Refractive Eye Surgery for Nearsight, Farsight and Astigmatism
Refractive eye surgery includes a number of procedures aimed at altering the parts of the eye that bend light, namely the cornea on the outside and lens in the eyeball. It is these errors in refraction that cause the most common vision problems – myopia (nearsightedness), hyperopia (farsightedness) and astigmatism. This has reduced the need for and inconveniences associated with the use of eyeglasses and contact lenses to correct these refractive errors. However, it has not totally removed the need for these other corrective measures as some persons may still require eyeglasses and contact lens for optimal visual acuity. Refractive eye surgery was drastically improved with the advent of the excimer laser that allowed for laser-based procedures such as LASIK, LASEK and PRT which are now more commonly done. Nevertheless there are several other, non-laser procedures that can be done to correct refractive errors of the eye.
Most surgeries involve the cornea but some may also involve the lens. The most important surgical procedures currently employed in surgical correction of refractory errors are :
Laser-assisted in situ keratomileusis (LASIK), laser assisted sub-epithelium keratomileusis (LASEK), photorefractive keratectomy (PRK) and laser thermal keratoplasty (LTK) have been discussed under laser eye correction. LASIK remains the most commonly performed procedure for correcting refractive errors of the eye.
Keratotomy procedures involve surgical incision of cornea. Corneal surgery aims to flatten the cornea. Two types of procedures for corneal incision are utilized :
- Radial keratotomy (RK)
- Arcuate keratotomy (AK)
Radial keratotomy (RK)
Radial keratotomy involves making microscopic incisions in a radial-pattern on the periphery of the cornea. This relaxes the cornea. It flattens the central part of the cornea which retains this shape permanently once it heals. This effect corrects the refractive error. The procedure is usually performed using a diamond knife. Radial keratotomy produces reasonably good results with myopia of low degree.
The procedure is associated with a number of critical complications including corneal perforation, introduction of infection and rarely eyeball rupture. Fluctuating refractive errors with day-night variation and over-correction of the myopia are also seen with radial keratotomy. The procedure is no longer a preferred method after the introduction of safer and superior laser-based procedures.
Arcuate keratotomy (AK)
Arcuate keratotomy is also a procedure to correct astigmatism and is similar to that of the radial keratotomy. Arcuate incisions are done in pairs on the sides of the cornea opposite to the axis requiring correction. The procedure may be performed even in some select patients for correcting any residual astigmatism following procedures like keratoplasty or cataract surgery. The complications associated with arcuate keratotomy are similar to that of radial keratotomy.
Intrastromal corneal ring (ICR)
ICR involves placement of a ring made of polymethylmethacrylate into the corneal periphery. The ring corrects the refraction error by flattening the cornea. It is a potentially reversible procedure that is useful for correcting refractory error in patients with low grade myopia (below -3D). The recovery of vision following ICR is rapid. The ring can be removed at any point of time if the result is not satisfactory. Complications associated with the procedure include astigmatism and an increased risk of infection.
Automated lamellar keratoplasty (ALK) is procedure that involves making a thin corneal flap with a microkeratome. A calculated amount of corneal stroma is then removed with the microkeratome and the flap is replaced. The procedure has been widely replaced by the laser-based flap procedures.
Most surgical procedures to correct refractive errors involves shaping the cornea. However, refractive errors can also be corrected by surgery to the lens. These procedures include :
- Extraction of clear lens
- Posterior chamber intraocular lens (IOL) implantation
- Anterior chamber IOL implantation
Other lens based refraction corrective procedures that have not been discussed here include photophacomodulation and photophacoreduction.
Extraction of clear lens
Extraction of the clear lens can give reasonably good improvement in vision. The procedure has an increased risk of retinal detachment.
Posterior chamber intraocular lens (IOL) implantation
Posterior chamber IOL implantation is useful in patients with high-degree myopia. The lens made from collagen acts like an implanted contact lens. The implanted lens is placed behind the iris and in front of the natural crystalline lens in the eye of the individual. Improvement is good in the short-term. The procedure is associated with uveitis and cataract formation.
Anterior chamber IOL implantation
In this procedure, the lens is implanted in the anterior chamber of the eye inwith angle support. It yields good results in high-grade myopia. The major draw-back of this procedure is the possibile distortion of the pupil.
Red Flag Symptoms After Surgery
Some of the signs and symptoms that develop following the refractive surgery are considered as danger signals. Development of these symptoms should be brought to medical attention at the earliest. These danger signals include decrease in the vision, development of pain or increase in the pain and redness of the eye which may be associated with discharge from the eye.
Surgery for Nearsightedness (Myopia)
The procedures utilized for correcting myopia include those which can flatten the cornea or which can correct refraction with lens surgery.
- LASIK for low grade to high grade myopia (up to -12D)
- ICR for low grade myopia (less than -3D)
- PRK for low grade to moderate grade myopia (up to -6D)
- Radial keratotomy for low grade myopia
- Lens surgery usually for high myopia (clear lens extraction or intraocular lens implantation)
Surgery for Farsightedness (Hyperopia)
Refractive surgeries for correcting hyperopia (hypermetropia) include procedures that make the central cornea steeper.
- PRK can be used to correct low grade hyperopia.
- LASIK for correction of hyperopia of low grade (up to ?4 D)
- LTK/TK for low grade hyperopia correction
Surgery for Astigmatism
The procedures for correcting astigmatism aim to correct refractive errors in specific axes. This may include :
- Arcuate keratotomy
- PRK can correct astigmatism up to 3D
- LASIK can correct astigmatism of up to 5D
- Lens surgery may be used occasionally for correction of astigmatism alone using specific lens for implantation.