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Cataracts & cataract surgery

What is cataract?

               

In much the same way as a lens focuses images within a camera, the lens in each of our pet’s eyes focuses images on the light sensitive layer at the back of the eye (= the retina). The lens is usually clear and shows up as black in the centre of the eye i.e. the pupil. The lens looks black because the darkness inside the eye shows through it. A cataract is a white opacity within the lens i.e. part of the pupil appears white. When a small amount of your pet’s lens becomes opaque, we call this an incipient cataract. This type of cataract is unlikely to affect vision and surgery is rarely necessary. However, if the majority or the entire lens becomes opaque, we call these types of cataract immature and mature, respectively. These cataracts nearly always affect vision and surgery will restore your pet’s vision.

Cataracts can occur in one or both eyes and can progress.

What causes cataract?

The most common causes of cataract in dogs are diabetes and retinal disease. Inherited cataracts also occur. Just like people, older pets commonly get cataracts. However, all older pet’s lenses appear cloudy to some degree. This cloudiness is the result of an aging change (nuclear sclerosis) within the lens and is not commonly associated with a significant visual deficit: surgery is not usually indicated. Finally, some cataracts occur for unknown reasons.

How & when are cataracts treated?

Unfortunately, there is no simple medical treatment available for cataract. Surgery remains the treatment option of choice for cataracts that interfere with vision.

All canine eyes affected by cataract develop potentially vision threatening inflammation within the eye. This condition is called lens induced uveitis and is associated with the release of toxins from the lens. Lens induced uveitis can be subtle and easily missed. In some cases it can be severe, causing an obviously sore and inflamed eye. If left untreated, many eyes with long standing cataracts will become irreversibly blind: lens induced uveitis can cause retinal detachment (where the light sensitive retina comes away from the back of the eye and stops working) and glaucoma (increased pressure within the eye causing blindness and pain). The longer the cataracts have been present and the more severe the inflammation, the more likely there will be irreparable cataract complications.

Therefore, the earlier the cataract surgery is performed, the more successful the surgical outcome is likely to be. In general, we recommend that surgery is carried out once a cataract starts to interfere significantly with vision. Cataracts in young and diabetic patients usually progress quickly and often result in significant complications if treatment is delayed.  Slowly progressive cataracts not interfering with vision may be monitored regularly. We recommend the use of preventative anti-inflammatory drugs in these cases to counter the negative effects of lens induced uveitis.

What happens before the surgery?

Each patient is individually assessed during a 60 minute consultation by our ophthalmologist. Unfortunately, some patients are not candidates for surgery e.g. if a patient has advanced retinal disease, cataract surgery will not restore vision. Each patient has an ocular ultrasound examination to check for problems such as retinal detachment or rupture (bursting) of the lens. In some patients, an electroretinogram is performed to ensure the retina is functioning correctly.

What happens at the time of surgery?

                          

Pets are usually admitted the night before the surgery. This allows our staff to prepare each patient meticulously. On the morning of the surgery, preparation involves withholding food and frequent application of eye drops to dilate the pupil and reduce the effects of inflammation (which always happens in pets having cataract surgery).

Cataract surgery is carried out under general anaesthesia. The general anaesthetic is complicated by the need to administer paralysing neuromuscular blocking agents (so that the eye comes into the correct position for the surgical procedure) and artificial ventilation. These practices are routine in human medicine. We commonly perform cataract surgery and we have specially trained staff responsible for your pet’s anaesthetic safety. Each patient is monitored very carefully throughout the anaesthetic process (link to PDF and web page).

The operation is a very intricate procedure and is carried out using an operating microscope and tiny instruments. Initially, two small surgical incisions are made at the edge of each cornea where the ‘white’ of the eye starts. After inflating each eye with a protective jelly like substance called viscoelastic, a small circular hole is made in the delicate ‘bag’ (or capsule) that surrounds each of the cataracts. The cataracts are removed using a surgical procedure called “phacoemulsification”, leaving the capsule in place. Phacoemulsification uses ultrasound energy to break up the cataract into small fragments in the same way our dentists use an ultrasonic scaler to remove tartar from our teeth. The small fragments are then “sucked out” of each eye. Phacoemulsification is a sophisticated process and uses complex equipment similar to that used for human cataract surgery.

After the old, damaged lens is removed, a new artificial lens  (picture above and to the right) is implanted into the remaining capsule of each eye. The artificial lens improves the post operative vision to a level similar to that prior to the cataracts developing. For technical reasons it is not possible to implant an artificial lens in some eyes. Not having a lens implanted does not make the difference between being blind and having sight. It is similar to someone who wears glasses not putting them on.

After the new lens is implanted the surgical incisions are closed with dissolvable stitches which are absorbed over the next few weeks.

All patients stay in over night after their operation and are discharged over the following 1-2 days (provided that progress is satisfactory). Most pets see quite well after surgery. However vision will improve further over the following few weeks as the eye adjusts to the new lens and the intraocular inflammation subsides.

What aftercare is involved?

Because all patients develop inflammation after the surgery, the aftercare required is intensive. The post operative inflammation is more significant in pets than people. Therefore, the aftercare is more involved.  The aftercare involves 3-4 ocular assessments at our clinic in the first few weeks. During this period several types of drops are used e.g. topical antibiotics & topical anti-inflammatories. Initially, drops are applied 12-16 times per day. After the first 2 weeks, the number of applications gradually decreases over the following two months. There are also tablets to be given for a few weeks after the surgery.

Each patient must be kept as quiet as possible for a few weeks after the surgery. This can obviously be difficult with many of our patients and owners can only do their best in this regard. Fitting a harness will prevent your pet pulling on the lead. The latter can put up the pressure inside the eye and can encourage bleeding. A plastic Elizabethan collar should be worn for about a week after the operation.

Success rates and prognosis

Most patients do well after cataract surgery and the success rate is about 90 to 95% initially. Unfortunately, this means that 5 to 10% of patients cannot see in the operated eye after surgery. There are a number of reasons why cataract surgery is not successful and these include:

Inflammation
Although every patient gets inflammation after surgery, the occasional pet gets more inflammation than average, and this can lead to changes in the eye. These changes are often inconsequential, but sometimes they cause reduced vision, necessitating an injection into the eye to dissolve the inflammatory material. Inflammation is the single most problem in pets after surgery, and is the major reason why frequent medications and regular post-operative check-ups are required.

Glaucoma
Increased pressure within the eye can sometimes occur during the first few days of surgery. This increase in pressure is usually controlled with additional topical medication. Rarely a more severe increase in pressure occurs (glaucoma) which can lead to blindness and even loss of the eye in cases that do not respond to treatment. Some breeds appear more prone to post operative glaucoma e.g. Boston terriers, Staffordshire Bull terriers.

Ulceration of the cornea
This occurs when the surface layer of the cornea sloughs after surgery. This is usually a very minor problem which normally resolves within about a week.

Water-logging of the cornea
Corneal oedema or water logging rarely occurs and causes the front of the eye to become blue. If corneal oedema does occur, it usually does so in those pets already predisposed to corneal oedema e.g. older animals and certain breeds e.g. Boston terriers. Careful surgery and the use of viscoelastic gel help to reduce the chances of oedema developing.

Infection
Thankfully this vision threatening complication is very rare. Antibiotics in the form of tablets and ointment are used before and after the surgery to help to prevent this.

Retinal detachment
Again, this vision threatening complication is rare. It is more common in long standing cataracts with excessive lens induced uveitis. A routine ultrasound scan before the surgery helps to identify at-risk patients.

‘After-cataract’
All cataract patients develop some degree of ‘after-cataract’ or clouding of the capsule left in situ. Fortunately, this rarely affects vision. In some cases the ‘after-cataract’ can be more severe leading to reduced vision. Having a plastic lens implant has been shown to help to prevent the clouding of the capsule. If after-cataract becomes very severe it can be removed surgically, although this is very rarely necessary.

Conclusion

There is no doubt that cataract surgery in cats and dogs is a major undertaking. However, the procedure is commonly employed at Woodcroft Referrals and the success rate of surgery is good. Cataract surgery is a chance to give your pet improved vision and we are always on hand to provide any support or guidance you feel necessary. 

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