Fine structure of the retinal pigment epithelium, Bruch's membrane and choriocapillaris in the horse

The fine structure of the retinal pigment epithelium (RPE), Bruch's membrane and choriocapillaris was investigated by light and transmission electron microscopy in both the tapetal and non-tapetal fundus of the horse eye. In all locations, the RPE consisted of a single layer of low cuboidal cells. The epithelial cells were joined laterally by apically located tight junctions. These cells displayed numerous basal infoldings and abundant thin apical processes which enclosed the rod outer segments. The epithelial cell nuclei were large and located basally. Within the epithelial cells, smooth endoplasmic reticulum was very abundant, while rough endoplasmic reticulum was scarce, polysomes and mitochondria, which often display a ring-shaped structure, were abundant. Melanosomes were abundant in the non-tapetal area but absent in the tapetal area. Bruch's membrane was pentalaminate throughout the retina. The endothelium of the choriocapillaris was heavily fenestrated.     

Retinal Epithelial Fine Structure in the Domestic Cat (Felis catus)

The morphology of the retinal epithelium (RPE) and closely associated choriocapillaris and Bruch's membrane (complexus basalis) has been investigated in the eye of the domestic cat (felis catus) by light and electron microscopy. The RPE consists of a single layer of cuboidal cells joined laterally by apically-located junctional complexes. Basally (sclerally) these cells display numerous infoldings while apically (vitreally) two distinct types of processes enclose photoreceptor outer segments. Internally the large vesicular nucleus is centrally located. Smooth endoplasmic reticulum, mitochondria, polysomes and lysosome-like bodies are abundant. Rough endoplasmic reticulum while present is not plentiful. Over the tapetum lucidum, melanosomes are absent from the RPE cells while in non-tapetal locations melanosomes are large and plentiful. The endothelium of the choriocapillaris is highly fenestrated and these capillaries are deeply indented into the epithelial layer over the tapetum. Bruch's membrane (complexus basalis) is non-tapetal regions is the typical pentalaminate structure noted for most mammals. Over the tapetum however it is reduced to a trilaminate structure and when associated with the indented capillary profiles is further reduced to a single thickened basal lamina.     

Fine structure of the retinal pigment epithelium, Bruch's membrane and choriocapillaris in the camel

The morphology of the retinal pigment epithelium (RPE) and closely associated Bruch's membrane and choriocapillaris was investigated by light and transmission electron microscopy in the camel (Camelus dromedarius). The study showed that RPE is composed of a single layer of hexanocuboidal cells that were joined laterally by a series of apically located tight junctions. In addition, adjacent from internal side of cell membrane at the level of tight junctions, an undefined structure which resembled the myofibrillar organization of skeletal muscles in appearance was located. These cells displayed numerous short basal infoldings and abundant thin apical processes which enclosed the rod outer segments. The epithelial cell nuclei were large, vesicular and eccentrically located. Within the epithelial cells, smooth endoplasmic reticulum was very abundant, while rough endoplasmic reticulum was present only in small amounts. Polysomes were also numerous and the mitochondria often displayed a ring-shaped structure. Lipofuscin granules were plentiful in all locations. Bruch's membrane (complexus basalis) was typically pentalaminate throughout the retina. The endothelium of the choriocapillaris facing Bruch's membrane was extremely thin and heavily fenestrated. These fenestrations displayed typical single-layered diaphragm as noted in most species.     

Fine structure of the retinal pigment epithelium, Bruch's membrane and choriocapillaris in the ostrich (Struthio camelus)

The fine structure of the retinal pigment epithelium (RPE), Bruch's membrane and choriocapillaris in the ostrich (Struthio camelus) was investigated by using light microscopy and transmission electron microscopy. In this species, the RPE consisted of a single layer of low columnar cells. The epithelial cells were joined laterally by two type junctions, zonulae occludentes and zonulae adherentes located in the midregion of the cells. These cells displayed numerous deep basal infoldings and thick extensive apical processes, which enclosed the outer segments of the rods. The epithelial cell nuclei were large, vesicular and located basally within the epithelial cells. Smooth endoplasmic reticulum was very abundant, while rough endoplasmic reticulum was scarce. Mitochondria of various shapes were abundant basally while polysomes were plentiful and widespread. In the light-adapted state melanosomes were located in the apical region and in apical processes of the epithelial cells. Myeloid bodies were large, numerous and often showed ribosomes on their outer surface. Bruch's membrane (complexus basalis) was typical pentalaminate throughout the retina, as noted in the majority of other vertebrates. The endothelium of the choriocapillaris facing Bruch's membrane was extremely thin but only moderately fenestrated. Some of the fenestrations displayed a double-layered diaphragm while the majority showed the more typical single-layered diaphragm noted in most species.     

Fine Structure of the Bovine Tapetum Fibrosum

The fine structure of the tapetum lucidum of the domestic cow was studied by electron microscopy. In this ungulate the reflective layer is a tapetum fibrosum situated in the choroid and mainly restricted to the superior fundus. The tapetum is composed of a large array of fine extracellular collagen fibrils separated into lamellae by fibrocytes. The collagen fibrils display the normal cross-striations of native collagen, are 0.2 μm in diameter and are arranged in a hexagonal pattern with a center-to-center spacing of about 0.2 μm. The diameter and spacing of these fibrils is consistent with the constructive interference of reflected light. A vascular lamella adjacent to the retinal epithelial layer contains the choriocapillaris and some irregularly arranged collagen fibrils. The tapetum is pierced by blood vessels which supply the choriocapillaris. Over the tapetum the retinal epithelium is non-pigmented while in nontapetal regions this layer is pigmented. The choriocapillaris is not indented into the retinal epithelium as is the case in species with a tapetum cellulosum.     

Retinal Pigment Epithelial Fine Structure in the Great Blue Heron (Ardea herodias)

The fine structure of the retinal epithelium (RPE), choriocapillaris and Bruch's membrane (complexus basalis) has been studied by light and electron microscopy in the great blue heron (Ardea herodias). In this species the RPE consists of a single layer of cuboidal cells which display numerous basal (scleral) infoldings and plentiful apical (vitreal) processes which surround photoreceptor outer segments. These epithelial cells are joined laterally by a series of tight junctions located in the mid to basal region. Within the epithelial cells, smooth endoplasmic reticulum is very abundant while rough ER is not. Mitochondria (some of which are ring-shaped) and polysomes are abundant. In light-adaptation the RPE nuclei are large vesicular and basally located while the melanosomes of these cells are almost exclusively located within the apical processes. Myeloid bodies are large and numerous and often show ribosomes on their outer surface. Bruch's membrane (complexus basalis) shows the typical pentalaminate structure noted in the majority of vertebrates except teleosts. The choriocapillary endothelium is very thin facing Bruch's membrane but is only moderately fenestrated. The majority of these fenestrations show a single-layered diaphragm but double-layered diaphragms are also noted.     

Retinal Pigment Epithelial Fine Structure in the Red-Tailed Hawk (Buto jamaicensis)

As part of a comparative morphological study, the fine structure of the retinal epithelium (RPE), choriocapillaris and Bruch's membrane (complexus basalis) has been studied by electron microscopy in the red-tailed hawk (Buteo jamaicensis). In this species the RPE consists of a single layer of low cuboidal cells which display numerous basal (scleral) infoldings and extensive apical (vitreal) processes which interdigitate with photoreceptor outer segments. These epithelial cells are joined laterally by a series of basally located tight junctions. Internally SER is the most abundant cell organelle while only small amounts of RER are present. Polysomes are however abundant as are mitochondria. The RPE cell nucleus is large and vesicular. Melanosomes are mainly located in the apical processes of the RPE cells in light-adaptation. Myeloid bodies are large and numerous in light-adaptation and often show ribosomes on their outer border. Bruch's membrane (complexus basalis) shows the typical pentalaminate structure noted in most vertebrates but with only a poorly defined central elastic layer. The endothelium of the choriocapillaris is very thin facing the RPE but is only moderately fenestrated. The choriocapillaris in this species is unusual however in that many of the fenestrae show a double-layered diaphragm.     

Retinal Pigment Epithelial Fine Structure in the American Crow (Corvus brachyrhynchos)

The fine structure of the retinal epithelial (RPE) region has been investigated by light and electron microscopy in the American crow (Corvus brachyrhynchos). In this species the RPE consists of a single layer of cuboidal cells which display numerous deep basal (scleral) infoldings and plentiful apical (vitreai) microvillar processes which surround photoreceptor inner and outer segments. The RPE cells are joined laterally by a series of tight junctions (VERHOEFF'S membrane) located in the mid to basal region. Within the epithelial cells, smooth endoplasmic reticulum is very abundant while rough endoplasmic reticulum (RER) is scarce. Mitochondria of various shapes are abundant basally while polysomes are plentiful and widespread. In the light-adapted state RPE nuclei are large and vesicular and basally located while the melanosomes of these cells are predominantly located with the apical processes indicating photomechanical movements. Myeloid bodies are large and numerous and often have ribosomes on their outer surface. Bruch's membrane (complexus basalis) is typical of avian species in that it is pentalaminate and the lamina densa is displaced near the cho-riocapillaris. The endothelium of the choriocapillaris is thin facing Bruch's membrane but is only moderately fenestrated. Some of these fenestrations display a double-layered diaphragm while the majority show the more typical single-layered diaphragm noted in most species.     

Heritability of multifocal retinal dysplasia in American Cocker Spaniels

Multifocal retinal dysplasia was detected in 96 American Cocker Spaniels. Affected dogs were part of approximately 500 American Cocker Spaniels examined from 1972 to 1976 in statewide survey clinics for inherited cataracts and progressive retinal atrophy. The dysplastic retina was observable ophthalmoscopically in dogs as young as 3 to 4 weeks and as old as 7 years. Ophthalmoscopic features varied, depending on whether the dysplastic foci were in the tapetal or non-tapetal portion of the fundus. Over the tapetum, dysplastic foci appeared as multiple small irregularities of diminished and altered tapetal reflectivity. In the non-tapetal fundus, dysplasia appeared as areas of decreased pigmentation. Blindness or other apparent visual deficits were not observed in affected dogs. Histologic examination of affected eyes revealed focal dysplasia limited to the retina and optic nerve. Abnormalities included localized areas of retinal folding, rosettes, and retinal pigment epithelium hypertrophy and hyperplasia. Pedigree analysis demonstrated that 71 of the 96 affected dogs were related and could be identified in an extended pedigree. A recessive mode of inheritance was suggested, because in 5 litters (born to 10 affected parents), all 23 progeny that lived were affected. A dominant or polygenic mode of inheritance could not be ruled out.     

Transpupillary diode laser retinopexy in dogs: ophthalmoscopic,fluorescein angiographic and histopathologic study

Objective To evaluate the ophthalmoscopic, fluorescein angiographic and light microscopic effects of diode laser retinopexy application in the tapetal and nontapetal fundus in the dog, and to ascertain appropriate laser power settings for production of photocoagulative lesions in these two regions. Animals studied Three adult female Beagle dogs. Procedures Laser burns were applied to selected areas in the fundus with an indirect headset delivery system using settings varying from 100 to 200 milliWatts (mW) and from 100 to 600 milliSeconds (mS) with total delivered energy ranging between 15 and 100 milliJoules (mJ). The dogs were then monitored by ophthalmoscopic examination and fluorescein angiography at regular intervals for 7–28 days. Histopathologic studies were performed at 7, 14 and 28 days after laser application. Results The diode laser produced ophthalmoscopically visible lesions in the nontapetal fundus with all laser settings used, and the appearance of these lesions corresponded to the energy levels used, and degree of pigment in the lased region. Gray‐white colored lesions with minimal subsensory retinal edema were seen with settings as low as 100 mWatts/150 mSeconds. In the tapetal fundus, laser burns were more difficult to produce, less repeatable, and required higher energy levels. Laser burns appeared as bronze, dark green or black discolorations of the tapetum with varying degrees of subsensory retinal edema. Lesions were more reproducible and were achieved with lower settings in the tapetal area of the tapetal/nontapetal junction. Ophthalmoscopically, depigmentation and repigmentation of the RPE (nontapetal fundus) and degenerative changes in the overlying retina (tapetal fundus) developed in the laser burns over the 28‐day study period. Fluorescein angiographic studies showed disruption of the blood–retinal barrier at the level of the RPE and fluorescein leakage into the subsensory retinal space was seen in most lesions at 24 h, was minimal at 3 days, and had resolved by 7 days. Histologically, grayish‐white lesions in the nontapetal fundus, and bronze to small black lesions in the tapetal fundus were typically characterized by outer retinal necrosis and RPE migration. Gliosis was considered minimal, was confined to the retina, and no inflammatory cells were seen. Peripheral intense white lesions (nontapetum) and lesions with a black center (tapetal fundus) were characterized by more extensive panretinal and choroidal necrosis. Most of the nontapetal lesions and a few in the tapetal fundus showed the formation of a central retinal detachment. Conclusions The diode laser effectively produces lesions suitable for retinopexy in both the nontapetal, pigmented fundus and the tapetal fundus, although variably so in the latter region. Initial laser settings of 100–150 mW/200 mS for the pigmented fundus, and 150 mW/200–300 mS for the peripheral tapetal fundus are recommended, and the clinician should gradually increase time interval settings to achieve a grayish‐white lesion in the nontapetum, and a bronze to slightly black lesion in the tapetal fundus. If possible, retinopexy should be applied to the peripheral tapetal area or tapetal/nontapetal junction.     

Ultrastructural ocular lesions of 6-aminonicotinamide toxicosis in rabbits

6-Aminonicotinamide, given by intraperitoneal injection to male and female Dutch belted rabbits, produced swelling and vacuolation of ciliary and iridal epithelium plus vacuolation of the retinal pigment epithelial and outer plexiform layers of the retina. By transmission electron microscopy, inner and outer ciliary epithelial cells and inner iridal epithelial cells contained numerous coalescing, membrane-bound vacuoles of the cytocavitary network. These vacuoles were viewed as numerous interconnecting, intracytoplasmic cavities in scanning electron micrographs. Swelling of vacuolated epithelial cells and the presence of fibrin and proteinaceous fluid in the ciliary stroma resulted in thickening of the anterior ciliary processes with the formation of surface alterations detectable by scanning electron microscopy. In transmission electron micrographs the vacuoles in the retinal pigment epithelium were large, electron-lucent spaces and the vacuoles in the outer plexiform layer of the retina appeared to be intracytoplasmic spaces in axons of photoreceptor cells. Distention of cytocavitary structures has been reported in glial cells of animals given 6-aminonicotinamide and this change was apparently due to alterations in ion and water movement across cellular membranes that resulted in intracellular edema.     

Multifocal chorioretinal lesions in Borzoi dogs

OBJECTIVES: To identify the prevalence of Borzoi chorioretinopathy in western Canada, characterize lesions with fluorescein angiography, determine if lesions were progressive, clarify the association of progressive retinal atrophy and investigate the etiology. MATERIALS AND METHODS: Serial ophthalmic examination, fundus photography, electroretinography, and fluorescein angiography were used to evaluate Borzoi dogs with lesions of Borzoi chorioretinopathy. Pedigree analysis and test breeding of two affected dogs were completed to determine the heritability of Borzoi chorioretinopathy. RESULTS: One hundred three Borzoi dogs were examined between 1998 and 2003. Focal, peripheral, tapetal, hyper-reflective and pigmented areas consistent with focal retinal degeneration and RPE pigmentation were identified in 12 dogs between 7 months and 7 years of age. Seven males and five female dogs were affected. Ophthalmoscopy and fundus photography over 5 years revealed individual lesions that did not progress or coalesce in 12 affected dogs. Electroretinography of affected and normal Borzoi dogs confirmed that retinal function was similar in normal and affected dogs up to 7 years of age. Fluorescein angiography was performed in three affected dogs and confirmed intact blood-ocular barriers, focal retinal pigment epithelium hypertrophy, and focal absence of choroiocapillaris corresponding to chronic, focal lesions. Pedigree analysis precluded simple dominant, X-linked dominant, or X-linked recessive inheritance. One male dog from the test-bred litter developed bilateral lesions at 14 months of age. Simple recessive, polygenetic, and acquired etiologies of these lesions cannot be ruled out at this time. CONCLUSIONS: Borzoi chorioretinopathy is an acquired condition that initially manifests as focal retinal edema and loss of choriocapillaris and tapetum. With time the retina degenerates becoming hyper-reflective and with RPE hyper-pigmentation and clumping within the borders of the tapetal lesions. Choriocapillaris remains hypofluorescent on fluorescein angiography. Progressive retinal atrophy was excluded as an etiology of multifocal chorioretinopathy in Borzois dogs. This condition is not inherited by simple autosomal dominant or sex-linked modes of inheritance.     

Ophthalmoscopic characteristics in sheep and goats: comparative study

The ocular fundus was examined in 40 goat eyes and 40 sheep eyes by studying ophthalmoscopic characteristics and retinograms. Similarities and differing characteristics were described. In common: tapetal colour; peripheral yellowish area surrounding the Winslow stars; unpigmented areas in the non-tapetal zone; a great amount of myelin in the optic disc; the Bergmeister's papilla and the holoangiotic retinal vascular pattern. Differences: big size of the Winslow stars in goats; myelinizated fibre over the non-tapetal zone in sheep; shape, position and myelin distribution of the optic disc; and the presence of a 'primary artery' in goats.     

Spatial relationships among the cellular tapetum,visual streak and rod density in dogs

The dog visual system is well suited to dim light conditions due to rod-dominated retina and the reflective tapetum. The topographical distributions of rods and thickness of the tapetum of the dog were quantified in retinal whole mounts stained with thionine, and spatial relationships among the tapetum, rod density and visual streak of high ganglion cell density were elucidated. The relationship between the retina and tapetum was analyzed in parasagittal sections stained with thionine or hematoxylin-eosin. The tapetum was thick in its center, and the thickest part consisted of 9 to 12 tapetal cell layers. Rod density ranged from 200,000 to 540,000/mm². Maximum rod density was found in the area dorsal to the visual streak, and the density in that area was significantly higher than the rod density in the visual streak and accorded spatially with the thickest part of the tapetum. The horizontal visual streak was found over the horizontal line through the optic disc in the temporal half and extended slightly into the nasal half. The central area of the highest density of ganglion cells was approximately located midway between the nasal and temporal ends of the visual streak. The visual streak was located within the tapetal area, but ventrally to the thick part of the tapetum.     

Unilateral ocular subalbinism in a laboratory Beagle dog

Blue discoloration of the iris was found in the left eye of a male laboratory Beagle dog, which had a normal tricolor coat and clinically showed no visual impairment. Ophthalmoscopically, the affected eye revealed red-colored tigroid fundus, in which no tapetum was present. The retinal vasculature and the optic disc showed no noticeable changes. Histopathologically, in the left eye melanocytes had extremely few melanin granules in the anterior segment, including the anterior border layer, in the stroma and sphincter muscle of the iris and in the stroma of the ciliary body and choroid. However, the posterior pigment epithelium of the iris, the pigment epithelium of the ciliary body and the retinal pigment epithelium showed normal pigmentation. The tapetal elements were completely absent. Number and distribution of the S-100 protein-positive melanocytes with or without melanin granules in the iris, ciliary body and choroid of the left eye were similar to those of the normal right eye. Ultrastructurally, melanocytes in the anterior segment of the affected iris possessed no or few melanosomes which were incompletely melanized. In the right eye, no abnormal features were observed. Based on these results, the present case was diagnosed as unilateral ocular subalbinism with tapetal aplasia in a Beagle dog.     

Cytologic appearance of retinal cells included in a fine‐needle aspirate of a meningioma around the optic nerve of a dog

A 6‐year‐old Wirehair Dachshund had a meningioma around the optic nerve that caused exophthalmos. A benign mesenchymal tumor was suspected based on the cytologic pattern of a fine‐needle aspirate, and a meningioma was diagnosed by histopathologic examination. In addition to the meningioma cells, the cytologic smears included groups of cells from apparently 4 layers of normal retina. In particular, uniform rod‐shaped structures in the cytologic sample could suggest rod‐shaped bacteria, but these structures were identified as cylindrical outer segments of photoreceptor rod cells. Other retinal structures recognized included pigmented epithelial layer cells with their uniquely formed pigment granules, the characteristic bi‐lobed, cleaved nuclei from the outer nuclear layer, and nerve tissue likely from the outer plexiform layer of the retina.     

Characteristics of structures and lesions of the eye in laboratory animals used in toxicity studies

Histopathology of the eye is an essential part of ocular toxicity evaluation. There are structural variations of the eye among several laboratory animals commonly used in toxicity studies, and many cases of ocular lesions in these animals are related to anatomical and physiological characteristics of the eye. Since albino rats have no melanin in the eye, findings of the fundus can be observed clearly by ophthalmoscopy. Retinal atrophy is observed as a hyper-reflective lesion in the fundus and is usually observed as degeneration of the retina in histopathology. Albino rats are sensitive to light, and light-induced retinal degeneration is commonly observed because there is no melanin in the eye. Therefore, it is important to differentiate the causes of retinal degeneration because the lesion occurs spontaneously and is induced by several drugs or by lighting. In dogs, the tapetum lucidum, a multilayered reflective tissue of the choroid, is one of unique structures of the eye. Since tapetal cells contain reflecting crystals in which a high level of zinc has been demonstrated chemically, drug-induced tapetum degeneration is possibly related to zinc chelation. The eye of the monkey has a macula similar to that of humans. The macula consists only of cones with a high density, and light falls directly on the macula that plays an important role in visual acuity. Macular degeneration occurring in monkeys resembles histopathologically that of humans. Hence, the eye of the monkey is a suitable model to investigate macular degeneration and to assess drug-induced macular lesions.     

Ocular manifestations of equine motor neuron disease

The characteristics of the ocular manifestations of equine motor neuron disease (EMND) are described. Forty-two horses with histories, clinical signs and necropsies compatible with EMND were the subjects of this study. Ophthalmoscopic lesions that varied in severity were found in 40 of 42 horses and appeared as a distinct pigmented reticulated pattern at the tapetal-nontapetal junction or throughout the fundus, depending upon severity. The pattern colours ranged from yellow brown to black. Areas of hyperreflectivity formed mosaic patterns in the tapetal fundus. ERG B-wave amplitudes were usually at least 50% reduced and many animals showed extinguished amplitudes. None of the horses had apparent visual impairment. Histopathologically, all 42 horses had retinal pigment epithelial (RPE) congestion with ceroid-lipofuscin. Retinal degeneration was variable even within the eyes. Thin layer chromatography (TLC) analysis of the RPE and neural retina identified both green and orange emitting fluorescent compounds not found in normal horses. All unsupplemented horses had plasma vitamin E levels <1.0 microg/ml. The potential significance of this report is the pathognomonic role the ocular manifestations exhibit in helping to diagnose equine motor neuron disease.     

A slowly progressive retinopathy in the Shetland Sheepdog

Objective To describe a slowly progressive retinopathy (SPR) in Shetland Sheepdogs. Animals Forty adult Shetlands Sheepdogs with ophthalmoscopic signs of SPR and six normal Shetland Sheepdogs were included in the study. Procedure Ophthalmic examination including slit‐lamp biomicroscopy and ophthalmoscopy was performed in all dogs. Electroretinograms and obstacle course‐test were performed in 13 affected and 6 normal dogs. The SPR dogs were subdivided into two groups according to their dark‐adapted b‐wave amplitudes. SPR1‐dogs had ophthalmoscopic signs of SPR, but normal dark‐adapted b‐wave amplitudes. Dogs with both ophthalmoscopic signs and subnormal, dark‐adapted b‐wave amplitudes were assigned to group SPR2. Eyes from two SPR2 dogs were obtained for microscopic examination. Results The ophthalmoscopic changes included bilateral, symmetrical, greyish discoloration in the peripheral tapetal fundus with normal or marginally attenuated vessels. Repeated examination showed that the ophthalmoscopic changes slowly spread across the central parts of the tapetal fundus, but did not progress to obvious neuroretinal thinning presenting as tapetal hyper‐reflectivity. The dogs did not appear seriously visually impaired. SPR2 showed significantly reduced b‐wave amplitudes throughout dark‐adaptation. Microscopy showed thinning of the outer nuclear layer and abnormal appearance of rod and cone outer segments. Testing for the progressive rod–cone degeneration ( prcd )‐mutation in three dogs with SPR was negative. Conclusion Slowly progressive retinopathy is a generalized rod–cone degeneration that on ophthalmoscopy looks similar to early stages of progressive retinal atrophy. The ophthalmoscopic findings are slowly progressive without tapetal hyper‐reflectivity. Visual impairment is not obvious and the electroretinogram is more subtly altered than in progressive retinal atrophy. The etiology remains unclear. SPR is not caused by the prcd‐mutation.     

Anatomy of the California sea lion globe

Objective This study analyzed the morphology of the California sea lion globe to determine what features may contribute to their characteristic visual abilities. Procedure Globes from the Comparative Ocular Pathology Laboratory of Wisconsin (COPLOW) collection were examined from gross photographs and microscopic sections stained with hematoxylin and eosin, trichrome, smooth muscle actin, and alcian blue periodic acid–Schiff (PAS). Transmission electron microscopy of the cornea and iris was also performed. Clinical results There was a round, flattened area ventromedial to the axial cornea. The pupil was tear‐drop shaped. Pectinate ligaments were visible without magnification. The retina was holangiotic, containing numerous spoke‐like venules and arterioles. The tapetum was green encompassing the entire fundus. The optic nerve was unmyelinated. Histological results The sclera was thinnest equatorially and thickest at the limbus and posterior pole. Bowman’s layer was difficult to see by light microscopy but clear with transmission electron microscopy. The cornea had a thick epithelium, thin endothelium and Descemet’s membrane, and the stroma thinned axially. The dilator muscle was absent near the pupil, but enlarged and mingled with the sphincter muscle near the iris base. A large, wide ciliary cleft with prominent trabeculae and a single continuous pectinate ligament was present. The corneoscleral trabecular meshwork was discontinuous. A round lens attached to the ciliary body via direct attachment to ciliary processes and delicate zonular ligaments. There was a circumferential muscle at the base of the ciliary processes. A thick tapetum covered the entire fundus except peripherally. The retina was characterized by sparse, large ganglion cells.