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.     

Comparative fluorescein angiography of the normal sheep and goat ocular fundi

Fluorescein angiography without sedative or anesthetic agents was evaluated in 20 normal goats and 20 normal sheep. All of the angiographic phases were observed using 20 mg/kg fluorescein IV in both species. Fundus fluorescein angiography results revealed wide stars of Winslow in the tapetal fundus, central or marginal flow during the first part of the arterial phase, delayed filling of the focal areas in the choroid near the optic disc that often coincided with others in the disc, and lack of evidence of the 'striate area' in the tapetal fundi. In goats, the angiographic times were 6.54+/-1.25 s for the arterial phase (TA), 7.80+/-1.37 s for the arterio-venous phase (TAV), and 14.13+/-2.01 s for the venous phase (TV). I1: 1.30+/-0.30 s (time elapsing between TA and TAV), and I2: 6.20+/-1.60 s (time elapsing between TAV and TV). In sheep, times were 9.54+/-2.18 s TA, 11.73+/-2.10 s TAV, and 20.86+/-2.74 s TV. I1: 2.04+/-0.75 s and I2: 8.98+/-2.47 s, respectively. Due to the large size of the fundic vessels in sheep and goats, fluorescein angiography of the retinal vasculature can facilitate the study of the different vascular diseases in these species.     

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.     

Phenotypic description of multiple congenital ocular anomalies in Comtois horses

Multiple congenital ocular anomalies (MCOA) and their relation to coat colour genotype have not yet been described in Comtois horses, unlike in Rocky Mountain Horses. The objectives of the study were to describe prevalence, nature and severity of congenital ocular anomalies relating to the PMEL17 (Silver) mutation in Comtois horses. Seventy‐four purebred Comtois and one half‐cross Comtois horses, aged 10 days to 18 years, were examined by transillumination, direct ophthalmoscopy and ultrasonography. Hair samples were collected from 34 horses for coat colour genotyping. Sixty‐six horses (88%) revealed cysts (65 horses) or abnormal thickness (one horse) of the ciliary bodies, most of them only diagnosed by ultrasonography. Cysts were localised in the nasal part of the eye in 8 horses. All these horses presented the silver phenotype with mane and tail being white or flaxen, or were chestnut with genetic testing confirming PMEL17 mutation. Of these, 39 (58%) showed MCOA‐syndrome with iridal hypoplasia (100%), cataract (85%), cornea globosa (56%) and lens luxation (8%). Only 8 bay mature horses (11%) were classified as being disease‐free. Genetic testing confirmed that cyst‐phenotype horses were heterozygous carriers for the Silver mutation, MCOA‐phenotype horses were homozygous carriers, and bay horses were noncarriers. Bay homozygous carriers had significantly lighter coat colour than heterozygous carriers. One foal with heterozygous mutation had normal eyes. Thus, MCOA‐syndrome related to PMEL17 mutation is overrepresented in Comtois horses, and should be taken into consideration for breeding purposes. Ultrasonography permitted detection of cysts in all Silver carriers apart from one, some of them being localised in the nasal part of the eye.     

Multiple ocular colobomas in the snow leopard (Uncia uncia)

Two singleton female snow leopard cubs are reported with bilateral central upper lid colobomas. In addition, one cub had a coloboma of the fundus in one eye extending from the lower optic disc region. Surgical treatment by wedge resection was successful in both cases. Details of ocular colobomas in other snow leopards reported in the literature are described and it is suggested that the exact etiology of the condition in this species may be discovered by further study of similar colobomas in the domestic cat.     

Ectopic cilium in seven horses

Ectopic cilium was diagnosed by slit-lamp biomicroscopy and treated surgically by transconjunctival excision in seven adult horses. All cases presented with a common history of blepharospasm, ocular discharge and keratitis. Ophthalmic examination revealed a single translucent cilium in the upper eyelid palpebral conjunctiva, emerging approximately 5 mm from the eyelid margin. Corneal ulceration was not observed in any horse. Most horses responded well to transconjunctival surgical excision. There was recurrence of ectopic cilium 6 weeks postoperatively in one horse. Histopathologic examination was performed in two cases and confirmed the diagnosis of ectopic cilium in one horse. This is the first publication of ectopic cilia in horses and emphasizes their importance as etiology for epiphora, blepharospasm and keratitis.     

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.     

A pilot study on the corneal curvatures and ocular dimensions of horses less than one year of age

Intraocular lenses (IOLs) have been implanted in adult equine eyes after cataract surgery. Foals and weanlings comprise a large proportion of those horses undergoing cataract surgery. Due to potential differences in the size and corneal curvature of the juvenile eye, it is not currently known whether implantation of adult IOLs is appropriate in foals and weanlings. The objective of the study was to measure the anterior chamber depth (ACD), central lens thickness (CLT), vitreous chamber depth (VCD), axial globe length (AGL) and corneal curvature of horses less than one year of age. The axial dimensions from one eye of 10 foals were measured using simultaneous A and B scan ultrasonography. The corneal curvature from one eye of 7 weanlings was determined using a modified photokeratometer. Ultrasonography revealed a mean ACD of 4.94 mm, mean CLT of 9.38 mm, mean VCD of 18.96 mm and mean AGL of 33.32 mm for the foals. The mean corneal curvature was 15.4 diopters (D). The mean ACD, CLT, VCD and AGL of the foals were less than the measurements reported in the literature for adult horses. The mean corneal curvature was similar to the values reported by some authors for adult horses. Due to the differences in axial dimensions between adult and juvenile eyes, an IOL that corrects vision in an adult horse might not adequately correct vision in a horse less than one year of age.     

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.     

Indocyanine green angiography for examining the normal ocular fundus in dogs

In dogs, a variety of diseases of the retina and choroid have been reported, either separately or concomitantly; however, the canine choroid is difficult to evaluate by veterinary techniques currently available. Indocyanine green (ICG) angiography is widely used in human ophthalmology, but has not been investigated for use in canine ophthalmology. The aim of this study was to apply a new approach to ICG angiography and compare the resulting angiograms with fluorescein (FLUO) angiograms of the ocular fundus in dogs. With a fundus camera equipped with an infrared-sensitive charged coupled device (CCD), we performed angiography on eight healthy beagles under inhalation anesthesia. ICG angiography enabled clear visualization of the choroidal vasculature, whereas FLUO angiography showed only the retinal vessels. At 8.4 +/- 3.6 sec after administration of ICG dye into the cephalic vein, the choroidal arteries could be seen extending radially from the optic disc, then the choroidal veins became apparent at 10.2 +/- 4.1 sec, coursing alongside the choroidal arteries. Gradual fading of the choroidal vessels began 13.2 +/- 2.2 min after the dye was administered, and overall diffuse fluorescence of the fundus appeared. Diffuse fluorescence of the fundus continued after the choroidal vessels and optic disc faded at about 58.3 +/- 5.3 min from administration of the dye. In conclusion, ICG angiography provides clear resolution and is reliable and simple, thus offering promise as a diagnostic aid for clinical evaluation of the choroid in dogs.