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PRK

(P)hoto(R)efractive (K)eratectomy

PRK consists of excising a thin layer of corneal tissue from the top of the cornea with the excimer laser.  The procedure requires re-growth of the epithelium and it destroys a portion of the Bowman's membrane.  This creates a longer healing period and, for many, significant discomfort.  Additionally, many patients experience a haze beneath the surface which, in some patients, can cause significant interference with visual acuity.  This may require additional medications and frequent follow-up exams over a fairly long period of time.

The essential steps involved in PRK are:

• Gently removing the surface layer of epithelial cells.

• Ablating (or removing by molecular disruption) the corneal tissue to change its shape.  A crucial point here is that this involves going through the layer of the cornea immediately below the epithelium, called the Bowman's membrane.  This does not grow back and the long term significance, if any, of its not being there is not fully known.

• Healing requires usually two to four days for the surface epithelium to grow back across the 6 to 7 millimeter area over which it was removed.  During this time there can be very significant discomfort, although the use of certain drops and a type of soft contact lens as a "bandage" may help considerably.  The continued healing and apparent attempt of this surface epithelium to "replace its original shape" can lead to a period of up to 3 to 12 months for maximum stability and visual acuity to occur, although most people see quite well within a few weeks.

Perhaps the most significant issue with PRK is that in many patients, probably related to the necessity for re-growth of the epithelium and the absence of the Bowman's Membrane, there is some degree of haze that develops in the area beneath the surface.  In most patients, this has no appreciable affect on vision, but it can create an interference with visual acuity in some people - increasing in frequency the higher the range of myopia being corrected. Attempts to prevent or control this haze can involve the use of cortisone type eye drops and frequent follow-up exams, sometimes over a fairly long period of time.  In some people, the long term use of these cortisone type drops can cause a type of glaucoma or even cataract.

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