Non-tapetal Area Research Articles

Morphometric assessment of the choroid in dogs diagnosed with retinal atrophy (RA) with symptoms of progressive retinal atrophy, using spectral-domain optical coherence tomography (SD-OCT)

The aim of the study was to determine the thickness of choroidal layers in mixed breed dogs suffering from retinal atrophy (RA) and showing symptoms of progressive retinal atrophy (PRA), with the use of SD-OCT. The study was performed on 50 dogs divided into two groups: 25 dogs diagnosed with retinal atrophy (RA) with PRA symptoms aged 1.5-14 years and 25 healthy dogs aged 2-12 years. The dogs were examined using slit-lamp biomicroscopy, tonometry, ophthalmoscopy, fundus camera and SD-OCT (Topcon 3D OCT 2000). Measurements of the choroidal layers: RPE-Bruch membrane-choriocapillaris complex (RPE-BmCc) with tapetum lucidum in tapetal fundus, medium-sized vessel layer, (MSVL), large vessel layer with lamina suprachoroidea and (LVLS) whole choroidal thickness (WCT) were taken manually with the use of the caliper function integrated with the SD-OCT software. The measurements were performed dorsally (D) and ventrally (V) at a distance of 5000-6000 μm, and temporally (T) and nasally (N) at a distance of 4000-7000 μm from the optic disc with enhanced depth scans. The measurements were conducted temporally and nasally both in the tapetal (TempT, Nast) and nontapetal (TempNT, NasNT) fundus. Statistical analysis was performed using Statistica 10 software (Mann Whitney U Test). In all dogs affected by retinal atrophy (RA) with PRA symptoms, a statistically significant (p≤0,05) reduction in thickness of MSVL was observed in all the measured regions. A statistically significant reduction in thickness of LVLS and WCT was found in all nontapetal areas (p≤0,05). RA in mixed breed dogs with PRA symptoms was accompanied by choroid disorders such as reduction in thickness of the large vessel layer and decreased whole choroidal thickness in the nontapetal fundus as well as the medium vessel layer in all fundus regions.

Retinal response to light exposure in BEST1-mutant dogs evaluated with ultra-high resolution OCT

Mutations in BEST1 cause an autosomal recessive disease in dogs where the earliest changes localize to the photoreceptor-RPE interface and show a retina-wide micro-detachment that is modulated by light exposure. The purpose of this study was to define the spatial and temporal details of the outer retina and its response to light with ultra-high resolution OCT across a range of ages and with different BEST1 mutations. Three retinal regions were selected in each eye: near the fovea-like area, near the optic nerve, both in the tapetal area, and inferior to the optic nerve in the non-tapetal area. The OS+ slab thickness was defined between the peak near the junction of inner and outer segments (IS/OS) and the transition between basal RPE, Bruch membrane, choriocapillaris and proximal tapetum (RPE/T). In wildtype (WT) dogs, two tapetal regions showed additional hyperscattering OCT peaks within the OS+ slab likely representing cone and rod outer segment tips (COST and ROST). The inferior non-tapetal region of WT dogs had only one of these peaks, likely ROST. In dogs with BEST1 mutations, all three locations showed a single peak, likely suggesting optical silence of COST. Light-dependent expansion of the micro-detachment by about 10 um was detectable in both tapetal and non-tapetal retina across all ages and BEST1 mutations.

Fundus Imaging via Infrared Camera without Mydriatics in Holstein Calves

This study aimed to record the ocular fundus images of healthy Holstein calves under field conditions. The fundus of 34 eyes of healthy 17 Holstein calves was examined with a fundus camera, which does not require mydriatics, as it has been designed especially for animals and provides imaging with infrared light. The findings showed that the green-yellow tapetal zone was dominant in all calves, the optic disc was oval, and the number of primary arteries and veins originating from the center varied between 4 and 5. The vascular pattern was holangiotic. A remnant of the hyaloid artery (Bergmeister’s papilla) was detected as a gray dot in the middle of the disc. It was noted that the non-tapetal area was homogeneous, brown-black, and rich in choroidal vascular structure. Imaging the ocular fundus is essential in diagnosing some systemic and hereditary diseases in farm animals. However, herd-based ophthalmoscopic screening in farm animals is difficult under field conditions. By using this portable fundus camera, fundus examination can be performed easily under field conditions without taking the animals to the hospital. The standard ophthalmoscopic fundus images of healthy Holstein calves presented in this study will contribute to the literature.

Clinical studies on progressive retinal atrophy in 31 dogs.

During a 2-year period, 31 cases of a hereditary retinal degeneration in dogs bred in India were found mainly suspected for progressive retinal atrophy (PRA) with typical history of initial nyctalopia followed by hemeralopia. Out of 31 PRA suspected dogs, 8 dogs (26%) were from the age group of 1-5 years, 15 (48%) 6-10 years and the rest (26%) 11-15 years. The most predominant breed was Spitz (18 dogs, 58%). Detailed ophthalmologic examinations included Schirmer's tear test, fluorescein stain, applanation tonometry, slit lamp biomicroscopy and ocular ultrasound in appropriate cases. Ophthalmoscopic and fundoscopic changes included hyperreflectivity and discoloration of the tapetal area, marked attenuation of retinal vessels, depigmentation in non-tapetal area and optic disc atrophy with scalloped borders. Electroretinograms (ERG) recorded in 13 PRA-affected cases revealed non-recordable extinguished (flatline) ERG responses. A reduction mainly of a- and b-wave amplitudes in the ERG indicated a generalized photoreceptor disease.

Clinical and Electroretinographic Findings of Progressive Retinal Atrophy in Miniature Schnauzer Dogs of South Korea

ABSTRACTThe purpose of the study was to describe the clinical and electroretinographic features of clinical cases of progressive retinal atrophy (PRA) in miniature schnauzer (MS) of South Korea. Sixty-six MS (14 normal and 52 affected) were included. All animals underwent routine ocular examinations. Electroretinogram (ERG) was recorded in the 14 normal and 15 affected dogs. For normal dogs, the mean age ± SD was 4.1 ± 2.4 years (1 to 9 years), and there were no ocular abnormalities on the basis of ocular examinations and ERG results. For the PRA-affected dogs, it was shown that the mean age ± SD was 4.3 ± 1.1 years (2 to 7 years), and 44 dogs (84.6%) were 3 to 5 years old. Most of the PRA-affected dogs had abnormal menace responses (98.1%) and pupillary light reflexes (PLRs, 88.5%); some dogs showed normal menace response (1.9%) and PLRs (11.5%). Ophthalmoscopic abnormalities in the affected group included one or more of the following changes: hyperreflectivity and discoloration of the tapetal area, attenuation of retinal vessels, depigmentation in non-tapetal area and optic disc atrophy. ERG in the affected dogs showed non-recordable responses in all cases tested with clinical signs of PRA. The present study showed that PRA in MS was mainly observed between the age of 3 to 5 years. ERG revealed abnormal rod and cone responses in affected dogs at the ages studied.

Normal color variations of the canine ocular fundus, a retrospective study in Swedish dogs

BackgroundA retrospective study was made to demonstrate normal variations of the color and size of the tapetal area and color of the nontapetal area in the ocular fundus in dogs, correlating them to breed, age and coat color.MethodsThe study was based on protocols of five hundred and thirty-nine adult dogs describing eye examinations made during the years 1997-2001. The dogs were examined using an indirect ophthalmoscope in order to find heritable eye diseases. The following characteristics were recorded: breed; age; coat color; color and size of the tapetal area and color of the nontapetal area. Normal color variations in the fundus were studied and categorized with regard to breed, age and coat color. Chi-square analysis was used comparing distributions between factors. Differences between mean values were analysed with Student's t-test or one-way-ANOVA. A logistic regression analysis was performed on the color of the tapetal area with the color of the coat and breed.ResultsTwenty breeds were represented. The mean age was 42.8 months. The most common colors of the tapetal area were yellow-green and orange, and the most common colors of the nontapetal area were dark brown and black. The analysis revealed that coat-color and breed concomitantly did not significantly influence tapetal color. Brown coated dogs often had a striped red and brown nontapetal area. The color of the tapetal area influenced the color of the nontapetal area. Smaller-sized breeds (such as Papillon) had a smaller tapetal area. A tapetal area was completely absent in 1.9%. The age did not influence the color of the tapetal area.ConclusionsColor of the tapetal area was influenced by both coat color and breed, but neither of these was statistically more influential than the other. The color of the tapetal area influenced the color of the nontapetal area. The size of the tapetal area correlated to breed and to body size.

Choroidal microcirculation in Abyssinian cats with hereditary rod–cone degeneration

Blood flow in the choroid of eyes with retinal degeneration is normally reduced. In the Abyssinian cat, where no changes in choroidal blood flow were observed recently, a closer morphological analysis revealed that two factors might have lead to this finding. (a) The cat's eye consists of a tapetum lucidum where 15.5μm microspheres cannot reach the precapillary branching in contrast to the non-tapetal areas, where microspheres were located right next to the choriocapillaris. This fact has not yet been described and might be important for further physiological measurements in eyes of species with a tapetum lucidum. (b) The tapetal cells themselves might have a protective role for the choriocapillaris and RPE during retinal degeneration in this specific animal model. Even in late stages of retinal degeneration the RPE and choriocapillaris in areas covered by the tapetum lucidum were not affected whereas non-tapetal areas showed loss of RPE and capillaries.

Myelin Vacuolation, Optic Neuropathy and Retinal Degeneration after Closantel Overdosage in Sheep and in a Goat

Toxicity of closantel, a halogenated salicylanilide anthelmintic, is described in 11 sheep and a goat, humanely killed 4-70 days after accidental overdosage. Status spongiosis of the cerebrum and cerebellum was present, its severity decreasing with time after treatment. Ultrastructurally, vacuoles in the cerebral white matter were seen to be intramyelinic due to splitting of myelin lamellae at the intraperiod lines, indicating myelin oedema. In the optic nerves, Wallerian degeneration and eventual fibrosis and atrophy of the nerves followed myelin vacuolation. Lesions in the optic nerves were particularly advanced in the intracanalicular portion, indicating a compressive neuropathy within the optic canal. Acute retinal lesions consisted of papilloedema, necrosis of the outer retinal layers (especially the photoreceptor layer), and retinal separation in tapetal and non-tapetal areas. In more chronic cases, the outer nuclear layer was diffusely attenuated and generally reduced to a single row of cells.

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.

Ultrastructural changes of the retina and the retinal pigment epithelium in briard dogs with hereditary congenital night blindness and partial day blindness

The offspring of two Briard dogs (brother and sister) with congenital, clinically stationary night blindness showed an aggravation of the disease with severe impairment of day vision in addition to night blindness. This ultrastructural study was performed on four such second generation puppies at the age of 4 months. The neuroretina and retinal pigment epithelium (RPE) from four locations were studied: the central area (immediately temporal to the optic disc); the centre of the tapetal area; the upper periphery (border of tapetal area); and the lower periphery (non-tapetal area). The RPE showed large inclusions, seemingly lipid in nature, mainly in the central and tapetal areas of the retina. Small, membrane bound, electrondense inclusions were scattered in the RPE cytoplasm in all areas examined. The small inclusions were found to be less numerous in normal than in affected dogs and may be lysosomal in nature. Forty to fifty percent of the rod outer segments in the tapetal area showed disorientation of the disc membranes, whereas the corresponding figures were 20–40% in the central and lower peripheral areas and 6–25% in the upper peripheral area. No structural abnormalities were found in the rod inner segments or synaptic bodies. The cones were better preserved. The inner retina appeared normal. These electron microscopic findings seem to correspond to a previously published electrophysiologic evaluation, indicating a defective and delayed rod function (virtually no scotopic a- and b-waves), a better preserved cone function (photopic flicker responses present, although reduced) and impaired RPE activity (a prominent, slow negative potential of long latency at the site of the c-wave). It appears that these Briard dogs, showing structural changes of the rod outer segments in addition to pigment epithelial inclusions, mainly located in the posterior pole, comprise a pigment epitheliopathy and retinopathy morphologically different from other hereditary canine retinopathies that have been described earlier in the literature and different from animal models of congenital night blindness.

Histological study of choroidal melanocytes in animals with tapetum lucidum cellulosum

The distribution and morphology of choroidal melanocytes in dogs and cats which have a tapetum were compared with those of humans who do not. In dogs or cats, tapetal cell-like melanocytes were arranged in layers on the scleral side of the tapetum and underneath the choriocapillaris in the non-tapetal area. Although the tapetum of the dog occupied a smaller area than that of the cat, the tapetum plus the area of tapetal cell-like multilayered melanocytes occupied most of the fundus in the dog in almost the same way as in the cat. These multilayered melanocytes contained few intracytoplasmic organelles except for melanin granules, and some had regularly arranged melanin granules. In human eyes tapetal cell-like melanocytes were not found anywhere. It was concluded that the morphology and structural architecture of choroidal melanocytes of dogs or cats are different from those of human eyes and closely correspond to the tapetum.

Fine structure of the retinal epithelium and tapetum lucidum of the ranch mink Mustela vison.

The morphology of the retinal pigment epithelium (RPE), Bruch's membrane (complexus basalis), choriocapillaris and tapetum lucidum has been studied in the eye of the ranch mink (Mustela vison) by light and electron microscopy. The RPE is composed of a single layer of cells joined laterally by apically located junctional complexes. Basally (sclerally) these cells display numerous infoldings whereas apically (vitreally) two types of processes are associated with rod and cone outer segments. Smooth endoplasmic reticulum and mitochondria are abundant in these cells whereas rough endoplasmic reticulum and polysomes, although present, are not plentiful. An occasional wandering phagocyte is noted at the RPE-photoreceptor interface. In the posterosuperior part of the fundus, a degenerative tapetum lucidum is present. The presence of only a few layers of tapetal cells containing but little reflective material and the haphazard arrangement of this material makes it very unlikely that this area functions as an effective tapetum lucidum. The RPE over the aberrant tapetum, however, shows the morphology that is seen when a functioning tapetum cellulosum is present, namely the absence of melanosomes and an indented choriocapillaris. Bruch's membrane in non-tapetal areas is pentalaminate but, over the tapetum and where it is associated with capillary profiles, it is reduced to a single, thickened basal lamina. The choriocapillary endothelium is highly fenestrated and in nontapetal areas these capillaries are not indented into the epithelial layer.

Tapetal changes in beagle dogs following oral administration of CGS 14796C, a potential aromatase inhibitor

CGS 14796C, cis-1-[(4-[(1-imidazolyl)methyl]-cyclohexyl)methyl)imidazole succinate, has been evaluated as a potential aromatase inhibitor. As part of the safety evaluation program, a 3-month oral toxicity study was performed in which beagle dogs were administered CGS 14796C by gavage at 5, 15, or 50 mg/kg/day. Ophthalmoscopically, changes in the tapetum lucidum affecting dogs from the 15 and 50 mg/kg dose levels were diffuse areas of pigmentation varying in appearance from a brownish peppered or mottled to a more uniform brown similar to that of the nontapetal area of the fundus. Tapetal reflectivity was absent or markedly reduced. Within the pigmented area, multiple islets (yellow, green, or organe) of tapetal cells were visible, suggestive of destruction of the tapetum. In no instance was retinal destruction, edema, vascular changes, or detachment observed. Ophthalmoscopic examinations performed during recovery revealed changes of slight increase in tapetal islets, suggestive of a slight progression and organization within the tapetum followed by an arrest of the toxic insult within the tapetal tissue. At light and electron microscopic examination of the ocular tissues, the lesions were tapetal cell degeneration/atrophy. These results demonstrated that the taptetum lucidum was a target tissue of toxicity for CGS 14796C, and indicated that the findings are without toxicological significance in atapetal species, including man, whose globes do not have this structure.

Tapetal Changes in Beagle Dogs following Oral Administration of CGS 14796C, A Potential Aromatase Inhibitor

Tapetal Changes in Beagle Dogs following Oral Administration of CGS 14796C, A Potential Aromatase Inhibitor. SCHIAVO, D. M., GREEN, J. D., TRAINA, V. M., SPAET, R., AND ZAIDI, I. (1988) Fundam. Appl. Toxicol. 10, 329-334. CGS 14796C, m-l-[(4-[(l-imidazolyl)methyl]-cyclohexyl)methyl)imidazole succinate, has been evaluated as a potential aromatase inhibitor. As part of the safety evaluation program, a 3-month oral toxicity study was performed in which beagle dogs were administered CGS 14796C by gavage at 5, 15, or 50 mg/kg/day. Ophthalmos-copically, changes in the tapetum lucidum affecting dogs from the 15 and 50 mg/kg dose levels were diffuse areas of pigmentation varying in appearance from a brownish peppered or mottled to a more uniform brown similar to that of the nontapetal area of the fundus. Tapetal reflectivity was absent or markedly reduced. Within the pigmented area, multiple islets (yellow, green, or orange) of tapetal cells were visible, suggestive of destruction of the tapetum. In no instance was retinal destruction, edema, vascular changes, or detachment observed. Ophthalmoscopic examinations performed during recovery revealed changes of slight increase in tapetal islets, suggestive of a slight progression and organization within the tapetum followed by an arrest of the toxic insult within the tapetal tissue. At light and electron microscopic examination of the ocular tissues, the lesions were tapetal cell degeneration/atrophy. These results demonstrated that the taptetum lucidum was a target tissue of toxicity for CGS 14796C, and indicated that the findings are without toxicological significance in atapetal species, including man, whose globes do not have this Structure.

Retinal pigment epithelial dysfunction in early ovine ceroid lipofuscinosis: electrophysiologic and pathologic correlates.

Retinal degeneration is a major finding in the human and ovine ceroid lipofuscinosis. Sequential electroretinographic (ERG) studies in a young, asymptomatic, affected lamb are presented here, which demonstrate a progressive loss of the scotopic b-wave and unrecordable c-waves under halothane anesthesia. Even at this initial stage of disease, lesions were evident in the form of dystrophic retinal pigment epithelial (RPE) villi, and loss of photoreceptor cells and rod outer segments. Cone inner segments were enlarged and scanning electron microscopy emphasized these abnormalities. All cells in tapetal and nontapetal areas contained fluorescent inclusions with similar emission spectra (maximum = 539 nm). By transmission electron microscopy, storage bodies consisted of 'finger-print' profiles and were most prominent in bipolar cells. The pathological features of the retina correlate well with the observed ERG changes, reaffirming the sheep as a useful model to delineate early events in ceroid lipofuscinosis.

Fine structure of the choriocapillaris, Bruch's membrane and retinal epithelium in the sheep.

The fine structure of the choriocapillaris, Bruch's membrane and retinal epithelium was investigated by light and electron microscopy in both the tapetal and non-tapetal fundus of the domestic sheep. The choriocapillaris are heavily fenestrated on the side facing the retina. Overlying the tapetum, the choriocapillaris also displays fenestrae on the choroidal border. Bruch's membrane is pentalaminate throughout the retina and slightly thicker over the tapetal region. In all locations the retinal epithelium consists of a single layer of cells, which vary in height depending upon their location. The epithelial cells are joined laterally by apically located tight junctions and throughout the retina display numerous basal infoldings and apical processes which enclose rod outer segments. The epithelial cell nucleus is large and vesicular. All retinal epithelial cells are rich in smooth endoplasmic reticulum and phagosomes. Although not as abundant, mitochondria, Golgi zones, profiles of rough endoplasmic reticulum and polysomes are also noted in all locations. In non-tapetal areas, melanosomes are numerous whereas over the central tapetum fibrosum they are absent. While lysosomes are present throughout the epithelial layer, over the tapetal area they appear to be more numerous. The absence of melanosomes over a functional tapetum fibrosum is to be expected. The apparent increase in lysosomal numbers in this location may indicate an enhanced shedding of outer segment material over the tapetal region. Although some retinal epithelial cells are modified to accommodate a tapetum lucidum their morphology is basically similar throughout the retina and probably indicates that all regions of the retinal epithelium are capable of the normal functions of this indispensible retinal layer.

Fine structure of the retinal epithelium, Bruch's membrane (Complexus basalis) and choriocapillaris in the domestic ferret.

The fine structure of the retinal epithelium, choriocapillaris, and Bruch's membrane has been studied by electron microscopy in the domestic ferret. The ferret possesses a tapetum cellulosum in the superior fundus, and the morphology of the retinal epithelium and its associated structures varies depending upon its relation to the tapetum. Over the tapetum the retinal epithelium is a single layer of low cuboidal cells with basal infoldings and two types of apical process. Internally the cells are non-pigmented, display much smooth endoplasmic reticulum, little rough endoplasmic reticulum, lysosomes, phagosomes, and a basally located nucleus. The choriocapillaris is composed of large capillaries indented into the retinal epithelium. Bruch's membrane is thin and composed of three layers. In non-tapetal regions the retinal epithelial cells are pigmented but display most of the other features noted over the tapetum. The choriocapillaris is not indented in non-tapetal areas. Bruch's membrane appears identical to that noted over the tapetum. Wandering phagocytes are occasionally noted at the retinal epithelium-photoreceptor junction.

Photic retinopathy in the dog

The light of a Keeler binocular indirect ophthalmoscope was focused for one hour through either a colorless or yellow-tinted 35 mm diameter+20 diopter glass condensing lens on the tapetal and nontapetal retina of dogs. The effects of this illumination were studied sequentially by examining eyes clinically and histologically at varying intervals following light exposure. Retinal lesions were produced in 50% of the eyes in which the tapetal fundus was illuminated through the colorless lens, but did not develop in the nontapetal area with either lens or in the tapetal area when the yellow lens was used. The lesions began as circular areas of increased tapetal granularity followed by loss of retinal transparency, pigmentation, and eventually tapetal hyper-reflectivity. Histologically, initial changes included vacuolation and rupture of retinal pigment epithelial (RPE) cells, and vesiculation and shortening of the photoreceptor outer segments. As the post-illumination period increased, much of the RPE eventually became atrophic; the photoreceptor cells were absent almost entirely but the inner retinal layers remained intact.

Fine structure of the retinal epithelium in the bushbaby (<i>Galago senegalensis</i>)

The fine structure of the retinal epithelial layer has been studied by electron microscopy in the bushbaby (<i>Galago senegalensis</i>). The retinal epithelium over most of the retina is fairly typical of other vertebrates and consists of a single layer of heavily pigmented cuboidal cells joined laterally by cell junctions. These cells display extensive basal (scleral) infoldings and numerous apical (vitreal) processes which enclose photoreceptor outer segments. The bushbaby possesses a choroidal tapetum lucidum located in the posterior fundus. Over this tapetum the retinal epithelial cells are squamous and non-pigmented. However, as in the non-tapetal area, basal infoldings, apical processes and lateral cell junctions are present as are numerous mitochondria and large amounts of smooth endoplasmic reticulum. Rough endoplasmic reticulum is not abundant. Over the tapetal region the typical fenestrated choriocapillaris is displaced and indents the retinal epithelial layer. Bruch’s membrane in such an indented area is reduced to a single basal lamina from its normal pentalaminate structure seen in the non-tapetal area. In the non-tapetal region particularly the tips of the photoreceptor outer segments are composed of an amorphous material rather than typical outer segment discs.

Fine structure of the retinal epithelium of the spectacled caiman (Caiman sclerops).

The fine structure of the retinal epithelium, Bruch's membrane and choriocapillaries has been studied by electron microscopy in the spectacled caiman (Caiman sclerops). The retinal epithelium throughout most of the retina is morphologically very typical of that described for other vertebrates. This typical appearance involves a single layer of pigmented cuboidal cells with extensive basal (scleral) infoldings and numerous apical (vitreal) processes enclosing photoreceptor outer segments. A semicircular area of the retinal epithelium in the superior fundus is, however, further specialized as a tapetum lucidum. The reflecting material consists of a large array of guanine, diffusely scattered within the epithelial cells. Centrally in the tapetal area, no melanosomes are found, indicating a non-occlusible tapetum. At the edge of the tapetum, however, both guanine crystals and melanosomes are found within the epithelial cells. In most other respects, the morphology of the epithelial layer in the tapetal region is not strikingly different from that in the non-tapetal area. Bruch's membrane everywhere displays the typical pentalaminate structure described for most vertebrates. The choriocapillaris is also typical in that numerous fenestrations are present in the endothelium bordering Bruch's membrane.