Radial Keratototmy in a nutshell
Indication: To treat mild to moderate myopia or nearsightedness.
Variations: 1. HK or hexagonal keratotomy to treat hyperopia.
2. Ak or Astigmatic Keratotomy to cure astigmatism.
Procedure: 1. Use nomogram to determine the number and length of incisions.
2. Measure the corneal thickness at each location on the cornea.
3. Incise upto 90 % of depth of the thickness of cornea with a diamond blade.
Mechanism of action: The weakened site of the incision bulges forward. This bulging implies the cornea at that point of cut became more steep. That correspondingly flattens the central cornea. The explanation for this is as follows. Pressure is equal to force divided by the surface area. The force generated by the intraocular fluid remains the same, whereas after RK the surface area increases due to focal bulging. Therefore the force on the central cornea decreases leading to flattening, a decrease in corneal power and hence a reduction in nearsightedness.
Complications: 1. Perforation of the cornea.
2. Epithelium in growth into incisions
Introduced by: Professor Fyederov in Russia
You may be suffering from the following:
- Diurnal fluctuation
- Annual fluctuation
- Return to glasses
- Fluctuation in vision
- Decreased contrast senstivty
- Dry eyes
- Inability to see good inspite of glasses
- Intolerance to contact lenses
The PERK Study
The U.S. National Eye Institute did a ten-year study called the Prospective Evaluation of Radial Keratotomy (PERK) to evaluate the short-term and long-term effectiveness of the RK techniques. Researchers concluded that although RK did improve myopia, its effectiveness varied from patient to patient.
It also demonstrated that there was an annual drift towards corneal flattening, which caused the eye to become gradually more farsighted. The results of this study showed that a post-RK eye was permanently unstable, and this led to RK falling out of favor in the U.S.
Why RK Was Discontinued in the U.S.
Fluctuating vision as demonstrated by PERK study and the advent of precise excimer lasers sounded the deathshell of RK in the US.
Challenges in Operating on Post-RK Eyes
- There are too many incisions.
- Hesitation cuts.
- The incisions are in the pupillary zone.
- The central cornea is very flat
- There is astigmatism or irregular astigmatism
- The peripheral curvature is different
- The optical zone is small (the central area important in vision)
- Fluctuation between morning and evening require testing at different times of the day.
- Further annual hyperopic drift has to be taken into account.
- Ophthalmic diagnostic instruments may not be able to display accurate readings of the cornea
- IOL or Intraocular Lens, power calculations may also require modifications because of each post-RK cornea being different