Equine Multiple Congenital Ocular Anomalies (MCOA) syndrome in PMEL17 (Silver) mutant ponies: five cases

Objective To describe the clinical phenotype and genetics of equine Multiple Congenital Ocular Anomalies (MCOA) syndrome in PMEL17 (Silver) mutant ponies. Animals studied Five presumably unrelated ponies. Procedures The ponies were examined under field conditions in their barn by slit lamp biomicroscopy, indirect ophthalmoscopy, and applanation tonometry. Blood was collected and genomic DNA extracted for MCOA genotyping using the PMEL17ex11 marker. Results One pony solely presented with temporal ciliary body cysts, suggestive of the less severe Cyst phenotype of MCOA; the animal was heterozygous at the MCOA locus. Multiple bilateral anterior segment anomalies were identified in four ponies, consistent with the more severe MCOA phenotype characterized by cornea globosa, iris hypoplasia, encircling granula iridica along the pupillary ruff, and cataracts. These animals were homozygous for the mutant MCOA allele. Four of the ponies had a silver dapple or chocolate coat color with white or flaxen manes and tails. Silver dappling was masked by the palomino coloring of a 5th pony that was homozygous at the MCOA locus. Conclusions The MCOA syndrome can be seen in ponies. The results of both clinical evaluation and genotyping resembled the previously described MCOA of both Rocky Mountain and Kentucky Mountain Saddle horses.     

Post mortem magnetic resonance imaging of multiple congenital ocular anomalies in a Comtois mare

Multiple congenital ocular anomalies syndrome consists of several abnormalities mainly localised to the anterior segment of the eye. This condition, comprising iridal or ciliary cysts with or without iridal hypoplasia, an excessively protruding cornea (‘cornea globosa’), miotic pupils, retinal dysplasia, cataract, and other lesions, has been reported in several breeds and is strongly related to the silver coat colour, as a result of a dominant mutant allele at the PMEL17 locus. This report describes the macroscopic, ultrasonographic, histological and magnetic resonance imaging findings of the ocular abnormalities in a Comtois mare with multiple congenital ocular anomalies syndrome.     

Multiple congenital ocular anomalies syndrome in a family of Shetland and Deutsches Classic ponies in Belgium

The multiple congenital ocular anomalies (MCOA) syndrome has been associated with the Silver phenotype only in a few equine breeds. This report describes the phenotypic and genotypic characteristics of MCOA in a family of Silver‐coated Shetland ponies including a 20‐year‐old stallion, 17‐year‐old mare and their 1.5‐year‐old female offspring. Another 7‐year‐old Silver female Deutsches Classic Pony descending from the same dam but from a different sire, was also examined. Each pony underwent a complete ophthalmic examination, tonometry, ocular ultrasonography and genotyping for the silver coat colour. The stallion had a thickened iris, temporal retinal atrophy and bilateral iridociliary and peripheral retinal cysts. All females presented more severe anomalies: cornea globosa, iridocorneal adhesions, miosis, hypoplastic granula iridica and poorly responsive pupils to light and to pharmacological mydriasis. Iris hypoplasia, anterior cortical cataracts and temporal retinal atrophy were detected in 2 mares. One female presented bilateral lens subluxation. Supero‐temporal cystic structures were confirmed ultrasonographically in all ponies. The stallion was heterozygous for the Silver mutation, whereas all females were homozygous. This is the first report of the MCOA syndrome in a family of Shetland ponies and a Deutsches Classic Pony in association with the Silver phenotype, in Europe.     

Fluorangiographic study of the ocular fundus in normal horses

Purpose: To describe the protocol and appearance of fluorescein angiography (FA) in normal horses. Animals: A total of 25 healthy horses aged between 5 and 15 years. Materials and Methods: The horses were sedated with 15 µg/kg detomidine and 50 µg/kg butorphanol and dilated with topical tropicamide 1%. All angiograms were recorded after intravenous bolus injection of 10 mg/kg of fluorescein sodium solution. Results: Two successive angiographic phases could be discerned: the choriopapillary phase, starting at 46.95 ± 9.48 s, and the retinal vascular phase, starting at 47.79 ± 10.38 s. The retinal vascular phase was divided in three parts: filling phase, maximum fluorescence point, and fading phase. During the filling phase, the dye progressed into the retinal vessels, obtaining maximum fluorescence at 59.79 ± 10.39 s, termed the maximum fluorescence point. The fading phase started immediately following the maximum fluorescence point. During this phase, vascular fluorescence decreased to complete reduction at 74.76 ± 9.81 s. Also, areas of delayed choroidal filling, the presence of short retinal vessels in the ventral region of the optic disc, and a particular filling of the optic disc were also observed. Conclusions: The normal angiographic sequence was described in horses. FA may be a useful method for studying the integrity of the blood–retinal barriers in horses.     

Fluorangiographic study of the ocular fundus in normal horses

Purpose:  To describe the protocol and appearance of fluorescein angiography (FA) in normal horses.
Animals:  A total of 25 healthy horses aged between 5 and 15 years.
Materials and Methods:  The horses were sedated with 15 µg/kg detomidine and 50 µg/kg butorphanol and dilated with topical tropicamide 1%. All angiograms were recorded after intravenous bolus injection of 10 mg/kg of fluorescein sodium solution.
Results:  Two successive angiographic phases could be discerned: the choriopapillary phase, starting at 46.95 ± 9.48 s, and the retinal vascular phase, starting at 47.79 ± 10.38 s. The retinal vascular phase was divided in three parts: filling phase , maximum fluorescence point , and fading phase . During the filling phase, the dye progressed into the retinal vessels, obtaining maximum fluorescence at 59.79 ± 10.39 s, termed the maximum fluorescence point. The fading phase started immediately following the maximum fluorescence point. During this phase, vascular fluorescence decreased to complete reduction at 74.76 ± 9.81 s. Also, areas of delayed choroidal filling, the presence of short retinal vessels in the ventral region of the optic disc, and a particular filling of the optic disc were also observed.
Conclusions:  The normal angiographic sequence was described in horses. FA may be a useful method for studying the integrity of the blood–retinal barriers in horses.     

Survey of ocular abnormalities in draft horses

Objective

To determine the prevalence of ocular disease in draft horses in the United States.

Animals

Draft horses of various breeds and ages.

Procedure

Nondilated ophthalmic examination was performed using slit lamp biomicroscopy and indirect ophthalmoscopy. Intraocular pressures were measured when possible.

Results

One hundred sixty-five draft horses were examined. Age range: 10 days to 33 years (mean 10.8 years, median 10 years); 87 geldings (52.7%), 71 mares (43.0%), 7 stallions (4.2%); 64 Percherons (38.8%), 51 Belgians (30.9%), 29 Clydesdales (17.6%), 15 Shires (9%), and 6 other draft breed (3.6%). Intraocular pressure: mean 24.7 mmHg OD, range 13-37 mmHg; mean 25.0 mmHg OS, range 11-37 mmHg. Vision-threatening disease was present in 9 horses (5.5%): complete cataracts 1, post-traumatic optic nerve atrophy 1, uveitis and secondary glaucoma 1, retinal detachment 1, large chorioretinal scar 3, phthisis bulbi 2. Non-vision-threatening ocular disease was present in 56 horses (33.9%) involving one or more ocular structures: eyelid trauma/notch defect 14 (8.5%), SCC-type adnexal lesions 12 (7.3%), corneal scars 16 (9.7%), keratitis 6 (3.6%), corpora nigra cyst 15 (9.1%), incipient/punctate cataract 50 (30.3%), vitreous degeneration 10 (6.1%), asteroid hyalosis 1, “bullethole” chorioretinal scars 3, RPE coloboma 1. Linear keratopathy was present in 28 horses (17%) with 2/28 having concurrent vision threatening ocular disease.

Conclusions

Ocular abnormalities, in particular minor cataracts, were relatively common in this population, but not typically vision-threatening. Additionally, this survey demonstrated a greater prevalence of linear keratopathy in draft horses compared with reports in other breeds; however, it does not appear to be associated with concurrent ocular disease.     

Metastasis or delayed local extension of ocular squamous cell carcinoma in four horses

Four horses treated for ocular squamous cell carcinoma (SCC) that subsequently developed local tumour extension or local metastases without ocular recurrence are included in this study. Medical records were examined and long‐term follow‐up obtained through contact with owners and referring veterinarians. In 2 horses, SCC developed in the nasolacrimal duct and maxillary sinus one and 3.5 years, respectively, after treatment for SCC in the medial canthus of the eye. No recurrence of the SCC was noted in the ocular structures. Both were treated successfully with surgery and radiation therapy. Two additional horses had delayed metastasis of SCC to the parotid lymph node one and 2 years after excision of the ipsilateral third eyelid for SCC. No recurrence of the SCC was noted in the ocular structures. One was treated with surgery and radiation without success and one was not treated. Ocular SCC can spread to local tissues or lymph nodes without recurrence in the eye. The clinical manifestation of tumour recurrence may be delayed. Delayed local extension or local metastasis in horses after ocular SCC without recurrence in the eye itself has not been previously reported. Clinical signs of ocular squamous cell carcinoma should prompt immediate treatment and local recurrence despite successful treatment of the ocular disease is a possibility.     

Bilateral intraocular glandular choristomas in a Thoroughbred foal

Intraocular choristomas are rare anomalies in domestic animals and are often associated with multiple ocular malformations. A Thoroughbred foal presented for ocular abnormalities and was diagnosed with microphthalmia, corneal dermoids, severe anterior segment dysgenesis (including glandular choristomas), aphakia, retinal dysplasia, and optic nerve hypoplasia. Morphological, histochemical, and immunohistochemical comparisons were made between ocular choristomatous tissues from this foal and lacrimal gland, third eyelid gland, nasopharynx, trachea, and lacrimal sac/nasolacrimal duct from normal horses. Morphologically the choristomatous tissues (glands and epithelium lining the anterior segment) were most similar to the lacrimal sac. Histochemistry of glandular components found the glands associated with the lacrimal sac/nasolacrimal duct to be serous, as was the glandular intraocular choristomas. Our findings suggest that the origin of intraocular glandular choristomas in this case is from the lacrimal sac.     

Congenital ocular abnormalities of Rocky Mountain Horses

Objective: To determine the incidence and describe ocular abnormalities in a cross-section of the population of Rocky Mountain Horses.
Design: Prospective study.
Animals: Five-hundred and fourteen Rocky Mountain Horses.
Procedure: Ophthalmic examinations were performed using a slit-lamp biomicroscope and an indirect ophthalmoscope. Intraocular pressures were measured by applanation tonometry. Eyes from six horses were obtained for histologic examination.
Results: Cysts of the posterior iris, ciliary body, and peripheral retina were detected most frequently (249 horses), and were always located temporally. Curvilinear streaks of retinal pigmented epithelium extending from the peripheral temporal retina marked the boundary of previous retinal detachment in 189 horses. Retinal dysplasia was detected in 125 horses. Multiple ocular anomalies were evident in 71 horses and were always bilateral and symmetrical. Affected eyes had a large, clear cornea that protruded excessively and had an apparent short radius of curvature, a deep anterior chamber, miotic and dyscoric pupil, and iris hypoplasia. Pupillary light responses were decreased or absent and pupils failed to dilate after repeated instillation of mydriatic drugs in horses with multiple ocular anomalies. Less frequently encountered abnormalities included peripheral iridocorneal adhesions and goniosynechiae. Congenital cataract was always present in eyes with multiple abnormalities. Intraocular pressures did not differ among horses with normal eyes and horses with multiple ocular abnormalities. Histologic examination of eyes corroborated the clinical appearance.     

Phenotypic diagnosis of dwarfism in six Friesian horses

An extreme form of abnormal development, dwarfism, is common in man and some animals, but has not been officially reported in horses. Within the Friesian horse breed, congenital dwarfism has been recognised for many years, but no detailed report exists on its phenotype. The most salient feature of the dwarf syndrome is the physeal growth retardation in both limbs and ribs. Affected animals have approximately 25% shorter fore- and hindlimbs and approximately 50% reduced bodyweight. Postnatal growth is still possible in these animals, albeit at a slower rate: the head and back grow faster than the limbs and ribs leading to the characteristic disproportional growth disturbance. Thus, adult dwarfs exhibit a normal, but a relatively larger head conformation, a broader chest with narrowing at the costochondral junction, a disproportionally long back, abnormally short limbs, hyperextension of the fetlocks and narrow long-toed hooves. Furthermore, a dysplastic metaphysis of the distal metacarpus and metatarsus is radiographically evident. Microscopic analysis of the growth plates at the costochondral junction shows an irregular transition from cartilage to bone, and thickening and disturbed formation of chondrocyte columns, which is similar to findings in osteochondrodysplasia.     

Recurrent colics in a 9‐year‐old Arabian stallion due to several congenital anomalies

A 9‐year‐old Arabian stallion was presented for evaluation of recurrent colic problems of 2 years' duration. These colic episodes were associated with a right sided abdominal distension. An exploratory laparotomy revealed a colonic diverticulum that was resected en bloc. Two days later, following signs of acute colic, a second laparotomy showed incarceration of the distal jejunum into a mesodiverticular band combined with haemorrhage of a mesenteric arterial branch. In addition, an abnormally short jejunum (10 m) was also observed. An end‐to‐end jejunojejunostomy was performed. Following surgery the horse developed septic peritonitis, ptyalism and became dysphagic. Ten days after the second surgery, an infected oesophageal diverticulum causing regional inflammation was diagnosed endoscopically and euthanasia was performed. Post mortem examination showed a 40 cm long diverticulum lateral to the oesophagus. Histology suggested a congenital nature of the colonic and oesophageal diverticuli.     

Laparoscopic assisted surgical removal of a congenital rectal hamartoma in a foal

In this report we describe a 3‐week‐old Paint horse filly that presented with rectal bleeding associated with a protruding mass. Rectal bleeding in neonates can be caused by infectious agents, trauma, congenital defects, rectal tears or tumours. Histopathology was performed on an avulsed piece of tissue. A second mass was identified endoscopically and was removed using a stapling instrument per rectum under endoscopic guidance and laparoscopic assistance. The mass was diagnosed as a rectal hamartoma. Recovery was uneventful.     

Delayed metastasis of ocular squamous cell carcinoma following treatment in five horses

Identification of regional and/or distant metastasis following treatment and local resolution of primary ocular squamous cell carcinoma (SCC) was observed in 5 horses. In all cases, identification of metastasis occurred at least 18 months following treatment of the primary ocular lesions. In 3 cases, invasion of blood or lymphatic vessels by neoplastic cells was identified in the excisional biopsies of the primary tumour. Two horses developed SCC at 2 or more separate sites. At the time metastases were identified, there was no evidence of local recurrence of the ocular tumour in any of the horses. These cases confirm the importance of long‐term monitoring of horses for metastatic disease following treatment of ocular SCC even in the absence of local recurrence.     

Ultrasonographic description of the caudal and ventral lung borders in normal Warmblood horses

The aim of the study was to describe the caudal and ventral lung border in clinically normal horses more precisely than it had been described previously and also to resolve the contradictions of data published in standard textbooks. Twenty‐two healthy Warmblood horses were used in the study. The lung border was determined by 2‐dimensional ultrasonography at the following anatomical levels: tuber olecrani, tuberositas deltoidea of the humerus, tuberculum majus of the humerus, tuber ischiadicum and ventral, mid‐ and dorsal points of the tuber coxae. Examinations were performed bilaterally at the end of inspiration and expiration. Distances between the actual lung borders and corresponding anatomical levels were measured and compared statistically. The results showed that the olecranon could not be used as an anatomical landmark. Instead, the deltoid tuberosity could be used as an alternative, as the lung border was found in the 7th intercostal space (ICS) in 14 horses and in the 8th ICS in 8 horses. The lung border at the level of the tuberculum majus was found in the 10th ICS in every horse. At the level of the tuber ischiadicum, the lung border was detected equally in the 14th (11 horses) and 15th (11 horses) ICS. At the level of the ventral and midpoint of the tuber coxae, the lung border was found in the 15th or 16th ICS. No lung border was found at the level of the dorsal point of the tuber coxae or in the 17th ICS.