Canine glaucoma is often an aggressive disease process. There are several dog breeds commonly seen in veterinary practice for glaucoma, including the cocker spaniel, Boston terrier, bassett hound, Labrador, Siberian husky, chow chow, French bulldog, and shiba inu (due to goniodysgenesis). Other breeds, as well as mixed-breed dogs, can also present with the disease. Medical therapy may work initially, but then ultimately fail, leading to ocular pain, lethargy, and blindness. Surgical procedures for canine glaucoma have evolved tremendously throughout the years. Surgical interventions may be considered for long-term intraocular pressure (IOP) control and vision preservation. Gonioimplants (tube shunts for pressure control) are performed in dogs but are not consistently successful. The efficacy of a gonioimplant lasts longer in humans than in dogs. Valved implants can fail by occlusion of the tube shunt or scarring of the footplate device.1,2 Alternatively, cyclodestructive techniques (lasering of the ciliary body), such as endocyclophotocoagulation (ECP), are commonly performed in humans and dogs to prolong IOP control and vision preservation.3 Endocyclophotocoagulation is a cyclodestructive procedure that photocoagulates the ciliary body processes to reduce aqueous humor production and subsequently decrease the IOP. Intraoperative physical changes are noted as whitening of the laser-treated ciliary processes (Figure 1). Figure 1. Color schematic representation of the physical changes seen intra-operatively. Whitening of the ciliary processes following argon laser treatment is noted. Photo courtesy BVI Medical There are two surgical approaches to gain access to the ciliary processes: 1) Anterior approach. This is performed through a corneal limbal incision, which can be achieved in phakic, aphakic, and pseudophakic eyes. There are some limitations to the anterior approach. The shape and pressure of the eye must be maintained by viscoelastic substances. Also, visualization can be cumbersome due to variable IOP in the eye. Using the anterior approach, it is not possible to visualize 360 degrees of the ciliary body, which can ultimately result in an inadequate IOP drop or the need for a repeat surgery. In the author’s opinion, the anterior approach results in greater postoperative inflammation due to iris chafing and the placement of the probe in the anterior chamber. Additional inflammation can arise from the multidirectional forces required through a limbal-based incision and unnecessary manipulation of the eye. 2) Pars plana approach. By comparison, the pars plana approach involves inserting a laser endoscope through a fixed scleral port into the pars plana, enabling direct visualization of the ciliary processes for photocoagulation in pseudophakic or aphakic eyes. The endoscope has a camera, a light source, and a laser (Figure 2). The pars plana is considered the safest entry point for eye surgery because it lacks critical blood vessels and sensory retina. Using the safe gateway of the pars plana, a smooth flat band is wide enough to accommodate the endoscope sitting between the iris and retina. The profound advantage of a pars plana approach is the greatly enhanced visualization of the ciliary processes (Figure 3). Figure 2. The endoscope has a combined camera, light source, and laser to facilitate visualization, illumination, and treatment. Photo courtesy BVI Medical Figure 3. Intraoperative endoscopic view seen from a monitor. Note the treated (white) and untreated (brown) ciliary processes. The red light is the defocused aiming beam of the argon laser. Photo courtesy Dr. Allison Hoffman The endoscope can also be placed through each of the three ports, providing maximal visualization and a 360-degree view. This provides a more thorough treatment, especially in aggressive cases of glaucoma notoriously found in dogs. This technique is also quite effective in human patients whose IOP reduction has been refractory despite prior glaucoma surgeries.4 In a human study with a two-year follow-up, pars plana ECP combined with phacoemulsification and IOL placement achieved superior IOP control, and patients were maintained on fewer glaucoma medications compared to those that underwent an anterior ECP approach.5 Kaminsky and Hoffman published a case report of pars plana ECP for the treatment of refractory glaucoma in a canine patient. Successful IOP control with vision preservation was achieved in a dog that previously underwent phacoemulsification and failed goniovalve implantation in both eyes.6 The surgical procedure: Pars plana endocyclophotoablation A Barraquer eyelid speculum is positioned, and limbal stay sutures are placed with 6-0 polyglactin 910 at 3 and 9 o’clock positions. A small conjunctivectomy is performed over the sclerotomy sites, using blunt Wescott scissors. Bipolar cautery is used to gently coagulate the intrascleral venous plexus in preparation for three-port sclerotomy sites and valved cannula placement. An inferolateral stab incision is made through the pars plana 6 mm posterior to the limbus using a 23-gauge trocar and valved cannula one-step device. An infusion of balanced salt solution (BSS) is placed, and IOP control is fixed at the vitreoretinal console at 30 mmHg to maintain the shape of the globe for intraocular surgery. With the constant infusion in place, there are no viscoelastic substances needed to maintain the eye pressure. The same technique is used to place 23-gauge valved cannulas to house other 23-gauge instruments if needed, but foremost for the endoscope, superolaterally and superomedially. The three-valved cannulas will then facilitate entry, exit, and rotation of instrumentation throughout the procedure (Figure 4). Figure 4. The three-valved cannulas will facilitate entry, exit, and rotation of instrumentation throughout the procedure. Note the endoscope in the superotemporal port and infusion line ventrotemporally. Photo courtesy Dr. Allison Hoffman Patients that have had previous cataract surgery can occasionally present with white fibrinous webs that can obstruct visualization of the ciliary processes. These can be easily removed by a vitrectomy probe, which will maximize a clear view. Additionally, traction bands from a fibrinous uveitis that led to the glaucoma can be easily removed by the vitrector. An ophthalmic endoscopy system (Figure 5) with an external argon laser is used. A 23-gauge straight endoscope is inserted and alternated among all three valved cannulas to achieve 360-degree cyclophotocoagulation of the ciliary processes. The power setting ranges from 90 to 150 mW, with a continuous duration (ms) to treat the entire ciliary processes (head, tails, and valleys) until shrinkage and whitening occur, indicating effective photocoagulation. Figure 5. An ophthalmic endoscopy system (E4 console; Endo Optiks Inc., Waltham, MA, USA) with an external argon laser is used for pars plana ECP. Photo courtesy BVI Medical If indicated by the surgeon, a laser retinopexy is performed upon completion of the ECP to decrease the possibility of retinal detachment. This can be done for those predisposed breeds or when a small retinal tear is noted. Prior to closure, silicone oil can be infused into the eye. Silicone oil can act as an emollient on the acutely lasered ciliary processes, which reduces the post-operative inflammation. The presence of these three working ports in the posterior segment of the eye offers flexibility for additional interventions when indicated and to tailor treatment to the individual patient. The infusion and working ports are closed with a single cruciate suture using 6-0 polyglactin 910. The bulbar conjunctiva is closed with a single cruciate suture using 7-0 polyglactin 910. Patients are maintained on glaucoma medications until a successful reduction in the IOP is noted. Typically, patients will show a stable reduction in IOP by 10-14 days postoperatively. While there is only one published case report of ECP by the pars plana approach in a canine patient as of writing, a larger-scale study of 50 dogs will be presented at the annual ACVO Conference in October 2026. A study in humans observed an IOP decrease of 61-66 percent with a pars plana approach after being refractory to other glaucoma surgical interventions, compared to those who had an anterior ECP with an IOP decrease of approximately 31 percent.5 An abstract by Lutz et al. presented at the 2013 American College of Veterinary Ophthalmologists conference reported a success rate of 80 percent in IOP reduction and 70 percent in vision preservation at one-year following ECP by an anterior approach for primary and secondary glaucoma in canine patients.7 Complications of ECP by the anterior approach include intraocular inflammation with or without fibrin, cataract formation from lens touch, uncontrolled IOP, corneal ulceration, corneal edema, and phthisis bulbi. Similarly, these complications can also occur with the pars plana approach. The author believes postoperative uveitis is less likely with the posterior segment approach. The corneal edema is minimized with the posterior segment approach, as there is neither a perilimbal incision nor corneal endothelial disruption. An advantage of the pars plana approach includes enhanced direct visualization and 360-degree access to perform cyclophotocoagulation more effectively with less energy required, thereby reducing the risk of postoperative inflammation. A disadvantage of the pars plana approach is the need for additional surgical steps before endoscope placement; however, because eye pressure is static, the view is improved, which will speed up surgical cyclophotoablation time. Another disadvantage is that more equipment and a more advanced skill set are required. Pars plana ECP may benefit canine patients with glaucoma refractory to medical therapy, dogs predisposed to glaucoma, or cataract candidates with a glaucoma risk. Pars plana ECP can be considered as a first-line surgical treatment for dogs undergoing cataract surgery that are predisposed to glaucoma (goniodysgenic) or those dogs that have a history of glaucoma in the fellow eye. Higher success is achieved in patients that have had the fewest number of pressure spikes and the fewest episodes of vision loss. Good candidates are dogs developing a modest rise in pressure while still maintaining vision. The goal of surgery is vision preservation with minimal or no indication for post-operative glaucoma medication. Allison Hoffman, DVM, DACVO, is a board-certified veterinary ophthalmologist and vitreoretinal surgeon at Eye Care for Animals in Pasadena, Calif. She is a diplomate of the American College of Veterinary Ophthalmologists (ACVO) and a member of the Phi Zeta Veterinary Honor Society. Dr. Hoffman has advanced expertise in cataract surgery, combined retinal reattachment procedures, and pars plana endocyclophotoablation for glaucoma. She is the only veterinary ophthalmologist to complete a vitreoretinal surgery fellowship and is one of only three veterinarians worldwide elected to membership in the American Society of Retinal Specialists. References Saito A, Kazama Y, Iwashita H, et al. Outcome of anterior chamber shunt procedure in 104 eyes of dogs (abstract). 48th Annual Conference of the American College of Veterinary Ophthalmologists. 2017;41. Westermeyer HD, Hendrix DV, Ward DA. Long-term evaluation of the use of Ahmed gonioimplants in dogs with primary glaucoma: nine cases (2000-2008). J Am Vet Med Assoc. 2011;238(5):610-617. doi:10.2460/javma.238.5.610 Sosnowik S, Webb T, Bras D, Hartrum B, Micceri D. Retrospective evaluation of surgical outcomes in canine patients with primary and secondary glaucoma following diode endoscopic cyclophotocoagulation. Veterinary Ophthalmology. 2025 Mar;28(2):225–242. doi: 10.1111/vop.13176. Epub 2024 Jan 8 Tan JC, Francis BA, Noecker R, Uram M, Dustin L, Chopra V. Endoscopic Cyclophotocoagulation and Pars Plana Ablation (ECP-plus) to Treat Refractory Glaucoma. J Glaucoma. 2016;25(3):e117-e122. doi:10.1097/IJG.0000000000000278 Feinstein MA, Lee JH, Amoozgar B, et al. Comparison between pars plana and anterior endoscopic cyclophotocoagulation for the treatment of glaucoma. Clin Exp Ophthalmol. 2019;47(6):766-773. doi:10.1111/ceo.13501 Kaminsky M, Hoffman A, Konrade K. Endocyclophotocoagulation by pars plana approach in the management of refractory glaucoma with prior phacoemulsification and Ahmed gonioimplantation in a dog. Vet Ophthalmologists Nov 2022. doi.org/10.1111/vop.13036 Lutz EA, Webb TE, Bras ID, et al. Diode endoscopic cyclophotocoagulation in dogs with primary and secondary glaucoma: 292 cases (2004-2013). Vet Ophthalmol 2013;16(6):40.
