HOW-TO SESSION: OPHTHALMOLOGY


sometimes the attached tubing can be used to pull the footplate out through the skin exit hole. Alter- natively, the exit site in the eyelid skin can be infil- trated with a small amount of local anesthetic, and a simple cutdown surgery can be performed around the tubing stump to retrieve the footplate and asso- ciated remnant.


3. Results


Both veterinary ophthalmologists and general equine practitioners rely on these devices to treat their most difficult cases, and properly installed sys- tems usually work very well in both hospital and field situations. SPL tubes have been left in pa- tients for as long as 10 to 12 weeks. Treatment regimens range from multiple medications injected on an hourly basis for initial treatment of serious problems to treatment that is delivered just a few times a day for issues nearing resolution. The use of SPLs to deliver targeted treatment for serious equine ocular problems has preserved vision and saved thousands of eyes.


Complications


Although SPLs are managed in most horses without problems, complications do occur in some patients. The two major issues are iatrogenic corneal ulcer- ation from footplate irritation and lack of patency caused by damage to the tube lumen (breakage or development of small punctures). Corneal ulceration occasionally occurs after an


SPL is placed in the upper lid if the device is not inserted deep in the fornix and the footplate rubs against the cornea. It can also occur if the footplate is not snug against the conjunctiva. Removal and replacement of the SPL is necessary to stop further mechanical irritation. A new SPL should be placed and firmly secured to avoid SPL-associated corneal trauma. The second SPL is often placed in the ventronasal aspect of the lower lid because at this site, the nictitans provides a protective barrier be- tween the footplate and the cornea. Ulcers associ- ated with lavage tube irritation are often very slow to heal; choice of treatment medication is dependent on analysis of cytology and culture of the ulcer bed. Although the silicone tubing of an SPL is quite


strong, it can break or develop leaks if the horse snags it on an object. Breaks will be obvious, but leaks may not be noticed immediately. The person treating the horse should be suspicious that the system is not working if a horse stops reacting when enough of an air bolus is injected to push medication into the tear film—the lack of a reaction may indi- cate that the medication is leaking out of the tube before it reaches the globe surface. A simple method to check for patency is to tear off


a small piece of a fluorescein dye strip and mix it with saline solution. One to 2mLof the dyed saline is then flushed through the tube. The tear film will turn green as the dye/saline mixture exits the eyelid if the tube is patent. If the tube is leaking, the tear


film will remain clear, but the dyed saline mixture will leak from the damaged part of the tube. SPL tubing that breaks or tears near the withers


can be repaired by simply shortening the tube. The open end of the tube is flushed with a quantity of 1:50 betadine/saline antiseptic, and a new cathe- ter and cap are inserted. An injection port assem- bly is created as described above and taped and sutured to a more proximal braid. SPL tubing that breaks near the ear or above the


eyelid can be repaired with the use of a 20-gauge catheter as a splice to connect the two separated ends (Fig. 9A–D). The catheter is inserted into one end of the broken tubing, with the stylet retracted slightly back into the catheter lumen. The tubing is “shimmied” over half of the catheter length. The stylet is then removed, and the hub of the cath- eter is cut off. Half the Teflon catheter is exposed beyond the section that is sleeved with one end of the broken SPL tubing. The other end of the SPL tubing is then carefully pushed over the exposed catheter. This is somewhat difficult without the use of a stylet but can be done with a light touch and a little patience. When both of the broken ends of silicone tubing meet in the center of the catheter tubing, a small piece of white tape is wound around the junction to secure the splice. Patency of the spliced segment is tested with a saline flush, which should pass through the catheter lumen. The sec- tion of spliced tubing is then secured to the face or neck crest with a sutured tape wing.


4. Discussion


Horses diagnosed with deep stromal or melting ul- cers and stromal abscesses usually require an SPL to deliver the intense treatment that is required to save the eye and preserve vision. Horses with con- ditions such as severe uveitis or indolent ulcers may also benefit from an SPL when the problem is very painful or requires prolonged therapy. Many of these cases can be handled effectively in the field. However, some cases are best referred—even when a practitioner has the skills to insert an SPL, opti- mum outcome may only be realized with specialist evaluation and hospitalization. Practitioners must consider several factors beyond the simple mechan- ics of installing an SPL when making clinical deci- sions on a problem eye. Serious infections and melting ulcers can quickly progress and threaten vision and ocular integrity; therefore, it is important that the treatment plan is based on a comprehensive examination and appropriate diagnostic testing. Practitioners who install SPLs must have skills and experience in assessing such cases and a broad knowledge of rational therapy choices. SPL insertion is not inexpensive; the kit materials


and sedation are costly, and the process of placing and securing the tube is somewhat time-consuming. Owners who bring their horses to a referral facility are prepared for significant expense and readily give permission for SPL placement. However, the first


AAEP PROCEEDINGS  Vol. 59  2013 171


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