Gonioimplantation in Cats

Gonioimplantation in cats is a surgical procedure used to aid in relieving pressure within the eye caused by fluid buildup commonly associated with glaucoma. The term glaucoma is used when describing an increased amount of pressure within the eye, termed intraocular pressure or IOP, to the point where the eye loses complete functionality. In a gonioimplantation procedure, a tube-like device called a gonio implant is introduced into the feline’s eye to drain the aqueous fluid from the eye. The outcome the veterinary ophthalmologist will work to gain is the ability to drain the fluid from the eye out, retaining visual acuity to the feline. 

Intraocular pressure will be measured prior to conducting the gonioimplantation surgical procedure. The feline will receive a preoperative fluids of a dextrose-saline solution at a formula fixated by the veterinarian before initiating anesthesia. A preoperative antibiotic of the veterinarian’s choice, like Cefazolin, will be administered intravenously at an mg/kg formulation. An induction anesthetic, such as Propofol, will be administered before the feline is taken to the surgical area. 

1. The sedated patient will be positioned in lateral recumbency, with the affected eye facing upward. 
2. General anesthesia will begin, likely through tube oxygen administration. The esophageal tube will be placed prior to gas anesthetic. 
3. The upper eyelid cilia will be trimmed with delicate scissors. 
4. The preocular area will be cleansed with a sterile saline using gauze sponges. 
5. Povidine-iodine solution of a 1.25% value will be used to disinfect the conjunctival sac. 
6. Ethyl alcohol will be used to clean the remaining operative site.
7. The patient will be draped to provide a sterile surgical operative field. 
8. A conjunctival-Tenon’s capsule incision will be made parallel to the limbus in the superotemporal quadrant. The incision will continue down to the sclera and extend to the limbus, between the extraocular muscle to form the subconjunctival-Tenon’s capsule pocket. 
9. The newly created pocket will be irrigated with 45 ml of 0.9% normal saline. 
10. The gonio implant will be primed with the same 0.9% normal saline solution.
11. The implant is then anchored to the sclera with 8-0 monofilament Polyamide suture. The sutures will be placed 8mm posterior to the limbus. 
12. A 23-gauge needle will be entered into the anterior chamber of the eye to form a tunnel, where the gonio implant tube will be inserted. 
13. Once proper placement is obtained, the tip of the implant will be trimmed to size. 
14. The tube will be secured with a thick scleral flap to the limbus base, closing the capsule with a simple suture using 7-0 polyglactin. 

Gonioimplantation for cats is a highly successful procedure with benefits that take place immediately. However, placement of a gonio implant is not a permanent solution for intraocular pressure caused by fluid buildup glaucoma. The body will naturally form scar tissues surrounding the implant, approximately six months to a year following surgery. The newly formed tissues will block the regulation value of the gonio implant and fluid will not be allowed to escape from the globe of the eye. The gonioimplantation procedure will then need to be repeated or an alternative treatment plan will be put in place.

An Elizabethan collar will be sent home with the patient to reduce postoperative self-trauma. Anti-glaucoma drugs, such as dorzolamide and latanoprost, will continue in the form of drops. An anti-inflammatory drug, also in the form of drops, will likely be prescribed for the feline. The use of anti-glaucoma and anti-inflammatory drugs will continue for approximately two weeks.

The cost of a gonioimplantation surgical procedure for a feline can typically run from $600 to $1,000 on average. Costs can fluctuate depending on the feline’s overall state, surgical history, and the nature of the feline’s glaucoma. Aftercare medications and trauma prevention gear should also be considered. A follow-up after the surgery is to be expected to ensure the device is working properly.

Gonioimplantation in cats poses a risk for infection and inflammation if antibiotics are not properly used. Although rare, the gonio implant can shift out of place, causing discomfort and lost vision for the feline.

Glaucoma is classified into two categories; primary glaucoma and secondary glaucoma. Primary glaucoma is a hereditary condition that is caused by an abnormality in the felines DNA and cannot be prevented. Secondary glaucoma is essentially a complication of another eye disease. To prevent secondary glaucoma, routine veterinary consultation is key as early detection of eye conditions are important for a positive diagnosis.