Refractive surgeries

How are the results of refractive surgery?

Before undergoing any refractive surgery procedure, one must realize that none of these procedures can guarantee you perfect vision without glasses in all the cases. These surgeries are based on the average calculations from a large population, but as different individuals may respond differently to surgery, there might be some variation in the outcome results obtained. The aim is to decrease your dependence on glasses/contact lenses. The reliability of the procedure is quite good in mild to moderate levels of refractive errors, with most of people being able to carry out their daily activities without glasses. But for high degrees of refractive errors, the variation is more and some people may still need glasses, though of much lesser power than before, to see clearly.

Another thing to remember is that though these procedures are safe and without complications in majority of cases, there are a few uncommon but significant complications of these procedures, which may lead to a decrease in vision.

What are the various refractive surgeries?

The refractive power of the eye can be changed by any of the three approaches:

1. Changing the curvature of the cornea: this is the most popular mode of refractive surgery.
   
   
2. Removing the natural lens and replacing it with an artificial lens of adequate power: it is similar to a routine phacoemulsification surgery, except that it is done in a clear lens and not a lens with cataract. As it is an invasive procedure and it also increases the chances of retinal detachment in eyes with high myopia, it is not recommended nowadays.
   
   
3. Putting an additional artificial lens within the eye on top of the existing natural lens: this technique is still not very popular as it is also invasive and may increase the chances of cataract formation.

What are the ways of changing the curvature of cornea?

The commonly used methods for refractive surgery are:

1. Radial Keratotomy (RK)
2. Astigmatic Keratotomy (AK)
3. PhotoRefractive Keratotomy (PRK)
4. Laser-Assisted In-Situ Keratomileusis (LASIK)

The first two procedures (RK and AK) involved making incisions into the cornea with a diamond blade. PRK and LASIK are the newer procedures that make use of Excimer laser to remodel the shape of the cornea with great degree of precision. Since the advent of excimer laser, RK and AK are being done less commonly.

How does RK and AK correct refractive errors?

Before the development of Excimer laser, Radial Keratotomy (RK) was the main surgical procedure available for correction of myopia. In RK, partial thickness (90-95% depth) incisions are placed radial on the cornea (clear portion of the eye). These incisions make the cornea flatter and thus correct the refractive error (myopia).

Astigmatic Keratotomy (AK) is done for correcting astigmatism. In this procedure, the partial thickness incisions are placed like arcs in the peripheral part of the cornea.

What are the disadvantages of RK and AK?

• Unpredictability of refractive outcome: the results are less predictable in these procedures as compared to the laser procedures (PRK and LASIK).
  
  
• Weakening of the cornea which is vulnerable to rupture on trauma
  
  
• Fluctuation of vision, which may be temporary or permanent
  
  
• Glare or starbursts around lights, due to the incisions causing diffraction of light
  
  
• Complications at the time of surgery, such as perforation, irregular incision and infection are rare, but can be serious