User:TerryE/sandbox

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This article aims to provide a balanced perspective of the impact of cataracts and their treatment from the perspective of the patient rather than that of the medical professional. It uses plain English in preference to medical vernacular to describe exactly what a cataract is, how it is treated, and what you, as the potential patient in this process, need to understand and to do.

A cataract occurs when the eye's lens starts to become cloudy. The initial effects of a cataract can be subtle and you may first learn that you have one from your optician during a routine eye examination. However, cataracts are usually progressive and result in a variety of symptoms including near-sightedness, loss of depth vision, changes in colours and a greying of your vision. Cataracts, if left untreated, can ultimately cause vision loss and permanent blindness[1]. Cataracts are one of the most common ailments of the middle and old age with over 17% of US adults over 40 having at a cataract in at least one eye[2]. The primary treatment for cataracts is to remove the clouded lens by Cataract Surgery, a surgical procedure that has become routine over the past decade. You must agree important decisions with the consultant on treatment options and their timing. You play a key role in the entire course of treatment. How you prepare for this role and the decisions that you make will have life changing implications for yourself.

The Human Eye: Our Camera onto the World[edit]

Human eye cross-sectional view, showing position of human lens. Courtesy NIH National Eye Institute

In many respects the human eye is essentially a camera, with living rather than mechanical components. Most references which described this use medical terminology based on Greek and Latin words and there is a glossary of these at the end of this article.

  • The eye is roughly spherical of diameter about 25mm or 1 inch[3]. At the front of the eye is a lens system facing out onto the world, and at the back is a light and colour sensitive film called the retina, which is connected via the optical nerve to the visual centre within the brain.
  • Perhaps the most individual and noticeable part of the eye is the iris, the coloured ring which surrounds the pupil and controls the amount of light admitted to the eye.
  • The lens of the eye is made up of two parts, the cornea and the lens. The cornea sits in front of and protects the fragile iris. It is a rigid clear gel with a fixed focal length and provides about two thirds of the focusing power of the eye. The lens is made up of a flexible protein gel in a transparent bag which itself is supported by a ring of muscles. This sits behind the iris inside the eye, and contributes the remaining third of the focusing power.
  • The eye focuses or "accommodates" by contracting this muscle ring, which makes the bag and lens bulge. This changes the shape of lens and thus increases its focusing power. The lens can vary in power by up to 50% in a child, because the muscles are strong and the gel is very flexible. Unfortunately these muscles lose their strength as we get older and the gel becomes less flexible and we "lose accommodation", so that by the age of sixty or so the lens is almost rigid and can now only vary in power by a few percent. This means that whilst a child can focus on something 10cm or 4" from its nose, the average sixty year-old can't even focus at a distance of perhaps 1m or 3ft (which is why we need reading glasses by this age).
  • The lens can also start to go cloudy and lumpy; this is known as a cataract. Cataracts are normally associated with ageing, though there can be other contributory factors.

"Perfect vision" occurs when the resting eye (that is the muscle ring is fully relaxed) can naturally focus on a distant scene. Unfortunately human eyes vary quite considerably in the population, and only a minority have perfect vision. The two major visual defects are long sightedness and short sightedness. The other common visual defect is known as astigmatism, where the focusing of the lens has a directional aberration. The young eye can tolerate a range of visual defects without strain. However, we loose the ability to accommodate as we get older, and hence most cataract suffers already need glasses or some other form of visual correction to see clearly.

Cataract Surgery[edit]

Cataract surgery replaces the failing human lens with an artificial lens (know as an intraocular lens or IOL). For the IOL to give good vision, it must be correctly matched to the patient's eye. This mapping of the eye, specifically the shape and size of both the cornea and lens, is normally done in an evaluation a week or so before surgery.

Main article: Cataract surgery
Main article: Phacoemulsification

The cataract surgery itself is generally performed at a hospital or specialist surgical centre on a day care basis. The standard surgical procedure[4][5] takes only 20 minutes or so in the operating theatre, though pre-treatment and post-treatment typically extend the stay to 4-6 hours.

The entire surgical procedure is carried out through a small (2-3 mm) incision in the eye's surface. (This is roughly the size of the eye of a needle.) The surgeon then carries out a procedure known as Phaco to liquefy the clouded lens and to flush out the bag that contained it. The IOL is then implanted and positioned within the bag to replace the natural lens. The Wiki links and references below provide more details of this procedure.

The success of the surgery depends on many factors: the type of IOL, the procedure, the ability of the surgeon, and the care taken by the patient before, during and after the surgery. However over 90% of patients have materially improved vision. Most will continue to need spectacles or other visual assistance. Only a small percentage suffer long-term complications, or find that the surgery provides no tangible improvement [reference needed]. In a small number of cases the outcome can be worse. So each patient should consider the following:

  • What procedure is my surgeon going to use? Phaco has largely replaced the alternatives, such as conventional extracapsular cataract extraction (ECCE) and intracapsular cataract extraction (ICCE), because it is minimally invasive and leaves a small "sutureless" wound closure that requires no stitches in the eye. It also has excellent outcomes. However, there are certain situations where Phaco is not optimal and the surgeon may therefore recommend an alternative procedure. In such circumstances you should always ensure that you understand and accept the reasons for this.
  • When should I have the surgery? Following initial diagnosis, you should maintain a dialogue with your optician and primary care doctor to decide when to be referred to an ophthalmic specialist. In general, referral will not be recommended if you are not suffering visual symptoms and your lifestyle is not impacted. However, as the cataract progresses the symptoms may become unacceptable, for example when you no longer reach the minimum legal requirements for driving, or when you start to have difficulty in reading. Current practice is to schedule treatment once it has been established that the cataract is impacting on lifestyle.
  • What sort of anaesthesia should I choose? Current practice is to avoid the use of general anaesthetics, and use local anaesthetic options wherever practical because of reduced postoperative recovery time and reduced risks. However, whilst you will feel no pain under local anaesthetic, you will be able to feel the sensations of water on the side of your face, the buzzing of the surgical equipment, the general conversation in the theatre, and the rather surreal optical effects that occur as your lens is removed. This operation requires precision microsurgery on the part of the surgeon. You must therefore be confident that you can keep your eye and head immobile during the entire procedure. Some anaesthetic options can help here by freezing the orb of the eye. You might also consider discussing the option of mild sedation to reduce your general anxiety levels and to help you relax and stay still. You should therefore seek comprehensive counselling on the available anaesthetic options, before you agree the appropriate choice for you.
  • One eye or two? For those that are already blind in one eye, the potential risks of cataract surgery are more significant and they need to consider these carefully in consultation with their ophthalmologist. For those that have two working eyes, many discover that they have cataracts forming in both eyes by the time that the symptoms in the worst eye are starting to impact their lifestyle. If you are in this situation then you also need to discuss the pros and cons of your various options with your ophthalmologist; these include operating on both eyes, or operating on the first eye alone and deferring the second operation until needed.
If the short to medium term prognosis is that you will have cataract problems in both eyes, second eye surgery can give you significant additional gains in quality of life above and beyond those achieved after surgery to the one eye alone. For example, if you are long or short sighted then replacing both lenses offers the opportunity to reduce significantly the strength of visual correction needed and possibly even result in your not needing any. In this case, the normal practice is to separate the two operations by recovery period, in order to ensure that the prognosis for the first eye is acceptable before operating on the second. However some surgeons will offer to operate on both eyes in a single procedure "Simultaneous Bilateral Cataract Extraction (SBCE)", and in such a case you be aware of the risks associated with SBCE. You should discuss these with your surgeon and ensure that you both understand and accept the reasons for such a recommendation.
If only operating on one eye, the surgeon will select the IOL to match the prescriptions of both eyes, and in the case of operating on two eyes the surgeon will aim for perfect vision. However, you must recognise that the ultimate outcome can vary from the target, and that your eyes will be probably left with some residual error; most will find that some form of optical correction is needed to achieve acceptable vision. However, it is normally recommended to wait until four weeks after completion of surgery before having correction prescribed. In the case of one eye surgery, this inconvenience is mitigated by your being able to use the other eye. However, in the case two eye surgery, this means that you may have to cope with degraded vision for a period of up to six weeks.
  • What lens options do I have? The majority of cataract operations involve the use of monofocal IOLs, though during the past decade, a range of alternatives (such as the bifocal, multifocal, and accommodating IOLs) have received approval for use, but have not yet gained wide acceptance. This question merits its own section below.
  • Do I wish to have my astigmatism treated? Most IOLs provide a spherical refractive correction only. If you have material astigmatism, then without correction you will continue to need to wear spectacles or equivalent. Toric IOLs are now available but not yet established, and few surgeons have adopted their use. Most surgeons who treat astigmatism tend to use arcuate keratotomy (AK) to reduce residual astigmatism. This procedure itself carries risks with it, so again it is worth discussion the pros and cons with your surgeon.
  • What pre-operative and post-operative care do I need to do? For a few weeks prior to surgery you will be asked to carry out a cleaning regime around the eye lids and may be asked to avoid wearing eye make-up to minimise the risks of Blepharitis and other eye infections. After the surgery, you will be instructed to use anti-inflammatory and antibiotic eye drops for up to two weeks. Normal vision will start to return after 1-2 days, with some continuing discomfort, though again pain killers may be recommended for pain management. The eye should be largely recovered within a week, and complete recovery should be expected in about a month. The use of AK tends to extend this recovery time.
You should avoid any activities, even bending down abruptly, which can generate a sudden increase in blood pressure at the back of the eye until the incision has healed. You should also avoid all contact with the eye during this period, and you will be given an eye shield for wearing at night during the first days after the operation, and you should be careful around children etc. as even a light trauma to the eye at this time would be serious. You should not drive or participate in sporting activities until cleared to do so by the eye surgeon.
  • What are the main complications? The fall into three broad categories: operative, recovery and long term. The main operative risk is tearing of the rear of the lens bag, which occurs in less than 5% of operations. During recovery the main risks are infection exacerbated by poor post-operative care and hygiene, or by physical activities. The main long term risk is with clouding of the rear of the eye capsule that now holds the IOL which will require further treatment (posterior capsulotomy), though this is a routine laser based procedure. These issues are discussed further in the complications section of the main article.
  • What if I want further treatment options? the Phaco operation is designed to replace the eye lens material with an IOL. Subsequent extraction and replacement of an IOL may require conventional ECCE, and options even more complicated if a posterior capsulotomy has been carried out in the interim. It is therefore strongly recommended that you evaluate your options and make the right choice for initial treatment as subsequent treatments are a lot more complicated.

IOL Comparison Table[edit]

Type Description
Monofocal IOLs These IOLs have a fixed refractive power. This means that the focal length is also fixed, and for most patients this will be calibrated to distance vision. This means that they will require a reading proscription as well as possibly a distance glasses prescription, if there is a residual error in the IOL prescription or if they suffer material astigmatism. The primary advantages of Monofocal IOLs are their low coat, use of the simplest Phaco procedure, with the least risk of surgical complications. In a UK study of 2004, over 90% of cataract procedures used monofocal IOLs. From the patent's perspective this gives the best vision and contrast with the use of glasses, and as the majority were using glasses anyway before their operations, the restoration of visual function can be life changing, despite the loss of any residual (typically much less than one dioptre) accommodation with the removal of the natural lens.
Multifocal IOLs These are of two broad types: refractive and reflective. Both extend the depth of field giving "sweet spots" at far distance and reading distance. In various studies up to 80% of patents fitted with multifocal IOLs were able to de without glasses for everyday use, though some used glasses for extended reading. The main disadvantages of multifocal IOLs is a decreased contrast sensitivity, and increased "halo effect" and glare particularly when driving at night time facing on-coming traffic. Being a premium care option, AK can be used as an adjunct to multifocal IOLs to reduce any residual astigmatism.
Adaptive IOLs These couple the contraction of the ciliary muscles that surround the lens bag, with a lever mechanism on the periphery of the lens to displace the lens along the visual axis. This acts to modify the effective focal length of then lens typically by around one dioptre, though this falls over the first twelve months or so to perhaps half a dioptre. This is sufficient to give good accomodation is the IOL is correctly calibrated to the eye geometry from far distance to a metre or so. However, reading glasses will still be required with monofocal adaptive IOLs. Bifocal adaptive IOLs are currently undergoing trials but are not in wide use. AK can be used as an adjunct to adaptive IOLs to reduce any residual astigmatism.
Toric IOLs These also provide a toric correction which can be used to correct astigmatism. However, they are sensitive to placement and can be difficult to position, and therefore many surgeons prefer to use arcuate keratotomies (AK) or limbal relaxing incisions (LRI's) for mild astigmatic correction coupled with one of the previous IOL types. The limitation of AK or LRI is that these surgical procedures can really only effective correct up to 2 diopters of astigmatism and their effect is variable and not predictable.

Glossary[edit]

Term Description
Emmetropia Perfect Vision
Astigmatism Abberation in vision caused because the cornea is not radially symmetrical, leading to an orientation where the focal length in one plane is different to that at 90 degrees.
Hyperopia Long sightedness
Myopia Short sightedness
Presbyopia Age related loss of accomodation
Cornea The cornea is the transparent front part of the eye that covers the iris and serves as the first component in the eye's focal system.
Iris The iris that regulates the amount of light that enters the eye through the pupil
Lens The lens is the flexible structure behind the iris and serves as the adaptive second component in the eye's focal system.
Ciliary muscles The muscle ring used by the eye to focus the lens.
Glaucoma A serious disease of the optic nerve which may cause intraocular pressure and other serious implications. If left untreated, a cataract may trigger glaucoma.
Phacoemulsification (Phaco) A modern cataract surgery in which the eye's internal lens is liquified with an ultrasonic handpiece, and flushed from the eye.
Cataract Clouding of the lens in the eye
Extracapsular cataract extraction (ECCE)
Intracapsular cataract extraction (ICCE)
Arcuate keratotomy (AK) This is similar to radial keratotomy, but the incisions on the cornea are done at the periphery of the cornea to correct astigmatism. Although Lasik has now largel replaced most incisional procedures, AK is still used to correct mild (<2 dioptres) astigmatism during cataract surgery.

References[edit]

  1. ^ http://www.aafp.org/afp/990700ap/99.html
  2. ^ http://www.nei.nih.gov/eyedata/pbd6.asp%7C US National Eye Institute, Archives of Ophthalmology 2004;122:487-494
  3. ^ The Physics Facts Book. "Diameter of a Human Eye." Retrieved May 22, 2007.
  4. ^ Encyclopedia - Phacoemulsification for cataracts
  5. ^ BUPA Cataracts Fact Sheet. Note that this includes a Flash animation of the procedure.


External links[edit]

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