Anterior segment dysmorphogenesis of the eye and glaucoma in MG-W gerbils

Unilaterally swollen eyes were histopathologically characterized in four MG-W gerbils. The primary lesions resided in the anterior segment of the eye where neural crest cells play a critical role in embryonic development. They included indistinct filtration angle, unformed canal of Schlemm, hypoplastic iris, and ciliary body. The findings noted in the retina, optic nerve, optic tract, and lateral geniculate nucleus were consistent with the lesions induced following the persistent elevation of intraocular pressure as a result of insufficient drainage of aqueous humor. Thus, the present cases observed in the eyes of MG-W gerbils exemplified the anterior segment dysmorphogenesis associated with inadequate neural crest migration or differentiation, leading to subsequent glaucoma.     

Feline primary open angle glaucoma

Objectives We have documented the histomorphological features of feline primary open angle glaucoma. Design A retrospective morphologic study of eight affected eyes from eight cats, from 1992 to 2006 extracted from a pathology collection, which includes 4000 feline submissions and 1100 cases of feline glaucoma. Procedure Sections of affected globes, stained with H&E or with alcian blue were examined with a light microscope. Eyes that did not fulfill the criteria for primary open angle glaucoma were excluded from the study. Results The mean age was 9.1 years. Five cats were female and three cats were male. The breeds included five DSH, two Burmese, and one DLH cat. Significant histomorphological findings included an open irido‐corneal angle with an open ciliary cleft in all cases, loss of ganglion cells in eight of eight cases, cupping and gliosis of the optic nerve head in four of four cases in which the optic nerve was adequately sampled, and myxomatous changes of the stroma surrounding the vortex veins in seven of eight cases. Conclusions Primary open angle glaucoma in cats is a rare disease that should be taken into consideration when investigating cases of feline glaucoma. The pathogenesis of aqueous outflow obstruction in these cases is not known. This study describes eight additional cases of feline primary open angle glaucoma in cats without an identified cause.     

Gonioscopy in the dog

Gonioscopy is the examination of the iridocorneal angle of the eye utilizing a corneal contact lens. The technique is extensively practised in human ophthalmology and is particularly important in the differential diagnosis of the glaucoma complex. The author has practised the technique extensively in dogs, and his findings on the appearance of the normal canine iridocorneal angle are reported in this paper.     

Pectinate ligament dysplasia and narrowing of the iridocorneal angle associated with glaucoma in the English Springer Spaniel

Objective The aim of the study was to evaluate if tonometry and gonioscopy could serve as predictors of later glaucoma development in the English Springer Spaniel, a breed prone to developing primary glaucoma. Animals studied Gonioscopy was performed on 279 English Springer Spaniel dogs, 119 males and 160 females, with clinically normal eyes. In addition, 14 dogs, five males and nine females were examined for glaucoma. Results A positive relation between pectinate ligament dysplasia (PLD) and narrowing of the relative width of the ciliary cleft (RWOCC) and also between PLD, RWOCC and age was demonstrated. The prevalence of PLD was 25.5%, which is higher than in other breeds reported. A positive association was demonstrated between PLD and glaucoma, as well as between narrowing of the RWOCC and glaucoma. Glaucoma was not observed in dogs with normal appearance of the iridocorneal angle. English Springer Spaniels related to dogs with glaucoma show more narrowing of the RWOCC and more PLD than unrelated dogs. Conclusion This study demonstrates the positive association between PLD and glaucoma, between narrowing of the iridocorneal angle and glaucoma and the effect of age on the iridocorneal angle. Mating of dogs with normal iridocorneal angles appears to reduce the presence and degree of abnormal appearance of the iridocorneal angle in the offspring. However, breeding only dogs with normal iridocorneal angles without consideration of their relationship to dogs with glaucoma is not a guarantee for preventing glaucoma in the offspring.     

Long-term management of a glaucomatous eye in a dog treated with medical therapy alone.

An acute open angle glaucoma of the right eye was diagnosed in an 8-year-old male Yorkshire terrier which was presented with anorexia, depression, and trembling. Abnormal findings of the right eye on admission included elevated intraocular pressure (IOP; 40 mmHg), the presence of fibrin and flare in the anterior chamber, and immature cataract. Morphological abnormalities of the iridocorneal angle were not detected, and an open angle was seen in the eye. Although an elevated IOP was observed at one year after admission, lowering IOP (< or = 24 mmHg) was maintained with medical therapy using dichlorphenamide (DCPA) and timolol maleate, DCPA alone, or no-treatment for 1973 days. This case suggests that lower IOP can be maintained with medical therapy alone for a long period in a patient with open angle glaucoma.     

Ultrasound biomicroscopic findings of the iridocorneal angle in live healthy and glaucomatous dogs

By using ultrasound biomicroscopy (UBM), the cross-sectional structures of the entire iridocorneal angle (ICA) which are unable to assess with gonioscopic examination were evaluated objectively and quantitatively in live healthy and glaucomatous dogs. The ICAs of normotensive eyes in healthy dogs with normal open angle (NOR), a predisposition to primary closed angle glaucoma (PCAG) (PREDIS) and suffering from unilateral PCAG (UNI), as well as the ICAs of hypertensive eyes with acute and chronic PCAG (ACG and CRG), were assessed. The opening of the ciliary cleft in PREDIS was smaller than that in NOR. In UNI, the opening and area of the ciliary cleft were significantly decreased compared with those of NOR and PREDIS. ACG had widespread structural abnormalities including marked decrease in the ciliary cleft and scleral venous plexus, and a thinner sclera than those in normotensive eyes, whereas the ICA collapsed in CRG with the thinnest sclera. Medical therapy-responsive glaucomatous cases had wider ciliary cleft and scleral venous plexus than unresponsive ones. These findings suggest that the ciliary cleft and scleral venous plexus of the ICA are key structures contributing to not only the pathophysiology of canine glaucoma but also the responsiveness to medical therapy in glaucomatous eyes, and cross-sectional entire structures of the ICA should be evaluated quantitatively with UBM when diagnosing and managing canine glaucoma.     

Incidence of canine glaucoma with goniodysplasia in Japan : a retrospective study

The incidence of primary and secondary glaucoma in dogs was investigated. A total of 1244 dogs received ophthalmologic examinations, including tonometry and gonioscopy. Goniophotographs were taken using a goniolens to evaluate the iridocorneal angle (ICA) as well as pectinate ligament (PL). The anterior width of the ciliary cleft and the total distance from the origin of the PL to the anterior corneal surface were measured from the goniophotographs. Glaucoma was diagnosed based on the cupping of the optic nerve head, clinical signs, ocular changes, and high IOP, and it was synchronized with gonioscopic grades to differentiate between primary and secondary glaucoma. We investigated 1244 dogs of 29 breeds, including the mixed breed; among these, glaucoma was diagnosed in 127 dogs (162 eyes). Of 162 eyes, primary glaucoma was diagnosed in 129 eyes and secondary glaucoma in 33 eyes. Shiba Inu dogs (42 dogs, 33%) showed the highest incidence of glaucoma, followed by Shih-Tzu (21 dogs, 16.5%). Furthermore, all the glaucomatous Shiba Inu dogs had primary glaucoma with abnormal ICA grades and dysplastic PLs. The findings of our study reveal that the Shiba Inu breed in Japan may have a hereditary predisposition to glaucoma.     

The Treatment of Acute Glaucoma in Dogs and Cats

Objective: Glaucoma is an optic nerve disease that may result in rapid loss of vision. Early detection of acute glaucoma and aggressive treatment is important to preserve vision. Continued treatment is indicated in chronic glaucoma to alleviate discomfort associated with chronic elevated intraocular pressure.
Etiology: In primary glaucoma, an abnormal iridocorneal angle results in obstruction to outflow of aqueous humor. In secondary glaucoma, an otherwise normal iridocorneal angle is obstructed by abnormalities such as a luxated lens, neovascular membranes or inflammatory material.
Diagnosis: The diagnosis is made by a combination of clinical signs such as corneal edema, mydriasis, decreased vision, episcleral hyperemia, and confirmed by measuring an elevation in intraocular pressure. Complete ophthalmic examination, knowledge of breed predisposition to various ocular diseases and gonioscopy will aid in distinguishing between primary and secondary glaucoma
Therapy: Aggressive medical management is important in acute glaucoma. Surgical procedures are often indicated after initial emergency medical treatment of acute glaucoma. Chronic, painful blind eyes are best treated with one of various surgical procedures.
Prognosis: The prognosis for maintaining vision or regaining temporarily lost vision in acute glaucoma is related to numerous factors including time between onset of clinical signs and appropriate treatment, etiology of the glaucoma, initial response to therapy and client compliance.     

Pectinate ligament dysplasia and glaucoma in Flat Coated Retrievers. II. Assessment of prevalence and heritability

Pectinate ligament dysplasia (PLD) in dogs is a congenital ocular abnormality affecting the iridocorneal angle, the presence of which may be associated with adult-onset primary glaucoma. This study demonstrates a significant association between PLD and glaucoma in Flat Coated Retrievers, and also a higher prevalence of PLD in Flat Coated Retrievers compared with other breeds. It is shown that the association between PLD and glaucoma was robust and not due to a small increase in PLD with age. There was also a significant association between PLD in offspring and parents and, using the offspring–parents regression, the heritability of PLD was estimated as approximately 0.7. As glaucoma is significantly related to PLD, glaucoma may also be heritable. Thus, glaucoma can be controlled by gonioscopic examination and elimination of animals with a high degree of PLD from a breeding program. Breeding from only those animals with a moderate or low PLD value or score should limit the expected prevalence of glaucoma in the resulting population to < 0.2%. The preceding study describes in detail the PLD survey, gonioscopic technique and some initial results obtained prior to this epidemiological investigation.     

Use of a Baerveldt gonioimplant for secondary glaucoma in a horse

This case report describes the surgical placement of a Baerveldt glaucoma shunt in the right eye of a 14‐year‐old Arabian gelding. The glaucomatous right eye was refractory to aggressive medical and repeated surgical therapies yet maintained functional vision. Despite the need for intensive post operative management and continued daily topical therapy, shunt placement surgery was successful at maintaining normotension and vision for a period of 402 days. This is the first report of long‐term successful glaucoma filtration surgery in this species. Further studies are warranted to evaluate long‐term success of glaucoma shunt placement in equine glaucoma cases.     

Intraocular ALλ amyloidoma with plasma cell neoplasia in a cat

An 11-year-old, neutered male domestic short-hair cat was presented with buphthalmos of the right eye and diagnosed with advanced glaucoma. Sonographic examination revealed an iridial thickening. Neoplasia was suspected and an enucleation was performed. Histopathology of the enucleated eye revealed abundant amyloid deposition predominantly in the anterior uveal tract accompanied by few to moderate numbers of well-differentiated plasma cells. The amyloid deposits were identified by staining with Congo red and showing green birefringence under polarized light. Immunohistochemically, amyloid and plasma cells stained intensely only with anti-ALλ antibody, supporting the amyloid tumor being an immunoglobulin-λ-light chain origin. Additional abnormalities included narrowing of the filtration angle and collapse of the ciliary cleft, and trabecular meshwork. One year post-enucleation, the cat was still healthy without signs of systemic amyloidosis or apparent metastatic disease. This is the first report of a cat with noncutaneous extramedullary plasmacytoma originating in the anterior uveal tract with resulting local amyloid.     

Antemortem diagnosis of congenital glaucoma in a white‐bellied caique (Pionites leucogaster)

A 34‐day‐old, male, white‐bellied caique (Pionites leucogaster) was presented for a complaint of bilateral buphthalmos. Clinical examination was unremarkable apart from the ophthalmic findings. The ophthalmologic examination was negative for direct, consensual, and dazzle reflexes in both eyes. The intraocular pressure exceeded 40 mm Hg OU. Fluorescein stain demonstrated corneal surface lesions suggestive of exposure keratopathy subsequent to bilateral buphthalmos. Diagnostic imaging tests were conducted to perform ocular biometric measurements and investigate the intraocular structures, including the iridocorneal angle and lens, by means of high‐resolution ultrasonography (HRUS). The presence of congenital glaucoma in this young parrot was strongly suspected after clinical and ophthalmological examination and the results of diagnostic imaging. Pharmacological treatment to reduce intraocular pressure was initiated using dorzolamide hydrochloride 2% and timolol maleate 0.5%. A month later, the parrot's eyes did not show any visual improvement, but the intraocular pressure had returned to normal. The parrot was unable to feed itself and died during a feeding procedure. Postmortem examination revealed ab ingestis pneumonia. Both eyes were submitted for histopathology, with severe anterior segment dysplasia and goniodysgenesis found OU. Histological findings added to the clinical presentation, the ophthalmologic examination and the imaging findings, confirmed the presence of congenital glaucoma.     

Localization of smooth muscle actin in the iridocorneal angle of normal and spontaneous glaucomatous beagle dogs

Purpose To date, our knowledge of the canine trabecular meshwork (TM) with regard to contractility is incomplete. It is important to understand the potential contractile capability within the TM and possible changes associated with spontaneous hypertensive glaucoma. To that end we have examined the presence of actin, including smooth muscle (SM) actin, in the normal and glaucomatous canine iridocorneal angle (ICA) morphologically and immunohistochemically. Methods Sections from the ICAs of 12 Beagles with inherited glaucoma (3 months to 6 years old) and age‐matched normal Beagles were treated with target retrieval, protein and power blocked and sequentially incubated with the primary antibody (rat anticanine SM actin) and the secondary antibody (rabbit antirat immunoglobulin), followed by peroxidase labeled streptavidin and incubation with substrate‐chromogen solution (AEC). Smooth muscle fibers that lined an artery within canine heart tissue were used as positive controls. Separate specimens were prepared for ultrastructual observation. Results Ultrastructurally, cells within the inner, posterior region of the corneoscleral TM and outer, posterior region of the uveal TM contained many microfilaments, 6 nm in diameter (i.e. actin). Immunohistochemistry demonstrated that cells within these regions possessed SM actin, having been greatest posteriorly, but extended anteriorly to a lesser extent. In the preglaucomatous affected dog the localization pattern for SM actin was identical to that seen in the normal dogs. With the progression of the disease the pattern disappeared. Conclusions The interior presence of myofibroblastic cells within the canine ICA suggests that these cells and the smooth muscle cells of the ciliary body along the same plane of orientation function to facilitate the removal of aqueous humor and are likely to be influenced by vascular mediators. The contractile apparatus for the ICA in the dog with inherited glaucoma appeared identical to that of the normal dog prior to expression of the disease, but weakened as the disease progressed.     

Equine pectinate ligament descemetization is associated with age

Purpose

To evaluate the correlation between equine pectinate ligament descemetization and ocular disease.

Methods

The pathology database of the North Carolina State University Veterinary Medical Center was searched from 2010–2021 for all equine globes. Disease status was then assigned as affected by glaucoma, uveitis, or “other” based upon clinical records. The iridocorneal angles (ICA) of each globe were evaluated for the presence of pectinate ligament descemetization, the length of descemetization, as well as for the degree of angle collapse and the extent of cellular infiltrate or proteinaceous debris. One slide from each eye was evaluated by two separate, blinded investigators (HW & TS).

Results

A total of 66 eyes from 61 horses were identified, with a total of 124 sections of ICA of sufficient quality to review. 16 horses were affected by uveitis, 8 by glaucoma, 7 by both glaucoma and uveitis, and 30 horses by other ocular disease, most commonly ocular surface disease or neoplasia, which served as controls. Pectinate ligament descemetization was most prevalent in the control group compared to the glaucoma and uveitis groups. Pectinate ligament descemetization length was positively correlated with age, with an increase of 13.5 μm per year of age (p = .016). Infiltrate scores and angle closure scores were higher in both the glaucoma and uveitis group compared to the control group (p < .001).

Conclusions

Equine pectinate ligament descemetization appears to be correlated with increased age and should not be used as a histologic marker for the presence of glaucoma.     

Schwalbe line's cell in the normal and glaucomatous dog

Objective The canine iridocorneal angle contains an operculum, which is similar to that in nonhuman primates and consists of a peripheral extension of the inner cornea that overlies the anterior‐most portion of the corneoscleral trabecular meshwork. This region contains cells, the Schwalbe line’s (SL) cells, that have been found to have secretory and epithelial characteristics. This region of the iridocorneal angle represents the nonfiltering portion and becomes altered early during spontaneous glaucoma in the Beagle. The present study describes the SL cell for the first time in the dog and changes associated with canine primary open angle glaucoma. Procedures The iridocorneal angles from 18 Beagles with inherited glaucoma (3 months–8 years old) and 17 normal, age‐matched Beagles were placed in 10% buffered formalin for light microscopic evaluation, or 2.5% glutaraldehyde for ultrastructural evaluation. Using at least three fields from each region of the iridocorneal angle (opercular, corneoscleral, and uveal) at ×1000 magnification, trabecular cell nuclei were counted. Results The operculum in the canine iridocorneal angle consisted of the peripheral extension of the corneal endothelium and underlying anterior‐most corneoscleral meshwork, having no direct contact with the angular aqueous plexus. The SL cells associated with operculum‐retained epithelial morphology (polyhedral in shape with rER, Golgi apparatus, and secretory vesicles) in both normal, pre‐and early glaucomatous dogs. In animals with moderate and advanced stages the SL cells often became less epithelial and secretory in appearance. The number of SL cells in normal dogs declined by approximately one‐third by the end of their first year with gradual loss thereafter. In the glaucoma group the decline was more substantial and continuous through the first three years. Conclusions The SL cell is morphologically a distinct cell type within the canine iridocorneal angle that is specifically associated with the nonfiltering portion of the corneoscleral trabecular meshwork. Changes in the SL cells of the glaucomatous dog occurred with regard to age and progression of the disease.     

Abnormal ocular pigment deposition associated with glaucoma in the cairn terrier

A condition involving ocular pigment deposition was diagnosed in six cairn terriers. In each, there was pigment deposition in a number of ocular sites, including the episclera, and ventral anterior chamber and drainage angle. Four of the dogs (aged 10 years or older) had developed a chronic glaucoma, which was presumed to be secondary to pigment deposition in the drainage angle. The other two dogs (six-year-old litter mates) had not developed glaucoma but there were pigmented particles in the aqueous and abnormal pigment deposition within the episclera and drainage angle. They also had a raised circumferential band protruding from the periphery of the iris into the anterior chamber.     

A promising surgical approach to equine glaucoma

The preceding case report by Wilson et al. (2015) describes the surgical placement of a Baerveldt glaucoma shunt in a glaucomatous equine eye that had been refractory to aggressive medical and repeated surgical therapies yet maintained functional vision. Shunt placement surgery successfully maintained vision and intraocular pressure in the normal range in the affected eye. This is the first report of long‐term successful glaucoma filtration surgery in a horse. Glaucoma shunt placement shows promise for maintaining vision and comfort in equine eyes affected with glaucoma. There is much to be learned in terms of the most appropriate implant type for the equine eye, the risk of complications such as ocular hypotony or tube fibrosis, and the utility of combination therapy with transcleral cyclophotocoagulation and implant placement, but with the report of one case in which gonioimplant placement has been associated with intraocular pressure control for over one year, further investigations appear warranted. This case provides a glimmer of hope for long‐term treatment of a painful, blinding disease that has traditionally carried a poor prognosis in horses.     

The surgical treatment of canine glaucoma

The success of glaucoma therapy depends wholely upon the ability to restore rapidly an elevated intraocular pressure to normal, and subsequently to maintain adequate aqueous drainage. In the dog, the extent of synechial occlusion within the iridocorneal angle is often such that medical therapy proves to be of little or no lasting value, and a surgical approach is essential if ocular structure and function are to be preserved. The author has recently evaluated several techniques of glaucoma surgery in sixty-one patients, and his results now indicate that corneoscleral trephination combined with peripheral iridectomy offers the greatest chance of success in the treatment of this condition.     

A gonioscopic study of the iridocorneal angle in the English and American breeds of Cocker Spaniel and the Basset Hound

Closure of the iridocorneal angle is the cause of a primary form of glaucoma which occurs in certain breeds of dog, but the precise mechanism involved in that closure is not completely understood. However, narrowness of the angle is considered to be the important predisposing factor, and in gonioscopic survey work the author has demonstrated that angle narrowness occurs with some frequency in the English Cocker Spaniel and Basset Hound breeds.     

The efficacy of topical prophylactic antiglaucoma therapy in primary closed angle glaucoma in dogs: a multicenter clinical trial

The ability of either 0.5% betaxolol (1 drop topically, bid; n=31) or a combination of 0.25% demecarium bromide and a topical corticosteroid (gentamicin/betamethasone) (DB/GB; 1 drop of each topically, sid; n=55) to prevent glaucoma in the fellow eye of dogs with unilateral, primary closed angle glaucoma (PCAG) was investigated in a multicenter, open-label, clinical trial. Untreated control dogs (n=20) developed glaucoma significantly sooner (median, eight mos; p less than 0.001) than dogs treated either with DB/GB (median, 31 mos) or betaxolol (median, 30.7 mos). Although DB/GB and betaxolol equally delayed or prevented the onset of glaucoma in the second eye, a less frequent dosing schedule for DB/GB suggests demecarium bromide in combination with a topical corticosteroid may be preferable to betaxolol in preventing PCAG in dogs.