CATARACT AND REFRACTIVE SURGERY
PAO SUBSPECIALTY SOCIETY: PHIL. SOCIETY OF CATARACT & REFRACTIVE SURGERY
1. What is a cataract?
A cataract is defined as any opacity in the human lens. Throughout life, your crystal clear lenses at birth undergo changes which eventually produce opacification. This may be significant enough to interfere with ones vision later in life. The opacification is eventually progressive, though variable in speed from individual to individual, and can be influenced by genetic and environmental factors. There are also congenital and juvenile cataracts, as well as those initiated and/or hastened by concomitant ocular (eg. inflammation) or systemic (eg. diabetes) disease. Trauma, as well as certain drugs (both ocular and systemic) can also produce cataracts. A common misconception is the practice of letting the cataract ripen first before undergoing cataract surgery. Currently, cutting-edge technology and advanced techniques in cataract surgery allow surgeons to perform the procedure even in the early stages of cataract development, with remarkable and predictable results.
2. I want to have cataract surgery. Is it going to be by laser?
Another common misconception is that cataracts are conventionally removed by laser surgery nowadays. Unfortunately, many eye doctors themselves are guilty of perpetrating this misconception, as it appears to be more impressive to say, Sir, I am going to laser your cataracts. When we talk about modern-day cataract surgery, we usually refer to a procedure called phacoemulsification, sometimes referred to as no-stitch or sutureless cataract surgery. The old technique of cataract surgery (still widely practiced in the country) involves a large incision (> 7mm) in the eye to remove the cataract in toto. This procedure is performed either under general anesthesia, or locally, by injecting anesthetic behind the eyeball. The wound is closed by several sutures, which accounts for the old adage of myriad precautions after cataract surgery (eg. bawal magbuhat, bumahin, umubo, etc.). Phacoemulsification on the other hand, dissolves the cataract via a small (3-4mm) incision in the eye. This wound is self-sealing and usually needs no suture to close. The procedure is performed under topical (eyedrop) anesthesia and on out-patient basis. Most patients are in fact, back to their usual daily activities the day after the surgery.
(Strictly speaking, actual disintegration of ones cataract via laser light has already been developed and is currently in limited clinical use and trial around the world).
3. So what is this laser eye surgery I keep hearing about then?
There are many types of lasers used by ophthalmologists in the management of various eye diseases. There are lasers for glaucoma, for diabetic retinopathy, for macular diseases, etc.. When laymen speak of laser eye surgery though, we usually refer to the correction of one’ refractive error by Excimer Laser Surgery. An individual’s refractive error, whether one is nearsighted or farsighted, is determined by the anatomy of the eyeball. An eyeball that is too long, or whose cornea (front dome of the eye) is too steep makes an individual myopic (nearsighted). On the other hand, en eyeball that is too short, or whose cornea is too flat renders an individual hyperopic (farsighted). Excimer laser reshapes the contour of the cornea to neutralize this refractive error in the eye, either through a procedure called Photorefractive Keratectomy (PRK), or another called Laser-in-situ Keratomilieusis (LASIK). LASIK, by far, is the most common refractive eye laser procedure performed locally and worldwide. (more on this in numbers 11 to 13)
4. Will I still wear glasses after cataract surgery?
After removal of the cataractous lens during surgery, a small optical device called an intraocular lens (IOL) will be placed and left inside the eye. The patient will not feel this IOL throughout life, nor will it be visible in terms of gross eye appearance to an outside observer. Before undergoing cataract surgery, your doctor will perform a procedure called biometry to estimate the power (grade) of the IOL that will be implanted in your eye, with the aim of choosing a lens that will afford the patient good vision under normal conditions. Usually, one would like to aim for emmetropia (zero grade/refraction), where the patient can have excellent vision for distance without glasses. If this aim is achieved, the patient will still need glasses for reading up close. If the patient (intentionally or unintentionally) ends up being nearsighted after the surgery (over-aimed), it would be possible to read up close without glasses, but not for distance.
Recent advances in IOL technology have produced so called Multifocal IOLs that may allow for both distance and near reading vision. Ask your doctor about the availability of these new devices in his/her clinical practice.
5. What is Myopia?
Myopia is the medical term for "nearsightedness", a condition wherein the eyes can see close objects but are unable to see distant objects clearly. Compared to the normal eye, a myopic eye is longer from front to back. As a result, light is focused in front of the retina, rather than on the retina, resulting in the perception of a blurred image.
6. What is Astigmatism?
In order to have normal undistorted vision, the cornea should be smooth and spherical or equally curved in all meridians. Some eyes have some degree of astigmatism, or ovalness, to their cornea. Instead of being shaped like a basketball, the astigmatic eye is shaped more like an American football. Therefore, there is distortion or tilting of the images due to asymmetric bending of the light rays. This is sometimes perceived by the individual as a "shadow effect" or a doubling of the image.
7. What is Hyperopia?
Hyperopia is the medical term for "far-farsightedness." It is a misnomer, however, in that far sighted people do not necessarily see clearly for far. Vision may be blurred for both far and near. As opposed to myopia, a hyperopic eye is shorter when compared to a normal eye. This results in light being focused behind the retina causing the perception of a blurred image.
8. What is Presbyopia?
Presbyopia is not an EOR, but rather, an age-related loss of the focusing power for near. It usually sets in as one approaches the age of 40 or thereabouts. Normal and farsighted individuals usually require reading glasses once they reach this age. A presbyopic person with a moderate amount of nearsightedness may need only to remove his corrective spectacles for near work or reading.
9. How do we correct errors of refraction?
Eyeglasses and contact lenses properly focus the light rays on the retina and thus "correct" EORs. However, as soon as these devices are removed from the eye, the eye is again unable to focus light properly. To permanently correct EORs, the corneal surface must be reshaped: flattened for myopia, steepened for hyperopia, and made more spherical for astigmatism.
Before the advent of Excimer lasers, the option for permanent correction of EORs required incisional surgery in the form of Radial Keratotomy (RK) and Astigmatic Keratotomy (AK). The effectiveness of these procedures relied on weakening the corneal support to attain the desired change in corneal curvature. This compromised the corneal integrity with a potential danger of eye rupture following trauma. Furthermore, unpredictability of the attained amount of correction, fluctuation in refraction and impermanence of results were common. These limitations accelerated the development of laser technology for refractive surgery.
10. What is an Excimer Laser?
The Excimer laser is a cold laser which works via photochemical ablation. Unlike other lasers that utilize thermal energy to burn tissue, Excimer lasers make use of an argon-fluoride gas mixture to break the molecular bonds of corneal tissue. As a result, fragments of corneal tissue rapidly expand and are ejected at high speed from the corneal surface. The Excimer laser is computer-controlled, allowing precise removal of tissue to the micron level.
Vision correction by the Excimer laser was approved by the United States Food and Drug Administration (US FDA) in 1995 and is among the most commonly performed outpatient clinical procedures in ophthalmology. Over a million people with myopia (nearsightedness), hyperopia (farsightedness) and astigmatism in over 40 countries worldwide have undergone this procedure and have been enjoying functional vision without glasses and contact lenses ever since. Sight-threatening complications are exceedingly rare. This combination of high success and low complication rates has resulted in exceptional patient satisfaction.
11. What is Photorefractive Keratectomy (PRK)?
In contrast to incisional surgery which works by weakening the corneal structure, PRK corrects myopia and astigmatism by altering the shape of the cornea. Portions of the superficial and middle layers of the cornea corresponding to the degree of myopia and/or astigmatism are photoablated. This alters the curvature of the cornea and allows light rays to properly focus on the retina.
PRK is an out-patient procedure, which takes approximately 5 minutes per eye, but the actual laser exposure lasts less than a minute. It requires the removal of the corneal epithelium (the superficial layer of the cornea) prior to application of the laser and so patients will regain functional vision within 3 to 7 days after the procedure.
12. What is Laser-assisted in situ Keratomilieusis (LASIK)?
LASIK works like PRK, except that in LASIK, a special ophthalmic instrument - the microkeratome - is used to create a hinged corneal flap prior to actual photoablation of the underlying corneal tissue. After the laser treatment, the flap is repositioned and adheres spontaneously to the underlying bed. LASIK has been proven to be effective in treating even higher degrees of myopia and astigmatism.
LASIK is also an outpatient procedure that takes 5-7 minutes per eye but the actual laser exposure lasts less than a couple of minutes. However, LASIK requires more technical skill and surgical expertise and is seldom performed by the general eye MD. Because the flap preserves the superficial layer of the cornea, visual recovery and healing are dramatically rapid. Patients regain functional vision in 4 to 12 hours.