CLEARVISION EYE CLINIC



34) What is mono-vision correction?
Mono-vision correction is recommended by many Lasik surgeons for their patients aged 35 years and above who are presbyopic or who are likely to become so in the near future. The aim of mono-vision correction is to enable the patient to have a close to full range of vision with much reduced dependence on glasses for both distance and near vision. This is achieved by aiming at full or close to full correction in the master eye and mild under-correction in the other, non-master eye. To tell which is your master eye, cut a coin-sized opening in a piece of paper and hold it at arm's length in front of you. Next, with both eyes open, look at a distant object, such as a clock on the wall, through the opening. Now, without moving the paper, alternately shut your left and your right eye. Your master eye is the eye that sees the object.


35) What about other techniques? Should I consider them?
Most eye doctors worldwide now consider Lasik as the overall surgical procedure of choice for permanent surgical correction of myopia. However, there are other alternative surgical methods available that may be more appropriate in certain circumstances. These techniques, and the benefits and risks of each, are discussed in greater details here.
Radial Keratotomy In Radial Keratotomy, or RK as it is more popularly known, four to eight fine incisions are made in the cornea with a diamond knife. These cuts, made in a radial or spoke-like pattern, will allow the normal pressure inside the eye to steepen the sides of the cornea while the centre optical zone curvature flattens. This results in an effective reduction of myopia power. RK is considered the forefather of modern popular refractive surgery. The procedure has its beginnings 40 years ago when it was first introduced by Sato and associates in Japan. However, the early technique was fraught with complications until the Russian eye surgeon Fyodorov improved upon it and made it safer and thus more popular in the mid-seventies. Today, the RK technique has been further refined and has incorporated astigmatic correction into its protocol. Notwithstanding, the results are still less predictable and stable as compared to Lasik and the healing process is slow and painful. In addition, the cuts made have been shown to weaken the cornea, causing late onset hyperopia (farsightedness) and susceptibility to disastrous eyeball rupture should the eye suffer a strong knock. Die-hard proponents of the procedure tout the fact that RK will never cause scarring of the central optical zone of the eye and that it is much more cost effective. Presently, a modification of RK is commonly used by refractive surgeons during cataract and lens implantation surgery to correct astigmatism.
Photorefractive Keratectomy Photorefractive Keratectomy or PRK, is the predecessor laser refractive surgical technique before Lasik became popular. It uses the high energy ultra-violet rays of the excimer laser to directly sculpt the surface layers of the cornea, essentially flattening the curvature, to correct myopia. The excimer laser is not a new invention, being developed way back in the seventies by the computer industry for the precise etching of computer chips. It is a so-called cool laser, meaning that it can cut through various materials with minimal heat damage. That was just the kind of delicate tool that eye surgeons were looking for to improve the accuracy and predictability of refractive surgery. The first application of the excimer laser on the human eye was in 1983. However, it was only in the early nineties when PRK treatment protocols were established that the procedure became widely available to the general public. PRK is technically a simpler procedure compared to Lasik. There is no need to create a cornea flap thereby eliminating the risk of cornea flap related complications. Statistics show that 95% or more of patients with mild to low moderate myopia saw 6/12 or better without glasses after the surgery. However, the post-operative recovery period is longer and more painful then the Lasik procedure. The eye requires at least three days for the treated cornea surface to heal. The refractive power is also unstable for the first three months. Most importantly, the final refractive outcome is less predictable than with Lasik surgery, especially when treating more than - 5.00 dioptres of myopia. This is due to the marked individual variation in healing response when the superficial layers of cornea are treated. There is also an increased risk of severe cornea scarring of the central optical zone. As such, PRK soon became supplanted by Lasik. PRK if done, if best reserved for treatment of low myopia only.
Intra-ocular lens implantation This technique involves making a small wound at the side of the cornea and implanting an artificial lens made of a biologically inert material such as acrylic, PMMA (plastic) or silicone permanently into the eye. The artificial lens may be implanted in front of the natural crystalline lens or in its place following lens extraction. The major advantage of lens implantation surgery over laser refractive surgery is its effectiveness in treating severe to extreme levels of myopia of over -12.00 dioptres (over 1,200 degrees). In young patients, the artificial lens is implanted in front of the natural crystalline lens, thereby preserving accommodation or focusing ability for near. A drawback here is that the implanted artificial lens may rub on the internal structures of the eye causing inflammation of the iris (iritis), cataract and possible long term damage to the delicate inner endothelial layer of the cornea. In older patients, where accommodation (focusing ability) is absent and where there is evidence of lens opacity, intra-ocular lens implantation following extraction of the natural crystalline lens is usually the preferred method. This procedure is in fact akin to modern cataract operation. Cataract operation is one of the most common and safest operations in medicine. It is done as a twenty minutes outpatient procedure without stitches and under local anaesthesia. Post-operative recovery is quick and painless. Visual recovery following lens implantation is almost immediate. The results are also stable and predictable from early on. However, a major concern is the possibility of incurring an intra-ocular infection which cannot be controlled by antibiotics. The incidence is low at about 1 in 1,000 eyes but when it occurs, vision loss is usually severe.
Cornea Ring Implants (INTACS) Here a small cut is made at the side of the cornea and two halves of a clear plastic ring are implanted into the cornea tissue at its periphery to induce flattening of its central curvature. The thicker the ring, the more the cornea is flattened and the greater the myopia correction. The proponents of this technique tout its relative simplicity and lack of use of expensive, sophisticated laser machines. There is also no risk of scarring the central optical zone of the eye. Another attractive advantage is its easy reversibility. The rings can be removed if the patient is not satisfied or replaced to accommodate prescription changes. Unfortunately, ring implants are only effective for low levels of myopia with low or no astigmatism. It cannot correct above - 5.00 dioptres of myopia. Glare, haloes, double vision, difficulty with night vision and fluctuating distance vision are some of the visual side-effects reported.The post-op recovery and after care is also somewhat more tedious than that with Lasik surgery.


36) What is the most suitable age to go for Lasik surgery?
Lasik is suitable for those 18 years and above who have had stable myopia for at least two years. Below 18 years of age, myopia is frequently unstable and the eye is likely to heal with excessive scarring. Notwithstanding, some eye surgeons have performed Lasik selectively for teenagers who suffer from severe anisometropia. This is a condition caused by a gross imbalance of refractive powers between the eyes such that spectacles cannot be satisfactorily prescribed. Lasik is frequently contemplated by those aged 35 and above who have been wearing contact lenses for many years and who have developed problems of dry eyes, allergic eyelid disorders, cornea inflammation or contact lens wear intolerance. It is important that candidates considering surgery in this age group be forewarned that presbyopia (middle-age farsightedness) may become unmasked after the surgery. Dry eye condition if pre-existing, may also be aggravated. Those aged 60 and above are in the high risk group for cataract and should therefore be carefully examined for evidence of any developing lens opacity. If this is present, artificial intra-ocular lens implantation following crystalline lens extraction is the procedure of choice.