PRK for atypical corneas?

The issue of PRK or LASIK for patients with atypical corneas is extremely important for medical and legal reasons. Many experienced ophthalmologists have relied on Pentacam and Orbscan images to determine whether a patient with form fruste keratoconic findings on standard anterior curvature computerized video-keratography is suitable for LASIK or PRK. Following the link below you will see screen capture topography images of two patients.

Patient one underwent PRK OD for high cylinder plano - 5.00 x 020 (pre-op pach 565 microns OD) Her anterior topography you can see by following the link below and I dont have her color orbscan scanned but the posterior float is 0.030 at the central 3 mm optical zone with a normal pachymetric pattern. Her most recent refraction OD postop year 6 is is +3.50 - 2.0 x 020 (20/30)

Patient two had a thin cornea, 473 microns OD, 463 microns OS.
Preop MRX: -2.50 -3.50 x 020 OD and -2.50 -3.50 x 163 OS (2004)
Topos are available by clinking on the link below.
1 week postop: plano OD and plano OS
2 year postop: -0.50 -1.50 x 20 OD and plano - 1.50 x 160 OS



The above two cases are limited anecdotal case reports to suggest perhaps we should exercise caution in offering PRK to patients with atypical corneas in the form of thin pachymetry (less than 500 microns) and/or atypical corneal curvature.

In both cases above, each patient was consented regarding the potential for ectasia development. I think it is interesting to observe the time frame for refractive instability and the speed at which that change occurrs. When patients observe slow gradual change they actually tolerate this type of instability much better than rapid decompensation in the 3 to 6 month range.

Hopefully collagen crosslinking procedures can offer some form of stability either pre or postoperatively in these complex cases. In the mean time I offer these patients matrix metalloproteinase modulation (tetracycline class), mast cell stabilization, and Alphagan intraocular pressure reduction with mild miosis (avoid prostaglandin analog).

If the patient has any underlying risk factors for ectasia such as sleep apnea or eye rubbing, I attempt to address these issues as well.