Quantitative study of the optic nerve in buffaloes (Bos bubalis)

The total number, distribution and size of the optic axons of the buffalo (Bos bubalis) were studied in five optic nerves using light and transmission electron microscopes. Semithin sections were cut at 0.40 μm with an ultramicrotome and stained with 0.3% toluidine blue for light microscopic analysis. The ultrathin sections were cut at 70 nm, mounted on copper mesh grids (No. 200) and stained with saturated solution of uranyl acetate dihydrate and examined with the transmission electron microscope. The optic axons were assessed in 10 regions of roughly equal area. The total number of optic fibers was estimated on semithin and ultrathin sections. The measurements of the axonal diameters were made on electron micrographs taken from various regions across the optic nerve. The mean value of the total number of optic axons calculated was 1 397 099 ± 10 995 and 1 584 255 by light and electron microscopes, respectively. There was very little difference in the density of the optic fibers between the 10 regions of the optic nerve. The optic nerve area ranged from 18.2 to 22.4 mm² (mean, 21.3 mm²). The diameters of the optic axons ranged from 0.5 to 12.3 μm (mean, 3.3 μm).     

Structural and ultrastructural study of the intracranial portion of the oculomotor, trochlear and abducent nerves in dog

The right intracranial portion of the oculomotor, trochlear and abducent nerves were removed from six adult German shepherd dogs and analysed by light and electron microscopy. In all cases the nerve sectional area was calculated. Unmyelinated and myelinated fibres were analysed and number, diameter and cross-sectional area were calculated. In myelinated fibres, also calculated were the corresponding axon area and diameter, and myelin sheath thickness. The mean number of myelinated fibres was 8543.50 +/- 1231.85 being the unmyelinated 1402 +/- 241.58 in the oculomotor nerve; 1509 +/- 223.17 and 287.67 +/- 72.28 in the trochlear nerve and 2473.00 +/- 211.41 and 231.25 +/- 92.67 respectively in the abducent. The mean diameter was 10.23 +/- 0.68 microm in myelinated and 0.43 +/- 0.21 for unmyelinated in oculomotor nerve, 10.53 +/- 0.55 microm and 0.33 +/- 0.04 for the trochlear, and 10.45 +/- 1.27 microm and 0.47 +/- 0.09 in the abducent nerve respectively. This study reveals that oculomotor, trochlear and abducent nerves of the dog show structural and ultra-structural features similar to the same nerves in other species.     

Comparative retinal ganglion cell and optic nerve morphology

The optic nerve is divided in four regions: intraocular, intraorbital, intracanalicular, and intracranial. The vertebrate retinal ganglion cells are classified by morphology, physiology and soma size. Species differences and similarities occur with retinal ganglion cells. Alpha retinal ganglion cells have large somata, large dendritic fields, large-diameter axons, and are most dense in the peripheral retina. Beta retinal ganglion cells have smaller diameter somata, smaller dendritic fields, small diameter axons, and predominate in the central retina. Gamma retinal ganglion cells are a heterogenous class of cells and have small diameter axons, and slow axon conduction velocities. The spatial distribution and organization of the retinal ganglion cells extends retinotopically through the nerve fiber layer, optic nerve, optic chiasm, optic tract, lateral geniculate nucleus, and visual cortex. The retinal nerve fiber layer thickness decreases from the optic disk toward the periphery of the retina. The retrobulbar optic nerve axon counts and axon density vary by species, with larger nerves having higher axon counts. Decussation of the optic nerve axons at the optic chiasm varies with 100% decussation in most birds and fish, 65% in cats, 75% in dogs, 80–90% in large animals, and 50% in primates. Centrifugal axons also occur in the optic nerve and may represent a method by which the brain can influence retinal activity.     

Topography of ganglion cells in the retina of the horse

Topography of ganglion cells in the retina of the horse (Thoroughbred) was analyzed in the wholemount retina stained with cresyl violet, and a total number of ganglion cells were estimated. Sizes of ganglion cells were also measured and size spectra were analysed. The main results showed that: (1) a common point in 4 wholemount retinae, based on cell densities and retinal locations, was that a retina could be divided into 5 regions, namely visual streak, nasal, temporal, dorsal and ventral region to the visual streak. A maximum cell density of 4,000 cells/mm2 was found in the visual streak. And a total number of ganglion cells was estimated in a range of 398 x 10(3) - 469 x 10(3), with a mean of 441 x 10(3) +/- 31 x 10(3) (n=4). (2) cell sizes were measured as the mean lengths of the major and minor axes of the somas, and were in a range of 5-53.8 microm. The lowest mean diameter was 14.0 microm (+/- 3.7) in the visual streak and the highest was 25.9 microm (+/- 7.6) in the ventral region. Cell size spectra were unimodal and positively skewed. It is expected that these analyses will provide an anatomical and physiological background for further study of the visual system in the horse.     

A study of the ultrastructure and staining characteristics of the 'dental star' of equine incisors

The objective of this study was to examine the diameter, extent, orientation and contents of dentinal tubules in order to validate the hypothesis of pigment penetration into the dental star of equine incisival occlusal surfaces. The time of appearance and the configuration of the dental star on the incisival occlusal surface are macroscopically visible features that, along with other more reliable parameters, are used for the determination of horses' age. Although dental stars are an integral part of the equine incisor occlusive surface, the exact nature and microstructure of the dental star are poorly documented. Therefore, equine incisor dentine was examined macroscopically and by scanning electron microscopy to elucidate numerical density, diameter and 3-dimensional organisation of the dentinal tubules in the dental star. The dental star is surrounded by primary dentine and consists of a central core of tertiary dentine, an intermediate ring of pale secondary dentine and a peripheral rim of darker, yellowish-brown secondary dentine. The central core of tertiary dentine contains relatively few dentinal tubules (<8000/mm2) that have small diameters (mean +/- s.d. 1.67 +/- 034 microm) and are arranged in an irregular pattern. The surrounding pale ring of secondary dentine comprises manifestly more and wider tubules that lie almost parallel to the occlusal surface. The dark peripheral rim of the dental star contains high numbers of tubules (28,000-58,000/mm2) that have wide luminal diameters (mean +/- s.d. 3.09 +/- 0.31 microm) and open perpendicular to the occlusal surface. In contrast, the primary dentine surrounding the dental star is made up by a lower number of dentinal tubules (<25,000/mm2). The tubules of primary dentine, which are initially mean +/- s.d. 5.15 +/- 0.80 microm wide, are narrowed by circumferential deposits of peritubular dentine and are obliquely exposed at the occlusal surface. From these observations, it was concluded that the regional differences in numerical density, diameter and spatial orientation of the dentinal tubules may influence the penetration of food pigments into the equine occlusal surface and result in the particular staining of the dental star.     

Ophthalmic examination of the captive western lowland gorilla (Gorilla gorilla gorilla).

This study examined the captive western lowland gorilla (Gorilla gorilla gorilla) eye as compared and contrasted with the human eye. Bilateral ophthalmic examinations of western lowland gorillas (n = 5) while under general anesthesia were performed opportunistically, including slit-lamp biomicroscopy, dilated fundus examination, cycloplegic retinoscopy, Schiotz tonometry, corneal diameter and thickness measurements, A-scan and B-scan ultrasonography, keratometry, and cultures of the eyelid margins and bulbar conjunctiva. Mean spherical equivalent refractive error by cycloplegic retinoscopy was +1.20 +/- 0.59 diopters. Mean intraocular pressure by Schiotz tonometry was 12.0 +/- 4.3 mm Hg. Mean optic nerve head cup to disc ratio was 0.42 +/- 0.11. Mean horizontal corneal diameter was 13.4 +/- 0.8 mm, and mean vertical cornea diameter was 12.7 +/- 0.8 mm. Mean central corneal thickness by ultrasound pachymetry was 489 +/- 52 microm. Mean axial length of the eye by A-scan was 22.75 +/- 0.71 mm. Mean lens thickness by A-scan was 4.23 +/- 0.34 mm. Mean anterior chamber depth by A-scan was 4.00 +/- 0.26 mm. Mean keratometry reading was 44.38 +/- 1.64 diopters. Eyelid margin and bulbar conjunctival cultures isolated Candida sp. (n = 5), Staphylococcus aureus (n = 4), Staphylococcus epidermidis (n = 3), Staphylococcus saccharolyticus (n = 3), and Micrococcus sp. (n = 3). This study suggests important similarities between western lowland gorilla and human eyes. These similarities may allow diagnostics, techniques, and equipment for human eye surgery, such as those used for cataract extraction and intraocular lens implantation, to be successfully utilized for gorillas.     

Morphologic and morphometric studies of the vagus and recurrent laryngeal nerves in clinically normal adult dogs

Morphologic and morphometric studies were performed on the vagus nerve and its major branch, the recurrent laryngeal nerve (RLN): (1) to determine normal histologic data in myelinated fibers of clinically normal young adult dogs, (2) to establish reference values for mean fiber diameter in the vagus nerve and in the proximal and distal portions of the RLN, and (3) to delineate relative frequency distribution curves for each nerve. Few degenerative changes were observed in single teased-nerve fiber preparations. There was no statistical difference between left and right sides of the vagus nerve or between the proximal and distal portions of the RLN (right and left sides). In contrast to the unimodal distribution of fibers in the vagus nerve and the proximal portion of the RLN, the distribution of fibers in the distal portion of the RLN was bimodal. Mean (+/- SD) fiber diameters of the vagus nerve and in the proximal portion of the RLN (3.02 +/- 1.44 microns and 3.63 +/- 1.49 microns, respectively) were not significantly different, despite a shift to large-diameter fibers in the latter. However, mean fiber diameters of distal and proximal portions of the RLN (5.56 +/- 1.88 microns and 3.63 +/- 1.49 microns, respectively) were significantly (P less than 0.001) different. Approximately 86% of fibers in the vagus nerve and 76% of fibers in the proximal portion of the RLN, had a diameter less than 5 microns, and about 70% of fibers in the distal portion of the RLN had a diameter greater than 5 microns.(ABSTRACT TRUNCATED AT 250 WORDS)     

Size Distribution of Dispersed Luteal Cells During Oestrous Cycle in Angora Goats

The present study examines the size distribution of the goat steroidogenic luteal cells throughout the oestrous cycle. Corpora lutea (CL) were collected after laparatomy on days 5, 10 and 16 of the oestrous cycle. Luteal cells were isolated from CL by collagenase digestion. Steriodogenic luteal cells were identified by staining of the cells for 3beta-hydroxysteroid dehydrogenase activity, a marker for steroidogenic cells. Luteal cells having steroidogenic capacity covered a wide spectrum of sizes, ranging from 5 to 37.5 microm in diameter. There was a significant increase in mean cell diameters (p < 0.01) as CL aged. The mean cell diameter on day 5 was 11.55 +/- 0.12 microm, which was significantly increased and reached up to 19.18 +/- 0.24 mum by day 16 of the oestrous cycle. The ratio of large to small luteal cells was 0.06:1.0 on day 5 of the oestrous cycle. This ratio increased to 0.78:1.0 by day 16 of the oestrous cycle. Luteal cell size on days 5, 10 and 16 of the oestrous cycle reached its maximum at 7.5, 10 and 35 microm in diameter, respectively. Development of CL is associated with an increase in luteal cell size in goats. It is likely that small luteal cells could develop into large luteal cells as CL becomes older during oestrous cycle in goats.     

Growth Dynamics of White Muscle Fibres in Relation to Somatic Growth of Larvae of European Sea Bass (Dicentrarchus labrax, L.)

The body length and diameter of muscle fibres from the right hypaxial tail myomeres were measured in 100 sea bass larvae (Dicentrarchus labrax, L.) at ages of 40 to 90 days, from a fish farm in Croatia. The larvae were kept at a temperature of 19-20 degrees C and fed with standard feed for their respective ages. Body lengths of larvae 40-90 days old varied from 8 to 42 mm, increasing significantly in 10-day intervals (p < 0.001), except between days 50 and 60 when there was no increase in the body length. The measured diameters of muscle fibres ranged from 10 to 80 microm, the mean value increasing except between days 50 and 60. The fibre diameter in larvae aged up to 60 days was 10-40 microm, while that in larvae older than 70 days was 51-80 microm. In 90-day-old larvae there were no fibres of 10-20 microm in diameter; however, the number of fibers of 61-80 microm diameter increased. A statistically significant concordance was determined between the body length and fibre diameter of larvae 70 to 90 days old. Between days 50 and 60, arrested growth of the larval body and corresponding decrease in fibre diameter was observed. From day 45 until days 59, larvae were fed with Artemia nauplii and microparticles of formulated diets. From the day 60, minced fish was added to formulated diets. This change in diet probably resulted in the observed growth arrest.     

Morphologic and morphometric study of the facial nerve in clinically normal adult dogs.

A morphologic and morphometric study was carried out on the facial nerve: to determine normal histologic data in myelinated fibers of clinically normal young adult dogs; to establish reference values for mean fiber diameter, and to delineate the relative diameter frequency distribution curve. Few degenerative changes were observed in single teased-nerve fibers and semithin cross-sectional nerve preparations. Statistical difference was not observed between left and right facial nerves. The distribution of fiber diameters in the facial nerve was unimodal. Mean (+/- SD) fiber diameter of the facial nerve was 3.92 +/- 1.18 microns. Approximately 89% of fibers in the facial nerve had diameter between 3 and 6 microns. Fiber diameter ranged from 2 to 12 microns; however, less than 1% of fibers had diameter greater than 8 microns.     

In vitro maturation of oocytes derived from the brown bear (Ursus arctos)

This study was conducted to determine whether meiotic maturation could be induced in ovarian oocytes from the American brown bear (Ursus arctos), a model for gamete "rescue" techniques for endangered ursids. The bears were euthanized, and their ovaries were transported to the laboratory within 4 h. The mean ovarian size was 2.4 x 1.8 cm (range: 2.0-3.3 x 1.5-2.2 cm). The ovaries obtained from the 2 brown bears yielded 97 oocytes (48.5/female), and 88 (90.7%) of them were morphologically classified as normal quality. Oocytes were in vitro matured at 38.5 C in 5% CO2 for 24 or 48 h in TCM-199 supplemented with 10% FBS, 1 microg/ml estradiol-17beta, and 10 microg/ml FSH. In Exp. 1, morphologic evaluation of matured oocytes was conducted by measuring the diameters of oocytes with a zona pellucida (ZP) or cytoplasm without a ZP. In Exp. 2, activation was induced by applying two 20 microsec DC pulses of 2.0 kV/cm delivered by an Electro Cell Fusion Generator. The activated oocytes were cultured in TCM-199 containing 2 mM of 6-dimethylaminopurine for 4 h, in Charles Rosenkrans (CR) 1 for 3 days and the in CR2 for another 4 days. The diameters of the matured bear oocytes with a ZP and with cytoplasm without a ZP (161.8 +/- 6.0 and 135.3 +/- 7.5 microm, respectively) were significantly (P<0.05) larger than those of bovine oocytes (150.7 +/- 4.9 and 118.7 +/- 7.5 microm). The maturation rates of the bear oocytes were 17.6 and 59.4% at 24 and 48 h of in vitro maturation, the percentage of activated oocytes that developed to the 2 or 4-cell stage was 31.6%; however, no blastocysts were observed. These results indicate that bear oocytes can develop to metaphase II in an in vitro culture system and that activated oocytes can develop to the 2 or 4-cell stages.     

DETERMINATION OF CANINE PROSTATIC VOLUME USING TRANSABDOMINAL ULTRASONOGRAPHY

The prostate gland from cadavers of 12 intact adult male dogs euthanized less than 3 hour were used to compare prostatic volume measured by ultrasonography to volume measured by water displacement, and to determine specific gravity of the canine prostate. Prostate glands were scanned by transabdominal ultrasonography with a 4-7 MHz curved linear array transducer. The greatest craniocaudal (L), transverse (W), and dorsoventral (D) diameters of the prostate were recorded. Prostatic volume was calculated using formulas for an ellipsoid and for a box. Prostate glands were removed, and the prostate weight was measured and prostatic volume was measured by water displacement. The mean +/- SD specific gravity of the prostate was 1 +/- 0.05 (range = 0.90 to 1.09) g/cm. There were positive correlations (R2 = 0.94) between prostatic volume calculated from ultrasound measurement and measured volume. Measured prostatic volume (VM) can be predicted using the formula: VM = [1/2.6 (L x W x D)] + 1.8 (cm3).     

Morphologic and morphometric studies of the intrinsic laryngeal muscles in clinically normal adult dogs

To establish normal histologic and histochemical data and to determine reference values for fiber type proportions (percentages, mean fiber diameters, atrophy and hypertrophy factors, and variability coefficients), a histochemical study was carried out on intrinsic muscles of the larynx (cricothyroid, cricoarytenoid lateralis, cricoarytenoid dorsalis, and thyroarytenoid muscles) of clinically normal dogs. Using myosin adenosine triphosphatase stain under acidic preincubation (pH 4.3) conditions, 3 histochemical fiber types--1, 2A, and 2C--were recognized. The percentage of type-2C fibers varied from 1 to 2% in thyroarytenoid muscles to approximately 10% in cricoarytenoid lateralis muscles. There was no significant difference in mean diameter between left- and right-side specimens of each muscle for type 1 vs type 2. The largest fibers (mean +/- SD) of both types were observed in the cricothyroid muscles (type 1, 38.19 +/- 7.76 microns; type 2, 43.25 +/- 8.66 microns), and the smallest fibers were found in the thyroarytenoid muscles (type 1, 29.38 +/- 5.12 microns; type 2, 33.84 +/- 6.20 microns). Respective mean diameters of fiber types from cricoarytenoid dorsalis (type 1, 32.05 +/- 5.69 microns; type 2, 38.95 +/- 7.75 microns) and cricoarytenoid lateralis (type 1, 33.75 +/- 5.98 microns; type 2, 37.09 +/- 7.01 microns) muscles were similar. The histographic distribution of fiber type diameters was unimodal in all muscles. In each muscle, the mean fiber diameter of type-2 fibers was greater than that of type-1 fibers.(ABSTRACT TRUNCATED AT 250 WORDS)     

An ultrastructural study of spinal nerve roots and dorsal root ganglia in aging rats with spontaneous radiculoneuropathy

The spinal nerve roots and dorsal ganglia of 104- to 135-week-old rats with spontaneous radiculoneuropathy were examined by light and electron microscopy. Demyelination was common in myelinated fibers of various diameters of both ventral and dorsal roots. The most striking alteration was wide distention of myelin sheaths, which extended throughout the entire internode. The spaces formed between separated lamellae frequently were invaded by macrophages. Subsequent vesicular degeneration of myelin seemed to be mediated by invading macrophages. These processes caused complete myelin destruction, but most axons showed no degenerative changes except for obvious reduction in diameter. Occasionally, there were clumping and partial degradation of neurofilaments and ruptured axolemma in the severely demyelinated axons. A few fibers also were undergoing wallerian-type degeneration, perhaps secondary to the severe demyelinative changes. Remyelinating fibers in various phases of repair were coexistent with markedly demyelinated ones. Demyelinative changes described above also developed within some of these remyelinated internodes. There were no remarkable changes in neurons of the dorsal root ganglia, though accumulation of lipofuscin was common. Our findings suggest that the changes in the nerve roots are essentially a primary segmental demyelination in aging rats with radiculoneuropathy.     

Effects of betamethasone treatment on central myelination in fetal sheep: an electron microscopical study

The long-term effect of betamethasone on the myelination of commissural and associational fibres was investigated in fetal sheep. We studied the corpus callosum and subcortical white matter by electron microscopy. Axons were subdivided into classes according to their axonal diameter: class I: < or =0.65 microm; class II: 0.66-0.84 microm; class III: > or =0.85 microm. Under control conditions, the different functions of the white matter tracts examined were reflected by three morphological criteria: (1) there was a diverse percentage of axonal classes in the investigated areas. In corpus callosum the axons of class II predominate (47.1%). In the subcortical white matter, class I axons with small diameter are in majority (40.8%). (2) In the subcortical white matter more axons are present, with especially large diameter and hence of axonal class III. (3) The axons of subcortical white matter have thicker myelin sheaths than those of the corpus callosum. Betamethasone administration caused a significant decrease of class II axons in the corpus callosum (36.9%). In corpus callosum, axons of all classes present thicker myelin sheaths. Betamethasone administration resulted in a change in the formation of the myelin sheath in the commissural fibres of the corpus callosum but not in the associational fibres of the subcortical white matter. This could be the morphological correlate to behavioral and cognitive changes known to occur in humans after prenatal glucocorticoid treatment.     

Assessment of dorsal nerve root and spinal cord dorsal horn function in clinically normal dogs by determination of cord dorsum potentials

OBJECTIVE: To establish normal predictive values for cord dorsum potential (CDP) onset latency after thoracic and pelvic limb sensory or mixed nerve stimulation in adult dogs. ANIMALS: 26 clinically normal adult dogs. PROCEDURE: Sensory nerve action potentials (SNAP) were recorded proximally from tibial and lateral superficial radial nerves after distal stimulation. The CDP were recorded from the L4-L5 interarcuate ligament for the tibial nerve and from the C7-T1 interarcuate ligament for the radial nerve. Linear regression analyses were performed for CDP onset latency, and mean +/- SD was calculated for CDP onset to peak latency differences and sensory nerve conduction velocities (SNCV). RESULTS: For the tibial nerve, expected CDP onset latency (CDPOL) = -1.194 + 0.014 X pelvic limb length (mm; R2 = 0.912); CDPOL = -2.156 + 0.011 X pelvic limb/spinal length (mm; R2 = 0.911); and CDPOL = 0.941 + 2.197 X tibial nerve SNAP latency (milliseconds; R2 = 0.903). For the radial nerve, CDPOL = -0.9 + 0.014 x thoracic limb length (mm; R2 = 0.873); and CDPOL = 1.454 + 1.874 X radial nerve SNAP latency (milliseconds; R2 = 0.903). Mean +/- SD for CDP onset to peak latency difference for tibial and radial nerves was 3.1+/-0.3 and 3.0+/-0.4 milliseconds, respectively. CONCLUSIONS: Strong linear associations exist between CDPOL and a number of easily measured peripheral independent variables in dogs. There is also a narrow range of normal values for CDP onset to peak latency differences that is independent of limb length. CLINICAL RELEVANCE: CDP evaluation can be used to accurately assess functional severity and distribution of abnormalities in proximal sensory nerves, dorsal nerve roots, and spinal cord dorsal horns in dogs with suspected neuropathy, radiculopathy, or myelopathy involving the brachial or lumbosacral intumescences.     

Morphological features of the seminiferous epithelium in cat (Felis catus, L. 1758) testes

The aim of the present study was to assess the changes in the germinal epithelium in cats of different ages. Routine histological staining was applied to perform morphological and stereological examinations. The animals were divided into five groups according to age: under 8 months (n=28), 8-12 months (n=30), 12-36 months (n=33), 3-6 years (n=14) and older than 6 years (n=13). The appearance of the gonads of the males in the first group varied the most. The seminiferous tubules of the youngest cats consisted of a monolayer of supporting cells and a few spermatogonia. No tubular lumina were present, and the diameters of the seminiferous tubules reached 132.5 microm. We noted the typical arrangement of gametogenic cells with a tubule diameter of 191.83 microm in the second group. We observed multilayer germinal epithelia with the most significant production of gametes and a seminiferous tubule diameter of 202.61 microm in the third group. The diameters of the seminiferous tubules of the forth and fifth groups were 193.38 microm and 191.84 microm, respectively. The obtained data revealed that the most intensive morphological diversification of the seminiferous epithelium in cats occurs at about 7-8 months of age. The diameters of seminiferous tubules were highest in the third group of cats, and the activity of spermatogenesis of this group, expressed as the number of sperm per 10 mm(2), was also the most distinctive. The spermatogenesis process was most evident in cats between 12 and 36 months of age, which was also when the sperm concentration was highest per estimated surface.     

Histomorphometry of the porcine scleral lamina cribrosa surface

The lamina cribrosa surface of the pig was examined using trypsin digestion, scanning electron microscopy, and computerized image analysis. Six normal eyes from healthy pigs were studied. The total intralaminar scan area, total number of laminar pores, median individual laminar pore areas, median individual pore form factors, and mean pore density were determined for the dorsal, ventral, nasal and temporal hemicircles, the dorsal-nasal, dorsal-temporal, ventral-nasal, and ventral-temporal quadrants, and their central and peripheral subdivisions. The mean (+/- SD) total intralaminar scan area was 8.29 +/- 1.54 mm2. The mean (+/- SD) total laminar pore count was 517 +/- 73 pores. The mean pore count was significantly larger in the ventral than the dorsal hemicircle (292 +/- 39 vs. 225 +/- 38 pores, respectively; P = 0.001), and significantly greater in the periphery compared to the center (388 +/- 58 vs. 129 +/- 27 pores, respectively; P = 0.0001). The overall mean (+/- SD) pore density was 67 +/- 7 pores mm-2. Mean pore density was significantly greater in the ventral than the dorsal hemicircle (70 +/- 8 vs. 64 +/- 6 pores mm-2, respectively; P = 0.019), and significantly greater in the center compared to the periphery (75 +/- 9 vs. 60 +/- 8 pores mm-2, respectively; P = 0.020). The mean (+/- SD) median individual pore area was 3752 +/- 572 &mgr;m2. The mean (+/- SD) median pore form factor was 0.680 +/- 0.035. No significant regional differences were found in mean median pore form factor or mean median individual pore areas. The intralaminar optic nerve of pigs is 55.1% non-neural connective and vascular tissue. A pigmented ventral fascial groove in the scleral lamina cribrosa appears unique to the porcine lamina cribrosa, and may be a vestige of the embryonic optic fissure.     

Microvascular anatomy of the pig eye: scanning electron microscopy of vascular corrosion casts

The microvasculature of the eye of 10 pigs was investigated using scanning electron micrographs of corrosion casts. The ciliary body, iris and bulbar conjunctiva were supplied by the iridociliary ring artery via the long posterior ciliary artery. Capillaries of the ciliary process were of large diameter (23.2-27.5 microm) with an irregular bore, forming a thoroughfare channel draining blood in the ciliary arterioles into the pars plana venous vessels. Arterioles and venules in the iris exhibited a zigzag or spiral features. The third palpebra was supplied by the anterior ciliary artery. The capillary bed of the third palpebra was dense and was formed by many rows of fine hair-pin loops. Capillaries in the bulbar conjunctiva formed a sparse network disposing approximately parallel to the epithelium and formed a well-developed venous plexus, draining into the vortex veins. Retinal arterioles formed a slender and long course to capillaries. Retinal capillaries were extremely thin (3.0-4.0 microm in diameter). The choroid was supplied by the short posterior ciliary arteries. Choroidal arterioles exhibited a thick and short course to the choriocapillaris. The choriocapillaris was flat and sinusoid-like (8.9-13.9 microm in diameter), forming a dense sheet-like network. Blood from the choroid emptied into the episcleral vein via the vortex vein. Blood from the retina was drained by the posterior ciliary veins. The functional significance of this vascular architecture was discussed.