Current Therapeutics and Future Perspectives to Ocular Melanocytic Neoplasms in Dogs and Cats

Neoplasms of melanocytic origin are diseases relevant to dogs and cats' ophthalmic oncology due to their incidence, potential visual loss, and consequent decrease in life quality and expectancy. Despite its non-specific clinical presentation, melanocytic neoplasms can be histologically distinguished in melanocytomas, which present benign characteristics, and malignant melanomas. The diagnosis often occurs in advanced cases, limiting the therapeutic options. Surgery, cryotherapy, radiotherapy, photodynamic therapy (PDT), and laser are currently available therapeutic strategies. As no clinical guidelines are available, the treatment choice is primarily based on the clinician's preference, proficiency, and the owner's financial constraints. While surgery is curative in benign lesions, ocular melanomas present a variable response to treatments, besides the potential of tumour recurrences or metastatic disease. This review presents the currently available therapies for ocular melanocytic neoplasms in dogs and cats, describing the therapeutic, indications, and limitations. Additionally, new therapeutics being developed are presented and discussed, as they can improve the current treatment options.

Deep lamellar keratectomy and penetrating scleroplasty using CO2 laser photoablation and bimodal grafting for the treatment of a limbal melanoma in a dog

A novel approach for en bloc resection of a limbal melanoma using a CO2 laser in a dog. Benefits of this advanced technique include excellent surgical precision, improved hemostasis, and the induction of coagulative necrosis of neoplastic cells.

Use of four-layer porcine small intestinal submucosa alone as a scaffold for the treatment of deep corneal defects in dogs and cats: preliminary results

BACKGROUND

To describe the efficacy of four-layer porcine small intestinal submucosa (Vetrix BioSIS plus+) as single scaffold for the treatment of deep corneal lesions in dogs and cats.

METHODS

10 dogs and 3 cats with deep or full thickness corneal defects were treated surgically with BioSIS plus graft. Corneal transparency scores and vision were evaluated.

RESULTS

Lesions in dogs were four perforations, three descemetoceles, two limbal melanocytomas and one deep corneal ulcer. In cats, there were one limbal melanocytoma and two perforations. The average length of the follow-up was 86 days. In all, 12 out of 13 eyes treated were visual at last recheck (92.3 per cent). The scars were mild eight cases (66.7 per cent), but denser in four cases (33.4 per cent). Complication were partial collagenolysis in three cases (25 per cent), which resolved with medical therapy, mild corneal pigmentation in one case (8.4 per cent) and anterior synechia in one case (8.4 per cent). One case experienced severe collagenolysis and was enucleated 21 days postoperatively.

CONCLUSIONS

Four-layer porcine SIS graft was successfully used for surgical treatment of deep corneal lesions in selected corneal diseases in a small series of dogs and cats, with good results in terms of mechanic support and corneal transparency.

Cryopreservation (-20°C) of equine corneoscleral tissue: Microbiological, histological, and ultrastructural study

OBJECTIVE

To evaluate microbiological, histological, and ultrastructural characteristics of short-term cryopreserved (STC) equine corneoscleral tissue (<1 year), and to compare it with long-term cryopreserved (LTC) tissue (>7 years).

ANIMALS STUDIED

Thirty-four healthy equine globes.

PROCEDURE

After a decontamination protocol, globes were enucleated and stored at -20°C in broad-spectrum antibiotics. Corneoscleral tissue was evaluated at different storage periods: 1 month-1 year (20 eyes) and 7-9 years (12 eyes). Two eyes were used as controls. Microbiologic study included direct (blood, McConkey, and Sabouraud agars) and enrichment (brain-heart infusion broth) cultures. Cryopreservation artifacts were evaluated by hematoxylin-eosin. Corneoscleral collagen organization and number of normal and dead keratocytes were established by transmission electron microscopy.

RESULTS

All microbiologic direct cultures were negative. Enrichment cultures were positive in 12.5% of corneal and 59.4% of scleral tissues (p_cornea  = 0.136; p_sclera  = 1.000). Cryopreservation artifacts were most commonly observed in LTC tissues (P = 0.002). Normal keratocytes were predominant in STC corneas (STC 60% and LTC 0%) and apoptotic ones in LTC (STC 40% and LTC 90%), whereas necrotic keratocytes were only seen in LTC (LTC 10%) (P = 0.001). No structural differences were detected in collagen organization between STC and LTC (p_cornea  = 1.000; p_sclera  = 0.703).

CONCLUSIONS

Cryopreservation of equine corneoscleral tissue did not yield direct bacterial contamination. Apoptosis is the main cause of death of cryopreserved equine keratocytes. Based on the lack of significant structural differences between STC and LTC samples, these cryopreserved tissues could potentially be used for tectonic support for at least 9 years without structural or microbiological impediment.

Cryopreservation (-20 °C) of canine corneoscleral tissue: histological, microbiological, and ultrastructural study

OBJECTIVE

To evaluate microbiological, histological, and ultrastructural characteristics of short-term cryopreserved (STC) canine corneoscleral tissue (<1 year) and to compare it with long-term cryopreserved (LTC) tissue (>6 years).

ANIMALS STUDIED

Thirty-six healthy canine globes.

PROCEDURE

After a decontamination protocol, globes were enucleated and stored at -20 °C. Corneoscleral tissue was evaluated at different periods: <1 year (20 eyes) and >6 years (12 eyes). Four eyes were used as controls. Microbiologic study included direct (blood, McConkey and Sabouraud agars) and enrichment (brain-heart infusion broth) cultures. Cryopreservation artifacts were evaluated by hematoxylin-eosin. Corneoscleral collagen organization and number of normal and dead keratocytes were established by transmission electron microscopy (TEM). Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was also used for keratocyte characterization.

RESULTS

Corneal microbial growth was observed in 25% of the direct STC cultures, and in 47.4% and 16.7% of the enriched STC and LTC cultures, respectively. Scleral STC direct cultures were 30% positive, while enrichment cultures were positive in 66.7% and 16.7% of the STC and LTC, respectively (P = 0.011). Cryopreservation artifacts were higher in LTC tissues (P < 0.001). Apoptotic keratocytes were predominant by TEM and TUNEL, in both STC and LTC. Minimal structural differences were detected in collagen organization between STC and LTC.

CONCLUSIONS

Cryopreservation of canine corneoscleral tissue seems to reduce bacterial contamination over time. Apoptosis is the main way of death of cryopreserved canine keratocytes. Based on the lack of significant structural differences between STC and LTC samples, these cryopreserved tissues could potentially be used for tectonic support for at least 8 years without structural or microbiological impediment.

Cryopreservation (-20 °C) of feline corneoscleral tissue: histologic, microbiologic, and ultrastructural study

OBJECTIVE

To evaluate microbiological, histologic, and ultrastructural characteristics of short-term cryopreserved (STC) feline corneoscleral tissue (<1 year) and to compare it with long-term cryopreserved (LTC) tissue (>7 years).

ANIMALS STUDIED

Twenty healthy feline globes were obtained from 2003 to 2013.

PROCEDURE

After a decontamination protocol, globes were enucleated and stored at -20 °C in broad-spectrum antibiotics. Corneoscleral tissue was evaluated at different storage periods: <1 year (10 eyes) and >7 years (8 eyes). Two eyes were used as controls. Microbiologic study included direct (blood, McConkey, and Sabouraud agars) and enrichment (brain-heart infusion broth) cultures. Cryopreservation artifacts were evaluated by hematoxylin-eosin. Corneoscleral collagen organization and number of normal and dead keratocytes were established by transmission electron microscopy.

RESULTS

Although microbiologic cultures were positive only in STC [direct (20.8%); enrichment (37.5%)], significant differences between periods were only found in enrichment cultures (P = 0.006). Cryopreservation artifacts were most commonly observed in LTC tissues (P < 0.001). Normal keratocytes were predominant in STC corneas (STC 58.3%, LTC 12.5%) and apoptotic ones in LTC (STC 41.7%, LTC 75%), whereas necrotic keratocytes were only seen in LTC (LTC 12.5%) (P = 0.046). No structural differences were detected in collagen organization between STC and LTC (Pcornea = 0.147; Psclera = 0.362).

CONCLUSIONS

Cryopreservation of feline corneoscleral tissue seems to reduce bacterial contamination over time. Apoptosis is the main cause of death of cryopreserved feline keratocytes. Based on the lack of significant structural differences between STC and LTC samples, these cryopreserved tissues could potentially be used for tectonic support for at least 10 years without structural or microbiological impediment.

The combined use of surgical debulking and diode laser photocoagulation for limbal melanoma treatment: a retrospective study of 21 dogs

OBJECTIVE

To evaluate effectiveness and safety of debulking and diode laser photocoagulation (DPC) for the treatment of limbal melanoma (LM).

PROCEDURE

Retrospective multi-institutional case series. Medical records of animals diagnosed with LM at the Centro Veterinario Specialistico (CVS) and at the Long Island Veterinary Specialists from 1994 to 2014 were retrieved. Signalment, location, extent of tumors, recurrence rate, and early and late complications were reported. Patient follow-up information was obtained from veterinary ophthalmologists, primary care veterinarians, and where appropriate, owners.

RESULTS

Twenty-one eyes of 21 dogs (13 females and 8 males) were included in this study. The dogs' average age was 6 years (range: 7 months-11 years). The follow-up period ranged from 1-108 months (median 48 months) after the last DPC procedure. Long-term follow-up was obtained by telephone interviews in 6 of 20 cases and by clinical re-evaluations in 14 of 20 cases. The most common early complications were a moderate anterior uveitis and peripheral corneal edema (21/21 eyes). Late complications included corneal fibrosis and/or pigmentation (20/21). In one case, a severe bullous keratopathy associated with extensive corneal fibrosis was observed (1/21). One case was blind due to concurrent Sudden Acquired Retinal Degeneration (SARD). However, after surgery 2 of 20 eyes lost vision and one of these was enucleated.

CONCLUSIONS

Debulking, in addition to diode laser photocoagulation, was technically straightforward to perform, minimally invasive, well tolerated, and highly successful in this case series.

Melanocytic Ophthalmic Neoplasms of the Domestic Veterinary Species: A Review

Melanocytic neoplasms in veterinary species occur in various ophthalmic locations including the eyelid, conjunctiva, cornea, sclera, anterior and posterior uvea, and orbit. Histology usually provides the definitive diagnosis for melanocytic ocular neoplasias. The degree of tissue invasiveness and anaplastic cellular characteristics are more reliable indicators of biological behavior than is mitotic index in most ophthalmic melanocytic tumors. Melanocytic neoplasias of the eyelid are predominantly benign in canines and equines, though in felines, there is the potential for metastasis, especially if the conjunctiva is involved. Limbal melanocytic tumors are predominantly benign in all the studied species, though there is a bimodal occurrence with this tumor type in canines, where those that appear in dogs younger than 4 years tended toward active growth, whereas those that appear in dogs older than 8 years tended to progress more slowly, and may not require therapy. The most common location for melanocytic ocular neoplasias in both canines and felines is the anterior uvea. Feline diffuse iris melanoma in particular has a higher incidence of metastasis than does canine nodular anterior uveal melanocytoma. In contrast, posterior uveal melanocytic tumors are rare in both canine and feline species and are considered benign. Orbital melanoma is rare in both canine and feline species; however, it generally carries a grave prognosis owing to its malignant nature. Knowledge of the general biological behavior and its variability among locations within the eye and between species is essential in therapeutic planning.

Penetrating sclerokeratoplasty and autologous pinnal cartilage and conjunctival grafting to treat a large limbal melanoma in a dog

A four-year-old neutered male Labrador retriever presented to Portland Veterinary Specialists Ophthalmology Service for evaluation of a pigmented mass oculus sinister (OS) of approximately 4-month duration. Complete ophthalmic examination revealed a large, pigmented, raised, well-demarcated, epibulbar mass appearing to originate from the nasodorsal limbal region. The mass was smooth and roughly circular, extending approximately 4 mm into the sclera and 14 mm into the nasodorsal cornea. Gonioscopy directly under the mass was not possible due to mass size. The visible iridocorneal angle was normal. High-resolution B-scan ultrasound showed mass extension to Descemet's membrane and deep sclera, but no intraocular invasion. Penetrating sclerokeratoplasty was performed followed by autologous pinnal cartilage and conjunctival grafting to repair the corneoscleral defect (20 mm x 19 mm) and to restore globe integrity and function. Histopathology confirmed the mass to be a benign limbal melanoma with complete excision. The surgery site healed without complication, and the pinnal cartilage became fully incorporated into the globe. Twelve months postoperatively, the patient remains visual with a normal intraocular and fundic examination. The pinnal harvest site on the right ear healed without complication. To the authors' knowledge, this is the first reported case of corneoscleral grafting using autologous pinnal cartilage. This may represent a viable alternative to other corneoscleral grafting procedures for large defects and is an attractive treatment option due to lack of host rejection, readily available source of donor cartilage, and provision of tectonic support to the globe.