Worldwide, around 45 million people are blind and 135 million have only partial sight. This number could double by 2020.[1]
 |
Advances in medical technology to treat and correct eye-sight disorders have been astounding over the past two decades - from new extra thin spectacles and soft contact lenses, to synthetic intraocular lenses, sophisticated lasers and high precision surgical instruments of various kinds. For the patient the results of eye surgery are in many cases quite spectacular. The skill with which the eye-surgeon handles new devices and equipment is key; in this field as in cardiovascular or orthopaedic surgery, for example, education and training (often provided by the manufacturer) are fundamental. This edition of Medical Technology Focus provides an overview of some of the most common conditions and treatments available.
Optical disorders (or refractive disorders) are caused by a faulty optical system, preventing the eye from forming a crisp, sharp image.
The eye functions basically in the same way a camera does. Both a camera and the eye are composed of a lens and a light sensitive "film" on which the image is projected through the cornea and lens of the eye. The image received by the retina is smaller than the original and turned upside down. However, by combining the input from both eyes, the brain is capable of interpreting the received visual information correctly. The lens adjusts in order to guarantee clear vision of objects close by and far away.
The four most common refractive disorders are myopia, hypermetropia, astigmatism and presbyopia. Myopia (nearsightedness) occurs when the cornea is curved too steeply or the eyeball is too long, causing light rays to converge before reaching the retina and resulting in a blurry view of distant objects. Hypermetropia occurs when the eyeball is too short or the cornea is not curved steeply enough. In people with hypermetropia, light rays converge in a point behind the retina, resulting in a general blurred vision of objects both close by and at a distance. Astigmatism is a disorder often coinciding with myopia or hypermetropia and occurs when the eyeball is not convex but elliptical. Presbyopia is a natural part of the ageing process, typically manifesting itself from the age of 40 onwards. As people grow older, the lens becomes less flexible, making it more difficult to focus up close. These disorders are usually easily correctible with glasses and contact lenses, or via refractive surgery.
The most common way of correcting optical disorders is via lenses, either mounted in a frame or in the form of small plastic discs positioned directly over the cornea. Nowadays eye glasses can be equipped with bifocal and even trifocal glasses. They contain respectively two and three lenses, an upper lens for viewing distant objects and a lower lens for looking at objects close by. Trifocals contain an additional lens for viewing objects at middle distance.
An estimated 125 million people worldwide wear contact lenses[3]. New technology has greatly improved comfort and performance.
Contact lenses have become increasingly popular, in particular among people with relatively low eye-sight and for whom glasses have an unattractive distorting effect (magnifying or reducing the size of their eyes).
The main disadvantage of the first generation of contact lenses was the fact that they were (nearly) impermeable to oxygen. A major breakthrough was achieved in 1999, when the first silicone hydrogel contact lenses came on the market. These combined the benefits of silicone - with its extremely high oxygen permeability - with the comfort and clinical performance of conventional lenses.
Apart from the obvious difference between hard lenses and soft lenses, a distinction can be made between daily contact lenses (DW) - which have to be removed in the evening - and extended wear (EW) contact lenses which can be worn for 6 to up to 30 consecutive nights. Although the latter are more comfortable in usage, people wearing EW contacts are also more prone to various corneal infections, corneal ulcers and other vision-threatening complications. Different measures can be taken however to reduce the risk of infections: the contact lenses should be removed before swimming, never be cleaned with tap water, and daily contact lenses should always be removed to sleep.
Refractive surgery is a common denominator for "spectacle and contact lens replacing eye surgery".
Refractive surgery is a possible solution for people with decreased vision who do not tolerate contact lenses or prefer not to wear glasses. The three most common surgical procedures available today are excimer laser treatment, intraocular lens implantation and bioptic surgery. One treatment which does not fit one of the above categories is the RK treatment.
RK is the abbreviation of Radial Keratotomy and is the oldest known technique for surgically correcting refractive errors. The technique has been widely used to correct myopia by making between four and sixteen incisions in the cornea in a star shaped pattern. The cornea thus becomes unstable around the locations of the incisions. The internal pressure of the eye will consequently modify the curving of the eye, allowing light to be focussed correctly onto the retina. This technique enjoyed immense popularity because it was a relatively easy, cheap, well-known and quick procedure.
 |
Didier Léchaudé, France, extract from "Metamorphosis - From disability to an active lifestyle" (for more information or to get DVD of this film, please contact thomas.lindemans@eucomed.be
The excimer laser is a surgical tool used to alter the curving of the cornea so that light can be focussed correctly onto the retina. Although treatment is quick and fairly painless, there are certain risks associated with laser treatment, such as bleeding, increased pressure in the eye, clouding of the cornea, scarring of the retina and cataract formation. PRK, LASEK and LASIK are the three main treatments in which the excimer laser is currently used.
The Photorefractive Keratectomy (PRK) technique was developed around 1985 and was the precursor to the LASEK and LASIK techniques. It uses an excimer laser, a concentrated ray of ultraviolet light, to remove microscopically small amounts of cornea cells. It can remove 0,25 microns (1/200th of the diameter of a human hair) of tissue in a single pulse[4]. The procedure usually takes less than a minute per eye and is ideal for people who are not suitable for LASIK treatment (people with a thin cornea).
First, the epithelium, the soft outer layer of the eye, is detached using an alcohol solution. During the PRK procedure, the epithelium will be completely removed, based on the knowledge that it can completely replace itself from limbal stem cells in a matter of days with no loss of functionality. Next, the excimer laser ablates small portions of cornea tissue. After the cornea has been altered, the epithelium will be placed over the cornea again and covered by a protective bandage lens in case of LASEK surgery, or will be allowed to renew itself in the case of PRK surgery.
In the case of the Laser In Situ Keratomileusis (LASIK) procedure, the epithelium is not removed prior to laser treatment. Using a small knife (microkeratome), a flap is cut out off the outer corneal tissue. This flap is rolled up, after which the excimer laser reshapes the underlying corneal tissue. When the corneal tissue has been sufficiently altered, the flap is folded out again over the rest of the cornea. The healing process usually takes up to around 4 days.
Two sub-procedures that fall under LASIK surgery are Epi-LASIK (Epithelial LASIK) surgery whereby a specific type of microkeratome is used and Wavefront-Guided LASIK whereby a "map" is created of the way in which the eye focuses light. This helps the surgeon to notice small irregularities in the eye so that treatment can be personalised and risk of vision loss reduced.
Conductive Keratoplasty (CK) is sometimes used in older, farsighted patients. During the procedure, heat is applied to the cornea. This causes the outer edge of the cornea to tighten which in return will cause the central part of the cornea to curve more. The procedure is fairly painless and vision restoration occurs almost instantly. However, CK is a temporary treatment, unlike PRK, LASEK and LASIK which yield permanent vision restoration.
"With the PRK technique, the evolution of technology has been very important. We can now treat patients with severe myopia and lesser hypermetropia. The advantages are the reliability and simplicity of the procedure. The surgeon can fully control the operation. The new lasers, which use the flying-spot technology, eliminate the need for severe heating of the cornea…The procedure is very simple; it takes about one to two minutes. We apply a sterile gauze and an instrument to keep the eye open. The patient looks at a red light, linked to an eye-tracker. Then we clean the epithelium with a small brush. The treatment itself consists of three ablations of five seconds each. Then I cool down the cornea, which enhances recovery and reduces pain. Afterwards I apply a protective contact lens and the patient leaves the operation room… The advantage of this technique is that there are rarely complications. The patient can go home straight away. 25% of patients experience some inconvenience for two or three days. Vision becomes normal after that and they can once again take up their activities. The result is excellent and superior to contact lenses. 99% of people thank me and say they wish they had done it earlier".
Dr. C Castel - Excimer Laser Society Antwerp, Belgium, extract from "Metamorphosis - From disability to an active lifestyle" (for more information or to get DVD of this film, please contact thomas.lindemans@eucomed.be
Innovative technology and treatments have greatly contributed to improving outcomes and the quality of life of patients.
The front part of the eye is filled with a nutritious fluid that provides the lens, iris and cornea with necessary substances. In an eye in perfect condition this fluid is constantly renewed, whereby old fluid is drained via miniscule channels. In certain cases however, these channels can get clogged preventing excess fluid from being drained and thus increasing the pressure within the eye. Glaucoma is a set of disorders that arise when pressure in the eye is elevated to such an extent that the optic nerve is damaged. This causes small parts of the field of sight to get "stolen" unnoticed. As the disorder progresses however, more and more of the central field of sight is lost which can quickly lead to blurred vision and even total blindness. This chronic form of glaucoma is the most common type and is called open angle glaucoma. Eye injury, infections, tumours, cataract or diabetes can also lead to glaucoma which is then referred to as secondary glaucoma. This type of the disorder occurs when the iris narrows or completely blocks the drainage angle of the eye preventing the eye fluid from exiting the eye. Its onset can be very sudden and should be treated immediately if permanent damage to the eye is to be avoided. Secondary glaucoma is a painful disorder often causing nausea and vomiting.
At present, there is no permanent cure. There are treatments available to lower the pressure in the eye, consequently hindering the progression of the disorder, but the beneficial results usually last for about 3 years, after which additional treatment is required. Depending on the progression of the disorder, treatment can consist of eye drops, laser treatment or surgical treatment.
Eye drops for the treatment of glaucoma come in many different variations, adapted to the different factors that characterise glaucoma in an individual patient. To lower the pressure in the eye, eye drops will either lower the production of eye fluid, or stimulate drainage of eye fluid.
Laser treatment is recommended when intraocular pressure cannot be achieved via eye drops or when medication is not well-tolerated. The procedure is pain free and does not require the patient to be hospitalised.
The standard surgical procedure for treating glaucoma is the trabeculectomy and is recommended when glaucoma continues to progress despite the use of medication regimens and possibly laser treatments. The purpose of this treatment is to create a new "route" for the aqueous fluid to be drained. This is done by making a small incision in the sclera (the white of the eye). A flap of sclera tissue is left to cover the incision. This new opening allows fluid to drain out of the eye, bypassing the clogged drainage channels.
A modified version of the trabeculectomy is the deep sclerectomy which avoids entering the anterior chamber of the eye. Instead, a very deep dissection is performed in the sclera and trabecular meshwork (the network of drainage channels). The main advantage over a trabeculectomy is the reduced risk of inflammation.
Usually, surgical treatment for glaucoma is relatively painless.
Worldwide, cataract is the main cause of blindness[5]. About 50% of the population over 65 years over age suffers from a certain degree of cataract. This number rises by an additional 20% in people over 75 years of age[6].
 |
Cataract is part of the normal ageing process and consequently occurs frequently in people over 50 years of age. Women however appear to be more at risk than men[7]. If left untreated, the disorder can cause total blindness. The speed with which occurs differs greatly from one person to the other, varying from a couple of months to several years and also varying from one eye to the other.
Apart from age-related factors, the disorder can also be caused by other, non-related factors such as eye injuries; disorders such as diabetes, glaucoma, high blood pressure or arthritis; medication containing cortisone or psoralens; smoking and alcohol consumption. In some cases, cataract also manifests itself at a very young age. This childhood cataract can be transmitted by the mother during pregnancy if she was infected with rubella (German measles). It could also point to hereditary transmission of the disorder.
Up until now, there is no medication available which slows down the progress of cataracts. Initially however, the loss of vision due to early cataract development can be compensated by wearing stronger glasses. At the stage where the disorder seriously impairs the patient's vision, and where it prevents the patient from performing daily tasks, surgery is the only treatment available.
The most common procedures for surgically treating cataracts are intracapsular extraction (ICCE) and extracapsular extraction (ECCE).
Intracapsular extraction (ICCE) is the oldest procedure whereby the lens and its capsule are removed as a whole. Although this is the quickest and easiest operation to carry out, there is a greater risk of complications. After the surgery, the eye is left without a lens, so the patient will have to wear very thick aphakic glasses or contacts. Because of the higher risk of complications, such as astigmatism and infections, ICCEs are no longer widely used.
When performing extracapsular extraction (ECCE), the clouded lens is removed but the posterior capsule (which contains the lens) is left intact. That way, a new synthetic intraocular lens can be implanted to restore vision. This lens will ensure that light bundles are correctly focussed so no glasses or contacts will be necessary postoperatively. The entire operation takes less than an hour to perform, is relatively painless and becomes ever less invasive thanks to innovative developments in the materials used to create the intraocular lens. Around 1970, the average length of an incision during an ECCE was 12 - 14 mm[8]. Thanks to the development of foldable acrylic intraocular lenses, the length of incisions can nowadays be reduced to less than 3 mm.
In extracapsular extraction with phacoemulsification, the lens is "emulsified". This new technique was developed in search of a procedure which required even smaller incisions. By using an ultrasound probe which produces high frequency mechanical waves out of an electric current, the nucleus of the lens can be broken into smaller particles. These particles are removed and a foldable lens is inserted via the 3 mm incision. New technologies have enabled surgeons to make such small incisions that no stitches are required afterwards. This in turn reduces the recovery time and postoperative hospital visits for the patient. Moreover, the medical device used for phacoemulsification simultaneously assures proper irrigation of the eye and aspiration of the lens particles.
The macula lutea is a small area in the centre of the retina which enables us to distinguish details. This is possible because the centre of the retina contains most cones, the contrast and colour cells of the eye. The remaining part of the eye consists mostly of rods which enable us to perceive movement and distinguish between bright and dark shades.
Macular degeneration is a painless disorder which occurs when the macula of the eye is slowly decaying. Consequently, activities that require detailed sight like reading or knitting become difficult if not impossible. Given that the disease only affects the central vision, peripheral sight is maintained so that most people suffering from macular degeneration still manage to take care of themselves.
Macular degeneration is in most cases age-related and occurs frequently in people above 60 years of age. It is the main cause of visual impairment in the Western World[9]. Worldwide approximately 25-30 million people are affected by age-related macular degeneration[10]. Certain forms can be treated surgically.
There are a number of risk factors[11] that can increase the incidence of macular degeneration (see box). Consumption of a diet rich in antioxidants (beta carotene and the mixed carotenoids that are precursors of vitamin A, vitamins C and E, selenium, and zinc), or taking antioxidant nutritional supplements, may help prevent macular degeneration, particularly if started early in life[12]. Good dietary sources of antioxidants include citrus fruits, cauliflower, broccoli, nuts, seeds, orange and yellow vegetables, cherries, blackberries, and blueberries. Research has shown that nutritional therapy can prevent macular degeneration or slow its progression once established.
Risk factors:
_______________________________
[1] Vision 2020. (2000). Introducing Vision 2020: The right to sight.
[2] European Blind Union: http://www.euroblind.org/fichiersGB/visincen.html
[3] Barr, J. "2004 Annual Report". Contact Lens Spectrum. January 2005, http://www.clspectrum.com/article.aspx?article=12733
[4] The Eyecare Trust, Excimer Laser Photorefractive Surgery, February 2005, http://www.eye-care.org.uk/item_view.php?item_id=129&content_id=6
[5] WHO Fact Sheet N°282, Magnitude and causes of visual impairment, November 2004, http://www.who.int/mediacentre/factsheets/fs282/en/
[6] E.W. Trudo and W.J. Stark. Cataracts - lifting the clouds on an age-old problem (1998), Postgraduate Medicine vol. 103 no 5.
[7] S. Jacobzone, M. Jee-Hughes and P. Moise, OECD Ageing Related Disease Study (1999), p 35, http://www.oecd.org/dataoecd/28/12/1889895.pdf
[8] D C Minassiana, P Rosenc, J K G Dartb, A Reidyd, P Desaid, M Sidhue, Extracapsular cataract extraction compared with small incision surgery by phacoemulsification: a randomised trial, Br J Ophthalmol 2001;85:822-829 (July)
[9] WHO Fact Sheet N°282, Magnitude and causes of visual impairment, November 2004, http://www.who.int/mediacentre/factsheets/fs282/en/
[10] B. Thylefors, AD. Ngrel, R. Pararajasegaram, KY. Dadzie, Global data on blindness., Bull World Health Organ, 1995, vol. 73, pp. 115--121
[11] Smith, Wayne, et al., Risk Factors for Age-related Macular Degeneration. Pooled Findings from Three Continents., Ophthalmology, 2001, vol. 108, pp. 697--704
[12] AREDS, Age-Related-Eye-Disease-Study-Research-Group, A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8. Arch Ophthalmol 2001a ; 119: 1417-36.
