This paper aimed to report the clinical evaluation after the use of a new α-tricalcium phosphate bone cement as an implant for re-establishing the ocular volume after evisceration.

The spheres used in this work were molded from a α-tricalcium phosphate bone cement consisting of a powder composed by a α-tricalcium phosphate (α-TCP) and an aqueous solution of Na<sub>2<sub>HPO<sub>4<sub> as mixing liquid. An in situ polymerization system based on acrylamide and ammonium polyacrylate as liquid reducer was added to α-TCP cement to increase its mechanical strength. After mixing powder and liquid, α-TCP dissolves into the liquid and calcium deficient hydroxyapatite (CDHA) precipitates as an entanglement of crystals, which causes the setting and hardening of the cement. First case: an 8-year-old female Cocker spaniel presented a lens incarcerated in the pupil after anterior luxation. The animal was medicated in order to control the uveitis and secondary glaucoma. Despite the therapy, the intra-ocular pressure remained in a range from 30 to 45 mmHg, with mild buphthalmia and occasional signs of discomfort and pain. Second case: a 7-year-old female cat was presented with uveitis and secondary chronic glaucoma. The animal was initially topically medicated for inflammation and intra-ocular pressure control. Prior to the surgery, both animals had the contralateral cornea's horizontal diameter measured with a metric caliper and a sterile hydroxyapatite implant of the same diameter (dog) and 1mm smaller (cat) were selected. After routine preparation and draping of the eyes for intra-ocular surgery, a lateral canthotomy was performed in both animals. A 5mm, 1200 long, limbal-based flap of bulbar conjunctiva were prepared. The scleras were incised 5-6mm beyond and parallel to the limbus. The incisions were then enlarged with scissors. Eviscerations were performed with a spatula and an evisceration spoon. The remaining uvea and retina were removed with a conjunctival forceps. In the cat, the sphere introducer was carefully placed through the incision site and the sphere was slowly injected into the globe. In the dog, the scleral incision was 2 mm larger than the diameter of the implant, so it was manually inserted. The scleral and conjunctival incisions were individually closed with vicryl® sutures in a continuous pattern. The lateral canthotomies were repaired with simple-interrupted, maxon® sutures. After that a third eyelid flap were performed in both animals for corneal protection.

Aftercare included topical and systemic antibiotics and NSAIDS and subcutaneous buprenorphine injections for 5 days. The canthorrhaphy sutures and the third eyelid flap were removed 10 days post operatively (PO). A 360-degree-deep corneal neovascularization was observed after 2 to 4 weeks PO, which diminished over the following 4 weeks, leaving a satisfactory result. Further evaluations were made at 3 months PO for the dog and 8 months PO for the cat. The dog showed no signs of discomfort, discrete corneal neovascularization and a small almond of pigmentation. The cat presented an opaque cornea with a moderate deep neovascularization with pigment almost entirely covering the implant and providing a much better cosmetic appearance.

The intraocular synthetic CDHA implant provided excellent results in both animals, being an alternative for enucleation or intra-ocular pressure reducing procedures on blind glaucomatous eyes. The only encountered disadvantage was the need of a 15 days course postoperative therapy for controlling the inflammatory response.

The authors would like to thank CNPq for the scholarship provided.

Reference

1.  Dos Santos LA et al. Alpha-tricalcium phosphate cement "in vitro" cytotoxicity. Biomaterials 2002 23(9): 2035-42.