Most people do not have the time or the opportunity to read the article cited by our surgeon comparing LASIK and PRK, in Ophthalmology. 1998 Aug;105(8):1512-22, so here are some of the interesting features.

"There were three flap-related complications in the LASIK group. In the first case, the microkeratome stopped in the middle of the pass. The procedure was stopped, and the patient received uncomplicated LASIK treatment 3 months later. In the second case, the flap was completely cut off. The excimer ablation was completed without complication, and the corneal lenticule was replaced. In the third case, the flap was extremely thin. It was replaced without laser ablation. The procedure was completed without complication 1 month later".

In English - The two procedures are broadly similar, in the estimation of the authors, but three people had flap nightmares.

"Of these eight eyes in the PRK group, four decreased from a preoperative spectacle-corrected visual acuity of 20/16 to a postoperative acuity of 20/25, one decreased from 20/12.5 to 20/20, and one each decreased from 20/20 and 20/25 to 20/62.5, respectively."

In English - A very large slice of the PRK group who had a reduction in their best vision, using glasses if necessary, had unusually good best-corrected vision to start with. This might be what you would expect using a pretty basic laser, and might not be replicated with a more advanced laser, as the authors themselves admit in the conclusion. LASIK involves putting a flap over the ablation, so if the ablation is rough then the surface facing the light remains smooth. This “advantage” might well not be there with a better laser.

"Regarding the outcome of loss of spectacle corrected visual acuity of two Snellen lines or more at 6 months, no statistically significant difference between the two procedures was found."

In English - Although this old laser tended to produce a reduction in best corrected acuity using the surface PRK treatment, using the acid test "two lines lost at six months", there was no difference between PRK and LASIK.

"Return of good uncorrected visual acuity was more rapid in the LASIK group. This result was expected since LASIK in general preserves an intact epithelium, obviating the initial surface healing phase implicit in PRK. Early attainment of good uncorrected visual acuity, thus seems to be one of the major advantages of the LASIK procedure. By the 1-month follow-up, however, the PRK group in general had caught up to the LASIK group. Indeed, there was even a trend toward better uncorrected visual acuity in the PRK group at 6 months, although this was not statistically significant."

In English - LASIK gives you better vision more quickly, but wait a month and there does not seem to be a difference.

"A more rapid visual recovery in LASIK is also supported by the data on stability of uncorrected visual acuity. From 3 to 6 months, 19% of PRK eyes gained more than one line of uncorrected visual acuity compared with only 9% of LASIK eyes."
In English - PRK patients have more to look forward to during the time following surgery.

"Vaulting would be secondary to a tendency of the flap to retain its original curvature, a function of the elastic modulus (i.e., the amount of force required per unit deformation) of the corneal flap. Theoretically, this tendency would be greater for higher degrees of correction, in which the sagittal distance between the flap's preoperative position and the stromal bed would be greater; thus, the flap may not deform sufficiently to conform to the new stromal curvature. This hypothesis is supported by our finding of an association of higher refractive error with more undercorrections in the LASIK group."

In English - There is some evidence that the flap doesn't actually adhere to the rest of the cornea after LASIK and tends to sit proud of the underlying bed. (Horrific.)

"Although differences in lost spectacle-corrected visual acuity between the PRK and LASIK groups were found at 1, 3, and 6 months' follow-up, this finding was not statistically significant. Furthermore, there was a tendency for fewer patients to lose spectacle-corrected visual acuity with time, and the difference in this outcome between the two treatment groups diminished with time. At 6 months, only a small number of patients actually lost spectacle-corrected visual acuity. In addition, of those who did lose spectacle-corrected visual acuity, all but two patients had 20/32 visual acuity or better. Thus, it remains to be seen whether the difference between the PRK and LASIK eyes remains beyond 6 months or simply is a result of the lengthier healing time of the PRK-treated eye".

In English - There is some evidence that perhaps an even longer follow up, say a year, might see the PRK group close whatever gap remains. Certainly some doctors, such as Sylvia Norton, say that high myopes can take a year to reach their final outcome after PRK.

"Epithelialization was complete by 3 days in most eyes after PRK, and there was no incidence of persistent epithelial defect, recurrent epithelial dysadhesion within the treatment zone, sterile stromal ulceration, or corneal infection".

In English - The fears that LASIK surgeons dangle before patients regarding epithelial problems following PRK were not found in this study.

"Complications related to the corneal flap, however, are inherent to the LASIK procedure alone. Thin flaps, incomplete flaps, and completely removed corneal lamellar discs were all seen in this study. However, all procedures ultimately were completed without adverse outcomes. Whether advantages of early visual recovery and diminished corneal haze outweigh potential flap complications remains for further study."

In English - There are immediate problems involved in cutting flaps which might make the advantages of LASIK seem small. This leaves to one side the long-term consequences of cutting flaps.

Finally, remember this was a group with over 9 dioptres on average, the group where the supposed superiority of the LASIK procedure should be most manifest, using a laser that perhaps wasn't as good as some. At nine dioptres someone with a normal 550 micron cornea, a 160 micron flap and a 6mm treatment zone has 282 microns left (if my mental arithmetic serves me well, 550 minus 6 times 6 times 9 divided by 3 plus 160). Of course if the flap is a little thicker (and who is to say what a wrinkling cornea does under a blade, or whether the track follows the curve?), or if the laser ablates a little more (how much power does this particular beam have on this particular day on this particular, partially desiccated, cornea?), then maybe less than 282 remains. What does the FDA say? - 250 microns of undisturbed tissue is the absolute minimum, and there are plenty of doctors who think that is nowhere near enou gh and plenty of cases of ectasia with more tissue than that. If we do have an explosion in corneal ectasia cases in a few years what will the ophthalmologists be saying on "60 minutes" and Panorama - "There was a procedure which the professional body said worked as well but I used the cornea slicing procedure because...."; I'm glad I won't be having to make the case.

I don’t think that “confusion” will result from people reading the above themselves, but then perhaps I am culturally disposed to believe that the truth can shift for itself, that the people can see and hear everything and that they do not need a class to stand between them and the word.

I appreciate that people, as our surgeon says, arrive “asking specifically for LASIK”. I would think that that might be why we have managed to “get where we are today”.

Craig Ross