Complete resection of a corneal flap, otherwise known as a corneal free cap, is a rare complication of LASIK. As surgeons continue to adopt femtosecond laser-assisted flap creation, however, the occurrence of this and other flap complications may diminish and, hopefully, disappear. I have profound experience with femtosecond laser procedures in both theory and practice and perform femtosecond LASIK on a daily basis. On the other hand, I have limited experience with mechanical microkeratomes. The case described below, and in an accompanying video on Eyetube (eyetube. net/?v=vedod), occurred during one of the occasions when I used a mechanical microkeratome for flap creation.

FORMATION OF A FREE CAP

Bilateral LASIK was performed on a 32-year-old lawyer with a preoperative manifest refractive error of -3.00 -1.00 X 180º yielding visual acuity of 20/20 in her right eye and -3.50 D of sphere yielding visual acuity of 20/20 in her left. In the right and left eyes, mean preoperative keratometry (K) values were 44.30 and 44.40 D and pachymetry values were 554 and 543 μm, respectively.

The LASIK treatment on the right eye was completed successfully using the SBK One-Use Plus microkeratome (Moria; Figure 1); however, a free cap was created during the cut on the left eye. The free cap was not visible on the surface of the cornea, and therefore the microkeratome head was inspected carefully, revealing the cap with a wrinkled pattern but no tear or damage. Although a normal diameter of stroma was exposed, the laser ablation was abandoned because there was no marking on the cap. Using high magnification, the cap was repositioned with the epithelial side up and in proper orientation. Adequate time (5 to 8 minutes) was taken at the end of the procedure to ensure stromal adhesion, and a soft bandage contact lens was then placed over the repositioned cap without suture (Figure 2). The postoperative course included antibiotic (tobramycin 0.3%) and corticosteroid (dexamethasone 0.1%) eye drops administered 5 times per day.

POSTOPERATIVE OBSERVATIONS

One day after surgery, the left eye showed no visual loss and the cap in situ. The contact lens was removed at this time. During subsequent follow-up, we observed no striae, epithelial ingrowth, or displacement of the amputated flap, and no signs of irregular astigmatism were seen on corneal topography.

Manifest refraction of -3.50 -0.75 X 170º yielded a BCVA of 20/20. After postoperative values were stable for 1 month, the procedure was repeated by relifting the free cap, this time marking it carefully. The reoperation was completed successfully, and a bandage contact lens was applied. Postoperatively there were no complications, and the patient’s visual acuity improved to 20/20 without correction.

DISCUSSION

Several etiologies have been proposed to explain the formation of free caps. Gimbel et al¹ proposed that flat corneas are more prone to this complication because peripheral areas of the cornea may be below the adequate cutting plane during applanation, resulting in a thin or small flap. Additionally, loss of suction can result in the creation of a free cap owing to the same mechanism. In our case, however, neither explanation made sense. It is possible that we inadequately measured the corneal diameter, as reliable measurement is crucial for suction ring selection. In selecting ring sizes for corneas with diameters between 11.0 and 12.0 mm, we should ignore values as a function of the horizontal K and instead round the horizontal K value to the nearest whole number following this example: if 42.50 D ≤ horizontal K < 43.50 D, round to 43.00 D. In our case, the corneal diameter was measured at 12.2 mm, which is close to our nomogram.

Replacement of a free cap into its original anatomic position can usually be accomplished with the aid of corneal markings or noting of other cap asymmetries or landmarks. Preoperative BCVA and the predicted refraction are achieved in most cases. Theoretically, if the cap thickness is uniform, any rotation would have a neutral effect on the resultant corneal topography and manifest refraction. ² However, using Artemis very-high-frequency ultrasound (ArcScan, Inc.), variation in the thickness of microkeratome flaps has been shown.³ Therefore, misalignment of a free cap created with a mechanical microkeratome may result in irregular corneal topography and loss of BCVA, but one created with a femtosecond laser, which has a more uniform thickness, theoretically may not.

The case described above shows the importance of corneal marking to reposition a free cap, especially if a mechanical microkeratome is used for flap creation. We caution against using gentian violet markings for this purpose, as they may wash away, making exact orientation of the cap difficult.⁴ Cap rotation may be necessary when excessive residual astigmatism or higher-order aberrations (HOAs) are present, as these cases are often not suitable for customized ablations

For patients with loss of BCVA and visual symptoms due to LASIK free-cap complications, wavefront-guided PRK for HOAs followed by conventional PRK enhancement for residual lower-order aberrations, both with topical mitomycin C application, can be an efficacious strategy.⁴

CONCLUSION

In the case presented here, a symmetrical, well-centered free cap occurred during routine LASIK. Free cap replacement was performed without ablation; however, induced astigmatism still occurred (-0.75 X 170º). One month after the initial procedure, the astigmatism was corrected during LASIK retreatment.

Reinstein et al² demonstrated a method of diagnosing the correct orientation of a misaligned free cap using the Artemis 3. When the free cap was misaligned, its thickest portions were overlying the thick portions of the stromal bed and its thinnest portions were overlying the thin portions of the stromal bed, resulting in distorted anterior corneal topographies.

In the event of a free cap, correct orientation of the cap should be confirmed by corneal markings or anatomic clues, and the irregularities on the cap edge should be marked before proceeding with ablation.

Aylin Kiliç, MD, practices at Dunya Eye Hospital, Istanbul, Turkey. Dr. Kiliç states that she has no financial interest in the products or companies mentioned. She may be reached at e-mail: aylinckilicdr@gmail.com.

1. Gimbel HV, Anderson Penno EE, van Westenbrugge JA, et al. Incidence and management of intraoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology. 1998;105:1839-1847.
2. Reinstein DZ, Rothman RC, Couch DG, Archer TJ, Sci DC. Artemis very high-frequency digital ultrasound-guided repositioning of a free cap after laser in situ keratomileusis. J Cataract Refract Surg. 2006;32:1877-1883.
3. Reinstein DZ, Silverman RH, Trokel SL, Coleman DJ. Corneal pachymetric topography. Ophthalmology. 1994;101:432-438.
4. Miraldi V, Krueger RR. Management of irregular astigmatism following rotationally disoriented free cap after LASIK. J Refract Surg. 2008;24:383-391.