Seven CWW were presented to the South Florida Wildlife Center (SFWC). Four presented with bilateral (OU) corneal ulceration; two developed corneal ulceration OU; one had no ocular lesions. Treatment protocols for patients with corneal ulcers included the following: medical therapy only or medical therapy combined with an additional procedure. Four patients including the bird with no ocular lesions were euthanized, and one patient died. Their globes were submitted for histopathology. Two patients were released. RESULTS: Clinical findings prior to enucleation included superficial corneal ulceration with redundant epithelium persisting weeks to >1 month. On histopathology, epithelium in nonulcerated globes was remarkably thin; this was considered normal. Common histopathologic findings of ulcerated globes revealed epithelial and conjunctival attenuation with an acellular superficial stromal layer and hypercellular mid-stromal layer. One globe healed with medical therapy and cotton tip applicator debridement. Four globes healed by combination of medical therapy, equine amnion, nictitating membrane (NM) flap, and temporary tarsorrhaphy. No globes healed with diamond burr debridement or grid keratotomy. CONCLUSIONS: Factors that may be contributing to these corneal epithelial defects include, but are not limited to, normally thin epithelium, exposure keratopathy, neurotrophic disease, epithelial turnover and inadequate stem cell recruitment, inherited/genetic causes, and unidentified infectious agents (eg, viral etiologies). Of the 12 eyes treated, one healed with medical therapy/cotton tip applicator debridement, and four healed with medical therapy/equine amnion/nictitating membrane flap/temporary tarsorrhaphy.

The relative importance of phylogeny and habitat in determining the presence and prominence of a granula iridica in hooved mammals.

PURPOSE: To investigate the relationship between phylogeny and amount of shade in a species' habitat regarding the presence or absence of an iridal granula iridica (GI) in a large sample of Artiodactyl and Perissodactyl clades and using online resources. METHODS: The Comparative Ocular Pathology Laboratory of Wisconsin (COPLOW) archives were searched for glass slide material from Artiodactyl (even-toed) and Perissodactyl (odd-toed) ungulates. The slides were examined, and the presence or absence of the GI was noted. The phylogenetic tree of the ungulate species was inferred using TimeTree (http://www.timetree.org), and the habitat data are derived from Animal Diversity Web (https://animaldiversity.org/). We assessed the probability of the presence of GI occurring given the amount of shade in a species' environment using phylogenetic logistic regression. RESULTS: Forty-eight artiodactyl species were able to be evaluated and tabulated. Nine perissodactyl species were able to be evaluated. The phylogenetic logistic regression showed that the probability of GI presence was lower in artiodactyl species that inhabited shaded environments (ßshaded  = -1.774). Arctiodacyl species inhabiting a nonshaded environment were slightly more probable to have the GI present (ßnonshaded  = 0.023), with species inhabitating ambiguously shaded environments having a high probability of GI presence (ßambiguous  = 2.214). CONCLUSIONS: Our results suggest that the GI may be a common morphological feature to shade the pupil in nonshaded environments, and, in its absence, increase the amount of light reaching the retina to improve vision in shaded environments for hooved mammals. Further research on the functional optics of the GI and studies that include additional ungulate species would further elucidate phylogenetic and ecological factors influencing the occurrence of GI in hooved mammals.

A clinicopathological study of 17 cases of ocular surface xanthogranuloma in dogs.

OBJECTIVE: To evaluate the clinical, histopathological, and immunohistochemical features of 17 cases of ocular surface xanthogranuloma (OSX) in dogs. METHODS: Archived records from the Comparative Ocular Pathology Laboratory of Wisconsin (COPLOW) were searched for cases of canine OSX. Cases were evaluated for lipid-laden macrophages and Touton giant cells. Seventeen cases matching those criteria were identified (1993-2018). Clinical and epidemiological data were collected from the submission forms and additional follow-up survey. RESULTS: Ocular surface xanthogranuloma in dogs presented as small bland nodules. OSX commonly occurred at the limbus (8/17) or cornea (4/17). Three of 17 affected animals were less than 1-year-old and the average age was 6.9 years (range 0.7-14 years). Fourteen of 17 cases did not report any lipid or metabolic abnormalities. Histologically, lesions were composed mainly of dense sheets of vacuolated lipid-laden macrophages and Touton giant cells with scant additional inflammatory cells and an intact overlying epithelium. No recurrence was noted in cases where complete surgical resection was achieved, and medical treatment either pre or post-resection led to only partial resolution. CONCLUSIONS: Xanthogranulomas are histiocytic lesions characterized by abundant lipid-laden macrophages. The authors use the term, ocular surface xanthogranuloma, to describe nodules with rigidly defined cellular characteristics. Although these lesions share characteristics with human limbal xanthogranulomas, further investigation is needed to suggest the different subsets that have been reported in the medical literature. Complete surgical excision is the most effective treatment for OSX in dogs, and intralesional triamcinolone and topical steroids can be useful adjunctive therapies to surgery.

Clinical and histopathological classification of feline intraocular lymphoma.

This retrospective study aimed to describe and classify cats with intraocular lymphoma, determine the proportion of cases with presumed solitary ocular lymphoma (PSOL) compared with ocular manifestations of multicentric disease and assess the clinical outcomes of these patients. One hundred seventy-two cases identified through biopsy submissions were reviewed histologically; 163 of these cases were subtyped according to the WHO classification system. Cases were categorized as having PSOL or ocular lymphoma with suspected systemic involvement (SSI) based on submission forms and follow-up data. The majority of cases exhibited concurrent uveitis (75%) and secondary glaucoma (58%). Diffuse large B-cell lymphoma was the most common subtype (n = 86; 53%), followed by peripheral T-cell lymphoma (n = 44; 27%). Other subtypes included anaplastic large T- (n = 8; 5%) and B-cell (n = 4; 2.5%) lymphomas, and 15 cases (9%) were negative for all immunohistochemical markers. In sixty-nine cases (40%), adequate clinical data and sufficient survival data were obtained to distinguish PSOL from SSI. PSOL comprised the majority of cases (64%), while 36% had SSI. When covarying for age at diagnosis, the median survival time was significantly higher (P = 0.003) for cases of PSOL (154 days) versus those with SSI (69 days); hazards ratio of 0.47 for PSOL (95% CI: 0.241-0.937). The subtype of lymphoma did not affect survival time. Cats with PSOL represent a greater proportion of the disease population, and this subset of cats with intraocular lymphoma has a better clinical outcome.

A novel cellular structure in the retina of insectivorous birds.

The keen visual systems of birds have been relatively well-studied. The foundations of avian vision rest on their cone and rod photoreceptors. Most birds use four cone photoreceptor types for color vision, a fifth cone for achromatic tasks, and a rod for dim-light vision. The cones, along with their oil droplets, and rods are conserved across birds - with the exception of a few shifts in spectral sensitivity - despite taxonomic, behavioral and ecological differences. Here, however, we describe a novel photoreceptor organelle in a group of New World flycatchers (Empidonax spp.) in which the traditional oil droplet is replaced with a complex of electron-dense megamitochondria surrounded by hundreds of small, orange oil droplets. The photoreceptors with this organelle were unevenly distributed across the retina, being present in the central region (including in the fovea), but absent from the retinal periphery and the area temporalis of these insectivorous birds. Of the many bird species with their photoreceptors characterized, only the two flycatchers described here (E. virescens and E. minimus) possess this unusual retinal structure. We discuss the potential functional significance of this unique sub-cellular structure, which might provide an additional visual channel for these small predatory songbirds.

Bilateral Anterior Uveitis in a Northern Saw-whet Owl (Aegolius acadicus) With a Metastatic Pectoral Malignant Mesenchymoma.

A captive, adult, male northern saw-whet owl (Aegolius acadicus) was examined for blepharospasm of the left eye. The owl was diagnosed with bilateral anterior uveitis and a corneal ulceration in the left eye. It was treated with oral and topical nonsteroidal anti-inflammatory medications and a topical antibiotic. Multiple recheck examinations and medication adjustments were performed over the next 4 months, at the end of which time the bilateral anterior uveitis was controlled with a topical nonsteroidal anti-inflammatory applied 3 times per week to both eyes. The owl was re-examined 2 months later after 2 suspected neurologic episodes. On physical examination, the owl was quiet and had difficulty standing and ambulating. Five firm multilobular and immobile masses were identified overlying the pectoral muscle and sternum. Fine-needle aspiration from 1 mass revealed neoplastic cells consistent with a sarcoma. The owl was euthanatized. On the basis of results of histopathologic examination, the mass was diagnosed as a pleomorphic spindle cell sarcoma with features of rhabdomyosarcoma, liposarcoma, and osteosarcoma. Numerous tumor cells were immunopositive for myoglobin and desmin, indicating striated muscle origin. Although a metastatic lesion was present in 1 adrenal gland, lesions of inflammation or neoplasia were absent in either eye on histopathologic examination. This report describes an apparent ocular manifestation of systemic disease in an avian species with clinically diagnosed recurrent anterior uveitis.

A Transient Developmental Background Finding in the Retina Observed in Neonatal Dogs in Juvenile Toxicology Studies.

In a juvenile toxicology program, an unexpected finding of vacuolation of inner nuclear, ganglion cell, and nerve fiber layers of the retina was observed microscopically in routine Davidson's fixed and hematoxylin and eosin-stained tissue sections of eyes in beagle dogs at approximately 5 weeks of age. There was no necrosis or degeneration of the affected cells and no associated inflammation. Fluorescein angiography revealed no vascular leakage. Optical coherence tomography (OCT) indicated swollen cells in the same layers of the retina as observed at light microscopic examination. Transmission electron microscopy revealed that the retinal vacuolation likely was consistent with intracellular swelling of amacrine, horizontal, and/or bipolar cells of the inner nuclear layer as affected cells had an expanded cytoplasm but contained normal nucleus and organelles. As assessed by animal behavior and full-field electroretinography, the retinal vacuolation appeared to have no impact on visual function. Retinal vacuolation was seen in approximately 40% of dogs at 5 weeks of age using OCT and/or light microscopic examination. Because the change was transient and age related, did not result in degenerative retinal changes, and was not present in dogs older than 5 weeks of age, it was considered a background developmental observation in beagle dogs.

Diversity of photoreceptor arrangements in nocturnal, cathemeral and diurnal Malagasy lemurs.

The lemurs of Madagascar (Primates: Lemuriformes) are a monophyletic group that has lived in isolation from other primates for about 50 million years. Lemurs have diversified into species with diverse daily activity patterns and correspondingly different visual adaptations. We assessed the arrangements of retinal cone and rod photoreceptors in six nocturnal, three cathemeral and two diurnal lemur species and quantified different parameters in six of the species. The analysis revealed lower cone densities and higher rod densities in the nocturnal than in the cathemeral and diurnal species. The photoreceptor densities in the diurnal Propithecus verreauxi indicate a less "diurnal" retina than found in other diurnal primates. Immunolabeling for cone opsins showed the presence of both middle-to-longwave sensitive (M/L) and shortwave sensitive (S) cones in most species, indicating at least dichromatic color vision. S cones were absent in Allocebus trichotis and Cheirogaleus medius, indicating cone monochromacy. In the Microcebus species, the S cones had an inverse topography with very low densities in the central retina and highest densities in the peripheral retina. The S cones in the other species and the M/L cones in all species had a conventional topography with peak densities in the central area. With the exception of the cathemeral Eulemur species, the eyes of all studied taxa, including the diurnal Propithecus, possessed a tapetum lucidum, a feature only found among nocturnal and crepuscular mammals.

Canine, feline, and equine corneal vascular neoplasia: A retrospective study (2007-2015).

Corneal vascular neoplasms (hemangioma and hemangiosarcoma) are rare in all species. Reported cases are single case reports in a single species. Archived cases of corneal hemangioma and hemangiosarcoma from dogs, cats, and horses were obtained from the Comparative Ocular Pathology Lab of Wisconsin (COPLOW, Madison, WI), tabulated, and examined. This retrospective study describes the breeds, ages, tumor types, and characteristics of vascular neoplasms that appeared to be primarily corneal in location, in feline, canine, and equine patients, with gross and histologic images. There is a discussion of predisposing factors and speculated association with chronic ocular surface disease.

Feline Neovascular Vitreoretinopathy and Anterior Segment Dysgenesis With Concurrent Glaucoma in Domestic Cats.

Feline neovascular vitreoretinopathy (FNV) is a newly recognized rare condition affecting kittens and young domestic cats. This study investigated the clinical and pathologic findings in 22 cats with FNV. In affected cats, ophthalmoscopy of the fundus (when visible) revealed avascular peripheral retinae and epiretinal vascular membranes. Frequent nonspecific clinical findings were buphthalmos ( n = 21), medically uncontrollable glaucoma ( n = 22), and lenticular abnormalities ( n = 13). Anterior segment dysgenesis (ASD) was detected clinically in affected cats ( n = 6). The fellow eye was affected in 11 of 18 cats to a variable degree or appeared clinically normal in 7 of 18 cats. The globes were examined histologically and using immunohistochemistry for vimentin, glial fibrillary acidic protein (GFAP), synaptophysin, neurofilament, laminin, factor VIII-related antigen (FVIII-RA), and smooth muscle actin (SMA). Histologically, diagnostic features included laminin-positive epiretinal vascular membranes affecting the central retina, with an avascular peripheral retina and gliosis. Enucleated globes exhibited multiple additional abnormalities, including corneal disease ( n = 15), anterior segment dysgenesis ( n = 21), lymphoplasmacytic anterior uveitis ( n = 19), peripheral anterior synechiae ( n = 20), retinal degeneration ( n = 22), and retinal detachment ( n = 19). Gliotic retinae labeled strongly for GFAP and vimentin with reduced expression of synaptophysin and neurofilament, consistent with degeneration or lack of differentiation. While an avascular peripheral retina and epiretinal fibrovascular membranes are also salient features of retinopathy of prematurity, there is no evidence to support hyperoxic damage in cats with FNV. The cause remains unknown.

PRESUMED PHOTORECEPTOR DYSPLASIAS IN PEREGRINE FALCONS ( FALCO PEREGRINUS) AND PEREGRINE FALCON HYBRIDS.

We describe a case series of photoreceptor dysplasia with secondary retinal degeneration in juvenile Peregrine Falcons. Six Peregrine Falcons ( Falco peregrinus) and three Peregrine Falcon × Prairie Falcon ( Falco mexicanus) hybrids had early-life visual deficits. Eight birds had visual defects shortly after hatching, and one bird had visual deficits first noticed at 5 mo of age. Complete ophthalmic examinations were performed in each animal. Eight of the animals had electroretinograms, and nine of the animals had their eyes examined histologically after euthanasia. Ophthalmic examinations did not reveal consistent and potentially blinding abnormalities, including an absence of ophthalmoscopic retinal lesions. Electroretinographic findings included subnormal amplitudes (with rod responses more abnormal than cone responses), with a negative b-wave amplitude occurring in one bird. Histologically, a reduction in the number of photoreceptors was present with numerous degenerative changes to the remaining photoreceptors, including frequent blunting and disorganization of photoreceptor outer segments, decreased numbers of cells in the inner nuclear layer, decreased numbers of ganglion cells, decreased thickness of the nerve fiber layer, and decreased myelinated axons within the optic nerve. Ultrastructurally, only minor cone outer segment changes and occasional phagocytic cells were seen. Results strongly suggested a primary retinopathy, characterized by photoreceptor dysplasia and secondary retinal degeneration with loss of cellular elements throughout the retina. The presence of a similar spectrum of findings in related individuals, the early age of onset, and the relative lack of other environmental, ocular, or systemic abnormalities suggested possible heritability.

Ocular anatomy of the black pacu (Colossoma macropomum): gross, histologic, and diagnostic imaging.

OBJECTIVE: To describe the ocular anatomy of the black pacu (Colossoma macropomum), a freshwater teleost fish of the Amazon River basin, including an unusual choroid laden with adipose tissue. PROCEDURES: Three adult black pacu were anesthetized and examined clinically and with ocular ultrasonography, then euthanized. Three fish were euthanized and their heads imaged immediately postmortem using computed tomography. One fish was euthanized and its exenterated eyes imaged by high-resolution magnetic resonance imaging. The exenterated eyes of all seven fish were fixed in formalin; eyes from three fish were examined grossly and histologically. Additionally, archived histologic sections from two smaller black pacu specimens were examined. RESULTS: Findings were consistent among the ocular imaging modalities used. Intrinsic to the sclera were circumferential ossicles and scleral cartilage. The lens was spherical and protruded through the ovoid pupil with an aphakic space inferiorly when the accommodative mechanism was relaxed under anesthesia. Both a small falciform process and epiretinal vasculature were present in the posterior segment. The retina was cone-rich, and processes of the retinal pigment epithelium enveloped the photoreceptor outer segments. Remarkably, the choroid occupied one-third of the anteroposterior length of the globe; histology confirmed that the bulk of the choroid was composed of adipose tissue. CONCLUSIONS: The eye of the pacu overall is typical of teleosts but has the notable and consistent finding of a substantive store of choroidal fat of unknown function.