Dr Ben Wild
Overview |
The retina, located on the innermost portion of the back of the eye, senses light that later gets processed into vision by the brain. For clear vision, the light must be well focused on the retina. The cornea, the clear, outermost structure at the front of the eye and the lens, another clear structure located behind the iris, visible through the pupil, are the two structures that focus the light on the retina. A person is nearsighted if the cornea or lens is too strong or the eye is too long and a person is farsighted when the cornea or lens is too weak or the eye is too small.
Refractive eye surgery refers to a collection of surgeries that change the power of either the cornea or the lens. Laser eye surgery either strengthens or weakens the power of the cornea by changing its shape with the use of a laser. Refractive lens exchange (RLE) replaces the natural lens inside the eye with a plastic lens of appropriate strength. Implantable collamer lens (ICL) surgery changes the focusing power of the eye by adding a plastic lens behind the iris but in front of the natural lens.
To the left is a picture showing a healthy cornea, represented in blue on the left and lens represented as a semi transparent oblong lenticule on the inside of the eye on the right.
Laser Eye Surgeries |
Lasik is the most common laser eye procedure. It starts with a suction ring being applied to the eye to flatten the eye. A laser or a blade is then used to create a thin flap on the front of the cornea as demonstrated in the picture to the left. The flap is then lifted up and a laser is used to reshape the cornea. The flap is then lowered and recentered. Lasik can correct up to 4 Diopters (D) of hyperopia (farsightedness), 5D of astigmatism and 12D of myopia (nearsightedness) depending on the thickness of the cornea. It offers greater post-operative comfort, fast recovery time, and minimal haze formation. Intraoperative complications include errors in creating the flap and post-operative complications include dry eyes, wrinkling or dislocation of the flap, haze causing glare, growth of the corneal epithelium underneath the flap, inflammation, bacterial keratitis, and corneal ectasia (see corneal ectasia for more information).
Photorefractive keratectomy (PRK) is an older laser eye surgery technique whereby, instead of creating a flap, the surgeon removes the corneal epithelium (top layer of the cornea) with alcohol, scrubber or sponge and uses a laser to reshape the cornea. A bandage contact lens is then inserted onto the eye so that the epithelium can regrow (2-3 days). PRK can correct minor amounts of hyperopia, 3D of astigmatism, and 6D of myopia. It is a safer option for patients with thin corneas and there is less risk of serious intra and post operative complications. It is best for patients with risky jobs, corneal dystrophies (see corneal dystrophies for more information), prior laser surgery, and large pupils. It does however have a much slower recovery period and unpredictable post-operative discomfort, greater chance for haze formation and glare, decreased night vision and haloes for months, regression of prescription, abnormal healing, irregular astigmatism that cannot be fixed with glasses, inflammation and infections.
Small incision lenticule extraction (SMILE) surgery is the 3rd most common laser procedure quickly gaining popularity. It involves using a laser to form a removable piece of cornea in the shape of a lens and removing this piece through a small incision. It removes the risk of flap complications with Lasik but maintains all of the benefits of Lasik. There is evidence it causes less neurological damage thus reducing dry eye symptoms, and lowers infection rates.
Refractive Lens Exchange |
RLE changes the power of the eye by changing the strength of the lens. It is basically cataract surgery before cataracts develop. The surgeon creates 2 incisions in the cornea for his instruments, opens the natural capsule that contains the lens, separates the lens into many small pieces, vacuums up the lens fragments, inserts the plastic lens into the natural lens capsule, and closes the incisions. The plastic lens can correct a patient for either distance or near (single vision lens) or both (multifocal lens). Please note: multifocal lenses can enable patients to forgo the need for glasses altogether but cannot provide vision quite as sharp as single vision lenses and may cause permanent glare and haloes.
RLE has all of the same complications as cataract surgery. This procedure is ideal for patients who have already gone through presbyopia (50 years of age or older).
Implantable Collamer Lens |
ICL surgery alters the strength of the eye by inserting an additional lens into the eye. It starts with the surgeon creating an incision in the cornea. A plastic lens is then inserted past the entrance of the pupil in front of the natural lens. In some instances, a laser is used to create a hole in the iris before surgery to ensure eye pressures do not elevate post-operatively. ICL is best suited for hyperopes or myopes with thin corneas. Complications are similar to those of cataract surgery plus the added risk of the plastic lens rubbing against the natural lens causing a cataract or elevated eye pressures progressing to glaucoma.