Wavefront LASIK AK & PRK Initial Consultation Treatment Terminology Clear Lens Surgery STAAR ICL





Astigmatic Keratotomy and Photo Refractive Keratectomy

There are four main refractive surgical techniques currently available around the world:


    i           Radial Keratotomy      RK

    ii          Astigmatic Keratotomy      AK

    iii         Photo Refractive Keratectomy   PRK

    iv         Laser-Assisted In-Situ Keratomileusis   LASIK

Radial Keratotomy  (RK, mini-RK)

Radial keratotomy (RK) is where a diamond blade scalpel is used to make surgical incisions in the cornea, in a pattern resembling the spokes of a wheel.


These incisions are normally 90 to 95% of the thickness of the cornea and cause a reduction in the curve of the central cornea for the myopic eye. RK surgery has been found to have some limitations including fluctuation in vision and starbursts. Complications at the time of surgery, such as perforation, an irregular incision and infection are rare, but can be serious. In the USA and worldwide the use of RK in all its forms has rapidly declined.

Astigmatic Keratotomy  (AK)

Astigmatic keratotomy (AK) is a treatment normally used to treat astigmatism. AK surgical incisions are made as arcs in the corneal periphery.


Photorefractivc Keratectomy  (PRK)

PRK is applied to the central (optical zone) of the cornea to reduce its curvature. A modern excimer laser used for PRK sculpts an area 6.0 or more millimetres in diameter on the surface of the eye.


Vision is normally blurred for a few days after treatment. There may be a temporary apparent over correction towards hyperopia (long sight) with treatment for myopia and toward near sight for treatment of hyperopia. This is normal and later the over correction disappears in most patients.

PRK Treatment to One Eye Only 

Spectacle lens wearers who undertake PRK to the first eye must be aware that there may be difficulties in vision until the second eye is treated. If for any reason the second eye is not treated there may be continuing difficulties.


Potential PRK Complications:

Mild discomfort after treatment that can be controlled by the use of analgesic (pain relieving) medications

  • The clarity of vision can be reduced during this healing stage

  • Infection or abscess of the cornea before the surface corneal epithelial cells have healed

  • Reduced quality of vision due to cornea being an irregular shape

  • Glare or starbursts around lights, due to the treatment zone being irregular or of a size smaller than the pupil of the eye when dilated in dim lighting conditions (especially night driving)

  • Over correction or under-correction

  • Induced astigmatism due to surgery

  • Regression of refractive outcome that may need re-treatment

  • Reduction in contrast perception

  • Imbalance if only one eye is treated

  • Episodes of pricking or dryness occur

  • Reactivation of Herpes virus infection of the cornea

  • "Melting of the cornea" if there is a collagen autoimmune disease

  • Altered fitting of contact lenses, should they be required, due to the changed shape of the cornea

  • Haze formation over the treated area of the cornea

  • Drooping eyelid due to steroid drops or inflammation

  • Astigmatism may be over-corrected resulting in a change in axis of close to 90 degrees

Long Term Complications

Some haze at the treated area may occur and this may interfere with the quality of vision. It may lead to some scarring which reduces the quality of vision. The risk of haze increases with higher amounts of attempted PRK treatment. Re-treatment may have an unpredictable outcome and is usually performed by LASIK rather than further PRK.


PRK for Hyperopia (H-PRK)

Excimer laser PRK for hyperopia is less commonly performed than for myopia as the time for the corneal epithelium to heal over and stabilise after treatment is longer than for treatment of myopia. Many refractive surgeons feel that hyperopic LASIK has many advantages over hyperopic PRK, since with H-LASIK there is the same rapid healing as with myopic LASIK.



Hyperopia is treated by removing a ring of tissue from the edge of the cornea. This steepens the central cornea and has the result of bringing light into focus on the retina


Complications of H-PRK:

  • Those complications associated with myopic PRK are to be expected with hyperopic PRK 

  • Recurrent erosion syndrome due to the large area of corneal epithelium removed. This causes prickling or dry eye symptoms which often occur on awaking in the morning

  • Increased time for the epithelium of the cornea to heal (4 to 8 days) and hence increased duration of pain or discomfort

  • Regression to hyperopia again

  • Over correction to become myopic

LASIK is now often performed for all myopic and hyperopic treatment but some still prefer PRK for the lower refractive changes as it has a low complication rate.  However LASIK is now the procedure of choice for much refractive surgery.

next  >> initial consultation

back to top

Home / Contact / Site Map / Our People / Eye Conditions / Links / Cataract Surgery / Glaucoma / Macular Degeneration / News 


Page last updated on Saturday, 25 June 2005 12:36:31


Highgate Ophthalmic Practice     

Tel:    020 8318 7113    Fax:  020 8318 6970 

Email  -  hpheyes@aol.com