A cataract is any abnormal cloudiness in the lens of the eye. This may vary from a small area requiring no treatment through to total cataract and blindness. The cloudiness arises from a permanent alteration in the structure of the lens so where it is necessary cataracts can only be corrected by surgery.
The cataract is removed under general anesthesia by a procedure called phacoemulsification using the same equipment and techniques as in human surgery. We usually insert an artificial lens in the eye to take over the function of the lens which has been removed provided the eye is suitable at the time. An artificial lens is believed to reduce the time taken for the dog to see usefully again and improves the final vision that is achieved. You should not be too concerned, however, if the eye is not suitable for an artificial lens since an eye which was previously blind with a cataract will see much better when it is clear even without an artificial lens.
Pre- and post-operative care
Prior to surgery patients should be in as good a state of general health as is possible and diabetic dogs should be reasonably stable. We will often request a full blood screen to confirm this. In most cases the cataracts are not as urgent or important as the patient’s general health and so can wait until other problems are resolved or stabilised.
Some diabetic cataracts, however, are urgent and in this situation, it is best to proceed to surgery promptly with our usual close monitoring of the anesthesia and blood glucose. Owners should take into account the dog’s temperament. Very restless or aggressive dogs can make medication and clinical examination difficult, and this may even prevent us doing full post-operative checks.
Patients are always re-examined the morning following the operation. The following checks are one week later and then at one month. Subsequently two months, three months, six months and 12 months would be typical, but this very much depends on the individual case. It is important that clients can bring the patient back to us promptly if there is a problem. This applies especially in the first four weeks after the operation. Eye drops are required for a minimum of six months after surgery. All post-operative re-examinations and drugs are charged to the client along with any additional surgical procedures required.
Various complications may occur. We anticipate these and take every step to prevent them, but it is major surgery for the eye, and we cannot eliminate all risks. Although success rates are higher than they used to be complications can occur and an informed decision must be made. Complications may incur additional costs in terms of consultations, medications and procedures and may seriously affect the outcome.
The more important complications are:
All eyes become inflamed after surgery and in most cases, this is controllable by medication. Some dogs release a substance called fibrin into the eye which can have harmful consequences. When this occurs, it is usually in the first four weeks post-operatively. Fibrin can be dissolved by injection of the enzyme TPA into the eye under sedation and local anesthetic. TPA is required in 15% of all eyes.
Glaucoma is a raised pressure in the eye and is always potentially serious. We measure the pressure in the eye at the first consultation and at all subsequent ones as it is important to monitor it. We can identify dogs at exceptional risk of glaucoma by a test called gonioscopy which can be performed pre- operatively, but some risk of glaucoma is present in all dogs. Problems with pressure tend to occur in two situations:
- The immediate post-operative period, usually the same day or the first 24 hours. Some dogs sustain high pressures in this period. Although this is usually a temporary problem we take it seriously and may need to take emergency measures to bring the pressure down.
- Longer term. Longer term pressure rise is the most serious complication seen. It may cause pain and impair or destroy the patient’s sight. This will require ongoing medication and anti-glaucoma drugs are relatively expensive. Where there are unmanageable complications which are causing pain, despite everyone’s best efforts, the most effective means of pain relief may be removal of the eye. Chronic glaucoma is the most common cause. Eye removal is eventually required in 3% of all eyes undergoing cataract surgery.
“Can the cataract grow back?” is a logical question to ask before cataract surgery. Some lens cells are always left behind at the time of the operation and so some lens regrowth is quite common. In most cases, however, it is not vigorous and does no harm. In some cases it regrows out of control and can cause inflammation, re-clouding of the eye and other serious complications. If this is happening the regrowth needs to be removed under general anesthesia. This procedure is simpler and shorter than the original cataract operation. It is unusual to need to repeat it. This procedure is much more common in young dogs and owners of young dogs should allow for the possibility of the additional cost.
Other uncommon but serious complications include intraocular hemorrhage, intraocular infection and retinal detachment, all of which may be difficult to manage.
Clients need to be aware of all that is involved so that they can make an informed choice, weighing potential benefits against risks. With the modern methods of cataract surgery success rates are much higher than with older methods. With an incurable problem and a high success rate for the operation clients can embark on cataract surgery with as much confidence as with many other operations commonly performed on dogs.