Cataract Surgery: The Current State of the Art
Cataracts are a leading cause of blindness in dogs. Although they may develop as a result of ocular trauma or inflammation, cataracts occur most frequently in purebred dogs, where they are nearly always inherited. The age of onset is variable, usually from 5-8 years of age.
Years ago, we were taught to wait until a cataract “matures” (resulting in blindness) to perform surgery. With recent advances in techniques for cataract removal, it has become advantageous to perform surgery earlier, thus avoiding complications associated with lens-induced uveitis and secondary glaucoma. Now cataract surgery is more often performed unilaterally without waiting for both lenses to become completely opaque. In any case, it is always best to perform an initial examination early enough to visualize the fundus to be certain that there is no evidence of concurrent retinal degeneration.
Cataract Surgical Techniques
Currently, cataracts are removed either by extracapsular extraction or phacoemulsification. Both techniques leave the posterior lens capsule intact for placement of an intraocular lens. Extracapsular extraction involves a 180 degree incision in the peripheral cornea with removal of the anterior lens capsule and manual expression of the lens cortex and nucleus. This technique is necessary in the removal of very dense cataracts. Phacoemulsification utilizes ultrasound waves to break up the cataract with simultaneous irrigation and aspiration of the lens fragments. The advantages of this technique are:
- smaller corneal incision
- maintaining the anterior chamber with less damage to the corneal endothelium
- more thorough removal of lens fragments.
Phacoemulsification is most useful in the removal of softer (less mature) lenses. The high success rates (90.2%) associated with phacoemulsification have encouraged earlier removal of cataracts.
Following uncomplicated cataract extraction alone, vision is improved even if the lens is not replaced. This resulted in what has been called “functional vision”. Patients can generally navigate without bumping into things but often have difficulty with depth perception and playing with toys. Replacement intraocular lenses have been used following cataract removal in humans since the 1950s. In our animal patients where glasses or contacts are impractical, the need for intraocular correction is even greater. The refractive power needed is determined by the axial length of the globe, the curvature of the cornea, and the location of the replacement lens within the eye. In humans, a lens of 16-18 diopters is generally used; measurements in dog eyes indicates that a lens of 40-43 diopters is required. Thus, dogs stand to benefit greatly from use of a replacement intraocular lens. Intraocular lenses are most often made of an optical portion of polymethylmethacrylate (PMMA) with flexible haptics to fix the lens within the capsular bag. Complications following intraocular lens implantation are uncommon and not usually associated with the presence of the replacement lens itself. Evaluations of visual performance, although necessarily subjective, indicate significantly improved vision when a replacement lens is used.
Even in cases where the capsular bag is unstable (as with a luxated lens) it is still possible to implant a replacement lens which is then directly sutured into the ciliary sulcus. This procedure is becoming more commonly performed and has resulted in greatly improved visual acuity.
Phacoemulsification Videotape Available
We have a short (approximately 10 minutes) educational videotape about phacoemulsification for cataract extraction. The advantages of this procedure are discussed as well as answering the most frequently asked questions about the pre- and post-operative care. Footage of an actual cataract surgery filmed through the operating microscope illustrates the technique including implantation of a replacement intraocular lens. The narration is designed to be easily understood and may be helpful to clients considering this procedure. Please call our office to request a copy.