Long Term Temporal Changes in Structure and Function of Rat Visual System After Blast Exposure

Purpose

We identify long-term ocular sequelae subsequent to experimental blast exposure.

Methods

Male Long-Evans rats were exposed to 230 kPa side-on primary blast overpressure using a compressed air driven shock tube. Visual system function and structure were assessed for 8 weeks after exposure using optokinetic nystagmus and optical coherence tomography. Vitreous protein expression and histology (TUNEL, H&E) were performed at 1 day and 1, 4, and 8 weeks. IOP was recorded bilaterally during blast in a subset of animals.

Results

Blast pressure profiles resembled the Friedlander waveform indicative of an open field blast. Peak IOP in directly-exposed eyes (240 kPa) was similar to peak blast overpressure, but IOP in indirectly-exposed eyes was 30% lower. Contrast sensitivity of blast-exposed animals decreased significantly by 20% 1 day after blast and did not recover by 8 weeks. Significant swelling and structural damage to the corneal epithelial and stromal layers were observed 2 weeks after blast exposure. Swollen corneas increased 254 ± 143 μm from baseline by 6 weeks, and scarring developed by 8 weeks. Histology revealed additional lens pathology 1 week after blast, suggestive of cataract development. Endothelial cell density increased significantly in blast-exposed animals between 1 and 4 weeks. Neurofilament heavy chain significantly increased after blast and returned to near baseline values by 8 weeks. Inflammatory cytokine changes corroborated ocular pathology findings.

Conclusions

These data demonstrate immediate visual dysfunction and biochemical responses, but delayed structural pathology, in response to single primary blast exposure. The delayed pathology time course may provide a window to implement treatment strategies for improved visual outcome.

Performance Assessment of New Urinary Translational Safety Biomarkers of Drug-induced Renal Tubular Injury in Tenofovir-treated Cynomolgus Monkeys and Beagle Dogs

Newer urinary protein kidney safety biomarkers can outperform the conventional kidney functional biomarkers blood urea nitrogen (BUN) and serum creatinine (SCr) in rats. However, there is far less experience with the relative performance of these biomarkers in dogs and nonhuman primates. Here, we report urine protein biomarker performance in tenofovir-treated cynomolgus monkeys and beagle dogs. Tenofovir intravenous daily dosing in monkeys for 2 or 4 weeks at 30 mg/kg/day resulted in minimal to moderate tubular degeneration and regeneration, and tenofovir disoproxil fumarate oral dosing in dogs for 10 days at 45 mg/kg/day resulted in mild to marked tubular degeneration, necrosis, and regeneration. Among biomarkers tested, kidney injury molecule 1 (Kim-1) and clusterin (CLU) clearly outperformed BUN and SCr and were the most reliable in detecting the onset and progression of tenofovir-induced tubular injury. Cystatin C, retinol binding protein 4, β2-microglobulin, neutrophil gelatinase-associated lipocalin, albumin, and total protein also performed better than BUN and SCr and added value when considered together with Kim-1 and CLU. These findings demonstrate the promising utility of these urinary safety biomarkers in monkeys and dogs and support their further evaluation in human to improve early detection of renal tubular injury.

Cyclic Head Rotations Produce Modest Brain Injury in Infant Piglets

Repetitive back-and-forth head rotation from vigorous shaking is purported to be a central mechanism responsible for diffuse white matter injury, subdural hemorrhage, and retinal hemorrhage in some cases of abusive head trauma (AHT) in young children. Although animal studies have identified mechanisms of traumatic brain injury (TBI) associated with single rapid head acceleration-decelerations at levels experienced in a motor vehicle crash, few experimental studies have investigated TBI from repetitive head rotations. The objective of this study was to systematically investigate the post-injury pathological time-course after cyclic, low-velocity head rotations in the piglet and compare them with single head rotations. Injury metrics were the occurrence and extent of axonal injury (AI), extra-axial hemorrhage (EAH), red cell neuronal/axonal change (RCNAC), and ocular injury (OI). Hyperflexion/extension of the neck were purposefully avoided in the study, resulting in unscaled angular accelerations at the lower end of reported infant surrogate shaking kinematics. All findings were at the mild end of the injury spectrum, with no significant findings at 6 h post-injury. Cyclic head rotations, however, produced modest AI that significantly increased with time post-injury (p < 0.035) and had significantly greater amounts of RCNAC and EAH than noncyclic head rotations after 24 h post-injury (p < 0.05). No OI was observed. Future studies should investigate the contributions of additional physiological and mechanical features associated with AHT (e.g., hyperflexion/extension, increased intracranial pressure from crying or thoracic compression, and more than two cyclic episodes) to enhance our understanding of the causality between proposed mechanistic factors and AHT in infants.

Molecular umbrella conjugate for the ocular delivery of siRNA

The synthesis, computer modeling, and biological activity of an octawalled molecular umbrella short interfacing RNA (siRNA) conjugate is described. This molecular umbrella–siRNA conjugate exhibited mRNA knockdown activity in vitro in the absence of a transfection reagent. Evaluation of this molecular umbrella conjugate in vivo, using the rat eye via intravitreal injection, resulted in sequence specific mRNA knockdown in the retina with no obvious signs of toxicity, as judged by ophthalmic examination.

Pathology of canine cataract surgery complications

AIM

To compare pathological complications arising from 2 methods of canine cataract surgery, manual extracapsular cataract extraction (MECCE) and the more automated phacoemulsification and aspiration (PA).

METHODS

Case material presented to the Comparative Ophthalmic Pathology Laboratory, University of North Carolina over the previous 20 years (1979-1999) was searched for cases with a history of prior cataract surgery. Data were obtained from the pathology accession forms, and submitting veterinarians were contacted to verify and complete missing data where possible. The slides were re-examined, histological features of surgical complications were noted and secondary changes recorded.

RESULTS

Fourteen canine post-cataract-surgery cases were reviewed, the average age of the group being 7.7 years. Of the 14 eyes, 7 had surgery performed using MECCE, and 7 using PA. Of the 7 eyes that underwent MECCE surgery, 5 were enucleated and diagnosed on both clinical and pathological grounds with glaucoma. Of the 7 eyes that underwent PA, 4 were diagnosed with infectious endophthalmitis.

CONCLUSIONS

Complications observed were related to the surgical technique performed. Failures of manual extracapsular surgical procedures were more commonly associated with postoperative synechia and glaucoma, compared with failures of phacoemulsification, which were more commonly associated with infection and rhegmatogenous retinal detachments.

CLINICAL RELEVANCE

To minimise post surgical complications, MECCE should be accompanied by rigorous efforts to reduce surgically induced inflammation, while PA should be performed using excellent aseptic technique. It is important with both techniques to totally remove cortical material while maintaining the integrity of the posterior capsule.

Ocular hemorrhages in neonatal porcine eyes from single, rapid rotational events

PURPOSE

To characterize ocular hemorrhages from single, rapid head rotations in the neonatal pig.

METHODS

Three- to 5-day-old anesthetized piglets (n=51) underwent a single, rapid (117-266 rad/s) head rotation in the sagittal (n=13), coronal (n=7), or axial (n=31) planes. Six hours after injury, the animals were euthanatized and perfusion fixed, and the brain and eyes were harvested for gross and histopathologic examination by masked neuro- and ocular pathologists.

RESULTS

Ocular hemorrhage was found in 73% of animals (51% bilateral). Intraocular hemorrhage was primarily located near the vitreous base (70% of injured animals had ciliary body hemorrhage, and 11% had peripheral retinal hemorrhage). Hemorrhages were also found in the anterior chamber (11%), vitreous (5%), and optic nerve (disc, 8%; nerve sheath, 57%). Rapid axial head rotations resulted in a higher incidence of intraocular hemorrhage than coronal or sagittal head rotations, but the difference did not reach statistical significance (P=0.06). Control eyes had no injuries.

CONCLUSIONS

Optic nerve sheath and ciliary body hemorrhages were common in piglets that experienced a single, rapid head rotation. Retinal hemorrhage was present in a smaller number of animals. Most intraocular hemorrhages were located in regions of strong vitreous attachment, suggesting that this animal model will be useful in investigating the effect of vitreoretinal adhesion on ocular hemorrhage caused by inertial head rotations. Extrapolation of this model to the human infant should not be made until the effect of anatomic differences between the human and pig on the occurrence and patterns of ocular injuries is further investigated.

Congenital orbital cysts of neural tissue in two dogs

A 3-month-old English Cocker Spaniel and a 6-month-old miniature poodle presented with clinical signs related to an abnormal right eye since birth. In both dogs, the right globe could not be identified and was replaced by a fluctuant intraorbital mass covered by a vascularized mucous membrane. Ultrasonography demonstrated that both masses were cystic structures markedly larger in size than the normal contralateral globes. In both cases, surgical excision revealed a multilobular cyst filling the whole orbital cavity. Histopathologic examination and immunostaining for glial fibrillary acid protein and S100 protein supported a diagnosis of neural cysts associated with ocular dysplasia. The definitive diagnosis was congenital cystic eye and microphthalmos with cyst for the Cocker Spaniel and miniature poodle, respectively. Karyotype was normal in both dogs. Congenital cystic eye and microphthalmos with cyst result from defects in early embryonic life that arise following formation of the optic vesicle and prior to closure of the optic fissure. To the authors' knowledge neither has been reported in the canine species. They should be considered in the differential diagnosis of orbital cysts in dogs.

Goniodysgenesis associated with primary glaucoma in an adult European Short-haired cat

A 9.5-year-old, male castrated European Short-haired (ESH) cat was presented with bilateral glaucoma associated with pectinate ligament dysplasia and an open iridocorneal angle (ICA) upon gonioscopy. The right eye (OD) was avisual and slightly enlarged; the left eye (OS) was still visual. Intraocular pressure (IOP) had been controlled with medical therapy over a 1.5 year-period in both eyes (OU). Eventually IOP could not be adequately controlled medically and the painful and blind right eye was enucleated and transscleral diode laser cyclophotocoagulation was performed twice in the left eye with less than optimal results and progressive loss of vision. Histopathology of the right eye showed goniodysgenesis characterized by failure of differentiation of the pectinate ligament, which existed as a solid sheet of uveal tissue at the entrance of a hypoplastic ciliary cleft, which contained loose mucoid mesenchymal tissue. The trabecular meshwork was hypoplastic and the scleral venous plexus could not be identified. Other findings of chronic glaucoma were inner retinal atrophy, optic nerve atrophy with disc cupping, scleral thinning, peripheral corneal vascularization and pigmentation, and mild focal iridal mononuclear inflammatory cell infiltrate.

Central corneal dermoid in a Labrador retriever puppy

An eight-week-old, male Labrador retriever puppy was presented with an abnormal appearance of the left cornea, observed after the eyelids opened in the second week of life. Ocular examination showed a large central dermoid of the left cornea. The dermoid was excised by superficial keratectomy, and healing was uneventful. The dermoid was classified as a Mann's second type. To the authors' knowledge, a Mann's second type corneal dermoid has not previously been reported in a dog.

Classification of feline intraocular neoplasms based on morphology, histochemical staining, and immunohistochemical labeling

The objectives of this study were to evaluate morphologic, histochemical, and immunohistochemical characteristics of well-differentiated and anaplastic intraocular neoplasms of cats, and to develop a diagnostic algorithm for, and investigate the association of ruptured lenses with these neoplasms. Seventy-five feline globes with intraocular neoplasms were stained with hematoxylin and eosin and examined by light microscopy. Morphologic diagnoses included 33 intraocular sarcomas, 17 diffuse iris melanomas, 15 lymphosarcomas, three ciliary adenomas, one metastatic carcinoma, and six undifferentiated intraocular neoplasms. Sections of these globes were then stained with periodic acid Schiff (PAS), and immunohistochemical (IHC) labels for various cellular markers. Histochemical staining and IHC labeling confirmed cellular differentiation in 73/75 neoplasms but was discordant with morphologic diagnoses in 8/75. These included four neoplasms morphologically diagnosed as lymphosarcomas but which expressed differentiation antigens consistent with melanoma (n = 3) or ciliary adenocarcinoma (n = 1), and four tumors morphologically diagnosed as intraocular sarcomas that expressed differentiation antigens for melanoma (n = 2), metastatic carcinoma (n = 1), or remained undifferentiated (n = 1). Immunohistochemical labeling suggested a diagnosis in 5/6 morphologically undifferentiated neoplasms including one intraocular sarcoma, two diffuse iridal melanomas, and two ciliary adenocarcinomas. Based upon morphologic, histochemical, and IHC characterization, ruptured lens capsules were detected in 28/30 intraocular sarcomas, 3/24 diffuse iris melanomas and 1/11 lymphosarcomas, but not in ciliary epithelial neoplasms, metastatic carcinomas, or undifferentiated intraocular neoplasms. An algorithm is provided that facilitates stain and IHC label selection for differentiating anaplastic intraocular feline neoplasms.

Repeated spike exposure to the insecticide chlorpyrifos interferes with the recovery of visual sensitivity in rats

Reports from Japan and India and data submissions to the US EPA indicate that exposure to cholinesterase (ChE)-inhibiting organophosphorous insecticides (OP) can produce ocular toxicity, in particular long-lasting changes in retinal physiology and anatomy. We have examined the effects of a 1 year dietary exposure to the OP chlorpyrifos (CPF) on retinal structure and function. Adult male Long-Evans rats were fed CPF in their diet at the rate of 0, 1 (low), or 5 (high) mg/kg body weight/day. In addition, half of each feeding group received an oral (spike) dose of CPF in corn oil (45 mg/kg) or corn oil (VEH) alone every 2 months, resulting in six exposure groups: Control-VEH, Control-CPF, Low-VEH, Low-CPF, High-VEH, and High-CPF. Dark-adapted electroretinograms (ERG) were measured 3-5 months (n= 15-18/group) after the completion of dosing. There were no significant differences between dose or spike groups in a-wave, b-wave, or oscillatory potential amplitudes or implicit times. In addition, the time course of dark adaptation were measured in a subset of these rats (6-8/group) eight months after the completion of dosing by determining the flash intensity needed to elicit a 40 microV b-wave at selected intervals after bleaching 90% of the photopigment. Rats receiving the episodic oral spike of CPF showed a slowed recovery of dark-adapted sensitivity compared to rats receiving the corn oil VEH across chronic dosing conditions. No effects were seen on retinal morphology. This result suggests that episodic high dose exposures to CPF may result in altered retinal function. This effect, akin to effects seen in aging humans and humans exposed to other ChE-inhibiting compounds, may reflect alterations in the photoreceptors and retinal pigment epithelium (RPE) complex necessary for regenerating photopigment.

Cataract formation in a strain of rats selected for high oxidative stress

The primary purpose of this study was to define the clinical and morphological features of cataractogenesis in the OXYS strain of rats that generate excess reactive oxygen species. Rats were sequentially examined from birth to the development of mature cataracts with slit lamp biomicroscopy. Morphology of selected stages of cataract development was studied using light and transmission electron microscopy (TEM), immunohistochemical localization of the lipid peroxidation product 4-hydroxynonenal (HNE) and fluorescent antibody labeling for DNA oxidation products. Lenses from age-matched normal rats were used as controls. OXYS rats developed cataracts as young as two weeks of age with progression to maturity by 1 year. Clinically, cataracts appeared initially either as nuclear or sub-capsular cortical changes and progressed to pronounced nuclear cataracts within months. TEM confirmed the light microscopic impression of region-specific alterations in both fiber cell cytoplasmic protein matrix and membrane structure. The outer adult nuclear region showed extensive cellular damage similar to osmotic cataracts, which is consistent with the postulated high uptake of glucose in the OXYS strain. The adult and outer fetal nuclear cells displayed several types of focal damage. The inner fetal and embryonic nuclear cells demonstrated textured cytoplasm, suggesting protein degradation or redistribution. Staining for HNE was increased in epithelium, cortex and nucleus compared to control lenses. Fluorescent antibody probes demonstrated increased levels of DNA oxidation products in OXYS rat lenses compared to age-matched controls. Fourier analysis of nuclear cytoplasm revealed significant components with corresponding sizes greater than 100 nm and, using a new theoretical approach, the texturing of the cytoplasm was shown to be sufficient to cause opacification of the nucleus. The OXYS rat appears to be an ideal model for oxidative stress cataractogenesis. The potential oxidative damage observed is extensive and characteristic of the developmental region. The source of oxidative damage may in part be a response to elevated levels of glucose. Because oxidative stress is thought to be a major factor in cataract formation in both diabetic and non-diabetic aging humans, this animal model may be a useful tool in assessing efficacy of antioxidant treatments that may slow or prevent cataract formation.

Ocular histopathologic observations in Norwegian Elkhounds with primary open-angle, closed-cleft glaucoma

A retrospective histopathologic study of primary glaucoma in the Norwegian Elkhound was undertaken with the study of 9 clinically normal eyes and 22 glaucomatous eyes. All glaucomatous eyes showed goniodysgenesis as manifested by pectinate ligament dysplasia and/or trabecular meshwork dysplasia. Cystic degeneration of the iridociliary epithelial and/or peripheral retina was present in a high percentage of both normotensive and glaucomatous eyes. Utilizing the scheme proposed by Smith et al. (Veterinary and Comparative Ophthalmology 1993; 3: 16-28) the morphology of this disease in the Norwegian Elkhound would be classified as an open-angle, closed-cleft glaucoma, with histopathologic alterations of the outflow pathway similar to that described in other breeds with primary glaucoma.

Bilateral neuroepithelial choristomas of the optic disc in a cynomolgus monkey (Macaca fascicularis): a case report

A 6-year-old intact male cynomolgus monkey of Chinese origin was received at the Sierra Biomedical Facility. While physical examination revealed good body condition with no abnormalities, routine ophthalmic examination revealed bilateral proliferative optic neuropathy involving the dorsal aspect of the optic disc. No changes were noted in the appearance of the lesions over 8 months, and fluoroescein angiography revealed no abnormalities other than obstruction of the view of the retinal vessels by the lesions. Histopathologic studies revealed characteristics consistent with a diagnosis of bilateral neuroepithelial choristoma.

Diabetes mellitus and bilateral cataracts in a kitten

An 18-week-old male domestic long-hair kitten was presented with a history of polyuria and polydipsia for several weeks. The general condition was unremarkable, but the kitten was considerably smaller than expected for the age and showed cataracts in both eyes. Serum glucose concentrations were persistently elevated and based on clinical findings and an elevated serum fructosamine concentration, a diagnosis of diabetes mellitus was established. Diabetes mellitus is not commonly diagnosed in young kittens, nor are cataracts recognised as a frequent feature of this disease in cats. The cataracts progressed in spite of the insulin therapy and the kitten was euthanised 10 weeks after referral. Histopathological examination of the pancreas revealed few and small islets of Langerhans compared to the examination of pancreas from a healthy kitten of the same age. Histopathological changes in the eyes included cataracts affecting both cortex and nucleus.

Morphologic alterations in the anterior lens capsule of canine eyes with cataracts

OBJECTIVE

To examine the morphologic changes in the anterior lens capsule and lens epithelium of canine eyes with cataracts.

SAMPLE POPULATION

Anterior lens capsules from the eyes of 25 dogs with cataracts and from an additional 10 canine globes with lenses subjectively assessed to be normal.

PROCEDURE

Thickness of each anterior lens capsule was measured by use of a digital microscopic camera and imaging software. All 25 capsules from eyes with cataracts were submitted for light microscopy; 4 were also submitted for electron microscopy.

RESULTS

Thickness of the anterior lens capsule increased with age for the normal lenses and the lenses with cataracts; the change with age was similar for both groups. Light microscopy revealed fibrous metaplasia of lens epithelial cells in 7 of 25 anterior lens capsules with focal thickenings of the posterior aspect of the capsule. Electron microscopy revealed deposition of collagen and basement membrane-like material by fibroblast-like cells.

CONCLUSIONS

Results indicate that thickness of the anterior lens capsule in dogs increases with age and that this increase in thickness is not significantly different between normal lenses and lenses with cataracts. In addition, epithelial cells from lenses with cataracts may undergo metaplasia to form plaques composed of fibrous tissue and ectopic basement membrane produced by epithelial cells.

Assessment of ascorbate ocular disposition in the conscious rabbit: an approach using the microdialysis technique

PURPOSE

This study was performed to evaluate the transport kinetics of ascorbate in aqueous humor of conscious rabbits.

METHODS

Following the development of a spectrophotometric assay for ascorbate in serum, aqueous humor and microdialysate, and preliminary studies of ascorbate systemic disposition in the rabbit, microdialysis probes were placed into the anterior chamber of one eye, and the posterior chamber of the contralateral eye, of four New Zealand white rabbits. After a one-month recovery period, conscious rabbits were placed in restraining devices, and marginal ear veins were cannulated for repeat blood sampling and ascorbate administration. A tracer i.v. bolus of (14)C-ascorbate, followed by stepwise increasing i.v. infusions of unlabelled ascorbate, was administered. Estimates of basal ascorbate transport into aqueous were determined by analysis of tracer ( 14)C-ascorbate in microdialysis probe effluent and serum. Kinetic modeling was employed to assess ascorbate disposition during infusion.

RESULTS

Systemic disposition of exogenously administered ascorbate was well characterized by a two-compartment model. Kinetic modeling returned physiologically realistic volumes for the posterior chamber, and reliable estimates governing ascorbate flux into, between, and from the posterior and anterior chambers.

CONCLUSIONS

In vivo assessment of ascorbate kinetics in aqueous humor and blood of the rabbit was facilitated by the microdialysis technique. Contrary to reports in the literature, ascorbate saturable uptake from blood to aqueous was not observed at physiologic blood concentrations ( approximately 11 to 30 mg/L).

Implantation of a foldable intraocular lens in dogs

A 1-piece, tripod-shaped, acrylic intraocular lens was implanted in the posterior chamber after phacoemulsification to remove cataracts in 20 eyes of 16 dogs. Biomicroscopy and intraocular pressure measurements were performed at 1, 8, 30, and 90 days after surgery; retinoscopy was performed at day 30. Complications were not encountered during implantation of the lens. All dogs had mild ocular inflammation characterized predominantly by aqueous flare and mild corneal edema at day 1, which resolved completely by day 8; 3 eyes had mild hyphema at day 1, which resolved by day 8. Three eyes developed fibrin in the anterior chamber, which resolved by day 30. Two eyes developed distorted pupils caused by adherence of vitreous humor or fibrin to the incision site. Postoperative intraocular pressure ranged from 7 to 21 mm Hg. Implantation resulted in 9 emmotropic eyes, 5 myopic eyes, and 6 hyperopic eyes. Maintenance of central lens position was excellent in 19 eyes; in 1 eyes, a disclocated superior haptic at day 2 was easily repositioned.

Topical exposure of the eyes to the organophosphorus insecticide malathion: lack of visual effects

Concern for toxicity following exposure to organophosphorus insecticides led us to investigate whether topical application of either malathion or malathion mixed in a protein bait as used for aerial spray applications could be toxic to the ocular/visual system. Adult male Long-Evans rats were either untreated or treated with malathion alone (two drops per day in each eye), bait alone (six drops per day in each eye) or malathion and bait (six drops per day in each eye). The dose levels of malathion alone and malathion and bait were chosen based on pilot work and provided approximately equivalent amounts of active ingredient. The rats were treated 5 days a week for 4 weeks. During the final week of treatment, the rats were implanted surgically with cranial recording electrodes overlying the visual projection area of the cerebral cortex. Visual pattern-evoked potentials (PEPs) were elicited with vertical sinusoidal gratings at three levels of stimulus spatial frequency (0. 08, 0.16 and 0.32 cycles per degree) and three levels of visual contrast (0.15, 0.30 and 0.60). After spectral analysis of the PEP waveforms, the amplitude and phase at the stimulus rate (F1) and the first harmonic (F2) were determined. Although F1 and F2 parameters were influenced significantly by manipulation of the stimulus parameters, no significant differences were observed that could be attributed to treatment with the test substances. In addition, an ophthalmological examination of the eyes and a light microscopic evaluation of ocular tissues, including retina and optic nerve, revealed no treatment-related lesions. The dose levels used in this study were high-approximately 84000 times the exposure per unit surface area expected from aerial spraying-and yet the visual function of the treated subjects was apparently normal. This study identified no significant toxicological concerns regarding direct ocular contact exposure to malathion.

Microdialysis evaluation of the ocular pharmacokinetics of propranolol in the conscious rabbit

PURPOSE

This study was conducted to assess the effects of anesthesia and aqueous humor protein concentrations on ocular disposition of propranolol.

METHODS

Rabbits were anesthetized and a microdialysis probe was inserted into the anterior chamber of one eye; the contralateral eye served as a control. At timed intervals after probe placement, a 100-microl sample of aqueous humor was aspirated from each eye to determine protein concentration. In vitro protein binding parameters were used to simulate the impact of protein concentration on propranolol disposition. To assess the influence of anesthesia, probes were implanted in the anterior chamber of each eye. After >5-day stabilization, conscious and anesthetized rabbits (n = 3/group) received a 200-microg topical dose of [3H]DL-propranolol in each eye; propranolol was assayed in probe effluent.

RESULTS

Changes in aqueous humor protein concentrations were observed following probe insertion. Simulations demonstrated that the unbound propranolol AUC (approximately 2.4-fold) in aqueous humor should be reduced due to protein influx. Intraocular propranolol exposure in anesthetized rabbits was approximately 8-fold higher than in conscious rabbits, and approximately 1.9-fold higher than in rabbits without a post-surgical recovery period.

CONCLUSIONS

Anesthesia and time-dependent aqueous humor protein concentrations may alter ocular pharmacokinetics, and must be taken into account in the design of microdialysis experiments.

Primary corneal papilloma and squamous cell carcinoma associated with pigmentary keratitis in four dogs

Squamous cell carcinoma (SCC) and squamous papilloma are rarely reported as primary lesions of the cornea in dogs. One case of corneal papilloma and 3 cases of SCC, each arising as a primary central corneal neoplasm rather than spreading from adjacent limbal conjunctiva, were reviewed. The most common cause of SCC in animals is chronic exposure of lightly pigmented epithelium to UV light; however, all dogs in this study had a history of chronic pigmentary keratitis. Three of the 4 dogs were of brachycephalic breeds with naturally proptotic eyes and oversized palpebral fissures that may have exposed the cornea to greater excessive solar radiation. Alternatively, mechanical factors that caused chronic changes in the cornea may have been causative factors for induction of primary dysplastic or neoplastic changes. Primary corneal neoplasia should be considered in the differential diagnosis of corneal masses.

Ocular infections with dematiaceous fungi in two cats and a dog

Pigmented fungi were identified in ocular tissues from 2 cats and 1 dog. The first cat was euthanatized because of acute anterior uveitis that was unresponsive to treatment. On histologic examination, intraocular structures had been obliterated and replaced by a gray coagulum of inflammatory infiltrates and fungal elements. The second cat was treated for unilateral glaucoma that was unresponsive to treatment. A large retrobulbar mass, discovered and removed during an enucleation procedure, contained plant-origin foreign material. Keratitis, episcleritis, and orbital cellulitis with fungal elements were found on examination of the enucleated globe. The dog, examined because of a presumed corneal scratch of 2 weeks' duration that was unresponsive to treatment, had a corneal lesion subsequently removed by lamellar keratectomy that contained fungi on histologic examination. Infections caused by dematiaceous fungi are not common in domestic animals, and, to our knowledge, such infections in the eye have not been described.

The organophosphate pesticide chlorpyrifos affects form deprivation myopia

PURPOSE

The effects of the anti-cholinesterase organophosphate pesticide chlorpyrifos (CPF) on the refractive development of the eye were examined. Form deprivation was used to induce eye growth to address the previously reported relationship between organophosphate pesticide use and the incidence of myopia.

METHODS

Chickens, a well-established animal model for experimental myopia and organophosphate neurotoxicity, were dosed with chlorpyrifos (3 mg/kg per day, orally, from day 2 to day 9 after hatching) or corn oil vehicle (VEH) with or without monocular form deprivation (MFD) over the same period. The set of dependent measures included the refractive state of each eye measured using retinoscopy, axial dimensions determined with A-scan ultrasound, and intraocular pressure.

RESULTS

Dosing with CPF yielded an inhibition of 35% butyrylcholinesterase in plasma and 45% acetylcholinesterase in brain. MFD resulted in a significant degree of myopia in form-deprived eyes resulting from significant lengthening of the vitreal chamber of the eye. CPF significantly reduced the effect of MFD, resulting in less myopic eyes (mean refraction: VEH-MFD = -16.2 +/- 2.3 diopters; CPF-MFD = -11.1 +/- 1.8 diopters) with significantly shorter vitreal chambers. Nonoccluded eyes were, on average, slightly hyperopic. Treatment with CPF for 1 week in the absence of MFD led to no significant change in ocular dimensions or refraction relative to controls.

CONCLUSIONS

The use of form deprivation as a challenge suggests that CPF treatment interferes with the visual regulation of eye growth.

Evaluation of microdialysis sampling of aqueous humor for in vivo models of ocular absorption and disposition

The dynamics of beta-adrenergic-associated reductions in aqueous humor production for treatment of elevated intraocular pressure are not well understood. In particular, the relationship between ocular pharmacokinetics and pharmacodynamics has yet to be established. This study was undertaken to develop a procedure for examining the ocular absorption and disposition of topically administered ophthalmic beta-adrenergic antagonists in individual animals. Dogs were anesthetized with isoflurane and a microdialysis probe was implanted in the anterior chamber of one eye and perfused with 0.9% saline at a rate of 2 microliters min-1. 3H-propranolol was administered by intracameral injection or topically. Each dog received intracameral and topical propranolol, in alternate eyes on separate days, in a randomized cross-over fashion. Microdialysis probe effluent was collected every 5 min for > or = 2.5 h; concentrations of propranolol were determined by liquid scintillation spectroscopy and were corrected for probe recovery of the substrate as determined by in vivo retrodialysis (approximately 46%) to estimate aqueous humor concentrations. In separate experiments in rabbits, microdialysis probes were implanted in each eye. 3H-propranolol was administered topically to one eye; the contralateral eye received intracameral 3H-propranolol. Model-independent pharmacokinetic parameters for each treatment phase were calculated. The mean +/- S.D. times to peak concentration of propranolol in aqueous humor were 86.6 +/- 47.6 min in the dog and 54.1 +/- 20.4 min in the rabbit. The terminal rate constant was 0.0189 +/- 0.00429 min-1 in the dog vs. 0.00983 +/- 0.00546 min-1 in the rabbit. Intraocular tissue availability of propranolol differed markedly between the dog (n = 3) and rabbit (n = 3) (approximately 0.056 in the dog vs. approximately 0.55 in the rabbit). These results demonstrate the utility of microdialysis sampling for examination of ocular pharmacokinetics.

Internal sclerostomy with a mechanical trephine versus the neodymium:YAG laser in dogs

BACKGROUND AND OBJECTIVES

To experimentally compare and contrast the internal sclerostomy produced using a mechanical trephine with that made by an Nd:YAG laser, and to evaluate the healing patterns, efficacy, and technical advantages of each method.

MATERIALS AND METHODS

Four healthy dogs with normal eyes were used in this study. The left eye of each dog had an internal sclerostomy performed with an automated mechanical trephine. The right eye of each dog had an internal sclerostomy performed with an Nd:YAG laser. Postoperatively, the intraocular pressure of each eye was measured at regular intervals. The dogs were euthanized successively at 1, 2, 3, and 4 weeks postoperatively, and the morphology of the surgical sites was studied.

RESULTS

The Nd:YAG laser was easier to manipulate and technically less demanding than the mechanical trephine. However, the Nd:YAG laser induced more prominent corneal edema and conjunctival hyperemia compared with the automated trephine. Morphology of the tissue response showed tissue necrosis and greater inflammation with the Nd:YAG laser than with the automated trephine.

CONCLUSIONS

These two techniques demonstrate differences in technical demands and tissue response. Both are characterized by minimal reactive fibrosis of the episcleral and Tenon's capsule fibroblast.

Feline ocular epithelial response to growth factors in vitro

OBJECTIVE

To examine the proliferative abilities of growth factors known to participate in wound healing on feline lens, iris pigment, ciliary, and retinal pigment epithelium cultured in vitro.

ANIMALS

8 clinically normal cats.

PROCEDURE

Iris pigment, lens, ciliary, and retinal pigment epithelia of normal eyes of cats were isolated and cultured. Morphologic characteristics of primary cell cultures were studied by light and electron microscopy. Subcultures of epithelial cells were exposed to media supplemented with 0.5% fetal bovine serum plus various combinations of insulin and/or growth factors, including transforming growth factor-alpha, epidermal growth factor, acidic fibroblast growth factor, and basic fibroblast growth factor. Growth promoting effects were evaluated by counting with an electronic cell counter.

RESULTS

Cells retained many of the morphologic characteristics of in vivo cells. Cell proliferation assays indicated that transforming growth factor-alpha stimulated lens and ciliary epithelial cell growth, and epidermal growth factor enhanced lens and iris pigment epithelial cell growth. Acidic fibroblast growth factor had proliferative effects on lens, iris pigment, and ciliary epithelium. Basic fibroblast growth factor was the most potent stimulator of all mitogens used, and caused substantial proliferation in all cell types. Insulin alone stimulated lens and ciliary epithelial proliferation but, combined with other growth factors, had a synergistic effect with those causing cell proliferation, except acidic fibroblast growth factor with iris pigment epithelium.

CONCLUSION

Morphologic studies support the argument that pigment-producing cells are involved in feline ocular sarcoma. Growth factor studies indicated that ciliary epithelium has the most profound proliferative effect of all growth factors used. These data may help guide future studies in determining the cell of origin for feline ocular sarcoma.

The experimental antipsychotic agent 1192U90 targets tapetum lucidum in canine eyes

To assess the potential adverse effects in people of the antipsychotic agent 1192U90, we dosed mice, rats, beagles, and cynomolgus monkeys for up to 3 mo. In dogs, but not the other species, 1192U90 caused ocular changes detectable ophthalmoscopically as loss of tapetal reflectivity, altered tapetal color, and the appearance of black pigmentation on the tapetal fundus. Eyes from affected dogs had atrophic tapeta lucidum due to cell loss. Rodlets in remaining tapetal cells were separated by electron-lucent spaces or finely granular material, varied in size and shape, and often contained irregularly shaped electron-dense inclusions. Nontapetal ocular structures were unaffected. Because 1192U90 caused no ocular changes in nontapetal species, we hypothesized that it targeted only tapetum lucidum and spared other ocular structures. We tried to test this hypothesis by dosing congenitally atapetal dogs; however, although these dogs were ophthalmoscopically "atapetal," they had scattered tapetal cells visible by electron microscopy, and these tapetal cells had ultrastructural changes indistinguishable from those that occurred in treated normal-eyed dogs. Tapetal degeneration caused by 1192U90 resembled that described in hereditary tapetal degeneration in beagles. That 1192U90 caused no ocular changes in nontapetal species suggests that the ocular changes in dogs do not imply a risk for humans, whose eyes also lack a tapetum lucidum.

Experimental evaluation of a hydroxylapatite reservoir tube shunt in rabbits

BACKGROUND AND OBJECTIVES

Anterior chamber tube shunts of various design are of increasing importance in the surgical management of refractory glaucoma. However, the reservoirs that are commonly used today are made of a silicone or an acrylic material that may become enveloped by a fibrous capsule, which in turn may impede aqueous resorption. In this study, the authors investigated the properties of hydroxylapatite (HA) as a reservoir in gonioimplants, using three different types of HA reservoir designs. It has been demonstrated that HA orbital implants become vascularized, and the authors hypothesized that this feature of HA might modify the development of the fibrous capsule, enhancing the efficacy and decreasing the size of the implants.

MATERIALS AND METHODS

HA reservoirs with Silastic tube shunts were implanted in the right eyes of six Dutch-belted rabbits. Clinical examinations were performed and intraocular pressure was measured periodically for 16 weeks postoperatively. Prior to euthanasia, fluorescein-labeled latex microspheres were injected into the anterior chamber to demonstrate implant patency. Light microscopy was used to study the tissue response to the implants and the pathways of aqueous flow.

RESULTS

In general, the authors found a granulomatous inflammatory response to the HA accompanied by neovascularization into the implant and minimal fibrous encapsulation of the reservoir.

CONCLUSIONS

The use of HA as a suprascleral reservoir has several advantages, the major one being a theoretical increase in the functional lifetime of the implant.

The ocular effects of intralenticular iron foreign bodies in rabbits

Optimal treatment of intralenticular metallic foreign-body injuries remains controversial, especially in patients with clear lenses and good vision. Using 20 rabbit eyes, we examined the cataractogenic potential of intralenticular iron and its effects on the retina. Iron wire implanted into the lenses of 12 rabbit eyes caused cataracts in every eye within 4 weeks. However, after 4 1/2 weeks, none of these eyes showed evidence of retinal siderosis. No cataracts developed in five eyes with intralenticular glass, while three with intravitreal iron showed marked retinal toxicity. These results suggest that as long as the lenses remain clear, conservative management of these injuries carries minimal risk of permanent retinal damage.

Lens expression of TGF alpha in transgenic mice produces two distinct eye pathologies in the absence of tumors

Transgenic mice carrying the rat TGF alpha minigene linked to the alpha A crystallin promoter were generated to investigate the effects of expression of this growth factor in the lens of the eye. All transgenic mice exhibited eye abnormalities in the absence of overt tumors, and two distinct and heritable phenotypes were observed. Five lineages produced 'squinting' transgenic mice characterized by microphthalmic eyes with severe lens and retinal dysplasia, and four lineages produced 'bulged' transgenic mice with eyes that exhibited enlarged globes, lens epithelial hyperplasia, anterior segment dysgenesis, and in some cases retinal dysplasia. The eye perturbations of both phenotypes were evident histologically by 1 week of age, and the eyes of squinting mice were abnormal during embryonic development. The squinting phenotype was dominant over the bulged phenotype in intercrosses, suggesting that position effects from the transgene integration site resulted in differences in TGF alpha expression between the two phenotypes. In situ hybridization showed that TGF alpha transgene expression was confined to the lens or lens rudiment of all transgenic eyes despite the involvement of non-lenticular tissues in the pathology. These results show that inappropriate expression of TGF alpha in the eye can disrupt the communication required to coordinate normal eye development.

Ocular and associated neuropathologic observations in suspected whiplash shaken infant syndrome. A retrospective study of 12 cases

We examined the eyes of 12 infants who died with the clinical and pathologic diagnosis of the shaken baby syndrome. The ocular histopathologic findings and the neuropathologic findings were compared. Preretinal, intraretinal, and subretinal hemorrhages were observed; hemorrhages of the superficial retinal layers and subsensory retinal space predominated. Retinal hemorrhages were found in 12 cases, intracranial hemorrhage was found in 11 cases, and cerebral edema was found in 10 cases. The intraretinal and periretinal hemorrhages were most prevalent at the posterior pole. Five cases had retinal folds. There was a low incidence of optic disc edema and choroidal hemorrhage.

TGF alpha deficiency results in hair follicle and eye abnormalities in targeted and waved-1 mice

To explore the physiological roles of transforming growth factor alpha (TGF alpha), we disrupted the mouse gene by homologous recombination in embryonic stem cells. Homozygous mutant mice were viable and fertile, but displayed pronounced waviness of the whiskers and fur, accompanied by abnormal curvature, disorientation, and misalignment of the hair follicles. Homozygous and, to a lesser extent, heterozygous mice displayed eye abnormalities of variable incidence and severity, including open eyelids at birth, reduced eyeball size, and superficial opacity. Histological examination revealed eyelid and anterior segment dysgenesis, corneal inflammation and scarring, and lens and retinal defects. Although TGF alpha deficiency affected skin and eyes, wound healing in these tissues was not impaired. Similar hair and eye defects have been previously associated with the recessive mutation waved-1 (wa-1), and Northern analysis revealed reduced expression of TGF alpha in wa-1 mice. Crosses between wa-1 homozygotes and TGF alpha-targeted mice confirmed that wa-1 and TGF alpha are allelic.

Pathology of corneal endothelium in keratoconus

Keratoconus is characterized by stromal thinning and conical deformity of the cornea that affects a small but significant portion of the population. Although keratoconus has been well studied, endothelial changes have not been extensively investigated. We studied the endothelium of 14 keratoconus corneal buttons obtained over the past 6 years by penetrating keratoplasty using light microscopy, scanning electron microscopy and transmission electron microscopy. Observations were correlated with patient history. Corneas demonstrated: endothelial cell pleomorphism and polymegathism (6 corneas); endothelial cell degeneration (13), and evidence of anterior chamber inflammation (4). Patterns of endothelial damage were variable ranging from isolated cell membranolysis to denudement of Descemet's membrane. Less damage was present at the apex of the cones than that observed in a circumferential pattern at the bases. In general the damage observed correlated with the severity and duration of the keratoconus with 9 years being the dividing time between mild and severe endothelial cell damage. These observations support other studies that implicate contact lens wear as a cause of pleomorphism and polymegathism in these patients. Endothelial cell alterations are likely a secondary event occurring due to mechanical stresses.

Fibronectin as a component of pseudophakic acellular membranes

Avidin-biotin immunohistochemical staining for fibronectin was used to study 17 aphakic intraocular lens implanted globes and 12 explanted intraocular lenses. Fibronectin was identified as a component of acellular pseudophakic membranes and was also observed within lens epithelial cells and macrophages.

Ocular malformations associated with agnathia: a case report

Ocular malformations associated with agnathia in a 34-week gestational age infant were studied histopathologically and included asymmetric microphthalmos. Aphakia and retinal dysplasia were noted in the most severely affected globe; the fellow eye was characterized by microcornea, anterior segment dysgenesis, uveal colobomas, and retinal dysplasia. Aplasia of the optic nerve was seen bilaterally. The combination of agnathia and ocular malformation in the absence of holoprosencephaly is challenging to explain embryologically.

Eight years experience with Permalens intracorneal lenses in nonhuman primates

BACKGROUND

For the past 8 years, three independent laboratories have been researching the biocompatibility and performance of Permalens intracorneal lens implants in the corneas of nonhuman primates. Both myopic and hyperopic corrections have been achieved. This article describes the evolution of the intracorneal lens design and manufacturing process.

METHODS

During this time period, 63 surgeries were performed on various species of nonhuman primates. Follow-up examination extended between 30 months and 8.2 years. Objective measures of refractive performance, as well as biocompatibility were made using slit lamp, retinoscopy, autorefractor, specular microscope, etc. Additionally, histopathology was performed on many of the specimens, both acute and chronic.

RESULTS

Surgically successful implants were achieved in between 60% and 100% of eyes in the various series of lens implants outlined in the article. Levels of contamination in the preparation of hydrogels were felt to be responsible for many of the surgical failures. The removal of silicone and other contaminants seems to have significantly improved the biocompatibility of these materials within the cornea. The major histopathological finding was that there appeared to be some epithelial thinning over the implants, but in general excellent biocompatibility was obtained over the 8-year period outlined in this paper.

CONCLUSIONS

Although extensive studies of biocompatibility have been completed, the future of the performance of these materials remains to be proven in the human subject. Additionally, empirical relationships between lens implant power and refractive results will have to be determined in humans, prior to their general clinical usage.

Experimental evaluation of a phakic anterior chamber implant in a primate model. Part II. Pathology

Anterior chamber intraocular lenses were implanted in 50 phakic primate eyes and followed by serial histopathology for two years. Significant observations included corneal endothelial alterations, haptic erosion into and encapsulation by peripheral iris and ciliary body, and chronic low grade inflammation.

Experimental evaluation of a phakic anterior chamber implant in a primate model. Part I. Clinical observations

Anterior chamber intraocular lenses were implanted in phakic cynomolgus monkey eyes and followed clinically over two years. Significant observations included erosion and/or uveal envelopment of the haptic and a decrease in endothelial cell counts. There was good positional stability, no significant inflammation, initial ocular hypotension that returned to normal intraocular pressure, and no evidence of cataracts or cystoid macular edema.

RPE dysplasia with retinal duplication in a mutant mouse strain

An autosomal dominant mutation was produced by quadruple gonadal exposure of a male (C3H x 101)F1 mouse to 500 rad of X-irradiation. This mutation is maintained by the mating of affected heterozygous males to normal (C3H x C57B1)F1 females. Clinically apparent abnormalities were limited to the eyes and, in the affected adults, ranged from apparent anophthalmia to globes that were enlarged and exhibit large uveoscleral colobomas. Sequential evaluations of the embryogenesis of this condition have identified abnormal differentiation of the outer layer of the optic cup (presumptive retinal pigment epithelium-RPE) into a second layer of neural retina. The abnormality is identified as early as day 10 of gestation, during invagination of the optic cup and lens placode. The area of RPE dysplasia may be diffuse or regional with an abrupt transition from normal RPE and often demonstrates excessive and uncontrolled proliferation. The two symmetrical, apposed layers of photoreceptors fail to differentiate and begin to degenerate prenatally. Absence of normal RPE leads to failure of induction of adjacent choroid and sclera, resulting in a posterior segment consisting of a large neuroepithelial-lined cyst. Radiation-induced ocular malformations of this type have not been previously described. In addition, this model presents a unique opportunity to examine the processes leading to differentiation of a single, continuous epithelial layer into tissues as anatomically and functionally distinct as neural retina and RPE.

Relationship of cell death to cyclophosphamide-induced ocular malformations

C57BL/6J mice were used to study the ocular teratogenic effects of cyclophosphamide administered to pregnant females on d 9 of pregnancy at a dose of 5 mg/kg body weight. Nile blue staining demonstrated increased cell death at the base of the optic stalk, in the optic vesicle, and in the perivesicular mesenchyme in treated embryos. Malformations studied at gestational d 11 and 16 by light and scanning electron microscopy included microphthalmos, microphakia, and aphakia and were predictable based upon patterns of increased cell death. These anomalies are similar to those reported with exposure to ethanol or isotretinoin on gestational d 7.