A cataract is an opacity of the lens. This opacification results in less light reaching the nerve layer of the eye known as the retina. This in turn can lead to reduced vision and ultimately blindness. A cataract may start as a small opacity that gradually enlarges. It is very difficult to predict the rate of progression, but most cataracts will mature and lead to blindness.
Causes of cataracts
Many conditions have been known to cause cataracts. These include:
- Hereditary (genetic) predisposition
- Severe inflammation in the eye
- Blunt trauma to the eye or a perforating foreign body that can strike the lens
- Radiation (for example following radiation therapy to tumours near the eye)
- Electrocution following a pet biting an electrical cable
- Secondary to ageing
- Diabetes mellitus
- Retinal disease (for example progressive retinal atrophy)
Is my pet a good candidate for cataract surgery?F
Cataract surgery is an elective procedure. As such, it is important to ascertain that your pet is healthy and that there are no underlying conditions that may affect the outcome of the surgery. We may recommend that certain pre-operative blood tests are undertaken to ensure that your pet is a suitable candidate for surgery.
It has been shown in man that there is a close relationship between severe post-operative complications in patients undergoing orthopaedic and ophthalmic surgery, and severe dental or gingival disease. These complications are caused when bacteria enter the bloodstream through the inflamed gums. It is for this reason that one should ensure that dental hygiene is good. We may thus request that your pet have a dental scale and polish procedure 2-3 weeks prior to cataract surgery or start on oral antiseptic rinse to reduce bacterial oral bacterial load.
Because we cannot visualize the retina through an opaque lens, we have to resort to another diagnostic modality to ensure normal retinal function before the surgery. This modality is electroretinography - a test performed under topical anaesthesia and sedation if necessary. Using a computer, we measure the electrical response in the eye following its stimulation with light. A waveform very similar to an electrocardiogram is obtained and the different waves represent electrical activity of the different layers in the retina. Cataract surgery will only be done if your pet has normal retinal function.
If the electroretinogram is normal we routinely perform an ultrasound examination of the eyes. Ultrasonography allows one to see behind the opaque lens. We do this to ensure that there is no small retinal detachment and that the vitreous, (the jelly behind the lens) is normal.
If your pet is a candidate for surgery, treatment with anti inflammatory eye drops and tablets will commence 1 week prior to surgery.
A cataract can only be removed surgically, and not by medications. Techniques in man and animals have progressively improved over time and the current method for cataract removal is by a process called phacoemulsification. This is not laser treatment. In animals this surgery is done under a general anaesthetic. During the procedure a small incision [3.2mm] is made in the cornea and the front capsule of the lens is removed. The cloudy contents are then removed by a small ultrasonic probe which fragments and sucks out the lens material. Once the lens is removed it can be replaced with an artificial lens which can be folded and placed in the eye through the same small incision. The corneal wound is then sutured with very fine absorbable suture material. There are situations, however, when a lens cannot be replaced. In these cases the eye will remain longsighted and the animal will need more time to adapt before he/she starts to see better.
Going home and post-operative treatment
In most cases the patient will be discharged the day following surgery. We normally treat our cataract patients with antibiotics for a week and oral anti inflammatory tablets and eye drops for a number of weeks after surgery.
Much of the success during the post-operative recovery period will depend on owners complying to the re-evaluations we recommend. During these evaluations we shall give your pet a full examination and perform some routine procedures, such as taking the pressure in the eyes and monitoring for any signs of inflammation. We recommend these examinations at the following times after surgery:
Day 1: Done in clinic before discharge
Day 7: We are looking to see that the suture line is satisfactory, the cornea is clear, and that the eye is comfortable. Usually the retina [the light sensitive part of the eye] can be seen through the ophthalmoscope at this examination for the first time since the cataract appeared. Often visual responses are present to tell us how much your pet sees. Medications may be reviewed.
1 Month: Perhaps the best time to assess the success of the operation.
Two months,six months and then twelve months: These further check ups are used to monitor progress. It has been shown in human and animal cataract patients that "relapses" of the red eye may occur up to 6 months post operation.
Post-operative results and complications
The procedure generally is very successful, with most patients showing improved vision. The intention of cataract surgery in animals is for the patient to lead a more normal life than before surgery. All animals react differently after surgery and some may take longer to recover vision than others. Our success rate is in excess of 90%. This is comparable with success rates reported by veterinary ophthalmologists world-wide.
Serious complications are rare but one must realise that they could lead to failure of vision. Problems such as inflammation in the eye [uveitis], increased pressure [glaucoma], retinal detachment, severe intra-ocular bleeding and dullness of the cornea may occur.
Will the cataract grow back?
Some patients may have remnants of lens fibres re-growing and forming a scar on the remaining back capsule of the lens that can interfere with the visual axis and cause reduced vision. This is not a common complication and the incidence is much reduced by implanting an artificial lens. However, if it occurs it can be treated by entering the eye a second time to remove the opaque capsule. In some cases this capsule can be removed by laser which means it is not necessary to open the eye a second time. This phenomenon is not uncommon in man following surgery and usually is corrected by a subsequent laser surgery.