CATARACT

Cataract is the clouding of the natural lens, which sits just behind the pupil and helps to focus light on the retina.

The clouding of the lens is usually age-related, although in some cases a cataract may develop following injury to the eye or as a result of other eye conditions, such as longstanding inflammation or previous eye surgery. Certain systemic conditions, such as diabetes or renal disease, and medications, such as steroids, can also cause cataract. History of poor nutrition and dehydration, exposure to ionising radiation and alcohol consumption have also been linked to progressive cataract (invited review article Dhillon, Lascaratos 2009). Young individuals with cataract may have a positive family history and other features of associated systemic conditions such as myotonic dystrophy or Down syndrome.

Most patients with cataract experience blurred or hazy vision, and sometimes haloes or glare for example when driving at night. Cataract can also cause reduced contrast between objects and their background (reduced contrast sensitivity) which can lead to increasing problems reading grey text on a less-than-white background, often the case with newsprint. On the other hand, cataract can often change your prescription to become more short-sighted (refractive shift to myopia) induced by the hardening of the opacified lens and this may be welcomed by patients who may be able to read small print without reading glasses much to their surprise. If you only have early cataract with mild or no symptoms at all, surgery may not be indicated.

Cataract surgery involves removing your cloudy lens and replacing it with a clear plastic lens. It is a day case procedure usually under local anaesthetic. The operation normally takes approximately 15 minutes. You are usually awake during surgery and your eye doesn’t feel any pain during the operation, although you may occasionally feel some pressure. You will not be able to see properly during the operation, but you may notice bright lights or colours. It is important to lie relatively flat and still during the operation – if you need to cough or adjust your position, please warn your surgeon. The cataract is removed through small self-sealing incisions (cuts) on the cornea of the eye using ultrasonic energy to break up and remove the cloudy lens. Normally no stitches are required and most patients can see well even on the first day after the operation. The clear plastic lens will stay in your eye forever, only rarely needing replacement.

Several measurements (including biometry, corneal topography and macular OCT) performed by a specialist technician may be required before the operation to help us plan the procedure and decide which lens type and strength would be best for you. Contact lenses can alter the shape of your eye and influence these measurements, so if you normally wear soft contact lenses please remember to remove these 1 week before your biometry. For hard contact lenses please remove these 3 weeks before the measurements. You will also require a preassessment by an experienced nurse to review your general health and plan your anaesthetic and other requirements during the day of surgery.

With cataract surgery not only is it possible to improve your vision, but also reduce your dependence on glasses. A monofocal plastic lens would normally offer you good distance vision without glasses, although you would still need reading glasses. If you don’t mind wearing reading glasses, monofocal lenses aiming for clear distance vision in both eyes may be the best option for you and would offer good quality distance vision while avoiding the optical side effects of other types of lenses such as multifocals (see below). Sometimes it is possible to achieve good distance and intermediate (or near vision) by inserting a monofocal lens aiming for clear distance vision in one eye (usually the dominant eye) and another monofocal lens aiming for clear vision at arms’ length (or near) in the other eye. If you have astigmatism or another irregularity of the shape of your eye you may still need glasses (such as varifocals) both for distance and near after surgery. 

We can reduce or correct your astigmatism by using special lenses called toric lenses, or use multifocal lenses to reduce your dependence on glasses for far, intermediate and near. Not everyone would be suitable or benefit from these premium (toric or multifocal) lenses and the relative indications and limitations of these technologies will be discussed with you during the consultation. About four out of five patients may be completely free of glasses or contact lenses with a multifocal lens, although the side effect profile of these lenses (mainly haloes, glare and loss of contrast) and risks of surgery need to be carefully considered. If you prefer better image quality and you don’t mind having to wear reading glasses sometimes to get the best near vision especially in poor light, then an extended depth of focus (EDOF) lens (such as the Zeiss AT LARA) may be a better option. While standard multifocal lenses have two distinct foci with blurry vision in between, EDOF lenses work by having one elongated focal area giving an extended depth of focus. Due to their special design, the EDOF lenses can reduce the optical side effects of standard multifocal lenses, optimise contrast sensitivity and minimise light scatter and visual side effects. For more information about cataract surgery please see article by Dhillon, Lascaratos 2009 and Understanding Cataracts leaflet.

This is sometimes a difficult decision to make and will depend on your visual requirements and how prepared you are to accept the risks of surgery. In general, when activities of daily living become difficult due to cataract-related visual impairment the question of cataract surgery should be considered. The vast majority of patients do very well after cataract surgery, especially in the hands of an experienced surgeon. However, there is a very small risk of losing the sight as a result of infection or bleeding (less than 1:1000) and a small risk of needing a second operation (1-2% of cases) if there is a problem with the first operation. Your individual risk and treatment options will be discussed with you during the initial consultation and in my personal experience requiring a second operation is extremely rare despite the complexity of cataract operations I perform. Laser may be required months or years after the initial operation in 1:10 patients should the film behind the plastic lens become cloudy.

If you have glaucoma and have also developed visually significant cataract, meaning that the visual impairment from the cloudy lens is affecting your everyday activities, cataract surgery should be discussed. In certain types of glaucoma, such as primary angle closure glaucoma where the drainage angle of the eye is very narrow, cataract surgery may be offered even in the absence of visually significant cataract with the aim to open up the drainage angle of the eye and thus improve long-term eye pressure control. This is because the plastic clear lens inserted in the eye at the time of cataract surgery is less bulky than the natural cloudy lens being removed, thus creating additional space within the eye and allowing the drainage angle to open. Certain conditions, such as pseudoexfoliation glaucoma or angle closure glaucoma, carry in general a higher risk of complications during cataract surgery and the experience of the surgeon is critical in these cases. In the presence of very advanced glaucoma, cataract surgery carries a risk of ‘wipe out’ of vision and in some cases glaucoma surgery may need to precede cataract surgery. If you have previously undergone glaucoma filtration surgery, such as trabeculectomy surgery, the long-term function of the filtration bleb may be compromised by the inflammation caused during cataract surgery and the use of anti-scarring agents may be required at the time of the cataract operation to prevent this from happening. Your individual risk factors and circumstances will be taken into account during the consultation and an appropriate management plan formulated to meet your needs.

Clear lens extraction is a type of procedure that requires careful consideration, as the patient in many cases has healthy eyes, good vision and no visually significant cataract. If you have narrow drainage angles with raised eye pressure or narrow drainage angles with glaucoma, removing your natural lens and replacing it with a plastic lens may be the best option to allow the drainage angles to open and improve your long-term eye pressure control, especially if you are over the age of 50. In clear lens extraction the natural lens of the eye which is often quite bulky is removed and replaced by a plastic lens. The latter is much thinner than the natural lens, thus creating additional space within the eye and allowing the drainage angles to open, which in turn has been shown to help with the eye pressure control. Laser may be appropriate in some cases to open the drainage angles and additional tests such as a scan of the front part of the eye (anterior segment OCT) may be required in some cases to help with this decision, especially in younger patients.

You may also be suitable for lens surgery if you would like to reduce dependence on glasses or contact lenses and you are either not suitable for laser eye surgery or you are of an age where presbyopia (loss of elasticity of the natural lens and ability to focus for near) has developed. About four out of five patients may be completely free of glasses or contact lenses after lens extraction with a multifocal lens, although the side effect profile of these lenses (mainly haloes, glare and loss of contrast) and risks of surgery need to be carefully considered (patient information leaflet). If you prefer better image quality and you don’t mind having to wear reading glasses sometimes to get the best near vision especially in poor light, then an extended depth of focus (EDOF) lens may be a better option. Due to their special design, the EDOF lenses can avoid the optical side effects of standard multifocal lenses, optimise contrast sensitivity and minimise light scatter and visual side effects. Alternatives to reduce dependence on glasses include laser eye surgery, phakic intraocular lens insertion or corneal inlays, and these may often be the preferred options for younger patients. The balance shifts towards lens extraction as you get older and the flexibility and clarity of the natural lens diminish. If you have glaucoma, macular degeneration, diabetic retinopathy, recurrent eye inflammation or other underlying eye conditions you may not be suitable for multifocal lenses. An alternative approach to reduce dependence on glasses while avoiding the optical side effects of multifocal lenses or if you are not suitable for multifocal lenses would be to use standard monofocal lenses aiming for clear distance vision in one eye (usually the dominant eye) and clear vision at arms’ length in the other, although you would still probably need glasses for reading.  It is important to listen to what you would like to achieve, understand a bit more about your everyday activities, evaluate the health of your eyes and review your test results, before discussing your available treatment options.