So you want to see better without glasses or contact lenses. You would have seen lots of advertisements about Laser vision correction. Vision correction surgery however is rapidly evolving and includes a wide range of laser and nonlaser procedures, which allow for a customised surgical solution for every patient's visual needs. There is indeed a lot more to vision correction surgery than lasers. No single refractive surgical technique is suitable for all patients and it is critical that the surgery is tailored to fit the needs of each and every individual patient. Just as a size 14 dress would look terrible on a size 10 person, a particular surgical technique that is right for one patient may not be right for another patient. This analogy of course falls down in that unlike exchanging a dress of the wrong size correcting the effects of a wrongly chosen surgical option can be very difficult and traumatizing. This specialist run centre provides the full range of vision correction surgery options and can consider treating all types and severity of refractive errors. In general, the following table summarizes the options available.
Focusing or Refractive Error
Low Hypermetropia to Moderate
Myopia +3 to -8 Dioptres
High Myopia more than -8 Dioptres
High Hypermetropia more than +3 Dioptres
Astigmatism
Vision Correction Surgery Options
Excimer Laser PRK, LASIK, LASEK,
Phakic Intraocular lens or Phakic IOL,
Refractive Lens Exchange RELEX, rarely
LASIK, LASEK
Phakic Intraocular lens, Refractive Lens
Exchange RELEX,
Excimer Laser, AK , LRI
Presbyopia Presbyopic Lens Exchange: PRELEX
Presbyopia is the focusing error that occurs universally as the eyes capacity to alter its focus from distant to near objects decreases. This usually manifests after the age of 40 initially by having to read at a full arms length and as it gets worse reading glasses, bifocals or varifocal spectacles are used. The reason why everyone gets Presbyopia is due to the ageing of the natural lens of the eye, which loses its capacity to adjust focus from distant to near objects. Laser vision correction (LASIK, LASEK or PRK) can correct for distance or near vision but not both si multaneously. Thus, people in their 40’s needing bifocal, varifocal or reading glasses get limited improvement from laser vision surgery. Further Laser vision surgery works by altering the focus of the cornea and hence does not alter the ageing process of the natural lens of the eye. This process ultimately results in cataract formation. In the past, various surgical options to correct Presbyopia have met with very limited success.
Copyright: Mr. Milind Pande D.O., FRCS, FRCOphth, Consultant Ophthalmic Surgeon
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Pre sbyopic L ens Ex change ( PRELEX ) is a surgical procedure, designed to correct Presbyopia by exchanging the ageing natural lens of the eye for a new intra-ocular lens. This new lens could be either a Multifocal Lens (similar to a varifocal spectacle lens) or an Accommodating lens which mimics the natural lens and moves within the eye to adjust its focusing power depending on whether the eye is looking at distant or near objects. This surgery evolved from Refractive
Cataract Surgery where the cataract (cloudy natural lens) is exchanged for a
Multifocal or Accommodative lens. Thus, the PRELEX operation is very similar to a cataract operation but uses new replacement lens technology to restore good distance and near vision without traditional bifocal, varifocal spectacles or contact lenses. The vast majority of patients are able to function most of the time without spectacles or contact lenses while needing glasses or contact lenses for some visually demanding activities like driving, reading fine print etc. As the ageing lens is replaced, it eliminates the risk of developing a cataract and in some ways is like bringing forward your cataract operation by a few years.
An assessment of your visual needs, lifestyle, and a complete eye examination are critical factors in choosing an appropriate surgical technique for your particular eye. The eye examination includes a full assessment of the optical system of the eye i.e. Refraction, Scanning Slit Corneal Topography,
Pachymetry, Keratometry and Pupillometry.
As with all surgery, PRELEX Surgery is associated with certain risks for complications. There is very wide range of complications reported but generally, there is a minute chance of a blinding complication, while the chances of ending up with worse vision after surgery compared to before are less than 1%. Your decision to have PRELEX surgery should be a positive informed decision based on an individual and accurate assessment of the potential risks and benefits.
The rest of this guide is a more detailed exploration of these issues.
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Copyright: Mr. Milind Pande D.O., FRCS, FRCOphth, Consultant Ophthalmic Surgeon
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The eyeball is very similar to a camera with two focusing elements. The cornea
(the clear "window" in front of the pupil and iris) is the most powerful (in Dioptres) part of the focusing system of the eye, while the Lens (behind the pupil and Iris inside the eyeball) is a focusing element capable of changing focus from distance to near. Thus, a normal eye not only has the ability to focus clearly but also has a wide range of focus.
M y o p i i a H y p e r m e t t r o p i i a A s t i i g m a t t i i s m
Myopia (shortsightedness or near-sightedness ) is a very common condition in which the eye is too long for its own focusing power. Without spectacle correction, very near objects may appear sharply in focus but objects at distance appearing progressively blurred.
Hypermetropia/Hyperopia (long-sightedness or far-sightedness ) is a condition in which the eye is too short for its own focusing power. Without spectacles, objects appear blurred at both near and distance. In young patients with low degrees of Hypermetropia subjects may see distant objects more clearly than near, hence the description as long-sightedness.
Astigmatism is a condition in which the eye does not focus evenly and may be associated with long-sightedness, short-sightedness or both. It is usually related to the cornea demonstrating greater curvature in one meridian, often likened to
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the oval shape of a rugby ball rather than the more even, spherical shape of a football.
Presbyopia is the age related (40 onwards) reduction in the capacity of the eye to focus at near objects. Reading, bifocal or varifocal spectacles are needed to read and focus on near objects. However at this age, those who have mild myopia (shortsightedness) might be able to read close print simply by taking off their spectacles, this will obviously render their distance vision uncorrected and therefore blurred.
Normal, Non Presbyopic natural crystalline lens
Ageing crystalline lens thickens, causing Presbyopia and eventually Cataract
The natural lens of the eye thickens and undergoes a shape alteration with age.
Recent evidence shows that from the age of 20 onwards these changes start to reduce the functional quality of vision. This shape alteration increases the spherical aberration of the eye, a focusing error that reduced the quality of pictures from the Hubble space telescope. These ageing changes in the natural lens continue all through life giving rise to Presbyopia in the 40’s and eventually cataracts a few years later.
The cornea is a relatively stable optical element and does not seem to change through life. It follows that the natural lens of the eye is the optical element responsible for the age related deterioration in its optical performance. Initially subtle, this deterioration results in Presbyopia in the 40’s and eventually cataracts in the 60’s. Cataracts are the commonest cause of visual problems
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with more than 20 million people affected worldwide. It is likely that every one of us will get a cataract if we live long enough.
Traditionally Presbyopia is corrected by using reading glasses, bifocal or varifocal glasses or contact lenses. The strengths and weaknesses of these options are outlined below.
Non Surgical Methods of correcting Presbyopia
Strengths Weaknesses
Bifocal or Varifocal Glasses Traditional
Safe
Optical Aberrations
Haloes from Lenses
Bifocal Contact Lenses No Spectacles
Both together eyes working
Contact lens Problems e.g. dry eyes / infections
Quality of
Compromise
Vision
Monovison ( one eye for distance and the other for
No spectacles
Good Near vision
Loss of the capacity to use both eyes together near) with contact lenses Poor Distance Vision
Poor acceptance
Surgical approaches to correct Presbyopia like Anterior Sclerostomy, Scleral
Expansion Bands, and Infrared Scleral Ablation try to minimize the effects of the
Lens enlargement by attempting to enlarge the equatorial circumference of the eye. These operations have had limited success with poor predictability in their effects. PRELEX on the other hand works by replacing the ageing natural crystalline lens, which is responsible for most of the reduction in the optical performance of a human eye with a new intra ocular lens.
PRELEX: So who is it for?
You could be a candidate for PRELEX vision correction surgery if you fall within the following criteria. You can only be advised of your individual suitability after a comprehensive assessment of your eye, lifestyle, visual needs and employment.
1. Want to reduce your dependence on glasses or contact lenses . Do not expect perfect vision after surgery, you could still need spectacles or contact lenses for some visually demanding tasks like reading fine print.
2. Poor vision for distance and near i.e. need bifocal, varifocal glasses or contact lenses for distance and for reading. PRELEX is particularly suitable if you are long-sightedness, or have severe shortsightedness and
Presbyopia
3. If you have good sight for distance or near without glasses or contact lenses your benefits from PRELEX would be very limited and generally
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PRELEX is not suitable under these circumstances. However other vision correction options might be more suitable.
Before the Surgery:
Prior to any Presbyopic Lens Exchange Surgery a comprehensive evaluation of the Optical system of the eye is carried out. This includes Refraction, Scanning
Slit Corneal Topography, Pachymetry, Keratometry and Pupillometry. Almost all eyes have a combination of focusing errors and it is important to correct as many as possible in order to achieve the best quality of vision after surgery.
At this stage an individual risk benefit assessment is carried and the decision to carry out PRELEX surgery is confirmed.
Based on this evaluation an individual surgical plan is designed to achieve the best possible vision for distance and near without glasses or contact lenses. This includes the use an intraocular lens to correct myopia, hyperopia and
Presbyopia. Astigmatism is usually corrected on the cornea using some special incisions. This surgical plan is analogous to an optical prescription and can be thought of as a surgical prescription to correct the focusing errors of the eye.
The Surgery:
The surgery is normally carried out using a no injection local anesthetic technique. Some patients choose to have a short general anesthetic. A 2.5 mm incision is made and the natural crystalline lens is removed using an ultrasound probe called a phacoemulsifier. The Outer shell or capsule of the crystalline lens is left behind and used to encase the new intraocular lens inserted. The intraocular lens is a special folding lens, which is inserted and unfolded within the natural lens capsule. This way the new plastic lens has a natural covering and sits in the physiological position within the eye. The incision is constructed like a valve sealing itself without stitches. If Astigmatic corrective incisions are needed they are performed at the start of the surgery. A protective plastic shield is taped to the eye and patients recover within a few hours.
After Surgery:
Most patients are up and about as soon as they are back from surgery. The eye can feel a bit scratchy and light sensitive for a few hours. There are no restrictions on normal daily activities and there is usually a significant change in vision by 24 to 48 hours after surgery. The eye settles down and heals gradually over the next four weeks. Eye drops are prescribed for 4 weeks. The second eye is operated on after the first eye has settled down completely.
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Visual Recovery:
Visual recovery starts within the first 24 hours and continues for 4 to 6 weeks after surgery. Depending on the intraocular lens used it can take your visual system up to 3 months or more to adapt completely to the new improved vision.
The final focus of the eye depends not just on the surgery but also on the way the eye heals. This healing process is variable and sometimes can result in a suboptimal focus. In these rare cases a second enhancement operation is carried out to fine tune the focus. This enhancement surgery can be inserting an additional intraocular lens, exchanging the intraocular lens, astigmatism correction incisions or laser surgery.
Like all surgical procedures there are certain risks for complications with
PRELEX. PRELEX is technically very similar to small incision cataract surgery and the risks of complications is practically the same. In fact PRELEX can be thought of as bringing forward your cataract operation by a few years. Cataract surgery is the commonest surgery performed on eyes and in this country alone more than 200, 000 cataract operations are carried out every year.
There is a wide range of complications but the risk of any complication resulting in reducing your sight to levels below what you had prior to surgery is less than
1%. Some potentially serious complications that can result in reduced sight include infections or endophthalmitis, retinal detachment (more so if you are very short sighted) and cystoid macular edema.
The commonest long term complication known is capsular opacification, which is a thickening of the natural lens capsule. This occurs in 10 - 20 % of patients up to
5 years of surgery and is easily treatable as a minor outpatient procedure using a special laser.
Overall, PRELEX is a safe and effective procedure with good predictable results.
Individual risks can only be determined after a comprehensive assessment.
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The first replacement intraocular lens was inserted more that 50 years ago by Sir
Harold Ridley in St. Thomas’ Hospital London. Over the last 10 years the advances in evaluating the optics of the eye and surgical methods for removing the lens of the eye through tiny incisions has combined with an incredible improvement in Intra Ocular lens replacement technology to produce new vision correction operations. PRELEX is a viable proposition because of the development of Multifocal lenses in the mid nineties and recently the
Accommodative lens replacement technology. Both these lenses provide for distance and near vision correction. The accommodative lenses have the potential for a better optical performance.
Multifocal (Array) Intraocular Lens
This lens works by splitting incoming light into distance and near focus. The optical principle is similar to that of a vari-focal spectacle lens or a multifocal contact lens. The different zones of focus are arranged in a ring like fashion to provide the multiple foci.
The Array Intra-ocular Lens and its Multifocal zone arrangement
The lens requires a period of vision training and most patients are able to use this new vision system lens within 3 months. As the lens works by having multiple foci it can give rise to haloes around lights and reduce contrast sensitivity by a small amount. Studies have shown that these compromises are relatively unimportant for day to day visual activities but can be an issue for occupations, which require night time driving or good vision in low light conditions. This technology works extremely well within its well documented limitations. It is extremely rare to find patients who are unable to use this technology comfortably in which case the lens can be replaced.
The Array Multifocal vision system can reduce the need for spectacles and contact lenses for near and distance vision. Most patients need some spectacles for visually demanding tasks at both near and distance.
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The Accommodative Intraocular Lens
This Intraocular lens technology has the potential to provide reduced spectacle dependence for both distance and near without the optical compromises of the
Array Multifocal system. This new state of the art technology works by the lens moving within the eye to adjust focus from distant to near objects. It mimics the function of the natural lens, which adjusts focus by altering its shape. This centre is a reference centre for this technology and to date our experience with this lens is very good with most patients significantly reducing there spectacle needs and in some cases eliminating the need for spectacles. Again the majority of patients do need spectacles for some visually demanding tasks like reading fine print in dim light.
The Humanoptics Accommodative Lens: The Lens sits back in the eye when looking at distant objects, it moves forwards to change
(Accommodates) focus when the eye looks at near objects.
This new technology has now been used in more than 4000 eyes world wide over the last 3 years. In the UK this centre has the most experience of using this lens and to date (Nov 2002) more than 45 eyes have had this lens implanted successfully. Although a new technology it uses time tested materials. The new lens design developed in Germany allows the lens to move within the eye and alter focus. The design is based on finite element analysis and requires exacting technical surgery to achieve good results. The lens material being time tested, the safety of the material within the eye is proven and in fact many lenses made out of the same material but with more simple conventional designs have been used in cataract surgery for years. This is not an experimental lens and is approved by European Authorities by the CE mark for use as an intra ocular replacement lens.
Like all state of the art technologies long term results (5 years or more) are awaited. To date this lens seems to have a very good safety and efficacy profile.
The results are similar to the multifocal lens in terms of reducing spectacle dependence but as the lens does not have multiple foci it does not produce the optical aberrations, which can compromise the multifocal vision system.
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Copyright: Mr. Milind Pande D.O., FRCS, FRCOphth, Consultant Ophthalmic Surgeon