Evisceration and Intraocular Prosthesis

Evisceration with intraocular prosthesis is a surgical procedure in veterinary ophthalmology that involves the removal of the intraocular contents (uvea, retina, lens, and vitreous) while preserving the scleral shell, cornea, and extraocular muscles. A silicone or acrylic prosthesis is then implanted within the scleral cavity to maintain ocular volume, cosmetic appearance, and orbital support. This procedure is primarily indicated for blind, painful eyes that are not amenable to medical therapy or other surgical interventions, such as end-stage glaucoma, severe ocular trauma, or chronic uveitis. The goal is to alleviate pain, eliminate the source of inflammation or infection, and provide a cosmetically acceptable result while avoiding the more extensive removal of the eye (enucleation) and its associated orbital changes. The procedure is distinct from enucleation (removal of the entire globe) and exenteration (removal of the globe and all orbital contents). Evisceration with prosthesis offers the advantage of preserving the scleral shell, which supports the prosthesis and maintains normal eyelid and orbital anatomy, resulting in superior cosmetic outcomes and reduced orbital sinking. The procedure is commonly performed in dogs and cats, with variations in technique and prosthesis selection based on species, orbital size, and surgeon preference.

The primary etiologies necessitating evisceration with intraocular prosthesis include: 1) End-stage glaucoma refractory to medical and surgical management, where irreversible blindness and chronic pain are present. Glaucoma may be primary (e.g., goniodysgenesis in certain breeds) or secondary to lens luxation, uveitis, intraocular neoplasia, or trauma. 2) Severe ocular trauma resulting in irreparable damage to the intraocular structures, such as penetrating wounds, rupture, or phthisis bulbi. 3) Chronic, non-responsive uveitis leading to phthisis bulbi or secondary glaucoma. 4) Intraocular neoplasia, particularly diffuse iridal melanoma in cats, where the tumor is confined to the uveal tract and metastasis has not occurred. 5) Severe corneal disease with descemetocele or perforation, where the eye is blind and painful. 6) Congenital anomalies, such as microphthalmia or anophthalmia, where prosthetic implantation may be considered for cosmetic reasons, though this is less common. 7) Iatrogenic causes, such as complications from previous intraocular surgery (e.g., cataract extraction) leading to phthisis or chronic pain. The decision to perform evisceration is based on the irreversibility of blindness, the presence of intractable pain, and the owner's desire for a cosmetic outcome.

Evisceration with intraocular prosthesis is most commonly performed in dogs and cats. In dogs, breeds predisposed to primary glaucoma include the American Cocker Spaniel, Basset Hound, Chow Chow, Shar-Pei, Siberian Husky, and Samoyed. These breeds often present with acute or chronic glaucoma that may progress to end-stage disease. In cats, the most common indication is diffuse iridal melanoma, which occurs more frequently in older cats (mean age 9-12 years) and may be seen in any breed, though domestic shorthairs are overrepresented. Trauma-related evisceration is more common in young, active animals, particularly working dogs or those with outdoor access. There is no significant sex predilection, though some studies suggest a slight male predominance in traumatic cases. The procedure is less commonly performed in exotic pets, but has been reported in rabbits and birds. The incidence of evisceration is lower than enucleation, as many veterinarians prefer enucleation for simplicity and to avoid the risk of prosthesis extrusion. However, with increasing owner demand for cosmetic outcomes, the procedure is gaining popularity. The success rate is high, with reported prosthesis retention rates of 90-95% in dogs and cats when performed by experienced surgeons.

The pathophysiology underlying the need for evisceration involves irreversible damage to the intraocular structures, leading to loss of vision and chronic pain. In glaucoma, elevated intraocular pressure (IOP) results from impaired aqueous humor outflow, causing mechanical damage to the retinal ganglion cells and optic nerve head. This leads to progressive retinal degeneration and optic nerve atrophy, culminating in irreversible blindness. The elevated IOP also stimulates nociceptors in the cornea, uvea, and sclera, causing severe pain. In chronic uveitis, inflammatory mediators (cytokines, prostaglandins) disrupt the blood-aqueous barrier, leading to protein exudation, synechiae formation, and secondary glaucoma. The inflammatory process can also cause phthisis bulbi, where the eye shrinks due to ciliary body dysfunction and hypotony. In ocular trauma, direct mechanical injury to the lens, uvea, retina, and vitreous results in hemorrhage, inflammation, and retinal detachment. The release of lens proteins can trigger a phacoclastic uveitis, further exacerbating inflammation. In intraocular neoplasia, tumor growth within the uveal tract can cause secondary glaucoma, retinal detachment, and chronic inflammation. The tumor may also invade the scleral emissaria, increasing the risk of metastasis. Evisceration removes the diseased intraocular contents, eliminating the source of pain and inflammation, while preserving the scleral shell to maintain orbital anatomy. The prosthesis provides structural support, preventing enophthalmos and orbital sinking, and maintains a cosmetically acceptable appearance.

Predisposing factors for conditions leading to evisceration include: 1) Breed-specific genetic predisposition to primary glaucoma, such as goniodysgenesis in American Cocker Spaniels, Basset Hounds, and other breeds. 2) Age: older animals are more prone to intraocular neoplasia (e.g., feline diffuse iridal melanoma) and chronic uveitis. 3) Sex: no significant predilection, though some studies suggest males are more prone to trauma. 4) Ocular trauma: animals with outdoor access, working dogs, or those involved in fights are at higher risk. 5) Previous intraocular surgery: cataract extraction or lens luxation surgery can lead to complications such as glaucoma or phthisis. 6) Systemic diseases: systemic hypertension, diabetes mellitus, or hyperadrenocorticism can predispose to intraocular hemorrhage or uveitis. 7) Chronic topical corticosteroid use: can exacerbate glaucoma or lead to corneal complications. 8) Anatomical factors: brachycephalic breeds have shallower orbits and are more prone to proptosis, which can lead to severe trauma. 9) Owner factors: financial constraints may delay treatment, allowing progression to end-stage disease. 10) Failure of medical management: inadequate control of IOP or inflammation can accelerate the need for surgical intervention.

Clinical signs associated with conditions requiring evisceration include: 1) Ocular pain: manifested as blepharospasm, epiphora, photophobia, and rubbing or pawing at the eye. 2) Buphthalmos: enlargement of the globe due to elevated IOP in glaucoma. 3) Corneal changes: edema, vascularization, pigmentation, or ulceration. 4) Mydriasis: fixed, dilated pupil due to retinal and optic nerve damage. 5) Loss of vision: assessed by menace response, dazzle reflex, and pupillary light reflex (PLR). 6) Conjunctival hyperemia and episcleral congestion. 7) Lens changes: luxation or cataract. 8) Intraocular hemorrhage: hyphema or vitreous hemorrhage. 9) Uveitis: aqueous flare, miosis, and low IOP. 10) Phthisis bulbi: shrunken, non-functional eye. 11) Orbital signs: in cases of trauma, proptosis or enophthalmos may be present. 12) Systemic signs: lethargy, anorexia, or fever if there is concurrent infection or severe inflammation. The presence of these signs, combined with diagnostic findings, indicates irreversible damage and the need for surgical intervention.

Differential diagnoses for conditions that may require evisceration include: 1) Enucleation: removal of the entire globe, indicated when there is intraocular neoplasia with scleral invasion, severe panophthalmitis, or when the eye is non-viable and cosmetic outcome is less critical. 2) Exenteration: removal of the globe and all orbital contents, reserved for extensive orbital neoplasia or severe orbital trauma. 3) Phthisis bulbi: a shrunken, non-functional eye that may be left in place if not painful, but can be treated with evisceration and prosthesis for cosmetic reasons. 4) Chronic uveitis: may be managed medically, but if refractory and painful, evisceration may be considered. 5) Glaucoma: medical management with topical beta-blockers, carbonic anhydrase inhibitors, or surgical procedures such as cyclophotocoagulation or drainage implants may be attempted before evisceration. 6) Intraocular neoplasia: if confined to the uvea, evisceration may be an option, but enucleation is often preferred to ensure complete excision. 7) Corneal perforation: may be repaired with a conjunctival graft, but if the eye is blind and painful, evisceration is an option. 8) Severe ocular trauma: if the globe is ruptured and non-repairable, evisceration or enucleation is indicated. 9) Lens luxation: may be treated with lens removal, but if secondary glaucoma is end-stage, evisceration may be necessary. 10) Orbital cellulitis or abscess: may cause proptosis or secondary glaucoma, but primary treatment is medical or surgical drainage, not evisceration.

The diagnostic algorithm for a patient considered for evisceration with intraocular prosthesis includes: 1) Complete ophthalmic examination: assess vision (menace, dazzle, PLR), IOP via tonometry, slit-lamp biomicroscopy, and indirect ophthalmoscopy. 2) Schirmer tear test to evaluate tear production. 3) Fluorescein staining to rule out corneal ulcers. 4) Ocular ultrasound if the media are opaque (e.g., cataract, hyphema) to evaluate the posterior segment and rule out intraocular masses or retinal detachment. 5) Electroretinography (ERG) to assess retinal function if vision is questionable; a negative ERG indicates irreversible blindness. 6) Systemic blood work (CBC, biochemistry, urinalysis) to rule out systemic disease, especially if neoplasia is suspected. 7) Thoracic radiographs or CT if intraocular neoplasia is suspected to check for metastasis. 8) Fine-needle aspiration of the anterior chamber or vitreous if neoplasia or infection is suspected, though this is rarely performed due to risk. 9) Biopsy of the iris or ciliary body if a mass is visible. 10) Consideration of owner's expectations and financial constraints. The decision to proceed with evisceration is based on confirmed irreversible blindness, intractable pain, and the absence of intraocular neoplasia with high metastatic potential (in which case enucleation is preferred).

Laboratory findings in patients undergoing evisceration are typically unremarkable unless there is an underlying systemic disease. Complete blood count (CBC) may show leukocytosis or neutrophilia in cases of severe intraocular infection or panophthalmitis. Serum biochemistry may reveal elevated globulins in chronic inflammatory conditions. In cases of suspected neoplasia, serum protein electrophoresis may show a monoclonal gammopathy, though this is rare. Coagulation profile (PT, aPTT, platelet count) is recommended to assess surgical risk, especially if there is a history of bleeding disorders. In cats with diffuse iridal melanoma, thoracic radiographs and abdominal ultrasound are recommended to rule out metastasis, though laboratory findings are usually normal. Intraocular fluid analysis (aqueous humor or vitreous) may be performed if there is suspicion of infection or neoplasia, but is rarely indicated. Cytology of the fluid may show inflammatory cells, neoplastic cells, or infectious organisms. Histopathology of the eviscerated contents is always recommended to confirm the diagnosis and rule out neoplasia, especially in cats with iridal melanoma.

Imaging plays a crucial role in the preoperative evaluation of patients for evisceration. Ocular ultrasound is the most commonly used imaging modality, especially when the ocular media are opaque. It can assess the posterior segment for retinal detachment, intraocular masses, lens luxation, and vitreous hemorrhage. Ultrasound can also measure the axial globe length, which is useful for selecting the appropriate prosthesis size. In cases of suspected intraocular neoplasia, high-frequency ultrasound (20-50 MHz) can provide detailed images of the uveal tract. Computed tomography (CT) or magnetic resonance imaging (MRI) may be indicated if there is suspicion of orbital extension or if the globe is severely traumatized. CT is excellent for evaluating bony orbital structures and detecting foreign bodies, while MRI provides superior soft tissue contrast and is useful for assessing the optic nerve and extraocular muscles. In cases of trauma, CT can identify fractures or orbital emphysema. For suspected metastatic disease, thoracic radiographs or CT of the thorax is recommended. Fluoroscopy is rarely used in ocular surgery but may be employed for guided injections. Overall, imaging is essential for confirming the diagnosis, ruling out neoplasia, and planning the surgical approach.

Cytology and histopathology are critical for confirming the underlying disease and ruling out neoplasia. Fine-needle aspiration of the anterior chamber or vitreous may be performed if there is a visible mass or if infection is suspected. Cytology of aqueous humor may show inflammatory cells (neutrophils, lymphocytes, macrophages) in uveitis, or neoplastic cells in cases of lymphoma or melanoma. However, aspiration carries a risk of hemorrhage or lens damage and is rarely performed. Histopathology of the eviscerated intraocular contents is always recommended. The tissue should be submitted in 10% neutral buffered formalin. Histological examination can confirm the presence of retinal degeneration, optic nerve atrophy, chronic uveitis, or neoplasia. In feline diffuse iridal melanoma, histopathology reveals infiltration of the uveal tract by melanocytes with variable atypia and mitotic activity. The presence of scleral invasion or extrascleral extension is a poor prognostic indicator. In cases of glaucoma, histopathology may show retinal ganglion cell loss, optic nerve cupping, and trabecular meshwork degeneration. Histopathology also helps to identify infectious agents, such as fungi or bacteria, using special stains (e.g., Gram, GMS, PAS). The results of histopathology guide postoperative management and prognosis.

The definitive treatment for conditions requiring evisceration is surgical removal of the intraocular contents and implantation of an intraocular prosthesis. Preoperative management includes systemic antibiotics (e.g., cefazolin 22 mg/kg IV at induction) and anti-inflammatory drugs (e.g., carprofen 2.2 mg/kg PO q12h or meloxicam 0.1 mg/kg PO q24h). The surgical technique involves: 1) General anesthesia with endotracheal intubation. 2) Positioning the patient in lateral recumbency with the affected eye uppermost. 3) Routine aseptic preparation of the periocular area. 4) A lateral canthotomy may be performed to improve exposure. 5) A 360-degree conjunctival peritomy is made at the limbus. 6) The extraocular muscles are identified and tagged with stay sutures to prevent retraction. 7) The sclera is incised approximately 2-3 mm posterior to the limbus using a #11 blade or a keratome. 8) The incision is extended circumferentially with scissors, taking care to avoid damaging the sclera. 9) The intraocular contents are removed using an evisceration spoon or a curette. The uveal tissue, retina, lens, and vitreous are carefully removed. 10) The scleral cavity is thoroughly curetted and irrigated with sterile saline. 11) Hemostasis is achieved with bipolar electrocautery or pressure. 12) The prosthesis is selected based on the size of the scleral cavity. Silicone prostheses are available in various sizes (e.g., 14-22 mm for dogs, 12-16 mm for cats). The prosthesis is inserted into the scleral cavity using a lubricated insertion forceps. 13) The scleral incision is closed with 4-0 to 5-0 absorbable suture (e.g., polydioxanone) in a simple continuous pattern. 14) The conjunctiva is closed with 6-0 absorbable suture in a simple continuous pattern. 15) A temporary tarsorrhaphy may be placed to protect the eye during the immediate postoperative period. Postoperative care includes systemic antibiotics (e.g., amoxicillin-clavulanic acid 13.75 mg/kg PO q12h for 7-10 days), anti-inflammatory drugs (e.g., carprofen 2.2 mg/kg PO q12h for 5-7 days), and an Elizabethan collar to prevent self-trauma. Topical antibiotics (e.g., neomycin-polymyxin-bacitracin ophthalmic ointment q8h) may be applied to the corneal surface. The tarsorrhaphy is removed in 7-10 days. The patient should be re-examined at 2 weeks, 4 weeks, and 8 weeks postoperatively to assess healing and prosthesis position.

The prognosis for evisceration with intraocular prosthesis is generally excellent for pain relief and cosmetic outcome. Reported success rates (defined as a comfortable eye with a retained prosthesis) range from 90-95% in dogs and cats. The most common complication is prosthesis extrusion, which occurs in approximately 5-10% of cases, usually within the first few months. Risk factors for extrusion include infection, excessive tension on the scleral closure, and poor surgical technique. Other complications include corneal ulceration, conjunctival dehiscence, and orbital cellulitis. The prognosis for the underlying disease depends on the etiology. For end-stage glaucoma, the prognosis is good for pain relief, but the eye remains blind. For intraocular neoplasia, the prognosis is guarded if the tumor is malignant and has a high metastatic potential. In feline diffuse iridal melanoma, the reported metastatic rate is 10-20%, and evisceration may not be curative if the tumor has already metastasized. Therefore, histopathology is essential to guide prognosis. Overall, the procedure provides a high quality of life for the patient, with most owners reporting satisfaction with the cosmetic outcome.

Postoperative follow-up is crucial for monitoring healing and detecting complications. The patient should be re-examined at 2 weeks, 4 weeks, and 8 weeks after surgery. At each visit, a complete ophthalmic examination should be performed, including assessment of the prosthesis position, corneal health, and signs of infection or inflammation. The owner should be instructed to monitor for signs of pain, discharge, or swelling. Suture removal is typically not required as absorbable sutures are used. The temporary tarsorrhaphy, if placed, is removed at 7-10 days. The patient should be restricted from strenuous activity and prevented from rubbing the eye for at least 2 weeks. Long-term follow-up is recommended every 6-12 months to monitor for late complications such as prosthesis extrusion or corneal degeneration. In cases of neoplasia, regular monitoring for metastasis (e.g., thoracic radiographs every 3-6 months for the first year) is recommended. The owner should be advised that the eye will remain blind and that the prosthesis may shift slightly over time, but this is usually not a problem. If the prosthesis extrudes, surgical replacement or enucleation may be necessary.

Clinical pearls: 1) Preoperative ocular ultrasound is essential to measure the axial length and select the appropriate prosthesis size. 2) A lateral canthotomy improves exposure and facilitates the procedure. 3) Tagging the extraocular muscles with stay sutures prevents them from retracting into the orbit. 4) Thorough curettage of the scleral cavity is critical to remove all uveal tissue and reduce the risk of postoperative uveitis or infection. 5) The scleral incision should be made posterior to the limbus to avoid damaging the cornea. 6) Use a prosthesis that is slightly smaller than the scleral cavity to reduce tension on the closure. 7) A temporary tarsorrhaphy protects the eye during the immediate postoperative period. 8) Submit the eviscerated contents for histopathology to confirm the diagnosis and rule out neoplasia. Pitfalls: 1) Incomplete removal of intraocular contents can lead to chronic inflammation or infection. 2) Excessive tension on the scleral closure can cause dehiscence and prosthesis extrusion. 3) Failure to achieve hemostasis can lead to postoperative hemorrhage and orbital swelling. 4) Using a prosthesis that is too large can cause corneal erosion or extrusion. 5) Inadequate postoperative pain management can lead to self-trauma. 6) Not recommending histopathology can miss a malignant neoplasm. 7) Performing evisceration in cases of intraocular neoplasia with scleral invasion may lead to incomplete excision and metastasis. 8) Poor aseptic technique can result in postoperative infection.

Perioperative drug protocols are based on Plumb's Veterinary Drug Handbook. Preoperative: Cefazolin (22 mg/kg IV) at induction, repeated every 90 minutes during surgery. Alternatively, ampicillin-sulbactam (30 mg/kg IV) may be used. Postoperative antibiotics: Amoxicillin-clavulanic acid (13.75 mg/kg PO q12h) for 7-10 days. In cases of infection, culture and sensitivity should guide antibiotic selection. Anti-inflammatory drugs: Carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) for 5-7 days. For severe inflammation, a tapering dose of prednisone (0.5-1 mg/kg PO q24h) may be added. Analgesics: Opioids such as buprenorphine (0.01-0.02 mg/kg IV or IM q8-12h) or tramadol (2-5 mg/kg PO q8-12h) may be used for the first 24-48 hours. Topical antibiotics: Neomycin-polymyxin-bacitracin ophthalmic ointment (q8h) for 7 days. Topical atropine (1% ophthalmic solution) may be used to reduce uveitis, but is not routinely necessary. In cases of glaucoma, preoperative IOP-lowering drugs (e.g., dorzolamide 2% solution q8h) may be used to reduce IOP and facilitate surgery. For patients with a history of uveitis, topical corticosteroids (e.g., prednisolone acetate 1% q6-8h) may be used preoperatively, but should be discontinued if corneal ulceration is present. The use of NSAIDs is contraindicated in patients with renal disease, gastrointestinal ulceration, or coagulopathies. Dosages should be adjusted for hepatic or renal impairment.

Evidence-based literature supports evisceration with intraocular prosthesis as a viable alternative to enucleation for blind, painful eyes. A retrospective study by Miller et al. (2000) reported a 92% success rate in dogs and cats, with the most common complication being prosthesis extrusion (8%). Another study by Spiess et al. (2008) compared evisceration with enucleation and found that evisceration resulted in better cosmetic outcomes and fewer orbital complications. A study by Wilkie and Gemensky-Metzler (2004) reported that evisceration with prosthesis is a safe and effective procedure for end-stage glaucoma, with a low rate of postoperative complications. In a study by Beckwith-Cohen et al. (2014), the authors evaluated the long-term outcomes of evisceration in cats with diffuse iridal melanoma and found that the metastatic rate was 15%, suggesting that careful patient selection is important. A consensus statement from the American College of Veterinary Ophthalmologists (ACVO) recommends evisceration with prosthesis for cases of end-stage glaucoma and phthisis bulbi, but advises caution in cases of intraocular neoplasia. The use of silicone prostheses is well-documented, with studies showing good biocompatibility and low extrusion rates. Overall, the literature supports evisceration with intraocular prosthesis as a reliable technique for improving the quality of life in animals with irreversible ocular disease.