ARE YOU A POOR CANDIDATE FOR PRK?
The following conditions may make you a poor candidate, or at least a less-than-ideal candidate, for PRK:
THIN CORNEA
The major benefit of PRK is that it can be performed on patients with thin corneas. LASIK involves lifting a flap and then beginning the laser treatment in the middle layers of the cornea. In PRK, the laser treatment starts on the surface of the cornea, just below the epithelium, so PRK doesn’t penetrate as deeply into the cornea. That is a better option if your cornea is thin.
DEGREE OF REFRACTIVE ERROR
The best candidates for PRK have an eyeglass prescription that isn’t extreme. This means, if you are nearsighted, you may have myopia of up to –8.00 diopters. If you are farsighted, your hyperopia may be up to +3.00 diopters. Your level of astigmatism may be as high as +4.00 diopters. Patients outside of these ranges can still have PRK, but they require a large degree of corneal reshaping and expectations for crisp, clear vision are lower. Above –8.00 diopters of myopia, I usually recommend the implantable contact lens. Above +3.00 diopters of hyperopia, I prefer refractive lens exchange. Both of these options are covered in detail in later chapters.
KERATOCONUS
As described in chapter 6, keratoconus is an uncommon, hereditary condition that weakens the cornea. Keratoconus progresses gradually in younger people and then stabilizes around the age of forty. We don’t do LASIK on patients with keratoconus because the flap can accelerate the weakening of the cornea. Because PRK doesn’t penetrate as deeply into the cornea as LASIK and doesn’t require a flap, PRK is a better procedure for people with this condition. That isn’t to say that people with keratoconus are always good candidates for PRK, however. That depends on a variety of factors that your doctor will need to address at your comprehensive preoperative examination.
CATARACT
Just as with LASIK, if you have a cataract, you are not a good candidate for PRK. You are probably a good candidate for refractive lens exchange (covered in detail in chapter 8) because refractive lens exchange corrects both the vision and the cataract.
BASEMENT MEMBRANE DYSTROPHY
This is a hereditary condition that causes the epithelium, the clear skin that covers the cornea, to slough off spontaneously, resulting in a corneal abrasion. It is a relative contraindication for LASIK. Sometimes, PRK is a reasonable approach in patients with this condition because removing the epithelium is actually a treatment for basement membrane dystrophy. Your eye surgeon will advise you if PRK is a good option for you.
PRIOR EPISODES OF HERPES INFECTION OF THE CORNEA
This is a definite contraindication for PRK because the removal of the epithelium can stimulate a reactivation of the virus.
SIGNIFICANT DRY EYE
PRK makes the eyes drier to the same degree as LASIK does, so patients who start with significantly dry eyes can be uncomfortable after PRK. (PRK and dry eye is discussed in more detail later in this chapter.) On the other hand, mild dry eye can make contact lens wear very uncomfortable. Such people often do much better with PRK than with contact lenses. The surgeon will evaluate your tear production and advise you if PRK is a good alternative for you.
Although the conditions listed are generally contraindications to PRK, many are not absolute contraindications. If you have one of these conditions, consultation with an experienced PRK surgeon will help you determine whether PRK is still a possibility for you.
Seeing Better Than 20/20 With PRK
