Cataract and Phacoemulsification

Cataract is defined as any opacity of the lens or its capsule, leading to a decrease in visual acuity or blindness. In veterinary medicine, cataracts are a leading cause of vision loss in dogs and are also significant in cats, horses, and other species. The lens is a biconvex, avascular, transparent structure that focuses light onto the retina. It is composed of a central nucleus, surrounding cortex, and an elastic capsule. Cataracts can be classified by age of onset (congenital, juvenile, senile), etiology (hereditary, traumatic, metabolic, toxic, nutritional, inflammatory, degenerative), location (capsular, subcapsular, cortical, nuclear, equatorial), and stage of maturity (incipient, immature, mature, hypermature). Phacoemulsification is the surgical technique of choice for cataract removal in veterinary patients. It involves the use of ultrasonic energy to fragment and aspirate the lens material through a small corneal incision, followed by aspiration of cortical material and placement of an intraocular lens (IOL) to restore refractive power. The procedure requires specialized equipment, microsurgical instrumentation, and advanced training. Successful outcomes depend on appropriate patient selection, meticulous surgical technique, and aggressive postoperative management of inflammation and intraocular pressure.

The etiology of cataracts in animals is multifactorial. Hereditary cataracts are the most common cause in dogs, with over 100 breeds known to have inherited forms. These are often transmitted as autosomal recessive traits, but dominant and sex-linked forms exist. Specific genetic mutations have been identified in some breeds, such as the HSF4 gene mutation in the Staffordshire Bull Terrier and the Australian Shepherd. Congenital cataracts may result from genetic defects or intrauterine insults, such as infections (e.g., canine herpesvirus, feline panleukopenia), toxins, or nutritional deficiencies. Traumatic cataracts occur following penetrating or blunt ocular trauma, leading to lens capsule rupture and subsequent cataract formation. Metabolic cataracts are most notably associated with diabetes mellitus in dogs, where hyperglycemia leads to accumulation of sorbitol in the lens fibers via the polyol pathway, causing osmotic damage and opacification. Other metabolic causes include galactosemia, hypocalcemia, and aminoacidurias. Toxic cataracts can be induced by various drugs (e.g., corticosteroids, mitotane) or chemicals. Nutritional cataracts are rare but have been reported in puppies fed milk replacers deficient in arginine or other amino acids. Inflammatory cataracts may develop secondary to uveitis, either from infectious agents (e.g., Brucella canis, Leishmania, Toxoplasma) or immune-mediated processes. Degenerative cataracts are age-related and are common in senior dogs and cats. Radiation-induced cataracts can occur after therapeutic or accidental exposure. Finally, cataracts may be secondary to other ocular diseases such as progressive retinal atrophy, glaucoma, or lens luxation.

Cataracts are one of the most common ophthalmic disorders in dogs, with an estimated prevalence of 1-2% in the general population, but much higher in certain breeds. Hereditary cataracts are particularly prevalent in purebred dogs, including the American Cocker Spaniel, Bichon Frise, Boston Terrier, French Bulldog, Golden Retriever, Labrador Retriever, Miniature Schnauzer, Poodle (Miniature and Toy), Siberian Husky, and Staffordshire Bull Terrier. Age of onset varies by breed and genetic type; for example, cataracts in the Siberian Husky may appear as early as 6-12 months, while in the Golden Retriever they typically develop between 1-3 years. Senile cataracts are common in dogs over 8 years of age. In cats, cataracts are less common, with a prevalence of about 1-2%, and are often secondary to uveitis or trauma. Diabetic cataracts are a significant concern in dogs, with approximately 75-80% of diabetic dogs developing cataracts within 6-12 months of diagnosis. There is no sex predilection for cataracts in dogs or cats. Breed-specific anatomical factors, such as a shallow anterior chamber or microphthalmia, may increase surgical risk. Working dogs, such as those used for hunting or service, may have a higher functional impact from cataracts, necessitating earlier surgical intervention.

The lens is composed of highly organized crystalline proteins (crystallins) that maintain transparency. Cataract formation involves disruption of this architecture, leading to protein aggregation, loss of cellular homeostasis, and opacification. In hereditary cataracts, genetic mutations may cause abnormal protein synthesis or structural defects in lens fibers. In diabetic cataracts, hyperglycemia leads to increased glucose uptake in the lens, which is metabolized by aldose reductase to sorbitol. Sorbitol accumulates intracellularly, creating an osmotic gradient that draws water into lens fibers, causing swelling, vacuolization, and rupture of cell membranes. This leads to liquefaction of lens fibers and opacification. In age-related cataracts, oxidative stress and accumulation of damaged proteins contribute to lens clouding. Trauma can cause direct damage to lens fibers or capsule, leading to localized or diffuse cataract. Uveitis-induced cataracts result from inflammatory mediators that alter lens metabolism and increase protein denaturation. As cataracts progress, they may become mature (complete opacification) or hypermature (liquefaction of cortex, with the nucleus sinking inferiorly, known as Morgagnian cataract). Hypermature cataracts can lead to lens-induced uveitis (phacolytic uveitis) due to leakage of lens proteins into the anterior chamber, which can cause secondary glaucoma and other complications. Phacoemulsification works by using ultrasonic waves to fragment the lens nucleus and cortex, which are then aspirated, leaving the posterior capsule intact for IOL placement. The procedure aims to remove the opacified lens while minimizing trauma to surrounding ocular structures.

Predisposing factors for cataract development include breed, age, genetics, systemic diseases, and environmental factors. Hereditary predisposition is the most significant, with specific breeds having a high incidence of inherited cataracts. Age is a major factor, as senile cataracts are common in older animals. Diabetes mellitus is a strong predisposing factor for rapid cataract formation in dogs. Other metabolic diseases, such as hypocalcemia and galactosemia, can also predispose to cataracts. Ocular trauma, uveitis, and chronic glaucoma can lead to cataract development. Nutritional deficiencies, particularly in puppies, may predispose to cataracts. Exposure to certain drugs (e.g., corticosteroids, mitotane) or toxins (e.g., naphthalene) can increase risk. Additionally, animals with pre-existing ocular conditions, such as progressive retinal atrophy or lens luxation, may be more prone to cataracts. Surgical risk factors include age (very young or very old), presence of concurrent ocular disease (e.g., dry eye, glaucoma, retinal degeneration), and systemic health status (e.g., renal or hepatic disease).

Clinical signs of cataracts vary depending on the stage and location. Early (incipient) cataracts may cause no noticeable visual deficits, and the opacity may only be visible on ophthalmic examination. As the cataract progresses to immature, the animal may show mild visual impairment, such as bumping into objects in dim light or difficulty navigating unfamiliar environments. Mature cataracts cause significant vision loss, and the affected eye may appear white or gray. Hypermature cataracts may show a shrunken, wrinkled lens capsule with a yellowish appearance. Animals with cataracts may also exhibit signs of lens-induced uveitis, including conjunctival hyperemia, miosis, and decreased intraocular pressure. In cases of secondary glaucoma, the eye may be painful, with corneal edema and mydriasis. On ophthalmic examination, the lens opacity can be visualized using a slit-lamp biomicroscope. The examiner should note the location, extent, and stage of the cataract. Additionally, a complete ocular examination is essential to assess the retina and optic nerve, as concurrent retinal disease can affect surgical candidacy and prognosis.

Differential diagnoses for cataracts include conditions that cause a white or cloudy appearance of the eye. These include: 1) Nuclear sclerosis (lens sclerosis) – a normal aging change where the lens nucleus becomes denser and appears grayish-blue, but vision is not significantly affected; distinguished by the lack of visual impairment and the characteristic appearance on slit-lamp examination. 2) Corneal edema – opacity of the cornea due to fluid accumulation, often associated with glaucoma or endothelial dysfunction; differentiated by the location (cornea vs. lens) and the presence of other signs like corneal vascularization. 3) Corneal scarring or fibrosis – opacification of the cornea due to previous injury or inflammation; distinguished by the presence of corneal scarring and the absence of lens changes. 4) Anterior uveitis – inflammation of the uveal tract can cause aqueous flare and keratic precipitates, which may mimic a cloudy lens; differentiated by the presence of inflammatory signs, such as miosis, conjunctival hyperemia, and low intraocular pressure. 5) Glaucoma – increased intraocular pressure can cause corneal edema and mydriasis, which may be confused with a cataract; differentiated by tonometry and gonioscopy. 6) Lens luxation – displacement of the lens into the anterior chamber or vitreous, which can cause visual impairment and a cloudy appearance; differentiated by slit-lamp examination and ultrasound. 7) Retinal detachment – may cause a white reflex (leukocoria) in the pupil, but the lens is clear; differentiated by fundic examination and ultrasound. 8) Intraocular neoplasia – tumors such as ciliary body adenoma can cause a white mass in the eye; differentiated by ultrasound and histopathology. 9) Persistent hyperplastic primary vitreous (PHPV) – a congenital condition with a retrolental fibrovascular membrane; differentiated by the presence of a vascularized membrane behind the lens. 10) Phacolytic uveitis – inflammation secondary to lens protein leakage, which can cause a cloudy appearance; differentiated by the presence of lens opacity and inflammatory signs.

The diagnostic algorithm for a patient with suspected cataract begins with a thorough history and physical examination. The owner may report a gradual loss of vision or a change in the appearance of the eye. A complete ophthalmic examination is essential, including: 1) Neuro-ophthalmic examination: assessment of menace response, pupillary light reflexes (direct and consensual), dazzle reflex, and palpebral reflex. 2) Slit-lamp biomicroscopy: to evaluate the anterior segment, including the cornea, anterior chamber, iris, and lens. The cataract is characterized by location, extent, and stage. 3) Indirect ophthalmoscopy: to examine the fundus, including the retina and optic nerve, to rule out concurrent retinal disease. If the cataract prevents visualization of the fundus, electroretinography (ERG) is performed to assess retinal function. 4) Tonometry: to measure intraocular pressure (IOP) and rule out glaucoma. 5) Gonioscopy: to evaluate the iridocorneal angle and assess the risk of postoperative glaucoma. 6) Ocular ultrasound: if the fundus cannot be visualized, B-mode ultrasonography is used to assess the posterior segment for retinal detachment, vitreous degeneration, or intraocular masses. 7) Systemic work-up: complete blood count, serum biochemistry, urinalysis, and blood pressure measurement, especially in diabetic patients. 8) Additional tests: in cases of suspected uveitis, aqueous humor analysis or serology for infectious agents may be indicated. 9) Electroretinography (ERG): mandatory in patients with mature or hypermature cataracts to confirm retinal function, as cataracts can obscure retinal evaluation. 10) Ocular coherence tomography (OCT) or ultrasound biomicroscopy (UBM) may be used for detailed anterior segment imaging in research or complex cases. Based on these findings, the surgeon can determine the surgical candidacy and plan the appropriate surgical technique.

Laboratory findings in cataract patients are primarily used to identify underlying systemic diseases and assess surgical risk. In diabetic dogs, persistent hyperglycemia, glycosuria, and elevated fructosamine levels are common. Serum biochemistry may reveal elevated liver enzymes, renal parameters, or electrolyte imbalances. A complete blood count may show leukocytosis or other abnormalities if there is an underlying infection or inflammation. Urinalysis may reveal proteinuria, ketonuria, or signs of urinary tract infection. Coagulation profile (PT, aPTT, platelet count) is recommended to rule out bleeding disorders, especially if surgery is planned. In cases of suspected uveitis, aqueous humor analysis may show increased protein and inflammatory cells. Serology for infectious agents (e.g., Brucella canis, Toxoplasma gondii, Leishmania) may be performed in endemic areas. In geriatric patients, blood pressure measurement and thyroid function tests may be indicated. Additionally, pre-anesthetic blood work is essential to evaluate organ function and tailor the anesthetic protocol.

Imaging plays a crucial role in the preoperative evaluation of cataract patients. Ocular ultrasound (B-mode) is the most important imaging modality when the fundus cannot be visualized due to a mature or hypermature cataract. It can detect retinal detachment, vitreous degeneration, intraocular masses, and lens luxation. Ultrasound biomicroscopy (UBM) provides high-resolution images of the anterior segment, including the lens capsule and ciliary body, and can be useful in assessing the integrity of the posterior capsule. In cases of suspected glaucoma, gonioscopy is performed to evaluate the iridocorneal angle. Computed tomography (CT) and magnetic resonance imaging (MRI) are rarely used for cataract evaluation but may be indicated if there is suspicion of orbital or intracranial pathology. In research settings, optical coherence tomography (OCT) can provide cross-sectional images of the lens and retina. Preoperative biometry, including axial length measurement, is essential for calculating the power of the intraocular lens (IOL) to be implanted. This is typically performed using A-scan ultrasonography. Accurate biometry is critical for achieving optimal postoperative refractive outcomes.

Cytology and histopathology are not routinely performed for cataract diagnosis, as the condition is diagnosed clinically. However, in cases of lens-induced uveitis, aqueous humor cytology may reveal inflammatory cells, including lymphocytes, plasma cells, and macrophages. Histopathological examination of the lens may be performed after surgical removal or enucleation. In phacoemulsification, the aspirated lens material can be submitted for cytology or histopathology if there is suspicion of neoplasia or infection. Histologically, cataracts show disruption of normal lens fiber architecture, with protein aggregation, liquefaction, and Morgagnian globule formation. In diabetic cataracts, there may be evidence of osmotic damage, such as vacuolization and fiber swelling. In cases of traumatic cataracts, there may be evidence of capsule rupture and inflammation. Histopathology is also useful to confirm the presence of concurrent ocular diseases, such as uveitis or retinal degeneration.

The definitive treatment for cataracts is surgical removal. Phacoemulsification is the preferred technique in veterinary ophthalmology due to its smaller incision size, faster healing, and lower complication rates compared to extracapsular cataract extraction (ECCE). The surgical procedure involves: 1) Preoperative preparation: The patient is placed under general anesthesia. The eye is prepared with a dilute povidone-iodine solution. Mydriasis is achieved with topical atropine or tropicamide. 2) Surgical approach: A clear corneal incision is made, typically 2.8-3.2 mm in width, using a keratome. 3) Capsulorhexis: A continuous curvilinear capsulorhexis (CCC) is created to open the anterior capsule. This is performed using a cystotome or capsulorhexis forceps. 4) Hydrodissection: Balanced salt solution is injected between the capsule and cortex to separate the lens nucleus. 5) Phacoemulsification: The phacoemulsification handpiece is introduced, and ultrasonic energy is used to fragment the nucleus and cortex. The lens material is aspirated through the handpiece. 6) Cortical cleanup: Residual cortical material is aspirated using an irrigation/aspiration (I/A) handpiece. 7) Intraocular lens (IOL) implantation: A foldable or rigid IOL is implanted into the capsular bag. The power of the IOL is calculated based on preoperative biometry. 8) Wound closure: The corneal incision is closed with sutures (e.g., 9-0 or 10-0 nylon) or left to self-seal if small enough. Postoperative management includes topical antibiotics (e.g., neomycin-polymyxin-bacitracin) and anti-inflammatory agents (e.g., prednisolone acetate 1% or diclofenac 0.1%) applied 4-6 times daily, tapering over several weeks. Systemic anti-inflammatory drugs, such as carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h), may be used for 1-2 weeks. Atropine 1% may be used to prevent synechiae and reduce pain. In cases of lens-induced uveitis, aggressive anti-inflammatory therapy is initiated preoperatively. Complications of phacoemulsification include corneal edema, uveitis, glaucoma, retinal detachment, and IOL displacement. Alternative surgical techniques include extracapsular cataract extraction (ECCE) and intracapsular cataract extraction (ICCE), but these are less commonly performed. In cases where surgery is not feasible, medical management of lens-induced uveitis and secondary glaucoma may be attempted, but vision cannot be restored.

The prognosis for cataract surgery in dogs is generally good, with success rates (defined as restoration of vision) ranging from 80-95% in experienced hands. Factors that negatively affect prognosis include: 1) Pre-existing retinal disease, such as progressive retinal atrophy or retinal detachment, which can be detected by ERG or ultrasound. 2) Glaucoma, which is a common postoperative complication, especially in breeds predisposed to primary glaucoma. 3) Severe lens-induced uveitis, which can lead to synechiae, glaucoma, and cystoid macular edema. 4) Intraoperative complications, such as posterior capsule rupture, vitreous loss, or hemorrhage. 5) Postoperative complications, including persistent uveitis, corneal endothelial damage, and IOL decentration. In cats, the prognosis is more guarded due to a higher incidence of postoperative complications, such as uveitis and retinal detachment. Long-term vision retention rates are approximately 80-90% at 1 year, but may decline to 50-70% at 3-5 years due to the development of glaucoma or retinal degeneration. Early intervention and aggressive postoperative management can improve outcomes.

Postoperative follow-up is critical for successful outcomes. Patients are typically re-examined at 1 day, 1 week, 2 weeks, 4 weeks, 8 weeks, 12 weeks, and then every 3-6 months for the first year. At each visit, a complete ophthalmic examination is performed, including slit-lamp biomicroscopy, tonometry, and indirect ophthalmoscopy. The intraocular pressure is monitored closely for the development of glaucoma. The owner is instructed to administer topical medications as prescribed and to monitor for signs of discomfort, redness, or discharge. Activity restrictions are recommended for 2-4 weeks to prevent trauma to the eye. An Elizabethan collar is often used to prevent self-trauma. Systemic anti-inflammatory medications are tapered over 2-4 weeks. The sutures, if present, are removed at 2-3 weeks. Long-term follow-up is necessary to detect late complications, such as posterior capsule opacification (PCO), which can cause vision loss months to years after surgery. PCO can be treated with Nd:YAG laser capsulotomy. Regular monitoring for retinal degeneration and glaucoma is also recommended.

Clinical Pearls: 1) Always perform a thorough preoperative evaluation, including ERG and ocular ultrasound, to rule out retinal disease and posterior segment abnormalities. 2) Use a continuous curvilinear capsulorhexis to ensure a stable capsular bag for IOL placement. 3) Maintain a deep anterior chamber during phacoemulsification to prevent corneal endothelial damage. 4) Use low ultrasound power and vacuum settings to minimize trauma to the corneal endothelium and iris. 5) Consider the use of viscoelastic agents to protect the corneal endothelium and maintain space. 6) In diabetic patients, ensure good glycemic control before surgery to reduce the risk of postoperative uveitis. 7) Administer topical atropine preoperatively to achieve adequate mydriasis. 8) Use a foldable IOL to allow for a smaller incision and faster healing. 9) Postoperative uveitis is the most common complication; aggressive anti-inflammatory therapy is essential. 10) Monitor intraocular pressure closely in the early postoperative period, as glaucoma can develop rapidly. Pitfalls: 1) Operating on an eye with uncontrolled uveitis or glaucoma can lead to catastrophic complications. 2) Incomplete cortical cleanup can lead to posterior capsule opacification and visual impairment. 3) Posterior capsule rupture can lead to vitreous loss and retinal detachment. 4) Implanting an IOL with incorrect power can result in significant refractive error. 5) Inadequate postoperative anti-inflammatory therapy can lead to chronic uveitis and secondary glaucoma. 6) Failure to recognize and treat corneal endothelial damage can lead to corneal edema and bullous keratopathy. 7) Allowing the patient to rub or scratch the eye postoperatively can cause wound dehiscence or IOL displacement. 8) Using excessive ultrasound energy can cause thermal damage to the corneal incision. 9) Not using viscoelastic agents can lead to collapse of the anterior chamber and damage to intraocular structures. 10) Inadequate follow-up can lead to missed complications and poor outcomes.

Perioperative drug protocols for cataract surgery are based on Plumb's Veterinary Drug Handbook. Preoperative: 1) Topical mydriatics: Atropine sulfate 1% ophthalmic solution, applied 1-2 drops every 6-8 hours starting 24 hours before surgery, or Tropicamide 1% applied 1-2 drops every 15 minutes for 1 hour before surgery. 2) Topical anti-inflammatory: Prednisolone acetate 1% ophthalmic suspension, 1 drop every 6 hours for 24-48 hours before surgery, or Flurbiprofen 0.03% ophthalmic solution, 1 drop every 6 hours. 3) Systemic anti-inflammatory: Carprofen (Rimadyl) 2.2 mg/kg PO q12h, or Meloxicam (Metacam) 0.1 mg/kg PO q24h, starting 24 hours before surgery. 4) Prophylactic antibiotics: Cefazolin 22 mg/kg IV at induction, or Amoxicillin-clavulanate 13.75 mg/kg PO q12h starting 24 hours before surgery. Intraoperative: 1) Balanced salt solution (BSS) for irrigation. 2) Viscoelastic agents: Sodium hyaluronate (e.g., Healon) or hydroxypropyl methylcellulose (e.g., Ocucoat) to maintain anterior chamber depth and protect corneal endothelium. 3) Epinephrine 1:1000 added to irrigation solution (0.5 mL per 500 mL BSS) to maintain mydriasis. 4) Heparin (5000 units per 500 mL BSS) may be added to reduce fibrin formation. Postoperative: 1) Topical antibiotics: Neomycin-polymyxin B-bacitracin ophthalmic ointment, 1/2 inch every 6-8 hours for 7-10 days, or Ciprofloxacin 0.3% ophthalmic solution, 1 drop every 6 hours. 2) Topical anti-inflammatory: Prednisolone acetate 1% ophthalmic suspension, 1 drop every 6 hours, tapering over 4-6 weeks, or Diclofenac 0.1% ophthalmic solution, 1 drop every 6-8 hours. 3) Topical mydriatic/cycloplegic: Atropine 1% ophthalmic ointment or solution, 1 drop every 8-12 hours for 3-7 days, as needed to prevent synechiae and reduce pain. 4) Systemic anti-inflammatory: Carprofen 2.2 mg/kg PO q12h for 5-7 days, or Meloxicam 0.1 mg/kg PO q24h for 5-7 days. 5) Systemic antibiotics: Amoxicillin-clavulanate 13.75 mg/kg PO q12h for 7 days. 6) Analgesics: Tramadol 2-5 mg/kg PO q8-12h for 3-5 days, or Gabapentin 10 mg/kg PO q8-12h for pain management. 7) In cases of severe uveitis, systemic corticosteroids may be used: Prednisone 0.5-1 mg/kg PO q24h, tapering over 2-4 weeks. 8) For glaucoma prophylaxis, topical carbonic anhydrase inhibitors such as Dorzolamide 2% ophthalmic solution, 1 drop every 8 hours, may be used if IOP is elevated. 9) Lubricants: Artificial tears ophthalmic solution, 1 drop every 6-8 hours, to prevent corneal drying.

The veterinary literature supports phacoemulsification as the gold standard for cataract surgery in dogs. A landmark study by Davidson et al. (1991) reported a success rate of 86% for vision restoration in dogs undergoing phacoemulsification. More recent studies have shown success rates of 90-95% with modern techniques and IOL implantation. A study by Sigle and Nasisse (2006) found that the use of foldable IOLs resulted in less postoperative inflammation and faster visual recovery compared to rigid IOLs. The importance of preoperative ERG and ultrasound in predicting surgical outcomes has been emphasized in multiple studies. For example, a study by van der Woerdt et al. (1998) showed that dogs with normal ERG had a significantly higher success rate than those with abnormal ERG. The management of lens-induced uveitis is critical; a study by Wilkie and Colitz (2005) demonstrated that aggressive preoperative and postoperative anti-inflammatory therapy reduces the risk of glaucoma and other complications. The use of topical NSAIDs, such as flurbiprofen, has been shown to reduce intraoperative miosis and postoperative inflammation (Millichamp et al., 1991). Regarding IOL power calculation, a study by Gaiddon et al. (1991) established standard biometry techniques for dogs. The incidence of postoperative glaucoma has been reported to be 5-10% in dogs, with certain breeds at higher risk (e.g., Boston Terrier, Bichon Frise). A study by Biros et al. (2000) found that prophylactic use of topical carbonic anhydrase inhibitors may reduce the risk of postoperative glaucoma. Posterior capsule opacification (PCO) is a common long-term complication, with a reported incidence of up to 50% at 2 years postoperatively (Davidson et al., 2000). Nd:YAG laser capsulotomy is an effective treatment for PCO. In cats, phacoemulsification has a lower success rate (around 70-80%) due to a higher incidence of postoperative uveitis and retinal detachment (Olivero et al., 1991). Overall, the evidence supports that phacoemulsification with IOL implantation is a safe and effective procedure for restoring vision in dogs with cataracts, provided that appropriate patient selection and meticulous surgical technique are employed.