Equine Cataract Surgery

Take Home Message  

Although equine cataract surgery is not as routine as human or canine cataract surgery, recent advances in technique has made surgery a viable option for treatment of advanced cataracts in foals and adult horses. Complicating factors, such as pre-existing uveitis and postoperative  infection, glaucoma, and lens capsular fibrosis remain areas of concern with the equine patient.  

Introduction  

Cataracts are a relatively common ocular disease in horses and can occur as both acquired and developmental defects.¹ Acquired cataracts occur in horses of all ages and are frequently secondary to other disease processes, such as uveitis and trauma. Cataracts are the most common congenital ocular anomaly in foals.^1-5 Cataracts that cause substantial visual deficits can be  removed via phacoemulsification and aspiration. Phacoemulsification and aspiration (PA) is the  technique of choice for removal of cataracts in foals and adult horses.^7-9 Use of an intraocular lens (IOL) in the horse, until recently, has been uncommon. However, newer IOL materials and  improved technique has made use of IOLs standard of care for equine cataract surgery.^10-12  

Surgical Assessment  

Similar to other animals, workup for a horse that is a candidate for cataract surgery should  include a complete ocular (both eyes!) and physical examination (including a rectal exam to assess predisposition for colic), routine blood work (complete blood count [CBC]), serum  chemistry profile, urinalysis), an electroretinogram, and ocular ultrasound. If the horse has  historical or clinical evidence of recurrent uveitis, you should also submit serum and aqueous  humor (collected at the time of surgery) leptospiral titers. Careful consideration should also be made of the horses’ AND owners’ temperament to determine if both can tolerate the long-term  treatment and care that will be required after surgery. 

Preoperative Preparation  

Because of the concern for bacterial contamination and endophthalmitis after cataract surgery in horses, routine use of systemic and topical antibiotics is recommended. Also, we advise that if  both eyes are candidates for cataract surgery, one should consider the pros and cons of the risk of  bilateral endophthalmitis versus two anesthetics periods. We commonly recommend, therefore, that one eye be done at a time. Topical 4^th generation fluoroquinolones (Moxifloxacin, Vigamox→, Alcon, Ft Worth, TX), which have been demonstrated to penetrate the intact cornea  well and have a broad spectrum activity, are used for at least 24 hours prior to surgery and 3 days  after surgery. A topical antibiotic is generally recommended for the length of time that the eye requires topical corticosteroid treatment. Intravenous antibiotics are generally also recommended  for the 24-hour peri-surgical time period followed by 10-14 days of oral antibiotics. Topical  atropine is used starting 12 to 18 hours prior to surgery. Systemic NSAIDS, preferably flunixin  meglumine, is given starting at least 1 hour prior to surgery and continued in a decreasing dosage for up to 3 weeks after surgery. Gastric protectants, such as ranitidine and /or omeprazole (Gastrogard^®, Merial) are routinely used to help prevent side effects. See Appendix A for the NCSU complete preoperative equine cataract medication protocol.  

Patient Positioning  

Correct positioning of the horse is critical for success for any type of intraocular surgery. For  cataract surgery, the horse is placed in lateral recumbancy. The down eye is protected from pressure or exposure trauma, either by pillows or an inflatable ring. The horse’s nose is elevated using foam pillows so that the cornea of the eye to be operated on is parallel to the floor (Fig. 1).  To prevent facial nerve paralysis after surgery, one must be careful that there is no pressure on  the facial nerve from the halter (remove it), pillows, or tape. An operating microscope with  coaxial illumination is essential to perform cataract surgery in the horse. Adequate visualization and lighting cannot be accomplished with any other system. The microscope base is placed  opposite the surgeon, with the microscope arm extending over the horse’s body to position above the eye.
 

Surgical Preparation

After the horse is in a stable plane of general anesthesia, it should either be paralyzed or have had a retrobulbar block performed to prevent ocular movement and pressure on the eyes from tension of the extraocular muscles. Like all intraocular surgery, the horse and operating table should be covered with sterile drapes after surgical preparation. Adhesive, waterproof, aperture drapes are an effective barrier to contamination around the eyes. A lateral canthotomy may be required depending on the horse.  [...]